INCORPORATED BY REFERENCE

[0001] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes.

TECHNICAL FIELD

[0002] This disclosure relates generally to biometric devices and methods, including but not limited to ultrasonic sensor systems and methods for using such systems.

DESCRIPTION OF THE RELATED TECHNOLOGY

[0003] Fingerprint sensor systems are now widely deployed in various types of devices. Both convenience and enhanced security can be facilitated by fingerprint sensor systems. Some fingerprint sensor systems are based on optics, whereas other fingerprint sensor systems are based on capacitance or ultrasound. Although existing fingerprint sensor systems provide various benefits, improved fingerprint sensor systems would be desirable.

SUMMARY

[0004] The systems, methods and devices of the disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0005] One innovative aspect of the subject matter described in this disclosure may be implemented in an apparatus. The apparatus may include an ultrasonic sensor array, a temperature sensor and a control system that is configured for communication with the ultrasonic sensor array. In some examples, at least a portion of the control system may be coupled to the ultrasonic sensor array and the temperature sensor. In some implementations, a mobile device may be, or may include, the apparatus. For example, a mobile device may include an apparatus as disclosed herein.

[0006] The control system may include one or more general purpose single- or multi chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. According to some examples, the control system may be configured for receiving a first contact indication that a target object is in contact with a surface. The surface may be an ultrasonic fingerprint sensor surface or a surface of a device proximate an area in which the ultrasonic fingerprint sensor resides. The control system may be configured for receiving a first removal indication that the target object has been removed from the surface and for obtaining, subsequent to receiving the first removal indication, a first temperature measurement indicating a first temperature of at least a portion of the ultrasonic fingerprint sensor. The control system may be configured for determining at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the first temperature and for updating at least one setting of the ultrasonic fingerprint sensor based, at least in part, on the new ultrasonic fingerprint sensor parameter.

[0007] In some examples, the new ultrasonic fingerprint sensor parameter(s) may include a range gate delay, a bias voltage and/or a frequency of a transmitted ultrasonic wave. According to some implementations, the control system may be configured for determining a new background image and or obtaining an air noise measurement after receiving the indication that the target object has been removed from the surface.

[0008] In some implementations, determining at least one new ultrasonic fingerprint sensor parameter may involve obtaining the at least one new ultrasonic fingerprint sensor parameter from a portion of a data structure corresponding to the temperature. In some instances the data structure may be, or may include, a look-up table.

[0009] In some examples, the control system may be configured for receiving second through N' ¹ ' contact indications that a target object is in contact with the surface of the device, for receiving second through N' ^h removal indication that the target object has been removed from the surface, for obtaining, via the ultrasonic fingerprint sensor, first through N ^th sets of fingerprint image data and for determining the at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the second through N' ¹ ' temperatures and the first through N' ¹ ' sets of fingerprint image data.

[0010] According to some examples, the control system may be configured for determining a signal-to-noise ratio peak for fingerprint image data corresponding to the at least one new ultrasonic fingerprint sensor parameter. In some instances, the signal-to- noise ratio peak may correspond to a single temperature.

[0011] Still other innovative aspects of the subject matter described in this disclosure can be implemented in a method. The method may involve receiving a first contact indication that a target object is in contact with a surface. The surface may be an ultrasonic fingerprint sensor surface or a surface of a device proximate an area in which the ultrasonic fingerprint sensor resides. The method may involve receiving a first removal indication that the target object has been removed from the surface. The method may involve obtaining, subsequent to receiving the first removal indication, a first temperature measurement indicating a first temperature of at least a portion of the ultrasonic fingerprint sensor. The method may involve determining at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the first temperature. In some instances, the method may involve updating at least one setting of the ultrasonic fingerprint sensor based, at least in part, on the new ultrasonic fingerprint sensor parameter.

[0012] According to some examples, at least one new ultrasonic fingerprint sensor parameter may include at least one of a range gate delay, a bias voltage or a frequency of a transmitted ultrasonic wave. In some examples, the method may involve determining a new background image and/or an air noise measurement after receiving the indication that the target object has been removed from the surface.

[0013] In some implementations, determining the at least one new ultrasonic fingerprint sensor parameter may involve obtaining at least one new ultrasonic fingerprint sensor parameter from a portion of a data structure corresponding to the temperature. The data structure may be, or may include, a look-up table.

[0014] According to some examples, the method may involve receiving second through N' ¹ ' contact indications that a target object is in contact with the surface of the device, for receiving second through N' ¹ ' removal indication that the target object has been removed from the surface, for obtaining, via the ultrasonic fingerprint sensor, first through N' ^h sets of fingerprint image data and for determining the at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the second through N' ^h temperatures and the first through N' ¹ ' sets of fingerprint image data.

[0015] In some examples, the method may involve determining a signal-to-noise ratio peak for fingerprint image data corresponding to at least one new ultrasonic fingerprint sensor parameter. The signal-to-noise ratio peak may, in some instances, correspond to a single temperature.

[0016] Some or all of the operations, functions and/or methods described herein may be performed by one or more devices according to instructions (e.g., software) stored on one or more non-transitory media. Such non-transitory media may include memory devices such as those described herein, including but not limited to random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, some innovative aspects of the subject matter described in this disclosure can be implemented in one or more non-transitory media having software stored thereon.

[0017] For example, the software may include instructions for controlling one or more devices to perform a method. In some examples, the method may involve receiving a first contact indication that a target object is in contact with a surface. The surface may be an ultrasonic fingerprint sensor surface or a surface of a device proximate an area in which the ultrasonic fingerprint sensor resides. The method may involve receiving a first removal indication that the target object has been removed from the surface. The method may involve obtaining, subsequent to receiving the first removal indication, a first temperature measurement indicating a first temperature of at least a portion of the ultrasonic fingerprint sensor. The method may involve determining at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the first temperature. In some instances, the method may involve updating at least one setting of the ultrasonic fingerprint sensor based, at least in part, on the new ultrasonic fingerprint sensor parameter.

[0018] According to some examples, at least one new ultrasonic fingerprint sensor parameter may include at least one of a range gate delay, a bias voltage or a frequency of a transmitted ultrasonic wave. In some examples, the method may involve determining a new background image and/or an air noise measurement after receiving the indication that the target object has been removed from the surface. [0019] In some implementations, determining the at least one new ultrasonic fingerprint sensor parameter may involve obtaining at least one new ultrasonic fingerprint sensor parameter from a portion of a data structure corresponding to the temperature. The data structure may be, or may include, a look-up table.

[0020] According to some examples, the method may involve receiving second through N' contact indications that a target object is in contact with the surface of the device, for receiving second through N' ^h removal indication that the target object has been removed from the surface, for obtaining, via the ultrasonic fingerprint sensor, first through N' ^h sets of fingerprint image data and for determining the at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the second through N' ^h temperatures and the first through N' ¹ ' sets of fingerprint image data.

[0021] In some examples, the method may involve determining a signal-to-noise ratio peak for fingerprint image data corresponding to at least one new ultrasonic fingerprint sensor parameter. The signal-to-noise ratio peak may, in some instances, correspond to a single temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale. Like reference numbers and designations in the various drawings indicate like elements.

[0023] Figure 1 is a block diagram that shows example components of an apparatus according to some disclosed implementations.

[0024] Figure 2 is a flow diagram that provides an example of a method according to some implementations.

[0025] Figure 3 is a flow diagram that provides an example of a method according to some implementations.

[0026] Figure 4 shows an example of a data structure that may be used to implement some aspects of the present disclosure.

[0027] Figure 5 shows examples of acquisition time delays and acquisition time windows according to some implementations.

[0028] Figure 6 shows examples of acquisition time delays and acquisition time windows according to some alternative implementations.

[0029] Figures 7A and 7B show examples of fingerprint images.

[0030] Figure 8 shows examples of test results obtained by the present inventors.

[0031] Figure 9 is a flow diagram that provides an example of a method according to some disclosed implementations.

[0032] Figure 10 is a graph that shows examples of ultrasonic fingerprint sensor parameters and signal-to-noise ratio values for various transient temperatures.

[0033] Figure 11 is a flow diagram that provides an example of a method according to some implementations.

[0034] Figure 12 representationally depicts aspects of a 4 x 4 pixel array of sensor pixels for an ultrasonic sensor system.

[0035] Figures 13A and 13B show example arrangements of ultrasonic transmitters and receivers in an ultrasonic sensor system, with other arrangements being possible.

DETAILED DESCRIPTION

[0036] The following description is directed to certain implementations for the purposes of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein may be applied in a multitude of different ways. The described implementations may be implemented in any device, apparatus, or system that includes a biometric system as disclosed herein. In addition, it is contemplated that the described implementations may be included in or associated with a variety of electronic devices such as, but not limited to: mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, patches, etc., Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, facsimile devices, global positioning system (GPS) receivers/navigators, cameras, digital media players (such as MP3 players), camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e- readers), mobile health devices, computer monitors, auto displays (including odometer and speedometer displays, etc.), cockpit controls and/or displays, camera view displays (such as the display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, microwaves, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washers, dryers, washer/dryers, parking meters, packaging (such as in electromechanical systems (EMS) applications including microelectromechanical systems (MEMS) applications, as well as non-EMS applications), aesthetic structures (such as display of images on a piece of jewelry or clothing) and a variety of EMS devices. The teachings herein also may be used in applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion- sensing devices, magnetometers, inertial components for consumer electronics, parts of consumer electronics products, steering wheels or other automobile parts, varactors, liquid crystal devices, electrophoretic devices, drive schemes, manufacturing processes and electronic test equipment. Thus, the teachings are not intended to be limited to the implementations depicted solely in the Figures, but instead have wide applicability as will be readily apparent to one having ordinary skill in the art.

[0037] Ultrasonic sensors, such as ultrasonic fingerprint sensors, are sensitive to temperature changes. This is true in part because the velocity of sound and/or density of various ultrasonic sensor materials can change according to the temperature of the materials. Because acoustic impedance is a function of the velocity and density of a material, this means that acoustic impedance may also change according to the ambient temperature.

[0038] If, for example, the velocity of sound of the materials of which an ultrasonic fingerprint sensor is composed change according to the ambient temperature, the time required for ultrasound to travel from an ultrasonic transmitter through these materials to a target object (such as a finger) and the time for reflected ultrasound to travel from the target object to an ultrasonic receiver will also change according to the ambient temperature. This means that the acquisition time delay (also referred to herein as “range-gate delay” or “RGD”) should also be changed according to the ambient temperature. It may be beneficial to change other ultrasonic fingerprint sensor parameters, such as bias voltage and/or the frequency of transmitted ultrasonic waves, according to the ambient temperature.

[0039] In order to compensate for changes in ambient temperature, some ultrasonic fingerprint sensors use on-board temperature sensors to detect the ambient temperature and set the ultrasonic fingerprint sensor parameters according to the ambient temperature before obtaining image data. (Data received from an ultrasonic sensor may be referred to herein as “image data,” although the image data will generally be received in the form of electrical signals. Image data that is acquired by an ultrasonic fingerprint sensor from a surface of a target object may be referred to herein as “fingerprint image data,” although the image data may in some instances be obtained from a target object that is not a digit. Accordingly, without additional processing such image data would not necessarily be perceivable by a human being as an image. As used herein, the term “finger” may be used synonymously with the term “digit,” such that the term “fingerprint” will be broad enough to include a thumbprint.) For example, a control system of the ultrasonic fingerprint sensor may query a data structure that includes ultrasonic fingerprint sensor parameters and corresponding temperatures.

[0040] However, these methods for compensating for changes in ambient temperature are not always satisfactory. Particularly when an ultrasonic fingerprint sensor is subjected to extreme ambient temperatures, such as -10 C or 50 C, the temperature of the ultrasonic fingerprint sensor will be affected by the temperature of a person’s finger or other target object that is in contact with the ultrasonic fingerprint sensor, or in contact with a device in which the ultrasonic fingerprint sensor resides. Therefore, the temperature of the ultrasonic fingerprint sensor may not remain the same during the time of a fingerprint image scan, because of heat transfer caused by the difference in temperature between the target object and the ultrasonic fingerprint sensor. Such temperature fluctuations may be referred to herein as “transient temperature changes.” Such transient temperature changes have not previously been taken into account in prior methods of adjusting ultrasonic fingerprint sensor parameters according to ambient temperature.

[0041] Some disclosed methods involve detecting when a target object, such as a finger, is in contact with a surface. In some instances, the surface may be an ultrasonic fingerprint sensor surface, such as the surface of an ultrasonic fingerprint sensor platen. In other instances, the surface may be the surface of a device proximate an area in which the ultrasonic fingerprint sensor resides, such as the surface of a display that overlies the ultrasonic fingerprint sensor, the surface of a protective layer that resides on the display, etc. Some such examples may involve obtaining fingerprint image data from the target object while the target object is in contact with the surface.

[0042] Some such methods involve detecting when the target object is removed from the surface. Particularly in conditions of extreme ambient temperature, the temperature of the surface and the temperature of at least a portion of the ultrasonic fingerprint sensor will change soon after a finger is placed on the surface. According to some implementations, upon determining that the finger has been removed from the surface (e.g., lifted up), the temperature of at least a portion of the ultrasonic fingerprint sensor will be determined. Based at least in part on this temperature, at least one ultrasonic fingerprint sensor parameter may be determined. In some such implementations, the ultrasonic fingerprint sensor may be recalibrated according to the ultrasonic fingerprint sensor parameter.

[0043] In some examples, additional data may be obtained upon determining that the finger has been removed from the surface. For example, a new background image may be obtained. As used herein, a “background image” is an image obtained by an ultrasonic fingerprint sensor when no object is in contact with the ultrasonic fingerprint sensor, or in contact with a device in which the ultrasonic fingerprint sensor resides. In some examples, an air noise data sample also may be obtained upon (or soon after) determining that the finger has been removed from the surface. In some such implementations, the ultrasonic fingerprint sensor may be recalibrated according to the background image and/or the air noise data. In some instances, the recalibration may involve replacing or updating a previous background image with the air noise data. [0044] Particular implementations of the subject matter described in this disclosure may be implemented to realize one or more of the following potential advantages. Improved ultrasonic fingerprint sensor performance may be obtained by applying at least some of the disclosed methods of compensating for transient temperature changes. By applying at least some of the disclosed transient temperature compensation methods, the inventors have obtained relatively higher-quality fingerprint images, as compared to fingerprint images obtained when the transient temperature compensation methods are not being applied. In some instances, the fingerprint image quality of fingerprint images obtained after the ultrasonic fingerprint sensor is recalibrated may be of a higher quality than fingerprint images obtained before the ultrasonic fingerprint sensor was recalibrated. According to some examples, the fingerprint image quality of fingerprint images obtained before the ultrasonic fingerprint sensor was recalibrated also may be improved, e.g., by replacing a previously-used background image with an updated background image. The updated background image may correspond with an air noise measurement obtained after receiving an indication that the target object has been removed from the surface. Moreover, by applying at least some of the disclosed transient temperature compensation methods, the inventors have observed marked reductions in both the false rejection rate (FRR) and in the number of instances of failing to acquire (FTA) fingerprint images. Accordingly, some implementations may be capable of performing relatively more reliable enrollment and authentication processes that are based, at least in part, on fingerprint image data (or on fingerprint minutiae or fingerprint image features, such as keypoints, derived from fingerprint image data).

[0045] Figure 1 is a block diagram that shows example components of an apparatus according to some disclosed implementations. In this example, the apparatus 101 includes an ultrasonic sensor system 102, a control system 106 and a temperature sensor 108. In this example, the ultrasonic sensor system 102 includes at least one ultrasonic fingerprint sensor. Although not shown in Figure 1, the apparatus 101 may include a substrate. Some examples are described below. Some implementations of the apparatus 101 may include an interface system 104.

[0046] Various examples of ultrasonic sensor systems 102 are disclosed herein, some of which may include a separate ultrasonic transmitter and some of which may not. For example, in some implementations, the ultrasonic sensor system 102 may include a piezoelectric receiver layer, such as a layer of PVDF polymer or a layer of PVDF-TrFE copolymer. In some implementations, a separate piezoelectric layer may serve as the ultrasonic transmitter. In some implementations, a single piezoelectric layer may serve as the transmitter and as a receiver. In some implementations, other piezoelectric materials may be used in the piezoelectric layer, such as aluminum nitride (AIN) or lead zirconate titanate (PZT). The ultrasonic sensor system 102 may, in some examples, include an array of ultrasonic transducer elements, such as an array of piezoelectric micromachined ultrasonic transducers (PMUTs), an array of capacitive micromachined ultrasonic transducers (CMUTs), etc. In some such examples, a piezoelectric receiver layer, PMUT elements in a single-layer array of PMUTs, or CMUT elements in a single layer array of CMUTs, may be used as ultrasonic transmitters as well as ultrasonic receivers. According to some alternative examples, the ultrasonic sensor system 102 may include an ultrasonic receiver array and one or more separate ultrasonic transmitter elements. In some such examples, the ultrasonic transmitter(s) may include an ultrasonic plane- wave generator, such as those described below.

[0047] The control system 106 may include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. The control system 106 also may include (and/or be configured for communication with) one or more memory devices, such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, the apparatus 101 may have a memory system that includes one or more memory devices, though the memory system is not shown in Figure 2. The control system 106 may be capable of receiving and processing data from the ultrasonic sensor system 102, e.g., as described below. If the apparatus 101 includes one or more ultrasonic transmitters, the control system 106 may be capable of controlling the ultrasonic transmitter(s), e.g., as disclosed elsewhere herein. In some implementations, functionality of the control system 106 may be partitioned between one or more controllers or processors, such as a dedicated sensor controller and an applications processor of a mobile device.

[0048] The temperature sensor system 108 may include one or more temperature sensors. According to some examples, at least one temperature sensor of the temperature sensor system 108 may reside in an area of the apparatus 101 that is configured for obtaining fingerprint image data, e.g., a platen of a fingerprint sensor. In some implementations, the temperature sensor system 108 may include multiple temperature sensors that are distributed over an area of the apparatus 101.

[0049] Some implementations of the apparatus 101 may include an interface system 104. In some examples, the interface system may include a wireless interface system. In some implementations, the interface system may include a user interface system, one or more network interfaces, one or more interfaces between the control system 106 and a memory system and/or one or more interfaces between the control system 106 and one or more external device interfaces (e.g., ports or applications processors).

[0050] The interface system 104 may be configured to provide communication (which may include wired or wireless communication, such as electrical communication, radio communication, etc.) between components of the apparatus 101. In some such examples, the interface system 104 may be configured to provide communication between the control system 106 and the ultrasonic sensor system 102. According to some such examples, a portion of the interface system 104 may couple at least a portion of the control system 106 to the ultrasonic sensor system 102, e.g., via electrically conducting material. If the apparatus 101 includes an ultrasonic transmitter, the interface system 104 may be configured to provide communication between at least a portion of the control system 106 and the ultrasonic transmitter. According to some examples, the interface system 104 may be configured to provide communication between the apparatus 101 and other devices and/or human beings. In some such examples, the interface system 104 may include one or more user interfaces. The interface system 104 may, in some examples, include one or more network interfaces and/or one or more external device interfaces (such as one or more universal serial bus (USB) interfaces). In some implementations, the apparatus 101 may include a memory system. The interface system 104 may, in some examples, include at least one interface between the control system 106 and a memory system.

[0051] The apparatus 101 may be used in a variety of different contexts, many examples of which are disclosed herein. For example, in some implementations a mobile device may include at least a portion of the apparatus 101. In some implementations, a wearable device may include at least a portion of the apparatus 101. The wearable device may, for example, be a bracelet, an armband, a wristband, a ring, a headband or a patch. In some implementations, the control system 106 may reside in more than one device. For example, a portion of the control system 106 may reside in a wearable device and another portion of the control system 106 may reside in another device, such as a mobile device (e.g., a smartphone or a tablet computer). The interface system 104 also may, in some such examples, reside in more than one device.

[0052] Figure 2 shows an example of a cross-sectional view of an apparatus capable of performing at least some methods that are described herein. For example, the apparatus 101 may be capable of performing the methods that are described herein with reference to Figures 3, 9 and 11. The apparatus 101 is an example of a device that may be included in a biometric system such as those disclosed herein. Here, the apparatus 101 is an example of the apparatus 101 that is described above with reference to Figure 1. As with other implementations shown and described herein, the types of elements, the arrangement of the elements and the dimensions of the elements illustrated in Figure 2 are merely shown by way of example.

[0053] Figure 2 shows an example of ultrasonic waves reflecting from a target object. In this example, the target object is a finger 206 being insonified by transmitted ultrasonic waves 214. In this example, the ultrasonic waves are transmitted by an ultrasonic transmitter 208 that is separate from the ultrasonic receiver array 202. Accordingly, in this example the ultrasonic sensor system 102 that is described above with reference to Figure 1 includes an ultrasonic receiver array 202 and an ultrasonic transmitter 208. In the example shown in Figure 2, at least a portion of the apparatus 101 includes an ultrasonic transmitter 208 that may function as a plane-wave ultrasonic transmitter. In some implementations, the ultrasonic transmitter 208 may include a piezoelectric transmitter layer with transmitter excitation electrodes disposed on each side of the piezoelectric transmitter layer.

[0054] In some examples, the ultrasonic receiver array 202 may include an array of pixel input electrodes and sensor pixels formed in part from TFT circuitry, an overlying piezoelectric receiver layer 220 of piezoelectric material such as PVDF or PVDF-TrFE, and an upper electrode layer positioned on the piezoelectric receiver layer, which will sometimes be referred to herein as a receiver bias electrode. Examples of suitable ultrasonic transmitters and ultrasonic receiver arrays are described below. However, in alternative implementations, the ultrasonic receiver array 202 and the ultrasonic transmitter 208 may be combined in an ultrasonic transceiver array, e.g., as described above with reference to Figure 1.

[0055] In this example, the transmitted ultrasonic waves 214 have been transmitted from the ultrasonic transmitter 208 through a sensor stack 215 to an overlying finger 206. The various layers of the sensor stack 215 may, in some examples, include one or more substrates of glass or other material (such as plastic or sapphire) that is substantially transparent to visible light.

[0056] In this implementation, the substrate 210 is coupled to a thin- film transistor (TFT) substrate 212 for the ultrasonic receiver array 202. According to this example, a piezoelectric receiver layer 220 overlies the sensor pixels 202 of the ultrasonic receiver array 202 and a platen 225 overlies the piezoelectric receiver layer 220. In alternative examples, the apparatus 101 may include a display (such as an OLED display) that overlies the piezoelectric receiver layer 220 instead of a platen.

[0057] In various implementations, the apparatus 101 may be sensitive to temperature changes. For example, the velocity of sound and/or density of the materials in the sensor stack 215 may change according to the temperature of the materials. If, for example, the velocity of sound of the sensor stack 215 changes according to the ambient temperature, the time required for transmitted ultrasonic waves 214 to travel from the ultrasonic transmitter 208 through the sensor stack 215 to the finger 206, as well as the time for ultrasonic waves 216 to travel from the finger 206 (or from an air gap in a fingerprint valley between the finger 206 and the platen 225) to the ultrasonic receiver 202 will also change according to the ambient temperature. This means that the RGD for sampling fingerprint image data at or near the finger/platen interface should also be changed according to the ambient temperature. It may be beneficial to change other ultrasonic fingerprint sensor parameters, such as bias voltage and/or the frequency of transmitted ultrasonic waves, according to the ambient temperature.

[0058] Particularly in extreme temperature conditions, the finger 206 may cause transient temperature changes due to heat transfer between the finger 206 and the apparatus 210. Those portions of the sensor stack 215 that are relatively closer to the finger 206 (e.g., the platen 225) may be relatively more susceptible to such transient temperature changes. Various methods for compensating for such transient temperature changes will now be described.

[0059] Figure 3 is a flow diagram that provides an example of a method according to some implementations. The blocks of Figure 3 (and those of other flow diagrams provided herein) may, for example, be performed by the apparatus 101 of Figure 2 or by a similar apparatus. As with other methods disclosed herein, the method outlined in Figure 3 may include more or fewer blocks than indicated. Moreover, the blocks of methods disclosed herein are not necessarily performed in the order indicated.

[0060] In this example, method 300 is a method of controlling an apparatus that includes an ultrasonic sensor system. Method 300 may, for example, be performed by a control system configured for electrical communication with the ultrasonic sensor system. According to this implementation, block 305 involves receiving a first contact indication that a target object is in contact with a surface. The surface may be an ultrasonic fingerprint sensor surface (such as a platen of an ultrasonic fingerprint sensor) or a surface of a device proximate an area in which the ultrasonic fingerprint sensor resides (such as a surface of a display or a display cover glass that overlies an ultrasonic fingerprint sensor).

[0061] Accordingly, block 305 involves a target object and/or finger detection process. According to some implementations, block 305 may involve determining whether a target object is in contact with an apparatus according to sensor data from a touch sensor system or a gesture sensor system. In some instances, block 305 may involve determining whether an area of the device’s surface is not reflecting ultrasonic waves in a manner characteristic of an air/device boundary, but is instead absorbing ultrasonic waves in a manner consistent with a target object in contact with the device. According to some examples, block 305 may involve determining whether a target object is an appropriate size for a digit, or a part of a digit. In some examples, method 300 may involve obtaining fingerprint image data from the target object while the target object is in contact with the surface.

[0062] In this example, block 310 involves receiving a first removal indication that the target object has been removed from the surface. According to some implementations, block 310 may involve determining whether the target object has been removed from the surface according to sensor data from a touch sensor system or a gesture sensor system. In some examples, block 310 may involve determining whether an area of the device’s surface that was previously in contact with the target object is now reflecting ultrasonic waves in a manner characteristic of an air/device boundary.

[0063] According to this implementation, block 315 involves obtaining, subsequent to receiving the first removal indication, a first temperature measurement indicating a first temperature of at least a portion of the ultrasonic fingerprint sensor. In some examples, block 315 may involve determining a temperature of a portion of the ultrasonic fingerprint sensor that was proximate the target object. For example, block 315 may involve determining a temperature of a platen of the ultrasonic fingerprint sensor. Alternatively, or additionally, block 315 may involve determining a temperature of a portion of an apparatus that was between the ultrasonic fingerprint sensor and the target object, e.g., a temperature of an area of a cover glass, a temperature of an area of a display, etc., which was between the ultrasonic fingerprint sensor and the target object. Block 315 may involve a control system (e.g., the control system 106 of Figure 1) receiving temperature data from a temperature sensor system (e.g., from the temperature sensor system 108). In some examples, block 315 may involve the control system receiving temperature data from a portion of the temperature sensor system that was proximate the target object.

[0064] In this example, block 320 involves determining at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the first temperature. The at least one new ultrasonic fingerprint sensor parameter may, for example, include a range gate delay, a bias voltage or a frequency of a transmitted ultrasonic wave. Determining the at least one new ultrasonic fingerprint sensor parameter may, in some instances, involve obtaining the at least one new ultrasonic fingerprint sensor parameter from a portion of a data structure corresponding to the temperature. The data structure may be, or may include, a look-up table. For example, block 320 may involve a control system querying a data structure that includes temperature data and one or more corresponding ultrasonic fingerprint sensor parameters.

[0065] Figure 4 shows an example of a data structure that may be used to implement some aspects of the present disclosure. In this example, the data structure 405 includes fingerprint sensor parameters and corresponding temperatures in degrees Celsius. According to this example, the fingerprint sensor parameters include frequency, RGD and bias voltage. In this example, the data structure 405 is a look-up table (LUT).

[0066] In some examples, block 320 may involve querying a data structure such as the data structure 405 and determining one or more ultrasonic fingerprint sensor parameters corresponding to a temperature that is determined in block 315. In some examples, the data structure may include transient temperature values and one or more types of corresponding ultrasonic fingerprint sensor parameters. Some implementations involve determining ultrasonic fingerprint sensor parameters for corresponding transient temperature values.

[0067] Returning to Figure 3, in some implementations block 320 (or another process of method 300) may involve determining a new background image after receiving the indication that the target object has been removed from the surface. In some instances, method 300 may involve obtaining an air noise measurement after receiving the indication that the target object has been removed from the surface.

[0068] In this implementation, block 325 involves updating at least one setting of the ultrasonic fingerprint sensor based, at least in part, on at least one new ultrasonic fingerprint sensor parameter. In some instances, method 300 may involve updating at least one setting of the ultrasonic fingerprint sensor based on a newly-determined background image and/or according to newly-obtained air noise measurement data. According to some such examples, updating at least one setting of the ultrasonic fingerprint sensor may involve replacing a previously-used background image with an updated background image. The updated background image may correspond with newly-obtained air noise measurement data that is obtained after receiving an indication that the target object has been removed from the surface in block 310. In some instances, the fingerprint image quality of fingerprint images obtained after updating at least one setting of the ultrasonic fingerprint sensor may be of a higher quality than fingerprint images obtained before the ultrasonic fingerprint sensor is recalibrated. According to some examples, the fingerprint image quality of one or more fingerprint images obtained before at least one setting of the ultrasonic fingerprint sensor was updated also may be improved, e.g., by replacing a previously-used background image with an updated background image. The updated background image may correspond with an air noise measurement obtained after receiving an indication that the target object has been removed from the surface. For example, the fingerprint image quality of fingerprint image data obtained from the target object prior to receiving the first removal indication in step 310 may be improved by replacing a previously-used background image with the updated background image.

[0069] Method 300 may, in some instances, acquiring fingerprint image data via the ultrasonic fingerprint sensor after the ultrasonic fingerprint sensor has been reconfigured according to at least one new ultrasonic fingerprint sensor parameter. In some instances, method 300 may involve performing an authentication process that is based, at least in part, on the fingerprint image data. If the authentication process concludes successfully, method 300 may involve unlocking a device, enabling functionality of a device, allowing access to a secured area, etc.

[0070] Figure 5 shows examples of acquisition time delays and acquisition time windows according to some implementations. Figure 5 provides an example of what may be referred to herein as “DBIAS sampling,” in which the receiver bias voltage level changes when a signal is sampled. In this example, the receiver bias voltage level also changes when a signal is transmitted· In Figure 5, an acquisition time delay is labeled as “RGD,” an acronym for “range-gate delay,” and an acquisition time window is labeled as “RGW,” an acronym for “range-gate window.” Graph 502a shows a transmitted signal 504 that is initiated at a time to. The transmitted signal 504 may, for example, be a pulse of ultrasound. In alternative examples, multiple pulses of ultrasound may be transmitted.

[0071] Graph 502b shows examples of a first acquisition time delay RGDi and a first acquisition time window RGWi. In this example, RGDi (and in some instances RGWi) correspond to a first ultrasonic sensor temperature. The received waves 506a represent reflected compressional waves that are received by an ultrasonic sensor array and sampled during the first acquisition time window RGWi, after the first acquisition time delay RGDi. In some examples, the acquisition time delay may be in the range of about 10 nanoseconds to about 20,000 nanoseconds or more. In some implementations, the first acquisition time window may be in the range of 5 to 50 nanoseconds, or in the range of approximately 5 to 50 nanoseconds. In some examples, “approximately” or “about” may mean within +/- 5%, whereas in other examples “approximately” or “about” may mean within +/- 10%, +/- 15% or +/- 20%. However, in some implementations the first acquisition time window may be more than 50 nanoseconds.

[0072] According to some examples, the apparatus 101 may include a platen. The platen may be positioned with respect to the ultrasonic sensor system 102. For example, the platen may be positioned proximate the ultrasonic sensor system 102 and/or attached to the ultrasonic sensor system 102. In some such examples, the first acquisition time delay may correspond to an expected amount of time for an ultrasonic compressional wave reflected from a surface of the platen to be received by at least a portion of the ultrasonic sensor system 102. Accordingly, the first acquisition time delay and the first acquisition time window may be selected to capture one or more fingerprint features of a target object placed on a surface of a platen. For example, in some implementations with a platen about 400 microns thick, the acquisition time delay (RGD) may be set to about 1 ,000 nanoseconds and the acquisition time window (RGW) may be set to about 50 nanoseconds.

[0073] Graph 502c shows examples of a second acquisition time delay RGD2 and a second acquisition time window RGW2. In this example, RGD2 (and in some instances RGW2) correspond to a second ultrasonic sensor temperature. At the second ultrasonic sensor temperature, the speed of sound is relatively slower than the speed of sound that corresponds to the first ultrasonic sensor temperature. Therefore, in this example the second acquisition time delay is selected to be greater than the first acquisition time delay. In this example, the first acquisition time delay and the second acquisition time delay are both measured from the time to. However, in other implementations, the first acquisition time delay and the second acquisition time delay may be measured from a different initial time.

[0074] Figure 6 shows examples of acquisition time delays and acquisition time windows according to some alternative implementations. Figure 6 provides an example of what may be referred to herein as “peak to peak sampling.” Unlike DBIAS sampling, with peak to peak sampling the receiver bias voltage level (labeled Rbias in Figure 6) does not change when a signal is sampled.

[0075] As noted in Figure 6, this example of peak-to-peak involves sampling based on the times of a received negative signal peak and an adjacent received positive signal peak. According to this example, the RGW corresponds to the time interval between the received negative signal peak 605 and the received positive signal peak 610. In this example RGW corresponds to a half cycle of the driving frequency, which in some examples may be in the range of 10 to 200ns.

[0076] This example of peak-to-peak sampling involves 2 extra control signals, which are labeled SI and S2 in Figure 6. In this example of peak-to-peak sampling, RGW and RGD are used to control when to sample. However, the definition of RGD is different in this example from that of the DBIAS sampling example of Figure 5. In this example of peak-to-peak sampling, RGD changes when RGW changes. In other words, RGD is linked to the time of the received positive signal peak 610. One benefit of peak-to-peak sampling is that one can reduce the tone burst voltage, which in turn leads to a cost reduction on electronic components, better reliability etc.

[0077] Graph 650a shows a transmitted signal 660 that is initiated at a time to. The transmitted signal 660 may, for example, be a pulse of ultrasound. The pulse of ultrasound may, for example, correspond to the “first ultrasonic compressional wave” that is described above with reference to block 305 of Figure 3. In alternative examples, multiple pulses of ultrasound may be transmitted.

[0078] Graph 650b shows examples of a first acquisition time delay RGDi and a first acquisition time window RGWi. In this example, RGDi (and in some instances RGWi) correspond to a first ultrasonic sensor temperature. The received waves 670a represent reflected ultrasonic waves that are received by an ultrasonic sensor array and sampled during the first acquisition time window RGWi, after the first acquisition time delay RGDi. In some examples, the acquisition time delay may be in the range of about 10 nanoseconds to about 20,000 nanoseconds or more. In some implementations, the first acquisition time window may be in the range of 5 to 50 nanoseconds, or in the range of approximately 5 to 50 nanoseconds. In some examples, “approximately” or “about” may mean within +/- 5%, whereas in other examples “approximately” or “about” may mean within +/- 10%, +/- 15% or +/- 20%. However, in some implementations the first acquisition time window may be more than 50 nanoseconds.

[0079] Graph 650c shows examples of a second acquisition time delay RGD2 and a second acquisition time window RGW2. In this example, RGD2 (and in some instances RGW2) correspond to a second ultrasonic sensor temperature. At the second ultrasonic sensor temperature, the speed of sound is relatively slower than the speed of sound that corresponds to the first ultrasonic sensor temperature. Therefore, in this example the second acquisition time delay is selected to be greater than the first acquisition time delay. The received waves 670b represent reflected ultrasonic waves that are received by an ultrasonic sensor array and sampled during the second acquisition time window RGW2, after the second acquisition time delay RGD2. In this example, the first acquisition time delay and the second acquisition time delay are both measured from the time to. However, in other implementations, the first acquisition time delay and the second acquisition time delay may be measured from a different initial time.

[0080] Figures 7A and 7B show examples of fingerprint images. In this example, the ambient temperature was -20 C at the time the fingerprint images were captured. Figure 7A shows an example of a fingerprint image that was obtained pursuant to one of the disclosed methods of compensating for transient temperatures, whereas Figure 7B shows an example of a fingerprint image that was obtained without using one of the disclosed methods of compensating for transient temperatures. One may observe the relatively higher image quality of Figure 7 A, as compared to that of Figure 7B.

[0081] Figure 8 shows examples of test results obtained by the present inventors.

Row 805 of Figure 8 shows test results obtained without using one of the disclosed methods of compensating for transient temperatures, whereas row 810 shows test results obtained while using one of the disclosed methods of compensating for transient temperatures. In this example, the ambient temperature was -20 C at the time the fingerprint images were captured. According to this example, the inventors compared the false rejection rate (FRR) and the number of FTA (failure to acquire) image captures. The inventors observed a very large improvement in FRR when software for transient temperature handling is enabled. The inventors observed that the FRR improved because the number of FTA captures was reduced significantly due to the better quality of obtained fingerprint images.

[0082] Figure 9 is a flow diagram that provides an example of a method according to some disclosed implementations. The blocks of Figure 9 (and those of other flow diagrams provided herein) may, for example, be performed by the apparatus 101 of Figure 1 or by a similar apparatus. As with other methods disclosed herein, the method outlined in Figure 9 may include more or fewer blocks than indicated. Moreover, the blocks of methods disclosed herein are not necessarily performed in the order indicated.

[0083] In this example, method 900 is a method for determining ultrasonic fingerprint sensor parameters corresponding to transient temperatures. According to some examples, method 900 may be performed at a variety of ambient temperatures.

[0084] Blocks 905 through 915 may, in some instances, correspond with multiple iterations of blocks 305 through 315. Because blocks 305 through 315 are described in detail above, all of these details will not be repeated in this description of Figure 9.

[0085] According to this example, block 905 involves receiving first through N' ^h contact indications that a target object is in contact with a surface. The surface may be an ultrasonic fingerprint sensor surface or a surface of a device proximate an area in which the ultrasonic fingerprint sensor resides. In this implementation, block 910 involves receiving first through N' ^h removal indications that the target object has been removed from the surface. In this example, block 915 involves obtaining, subsequent to receiving each of the first through N ^th removal indications, first through N ^th temperature measurements of at least a portion of the ultrasonic fingerprint sensor.

[0086] According to this implementation, block 920 involves obtaining, via the ultrasonic fingerprint sensor, first through N ^th sets of fingerprint image data. Block 920 may, for example, involve obtaining each of the first through N' ^h sets of fingerprint image data after receiving a corresponding removal indication in a corresponding instance of block 910 and/or after obtaining a corresponding temperature measurement in a corresponding instance of block 915.

[0087] In this example, block 925 involves determining at least one new ultrasonic fingerprint sensor parameter based, at least in part, on the first through N' ^h sets of fingerprint image data and the first through N' ^h temperature measurements. In some examples, block 925 may involve determining a signal-to-noise ratio (SNR) peak for fingerprint image data corresponding to the at least one new ultrasonic fingerprint sensor parameter. According to some such examples, the SNR peak may correspond to a single temperature. In some such examples, the SNR peak may correspond to a single ultrasonic fingerprint sensor parameter. Optional block 930 involves updating a data structure to include the new ultrasonic fingerprint sensor parameter. [0088] Figure 10 is a graph that shows examples of ultrasonic fingerprint sensor parameters and signal-to-noise ratio values for various transient temperatures. In this example, ultrasonic fingerprint sensor parameters and SNR values for a particular type of ultrasonic fingerprint sensor are shown for three transient temperatures, Ti, T2 and T3. According to this example, the SNR peak 1001 for transient temperature Ti corresponds to an ultrasonic fingerprint sensor parameter value SP1, whereas the SNR peak 1002 for transient temperature T2 corresponds to an ultrasonic fingerprint sensor parameter value SP2. It may be observed that the ultrasonic fingerprint sensor parameter value SP2 is less than the ultrasonic fingerprint sensor parameter value SP1.

[0089] The present inventors have determined that appropriate ultrasonic fingerprint sensor parameter values may be obtained by determining an SNR peak for a particular transient temperature. By determining the SNR peak for a plurality of transient temperature values, a data structure (such as a look-up table) may be populated with transient temperature values and corresponding ultrasonic fingerprint sensor parameter values. Subsequently, appropriate ultrasonic fingerprint sensor parameter values may be obtained by determining a transient temperature of an ultrasonic fingerprint sensor, querying the data structure and determining a corresponding ultrasonic fingerprint sensor parameter value.

[0090] Figure 11 is a flow diagram that provides an example of a method according to some implementations. The blocks of Figure 11 (and those of other flow diagrams provided herein) may, for example, be performed by the apparatus 101 of Figure 1 or by a similar apparatus. As with other methods disclosed herein, the method outlined in Figure 11 may include more or fewer blocks than indicated. Moreover, the blocks of methods disclosed herein are not necessarily performed in the order indicated.

[0091] In this example, method 1100 is a method for determining ultrasonic fingerprint sensor parameters corresponding to transient temperatures. According to some examples, method 1100 may be performed at a variety of ambient temperatures.

[0092] Blocks 1105 through 1115 may, in some instances, correspond with multiple iterations of blocks 305 through 315. Because blocks 305 through 315 are described in detail above, all of these details will not be repeated in this description of Figure 11.

[0093] In this example, block 1120 involves determining and applying at least one new ultrasonic fingerprint sensor parameter. According to some examples, block 1120 may involve determining at least one previously-used ultrasonic fingerprint sensor parameter value corresponding to the transient temperature value determined in block 1115 (e.g., by querying a data structure of temperature values and corresponding ultrasonic fingerprint sensor parameter values). Block 1120 may involve modifying the at least one previously-used ultrasonic fingerprint sensor parameter value, e.g., by incrementing or decrementing at least one previously-used ultrasonic fingerprint sensor parameter value, and applying at least one modified ultrasonic fingerprint sensor parameter value to the ultrasonic fingerprint sensor. In some examples, only a single ultrasonic fingerprint sensor parameter value will be determined and applied in block 1120.

[0094] According to this implementation, block 1125 involves obtaining, via the ultrasonic fingerprint sensor, a set of fingerprint image data. In this example, block 1125 involves obtaining the set of fingerprint image data after applying the at least one new ultrasonic fingerprint sensor parameter in block 1120. Accordingly, by evaluating one or more of the properties of the set of fingerprint image data, the corresponding ultrasonic fingerprint sensor parameter(s) may also be evaluated.

[0095] In this example, block 1130 involves determining an SNR value for the set of fingerprint image data.

[0096] In this implementation, block 1135 involves determining whether the SNR value determined in block 1130 is a peak SNR value. For example, block 1135 may involve comparing the SNR value determined in block 1130 with one or more previously-determined SNR values. According to some implementations, block 1135 may involve a search for a local SNR value maximum. In some such implementations, if it is determined in block 1135 that a local SNR value maximum has not yet been found, the process may revert to block 1105. For example, a control system may cause a display, a speaker, etc., to prompt a user to place the user’s finger on the surface. In some such examples, after receiving the contact indication in block 1105, the control system may cause the user to receive a prompt to lift the user’s finger from the surface.

[0097] In the example shown in Figure 11, after it is determined in block 1135 that the SNR value determined in block 1130 is a peak SNR value, in block 1140 a data structure is updated to include the at least one new fingerprint sensor parameter. In some examples, only a single ultrasonic fingerprint sensor parameter value will be updated in block 1140.

[0098] Figure 12 representationally depicts aspects of a 4 x 4 pixel array of sensor pixels for an ultrasonic sensor system. Each pixel 1234 may be, for example, associated with a local region of piezoelectric sensor material (PSM), a peak detection diode (Dl) and a readout transistor (M3); many or all of these elements may be formed on or in a substrate to form the pixel circuit 1236. In practice, the local region of piezoelectric sensor material of each pixel 1234 may transduce received ultrasonic energy into electrical charges. The peak detection diode Dl may register the maximum amount of charge detected by the local region of piezoelectric sensor material PSM. Each row of the pixel array 1235 may then be scanned, e.g., through a row select mechanism, a gate driver, or a shift register, and the readout transistor M3 for each column may be triggered to allow the magnitude of the peak charge for each pixel 1234 to be read by additional circuitry, e.g., a multiplexer and an A/D converter. The pixel circuit 1236 may include one or more TFTs to allow gating, addressing, and resetting of the pixel 1234.

[0099] Each pixel circuit 1236 may provide information about a small portion of the object detected by the ultrasonic sensor system. While, for convenience of illustration, the example shown in Figure 12 is of a relatively coarse resolution, ultrasonic sensors having a resolution on the order of 500 pixels per inch or higher may be configured with an appropriately scaled structure. The detection area of the ultrasonic sensor system may be selected depending on the intended object of detection. For example, the detection area may range from about 5 mm x 5 mm for a single finger to about 3 inches x 3 inches for four fingers. Smaller and larger areas, including square, rectangular and non- rectangular geometries, may be used as appropriate for the target object.

[0100] Figure 13A shows an example of an exploded view of an ultrasonic sensor system. In this example, the ultrasonic sensor system 1300a includes an ultrasonic transmitter 20 and an ultrasonic receiver 30 under a platen 40. According to some implementations, the ultrasonic receiver 30 may be an example of the ultrasonic sensor system 102 that is shown in Figure 2 and described above. In some implementations, the ultrasonic transmitter 20 may be an example of the optional ultrasonic transmitter that is shown in Figure 2 and described above. The ultrasonic transmitter 20 may include a substantially planar piezoelectric transmitter layer 22 and may be capable of functioning as a plane wave generator. Ultrasonic waves may be generated by applying a voltage to the piezoelectric layer to expand or contract the layer, depending upon the signal applied, thereby generating a plane wave. In this example, the control system 106 may be capable of causing a voltage that may be applied to the planar piezoelectric transmitter layer 22 via a first transmitter electrode 24 and a second transmitter electrode 26. In this fashion, an ultrasonic wave may be made by changing the thickness of the layer via a piezoelectric effect. This ultrasonic wave may travel towards a finger (or other object to be detected), passing through the platen 40. A portion of the wave not absorbed or transmitted by the object to be detected may be reflected so as to pass back through the platen 40 and be received by at least a portion of the ultrasonic receiver 30. The first and second transmitter electrodes 24 and 26 may be metallized electrodes, for example, metal layers that coat opposing sides of the piezoelectric transmitter layer 22.

[0101] The ultrasonic receiver 30 may include an array of sensor pixel circuits 32 disposed on a substrate 34, which also may be referred to as a backplane, and a piezoelectric receiver layer 36. In some implementations, each sensor pixel circuit 32 may include one or more TFT elements, electrical interconnect traces and, in some implementations, one or more additional circuit elements such as diodes, capacitors, and the like. Each sensor pixel circuit 32 may be configured to convert an electric charge generated in the piezoelectric receiver layer 36 proximate to the pixel circuit into an electrical signal. Each sensor pixel circuit 32 may include a pixel input electrode 38 that electrically couples the piezoelectric receiver layer 36 to the sensor pixel circuit 32.

[0102] In the illustrated implementation, a receiver bias electrode 39 is disposed on a side of the piezoelectric receiver layer 36 proximal to platen 40. The receiver bias electrode 39 may be a metallized electrode and may be grounded or biased to control which signals may be passed to the array of sensor pixel circuits 32. Ultrasonic energy that is reflected from the exposed (top) surface of the platen 40 may be converted into localized electrical charges by the piezoelectric receiver layer 36. These localized charges may be collected by the pixel input electrodes 38 and passed on to the underlying sensor pixel circuits 32. The charges may be amplified or buffered by the sensor pixel circuits 32 and provided to the control system 106.

[0103] The control system 106 may be electrically connected (directly or indirectly) with the first transmitter electrode 24 and the second transmitter electrode 26, as well as with the receiver bias electrode 39 and the sensor pixel circuits 32 on the substrate 34. In some implementations, the control system 106 may operate substantially as described above. For example, the control system 106 may be capable of processing the amplified signals received from the sensor pixel circuits 32.

[0104] The control system 106 may be capable of controlling the ultrasonic transmitter 20 and/or the ultrasonic receiver 30 to obtain ultrasonic image data, e.g., by obtaining fingerprint images. Whether or not the ultrasonic sensor system 1300a includes an ultrasonic transmitter 20, the control system 106 may be capable of obtaining attribute information from the ultrasonic image data. In some examples, the control system 106 may be capable of controlling access to one or more devices based, at least in part, on the attribute information. The ultrasonic sensor system 1300a (or an associated device) may include a memory system that includes one or more memory devices. In some implementations, the control system 106 may include at least a portion of the memory system. The control system 106 may be capable of obtaining attribute information from ultrasonic image data and storing the attribute information in the memory system. In some implementations, the control system 106 may be capable of capturing a fingerprint image, obtaining attribute information from the fingerprint image and storing attribute information obtained from the fingerprint image (which may be referred to herein as fingerprint image information) in the memory system. According to some examples, the control system 106 may be capable of capturing a fingerprint image, obtaining attribute information from the fingerprint image and storing attribute information obtained from the fingerprint image even while maintaining the ultrasonic transmitter 20 in an “off’ state.

[0105] In some implementations, the control system 106 may be capable of operating the ultrasonic sensor system 1300a in an ultrasonic imaging mode or a force-sensing mode. In some implementations, the control system may be capable of maintaining the ultrasonic transmitter 20 in an “off’ state when operating the ultrasonic sensor system in a force-sensing mode. The ultrasonic receiver 30 may be capable of functioning as a force sensor when the ultrasonic sensor system 1300a is operating in the force-sensing mode. In some implementations, the control system 106 may be capable of controlling other devices, such as a display system, a communication system, etc. In some implementations, the control system 106 may be capable of operating the ultrasonic sensor system 1300a in a capacitive imaging mode.

[0106] The platen 40 may be any appropriate material that can be acoustically coupled to the receiver, with examples including plastic, ceramic, sapphire, metal and glass. In some implementations, the platen 40 may be a cover plate, e.g., a cover glass or a lens glass for a display. Particularly when the ultrasonic transmitter 20 is in use, fingerprint detection and imaging can be performed through relatively thick platens if desired, e.g., 3 mm and above. However, for implementations in which the ultrasonic receiver 30 is capable of imaging fingerprints in a force detection mode or a capacitance detection mode, a thinner and relatively more compliant platen 40 may be desirable. According to some such implementations, the platen 40 may include one or more polymers, such as one or more types of parylene, and may be substantially thinner. In some such implementations, the platen 40 may be tens of microns thick or even less than 10 microns thick.

[0107] Examples of piezoelectric materials that may be used to form the piezoelectric receiver layer 36 include piezoelectric polymers having appropriate acoustic properties, for example, an acoustic impedance between about 2.5 MRayls and 5 MRayls. Specific examples of piezoelectric materials that may be employed include ferroelectric polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymers. Examples of PVDF copolymers include 60:40 (molar percent) PVDF-TrFE, 70:30 PVDF-TrFE, 80:20 PVDF-TrFE, and 90:10 PVDR-TrFE. Other examples of piezoelectric materials that may be employed include polyvinylidene chloride (PVDC) homopolymers and copolymers, polytetrafluoroethylene (PTFE) homopolymers and copolymers, and diisopropylammonium bromide (DIPAB).

[0108] The thickness of each of the piezoelectric transmitter layer 22 and the piezoelectric receiver layer 36 may be selected so as to be suitable for generating and receiving ultrasonic waves. In one example, a PVDF planar piezoelectric transmitter layer 22 is approximately 28 pm thick and a PVDF-TrFE receiver layer 36 is approximately 12 pm thick. Example frequencies of the ultrasonic waves may be in the range of 5 MHz to 30 MHz, with wavelengths on the order of a millimeter or less. [0109] Figure 13B shows an exploded view of an alternative example of an ultrasonic sensor system. In this example, the piezoelectric receiver layer 36 has been formed into discrete elements 37. In the implementation shown in Figure 13B, each of the discrete elements 37 corresponds with a single pixel input electrode 38 and a single sensor pixel circuit 32. However, in alternative implementations of the ultrasonic sensor system 1300b, there is not necessarily a one-to-one correspondence between each of the discrete elements 37, a single pixel input electrode 38 and a single sensor pixel circuit 32. For example, in some implementations there may be multiple pixel input electrodes 38 and sensor pixel circuits 32 for a single discrete element 37.

[0110] Figures 13A and 13B show example arrangements of ultrasonic transmitters and receivers in an ultrasonic sensor system, with other arrangements being possible.

For example, in some implementations, the ultrasonic transmitter 20 may be above the ultrasonic receiver 30 and therefore closer to the object(s) to be detected. In some implementations, the ultrasonic transmitter may be included with the ultrasonic sensor array (e.g., a single-layer transmitter and receiver). In some implementations, the ultrasonic sensor system may include an acoustic delay layer. For example, an acoustic delay layer may be incorporated into the ultrasonic sensor system between the ultrasonic transmitter 20 and the ultrasonic receiver 30. An acoustic delay layer may be employed to adjust the ultrasonic pulse timing, and at the same time electrically insulate the ultrasonic receiver 30 from the ultrasonic transmitter 20. The acoustic delay layer may have a substantially uniform thickness, with the material used for the delay layer and/or the thickness of the delay layer selected to provide a desired delay in the time for reflected ultrasonic energy to reach the ultrasonic receiver 30. In doing so, the range of ti e during which an energy pulse that carries information about the object by virtue of having been reflected by the object may be made to arrive at the ultrasonic receiver 30 during a time range when it is unlikely that energy reflected from other parts of the ultrasonic sensor system is arriving at the ultrasonic receiver 30. In some implementations, the substrate 34 and/or the platen 40 may serve as an acoustic delay layer.

[0111] As used herein, a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. [0112] The various illustrative logics, logical blocks, modules, circuits and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. The interchangeability of hardware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0113] The hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or, any conventional processor, controller, microcontroller, or state machine. A processor also may be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes and methods may be performed by circuitry that is specific to a given function.

[0114] In one or more aspects, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and their structural equivalents thereof, or in any combination thereof. Implementations of the subject matter described in this specification also may be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage media for execution by, or to control the operation of, data processing apparatus.

[0115] If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium, such as a non- transitory medium. The processes of a method or algorithm disclosed herein may be implemented in a processor-executable software module which may reside on a computer-readable medium. Computer-readable media include both computer storage media and communication media including any medium that may be enabled to transfer a computer program from one place to another. Storage media may be any available media that may be accessed by a computer. By way of example, and not limitation, non- transitory media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Also, any connection may be properly termed a computer-readable medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and instructions on a machine readable medium and computer-readable medium, which may be incorporated into a computer program product.

[0116] Various modifications to the implementations described in this disclosure may be readily apparent to those having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the claims, the principles and the novel features disclosed herein. The word “exemplary” is used exclusively herein, if at all, to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

[0117] Certain features that are described in this specification in the context of separate implementations also may be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also may be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0118] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0119] It will be understood that unless features in any of the particular described implementations are expressly identified as incompatible with one another or the surrounding context implies that they are mutually exclusive and not readily combinable in a complementary and/or supportive sense, the totality of this disclosure contemplates and envisions that specific features of those complementary implementations may be selectively combined to provide one or more comprehensive, but slightly different, technical solutions. It will therefore be further appreciated that the above description has been given by way of example only and that modifications in detail may be made within the scope of this disclosure.