PACKAGING MULTIPLE MEASURANDS INTO A COMBINATIONAL SENSOR SYSTEM USING ELASTOMERIC SEALS

TECHNICAL FIELD

[001] Embodiments are generally related to sensor methods and systems. Embodiments are additionally related to methods and systems for manufacturing and packaging multiple sensors in a single package. Embodiments are also related to combinational sensors.

BACKGROUND OF THE INVENTION

[002] Many processes and devices have been implemented and used for measuring more then one measurand simultaneously. A miniature MEMS (Micro-Electro-Mechanical Systems) based flow or pressure transducer can be used to measure flow or pressure and with a reliable accuracy. Such MEMS based sensors have been implemented, for example, in various independent sensing devices, such as medical applications, some of which utilize silicon based thermal mass flow or piezoresistive sensing technology for measuring wide ranges of flow and pressure. Other multiple sensing implementations, for example, include instrumentation and environmental applications.

[003] MEMS involve the integration of micro-mechanical elements, sensor actuators, and electronic components on a common silicon substrate through the use of micro fabrication technology. While the electronics can be fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), the micromechanical components can be fabricated utilizing compatible "micromachining" processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.

[004] The majority of prior art transducers are either sold with calibrated or un-calibrated analog outputs or as transducers with small-signal

outputs, either of which may need to be conditioned and calibrated by the end user within their system. Further, the analog signals conditioned by the user must pass through an analog-to-digital converter so that the output signals can be processed by the system, which may be microcontroller- based. The most common measurands are flow, pressure, temperature and humidity and the output signals from the raw transducers are typically not linear and vary as a function of temperature.

[005] In some sending applications, it is preferred that a signal conditioning/signal amplification capability be incorporated into the sensor. It is believed that there are currently no sensors available for efficiently and accurately measuring multiple measurands. Therefore, to overcome the forgoing shortcomings, it is desirable to provide for a suitable packaging method and/or system for measuring multiple measurands. It is further believed that if such a sensor is implemented, the result sensor design can assist in lowering installation and development costs, while eliminating secondary operations and shortening the design cycle time.

BRIEF SUMMARY

[006] The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[007] It is, therefore, one aspect of the present invention to provide for improved sensor methods and systems.

[008] It is another aspect of the present invention to provide packaging for a combinational sensor for measuring multiple measurands.

[009] It is another aspect of the present invention to provide for a method of designing a combinational pressure sensor system for measuring multiple measurands.

[0010] The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A combinational sensor system for measuring multiple measurands includes a flow sensor, a pressure sensor and a humidity sensor. The pressure sensor and humidity sensor can have independent access to the media and is ratiomethc to the supply voltage, whereas the flow sensor is sensitive to openings to the flow path. The combinational sensor utilizes elastomehc seals in which at least one seal is electrically conductive. An Application Specific Integrated Circuit (ASIC) is generally associated with the combinational sensor, wherein the ASIC can be placed on a patterned electrically conductive substrate, e.g. printed circuit board or thick film based ceramic, or lead frame for signal conditioning in order to detect flow, pressure, humidity or temperature. The transducers can be arranged in order to optimize accuracy and/or response time of the combinational sensor system or optimal access to the media.

[001 1] The geometry of the combinational sensor system for measuring multiple measurands includes a pressure transducing silicon die which includes piezoresistive material. A MEMS (Microelectromechanical System) sensing diaphragm is generally associated with the piezoresistive material, wherein the sensing diaphragm deflects when a pressure is applied thereto. An impedance circuit is generally embedded with one or more piezoresistive elements on the sensing diaphragm to which the pressure to be detected is applied. Electrical connections to the piezoresistive elements are made to electrical contacts placed on either the front or back-side of the silicon die. The silicon die is located between a patterned sandwich combination of a conductive elastomehc seal and a non-conductive elastomeric pressure seal making electrical connections to respective electrical contacts on the surface of a silicon die. A non-conductive elastomeric pressure seal makes a mechanical seal on the opposite face on the silicon die.

[0012] The combinational sensor system can also include other silicon-based transducers which can include a humidity sensor. This embodiment of a transducer can be mounted in a similar manner to the pressure transducing silicon die in the above.

[0013] The patterned sandwich combination of conductive elastomeric seal and non-conductive elastomeric pressure seal can be used for providing an electrical contact from the impedance circuit associated with the silicon piezoresistive material to the patterned electrically conductive substrate or lead frame connected to the ASIC. This generally includes an un-amplified Wheatstone bridge output or an amplified output of the bridge response of a pressure transducer. The non-conductive elastomeric pressure seal can be placed on the non-conductive regions of a silicon die. The non-conductive pressure seal on each elastomeric seal will also provide a liquid seal allowing for very high humidity or liquid media.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.

[0015] FIG. 1 illustrates a perspective view of a combinational sensor system, which can be implemented in accordance with a preferred embodiment;

[0016] FIG. 2 illustrates a sectional view A-A of a combinational sensor system, which can be implemented in accordance with an alternative embodiment;

[0017] FIG. 3 illustrates a detailed view of the pressure sensor shown in FIGS. 1 -2, in accordance with a preferred embodiment; and

[0018] FIG. 4 illustrates a high level flow diagram of operations depicting logical operational steps of a method for designing a combinational sensor system, in accordance with a preferred embodiment.

DETAILED DESCRIPTION

[0019] The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.

[0020] FIG. 1 illustrates a perspective view of a combinational sensor system 100, which can be implemented in accordance with a preferred embodiment. The combinational sensor 100 can measure multiple measurands and includes a flow tube 180 in association with an mass flow die 130, a pressure sensor 150 and a humidity sensor 160. A pair of sampling ports 120 and 125 can be provided. The pressure sensor 150 and the humidity sensor 160 can each possess independent access to the media and are ratiomethc to the supply voltage (not shown), whereas the air flow die 130 is sensitive to openings to the flow path of the flow tube 180.

[0021 ] An ASIC 170 is generally associated with the combinational sensor system 100. The ASIC 170 can be placed on a patterned electrically conductive substrate or lead frame 190 for signal conditioning in order to detect flow, pressure, humidity and/or temperature. An electrical interconnect 1 10 can be utilized for the electrical connection of the combinational sensor system 100 to the supporting application. The pressure sensor 150, humidity sensor 160, and air flow die 130 can be arranged in a manner that distributes the transducers 130, 150, or 160 in order to optimize the accuracy and/or response time of the combinational sensor system 100.

[0022] FIG. 2 illustrates a sectional view A-A of a combinational sensor system 200 with a flow restrictor or pitot tube flow-sampling element 210, which can be implemented in accordance with an alternative embodiment. Note that in FIGS. 1-3, identical or similar parts or elements are generally indicated by identical reference numerals. For example, the flow tube 180, the air flow transducer 130, the pressure transducer 150 and the humidity transducer 160 depicted in FIG. 1 also appears in the configuration of sensor

200 depicted in FIG. 2. Arrow 280 indicates the bi-directional flow of air through the flow tube 180, which passes through the flow restrictor or over a flow-sampling element such as a pitot tube 210. In the case of a flow restrictor 210 disposed in the flow tube 180 creates a pressure drop in the air flow bypass chamber 140. A pair of sampling ports 120 and 125 is generally arranged in adjacent locations of flow tube 180. For the Pitot tube, ports 120 and 125 will reside on opposite sides of 210. Another pair of sampling ports 290 and 295 can be arranged in any position of flow tube 180. The media flows into the sampling ports 120 and 125 arranged in the flow tube 180 and which is exposed to the pressure sensor 150 and humidity sensor 160 for measurement.

[0023] The geometry of the transducers 150 and 160 for measuring multiple measurands includes a piezoresistive material or humidity sensitive dielectric material (not shown) located between a patterned sandwich combination of conductive elastomeric and non-conductive elastomeric pressure seal 230 and 250 and a non-conductive elastomeric pressure seal 220 and 260. The patterned sandwich combination of conductive elastomeric and non-conductive elastomeric pressure seal 230 and 250 can be used for the electrical connection of the sensors 160 and 150 to the substrate 190 that connects to the ASIC 170 and for mechanical "sealing" around the conductive connections to prevent shorting and leaking. The non-conductive elastomeric seal 220 and 260 can be utilized for mechanical "sealing" of the sensors 160 and 150 within the combinational sensor 100. The pressure sensor 150 includes a sensing diaphragm 270 that is generally associated with the piezoresistive material, wherein the sensing diaphragm 270 deflects when a pressure is applied thereto. The ASIC 170 is generally placed on a patterned electrically conductive substrate or lead frame 190 so that either a temperature sensor in the ASIC 170 or other temperature sensing mechanism local to the other measurands can be used for temperature compensation. The pressure sensor 150 and humidity sensor 160 are ratiomethc to the supply voltage (not shown).

[0024] FIG. 3 illustrates a detailed view of the pressure sensor 150 depicted in FIG. 1 , which can be implemented in accordance with a preferred embodiment. The pressure sensor 150 contains a diaphragm 270 that includes two sets of piezoresistors 310 and 320 buried in the face of a thin, chemically-etched silicon diaphragm 270. The pressure causes the diaphragm 270 to flex, inducing a stress or strain in the diaphragm 270 and the buried resistors 310 and 320. The resistors 310 and 320 values change in proportion to the stress applied and thereafter produces an electrical signal. The patterned sandwich combination of conductive elastomeric seal and non-conductive elastomeric pressure seal 230 can be utilized for providing an electrical contact from the impedance circuit associated with the silicon piezoresistors 310 and 320 to a patterned electrically conductive substrate or lead frame 190 connected to the ASIC 170.

[0025] Such a configuration generally includes the use of an un- amplified Wheatstone bridge output or an amplified output of the bridge response of the pressure sensor 150. The silicon piezoresistors 310 and 320 can be configured as a four-resistor Wheatstone bridge fabricated on a single monolithic die utilizing micromachining technology. The non- conductive elastomeric pressure seal 260 can be placed on the backside. The patterned sandwich combination of conductive elastomeric seal and non-conductive elastomeric pressure seal 230 and the non-conductive elastomeric pressure seal 260 also provide a liquid seal allowing for very high humidity or liquid media.

[0026] FIG. 4 illustrates a high level flow diagram of operations depicting a method 400 for designing a combinational sensor system, in accordance with a preferred embodiment. The pressure sensor 150, flow transducer 130, humidity transducer 160 and ASIC 170 can be arranged apart from each other on substrate 190, as depicted at block 410. Thereafter, as indicated at block 420, a flow resthctor or a flow-sampling

element such as a pitot tube 210 can be disposed in flow tube 180. Flow sensor die 130 can be disposed in sensing channel of flow tube 140, as shown at block 430. Next, as described at block 440, a sensing element of pressure transducer 150 and humidity transducer 160 can be sandwiched between two elastomeric seal 230, 260 and 220, 250 on the substrate 190.

[0027] The conductive elastomeric seal 230 and 250 can be patterned for providing an electrical contact to a patterned electrically conductive substrate or lead frame 190 connected to the ASIC 170, as depicted at block 450. The non-conductive elastomeric seal 220 and 260 can be patterned for providing mechanical sealing for the transducers 160 and 150, as illustrated at block 460. Non-conductive elastomeric seal can also be patterned for providing mechanical sealing for the sensor housing, as illustrated at block 470.

[0028] The combinational sensor system described herein can be inexpensively manufactured and marketed and can include temperature compensation and calibration capabilities, along with media flow-through ports and true "wet" differential sensing. Such a sensor system is also operable after exposure to frozen conditions with a choice of termination for gage sensors. The disclosed combinational sensor system can also provide interchangeability, proven elastomeric construction, ASIC-based signal conditioning and digital output and can be used to measure vacuum or positive pressure.

[0029] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.