OF DEVICE STRUCTURES AND MATERIALS

BACKGROUND

Cross-Reference To Related Applications

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 61/702839 filed on September 19, 2012 the content of which is relied upon and incorporated herein by reference in its entirety.

Field

[0002] The present disclosure relates generally to the field of resistance measurement methods and devices and more particularly to methods and devices for measuring resistance of a thermoelectric material or contact resistance of one or more interfaces within a structure of a thermoelectric material or device.

Technical Background

[0003] Thermoelectric ("TE") devices used in power generation or cooling/heating applications typically utilize p- or n-type semiconductor materials, as categorized by the dominant free carrier concentration present in the TE material. Although TE materials can generate a buildup of electrical charge in response to a temperature difference, it can be a challenge to allow the accumulated charge to flow efficiently to a place where it can do useful work.

[0004] Low electrical resistance materials such as copper or other metals are often used as electrode material to provide a low-resistance pathway for the accumulated or generated charge to move through, to allow the charge do useful work. Alternatively, such low resistance electrode materials may also be used to provide current to the TE material to cool (or heat) the TE material.

[0005] A major source of parasitic energy loss during operation of TE devices the electrical contact resistance at the interface between the electrode material and the TE material. The contact resistance is generally believed to be due to imperfection in the lattice structure where two materials meet. The negative effects of such contact resistance are illustrated with respect to the thermoelectric device 100 represented in Figure 1. In the example in Figure 1, a current / flows from left to right from an electrode material 104 into a TE material 102.

Accumulated resistance along the current path is represented by the trace 106. Negligible resistance is present in the electrode material 104 relative to the TE material 104, and a constant buildup of accumulated resistance occurs along the current path within the TE material 102. But at the interface between the electrode material 104 and the TE material 102, there is a dramatic step-like increase. This change is attributable to the contact resistance ARc between the electrode material 104 and the TE material 102. This contact resistance can be caused by either charge carrier deficiency or band offset between two materials. In order to minimize parasitic energy loss it is desirable to have low contact resistance at the interface between electrode material and the TE material. Accordingly, it would be desirable to provide a reliable measurement method and device to evaluate electrical resistance of a TE material and particularly to evaluate contact resistance between a TE material and an adjoining electrode material or other layer, desirably a method and device that can provide quick feedback regarding resistance and particularly contact resistance between layers during manufacturing or research.

SUMMARY

[0006] This disclosure describes methods and devices for measuring electrical contact resistance between layers of TE devices and resistance of TE materials generally. In addition, the methods and devices described here may be useful to measure electrical resistance variation (variation in bulk resistance) across any kind of material. The methods and devices of the present disclosure may be particularly useful in measuring the resistance between one region and another of a surface where one (or both) of the regions have one or more small dimensions, measured along the surface. For example, on the surface shown in plan view in Figure 2, the region or layer 130 and the region or layer 124 have a small dimension in the vertical direction of the page of the figure. The methods and devices of the present disclosure are particularly useful to enable quick and easy measurement of resistance from one such region or layer having a small dimension to another region or layer (which may or may not also have a small dimension).

[0007] According to one aspect of the disclosure, a method is provided for measuring resistance of a structure, with the method comprising the steps of (a) providing a structure, (b) providing a contact pin array electrically connected to one or more resistance measuring circuits via a switch, (c) contacting the structure with the contact pin array, (d) with the switch in a first configuration, measuring, with the one or more circuits, the resistance between a first pair of pins in the contact pin array, (e) without repositioning the contact pin array relative to the structure, and with the switch in a different configuration from a configuration of an immediately previous measurement, measuring, with the one or more circuits, the resistance between a different pair of pins in the contact pin array, and (f) repeating step (e).

[0008] According to a further aspect, the step of providing a contact pin array includes providing an array of contact pins arranged in rows and columns, and the step of contacting the structure with the contact pin array further comprises contacting such that said rows and columns are not aligned with said region's shortest direction. Desirably, the step of contacting the structure with the contact pin array comprises contacting such that the columns of the contact pin array form an angle with said region's shortest direction within the range of tan ^_1 (RS/N-CS) ± 15%, or more desirably ± 5% or even 1%, where RS is the row spacing distance and CS is the column spacing distance and N is the number of pins in a row.

[0009] According to yet another aspect of the disclosure, a device for measuring the electrical resistivity between multiple pairs of points on the surface of a structure is provided, with the device comprising a contact pin array comprising multiple contact pins, a switch electrically connected to the multiple contact pins, one or more resistance measuring circuits electrically connected to the switch, and an actuator arranged to bring the contact pin array into contact with a surface of the structure to be measured. The switch is structured so as to be reconfigurable to successively electrically connect the one or more resistance measuring circuits to successive pairs of the contact pins, such that electrical resistance may be measured at multiple locations on the surface of the structure without repositioning the contact pin array.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements, in which:

[0011] Figure 1 is a perspective view of a section of a thermoelectric device; [0012] Figure 2 is a plan view of a structure useful as, or in, a thermoelectric device;

[0013] Figure 3 is a flow diagram useful in explaining certain embodiments of methods according to the present disclosure;

[0014] Figure 4 is the plan view of Figure 2 together with a schematic diagram of certain aspects of an embodiment a device useful for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device according to embodiments of methods of the present disclosure;

[0015] Figures 5 and 6 are schematic diagrams of additional embodiments of a device for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device according to further embodiments methods of the present disclosure;

[0016] Figure 7 is a plan view of a structure useful as, or in, a thermoelectric device, showing one possible location and arrangement of an embodiment of contact pins of a contact pin array useful in certain devices and methods of the present disclosure for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device;

[0017] Figure 8 is a plan view similar to that of Figure 7 but showing another embodiment of an arrangement contact pins of a contact pin array useful in certain further devices and methods for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device;

[0018] Figure 9 is a schematic diagram showing yet another embodiment of a location and an arrangement of contact pins of a contact pin array useful in certain further devices and methods for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device; and

[0019] Figure 10 is a schematic elevation view of another embodiment or additional aspects of a device for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device, and useful in some embodiments of methods therefor.

DETAILED DESCRIPTION

[0020] Before turning to the figures, which illustrate several embodiments in detail, it should be understood that the application is not limited to the exact details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting.

[0021] Figure 2 is a plan view of a structure useful as, or in, a thermoelectric device 100.

The Device 100 includes multiple layers, including a TE (thermoelectric) material 102, two copper end electrodes 104, transition electrode materials 120 and 130, and at one end, (or optionally at both in alternative embodiments) one or more interlay ers 122, 124 for providing a low-contact-resistance transition from the TE material 102 to the transition electrode material 120.

[0022] Quick characterization of devices such as device 100 of Figure 2, and of thermoelectric materials generally, is desirable for both manufacturing and research. In particular, it is desirably to quickly and reliably measure the resistance between the various layers of the device to quickly detect any anomalously high contact resistance and identify the interface at which such resistance arises, so that the manufacturing conditions can quickly be corrected or optimized to keep the total contact resistance low. For research, quick measurement is desirable so that the cycle time for successive experiments can be minimized.

[0023] Figure 3 is a flow diagram representing certain embodiments of methods according to the present disclosure. Embodiments of the method will be described with respect to Figure 3 and with respect to Figures 4-10, which show various embodiments of devices 200 for measuring resistance, with the devices to be described in more detail below. (For

convenience in reviewing Figure 3, the reader may refer particularly to Figure 4 in addition to Figure 3.) According to an embodiment of the method of Figure 3, a method 10 for measuring resistance of a structure 100 is provided. The method 10 comprises a step 12 of providing a structure 100 the resistance of which is to be measured; a step 14 of providing a contact pin array 20 electrically connected to one or more resistance measuring circuits 40, 50 via a switch 30; a step 16 of contacting the structure 100 with the contact pin array 20 with the switch 30 in a first configuration; a step 18 of measuring, with the one or more circuits 40, 50, the resistance between a first pair of pins in the contact pin array 20; a step 19 of, without repositioning the contact pin array 20 relative to the structure 100, and with the switch 30 in a different configuration from a configuration of an immediately previous measurement, measuring, with the one or more circuits 40, 50, the resistance between a different pair of pins in the contact pin array 20; and repeating step 19. The contact pin array 20 is desirably comprised of spring-loaded or otherwise elastically-loaded pins, such that each pin makes individual physical contact with the structure 100 under an elastic load when the structure 100 is contacted with the array 20.

[0024] Figure 4 shows a schematic diagram of one embodiment of a device 200 useful in carrying out an embodiment of the method of Figure 3. The device 200 is capable of measuring the electrical resistivity between multiple pairs of points on the surface of a structure 100 or a thermoelectric material or device 100. The device 200 includes a contact pin array 20 comprising multiple contact pins 22, a switch 30 electrically connected to the multiple contact pins 22, one or more resistance measuring circuits 60 electrically connected to the switch 20, and (shown in Figure 10 only, and not in Figure 4) an actuator 204 arranged to bring the contact pin array 20 into contact with a surface of the material or device 100 to be measured. The one or more resistance measuring circuits 60 include in this embodiment a square-wave current reference 50 and a volt meter 40. The pin array 20 includes also, in this embodiment, a single contact pin 21 for contacting one end of the device 100 to be measured, such as at one of the metal (such as copper) electrodes 104, as shown. (In this particular embodiment of Figure 4, the square wave current reference 50 is electrically connected to the switch 20 via the electrode 104 of the device 100 and the contact pin 21.) The switch 30 is structured so as to be reconfigurable to

successively electrically connect the one or more resistance measuring circuits 60, 40, 50 to successive pairs of the contact pins 22, such that electrical resistance may be measured at multiple locations on the surface of the structure 100 without repositioning the contact pin array 20. This arrangement, together with the method of Figure 3, allows for quick and reliable resistance measurements without the need for repositioning the contact pin array 20, and without the resulting position error noise generated by such repositioning between measurements.

[0025] Figures 5 and 6 are schematic diagrams of additional embodiments of a device

200 for measuring the contact resistance of one or more interfaces within a structure of a thermoelectric device 100 according to further embodiments and methods of the present disclosure. In Figure 5, there are not separate contacts for the current source 50 and the voltage meter 40, but in this embodiment both are connected in parallel on the same circuit 60. An individual lead of the switch 30 is shown as closed, showing an example of one configuration of the switch 30. In Figure 6, the current source 50 and volt meter 40 are similarly paralleled, but the switch 30 in this case is a cross-bar type switch, rather than the one-to-many type switch 30 represented in Figures 4 and 5. In the cross-bar type switch, any input is selectably connectable to any output. Accordingly, all pins in that contact pin array 20 may be pressed onto one side of the device 100 to be tested, and a single contact pin at one end of the device 100 need not be used, as the test circuit may be completed between any two pins of the contact pin array 20.

[0026] According to another alternative aspect of the methods and devices of the present disclosure, the contact pin array 20 may be a linear array, with contact pins 22 in the positions shown in Figure 7, for instance. On the other hand, the contact pin array 20 may alternatively be a two-dimensional array, such as the one shown in the embodiment of Figure 8, in which the contact pins 22 are spread out in two dimensions across a surface of the device 100 to be tested. Such a two dimensional array, or such a linear array, may be used with either type of switch as described in Figures 5 and 6.

[0027] In the particular embodiment of Figure 8, the pins 22 are arranged in rows R with a consistent row spacing between them and columns C with a consistent column spacing between them. With such an evenly spaced array 20, if RS represents the row spacing distance and CS represents the column spacing distance, and if N represents the number pins in a given row (eight in the embodiment show), then it is desirable that, in the step of contacting the structure with the contact pin array, the contacting is performed such that the columns C of the contact pin array 20 form an angle with a small region's shortest direction (such as region 130 or region 124, which both have the vertical direction on the page of the figure as the shortest direction) within the range of tan ^_1 (RS/N ^» CS) ± 15%. This is because at an angle of tan ^_1 (RS/N ^» CS), the pins across one row will be evenly spaced in the region's shortest direction between the pins of the immediately next and the immediately previous row. This method allows an array with limited resolution to effectively obtain higher resolution in the shortest direction, such that

measurements of the surface of the small region(s) can be reliably taken without high precision positioning and re-positioning of the array 20. Desirably, the angle formed by the columns C with a small region's shortest direction is closer to the ideal, such as within the range of tan ^" '(RS/N'CS) ± 5%, or event tan ^_1 ( S/N-CS) ± 1%.

[0028] As represented in the schematic diagram of Figure 9, according to another aspect of the present methods and devices, the contact pin array 20 may be in the form of a three - dimensional contact pin array, such as a contact pin array that includes two or more two- dimensional contact pin arrays 20 applied to two or more sides of the device 100 to be measured. The two or more two-dimensional contact pin arrays may also be arranged in rows and columns, and may also be angularly offset from the smallest dimension direction, and may have rows aligned to form the equivalent of one row wrapping around the device 100 to be measured. Thus the resolution increasing technique described with respect to Figure 8 may be applied across multiple sides of the device 100, and the step of contacting the structure with the contact pin array 20 may include contacting the structure with the contact pin array on two or more sides of the structure 100.

[0029] According to the devices and methods of the present disclosure, and particularly according to the devices and methods of the embodiments of Figures 8 and 9 described above, a contact pin of the contact pin array may reliably contact a region having a shortest direction along the surface of the device 100, of 5 mm or less, or even 2 mm or less, desirably 1 mm or less or even 0.5 mm or less. Thus very small layers can be contacted without difficulty, and the contribution to the overall resistance of the device 100 of the interfaces between even such very thin layers can easily be detected.

[0030] Figure 10 shows an additional embodiment of a device 200 for carrying out one or more of the methods of the present invention. As shown in the embodiment of Figure 10, the device 200 includes a stage 202 for reliably positioning the device 100 to be measured, and an actuator 204 for bringing the device 200 and the contacting pin array 20 into contact. The actuator 204 and the stage 202 are desirably supported by a unitary frame 201.

[0031] For the purposes of describing and defining the present disclosure it is noted that the terms "substantially," "about," and "approximately" are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. For example, the microfluidic channel 20 diameter is between "about" 100 nm to "about" 1 mm signifies that the diameter of the microfluidic channel 20 encompasses not only variation that result from fabrication but also variations that are necessitated by the type of fluid or desired use of the microfluidic device 15. The terms

"substantially," "about," and "approximately" are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0032] Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Rather, the claims appended hereto should be taken as the sole representation of the breadth of the present disclosure and the corresponding scope of the various embodiments described herein. Further, it will be apparent that modifications and variations are possible without departing from the scope of the disclosure defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[0033] It is noted that one or more of the following claims utilize the term "wherein" as a transitional phrase. For the purposes of defining the present disclosure, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term "comprising."

[0034] While the present disclosure has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims.