Patent Publication Number: US-9412928-B2

Title: Thermoelectric device

Description:
BACKGROUND 
     1. Technical Field 
     This disclosure generally relates to thermoelectric devices and more particularly to thermoelectric devices having a respective electrical current and a respective thermal gradient aligned approximately parallel or anti-parallel. 
     2. Description of the Related Art 
     Microprocessors, laser diodes, and other electronic devices generate heat during operation, which may adversely affect the performance of these devices. Electronic devices may be cooled by passive or active cooling systems. Passive cooling systems, which include heat sinks and heat pipes, dissipate heat. Design considerations in determining whether an electronic device can be cooled by a passive cooling system include the size requirement of the passive cooling system, the amount of ventilation at the passive cooling system, the operating temperature of the electronic device and the ambient temperature range where the device will be operated. Passive cooling systems might not be appropriate for many small electronic devices where the passive cooling system would require too much space or in devices where there is an insufficient amount of ventilation to dissipate the heat. 
     Active cooling systems may include refrigerators, e.g., mechanical vapor compression refrigerators, and thermoelectric coolers. Refrigeration based cooling systems generally require significant hardware such as a compressor, a condenser and an evaporator and require a relatively large amount of space. In addition, refrigeration based cooling systems include a large number of moving mechanical parts, which may be costly and which may require maintenance. In many electronic devices, it would be impractical and commercially non-viable to have refrigeration based cooling systems. Consumers may avoid purchasing an electronic device that needs to be maintained. 
     Active cooling systems also include thermoelectric cooling systems such as a Seebeck-Peltier (hereinafter “Seebeck”) device. Seebeck devices provide cooling (or heating) by passing an electrical current through a thermoelectric device. A typical Seebeck thermoelectric device includes a layer of a Seebeck effect material, which conducts electricity, and another layer of an electrical conductor. When a voltage is applied across the terminals of a Seebeck thermoelectric device, heat is absorbed or produced at the interface of the Seebeck effect material and the other electrical conductor, depending on the direction of the electrical current flow. 
     Seebeck thermoelectric devices offer many advantages over refrigeration based cooling systems. Seebeck thermoelectric devices may be relatively small, have no moving parts, may be operated in harsh environments such as a vacuum, and may be operated in any orientation. Thus, Seebeck thermoelectric devices may be utilized for providing solid-state cooling of small electronic devices. However, current Seebeck thermoelectric devices require cumbersome electrical connections and are not as efficient for their size as some of the other cooling systems. 
     There is a need for improved Seebeck thermoelectric devices. 
     BRIEF SUMMARY 
     In one aspect, a thermoelectric device includes a support structure and a plurality of thin-film thermoelectric elements. The support structure includes electrically insulating frame members that have a number of openings. The thin-film thermoelectric elements are electrically coupled together in parallel. Each respective thin-film thermoelectric element has a respective electrically conductive member and a respective Seebeck effect member that is electrically coupled to the respective electrically conductive member, and each thin-film thermoelectric element is at least partially positioned within a respective one of the plurality of openings. 
     In another aspect, a method of manufacturing a thermoelectric device having multiple thin-film thermoelectric elements includes forming a layer of a first material at a plurality of thin-film thermoelectric element locations on a generally planar first surface of a substrate; forming a layer of a second material over at least the layer of the first material at the plurality of thin-film thermoelectric element locations. The first material is either a Seebeck effect material or an electrically conductive non-Seebeck effect material, and the second material is the other one of the Seebeck effect material or an electrically conductive non-Seebeck effect material. The method further includes physically isolating the respective layer of the first material at a respective thin-film thermoelectric element location from the respective layer of the first material at all of the other thin-film thermoelectric element locations for each thin-film thermoelectric element location; physically isolating the respective layer of the second material at a respective thin-film thermoelectric element location from the respective layer of the second material at all of the other thin-film thermoelectric element locations for each thin-film thermoelectric element location; and electrically coupling a plurality of thin-film thermoelectric elements in parallel, where each respective thin-film thermoelectric element of the plurality of thin-film thermoelectric elements is at a respective one of the plurality of thin-film thermoelectric element locations, and each respective thin-film thermoelectric element includes the respective layer of the first material and the respective layer of the second material at the respective thin-film thermoelectric element location. 
     In another aspect, a method of manufacturing a thermoelectric device having a plurality of thin-film thermoelectric elements includes forming a respective opening in a first surface of a generally planar substrate at a first plurality of thin-film thermoelectric element locations; and least partially filling each respective opening with a layer of a first material of a respective thin-film thermoelectric element, the first material being one of a Seebeck effect material or a first electrically conductive non-Seebeck effect material. The method further includes providing a layer of a second material of a respective thin-film thermoelectric element material at each one of the first plurality of thin-film thermoelectric element locations. The second material is the first electrically conductive non-Seebeck effect material when the first material is the Seebeck effect material, or the second material being the Seebeck effect material when the first material is the first electrically conductive non-Seebeck effect material. A respective thin-film thermoelectric element includes the first material and the second material at the respective thin-film thermoelectric element location of the respective thin-film thermoelectric element. The method further includes providing a layer of a second electrically conductive non-Seebeck effect material that physically couples the first plurality of thin-film thermoelectric elements together, the second electrically conductive non-Seebeck effect material physically connected to a respective bottom surface of each thin-film thermoelectric element of the first plurality of thin-film thermoelectric elements; and providing a layer of a third electrically conductive non-Seebeck effect material that physically couples the first plurality of thin-film thermoelectric elements together, the third electrically conductive non-Seebeck effect material physically connected to a respective top surface of each thin-film thermoelectric element of the first plurality of thin-film thermoelectric elements. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a thermoelectric device according to one embodiment. 
         FIG. 2  is a cross sectional view of a portion of the thermoelectric device of  FIG. 1  according to one embodiment. 
         FIGS. 3A-3E  are cross sectional views of portion of a thermoelectric device during various stages of manufacture according to one embodiment. 
     
    
    
     In the drawings, identical reference numbers identify identical elements or elements in the same group and class. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements are enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not intended to convey any information regarding the actual shape of the particular elements and have been selected for ease of recognition in the drawings. 
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. Well-known structures associated with fabrication of semiconductor devices and/or with thermoelectric devices have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the preferred embodiments. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, for example “including, but not limited to.” 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. The term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
       FIG. 1  is a schematic side view of a thermoelectric device  100  according to one embodiment. The thermoelectric device  100  has an upper thermal surface  102  and a lower thermal surface  104 . The upper thermal surface  102  may have heat dissipating fins (not shown) in one embodiment. The lower thermal surface  104  may be sized and shaped to thermally couple to a surface of an object (not shown). For example, the lower thermal surface  104  may be generally flat or planar and sized to couple to or contact a surface of a processor or micro-processor. Alternatively, the lower thermal surface  104  may curved and sized and shaped to couple to or contact a non-planar surface such as a cylindrical surface. 
     In some embodiments, the upper thermal surface  102  may be sized and shaped to have a surface area as large as or larger than the surface area of lower thermal surface  104  and may be sized and shaped to efficiently transfer thermal energy. For example, the upper thermal surface  102  may include one or more fins, e.g., relatively thin strips of a material such as a metal that extend outward from the upper thermal surface  102 . 
     The thermoelectric device  100  includes terminals  106  and  108 , each of which is connected to an electrical conductor  110 ,  112 , respectively. An electrical current  114  is provided to the thermoelectric device  100  at the upper terminal  106 , via electrical conductor  110 . The electrical current  114  passes through the thermoelectric device  100  and exits at the lower terminal  108 , where the electrical current  114  is conducted away from the thermoelectric device  100  via electrical conductor  112 . 
     Passing the electrical current  114  through the thermoelectric device  100  produces a thermal gradient  116  between the upper and lower thermal surfaces  102 ,  104 , respectively. In the embodiment shown in  FIG. 1 , the lower thermal surface  104  is at a temperature lower than the temperature of the upper thermal surface  102 . If the direction of the electric current  114  is reversed such that the electric current  114  enters at terminal  108  and exits at terminal  106 , then the direction of the thermal gradient  116  is reversed such that the lower thermal surface  104  would be at a temperature higher than the temperature of the upper thermal surface  102 . 
     The direction of the thermal gradient  116  relative to the direction of current flow depends at least in part on materials used in the thermoelectric device  100 . In other words, if one class of materials such as n-type doped Seebeck effect materials are used, then the temperature variations from higher to lower may be in the same direction of the current flow. However, if another class of materials such as p-type doped Seebeck effect materials are used, then the temperature variations from higher to lower may be in the opposite direction of the current flow. 
       FIG. 2  shows a cross-sectional view of a portion of the thermoelectric device  100  of  FIG. 1 . The dashed box  118  shown in  FIG. 1  is representative of the portion of the thermoelectric device  100  shown in  FIG. 2 . 
     The thermoelectric device  100  includes a plurality of thin-film thermoelectric elements  120  and a support structure  122 . The support structure  122  includes a plurality of frame members  124 . The frame members  124  are spaced apart, and a plurality of legs  126  interpose adjacent frame members  124 . The support structure may be formed from a sacrificial material such as a silicon wafer using various conventional semi-conductor fabricating processes. 
     The thermoelectric device  100  further includes a layer of a first electrical terminal material  128  that forms upper thermal surface  102  of the thermoelectric device  100 , and a layer of a second electrical terminal material  130  that forms the bottom thermal surface  104  of the thermoelectric device  100 . The first electrical terminal material  128  and the second electrical terminal material  130  are electrically conductive and may be a metal or metal alloy such as, but not limited to, aluminum, copper, brass, etc. 
     A thin-film thermoelectric element  120  has an upper surface  132  and a bottom surface  134 . The upper surface  132  and bottom surface  134  are generally planar and are approximately parallel to each other. Each one of the upper surface  132  and the bottom surface  134  has a respective surface area in the range of 25-2500 m 2 . 
     A thin-film thermoelectric element  120  includes a layer of a first electrically conductive material  136 , and a layer of a Seebeck effect material  138 . The layer of the first electrically conductive material  136  may have a thickness in the range of 0.5-5 m, and the Seebeck effect layer  138  may have a thickness in the range of 2,000-20,000 angstroms. The first electrically conductive material  136  may be a metal such as copper, aluminum, gold, and silver and/or other metals or metal alloys. The layer of the first electrically conductive material  136  may be disposed in an opening  140  and may extend between adjacent frame members  124 . 
     The frame members  124  may be formed from an electrically insulative material and may be formed such that the first electrically conductive material  136  of one thin-film thermoelectric element  120  is physically isolated from all other thin-film thermoelectric elements  120  by various frame members  124 . The amount of the first electrically conductive material  136  deposited in one of the openings  140  is generally sufficient to at least partially or completely fill the respective opening  140  with the first electrically conductive material  136 . 
     The Seebeck effect material  138  is a material such as p-type or n-type doped material, such as, but not limited to, Tellurium. All of the Seebeck effect material  138  is doped with the same type of dopant. Namely, it is either all P-type or N-type. This permits the Seebeck effect material to be doped in a single step, such as when they are first deposited or after they are formed and doped with a blanket implant. This saves process steps and cost as compared to having adjacent Seebeck effect material doped with opposite conductivity type with respect to each other. Other Seebeck effect materials may be found in U.S. Publication 2005/0150536. 
     In some embodiments, a thin-film thermoelectric element  120  may include a layer of an optional electrically conductive barrier material  142  interposing the Seebeck effect material  138  and the first electrically conductive material  136 . Depending on materials selected for the first electrically conductive material  136  and the Seebeck effect material  138 , there may be an undesirable interaction such as a chemical reaction and/or electromigration therebetween. The electrically conductive barrier layer  142 , if present, will coat a top surface of the first electrically conductive material  136  (and/or a bottom surface of the Seebeck effect material  138 ) so as to prevent and/or inhibit undesirable interactions between the Seebeck effect material  138  and the first electrically conductive material  136 . The electrically conductive barrier layer  142 , if present, may be substantially chemically inert with one or the other or both of the Seebeck effect material  138  and the first electrically conductive material  136 . 
     Similarly, the materials selected for the first electrical terminal material  128  and the Seebeck effect material  138  may undesirably interact. In that case, a layer of an electrically conductive barrier material  144  may interpose the first electrical terminal material  128  and the Seebeck effect material  138 . The electrically conductive barrier material  144 , if present, will coat an upper surface of the Seebeck effect material  138  (and/or a bottom surface of first electrical terminal material  128 ) so as to prevent and/or inhibit undesirable interactions between the Seebeck effect material  138  and the first electrical terminal material  128 . In that case, the electrically conductive barrier material  144  forms the upper surface  132  of the thin-film thermoelectric element  120 . The electrically conductive barrier layer  144 , if present, may be substantially chemically inert with one or the other or both of the Seebeck effect material  138  and the first electrical terminal material  128 . 
     Nonlimiting examples of materials that may be used for the electrically conductive barrier materials  142 ,  144  include Ta, TaN, Pt, and TiW. The electrically conductive barrier layer  142 ,  144  are generally a thin film, if present in the thermoelectric device  100 . 
     The thermoelectric device  100  further includes a plurality of frame caps  146 . The frame caps  146  extend generally transversely and longitudinally above the frame members  124 . The frame caps  146  may be formed and shaped such that the Seebeck effect material  138  of one thin-film thermoelectric element  120  is physically isolated from all other thin-film thermoelectric elements  120 . The frame caps  146  may be an electrically insulative material such as, but not limited to, silicon dioxide, silicon nitride, polyimide, etc. 
     The layer of the first electrical terminal material  128  is disposed over the thin-film thermoelectric elements  120  and generally over the support structure  122  including the frame caps  146 . The first electrical terminal material  128  electrically couples each thin-film thermoelectric element  120  of the thermoelectric device  100  in parallel at the respective upper surfaces  132 . The first electrical terminal material  128  may be a metal such as aluminum, copper, gold, silver, brass alloy, or other electrical conductor. 
     The support structure  122  includes a plurality of openings  148 . A respective opening extends between adjacent legs  126  or between a frame member  124  and a leg  126  adjacent thereto. The layer of the second electrical terminal material  130  is disposed beneath the support structure  122  and fills the plurality of openings  148 . The second electrical terminal material  130  is in physical and electrical contact with the bottom surface  134  of each thin-film thermoelectric element  120 . The second electrical terminal material  130  electrically couples each thin-film thermoelectric element  120  of the thermoelectric device  100  in parallel at the respective bottom surfaces  134 . 
       FIGS. 3A-3E  show a process for manufacturing a thermoelectric device  100  according to one embodiment. The thermoelectric device  100  may be formed using conventional semiconductor processing techniques such as, but not limited to, physical vapor deposition, chemical vapor deposition, e-beam evaporation, contact lithography, UV stepper, masking, and etching, e.g., plasma etch, wet etch. 
     A substrate  200  such as an undoped silicon wafer is shown in  FIG. 3A . The substrate  200  includes a first surface  202  and a second surface  204 . Prior to patterning the substrate  200 , the first and second surfaces  202 ,  204  are generally parallel and planar. After patterning the substrate  200 , the first surface  202  has a plurality of thin-film thermoelectric element locations  206  formed therein. Each thin-film thermoelectric element location  206  includes recesses  140  extending from the first surface  202  inward toward the second surface  204  of the thin-film thermoelectric element. The openings  140  may be formed in the substrate  200  via conventional semiconductor fabrication processes such as chemical etching. 
     The recesses  140  are etched into the substrate to a desired depth. After the recesses  140  have been formed in the substrate  200 , a layer of the first electrically conductive material  136  is formed over the substrate  200  at least partially filling each opening  140  and covering the first surface  202  of the substrate  200 . In one embodiment, the first electrically conductive material  136  completely fills each one of the openings  140 . Portions of the first electrically conductive material  136  are selectively removed such as by chemical mechanical polishing processing so that each portion of the first electrically conductive material  136  in a respective opening  140  is electrically and physically isolated from all other portions of first electrically conductive material  136  in other openings  140 . 
     As shown in  FIG. 3B , a layer of the Seebeck effect material  138  is formed over the etched electrically conductive material  136 . The Seebeck effect material  138  covers the first surface  202  of the substrate  200  and the remaining portions of the first electrically conductive material  136 . Portions of the Seebeck effect material  138  are selectively removed such that the Seebeck effect material  138  at a respective thin-film thermoelectric element location  206  is physically isolated from the Seebeck effect material  138  at adjacent thin-film thermoelectric element locations  206 , as shown in  FIG. 3C . 
     In some embodiments, after patterning the first electrically conductive material  136  and prior to forming the layer of the Seebeck effect material  138 , a layer of the electrically conductive barrier material  142  (see  FIG. 2 ) may be formed over the substrate  200  so as to cover the patterned electrically conductive material  136  and the exposed portions of the first surface  202  of the substrate  200 . The layer of the electrically conductive barrier material  142  is then patterned such that selective portions of the electrically conductive barrier material  142  are removed. The removed portions generally correspond to portions of the electrically conductive barrier material  142  outside of the respective thin-film thermoelectric element locations  206 . Then, the layer of the Seebeck effect material  138  is formed over the wafer  200 . 
     As shown in  FIG. 3C , after patterning and removing portions of the layer of the Seebeck effect material  138 , a layer of an electrically insulative material  216  is formed over the wafer  200 . The electrically insulative layer  216  may be a material such as a polyimide or silicon dioxide or silicon nitride or other electrically insulative materials. Portions of the electrically insulative layer  216  are selectively removed. The removed portions are generally removed from inside of the thin-film thermoelectric element locations  206 . The layer of the electrically insulative material  216  is patterned and etched to form the frame caps  146  (see  FIG. 3D ). 
     As shown in  FIG. 3D , after forming the frame caps  146 , the layer of the first electrical terminal material  128  is formed over the wafer  200 . The first electrical terminal material  128  is in physical and electrical contact with the Seebeck effect material  138  at each thin-film thermoelectric element location  206  in one embodiment. 
     In some embodiments, after forming the frame caps  146  and prior to forming the layer of the first electrical terminal material  128 , a layer of a barrier material  144  (see  FIG. 2 ) may be formed over the substrate  200  thereby covering the frame caps  146  and the exposed portions of the Seebeck effect material  138 . The layer of the barrier material  144  is then patterned such that selective portions of the barrier material  144  are removed. The removed portions generally correspond to portions of the barrier material outside of respective thin-film thermoelectric element locations  206 . Then, the first electrical terminal material  128  is formed over the wafer  200 . In this embodiment, the barrier material  144  provides electrical contact between the Seebeck material  138  and the conductive layer  128 . 
     As shown in  FIG. 3E , the second surface  204  of the substrate  200  is patterned and selective portions of the substrate  200  are removed therefrom to form the openings  148 , which extend from the second surface  204  of the substrate  200  to the thin-film thermoelectric element location bottom surface  134  of the respective thin-film thermoelectric element locations  206 . After the openings  148  are formed, the layer of the second electrical terminal material  130  is formed. The second electrical terminal material  130  covers the second surface  204  of the substrate  200  and at least partially fills the openings  148 . The second electrical terminal material  130  electrically couples together the respective bottom surfaces  134  of the thin-film thermoelectric elements  120  together. In operation, current flows from the back electrical terminal  130  to the front electrical terminal  128 . Electrical voltage connections are provided (not shown) to cause current to flow in this direction. Heat therefore flows from the front to the back, causing the top to cool and the back to heat for a P-type Tellurium Seebeck material. If it is desired to have the bottom cool and the top to heat, the direction of the current can be reversed or the Seebeck material can be doped N-type. 
     By having only one doping type of Tellurium, a larger portion of the wafer is Tellurium and efficient cooling is achieved. Much fewer masking steps are also needed than if two types of doped Tellurium are used and the electrical terminals are both on the top surface. 
     The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. 
     The various embodiments described above can be combined to provide further embodiments. To the extent that they are not inconsistent with the specific teachings and definitions herein, all of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary, to employ systems and concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.