Patent Application
20070028956
The present invention relates to the field of electronics, and more particularly to methods of forming thermoelectric devices for thermoelectric cooling and/or power generation and related devices.
Thermoelectric materials may be used to provide cooling and/or power generation according to the Peltier effect. Thermoelectric materials are discussed, for example, in the reference by Venkatasubramanian et al. entitled “Phonon-Blocking Electron-Transmitting Structures” (18th International Conference On Thermoelectrics, 1999), the disclosure of which is hereby incorporated herein in its entirety by reference.
Application of solid state thermoelectric cooling may be expected to improve the performance of electronics and sensors such as, for example, RF receiver front-ends, infrared (IR) imagers, ultra-sensitive magnetic signature sensors, and/or superconducting electronics. Bulk thermoelectric materials typically based on p—BixSb2-xTe3 and n—Bi2Te3-xSex alloys may have figures-of-merit (ZT) and/or coefficients of performance (COP) which result in relatively poor thermoelectric device performance.
The performance of a thermoelectric device may be a function of the figure(s)-of-merit (ZT) of the thermoelectric material(s) used in the device, with the figure-of-merit being given by:
ZT=(α2T/σKT) (equation 1)
where α, T, σ, KT are the Seebeck coefficient, absolute temperature, electrical conductivity, and total thermal conductivity, respectively. The material-coefficient Z can be expressed in terms of lattice thermal conductivity (KL), electronic thermal conductivity (Ke) and carrier mobility (μ), for a given carrier density (ρ) and the corresponding α, yielding equation (2) below:
Z=α2σ/(KL+Ke)=α2/[KL/(μρq)+L0T)] (equation 2)
where, L0 is the Lorenz number (approximately 1.5×10−8V2/K2 in non-degenerate semiconductors). State-of-the-art thermoelectric devices may use alloys, such as p—BixSb2-xTe3-ySey(x≈0.5, y≈0.12) and n—Bi2(SeyTe1-y)3 (y≈0.05) for the 200 degree K to 400 degree K temperature range. For certain alloys, KL may be reduced more strongly than μ leading to enhanced ZT.
A ZT of 0.75 at 300 degree K in p-type BixSb2-xTe3 (x≈1) was reported forty years ago. See, for example Wright, D. A., Nature vol. 181, pp. 834 (1958). Since then, there has been relatively modest progress in the ZT of thermoelectric materials near 300 degree K (i.e., room temperature). A ZT of about 1.14 at 300 degree K for bulk p-type (Bi2Te3)0.25 (Sb2Te3)0.72 (Sb2Se3)0.03 alloy has been discussed for example, in the reference by Ettenberg et al. entitled “A New N-Type And Improved P-Type Pseudo-Ternary (Bi2Te3)(Sb2Te3)(Sb2Se3) Alloy For Peltier Cooling,” (Proc. of 15th Inter. Conf. on Thermoelectrics, IEEE Catalog. No. 96TH8169, pp. 52-56, 1996), the disclosure of which is hereby incorporated herein in its entirety by reference.
Accordingly, there continues to exist a need in the art for thermoelectric materials providing improved thermoelectric cooling and/or power generation.
According to some embodiments of the present invention, a method of forming a thermoelectric device may include forming a thermoelectric superlattice including a plurality of alternating layers of different thermoelectric materials a period of the alternating layers varying over a thickness of the superlattice. More particularly, forming the superlattice may include depositing the superlattice on a single crystal substrate using epitaxial deposition. In addition, the single crystal substrate may be removed from the superlattice, and a second thermoelectric superlattice may be formed with the first and second thermoelectric superlattices having opposite conductivity types. Moreover, the first and second thermoelectric superlattices may be thermally coupled in parallel between two thermally conductive plates and the first and second thermoelectric superlattices may be electrically coupled in series.
The alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Sb2Te3, and/or the superlattice may include a p-type conductivity superlattice. In an alternative, the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Bi2Te3-xSex, or alternating layers of n—PbTe and n—PbTeSe, or alternating layers of n—Bi2Te3 and n—InxTey, and the superlattice may include an n-type conductivity superlattice.
The alternating layers may include alternating layers of two different materials with a period of the alternating layers being defined as a combined thickness of two adjacent layers of the different materials. A first period of a first region of the superlattice may be at least 10 percent greater than a second period of a second region of the superlattice, and more particularly, at least 20 percent greater than a second period of a second region of the superlattice, and still more particularly, at least 40 percent greater than a second period of a second region of the superlattice.
For example, a first region of the superlattice may have a first thickness in the range of about 1 micrometer to about 7 micrometers, a second region of the superlattice may have a second thickness in the range of about 1 micrometers to about 7 micrometers. Moreover, the first region may have a first period in the range of about 20 Angstroms to about 100 Angstroms, the second region may have a second period in the range of about 0.20 Angstroms to about 100 Angstroms, and the second period may be at least 10 percent greater than the first period. In addition, a third region of the superlattice may have a third thickness in the range of about 1 micrometer to about 7 micrometers, the third region may have a third period in the range of about 20 Angstroms to about 100 Angstroms, and the third period may be at least 10 percent greater than the second period. More particularly, the superlattice may have a total thickness in the range of about 3 micrometers to about 15 micrometers, and more particularly, in the range of about 5 micrometers to about 15 micrometers.
According to some other embodiments of the present invention, a thermoelectric device may include a thermoelectric superlattice having a plurality of alternating layers of different thermoelectric materials, and a period of the alternating layers may vary over a thickness of the superlattice. In addition; a second thermoelectric superlattice may be provided with the first and second thermoelectric superlattices having opposite conductivity types, the first and second thermoelectric superlattices may be thermally coupled in parallel between two thermally conductive plates, and the first and second thermoelectric superlattices may be electrically coupled in series.
For example, the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Sb2Te3, and/or the superlattice may be a p-type conductivity superlattice. In an alternative, the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Bi2Te3-xSex, or alternating layers of n—PbTe and n—PbTeSe, or alternating layers of n—Bi2Te3 and n—InxTey, and/or the superlattice may include an n-type conductivity superlattice.
The alternating layers may include alternating layers of two different materials with a period of the alternating layers being defined as a combined thickness of two adjacent layers of the different materials. For example, a first period of a first region of the superlattice may be at least 10 percent greater than a second period of a second region of the superlattice, and more particularly, at least 20 percent greater than a second period of a second region of the superlattice, and still more particularly, at least 40 percent greater than a second period of a second region of the superlattice.
A first region of the superlattice may have a first thickness in the range of about 1 micrometer to about 7 micrometers, a second region of the superlattice may have a second thickness in the range of about 1 micrometers to about 7 micrometers. Moreover, the first region may have a first period in the range of about 20 Angstroms to about 100 Angstroms, the second region may have a second period in the range of about 20 Angstroms to about 100 Angstroms, and the second period may be at least 0 percent greater than the first period. In addition, a third region of the superlattice may have a third thickness in the range of about 1 micrometer to about 7 micrometers, the third region may have a third period in the range of about 20 Angstroms to about 100 Angstroms, and the third period may be at least 10 percent greater than the second period. For example, the superlattice may have a total thickness in the range of about 3 micrometers to about 15 micrometers, and more particularly, in the range of about 5 micrometers to about 15 micrometers.
According to still other embodiments of the present invention a method of forming a thermoelectric device may include providing first and second thermoelectric elements of a same conductivity type, with each of the first and second thermoelectric elements including a respective superlattice of alternating layers of different thermoelectric materials. Moreover, respective surfaces of the first and second thermoelectric elements may be bonded so that a path of current through the first and second thermoelectric elements passes through the alternating layers of the first and second thermoelectric elements.
Bonding the respective surfaces may include solder bonding the respective surfaces of the first and second thermoelectric elements, for example, using a solder such as tin (Sn). More particularly, bonding the respective surfaces may include forming first and second barrier metal layers on the respective surfaces of the first and second thermoelectric elements and forming a solder bond between the first and second barrier metal layers. Moreover, the solder bond and the first and second barrier metal layers may include different metals. Bonding the respective surfaces may also include forming first and second adhesion metal layers on the respective surfaces of the first and second thermoelectric elements before forming the first and second barrier metal layers, and the first and second adhesion metal layers and the first and second barrier metal layers may include different metals.
The first and second thermoelectric elements may be thermally coupled in series between two thermally conductive plates, and the first and second thermoelectric elements may have a first conductivity type. In addition, a third thermoelectric element may be thermally coupled between the two thermally conductive plates with the third thermoelectric element having a second conductivity type different than the first conductivity type, and the first, second, and third thermoelectric elements may be electrically coupled in series. A fourth thermoelectric element having the second conductivity type may also be thermally coupled in series with the third thermoelectric element between the first and second thermally conductive plates, and the first, second, third, and fourth thermoelectric elements may be electrically coupled in series.
The first and second thermoelectric elements may include alternating layers of Bi2Te3 and Sb2Te3, and/or the first and second thermoelectric elements may be p-type conductivity thermoelectric elements. In an alternative, the first and second thermoelectric elements may include alternating layers of Bi2Te3 and Bi2Te3-xSex, or alternating layers of n—PbTe and n—PbTeSe, or alternating layers of n—Bi2Te3 and n—InxTey, and/or the first and second thermoelectric elements may be n-type conductivity thermoelectric elements. Moreover, each of the first and second thermoelectric elements may have a same thickness, and a combined thickness through the first and second thermoelectric elements after bonding the first and second thermoelectric elements may be in the range of about 10 to about 20 micrometers.
According to yet other embodiments of the present invention, a thermoelectric device may include first and second thermoelectric elements of a same conductivity type with each of the first and second thermoelectric elements including a respective superlattice of alternating layers of different thermoelectric materials. Respective surfaces of the first and second thermoelectric elements may be bonded with metal therebetween so that a path of current through the first and second thermoelectric elements passes through the alternating layers of the first and second thermoelectric elements.
The respective surfaces may be bonded using solder, such as a solder including tin (Sn). Moreover, first and second barrier metal layers may be provided on the respective surfaces of the first and second thermoelectric elements, and a solder bond may be provided between the first and second barrier metal layers with the solder bond and the first and second barrier metal layers including different metals. In addition, first and second adhesion metal layers may be provided on the respective surfaces of the first and second thermoelectric elements, and the first and second adhesion metal layers and the first and second barrier metal layers may include different metals.
The first and second thermoelectric elements may be thermally coupled in series between first and second thermally conductive plates, and the first and second thermoelectric elements may have a first conductivity type. In addition, a third thermoelectric element may be thermally coupled between the two thermally conductive plates with the third thermoelectric element having a second conductivity type different than the first conductivity type, and the first, second, and third thermoelectric elements may be electrically coupled in series. A fourth thermoelectric element having the second conductivity type may be thermally coupled in series with the third thermoelectric element between the first and second thermally conductive plates, and the first, second, third, and fourth thermoelectric elements may be electrically coupled in series.
The first and second thermoelectric elements may each include alternating layers of Bi2Te3 and Sb2Te3, and/or the first and second thermoelectric elements may be p-type conductivity thermoelectric elements. In an alternative, the first and second thermoelectric elements may each include alternating layers of Bi2Te3 and Bi2Te3-xSex, or alternating layers of n—PbTe and n—PbTeSe, or alternating layers of n—Bi2Te3 and n—InxTey, and/or the first and second thermoelectric elements may be n-type conductivity thermoelectric elements. Moreover, each of the first and second thermoelectric elements may have a same thickness, and a combined thickness through the first and second thermoelectric elements after bonding the first and second thermoelectric elements may be in the range of about 10 to about 20 micrometers.
According to additional embodiments of the present invention, a method of forming a thermoelectric device may include forming a single crystal thermoelectric superlattice having a plurality of alternating layers of different thermoelectric materials. Moreover, a thickness of the single crystal thermoelectric superlattice may be at least about 3 micrometers, and more particularly, at least about 7 micrometers.
The single crystal thermoelectric superlattice may include a p-type conductivity superlattice, and/or the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Sb2Te3. The thickness of the p-type single crystal thermoelectric superlattice may be at least about 10 micrometers, and a resistivity of the single crystal thermoelectric superlattice may be at least about 0.6×10−3 ohm-cm, and more particularly, the resistivity of the single crystal thermoelectric superlattice may be about 0.8×10−3 ohm-cm.
In an alternative, the single crystal thermoelectric superlattice may include an n-type conductivity superlattice, and/or the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Bi2Te3-xSex, or alternating layers of n—PbTe and n—PbTeSe, or alternating layers of n—Bi2Te3 and n—InxTey. The thickness of the single crystal thermoelectric superlattice may be at least about 8 micrometers, and a resistivity of the single crystal thermoelectric superlattice may be at least about 2×10−3 ohm-cm, and more particularly, the resistivity of the single crystal thermoelectric superlattice may be about 2.5×10−3 ohm-cm.
In addition, a second single crystal thermoelectric superlattice may be formed with the first and second single crystal thermoelectric superlattices having different conductivity types. The first and second single crystal thermoelectric superlattices may be thermally coupled in parallel between first and second thermally conductive plates, and the first and second single crystal thermoelectric superlattices may be electrically coupled in series. Moreover, forming the single crystal thermoelectric superlattice may include forming the single crystal thermoelectric superlattice on a single crystal substrate, and removing the single crystal substrate to allow a device structure to be fabricated.
According to further embodiments of the present invention, a thermoelectric device may include a single crystal thermoelectric superlattice having a plurality of alternating layers of different thermoelectric materials. Moreover, a thickness of the single crystal thermoelectric superlattice may be at least about 3 micrometers, and more particularly, at least about 7 micrometers.
The single crystal thermoelectric superlattice may include a p-type conductivity superlattice, and/or the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Sb2Te3. The thickness of the p-type single crystal thermoelectric superlattice may be at least about 10 micrometers, and a resistivity of the single crystal thermoelectric superlattice may be at least about 0.6×10−3 ohm-cm, and more particularly, the resistivity of the single crystal thermoelectric superlattice may be about 0.8×10−3 ohm-cm.
In an alternative, the single crystal thermoelectric superlattice may include an n-type conductivity superlattice, and/or the alternating layers of different thermoelectric materials may include alternating layers of Bi2Te3 and Bi2Te3-xSex, or alternating layers of n—PbTe and n—PbTeSe, or alternating layers of n—Bi2Te3 and n—InxTey. The thickness of the single crystal thermoelectric superlattice may be at least about 3 micrometers, and more particularly, at least about 8 micrometers, and a resistivity of the n-type single crystal thermoelectric superlattice may be at least about 2×10−3 ohm-cm, and more particularly, the resistivity of the single crystal thermoelectric superlattice may be about 2.5×10−3 ohm-cm.
In addition, a second single crystal thermoelectric superlattice may be provided such that the first and second single crystal thermoelectric superlattices have different conductivity types. Moreover, the first and second single crystal thermoelectric superlattices may be thermally coupled in parallel between the first and second thermally conductive plates, and the first and second single crystal thermoelectric superlattices may be electrically coupled in series.
a-d are cross-sectional views illustrating operations of forming thermoelectric elements having regions of different superlattice periods and related devices according to embodiments of the present invention.
a-d are cross-sectional views illustrating operations of forming thermoelectric elements including bonded sub-elements and related devices according to embodiments of the present invention.
a-c are cross-sectional views illustrating operations if forming thick superlattice thermoelectric elements according to embodiments of the present invention.
The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout.
It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element, or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Also, as used herein, “lateral” refers to a direction that is substantially orthogonal to a vertical direction.
The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Examples of embodiments of the present invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the present invention.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Accordingly, these terms can include equivalent terms that are created after such time. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the present specification and in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.
As integrated circuit chip manufacturers reduce line widths and/or feature sizes (for example, to 90 nm and even 65 nm) and/or as integrated circuit chips are used to run more computationally-complex applications, power densities may increase further. Higher temperature and/or more integrated circuit chip hot spots may thus impact reliability and/or performance. Cooling of these hot spots, for example, may thus be provided for integrated circuit chips used in wireless, cellular, and/or mobile communications devices running advanced (e.g., high speed) algorithms for digital voice, video, and/or data operations, particularly where error detection and/or error correction algorithms are used. Currently, integrated circuit hot spots may generate heat in the range of 100 W/cm2 to 200 W/cm2 on the backside of the silicon chip resulting from heat-fluxes of over 1800 W/cm2 on the active side of the silicon chip. In the near future, hot spots on a backside of an integrated circuit chip may be expected to approach 1000 W/cm2. Moreover, lower junction temperatures (for transistors on the active side of the integrated circuit chip) may be desired to reduce power consumption and/or to provide more stable operation, for example, by reducing leakage currents for transistors in the off-state.
Accordingly, coolers for integrated circuit devices may be used to provide cooling-on-demand and/or to increase system efficiency while managing a higher density of heat fluxes at an integrated circuit chip hot spot(s). More particularly, relatively low-profile solid-state thermoelectric coolers using superlattice thermoelectric materials may provide hot spot cooling for integrated circuit chips and/or scalable refrigeration for an entire integrated circuit chip, for example, to reduce leakage currents. Thermoelectric superlattice materials are discussed, for example, in the reference by Venkatasubramanian et al. entitled “Phonon-Blocking Electron-Transmitting Structures” (18th International Conference On Thermoelectrics, 1999), the disclosure of which is hereby incorporated herein in its entirety by reference. Thermoelectric superlattice materials are also discussed, for example, in U.S. Pat. Nos. 6,722,140; 6,662,570; 6,505,468; 6,300,150; and 6,071,351; the disclosures of which are hereby incorporated herein in their entirety by reference. In addition, thermoelectric superlattice materials are discussed, for example, in U.S. Patent Publication Nos.: 2003/0230332; 2003/0131609; 2003/0126865; 2003/0100137; 2003/0099279; 2002/0174660; and 2001/0052234; the disclosures of which are hereby incorporated herein in their entirety by reference.
Superlattice Bi2Te3-based thermoelectric materials providing increased figures-of-merit are discussed, for example, in the reference by Venkatasubramanian et al. entitled “Thin-Film Thermoelectric Devices With High Room-Temperature Figures Of Merit” (Nature, Vol. 413, 11 Oct. 2001, pages 597-602) the disclosure of which is hereby incorporated herein in its entirety by reference. Further developments in thermoelectric materials may provide average figures-or-merit (ZTavg) of about 2.4 at 300 degree K (i.e., room temperature) for use in cooling and/or power generation modules. Increased figures-or-merit and site-specific thermal management capability may enable power-efficient system level cooling, cooling for commercial high-performance electronics, and/or power generation for military application. Superlattice thermoelectric couples may provide a temperature differential of about 85 degree K. At volume production, cooling may be provided at a cost of about $0.2/Watt. Superlattice thermoelectric materials may thus be used to provide thermoelectric coolers for microprocessor chip cooling for hot-spot thermal management, for leakage current control, and/or for threshold voltage control.
As discussed in the reference by Venkatasubramanian et al. entitled “Thin-Film Thermoelectric Devices With High Room-Temperature Figures Of Merit”, Bi2Te3-based thermoelectric superlattice materials may provide both phonon-blocking and electron-transmission to increase intrinsic figures-of-merit for thermoelectric materials. These Bi2Te3-based thermoelectric superlattice materials and/or other thermoelectric materials may be incorporated into p-n couples and into pluralities of p-n couples and/or modules to provide thermoelectric cooling devices with relatively high effective figures-of-merit for laser cooling and/or microprocessor hot-spot cooling.
Semiconductor process technologies used to form thermoelectric superlattice thin films may allow flexible module design for a wide range of applications and/or for reductions in design cycle times and/or cost. Sizes of cooling modules may range from relatively small footprint high heat-flux cooling thermoelectric modules for laser cooling and/or microprocessor hot-spot thermal management as shown in
As shown in
As shown in
In
As shown in
When combining p-type and n-type thermoelectric elements into couples and/or modules, a “loss” of “intrinsic ZT” may occur as a result of processing, interconnections, etc., together referred to as “parasitics”.
As discussed in greater detail below, thermoelectric device modules with relatively thin epitaxial thermoelectric superlattice layer thicknesses may provide improved high heat-flux pumping conditions. A thinner epitaxial thermoelectric superlattice layer thickness may allow a reduction in defects that may result from strained layer superlattices that may result when using lattice-mismatch between different superlattice layers to provide an acoustic mismatch and a dielectric phonon localization-like effects for reduction in thermal conduction. A thickness of about 5 micrometers for the epitaxial thermoelectric superlattice layer may provide a relatively high extrinsic figure-of-merit at the thermoelectric element level together with relatively low fabrication cost. While 5 and 10 micrometer thicknesses are discussed by way of example, thinner epitaxial thermoelectric superlattice layers/elements may be used for higher heat-flux cooling conditions.
According to embodiments of the present invention, 5 micrometer thick epitaxial thermoelectric superlattice layers/elements may be used to fabricate thermoelectric device modules having thicknesses in the range of about 20 micrometers to about 110 micrometers. Thermoelectric device modules having thicknesses in the range of about 20 to 110 micrometers may facilitate packaging with integrated circuit devices.
As discussed above, thermoelectric elements including superlattices of alternating layers of different thermoelectric materials may be used in thermoelectric devices to provide thermoelectric cooling and/or power generation while reducing undesirable thermal conduction through the superlattice. According to some embodiments of the present invention, a thermoelectric element may include a superlattice wherein a period of the alternating layers of the superlattice varies over a thickness of the superlattice. As discussed herein, the period of a superlattice including alternating layers may be defined as the combined thickness of two adjacent layers of the different materials. While superlattices of repetitive two layer patterns are discussed herein by way of example, superlattices of different patterns may be used according to embodiments of the present invention with a period of the superlattice being defined as a thickness of one cycle of the pattern. In a superlattice including a repetitive pattern of three layers of three different materials, for example, the period may be defined as the combined thickness of three adjacent layers of the three different materials defining one cycle of the pattern. By providing different periods of the superlattice within a same thermoelectric element, performance of the thermoelectric element may be further improved.
As shown in
According to other embodiments of the present invention, the thermoelectric element 1201 may have an n-type conductivity, and the superlattice may include alternating layers of Bi2Te3 and BixTe3-xSex, and/or alternating layers of n—PbTe (n-type conductivity PbTe) and n—PbTeSe (n-type conductivity PbTeSe), and/or alternating layers of n—Bi2Te3 (n-type conductivity Bi2Te3) and n—InxTey (n-type conductivity InxTey). By way of example, the superlattice may include alternating layers of Bi2Te3 and Bi2Te3-xSex, (with x in the range of about 0.2 to about 0.4). By way of example: the first region 1203a may have alternating layers of 10 Angstrom thick Bi2Te3 and 30 Angstrom thick Bi2Te3-xSex with a period of about 40 Angstroms; the second region 1203b may have alternating layers of 10 Angstrom thick Bi2Te3 and 40 Angstrom thick Bi2Te3-xSex with a period of about 50 Angstroms; and the third region 1203c may have alternating layers of 10 Angstrom thick Bi2Te3 and 50 Angstrom thick Bi2Te3-xSex with a period of about 60 Angstroms. While thermoelectric elements with three regions having different superlattice periods are discussed by way of example, any number of regions having different superlattice periods greater than two may be provided according to embodiments of the present invention.
According to some embodiments of the present invention, a period of one of the regions 1203a-c may be at least 10 percent greater than a period of another of the regions, and more particularly, at least 20 percent greater, and even at least 40 percent greater. According to embodiments of the present invention with the regions 1203a-c having respective periods of 40 Angstroms, 50 Angstroms, and 60 Angstroms: the period of region 1203b may be about 25 percent greater than the period of region 1203a; the period of region 1203c may be 20 percent greater than the period of region 1203b; and the period of region 1203c may be 50 percent greater than the period of region 1203a.
With either a p-type and/or an n-type thermoelectric element, each of the first second, and third regions 1203a-c may have a thickness in the range of about 1 micrometers to about 7 micrometers; periods of the superlattices in each of the regions 1203a-c may be in the range of about 20 Angstroms to about 100 Angstroms; and a period of one of the regions may be at least 10 percent greater than a period of another of the regions. According to some embodiments of the present invention, each of the first, second, and third regions 1203a-c may have a thickness in the range of about 3 micrometers to about 6 micrometers, and the thermoelectric element 1201 may have a thickness in the range of about 9 micrometers to about 18 micrometers. According to some more embodiments of the present invention, each of the regions 1203a-c may have a thickness of about 5 micrometers, and the thermoelectric element 1201 may have a thickness of about 15 micrometers. According to still other embodiments of the present invention, the thermoelectric element 1201 may have a total thickness in the range of about 3 micrometers to about 15 micrometers.
Operations of forming thermoelectric elements and/or devices discussed above with reference to
After forming the buffer layer 1303, the thermoelectric superlattice layers 1203a′, 1203b′, and 1203c′ may be formed using epitaxial deposition to provide the superlattice structures discussed above with respect to
After forming the superlattice layers discussed above, the substrate 1301 and the layers thereon may be diced to provide a separate thermoelectric element 1311 with a portion 1301′ and 1303′ of the substrate and buffer layer remaining thereon as shown in
As shown in
In addition, a second thermoelectric element 1343 may be bonded to the conductive trace 1321 using interconnection metallization 1345. Moreover, the first thermoelectric element (including superlattice regions 1203a-c) and the second thermoelectric element 1343 may have different conductivity types to provide a p-n thermoelectric couple for a thermoelectric device providing thermoelectric heating and/or cooling. The second thermoelectric element 1343 may have a homogeneous superlattice period as discussed, for example, in the reference by Venkatasubramanian et al. entitled “Phonon-Blocking Electron-Transmitting Structures”, or a heterogeneous superlattice period as discussed above with respect to
As shown in
According to additional embodiments of the present invention, relatively thick thermoelectric elements may be provided by bonding two thermoelectric elements of the same conductivity type, and the two bonded thermoelectric elements may be thermally coupled in series between two thermally conductive plates of a thermoelectric device. Accordingly, two relatively thin thermoelectric elements with relatively high quality crystal structure may be bonded to provide a relatively thick thermoelectric element without requiring a single thick epitaxial deposition that may otherwise result in a reduced quality of crystal structure. Stated in other words, a quality of two bonded thermoelectric elements may be higher than that of a single thick thermoelectric element because of possible difficulties in the epitaxial deposition of a single thick thermoelectric layer.
As shown in
More particularly, respective surfaces 1407a-b of the first and second thermoelectric elements 1401a-b may be bonded so that a path of current through the first and second thermoelectric elements passes through the alternating layers of the first and second thermoelectric elements. Stated in other words, the first and second thermoelectric elements 1401a-b may be bonded so that the alternating layers of the superlattices of the first and second thermoelectric elements are substantially parallel.
A solder bond may thus be used to bond the first and second thermoelectric elements 14011a-b, and the solder bond may be provided using solder 1405. More particularly, the solder 1405 may include tin (Sn). The solder 1405, for example, may be a lead-tin solder or a lead free solder. According to some embodiments of the present invention, the thermoelectric elements 1401a-b may have a p-type conductivity including a superlattice of alternating layers of Bi2Te3 and Sb2Te3. According to some other embodiments of the present invention, the thermoelectric elements 1401a-b may include a superlattice may have an n-type conductivity including alternating layers of Bi2Te3 and Bi2Te3-xSex, and/or alternating layers of PbTe and PbTeSe, and/or alternating layers of Bi2Te3 and InxTey. By way of example, the thermoelectric elements 1401a-b may have an n-type conductivity including a superlattice of alternating layers of Bi2Te3 and Bi2Te3-xSex, (with x in the range of about 0.2 to about 0.4). According to some embodiments of the present invention, the first and second thermoelectric elements 1401a-b may have a same thickness, and a combined thickness through the first and second thermoelectric elements 1401a-b (including interconnection metallizations 1403a-b and solder 1405) after bonding may be in the range of about 10 micrometers to about 20 micrometers.
Operations of forming thermoelectric elements and/or devices discussed above with reference to
After forming the buffer layer 1503, the thermoelectric superlattice layer 1401′ may be formed using epitaxial deposition to provide a superlattice structure as discussed above with respect to
After forming the superlattice layers discussed above, the substrate(s) 1501 and the layers thereon may be diced to provide separate thermoelectric elements 1401a and 1401b with portions 1501a-b and 1503a-b of the substrate and buffer layer remaining thereon. Moreover, interconnect metallizations 1403a-b may be provided on surfaces of the resulting thermoelectric elements either before or after dicing the substrate(s). The interconnect metallizations 1403a-b, for example, may include an adhesion metal layer (such as a layer of chromium, titanium, and/or tungsten) and a barrier metal layer (such as a layer of gold and/or nickel), with the adhesion metal layer between the barrier metal layer and the respective thermoelectric superlattice structure. Moreover, the resulting thermoelectric elements 1401a-b may be the same as discussed above with respect to
As shown in
As shown in
In addition, a second thermoelectric element 1543 may be bonded to the conductive trace 1321 using interconnection metallization 1545. Moreover, the first thermoelectric element 1559 (including first and second thermoelectric elements 1401a-b of the same conductivity type) and the second thermoelectric element 1543 may have different conductivity types to provide a p-n thermoelectric couple for a thermoelectric device providing thermoelectric heating and/or cooling. The second thermoelectric element 1543 may have a homogeneous superlattice period as discussed, for example, in the reference by Venkatasubramanian et al. entitled “Phonon-Blocking Electron-Transmitting Structures”; a heterogeneous superlattice period as discussed above with respect to
In addition, the thermoelectric elements 1559 and 1543 may be bonded to respective conductive traces 1551a-b on the thermally conductive substrate 1553 using interconnection metallizations 1527 and 1547. The interconnection metallization 1527 may include an adhesion metal layer (such as a layer of chromium, titanium, and/or tungsten) between a barrier metal layer (such as a layer of gold and/or nickel) and the combined thermoelectric element 1559, and a solder layer between the barrier metal layer and the conductive trace 1551a. Similarly, the interconnection metallization 1547 may include an adhesion metal layer (such as a layer of chromium, titanium, and/or tungsten) between a barrier metal layer (such as a layer of gold and/or nickel) and the thermoelectric element 1543, and a solder layer between the barrier metal layer and the conductive trace 1551b. The thermoelectric elements 1559 and 1543 are thus thermally coupled in parallel between the two thermally conductive substrates 1523 and 1553 and electrically coupled in series through the conductive traces 1521 and 1553a-b to provide thermoelectric cooling and/or power generation. Moreover, the thermoelectric elements 1401a-b are electrically and thermally coupled in series between the thermally conductive substrates 1523 and 1553 to provide a combined thermoelectric element 1559 having an increased thickness;
According to some additional embodiments of the present invention, relatively thick and/or high resistivity thermoelectric elements having superlattice structures may provide improved performance. A thermoelectric element, for example, may include a plurality of alternating layers of different thermoelectric materials, and a thickness of the superlattice may be at least about 3 micrometers, and more particularly, at least about 7 micrometers. According to some embodiments of the present invention, the superlattice may be a p-type conductivity superlattice including alternating layers of Bi2Te3 and Sb2Te3. Moreover, the p-type conductivity superlattice may have a thickness of at least about 10 micrometers, and a resistivity of at least about 0.6×10−3 ohm-cm, and more particularly, a thickness of about 0.8×10−3 ohm-cm. According to other embodiments of the present invention, the superlattice may be an n-type conductivity superlattice including alternating layers of Bi2Te3 and Bi2Te3-xSex, and/or alternating layers of n—PbTe and n—PbTeSe, and/or alternating layers of n—Bi2Te3 and n—InxTey. By way of example, the superlattice may be an n-type conductivity superlattice including alternating layers of Bi2Te3 and Bi2Te3-xSex (with x in the range of about 0.2 to about 0.4). Moreover, the 1-type conductivity superlattice may have a thickness of at least about 10 micrometers, and a resistivity of at least about 2×10−3 ohm-cm, and more particularly, a thickness of about 2.5×10−3 ohm-cm.
As shown in
After forming the buffer layer 1603′, the thermoelectric superlattice 1605′ may be formed using epitaxial deposition to provide the superlattice structures discussed above. Epitaxial deposition of thermoelectric superlattices is discussed, for example, in U.S. Pat. Nos. 6,300,150 and 6,071,351 and in U.S. Patent Publication No. 2003/0099279, the disclosures of which are hereby incorporated herein in their entirety by reference. Superlattice structures are further discussed in the references by Venkatasubramanian et al. entitled “Phonon-Blocking Electron-Transmitting Structures” (18th International Conference on Thermoelectrics, 1999, pages 100-103) and “Thin-Film Thermoelectric Devices With High Room-Temperature Figures Of Merit” (Nature, Vol. 413, 11 Oct. 2001, pages 597-602), the disclosures of which are hereby incorporated herein in their entirety by reference. Separate substrates may be used to form thermoelectric superlattice layers for n-type and p-type thermoelectric elements. Stated in other words, one substrate (or a plurality of substrates) may be diced to form p-type thermoelectric elements, and another substrate (or another plurality of substrates) may be used to form n-type thermoelectric elements.
According to some embodiments of the present invention, the superlattice 1605′ may be a p-type conductivity superlattice including alternating layers of Bi2Te3 and Sb2Te3. Moreover, the p-type conductivity superlattice may have a thickness of at least about 10 micrometers, and a resistivity of at least about 0.6×10−3 ohm-cm, and more particularly, a thickness of about 0.8×10−3 ohm-cm. According to other embodiments of the present invention, the superlattice 1605′ may be an n-type conductivity superlattice including alternating layers of Bi2Te3 and Bi2Te3-xSex, and/or alternating layers of n—PbTe and n—PbTeSe, and/or alternating layers of n—Bi2Te3 and n—InxTey. By way of example, the superlattice 1605′ may be an n-type conductivity superlattice including alternating layers of Bi2Te3 and Bi2Te3-xSex (with x in the range of about 0.2 to about 0.4). Moreover, the n-type conductivity superlattice may have a thickness of at least about 10 micrometers, and a resistivity of at least about 2×10−3 ohm-cm, and more particularly, a thickness of about 2.5×10−3 ohm-cm.
After forming the superlattice 1605′ as discussed above, the substrate 1601′ and the layers thereon may be diced to provide a separate thermoelectric element 1605 with a portion 1601 and 160′ of the substrate and buffer layer remaining thereon as shown in
As shown in
In addition, a second thermoelectric element 1643 may be bonded to the conductive trace 1621 using interconnection metallization 1645. Moreover, the first thermoelectric element including superlattice 1605 and the second thermoelectric element 1643 may have different conductivity types to provide a p-n thermoelectric couple for a thermoelectric device providing thermoelectric heating and/or cooling. The second thermoelectric element 1643 may have a homogeneous superlattice period as discussed, for example, in the reference by Venkatasubramanian et al. entitled “Phonon-Blocking Electron-Transmitting Structures”, or a heterogeneous superlattice period as discussed above with respect to
In addition, the interconnection metallizations 1627 and 1647 may be bonded to respective conductive traces 1651a-b on the thermally conductive substrate 1653, for example, using solder. The thermoelectric elements are thus thermally coupled in parallel between the two thermally conductive substrates 1623 and 1653 and electrically coupled in series through the conductive traces 1621 and 1653a-b to provide thermoelectric cooling and/or power generation.
While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
The present application claims the benefit of priority from U.S. Provisional Application No. 60/670,583 filed Apr. 12, 2005, the disclosure of which is hereby incorporated herein in its entirety by reference.
This invention was made with Government support under U.S. Navy Contract No. N00014-97-C-0211 awarded by the Defense Advanced Research Projects Agency through the Office of Naval Research, and under U.S. Army Contract No. DAAD19-01-C-0010 awarded by the Defense Advanced Research Projects Agency through the Army Research Office. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60670583 | Apr 2005 | US |
