U.S. patent application number 14/268653 was filed with the patent office on 2015-11-05 for thermoelectric device and method for fabrication thereof.
This patent application is currently assigned to United Arab Emirates University. The applicant listed for this patent is United Arab Emirates University. Invention is credited to Mahmoud Al Ahmad.
Application Number | 20150316298 14/268653 |
Document ID | / |
Family ID | 54355013 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150316298 |
Kind Code |
A1 |
Al Ahmad; Mahmoud |
November 5, 2015 |
Thermoelectric Device And Method For Fabrication Thereof
Abstract
A thermoelectric device and a method for fabrication thereof are
disclosed. The thermoelectric device includes one or more
thermocouples electrically connected in series. Each thermocouple
includes at least one first thermoelectric element and at least one
second thermoelectric element, wherein the thermoelectric elements
are maintained in a spaced apart relationship forming an internal
cavity there between.
Inventors: |
Al Ahmad; Mahmoud; (Al Ain,
AE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United Arab Emirates University |
Al Ain |
|
AE |
|
|
Assignee: |
United Arab Emirates
University
Al Ain
AE
|
Family ID: |
54355013 |
Appl. No.: |
14/268653 |
Filed: |
May 2, 2014 |
Current U.S.
Class: |
62/3.7 ;
29/830 |
Current CPC
Class: |
H01L 35/32 20130101;
Y10T 29/49128 20150115 |
International
Class: |
F25B 21/02 20060101
F25B021/02 |
Claims
1. A thermoelectric device comprising at least a first substrate
and at least a second substrate arranged substantially parallel to
a reference plane, said reference plane defining a first axis, a
second axis, and a third axis, said axes being mutually orthogonal,
wherein said first axis is orthogonal to said reference plane and
said second and said third axes are aligned to said reference
plane, wherein said first and said second substrates are retained
in a spaced apart relationship along said first axis, and at least
one thermocouple, said thermocouple comprising: at least one first
thermoelectric element disposed on said first substrate extending
towards said second substrate along said first axis, wherein said
first thermoelectric element comprises a first basal surface facing
towards said first substrate, a first apical surface substantially
opposite to said first basal surface, and a first lateral surface
there between, at least one second thermoelectric element disposed
on said second substrate extending towards said first substrate
along said first axis, wherein said second thermoelectric element
comprises a second basal surface facing towards said second
substrate, a second apical surface substantially opposite to said
second basal surface, and a second lateral surface there between,
wherein said first thermoelectric element and said second
thermoelectric element are disposed such that said first and said
second apical surfaces are spaced apart along said first axis,
whereby an internal cavity is defined there between.
2. The thermoelectric device according to claim 1, wherein each of
said first and said second lateral surfaces of said first and said
second thermoelectric elements respectively is electrically and
thermally insulated such that a direction of electrical and thermal
flux through each of said first and second thermoelectric elements
is aligned with said first axis.
3. The thermoelectric device according to claim 1, wherein said
first and said second substrates are formed of a thermally
conducting and electrically insulating material.
4. The thermoelectric device according to claim 3, wherein said
first and said second substrates are provided with one or more
structural features and/or one or more material coatings to permit
heat dissipation.
5. The thermoelectric device according to claim 3, wherein said
first and said second substrates are provided with one or more
structural features and/or one or more material coatings to permit
heat absorption.
6. The thermoelectric device according to claim 1, wherein said
first and said second thermoelectric elements correspond to
mutually opposite types of electrical conductivity.
7. The thermoelectric device according to claim 1, wherein said
first and said second apical surfaces are electrically
interconnected through an intra-couple bridge, wherein said
intra-couple bridge comprises individual electrically connecting
layers deposited on said first and said second apical surfaces and
an intra-couple metallization layer extending along said first axis
and interconnecting said individual electrically connecting layers,
wherein said intra-couple bridge is at least electrically insulated
at a non-contact surface thereof.
8. The thermoelectric device according to claim 1, wherein a first
electrically coupling layer is disposed between said first basal
surface and said first substrate; and a second electrically
coupling layer is disposed between said second basal surface and
said second substrate, such that an aggregate of individual
electrical potentials across said first and said second
thermoelectric elements is accessible across said first and said
second electrically coupling layers.
9. The thermoelectric device according to claim 8 further
comprising at least a first thermocouple and at least a second
thermocouple adjacently disposed thereto between said first and
said second substrates, wherein individual aggregate electrical
potentials across said first and said second thermocouples are
formed across corresponding said first and said second electrically
coupling layers, and further wherein, said first electrically
coupling layer of said first thermocouple is electrically
interconnected to said second electrically coupling layer of said
second thermocouple through an inter-couple bridge, whereby said
first and said second thermocouples are electrically connected in
series; wherein said inter-couple bridge comprises an inter-couple
metallization layer electrically extending along said first axis
from substantially adjacent to said first substrate to
substantially adjacent to said second substrate, and electrically
interconnecting said first and said second electrically coupling
layers, and wherein said inter-couple bridge is at least
electrically insulated at a non-contact surface thereof.
10. The thermoelectric device according to claim 1, wherein a
plurality of thermocouples extending between said first substrate
and said second substrate are arranged in a two dimensional matrix
relative to said reference plane, wherein a set of thermocouples
arranged in individual rows are electrically interconnected in
series and further, individual rows of thermocouples are
electrically connected in series, wherein said internal cavity of
corresponding thermocouples in adjacent rows is in continuum.
11. A method for fabricating a thermoelectric device, said method
comprising: providing a first substrate arranged substantially
parallel to a reference plane, said reference plane defining a
first axis, a second axis, and a third axis, said axes being
mutually orthogonal, wherein said first axis is orthogonal to said
reference plane and said second and said third axes are aligned to
said reference plane, forming at least a first thermoelectric
element on said first substrate, wherein said first thermoelectric
element extends along said first axis and comprises a first basal
surface facing towards said first substrate, a first apical surface
substantially opposite to said first basal surface, and a first
lateral surface there between, disposing a sacrificial layer on
said first thermoelectric element, forming at least a second
thermoelectric element on said sacrificial layer, wherein said
second thermoelectric element extends along said first axis and
comprises a second basal surface facing away from said first
substrate, a second apical surface substantially opposite to said
second basal surface and facing towards said sacrificial layer, and
a second lateral surface there between, disposing a second
substrate on said second thermoelectric element such that said
second substrate is retained in a spaced apart relationship from
said first substrate along said first axis and extends in a spatial
plane substantially parallel to said reference plane, and removing
said sacrificial layer such that said first and said second apical
surfaces of said first thermoelectric element and said second
thermoelectric element respectively are spaced apart along said
first axis, whereby an internal cavity is defined there between,
whereby at least one thermocouple is formed between said first and
said second substrates.
12. The method according to claim 11 further comprising
electrically and thermally insulating each of said first and said
second lateral surfaces of said first and said second
thermoelectric elements respectively such that a direction of
electrical and thermal flux through each of said first and second
thermoelectric elements is aligned with said first axis.
13. The method according to claim 11, wherein said first and said
second substrates are formed of a thermally conducting and
electrically insulating material.
14. The method according to claim 13 further comprising providing
one or more structural features and/or one or more material
coatings on said first and said second substrates to permit heat
dissipation therefrom.
15. The method according to claim 13 further comprising providing
one or more structural features and/or one or more material
coatings on said first and said second substrates to permit heat
absorption therefrom.
16. The method according to claim 11, wherein said first and said
second thermoelectric elements correspond to mutually opposite
types of electrical conductivity.
17. The method according to claim 11 further comprising forming an
intra-couple bridge electrically interconnecting said first and
said second apical surfaces, wherein forming said intra-couple
bridge comprises: disposing a first electrically connecting layer
on said first apical surface of said first thermoelectric element
prior to disposing said sacrificial layer, forming an intra-couple
metallization layer through said sacrificial layer, and disposing a
second electrically connecting layer on said sacrificial layer
prior to disposing said second thermoelectric element, wherein said
intra-couple bridge extends along said first axis and interconnects
said first and said second electrically connecting layers and
further wherein, said intra-couple bridge is at least electrically
insulated at a non-contact surface thereof.
18. The method according to claim 11 further comprising disposing a
first electrically coupling layer on said first substrate prior to
disposing said first thermoelectric element such that said first
electrically coupling layer is disposed between said first basal
surface and said first substrate, and disposing a second
electrically coupling layer on said second thermoelectric element
prior to disposing said second substrate such that said second
electrically coupling layer is disposed between said second basal
surface and said second substrate, further such that an aggregate
of individual electrical potentials across said first and said
second thermoelectric elements is accessible across said first and
said second electrically coupling layers.
19. The method according to claim 18 further comprising forming at
least a first thermocouple and at least a second thermocouple
adjacently disposed thereto between said first and said second
substrates, wherein individual aggregate electrical potentials
across said first and said second thermocouples are formed across
corresponding said first and said second electrically coupling
layers, electrically interconnecting said first electrically
coupling layer of said first thermocouple to said second
electrically coupling layer of said second thermocouple through an
inter-couple bridge, whereby said first and said second
thermocouples are electrically connected in series; wherein said
inter-couple bridge comprises an inter-couple metallization layer
extending along said first axis from substantially adjacent to said
first substrate to substantially adjacent to said second substrate,
and electrically interconnecting said first and said second
electrically coupling layers, and wherein said inter-couple bridge
is at least electrically insulated at a non-contact surface
thereof.
20. The method according to claim 11 further comprising forming a
plurality of thermocouples extending between said first and said
second substrates, said plurality of thermocouples being arranged
in a two dimensional matrix relative to said reference plane,
wherein a set of thermocouples arranged in individual rows are
electrically interconnected in series and further, individual rows
of thermocouples are electrically connected in series, wherein said
internal cavity of corresponding thermocouples in adjacent rows is
in continuum.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to thermoelectric
devices. More specifically, the present invention relates to a
thermoelectric device with relatively high voltage output, compact
form factor, and enhanced portability; and a fabrication method
therefor.
DESCRIPTION OF THE RELATED ART
[0002] Thermoelectric devices used for thermoelectric power
generation, thermoelectric heating/cooling, and sensing and
measurement applications are well known in the state of the
art.
[0003] The thermoelectric generators, in accordance with the
Seebeck effect, convert the temperature gradient across two ends of
a thermoelectric element to generate an electrical potential, which
may be used to drive an electrical current through an electrical
load.
[0004] In a reverse principle, the thermoelectric heating/cooling
devices, in accordance with the Peltier effect, draw an electrical
current from an external power supply, and provide controlled
heating/cooling of a desired surface.
[0005] The thermoelectric devices also find several applications in
the fields of sensing and measurement by way of facilitating
temperature sensing and/or constituting a power supply for driving
sensing devices based on other sensing modalities.
[0006] Referring now to FIG. 1, a conventional semiconductor based
thermoelectric generator 100 is shown.
[0007] The thermoelectric generator 100 typically includes multiple
thermocouple modules 102 arranged between a heat source 104 and a
heat sink 106. Each thermocouple module 102 includes a first type
(for example, n-type) of semiconductor element 108a and a second
type (for example, p-type) of semiconductor element 108b
electrically interconnected through a metallic bridge 110. The
thermocouple modules 102 are electrically interconnected in series
using additional metallic bridges 112.
[0008] As will be apparent from the adjoining figure, the
semiconductor elements 108 are thermally connected in parallel and
electrically connected in series.
[0009] Owing to intrinsic material properties of the semiconductor
elements 108, when a temperature gradient is maintained across the
heat source 104 and the heat sink 106, free charge carriers
therein, namely, electrons in the n-type semiconductor element 108a
and holes in the p-type semiconductor element 108b diffuse towards
the heat sink 106 resulting in an electrical potential across the
length of the semiconductor elements 108 between the heat source
104 and the heat sink 106. As the n-type semiconductor element 108a
and the p-type semiconductor element 108b have mutually opposite
electrical conductivity types, the electrical potentials therein
build in opposite directions as free charge carriers have opposite
polarity, the resulting electrical potential is aggregated across
the series combination of the n-type semiconductor element 108a and
the p-type semiconductor element 108b.
[0010] The electrical potential developed across the ends of a
thermoelectric element is proportional to the thermal gradient with
Seebeck coefficient as the constant of proportionality. The Seebeck
coefficients of well known thermoelectric materials typically range
from about 100 .mu.V/degree C. to about 300 .mu.V/degree C. Owing
to low values of Seebeck coefficients, multiple thermocouple
modules 102 are electrically connected in series to obtain a
sufficiently high output voltage for use in practical applications.
With increased output voltage requirement, the thermoelectric
devices are forced to be expanded laterally and thereby, tend to
become bulky and attain a cumbersome form factor.
[0011] The thermal efficiency of a thermoelectric material is
defined in terms of its figure of merit, which depends not only on
its `thermal power` (absolute value of Seebeck coefficient) but
also a complex interplay of its electrical and thermal properties.
The thermoelectric material should ideally have high electrical
conductivity and low thermal conductivity; and this requirement
proves to be contradictory with regard to most of the commonly
available materials. The best known thermoelectric materials
currently available provide a figure of merit of about 1.
[0012] In recent years, significant efforts have been made in
developing new thermoelectric materials with improved figure of
merit such that various theoretical applications of thermoelectric
devices may indeed be realized.
[0013] While research and development of new thermoelectric
materials is important, efforts to improve design of thermoelectric
devices to enhance output voltage without adversely affecting their
form factor is also desirable.
[0014] Moreover, the state of the art thermoelectric devices
typically rely on a heat source and/or a heat sink and need to be
thermally coupled thereto in order to generate electrical power,
and hence, imposing constraints on spatial positioning and thereby,
diminishing portability and ease-of-use of such thermoelectric
devices.
[0015] In light of the foregoing, there is a need for a
thermoelectric device with increased output voltage, compact form
factor, and enhanced portability.
SUMMARY OF THE PRESENT INVENTION
[0016] It is an object of the present invention to provide a
thermoelectric device with an improved form factor for a specified
output voltage.
[0017] It is another object of the present invention to provide a
thermoelectric device with improved portability.
[0018] It is yet another object of the present invention to provide
a method for fabrication of such thermoelectric device.
[0019] The object is achieved by providing a thermoelectric device
according to claim 1 and a method for fabricating the same
according to claim 11. Further embodiments of the present invention
are addressed in respective dependent claims.
[0020] The underlying concept of the present invention is to
fabricate a thermoelectric device in a manner that one or more
layers of thermoelectric elements may be stacked one atop another
in such manner that an internal cavity is created therein. The
external boundary includes two thermally conducting substrates
arranged substantially parallel to each other with the
thermoelectric device being configured such that a direction of
thermal flux within the thermoelectric device is substantially
orthogonal to each substrate.
[0021] The internal cavity is accessible from an external boundary
of the thermoelectric device, and is configured to receive
thermally active materials therein. In one embodiment, the
thermoelectric device is configured as a flow-through device such
that the thermally active material enters the internal cavity
through an inlet interface and exits from an outlet interface. In
another embodiment, the thermally active materials are placed
inside a cartridge, which has such form factor that is suitable for
inserting the cartridge in the thermoelectric device. As used
herein, the term `thermally active` is intended to characterize a
subject as endothermic or exothermic.
[0022] When such a thermally active cartridge is present within the
internal cavity of the thermoelectric device, a thermal gradient is
created across the thermoelectric elements, which extend between
the internal cavity and at least one of the substrates.
Accordingly, an electrical potential is created across individual
thermoelectric elements. The individual thermoelectric elements are
electrically connected in series and an aggregate electrical
potential across all thermoelectric elements included in the
thermoelectric device is tapped through a suitable electrical
interface provided therein.
[0023] In a first aspect of the present invention, a thermoelectric
device is provided. The thermoelectric device includes at least a
first substrate and at least a second substrate arranged
substantially parallel to a reference plane. The reference plane
defines three mutually orthogonal axes, namely, a first axis, a
second axis, and a third axis. The first axis is orthogonal to the
reference plane and the second and the third axes are aligned to
the reference plane. The first and the second substrates are
retained in a spaced apart relationship along the first axis. The
thermoelectric device further includes at least one thermocouple.
The thermocouple includes at least one first thermoelectric element
and at least one second thermoelectric element.
[0024] The first thermoelectric element is disposed on the first
substrate and extends towards the second substrate along the first
axis. The first thermoelectric element includes a first basal
surface facing towards the first substrate, a first apical surface
substantially opposite to the first basal surface, and a first
lateral surface there between.
[0025] The second thermoelectric element is disposed on the second
substrate and extends towards the first substrate along the first
axis. The second thermoelectric element includes a second basal
surface facing towards the second substrate, a second apical
surface substantially opposite to the second basal surface, and a
second lateral surface there between.
[0026] The first thermoelectric element and the second
thermoelectric element are disposed such that the first and the
second apical surfaces are spaced apart along the first axis,
whereby an internal cavity is defined there between.
[0027] In a second aspect of the present invention, a method for
fabricating a thermoelectric device, as described in accordance
with the first aspect of the present invention, is provided.
[0028] At a first step, a first substrate arranged substantially
along a reference plane is provided. The reference plane defines
three mutually orthogonal axes, namely, a first axis, a second
axis, and a third axis. The first axis is orthogonal to the
reference plane and the second and the third axes are aligned to
the reference plane.
[0029] At least a first thermoelectric element is formed on the
first substrate. The first thermoelectric element extends along the
first axis and includes a first basal surface facing towards the
first substrate, a first apical surface substantially opposite to
the first basal surface, and a first lateral surface there between.
A sacrificial layer is disposed on the first thermoelectric
element. After disposing the sacrificial layer, at least a second
thermoelectric element is formed on the sacrificial layer. The
second thermoelectric element extends along the first axis and
includes a second basal surface facing away from the first
substrate, a second apical surface substantially opposite to the
second basal surface and facing towards the sacrificial layer, and
a second lateral surface there between. After forming the second
thermoelectric element, a second substrate is disposed on the
sacrificial layer. The second substrate is retained in a spaced
apart relationship from the first substrate along the first axis
and extends in a spatial plane substantially parallel to the
reference plane. Finally, the sacrificial layer is removed such
that the first and the second apical surfaces of the first
thermoelectric element and the second thermoelectric element
respectively are spaced apart along the first axis, whereby an
internal cavity is defined there between.
[0030] Thus, at least one thermocouple is formed between the first
and the second substrates provided in the thermoelectric
device.
[0031] Accordingly, the present invention provides a thermoelectric
device and a method for fabrication thereof such that a relatively
compact form factor is achieved for a specified output voltage. The
techniques of the present invention provide a thermoelectric device
that is not constrained to be spatially positioned such as to be
coupled to a heat source and/or a heat sink, thereby greatly
enhances ease-of-use and portability thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The present invention is further described hereinafter with
reference to illustrated embodiments shown in the accompanying
drawings, in which:
[0033] FIG. 1 illustrates a schematic view of a thermoelectric
device in accordance with the state of the art,
[0034] FIG. 2 illustrates a perspective view of a partially
cut-away thermoelectric device in accordance with an exemplary
embodiment of the present invention,
[0035] FIGS. 3A-3C illustrate cross-sectional views of a
thermoelectric device in accordance with various exemplary
embodiments of the present invention, and
[0036] FIGS. 4-18 illustrate cross-sectional views of a
thermoelectric device depicting a method for fabrication thereof in
accordance with an exemplary embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0037] Various embodiments are described with reference to the
drawings, wherein like reference numerals are used to refer to like
elements throughout. In the following description, for purpose of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of one or more embodiments. It may
be evident that such embodiments may be practised without these
specific details.
[0038] The present invention will hereinafter be explained
primarily in the context of solid-state thermoelectric generation.
However, it should be noted that various techniques of the present
invention are not limited in any manner to semiconductor based
thermoelectric generation per se, and are equally applicable to
thermoelectric devices based on other materials and further, to any
desired application of thermoelectric effect, as presently known or
as may be developed in future.
[0039] Referring now to FIGS. 2 and 3A through 3C, a perspective
view of a partially cut-away thermoelectric device 200 and
cross-sectional views thereof are respectively shown in accordance
with exemplary embodiments of the present invention.
[0040] The thermoelectric device 200 includes one or more
thermocouples 202 arranged between a first substrate 204 and a
second substrate 206. Each thermocouple 202 includes a first
thermoelectric element 208 and a second thermoelectric element 210.
The thermoelectric device 200 further includes an internal cavity
212.
[0041] The structure of thermoelectric device 200 will now be
explained with respect to a reference plane (P), X-Y plane in the
adjoining figure. The reference plane (P) defines three mutually
orthogonal axes, namely, a first axis (z-axis), a second axis
(x-axis), and a third axis (y-axis). The first axis (z-axis) is
orthogonal to the reference plane (P) whereas the second axis
(x-axis) and the third axis (y-axis) are aligned to the reference
plane (P).
[0042] Each substrate 204, 206 is substantially planar and is
arranged substantially parallel to the reference plane (P). The
first substrate 204 and the second substrate 206 are retained in a
spaced apart relationship along the first axis (z-axis).
[0043] The first thermoelectric element 208 is disposed on the
first substrate 204 and extends towards the second substrate 206
along the first axis (z-axis). The first thermoelectric element 208
includes a first basal surface 208(b) facing towards the first
substrate 204, a first apical surface 208(a) substantially opposite
to the first basal surface 208(b), and a first lateral surface
208(l) there between.
[0044] The second thermoelectric element 210 is disposed on the
second substrate 206 and extends towards the first substrate 204
along the first axis (z-axis). The second thermoelectric element
210 includes a second basal surface 210(b) facing towards the
second substrate 206, a second apical surface 210(a) substantially
opposite to the second basal surface 210(b), and a second lateral
surface 210(l) there between.
[0045] As can be seen from the adjoining figure, the relative
spacing between the first substrate 204 and the second substrate
206 and the respective dimensions of the first thermoelectric
element 208 and the second thermoelectric element 210, in
particular, the respective dimensions along the first axis
(z-axis), are regulated in such manner that the first apical
surface 208(a) and second apical surface 210(a) are spaced apart
along the first axis (z-axis), whereby an internal cavity 212 is
defined there between.
[0046] Having broadly described the structure of the thermoelectric
device 200, further structural details thereof will now be
explained. The flow of thermal and electrical currents within the
thermoelectric device 200 will also be explained.
[0047] The first thermoelectric element 208 and the second
thermoelectric element 210 are formed using thermoelectric material
of mutually opposite types of electrical conductivity. In one
example, the first thermoelectric element 208 is an n-type
semiconducting material and the second thermoelectric element 210
is a p-type semiconducting material.
[0048] In various exemplary embodiments of the present invention,
any suitable thermoelectric material may be used. In order to
achieve a better figure of merit, generally, heavily doped
semiconducting materials are used. In the current state of the art,
thermoelectric materials formed using alloys of Bismuth telluride
and Antimony telluride are shown to display good thermoelectric
properties. However, the present invention is not limited to any
specific examples of thermoelectric materials, and any suitable
thermoelectric material currently available or developed in future
may be used to practice the techniques of the present
invention.
[0049] In an exemplary embodiment of the present invention, each of
first lateral surface 208(l) and the second lateral surface 210(l)
of the first thermoelectric element 208 and the second
thermoelectric element 210 respectively is electrically and
thermally insulated such that a direction of electrical and thermal
currents through the first thermoelectric element 208 and the
second thermoelectric element 210 is aligned with the first axis
(z-axis). In one example, the desired insulation may be achieved
using Silicon nitride.
[0050] The first thermoelectric element 208 and the second
thermoelectric element 210 are electrically interconnected through
disposing an intra-couple bridge 214 between the first apical
surface 208(a) and the second apical surface 210(a). The
intra-couple bridge 214 includes a first electrically connecting
layer 216, a second electrically connecting layer 218, and an
intra-couple metallization layer 220.
[0051] The first electrically connecting layer 216 is deposited on
the first apical surface 208(a). Similarly, the second electrically
connecting layer 218 is deposited on the second apical surface
210(a). The intra-couple metallization layer 220 extends along the
first axis (z-axis) and interconnects the electrically connecting
layers 216, 218. Any suitable metal such as aluminum, gold, and so
on may be used to form the intra-couple bridge 214.
[0052] The intra-couple bridge 214 is at least electrically
insulated at a non-contact surface thereof. The term non-contact
surface refers to an external surface of the intra-couple bridge
214 excluding such portion of the electrically connecting layers
216, 218 that are in electrical contact with the first apical
surface 208(a) and second apical surface 210(a). Such electrical
insulation ensures that the electrical current flowing from the
first thermoelectric element 208 to the second thermoelectric
element 210 is prevented from any leakage.
[0053] In an exemplary embodiment of the present invention, the
electrically connecting layers 216, 218 entirely cover the first
apical surface 208(a) and the second apical surface 210(a)
respectively. In an alternative exemplary embodiment of the present
invention, the electrically connecting layers 216, 218 partially
cover the respective apical surfaces 208(a) and 210(a), the
remaining portions of the first apical surface 208(a) and the
second apical surface 210(a) are electrically insulated. It should
be noted that the material used for electrical insulation of the
remaining portions of the first apical surface 208(a) and the
second apical surface 210(a) should be thermally conducting. In
this embodiment, the intra-couple bridge 214 is provided both
electrical and thermal insulation such that not only the electrical
but the thermal currents are also aligned with the first axis
(z-axis).
[0054] The thermoelectric device 200 further includes an
inter-couple bridge 222. The inter-couple bridge 222 includes a
first electrically coupling layer 224, a second electrically
coupling layer 226, and an inter-couple metallization layer
228.
[0055] The first electrically coupling layer 224 is disposed
between the first basal surface 208(b) and the first substrate 204.
Similarly, the second electrically coupling layer 226 is disposed
between the second basal surface 210(b) and the second substrate
206. As will now be apparent, an aggregate of individual electrical
potentials across the first thermoelectric element 208 and the
second thermoelectric element 210 is accessible across the first
electrically coupling layer 224 and the second electrically
coupling layer 226.
[0056] Each of the first substrate 204 and the second substrate 206
are formed of a thermally conducting and electrically insulating
material. In one example, each substrate 204, 206 is formed using
alumina, which is a thermal conductor but an electrical insulator.
In general, any ceramic material or any other suitable material may
be used for forming the substrates 204, 206.
[0057] In an exemplary embodiment of the present invention, each of
the first substrate 204 and the second substrate 206 are provided
with one or more structural features 232 and/or one or more
material coatings 234 to permit heat dissipation, as shown in FIGS.
3B and 3C. Such structural features 232 may, for example, include
fins to increase the heat dissipation surface area.
[0058] In an alternative exemplary embodiment of the present
invention, each of the first substrate 204 and the second substrate
206 are provided with one or more structural features 232 and/or
one or more material coatings 234 to permit heat absorption, as
shown in FIGS. 3B and 3C. In particular, any heat absorbing
material generally known in the art may be used to provide the
material coating on the first substrate 204 and the second
substrate 206.
[0059] These embodiments of the present invention will be further
understood in relation to operation of the thermoelectric device
200, as will be explained later.
[0060] As described earlier, the Seebeck coefficient of currently
available thermoelectric materials is quite low. Accordingly,
multiple thermocouples 202 are usually formed and are electrically
connected in series to provide desired output voltage. This aspect
of the present invention will now be explained.
[0061] In an embodiment of the present invention, at least a first
thermocouple 202(a) and at least a second thermocouple 202(b) are
formed. Each of the first thermocouple 202(a) and the second
thermocouple 202(b) has the same configuration as that of the
thermocouple 202, as described in the preceding description.
[0062] Thus, the individual aggregate electrical potentials across
the first thermocouple 202(a) and second thermocouple 202(b) are
formed across corresponding first electrically coupling layer 224
and the second electrically coupling layer 226.
[0063] The first thermocouple 202(a) and the second thermocouple
202(b) are adjacently disposed between the first substrate 204 and
the second substrate 206.
[0064] The first electrically coupling layer 224 of the first
thermocouple 202(a) is electrically interconnected to the second
electrically coupling layer 226 of the second thermocouple 202(b)
through an inter-couple bridge 222. Thus, the first thermocouple
202(a) and the second thermocouple 202(b) are electrically
connected in series.
[0065] The inter-couple bridge 222 includes an inter-couple
metallization layer 228 which extends along the first axis (z-axis)
from substantially adjacent to the first substrate 204 to
substantially adjacent to the second substrate 206, and
electrically interconnects the first and the second electrically
conductive layers 224, 226.
[0066] The inter-couple bridge 222 is at least electrically
insulated on a non-contact surface thereof in a manner similar to
that of the intra-couple bridge 214.
[0067] Similar to the manner explained in the context of
intra-couple bridge 214, the term non-contact surface refers to an
external surface of inter-couple bridge 222 excluding such portion
of the electrically coupling layers 224, 226 that are in electrical
contact with the first basal surface 208(b) and the second basal
surface 210(b). Such electrical insulation ensures that the
electrical current flowing from the first thermocouple 202(a) to
the second thermocouple 202(b) is prevented from any leakage. In
one embodiment, the inter-couple bridge 222 is at least partially
provided with thermal insulation also such as to avoid formation of
an undesirable thermal flow paths between the first substrate 204
and the second substrate 206 and various intermediate
components.
[0068] The aggregate electrical potential of the first thermocouple
202(a) and the second thermocouple 202(b) are available across the
first electrically coupling layer 224 of the first thermocouple
202(a) and the second electrically coupling layer 226 of the second
thermocouple 202(b).
[0069] As will be readily understood, the thermoelectric device 200
is suitable for scaling up to include multiple thermocouples 202a,
202b, 202c through 202n.
[0070] Accordingly, in an exemplary embodiment of the present
invention, multiple thermocouples 202a through 202n (collectively,
thermocouples 202) are disposed between the first substrate 204 and
the second substrate 206 in such manner as to form a two
dimensional matrix relative to the reference plane (P). While
arranging the thermocouples 202 in a two-dimensional matrix, a set
of thermocouples 202 are arranged in individual rows extending
along the second axis (x-axis) and multiple such rows are formed
along the third axis (y-axis). The thermocouples 202 along an
individual row are electrically interconnected in series and
individual rows of thermocouples 202, are in turn, electrically
connected in series, as can be seen in FIG. 2.
[0071] When the thermocouples 202 are arranged in the manner
described above, the internal cavities of corresponding
thermocouples 202 in adjacent rows are in continuum.
[0072] In accordance with the second aspect of the present
invention, the method for fabrication of the thermoelectric device
200 will now be explained in conjunction with FIGS. 4 through
18.
[0073] Referring to FIG. 4, the first substrate 204 is arranged
substantially along the reference plane (P) is provided. As
mentioned earlier, the reference plane (P) defines three mutually
orthogonal axes, namely, the first axis (z-axis), the second axis
(x-axis), and the third axis (y-axis). The first axis (z-axis) is
orthogonal to the reference plane (P) and the second axis (x-axis)
and the third axis (y-axis) are aligned to the reference plane
(P).
[0074] The first substrate 204 is formed of a thermally conducting
and electrically insulating material. As mentioned previously, the
first substrate 204 may be formed using ceramic materials, for
example, alumina and so on; or any material exhibiting the desired
properties.
[0075] The first substrate 204 is provided with one or more
structural features and/or one or more material coatings either to
permit heat dissipation, for example, by providing fins to increase
the heat dissipation surface area, or to permit heat absorption,
for example, by providing a material coating using any heat
absorbing material generally known in the art.
[0076] Still referring to FIG. 4, the first electrically coupling
layer 224 is disposed on the first substrate 204. The first
electrically coupling layer 224 may be formed using any standard
metallization technique used in semiconductor fabrication.
[0077] Referring now to FIG. 5, the first thermoelectric element
208 is then formed. As can be seen in the adjoining figure, the
first thermoelectric element 208 extends along the first axis
(z-axis) and includes the first basal surface 208(b) facing towards
the first substrate 204, the first apical surface 208(a)
substantially opposite to the first basal surface 208(b), and a
first lateral surface 208(l) there between.
[0078] As will now be evident, the first electrically coupling
layer 224 is disposed between the first basal surface 208(b) and
the first substrate 204.
[0079] The first thermoelectric element 208 is formed using a
suitable thermoelectric material. In one example, the first
thermoelectric element 208 is formed using a heavily doped n-type
semiconducting material.
[0080] Any suitable technique may be used to form the first
thermoelectric element 208. In one example, the n-type first
thermoelectric element 208 is grown on the first substrate 204 on
top of the first electrically coupling layer 224 using a deposition
technique.
[0081] Referring now to FIGS. 6 and 7, after forming the first
thermoelectric element 208, an electrically insulating material is
deposited on the first thermoelectric element 208 to partially form
an insulating layer 230. In one example, silicon nitride is used as
the insulating material. The silicon nitride is first deposited and
subsequently, etched and polished to form the structure shown in
FIG. 7.
[0082] As will be easily understood, such insulation is required to
ensure that direction of electrical current through the first
thermoelectric element 208 is aligned with the first axis (z-axis)
and there is no leakage of electrical current.
[0083] Referring now to FIG. 8, a metallization step is performed
such that a first electrically connecting layer 216 is created on
the first apical surface 208(a) of the first thermoelectric element
208. In addition, the inter-couple metallization layer 228 is also
partially formed.
[0084] Referring now to FIGS. 9 and 10, another iteration of
deposition of insulating material and metallization layer is
performed such that the intra-couple metallization layer 220 is
also partially formed while the inter-couple metallization layer
228 is further grown. In addition, an external surface of the first
electrically connecting layer 216 which is not in contact with the
first thermoelectric element 208, namely, the so-called non-contact
surface, is provided with the insulation layer 230.
[0085] Referring now to FIGS. 11 and 12, a sacrificial layer (SL)
is disposed on the first thermoelectric element 208. The insulation
layer 230, and the intra-couple metallization layer 220 and the
inter-couple metallization layer 228 are further grown through the
sacrificial layer (SL) such that part of the intra-couple
metallization layer 220 and the inter-couple metallization layer
228 are covered with the insulating layer 230.
[0086] Referring now to FIGS. 13 and 14, the insulating layer 230,
and the metallization layers 220 and 228 are further grown. In
addition, the second electrically connecting layer 218 is
formed.
[0087] Referring now to FIG. 15, the second thermoelectric element
210 is formed.
[0088] As evident from the adjoining figures, the second
thermoelectric element 210 extends along the first axis (z-axis).
The second thermoelectric element 210 includes the second basal
surface 210(b) facing away from the first substrate 204, the second
apical surface 210(a) substantially opposite to the second basal
surface 210(b) and facing towards the sacrificial layer (SL), and
the second lateral surface 210(l) there between.
[0089] As with the first thermoelectric element 208, the second
thermoelectric element 210 is formed using a suitable
thermoelectric material. However, the second thermoelectric element
210 has an opposite type of electrical conductivity with respect to
that of the first thermoelectric element 208. Thus, in one example,
while the first thermoelectric element 208 is formed using a
heavily doped n-type semiconducting material, the second
thermoelectric element 210 is formed using a heavily doped p-type
semiconducting material.
[0090] Any suitable fabrication technique may be used to form the
second thermoelectric element 210. In one example, the p-type
second thermoelectric element 210 is grown using a deposition
technique.
[0091] Referring now to FIGS. 16 and 17, the insulating layer 230
is grown further such that the second lateral surface 210(l) is
electrically insulated. In addition, the inter-couple metallization
layer 228 is also further grown and the second electrically
coupling layer 226 is also disposed on the second thermoelectric
element 210.
[0092] Referring now to FIG. 18, after forming the second
thermoelectric element 210, the second substrate 206 is disposed in
the manner shown in the adjoining figure.
[0093] As evident from the adjoining figure, the second substrate
206 extends in a spatial plane substantially parallel to the
reference plane (P).
[0094] Subsequently, the sacrificial layer (SL) is removed using a
suitable technique. Thus, at this stage, the first apical surface
208(a) of the first thermoelectric element 208 and the second
apical surface 210(a) of the second thermoelectric element 210
respectively are spaced apart along the first axis (z-axis) and the
internal cavity 212 is formed there between.
[0095] In various embodiments of the present invention, the second
substrate 206 is retained in a spaced apart relationship from the
first substrate 204 along the first axis (z-axis). This is achieved
through disposing additional columnar structures, extending along
the first axis (z-axis), along the peripheral boundary of the first
substrate 204 and the second substrate 206. Such columnar
structures not only provide necessary spaced relationship between
the first substrate 204 and the second substrate 206 but also
provide mechanical stability and robustness to the resulting
thermoelectric device 200.
[0096] The entire thermoelectric device 200 is then packaged using
generally known packaging techniques to provide further mechanical
stability thereto.
[0097] As evident from the preceding description, the intra-couple
bridge 214 extends along the first axis (z-axis) and interconnects
the first electrically connecting layer 216 and the second
electrically connecting layer 218. The first and the second
electrically connecting layers 216, 218 are in electrical contact
with the first and the second thermoelectric elements 208, 210
through the respective apical surfaces 208(a), 210(a). Thus, the
intra-couple bridge 214 electrically interconnects the first
thermoelectric element 208 and the second thermoelectric element
210. The intra-couple bridge 214 is electrically insulated at the
non-contact surface thereof.
[0098] It should be noted that for ease of understanding, a single
insulating layer 230 has been referred to while describing the
fabrication method. In various embodiments of the present
invention, different insulating layers with desired electrical and
thermal properties may be used in different regions of the
thermoelectric device 200, for example, to achieve the insulating
layer properties as explained in conjunction with FIGS. 2 and
3.
[0099] As evident from FIGS. 4 through 18, multiple thermocouples
202 are formed between the first substrate 204 and the second
substrate 206.
[0100] As explained in conjunction with FIGS. 2 and 3, the
thermocouples 202 are arranged in a two dimensional matrix relative
to the reference plane (P). While arranging the thermocouples 202
in a two-dimensional matrix, a set of thermocouples 202 are
arranged in individual rows extending along the second axis
(x-axis) and multiple such rows are formed along the third axis
(y-axis). The thermocouples 202 along an individual row are
electrically interconnected in series and individual rows of
thermocouples 202, are in turn, electrically connected in series.
When the thermocouples 202 are arranged in the manner described
above, the internal cavities of corresponding thermocouples 202 in
adjacent rows are in continuum.
[0101] A suitable electrical interface, for example two electrodes,
is provided such that the aggregate electrical potential of the
thermoelectric device 200 is available for driving external
electrical loads.
[0102] In a further aspect of the present invention, the
thermoelectric device 200 is provided with an external housing. The
external housing of the thermoelectric device 200 includes one or
more removable covers in an external packaging substantially along
X-Z plane such that the removable covers may be removed to access
the internal cavity 212.
[0103] In one example of the present invention, the thermoelectric
device 200 of the present invention is operated in flow-through
mode. In this mode of operation, the external housing is provided
with removable covers on two opposite sides thereof such that the
internal cavity 212 is accessible from each of the two sides, one
side acts as an inlet interface and the other side acts as an
outlet interface. Referring to FIGS. 4 through 18, these sides are
substantially parallel to the plane of the drawings, that is, X-Z
plane. In this mode of operation, a heat source, such as heated
water, steam, oil, and so on enters the internal cavity through the
inlet interface and exits from the outlet interface. As will now be
readily understood, the thermoelectric device 200 in flow-through
configuration may be used for electrical power generation in
myriads of waste heat recovery applications such as industrial,
power plants, automotive, oil and water supply lines, and so
on.
[0104] In another example, the thermoelectric device 200 is
operated in a stand-alone mode. In this mode of operation, the
external housing is provided with removable covers on at least one
side, which is substantially parallel to the plane of the drawing,
that is, X-Z plane. An external cartridge may be inserted inside
the thermoelectric device 200 through opening one of the
covers.
[0105] The cartridge is made using thermally conducting material
and has a structure which is essentially a collection of tubular
elements arranged is a grid-like manner on a support such that
tubular elements may be filled with a desirable thermally active
material and the cartridge inserted inside the thermoelectric
device 200. In one exemplary embodiment, the cartridge is further
configured to serve the purpose of removable cover by way of
locking onto the external housing of the thermoelectric device
200.
[0106] As per techniques of the present invention, the first
thermoelectric element 208 and the second thermoelectric element
210 are formed using thermoelectric material of opposite
conductivity types. Thus, while the first thermoelectric element
208 is formed using an n-type material, the second thermoelectric
element 210 is formed using a p-type material. The charge carriers
within the first thermoelectric element 208 and the second
thermoelectric element 210 diffuse towards the respective adjoining
substrates. Thus, the electrical potentials across are aligned and
an aggregate electrical potential is formed across the first basal
surface 208(b) and the second basal surface 210(b). As already
explained, the electrical potentials across individual
thermocouples 202 are aggregated through a series combination of
these thermocouples 202 using inter-couple bridges 222.
[0107] It should be noted that the first and the second
electrically connecting layers and also, the first and the second
electrically coupling layers respectively interface with the first
thermoelectric element 208 and the second thermoelectric element
210 through a diffusion barrier preventing diffusion of charge
carrier in metals into the thermoelectric material and hence
preventing a functional failure of the thermoelectric element.
[0108] Several such standard aspects associated with fabrication of
thermoelectric devices are generally known and have not been
explained herein for sake of brevity.
[0109] The operation of the thermoelectric device 200 will now be
explained.
[0110] In accordance with various exemplary embodiments of the
present invention, a thermally active material, either directly or
through use of a cartridge, is inserted within the internal cavity
212 of the thermoelectric device 200.
[0111] The thermally active material may be any such material that
is endothermic or exothermic in nature. The present invention
contemplates use of any such materials and/or mixtures that may
lead to sustained heat generation over prolonged time periods.
Various examples include, but are not limited to, phase change
materials, biochemical mixtures, biological materials, and so on.
If so desired, any suitable material that may act as a heat source
for even for short time periods may be employed. Such examples may
include hot water, soil, sand, and so on.
[0112] The operation of thermoelectric device 200 will now be
explained with the internal cavity 212 filled with such material
that acts as a heat source.
[0113] Owing to presence of a heat source within the internal
cavity 212, the temperature therein increases above the ambient
temperature. Accordingly, a thermal gradient is established across
each of the first thermoelectric element 208 and the second
thermoelectric element 210 wherein the respective apical surfaces
208(a) and 210(a) are maintained at higher temperature while the
respective basal surfaces 208(b) and 210(b) are maintained at an
ambient temperature.
[0114] As previously explained, owing to intrinsic material
properties of the thermoelectric materials, when a thermal gradient
is applied across a thermoelectric element, free charge carriers
diffuse along the direction of thermal flux and accordingly, an
electrical potential is developed.
[0115] The first substrate 204 and the second substrate 206 act as
heat sinks and are provided with structural features such as fins
to ensure rapid dissipation of heat.
[0116] In case an endothermic material is inserted inside the
internal cavity 212, the direction of thermal and electrical
currents is reversed. However, the basic principle of operation
remains the same.
[0117] In this case, the first substrate 204 and the second
substrate 206 are provided with features to absorb heat from
ambient environment, for example, the thermoelectric device 200 may
be operated through exposure to sunlight whereby the first
substrate 204 and the second substrate 206 are configured to absorb
infra-red component of the solar radiation. Alternatively, the
thermoelectric device 200 may be thermally coupled to a heat source
at the first substrate 204 and the second substrate 206.
[0118] Thus, the present invention provides a thermoelectric device
and a method for fabrication thereof such that a relatively compact
form factor is achieved for a specified output voltage. The
techniques of the present invention provide a thermoelectric device
that is easily portable and does not necessarily need to be coupled
to a heat source or a heat sink, thereby greatly enhancing
ease-of-use.
[0119] The present invention offers several advantages over prior
art techniques. In particular, owing to stacking of individual
thermoelectric elements considerable substrate real estate is
preserved. The form factor of the thermoelectric device becomes
more compact and convenient. The ease-of-use and portability of the
thermoelectric device significantly improves not only because of
improved form factor but also due to an autonomous mode of
operation, which is to say that the potential uses of the
thermoelectric device is not constrained by the need to couple the
thermoelectric device to a heat source or a heat sink. The required
heat source (or sink) is integrated with the thermoelectric device,
while the ambient environment acts as the heat sink (or
source).
[0120] While the present invention has been described in detail
with reference to certain embodiments, it should be appreciated
that the present invention is not limited to those embodiments. In
view of the present disclosure, many modifications and variations
would present themselves, to those of skill in the art without
departing from the scope of various embodiments of the present
invention, as described herein. The scope of the present invention
is, therefore, indicated by the following claims rather than by the
foregoing description. All changes, modifications, and variations
coming within the meaning and range of equivalency of the claims
are to be considered within their scope.
* * * * *