A thermoelectric device formed of nanowires on the nm scale. The nanowires are preferably of a size that causes quantum confinement effects within the wires. The wires are connected together into a bundle to increase the power density

Borshchevsky, Alexander

Fleurial, Jean-Pierre

Herman, Jennifer

Ryan, Margaret A.

NASA Technical Reports Server

(12) United States Patent (io) Patent No.: US 7,098,393 B2 
Fleurial et al. (45) Date of Patent: Aug. 29,2006 
THERMOELECTRIC DEVICE WITH 
MULTIPLE, NANOMETER SCALE, 
ELEMENTS 
Inventors: 
Assignee: 
Notice: 
Appl. No.: 
Filed: 
Jean-Pierre Fleurial, Altadena, CA 
(US); Margaret A. Ryan, Pasadena, 
CA (US); Alexander Borshchevsky, 
Santa Monica, CA (US); Jennifer 
Herman, Pasadena, CA (US) 
California Institute of Technology, 
Pasadena, CA (US) 
Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 198 days. 
10/150,772 
May 17, 2002 
Prior Publication Data 
US 200310047204 A1 Mar. 13. 2003 
Related U.S. Application Data 
Provisional application No. 601292,052, filed on May 
18, 2001. 
Int. C1. 
HOlL 35/16 (2006.01) 
HOlL 35/18 (2006.01) 
HOlL 35/14 (2006.01) 
U.S. C1. ...................... 136/240; 1361201; 1361205; 
1361212; 1361236.1; 2571467 
Field of Classification Search ................ 1361201, 
1361205,212, 240, 236.1; 438154; 2571467 
See application file for complete search history. 
References Cited 
U.S. PATENT DOCUMENTS 
6,159,831 A * 12/2000 Thmsh et al. .............. 438/582 
6,231,744 B1 * 5/2001 Ying et al. .................. 205/324 
6,359,288 B1 * 3/2002 Ying et al. .................... 257/14 
6,388,185 B1 * 5/2002 Fleurial et al. ............. 136/205 
6,492,585 B1 * 12/2002 Zamboni et al. ............ 136/201 
6,598,403 B1 * 7/2003 Ghoshal ....................... 62/3.2 
6,670,539 B1 * 12/2003 Heremans et al. .......... 136/240 
2002/0158342 A1 * 10/2002 Tuominen et al. .......... 257/784 
2002/0172820 A1 * 11/2002 Majumdar et al. .......... 428/357 
2003/0041892 A1 * 3/2003 Fleurial et al. ............. 136/227 
FOREIGN PATENT DOCUMENTS 
wo WO-03/046265 A2 * 6/2003 
OTHER PUBLICATIONS 
Huber et al, “Thermoelectric Properties of Bi and Bi2Te3 Composi- 
ties,” 16th International Conference of Thermoelectrics, (1997), pp. 
404-408.* 
Cronin et al, “Thermoelectric Investigation of Bismuth Nanowires,” 
18th International Conference on Thermoelectrics, (1999), pp. 554- 
557.* 
US .  Appl. No. 60/275,984, filed on Mar. 14, 2001.* 
Peng et al, “Bismuth quantum-wires arrays fabricated by 
electrodeposition in nanoporous anodic aluminum oxide and its 
stmctural properties,” Materials Science and Engineering B77 
(2000), pp. 246-249, avalable online Oct. 27, 2000.* 
(Continued) 
Primary Examiner-Alan Diamond 
(74) Attorney, Agent, or Firm-Fish & Richardson P.C. 
(57) ABSTRACT 
A thermoelectric device formed of nanowires on the nm 
scale. The nanowires are preferably of a size that causes 
quantum confinement effects within the wires. The wires are 
connected together into a bundle to increase the power 
density. 
6,002,081 A * 12/1999 Sakuragi ..................... 136/203 21 Claims, 3 Drawing Sheets 
https://ntrs.nasa.gov/search.jsp?R=20080008691 2019-08-30T03:32:37+00:00Z
US 7,098,393 B2 
Page 2 
OTHER PUBLICATIONS Fleurial et al., “Thick-Film Thermoelectric Microdevices,” The 18th 
International Conference on Thermoelectrics: ICT Symposium Pro- 
ceedings, IEEE, pp, 294-300 (1999), 
Hicks and Dresselhaus, “Thermoelectric figure of merit of a one- 
dimeinsional conductor,” Physical Review B, vo1.47, pp. 16631- 
Rabin et al., “Anomalously high thermoelectric figure of merit in 
Bi,.,Sb, nanowires by carrier pocket alignment,” Applied Physics 
Letters, vol. 73(20), pp. 2950-2952 (1998). 
Lin et al, “Fabrication and Transport Properties of Te-Doped Bi 
Nanowire Arrays,” MS Symposium H, Molecular Electronics as 
heid at the 199 MRS ~ ~ 1 1  Meeting, Boston, N ~ ~ ,  29 to D ~ ~ ,  2, 
1999.* 
Ryan et al, “Electrochemically deposited semiconductor 16634 (1993). 
nanowires,” The Electrochemical Society , Mar. 23, 2006.* 
Dresselhaus et al., “Advances in 1D and 2D Thermoelectric Mate- 
rials,’’ The 18th International Conference on Thermoelectrics: ICT 
Symposium Proceedings, IEEE, pp. 92-99 (1999). 
Dresselhaus et al., “Low Dimensional Thermoelectrics,” The 16th 
International Conference on Thermoelectris: ICT Symposium Pro- 
ceedings, IEEE, pp. 12-20 (1997). * cited by examiner 
U.S. Patent Aug. 29,2006 Sheet 1 of 3 US 7,098,393 B2 
POWER GENERATION USING 
WASTE HEAT RECOVERY 25-2orc 
FIG. IA 
0.5 1.0 1.5 2.0 2.5 3.0 
Average ZT of Thermoelectric Material 
. . . . . . . . . . . . .. . .. . 
I I I I I Ill I I I I I 1 1 1  I I I l 1 1 l 1  I I I I l l 1  
0.00 1 0.01 0. I I 10 
Leg Thickness of Thermoelectric Generator (mm) 
FIG. 7B 
U.S. Patent Aug. 29,2006 Sheet 2 of 3 US 7,098,393 B2 
P 
r 2 7 5  
-200 
FIG. 2 
N G .  3 
U.S. Patent Aug. 29,2006 Sheet 3 of 3 
5007- 
US 7,098,393 B2 
d/ 520 
I 
SENSOR r 524 
4 )  COMMUN 
0-0 O-0-J- 
0-0 ou-- 
I 
I 
I 
I 
I 
I 
- - CLC 
522 
METALLIC LAYER FOR SERIES CONNECTION OF BUNDLES 
METALLIC LAYER FOR ELECTROCHEMICAL GRO W7H AND 
FOR SERIES CONNECTION OF BUNDLES 
FIG. 4 
70 
FIG. 5 
US 7,098,393 B2 
1 
THERMOELECTRIC DEVICE WITH 
MULTIPLE, NANOMETER SCALE, 
ELEMENTS 
CROSS-REFERENCE TO RELATED 
APPLICATIONS 
This application claims benefit of U.S. Provisional Appli- 
cation No. 601292,052, filed May 18, 2001. 
STATEMENT AS TO FEDERALLY-SPONSORED 
RESEARCH 
The invention described herein was made in the perfor- 
mance of work under a NASA 7-1407 contract, and is 
subject to the provisions of Public Law 96-517 (U.S.C. 202) 
in which the contractor has elected to retain title. 
BACKGROUND 
Thermoelectric devices may operate to create energy 
based on a temperature difference, or conversely, create a 
temperature difference based on applied energy. Thermo- 
electric devices may be used in harsh environments to create 
electrical power. 
Miniaturized solid-state devices may be of interest for 
various miniaturized applications. 
SUMMARY 
The present invention recognizes that smaller thermoelec- 
tric devices may be used to create increased conversion 
efficiency. A number of individual “nano wires” are formed. 
These wires may be connected in bundles to create a 
composite positive device formed of many individual small 
elements. 
BRIEF DESCRIPTION OF THE DRAWINGS 
These and other aspects will now be described in detail 
FIGS. 1A and 1B show representative curves for a ther- 
FIG. 2 shows a representative device with thermoelectric 
FIG. 3 shows the way in which the thermoelectric wires 
FIG. 4 shows another embodiment in which connections 
FIG. 5 shows other circuitry being formed on the same 
with reference to the accompanying drawings, wherein: 
moelectric material; 
wires; 
can be interconnected; 
are carried out both on the top and bottom portions; 
substrate as the thermoelectric device. 
DETAILED DESCRIPTION 
An embodiment is shown in FIG. 2. In the embodiment, 
a plurality of thermoelectric legs 200 are formed. Each of the 
thermoelectric legs is in the form a thin nanometer scale 
wire, that is a leg having an outer diameter or outer extent 
which is of the scale of nanometers: less than one micron in 
maximum outer extent. More preferably, the outer extent of 
the wire is less than 500 nm in outer extent, and even more 
preferably is 100 nm or less. 
The thermoelectric elements are formed within a “tem- 
plate” 205, which is a device made of a specified material 
formed with a number of holes 210 therein. Any porous 
material with consistent size pores can be used as the 
2 
device. The pores are filled with thermoelectric material, 
which become the legs of the thermoelectric device. A 
connection to the legs is made. 
A state-of-the-art thermoelectric material may form such 
5 a miniaturized thermoelectric power source based on a 
Bi,Te, alloy, although other thermoelectric materials can be 
used. 
FIG. 1A shows a representative material conversion effi- 
ciency for an application of power generation using waste 
i o  heat recovery using such devices, as a function of the figure 
of merit, ZT, of the material. For temperature differentials in 
the range of 20 to 200 degrees Kelvin, the graph of FIG. l a  
shows that conversion efficiency between 1 and 15 percent 
may be possible. FIG. 1B shows the specific power obtained 
15 in watts/cm3. It may be possible, as shown, to obtain in 
excess of 1000 watts/cm3, depending on the temperature 
differential and other factors. FIG. 1B specifically illustrates 
that a greater power per cc is obtained when the leg 
thickness of the thermoelectric generator becomes smaller. 
20 This has lead to the conclusion that smaller legs may be 
desirable. However, current manufacturing techniques have 
often been limited. For example, bulk devices may be 
limited to 100 thermoelectric devices per square cm. 
Devices using micro techniques may be limited to 100,000 
25 devices per square cm. The present system may have 10 
times this, at least one million elements per square cm, and 
as many as one billion elements per square cm. 
The present application teaches formation of vertically 
integrated thermoelectric microdevices that use a combina- 
30 tion of thick film electrochemical deposition and integrated 
circuit processing techniques. In the embodiment, the legs 
are produced that are no thicker than 50 to 100 microns. 
Even for small temperature differences such as 10-20 
degrees K., specific power outputs in the 1-10 watts/cm3 
The present system may operate using templates of 
porous alumina. Such templates are commercially available, 
or can be formed using semiconductor techniques. Tem- 
plates which have holes on the order of 100 nm by 60 um can 
One aspect of the present system recognizes that the 
efficiency of the thermoelectric device is increased by 
decreasing the leg diameter to a size at which quantum 
confinement effects will occur. A preferred system, there- 
45 fore, increases the performance efficiency by enhancing the 
charge carrier mobility using Quantum confinement effects. 
The thermoelectric devices may be for example of molecular 
scale in diameter, for example on the order of magnitude of 
10 nm diameter (more specifically, anything less than around 
50 100 nm). In addition, these elements may have a high aspect 
ratio. For example, it may be desirable for the height of the 
nanowire to be three orders of magnitude greater than the 
diameter of the nanowire. One example is a nanowire of the 
order of 10 nm in diameter by 20 to 50 um tall. This may 
55 maintain a large AV at low heat fluxes, thus further increas- 
ing the generator capability. 
It may be difficult to contact individual wires of this size. 
Accordingly, in this embodiment, the wires are contacted in 
bundles 215 as shown in FIG. 2. The bundles can be, for 
60 example, a bundle of multiple wires collectively measuring 
approximately 10 microns. Each bundle may have a fill 
factor of approximately 50 percent, representing the ratio 
between opening areas that have been filled with thermo- 
electric material, and closed areas representing areas of the 
The formation of the device can be made by filling the 
35 range become achievable. 
40 be commercially purchased. 
65 template. 
template. The holes forming the pores extend through the pores with thermoelectric material, for example using a 
US 7,098,393 B2 
3 
growth technique. Each pore may be over filled, which 
hence overgrows the material onto the top of the template. 
This is then followed by polishing the template back to a 
level of fill. 
After this polishing, the wire bundles are contacted by 
electrochemically depositing a metallic material such as 
nickel, on top of the wires. This electrochemically grown 
metal cap on each wire allows the metal to spread and 
contact adjacent metal caps. 
As noted above, the templates may be porous templates 
formed of alumina, having pores of 100 nm or in another 
embodiment, pores of 40 nm. 
FIG. 3 shows an embodiment, with Bi,Te, nanowires 300 
of 100 nm by 40 microns long, although the figure is not 
shown to scale. The thermoelectric material overgrows the 
top portion 305 of the template, forming caps which contact 
one another, such as at the contact area 310 between the caps 
311 and 312. These wires may have a measured Seebeck 
coefficient of -125 uVIK. The caps contacting one another 
may form the connections of the bundles. A separation area 
320 separates between between adjacent bundles. 
The inventors found that even though several wires are 
contacted in parallel to form a group, the Quantum effects 
are not effected by this contact and each wire remains 
isolated from the other wires except at the area of the 
contact. The alumina template is left in place. 
FIG. 4 shows how multiple wires can be grown in groups 
by masking the template and patterning the bottom contact. 
The electrochemical growth begins at the bottom, and then 
the groups of wires are contacted with an electrochemically 
grown metal cap. FIG. 4 shows n type and p type nanowires 
being grown within the template. Wires within a group are 
contacted in parallel. The groups are contacted in series to 
make a thermoelectric device in the same way that thermo- 
electric Microdevices are fabricated. The bottom metallic 
layer is used for the electrochemical growth and for the 
series connection of the bundles. 
The above has described forming the thermoelectric mate- 
rial within templates. However, other techniques may 
include photoresist masking and microfabrication. 
Another embodiment is shown in FIG. 5. In this embodi- 
ment, semiconductor techniques are used to form a chip 499 
which includes both a thermoelectric device 500, and other 
operative structures 510 on the chip. For example, the FIG. 
5 device shows a whole system on a chip, including the 
functions of sense, compute, actuate, control, communicate 
and power on the single chip. The system shows power 
output lines 501 from the thermoelectric device which are 
used to drive a sensor part 520, a microcomputer or micro- 
processor part 522, and a communication part 524. All of 
this is formed on the same semiconductor substrate. 
In addition, this system may be used for any thermoelec- 
tric application, including but not limited to a micro cooler, 
or a microchip or generator based on thermoelectric con- 
version. The device can be used in sensors, detectors, 
microprobes and micro Rovers. This may also be used in 
consumer electronics, automotive applications, wearable 
and flexible power generating device structures as well as 
biological and medicinal applications. 
Although only a few embodiments have been disclosed in 
detail above, other modifications are possible. For example, 
the above has described nanoscale wires which are effec- 
tively one-dimensional devices. Nanoscale layers, effec- 
tively two-dimensional devices, are also contemplated. Also, 
and zero dimensional devices, effectively Quantum dots, are 
contemplated. 
4 
What is claimed is: 
1. A thermoelectric device, comprising: 
a porous semiconductor having pores therein; 
a plurality of discrete thermoelectric nanowires formed in 
said pores of said porous semiconductor, each of the 
nanowires formed of a BiiTe alloy, and each having an 
outer extent of a size at which thermoelectrically sig- 
nificant quantum confinement effects occur, said plu- 
rality of thermoelectric nanowires connected to one 
another to form an operative thermoelectric device. 
2. A thermoelectric device as in claim 1, wherein said 
BiiTe alloy is Bi,Te,. 
3. A thermoelectric device as in claim 1, wherein said 
thermoelectric nanowires are three orders of magnitude 
l5 taller than their outer extent. 
4. A thermoelectric device as in claim 1, wherein said 
operative thermoelectric device has a specific power output 
greater than 1 watt per cc for a 10 to 20 degrees Kelvin 
temperature difference. 
5. A thermoelectric device as in claim 1, further compris- 
ing a contact to said thermoelectric nanowires. 
6. A thermoelectric device as in claim 5, wherein said 
contact is a contact to a bundle of multiple wires. 
7. A thermoelectric device as in claim 6, wherein said 
bundle of multiple wires is a bundle of approximately 10 
microns in diameter. 
8. A thermoelectric device as in claim 1, wherein said 
porous semiconductor has a till factor for the BiiTe alloy of 
9. A thermoelectric device as in claim 1, further compris- 
ing a connection between adjacent thermoelectric nanow- 
ires. 
10. A thermoelectric device as in claim 9, wherein said 
35 connection includes an overgrown material cap on a top 
portion of said porous semiconductor which contacts 
between adjacent nanowires. 
11. A thermoelectric device as in claim 9, wherein said 
connection includes a grown cap on one end, and a patterned 
12. A thermoelectric device as in claim 1, further com- 
prising additional circuitry within said semiconductor, pow- 
ered by said thermoelectric device. 
5 
10 
2o 
25 
3o approximately 50 percent. 
40 portion on another end. 
13. A thermoelectric device, comprising: 
a porous substrate, having pores therein; 
a plurality of thermoelectric nanowires, formed in said 
pores of said porous substrate, each having an outer 
extent of less than approximately 100 nm, connected to 
one another to form an operative thermoelectric device. 
14. A device as in claim 13, wherein said thermoelectric 
material includes Bi,Te,. 
15. A device as in claim 13, wherein said thermoelectric 
nanowires are three orders of magnitude taller than their 
16. A thermoelectric device as in claim 13, wherein said 
device has a specific power output greater than 1 watt per cc 
for a 10 to 20 degrees Kelvin temperature difference. 
17. A thermoelectric device as in claim 13, wherein said 
60 nanowires have a diameter of a size at which quantum 
confinement effects will occur. 
18. A thermoelectric device as in claim 13, wherein said 
porous substrate has an open space to closed space ratio of 
approximately 50 percent. 
19. A thermoelectric device as in claim 13, further com- 
prising additional circuitry formed in said porous semicon- 
ductor and powered by said thermoelectric device. 
45 
50 
55 outer extent. 
65 
US 7,098,393 B2 
5 6 
20. A thermoelectric apparatus, comprising: 
a porous semiconductor having pores therein; 
a plurality of thermoelectric devices that each include a 
collection of N tvne thermoelectric nanowires in nar- 
an overgrown material cap series connection between two 
devices in the plurality, the overgrown material cap 
series connection allowing said devices to operate in 
thermoelectric material in the pores of the porous 
semiconductor and having an outer extent which is less 
than one micron in maximum outer diameter; and * * * * *  


Thermoelectric device with multiple, nanometer scale, elements

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