U.S. patent number 8,853,814 [Application Number 14/110,141] was granted by the patent office on 2014-10-07 for miniature thermoelectric energy harvester and fabrication method thereof.
This patent grant is currently assigned to N/A, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences. The grantee listed for this patent is Yuelin Wang, Bin Xiong, Dehui Xu. Invention is credited to Yuelin Wang, Bin Xiong, Dehui Xu.
United States Patent |
8,853,814 |
Xu , et al. |
October 7, 2014 |
Miniature thermoelectric energy harvester and fabrication method
thereof
Abstract
A miniature thermoelectric energy harvester and a fabrication
method thereof. Annular grooves are fabricated on a low-resistivity
silicon substrate to define silicon thermoelectric columns, an
insulating layer is fabricated on the annular grooves, a
thermoelectric material is filled in the annular grooves to form
annular thermoelectric columns, and then metal wirings, passivation
layers and supporting substrates are fabricated, thereby completing
the fabrication process. The silicon thermoelectric column using a
silicon base material simplifies the fabrication process. The
fabrication of the thermocouple structure is one thin-film
deposition process, which simplifies the process. The use of
silicon as a component of the thermocouple has a high Seebeck
coefficient. The use of vertical thermocouples improves the
stability. Since the thermocouple structure is bonded to the upper
supporting substrate and lower supporting substrate by wafer-level
bonding, the fabrication efficiency is improved.
Inventors: |
Xu; Dehui (Shanghai,
CN), Xiong; Bin (Shanghai, CN), Wang;
Yuelin (Shanghai, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
Xu; Dehui
Xiong; Bin
Wang; Yuelin |
Shanghai
Shanghai
Shanghai |
N/A
N/A
N/A |
CN
CN
CN |
|
|
Assignee: |
Shanghai Institute of Microsystem
and Information Technology, Chinese Academy of Sciences
(Shanghai, CN)
N/A (N/A)
|
Family
ID: |
49081564 |
Appl.
No.: |
14/110,141 |
Filed: |
April 6, 2012 |
PCT
Filed: |
April 06, 2012 |
PCT No.: |
PCT/CN2012/073565 |
371(c)(1),(2),(4) Date: |
October 04, 2013 |
PCT
Pub. No.: |
WO2013/127114 |
PCT
Pub. Date: |
September 06, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140021576 A1 |
Jan 23, 2014 |
|
Foreign Application Priority Data
|
|
|
|
|
Feb 28, 2012 [CN] |
|
|
2012 1 0049164 |
|
Current U.S.
Class: |
257/467;
438/54 |
Current CPC
Class: |
H01L
35/32 (20130101); H01L 27/16 (20130101); H01L
35/34 (20130101); H01L 35/22 (20130101); H01L
35/10 (20130101) |
Current International
Class: |
H01L
35/10 (20060101) |
Field of
Search: |
;257/467 ;438/54 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Armand; Marc
Attorney, Agent or Firm: Gu; Tianhua Global IP Services
Claims
What is claimed is:
1. A method for fabricating a miniature thermoelectric energy
harvester, at least comprising: 1) providing a silicon substrate,
and etching an upper surface of the silicon substrate to form at
least two annular grooves, two neighboring of which are arranged at
an interval, so that all the annular grooves and silicon columns
surrounded by the annular grooves form a thermopile region; 2)
forming an insulating layer on a surface of the annular groove, and
then filling a thermoelectric material in the annular groove to
form an annular thermoelectric column, so that the annular
thermoelectric column and the silicon column surrounded by the
annular thermoelectric column form a thermocouple; 3) fabricating
an upper metal wiring to connect the silicon column and the annular
thermoelectric column in a same thermocouple, and then fabricating
an upper passivation layer on the upper surface of the silicon
substrate; 4) providing an upper supporting substrate, and bonding
the upper supporting substrate to the upper surface of the silicon
substrate; 5) thinning the silicon substrate until a lower surface
of the thermocouple is exposed; 6) fabricating a lower metal wiring
to connect the annular thermoelectric column and the silicon column
in two neighboring annular thermocouples, and then fabricating a
lower passivation layer on a lower surface of the silicon
substrate; 7) etching the silicon substrate between two neighboring
thermocouples to form an isolation structure; and 8) providing a
lower supporting substrate, and bonding the lower supporting
substrate to the lower surface of the silicon substrate, thereby
completing fabrication of a miniature thermoelectric energy
harvester.
2. The method for fabricating a miniature thermoelectric energy
harvester as in claim 1, wherein the annular thermoelectric column
is a column structure having a rectangular ring or circular ring
cross section, and the silicon column is a column structure having
a rectangular or circular cross section.
3. The method for fabricating a miniature thermoelectric energy
harvester as in claim 1, wherein the step 7) further comprises a
step of filling an electrical and thermal insulating material in
the isolation structure.
4. The method for fabricating a miniature thermoelectric energy
harvester as in claim 1, wherein the step 7) further comprises a
step of selectively etching a periphery around the thermopile
region to form an annular isolation groove.
5. The method for fabricating a miniature thermoelectric energy
harvester as in claim 4, wherein the bonding process in the step 4)
is wafer-level hermetic bonding, and the bonding process in the
step 8) is wafer-level vacuum bonding.
6. The method for fabricating a miniature thermoelectric energy
harvester as in claim 1, wherein the lower supporting substrate
comprises a CMOS circuit structure, the lower passivation layer is
etched to form a contact hole, and the CMOS circuit structure is
connected to the lower metal wiring through the contact hole.
7. The method for fabricating a miniature thermoelectric energy
harvester as in claim 1, wherein the annular thermoelectric column
is made of a BiTe-based material, a polysilicon material, or metal
Cu, Ni or Au, and the silicon column is made of low-resistivity
silicon.
8. A miniature thermoelectric energy harvester, at least
comprising: a thermopile, comprising: at least two thermocouples,
wherein each of the thermocouples is formed by a silicon column and
an annular thermoelectric column surrounding the silicon column,
and an isolation structure is formed between neighboring two
thermocouples; an insulating layer, combined between the annular
thermoelectric column and the silicon column; an upper metal
wiring, connected to upper surfaces of the annular thermoelectric
column and the silicon column in a same thermocouple; and a lower
metal wiring, connected to lower surfaces of the annular
thermoelectric column and the silicon column in two neighboring
thermocouples; passivation layers, comprising: an upper passivation
layer, combined to an upper surface of the thermopile; and a lower
passivation layer, combined to a lower surface of the thermopile;
and supporting substrates, comprising: an upper supporting
substrate, combined to a surface of the upper passivation layer;
and a lower supporting substrate, combined to a surface of the
lower passivation layer.
9. The miniature thermoelectric energy harvester as in claim 8,
wherein the annular thermoelectric column is a column structure
having a rectangular ring or circular ring cross section, and the
silicon column is a column structure having a rectangular or
circular cross section.
10. The miniature thermoelectric energy harvester as in claim 8,
wherein the miniature thermoelectric energy harvester further
comprises an electrical and thermal insulating material filled in
the isolation structure.
11. The miniature thermoelectric energy harvester as in claim 8,
wherein the lower supporting substrate comprises a CMOS circuit
structure, the lower passivation layer has a contact hole, and the
CMOS circuit structure is connected to the thermopile through the
contact hole.
12. The miniature thermoelectric energy harvester as in claim 8,
wherein the annular thermoelectric column is made of a BiTe-based
material, a polysilicon material, or metal Cu, Ni or Au, and the
silicon column is made of low-resistivity silicon.
Description
BACKGROUND OF THE PRESENT INVENTION
1. Field of Invention
The present invention relates to the semiconductor field, and
specifically to a miniature thermoelectric energy harvester and a
fabrication method thereof.
2. Description of Related Arts
With the development of wireless network sensor technology, its
applications in the industrial, commercial, medical, consumption
and military fields are gradually expanded. Power source is always
critical to prolonging the service life and reducing the cost of
wireless network sensors. In environmental extremes or other
occasions unreachable to human beings, or when a network node moves
or changes, it is difficult or even impossible to replace a
battery, making it crucial to effectively provide energy to a
wireless network sensor. An effective solution is to harvest
ambient energy through energy harvesting, store the energy and
provide the energy to the wireless network sensor. Currently, the
most commonly used energy harvesting method is to use the Seebeck
effect to convert a temperature difference in an environment to
electrical energy for energy harvesting. On the other hand, as
system miniaturization leads to decreasing system size and power
consumption, energy required for system operation also decreases;
therefore, a thermoelectric chip may be used to harvest ambient
energy so as to supply power to the system.
Current miniature thermoelectric energy harvesters are mainly
classified into two types, that is, planar type and vertical type.
FIG. 1A is a schematic structural view of a planar-type miniature
thermoelectric energy harvester, wherein the direction of heat flow
is parallel to the substrate, and thermocouples are arranged
parallel to the substrate. Since the planar-type thermoelectric
energy harvester is in contact with the ambient environment through
cross sections of its components, there is a small contact area
between the thermoelectric energy harvesting chip and the
environment, leading to undesirable thermal contact between the
thermoelectric energy harvesting chip and the environment, and
affecting the operating efficiency of the thermoelectric energy
harvesting chip. However, the thermocouples on the substrate are
generally fabricated by a planar semiconductor process, and the
thermocouple length is 1-1000 .mu.m dependent upon the
photolithographic process, and the thermocouple length can be
controlled through pattern design. In addition, to increase the
thermal resistance of the thermoelectric energy harvesting chip,
the thermocouple structure generally needs to be thermally
insulated, that is, the substrate below the thermocouple is
hollowed out. As a result, the thermocouple structure is eventually
suspended on the substrate, with a cross-sectional structure as
shown in FIG. 1B. Since the thermocouple is a suspended structure,
the thermocouple microstructure is easily broken, degrading the
reliability of the chip.
FIG. 1C is a schematic structural view of a vertical-type miniature
thermoelectric energy harvester, where the direction of heat flow
is perpendicular to the substrate, and thermocouples are arranged
perpendicular to the substrate. Since the vertical-type
thermoelectric energy harvester is in contact with the ambient
environment through the whole substrate, there is a large contact
area between the thermoelectric energy harvesting chip and the
environment, so that good thermal contact is achieved between the
thermoelectric energy harvesting chip and the environment, thereby
improving the operating efficiency of the thermoelectric energy
harvesting chip. However, since the thermocouples are arranged
perpendicular to the substrate, the planar semiconductor process
cannot be adopted, and instead, the thermocouples are generally
fabricated by an electroplating or thin-film sputtering deposition
process, resulting that the thermocouple length is limited by the
process. The thickness of a film fabricated by the thin-film
sputtering deposition process is generally smaller than 100 .mu.m,
while the thickness of a film fabricated by the electroplating
process is generally smaller than 1000 .mu.m. Current vertical-type
thermoelectric energy harvesting chips generally adopt a BiTe-based
material or a metal material such as Cu or Ni as the thermoelectric
material. Since the metal material such as Cu or Ni has a small
Seebeck coefficient, thermoelectric energy harvesting chips
fabricated by using the metal material such as Cu or Ni as the
thermoelectric material generally have low efficiency. Since the
BiTe-based material has a high Seebeck coefficient, thermoelectric
energy harvesting chips fabricated by using the BiTe-based material
generally have high efficiency. However, the BiTe-based material
requires a high cost, and contains toxic substances, which limits
the use of BiTe thermoelectric energy harvesting chips. In
addition, since the composition of a thermocouple requires two
thermoelectric materials, the vertical-type thermoelectric energy
harvester generally needs to be subjected to two electroplating or
thin-film sputtering deposition processes in order to fabricate a
thermocouple material, which further increases the cost of the
thermoelectric energy harvesting chip. Moreover, the fabrication
efficiency of the vertical-type thermoelectric energy harvester is
low, because the thermoelectric energy harvester is thermally and
mechanically connected to upper and lower substrates through
chip-level bonding.
SUMMARY OF THE PRESENT INVENTION
In view of the disadvantages in the prior art, a purpose of the
present invention is to provide a miniature thermoelectric energy
harvester and a fabrication method thereof, so as to solve the
problems of high fabrication cost, low fabrication efficiency and
low energy harvesting efficiency in the prior art.
In order to accomplish the above and other purposes, the present
invention provides a method for fabricating a miniature
thermoelectric energy harvester, at least comprising: 1) providing
a silicon substrate, and etching an upper surface of the silicon
substrate to form at least two annular grooves, two neighboring of
which are arranged at an interval, so that all the annular grooves
and silicon columns surrounded by the annular grooves form a
thermopile region; 2) forming an insulating layer on a surface of
the annular groove, and then filling a thermoelectric material in
the annular groove to form an annular thermoelectric column, so
that the annular thermoelectric column and the silicon column
surrounded by the annular thermoelectric column form a
thermocouple; 3) fabricating an upper metal wiring to connect the
silicon column and the annular thermoelectric column in a same
thermocouple, and then fabricating an upper passivation layer on
the upper surface of the silicon substrate; 4) providing an upper
supporting substrate, and bonding the upper supporting substrate to
the upper surface of the silicon substrate; 5) thinning the silicon
substrate until a lower surface of the thermocouple is exposed; 6)
fabricating a lower metal wiring to connect the annular
thermoelectric column and the silicon column in two neighboring
annular thermocouples, and then fabricating a lower passivation
layer on a lower surface of the silicon substrate; 7) etching the
silicon substrate between two neighboring thermocouples to form an
isolation structure; and 8) providing a lower supporting substrate,
and bonding the lower supporting substrate to the lower surface of
the silicon substrate, thereby completing fabrication of a
miniature thermoelectric energy harvester.
In the method for fabricating a miniature thermoelectric energy
harvester consistent with the present invention, the annular
thermoelectric column is a column structure having a rectangular
ring or circular ring cross section, and the silicon column is a
column structure having a rectangular or circular cross
section.
As a preferred solution of the method for fabricating a miniature
thermoelectric energy harvester consistent with the present
invention, the step 7) further comprises a step of filling an
electrical and thermal insulating material in the isolation
structure.
As a preferred solution of the method for fabricating a miniature
thermoelectric energy harvester consistent with the present
invention, the step 7) further comprises a step of selectively
etching a periphery around the thermopile region to form an annular
isolation groove.
As a preferred solution of the method for fabricating a miniature
thermoelectric energy harvester consistent with the present
invention, the bonding process in the step 4) is wafer-level
hermetic bonding, and the bonding process in the step 8) is
wafer-level vacuum bonding.
As a preferred solution of the method for fabricating a miniature
thermoelectric energy harvester consistent with the present
invention, the lower supporting substrate comprises a CMOS circuit
structure, the lower passivation layer is etched to form a contact
hole, and the CMOS circuit structure is connected to the lower
metal wiring through the contact hole.
In the method for fabricating a miniature thermoelectric energy
harvester consistent with the present invention, the annular
thermoelectric column is made of a BiTe-based material, a
polysilicon material, or metal Cu, Ni or Au, and the silicon column
is made of low-resistivity silicon.
The present invention further provides a miniature thermoelectric
energy harvester, at least comprising:
a thermopile, comprising at least two thermocouples, wherein each
of the thermocouples is formed by a silicon column and an annular
thermoelectric column surrounding the silicon column, and an
isolation structure is formed between neighboring two
thermocouples; an insulating layer, combined between the annular
thermoelectric column and the silicon column; an upper metal
wiring, connected to upper surfaces of the annular thermoelectric
column and the silicon column in a same thermocouple; and a lower
metal wiring, connected to lower surfaces of the annular
thermoelectric column and the silicon column in two neighboring
thermocouples;
passivation layers, comprising: an upper passivation layer,
combined to an upper surface of the thermopile; and a lower
passivation layer, combined to a lower surface of the thermopile;
and
supporting substrates, comprising: an upper supporting substrate,
combined to a surface of the upper passivation layer; and a lower
supporting substrate, combined to a surface of the lower
passivation layer.
In the miniature thermoelectric energy harvester consistent with
the present invention, the annular thermoelectric column is a
column structure having a rectangular ring or circular ring cross
section, and the silicon column is a column structure having a
rectangular or circular cross section.
As a preferred solution of the miniature thermoelectric energy
harvester consistent with the present invention, the miniature
thermoelectric energy harvester further comprises an electrical and
thermal insulating material filled in the isolation structure.
As a preferred solution of the miniature thermoelectric energy
harvester consistent with the present invention, the lower
supporting substrate comprises a CMOS circuit structure, the lower
passivation layer has a contact hole, and the CMOS circuit
structure is connected to the thermopile through the contact
hole.
In the miniature thermoelectric energy harvester consistent with
the present invention, the annular thermoelectric column is made of
a BiTe-based material, a polysilicon material, or metal Cu, Ni or
Au, and the silicon column is made of low-resistivity silicon.
As described above, the miniature thermoelectric energy harvester
and fabrication method thereof consistent with the present
invention have the following beneficial effects: Annular grooves
are fabricated on a low-resistivity silicon substrate to define
silicon thermoelectric columns, an insulating layer is fabricated
on the annular grooves, a thermoelectric material is filled in the
annular grooves to form annular thermoelectric columns, and then
metal wirings, passivation layers and supporting substrates are
fabricated, thereby completing the fabrication process. In the
present invention, the silicon thermoelectric column is fabricated
by directly using a silicon base material, which simplifies the
fabrication process. Compared with a miniature thermoelectric
energy harvester in the prior art, the present invention has the
following advantages:
1) Fabrication of the thermocouple structure is completed by only
one thin-film deposition process, which simplifies the fabrication
process.
2) The use of silicon as a component of the thermocouple ensures
that the thermocouple has a high Seebeck coefficient.
3) The use of vertical thermocouples having a column structure
avoids suspended microstructures, thereby improving the mechanical
stability of the thermoelectric energy harvester.
4) Since the thermocouple structure is bonded to the upper
supporting substrate and the lower supporting substrate by
wafer-level bonding, the fabrication efficiency is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A to FIG. 1C are schematic structural views of a
thermoelectric energy harvester in the prior art.
FIG. 1A and FIG. 2B are respectively schematic structural top and
cross-sectional views of step 1) of a method for fabricating a
miniature thermoelectric energy harvester consistent with the
present invention.
FIG. 3A to FIG. 3D are respectively schematic structural top and
cross-sectional views of step 2) of the method for fabricating a
miniature thermoelectric energy harvester consistent with the
present invention.
FIG. 4A and FIG. 4B are respectively schematic structural top and
cross-sectional views of step 3) of the method for fabricating a
miniature thermoelectric energy harvester consistent with the
present invention.
FIG. 5 is a schematic structural view of step 4) of the method for
fabricating a miniature thermoelectric energy harvester consistent
with the present invention.
FIG. 6 is a schematic structural view of step 5) of the method for
fabricating a miniature thermoelectric energy harvester consistent
with the present invention.
FIG. 7A and FIG. 7B are respectively schematic structural top and
cross-sectional views of step 6) of the method for fabricating a
miniature thermoelectric energy harvester consistent with the
present invention.
FIG. 8 is a schematic structural view of step 7) of the method for
fabricating a miniature thermoelectric energy harvester consistent
with the present invention.
FIG. 9 is a schematic structural view of step 8) of the method for
fabricating a miniature thermoelectric energy harvester consistent
with the present invention.
FIG. 10 is a schematic structural view of a miniature
thermoelectric energy harvester consistent with the present
invention when the lower supporting substrate has a CMOS circuit
structure.
FIG. 11 is a schematic structural view of a miniature
thermoelectric energy harvester consistent with the present
invention when an isolation structure is filled with an electrical
and thermal insulating material.
FIG. 12 is a schematic structural view of a miniature
thermoelectric energy harvester consistent with the present
invention, which has an annular isolation groove and adopts vacuum
bonding.
LIST OF REFERENCE NUMERALS
101 Silicon substrate 102 Silicon column 103 Annular groove 104
Insulating layer 105 Annular thermoelectric column 106 Upper metal
wiring 107 Lower metal wiring 108 Isolation structure 109
Electrical and thermal insulating material 110 Annular isolation
groove 111 Upper supporting substrate 112 Lower supporting
substrate 113 CMOS circuit structure 114 Contact hole 121 Upper
passivation layer 122 Lower passivation layer
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention are described in the
following through specific examples, and one of ordinary skill in
the art can easily understand other advantages and effects of the
present invention according to the content disclosed in the
specification. The present invention may also be implemented or
applied through other different specific examples, and various
modifications and variations may be made to the details in the
specification on the basis of different opinions and applications
without departing from the principle of the present invention.
Reference is made to FIG. 1A to FIG. 12. It should be noted that,
the drawings provided in the embodiment merely exemplarily describe
a basic concept of the present invention, and the drawings merely
show components related to the present invention, but are not drawn
according to the numbers, shapes and sizes of components in actual
implementation. The shapes, the numbers and the sizes of the
components can be randomly changed in the actual implementation,
and the layout of components may be more complicated.
Embodiment 1
Referring to FIG. 1A to FIG. 9, the present invention provides a
method for fabricating a miniature thermoelectric energy harvester,
which at least includes the following steps.
First, as shown in FIG. 1A to FIG. 2B, step 1) is performed,
wherein a silicon substrate 101 is provided, and an upper surface
of the silicon substrate 101 is etched to form at least two annular
grooves 103, two neighboring of which are arranged at an interval,
so that all the annular grooves 103 and silicon columns 102
surrounded by the annular grooves 103 form a thermopile region. In
this embodiment, the silicon substrate 101 is a low-resistivity
silicon substrate 101, which has a high Seebeck coefficient and low
resistivity, and therefore can ensure high thermoelectric
efficiency when being fabricated into a thermoelectric column. A
photolithographic pattern is fabricated on a surface of the
low-resistivity silicon substrate 101, and the surface of the
low-resistivity silicon substrate 101 is etched to form, on the
low-resistivity silicon substrate 101, at least two annular grooves
103, two neighboring of which are arranged at an interval, so that
all the annular grooves 103 and silicon columns 102 surrounded by
the annular grooves 103 form a thermopile region. Considering the
process consistency and smoothness of components, the cross section
of the annular groove 103 is a rectangular ring structure.
Definitely, in other embodiments, the cross section of the annular
groove 103 may also be ring structures of other shapes such as a
circular ring structure. The silicon column 102 is a region
surrounded by the annular groove 103, and therefore, the cross
section of the silicon column 102 is rectangular. Definitely, in
other embodiments, the silicon column 102 may also be column
structures of other shapes such as a circular column structure.
Next, as shown in FIG. 3A to FIG. 3D, step 2) is performed, wherein
an insulating layer 104 is formed on a surface of the annular
groove 103, and then a thermoelectric material is filled in the
annular groove 103 to form an annular thermoelectric column 105, so
that the annular thermoelectric column 105 and the silicon column
102 surrounded by the annular thermoelectric column 105 form a
thermocouple. In this embodiment, a SiO.sub.2 film is deposited in
the annular groove 103 by chemical vapor deposition or physical
vapor deposition to insulate the surface of the annular groove 103.
Definitely, a material such as Si.sub.3N.sub.4 may also be used to
fabricate a thin-film insulating layer 104. Afterward, a
thermoelectric material is deposited in the annular groove 103 by
using a thin-film deposition technique such as chemical vapor
deposition or physical vapor deposition. In this embodiment, the
thermoelectric material is a BiTe-based material in order to ensure
high thermoelectric conversion performance. Definitely, in other
embodiments, the thermoelectric material may be a polysilicon
material, or metal Cu, Ni or Au, or the like. The annular
thermoelectric column 105 and the silicon column 102 surrounded by
the annular thermoelectric column 105 form a thermocouple.
Then, as shown in FIG. 4A and FIG. 4B, step 3) is performed,
wherein an upper metal wiring 106 is fabricated to connect the
silicon column 102 and the annular thermoelectric column 105 in a
same thermocouple, and then an upper passivation layer 121 is
fabricated on the upper surface of the silicon substrate 101. In
this embodiment, an upper metal wiring 106 is fabricated on the
upper surface of each thermocouple by using photolithography and
deposition techniques, so as to connect the annular thermoelectric
column 105 and the silicon column 102 in each thermocouple.
Afterward, an upper passivation layer 121 is fabricated on the
upper surface of the silicon substrate 101 by chemical vapor
deposition, wherein the upper passivation layer 121 is made of
SiO.sub.2, Si.sub.3N.sub.4 or the like.
Then, as shown in FIG. 5, step 4) is performed, wherein an upper
supporting substrate 111 is provided, and the upper supporting
substrate 111 is bonded to the upper surface of the silicon
substrate 101. In this embodiment, the upper supporting substrate
111 has good thermal conduction properties.
Then, as shown in FIG. 6, step 5) is performed, wherein the silicon
substrate 101 is thinned until a lower surface of the thermocouple
is exposed. In this embodiment, a lower surface of the silicon
substrate 101 is etched by chemical corrosion with HF or a mixture
of HF and HNO.sub.3 as an etching solution, wherein the structure
of the insulating layer 104 at the bottom of the annular groove 103
is etched until the lower surface of the thermocouple is exposed,
and the surface after etching may be polished by mechanical
chemical polishing to prepare for subsequent processes. Definitely,
the silicon substrate 101 may also be thinned by directly using
mechanical chemical polishing, optionally in combination with a
smart-cut technique.
Then, as shown in FIG. 7A and FIG. 7B, step 6) is performed,
wherein a lower metal wiring 107 is fabricated to connect the
annular thermoelectric column 105 and the silicon column 102 in two
neighboring annular thermocouples, and then a lower passivation
layer 122 is fabricated on a lower surface of the silicon substrate
101. In this embodiment, the lower metal wiring 107 is fabricated
by using photolithography and deposition techniques, so as to
connect the annular thermoelectric column 105 and the silicon
column 102 in two neighboring thermocouples. For example, there are
two thermocouples, respectively defined as a first thermocouple and
a second thermocouple. In this case, during fabrication of the
lower metal wiring 107, first, one side, opposite to the first
thermocouple, of the annular thermoelectric column 105 in the
second thermocouple is insulated, and the silicon substrate between
the first thermocouple and the second thermocouple is also
insulated, and then the lower metal wiring 107 is fabricated by
using photolithography and deposition techniques, so as to connect
the annular thermoelectric column 105 of the first thermocouple and
the silicon column 102 of the second thermocouple. Afterward, a
lower passivation layer 122 is fabricated on the lower surface of
the silicon substrate 101 by a method such as chemical vapor
deposition, wherein the lower passivation layer 122 is made of
SiO.sub.2, Si.sub.3N.sub.4 or the like.
Then, as shown in FIG. 8, step 7) is performed, wherein the silicon
substrate 101 between two neighboring thermocouples is etched to
form an isolation structure 108. In this embodiment, a region
between the two thermocouples on the surface of the silicon
substrate 101 is etched by chemical corrosion with the
photolithographic pattern as a mask, wherein the etching is
performed until reaching the upper passivation layer 121.
Finally, as shown in FIG. 9, step 8) is performed, where a lower
supporting substrate 112 is provided, and the lower supporting
substrate 112 is bonded to the lower surface of the silicon
substrate 101, thereby completing fabrication of the miniature
thermoelectric energy harvester. The lower supporting substrate 112
also has good thermal conduction properties.
Embodiment 2
Referring to FIG. 1A to FIG. 10, basic steps of the method for
fabricating a miniature thermoelectric energy harvester in this
embodiment are as described in Embodiment 1. To achieve monolithic
integration of the miniature thermoelectric energy harvester
consistent with the present invention and a circuit so as to
directly supply power to the circuit on-chip, the method for
fabricating a miniature thermoelectric energy harvester consistent
with the present invention further includes a step of fabricating a
CMOS circuit structure 113 on the lower supporting substrate 112,
where the lower passivation layer 122 is etched to form a contact
hole 114, and then a metal wire is fabricated through the contact
hole 114 to connect the CMOS circuit structure 113 and the lower
metal wiring 107. Afterward, the lower passivation layer 122 is
bonded to the lower supporting substrate 112. In this embodiment,
to completely adopt the CMOS process so as to reduce the
fabrication cost, the filled thermoelectric material may be
replaced with a polysilicon material of a different doping type
from the silicon substrate 101.
Embodiment 3
Referring to FIG. 1A to FIG. 9 and FIG. 11, basic steps of the
method for fabricating a miniature thermoelectric energy harvester
in this embodiment are as described in Embodiment 1. To further
improve the mechanical stability and thermoelectric efficiency of a
thermopile, the step 7) further includes a step of filling an
electrical and thermal insulating material 109 in the isolation
structure 108. Definitely, a periphery around the thermopile region
may be etched first, following by filling a thermoelectric material
in the etched structure and the isolation structure 108 at the same
time.
Embodiment 4
Referring to FIG. 1A to FIG. 9 and FIG. 12, basic steps of the
method for fabricating a miniature thermoelectric energy harvester
in this embodiment are as described in Embodiment 1. The step 7)
further includes a step of selectively etching the periphery around
the thermopile region to form an annular isolation groove 110. The
bonding process in the step 4) is wafer-level hermetic bonding, and
the bonding process in the step 8) is wafer-level vacuum
bonding.
Embodiment 5
Referring to FIG. 9, the present invention further provides a
miniature thermoelectric energy harvester, which at least
includes:
a thermopile, including at least two thermocouples, wherein each of
the thermocouples is formed by a silicon column 102 and an annular
thermoelectric column 105 surrounding the silicon column 102, and
an isolation structure 108 is formed between neighboring two
thermocouples. The annular thermoelectric column 105 is a column
structure having a rectangular ring or circular ring cross section,
and the silicon column 102 is a column structure having a
rectangular or circular cross section. Definitely, in other
embodiments, the annular thermoelectric column 105 and the silicon
column 102 may also be column structures of other shapes. The
annular thermoelectric column 105 is made of a BiTe-based material
so as to ensure the thermoelectric conversion efficiency of the
thermocouple. Definitely, in other embodiments, the annular
thermoelectric column 105 may also be made of a polysilicon
material, or metal Cu, Ni or Au, or other thermoelectric materials.
The silicon column 102 is made of a low-resistivity silicon
material, which has a high Seebeck coefficient and low resistivity,
and therefore can ensure high thermoelectric efficiency when being
fabricated into a thermoelectric column. An isolation structure 108
is formed between neighboring two thermocouples so as to ensure the
thermoelectric energy harvesting efficiency.
The thermopile further includes an insulating layer 104, combined
between the annular thermoelectric column 105 and the silicon
column 102 to insulate the annular thermoelectric column 105 and
the silicon column 102 in a same thermocouple. The insulating layer
104 may be made of SiO.sub.2, Si.sub.3N.sub.4 or the like.
The thermopile further includes an upper metal wiring 106 connected
to upper surfaces of the annular thermoelectric column 105 and the
silicon column 102 in a same thermocouple and a lower metal wiring
107 connected to lower surfaces of the annular thermoelectric
column 105 and the silicon column 102 in two neighboring
thermocouples.
The miniature thermoelectric energy harvester further includes
passivation layers, including an upper passivation layer 121
combined to an upper surface of the thermopile and a lower
passivation layer 122 combined to a lower surface of the
thermopile. The upper passivation layer 121 and the lower
passivation layer 122 have thicknesses greater than those of the
upper metal wiring 106 and the lower metal wiring 107, and are made
of SiO.sub.2, Si.sub.3N.sub.4 or the like.
The miniature thermoelectric energy harvester further includes
supporting substrates, including an upper supporting substrate 111
combined to a surface of the upper passivation layer 121 and a
lower supporting substrate 112 combined to a surface of the lower
passivation layer 122. Both the upper supporting substrate 111 and
the lower supporting substrate 112 have good thermal conduction
properties.
Embodiment 6
Referring to FIG. 10, the basic structure of the miniature
thermoelectric energy harvester in this embodiment is as described
in Embodiment 5. To achieve monolithic integration of the miniature
thermoelectric energy harvester consistent with the present
invention and a circuit so as to directly supply power to the
circuit on-chip, the lower supporting substrate 112 of the
miniature thermoelectric energy harvester in this embodiment
includes a CMOS circuit structure 113, the lower passivation layer
122 has a contact hole 114, and the CMOS circuit structure is
connected to the thermopile through the contact hole 114.
Embodiment 7
Referring to FIG. 11, the basic structure of the miniature
thermoelectric energy harvester in this embodiment is as described
in Embodiment 5. To further improve the mechanical stability and
thermoelectric efficiency of the thermopile, the miniature
thermoelectric energy harvester further includes an electrical and
thermal insulating material 109 filled in the isolation structure.
Definitely, the electrical and thermal insulating material 109 may
also be filled after a periphery around the thermopile of the
miniature thermoelectric energy harvester is removed, so that this
structure has better mechanical stability.
Embodiment 8
Referring to FIG. 12, the basic structure of the miniature
thermoelectric energy harvester in this embodiment is as described
in Embodiment 5. The silicon substrate 101 is still maintained at
the periphery around the thermopile of the miniature thermoelectric
energy harvester. Here, the silicon substrate 101 has an annular
isolation groove 110 surrounding the thermopile, the upper
supporting substrate 111 is airtight bonded to the upper
passivation layer 121, and the lower supporting substrate 112 is
vacuum bonded to the lower passivation layer 122.
In summary, in the miniature thermoelectric energy harvester and
fabrication method thereof consistent with the present invention,
annular grooves are fabricated on a low-resistivity silicon
substrate to define silicon thermoelectric columns, an insulating
layer is fabricated on the annular grooves, a thermoelectric
material is filled in the annular grooves to form annular
thermoelectric columns, and then metal wirings, passivation layers
and supporting substrates are fabricated, thereby completing the
fabrication process. In the present invention, the silicon
thermoelectric column is fabricated by directly using a silicon
base material, which simplifies the fabrication process. Compared
with a miniature thermoelectric energy harvester in the prior art,
the present invention has the following advantages:
1) Fabrication of the thermocouple structure is completed by only
one thin-film deposition process, which simplifies the fabrication
process.
2) The use of silicon as a component of the thermocouple ensures
that the thermocouple has a high Seebeck coefficient.
3) The use of vertical thermocouples having a column structure
avoids suspended microstructures, thereby improving the mechanical
stability of the thermoelectric energy harvester.
4) Since the thermocouple structure is bonded to the upper
supporting substrate and the lower supporting substrate by
wafer-level bonding, the fabrication efficiency is improved.
Therefore, the present invention effectively overcomes the
disadvantages in the prior art, and has high industrial
applicability.
The above description of the detailed embodiments is only to
illustrate the preferred implementation according to the present
invention, and it is not to limit the scope of the present
invention. Accordingly, all modifications and variations completed
by one of ordinary skill in the art should fall within the scope of
the present invention defined by the appended claims.
* * * * *