CN117401643A - MEMS micro-hotplate and preparation method thereof - Google Patents
MEMS micro-hotplate and preparation method thereof Download PDFInfo
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims abstract description 22
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
- B81B7/0083—Temperature control
- B81B7/009—Maintaining a constant temperature by heating or cooling
- B81B7/0096—Maintaining a constant temperature by heating or cooling by heating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
- B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
- B81C1/00642—Manufacture or treatment of devices or systems in or on a substrate for improving the physical properties of a device
- B81C1/0069—Thermal properties, e.g. improve thermal insulation
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/02—Details
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/02—Details
- H05B3/03—Electrodes
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2201/00—Specific applications of microelectromechanical systems
- B81B2201/02—Sensors
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- Microelectronics & Electronic Packaging (AREA)
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Abstract
The invention discloses a MEMS micro-hotplate in the technical field of MEMS sensors, which comprises: a silicon substrate; the heat insulation layer is arranged on the upper part of the silicon substrate and is made of porous silicon; the insulating layer is arranged above the heat insulating layer and sequentially comprises a first silicon oxide layer, a silicon nitride layer and a second silicon oxide layer from bottom to top; the metal layer is arranged above the insulating layer and comprises a coplanar heating electrode and a test electrode, the test electrode is surrounded by the heating electrode, and an isolating ring is arranged between the test electrode and the heating electrode. Compared with a suspended structure, the MEMS micro-thermal plate has good structural stability and low manufacturing difficulty; the insulating layer of the device adopts a silicon oxide-silicon nitride-silicon oxide composite structure, so that the mechanical strength and the cold and hot impact resistance of the device are improved; in addition, the heating area and the testing area of the MEMS micro-hotplate are mutually independent, so that short circuit is avoided when the gas sensitive material is coated.
Description
Technical Field
The invention relates to the technical field of Micro-Electro-Mechanical Systems (MEMS) sensors, in particular to an MEMS Micro-hotplate and a preparation method thereof.
Background
The rapid development of science and technology brings many convenience to people and simultaneously brings the problems of resources, environment and the like. Especially, some polluted gas treatment and emission are not standard, so that the air quality is seriously influenced, and the physical health of people is influenced at any time. In some indoor operating environments, the gas in a narrow space is not easy to diverge, and concentration of harmful substances in the air is more required to be focused. The gas sensor can effectively detect and prevent the air environment, is widely applied to the fields of environment monitoring, disaster prevention alarm, chemical industry and the like, and becomes an indispensable part in daily production and life.
The traditional gas sensor has the advantages of large volume, high power consumption and low circuit integration level. The MEMS gas sensor has the advantages of micro-nano structure, low power consumption, high integration level, good repeatability and the like, and becomes a research hot spot in portable and distributed monitoring application. The metal oxide semiconductor type gas sensor based on the silicon wafer has high sensitivity and good response and stability, and is a type of gas sensor widely used at present. The micro-hotplate is a core structure of the MEMS gas sensor and is used for heating a gas-sensitive material (metal oxide semiconductor) coated on the sensor to enable the gas-sensitive material to reach the working temperature and improve the gas-sensitive response of the gas-sensitive material.
The conventional micro-heating plates are of a suspension type structure, the suspension type structure is mainly provided with a plurality of cantilever beams serving as mechanical supports, a heating platform and an insulating layer are connected, the heating platform and the insulating layer are suspended through a front-side bulk silicon process or a sacrificial layer process, the manufacturing difficulty is high, the mechanical strength is low, and the practical requirements are difficult to meet.
Disclosure of Invention
The MEMS micro-hotplate and the preparation method thereof solve the problems of high manufacturing difficulty and low mechanical strength of the conventional micro-hotplate in the prior art, reduce the manufacturing difficulty of the micro-hotplate and improve the mechanical strength of the micro-hotplate.
The embodiment of the application provides a MEMS micro-hotplate, which comprises:
a silicon substrate;
the heat insulation layer is arranged at the upper part of the silicon substrate, and is made of porous silicon;
the insulating layer is arranged above the heat insulating layer and comprises a first silicon oxide layer, a silicon nitride layer and a second silicon oxide layer from bottom to top in sequence;
the metal layer is arranged above the insulating layer and comprises a coplanar heating electrode and a test electrode, the test electrode is surrounded by the heating electrode, and an isolating ring is arranged between the test electrode and the heating electrode.
The beneficial effects of the above embodiment are that: compared with a suspended structure, the MEMS micro-hotplate has good structural stability, does not need a suspended heating area process and is low in manufacturing difficulty, so that the stability and the practicability of the MEMS micro-hotplate are enhanced; the insulating layer of the MEMS micro-hotplate is of a silicon oxide-silicon nitride-silicon oxide composite structure, the power consumption required by maintaining the stable state of the silicon oxide is small, but the fluctuation range of the temperature distribution is large; the silicon nitride has high power consumption required by maintaining a steady state, but the temperature distribution is relatively uniform, the first silicon oxide layer is used as a contact layer to protect the silicon substrate, the silicon nitride layer is used as a filling layer to enable the temperature distribution to be relatively uniform and the thermal stability to be good, the second silicon oxide layer is used as a protective layer, the silicon oxide has small heat conductivity coefficient, the heating area has higher temperature to avoid the diffusion of the temperature to the edge, the lower layer structure is protected, and the thermal response of the micro-hotplate is improved by being close to the metal layer, so that the mechanical strength and the cold and hot impact resistance of the device are improved, and meanwhile, the composite structure also has good electrical insulation property and the impurity blocking capability; in addition, the heating electrode and the testing electrode of the MEMS micro-hotplate adopt coplanar structures, so that the influence of parasitic parameters on the device is avoided; meanwhile, the heating area and the testing area are mutually independent, so that short circuit caused by coating of the gas sensitive material is avoided.
Based on the above embodiments, the present application may be further improved, specifically as follows:
in one embodiment of the present application, the silicon substrate is P-type silicon with resistivity of 0.01-0.02 Ω cm and thickness of 380-420 μm, and crystal orientation <100>.
In one embodiment of the present application, the porosity of the porous silicon is 65% -70%. The abundant holes in the porous silicon can absorb air, so the heat conductivity is low, but because the silicon substrate and the insulating layer of the micro-heating plate are connected through the heat insulation layer, the porous silicon needs to have supporting effect, and the mechanical strength is too low due to too high porosity, so the porosity of the porous silicon cannot be higher than 70%.
In one embodiment of the present application, the thickness of the insulating layer is 11000 a, and the thickness ratio of the first silicon oxide layer, the silicon nitride layer and the second silicon oxide layer is 3:5:3. The mechanical strength of the device is improved, and the cold and hot impact resistance of the device is improved.
In one embodiment of the present application, the heating electrode surrounds the test electrode in a serpentine structure, the test electrode adopts a symmetrical comb-like interdigital electrode structure, and a bending angle between the test electrode and the Pad end connection section is 135 °. If the test electrode wires are at right angles or acute angles, strong charge edges are generated, and the edges are in a concentrated energy state, so that electromagnetic interference is caused; the bending angle of the test electrode is 135 degrees, so that the edge distribution is more uniform, the current is smoother, and the reflection of signals is reduced; the symmetrical distribution of the electrodes counteracts the magnetic field generated by the conduction, so that the symmetrically designed test electrodes and connecting sections in the micro-thermal plate are bent at 135 degrees, and the electromagnetic interference and signal loss to test signals are reduced.
In one embodiment of the present application, the width of the connection part between the end of the test electrode and the Pad end is gradually increased. The end of the test electrode is designed in an extension type and is connected to the side surface of the Pad end, and the test electrode is contacted with the Pad end in an increased manner to fix the electrode.
In one embodiment of the present application, the spacer ring is made of silicon nitride. Silicon nitride has certain thermal conductivity, low thermal expansion coefficient and good stability, is a good insulating material, and adopts silicon nitride as an isolation layer to prevent the short circuit between a heating area and a testing area from influencing the normal operation of a device when the conductive gas-sensitive material is coated.
In one embodiment of the present application, a passivation layer is disposed under the silicon substrate. The passivation layer is silicon oxide for protecting the silicon substrate.
The embodiment of the application provides a preparation method of the MEMS micro-hotplate, which comprises the following steps:
s1: preparing a P-type silicon substrate;
s2: preparing porous silicon on the surface of the silicon substrate by adopting electrochemical corrosion to form the heat insulation layer;
s3: depositing a thermal insulating layer over the insulating layer using a chemical vapor deposition method;
s4: forming a photoresist pattern by adopting a photoetching combined etching mode, and depositing metal on the insulating layer by magnetron sputtering to form the metal layer;
s5: depositing silicon nitride above the metal layer, and forming the isolating ring between the heating electrode and the test electrode of the metal layer after photoetching and etching;
s6: a PVD sputter is used to thicken the electrode at Pad on the metal layer.
In one embodiment of the present application, in step S2, the porous silicon preparation method is as follows: at a current density of 60mA/cm 2 Is etched in a mixed solution of hydrofluoric acid and ethanol for 30 minutes. In the mixed solution of hydrofluoric acid and ethanol, a certain current density is applied to the silicon wafer, so that porous silicon is obtained, and redundant porous silicon can be corroded by KOH solution.
In one embodiment of the present application, the silicon oxide in the insulating layer is prepared by LPCVD, the silicon nitride in the insulating layer is prepared by PECVD, and the silicon nitride of the spacer is prepared by PECVD. The silicon oxide has good insulating property, low thermal expansion coefficient, more compact silicon nitride structure and strong cold and hot impact resistance; and preparing silicon nitride by PECVD, wherein the preparation temperature is in accordance with the bearing temperature after the MEMS micro-hotplate is metallized.
One or more technical solutions provided in the embodiments of the present application at least have the following technical effects or advantages:
1. compared with a suspended structure, the MEMS micro-hotplate has good structural stability, does not need a suspended heating area process and is low in manufacturing difficulty, so that the stability and the practicability of the MEMS micro-hotplate are enhanced;
2. the insulating layer of the MEMS micro-hotplate is of a silicon oxide-silicon nitride-silicon oxide composite structure, and the composite structure improves the mechanical strength and the cold and hot impact resistance of the device;
3. the heating electrode and the testing electrode of the MEMS micro-hotplate adopt coplanar structures, so that the influence of parasitic parameters on the device is avoided; meanwhile, the heating area and the testing area are mutually independent, so that short circuit caused by coating of the gas sensitive material is avoided;
4. the test electrodes and the connecting sections which are symmetrically designed are bent at 135 degrees in the micro-thermal plate, so that electromagnetic interference and signal loss to test signals are reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. Like elements or portions are generally identified by like reference numerals throughout the several figures. In the drawings, elements or portions thereof are not necessarily drawn to scale.
FIG. 1 is a schematic cross-sectional view of a MEMS micro-hotplate according to an embodiment of the invention;
FIG. 2 is a schematic diagram showing distribution of a heating electrode and a test electrode according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of connection between a test electrode and a Pad terminal according to an embodiment of the present invention;
FIG. 4 is a flow chart showing steps of a method for manufacturing a MEMS micro-hotplate according to an embodiment of the invention;
the device comprises a silicon substrate 1, a heat insulation layer 2, an insulation layer 3, a first silicon oxide layer 31, a silicon nitride layer 32, a second silicon oxide layer 33, a metal layer 4, a heating electrode 41, a test electrode 42, a separation ring 5, a Pad end 6 and a passivation layer 7.
Detailed Description
The present invention is further illustrated below in conjunction with the specific embodiments, it being understood that these embodiments are meant to be illustrative of the invention only and not limiting the scope of the invention, and that modifications of the invention, which are equivalent to those skilled in the art to which the invention pertains, will fall within the scope of the invention as defined in the claims appended hereto.
It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
In the description of the present invention, it should be noted that the azimuth or positional relationship indicated by the terms "vertical", "peripheral surface", etc. are based on the azimuth or positional relationship shown in the drawings, or the azimuth or positional relationship that the inventive product is conventionally put in use, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or elements to be referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used merely to distinguish between descriptions and should not be construed as indicating or implying relative importance.
In the description of the present invention, it should also be noted that, unless explicitly specified and limited otherwise, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
In the description of the present invention, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the various embodiments or examples of the invention described and the features of the various embodiments or examples may be combined and combined by those skilled in the art without contradiction.
The MEMS micro-hotplate and the preparation method thereof solve the problems of high manufacturing difficulty and low mechanical strength of a conventional micro-hotplate in the prior art, reduce the manufacturing difficulty of the micro-hotplate and improve the mechanical strength of the micro-hotplate.
The technical scheme in the embodiment of the application aims to solve the problems, and the overall thought is as follows:
example 1:
as shown in fig. 1-3, a MEMS micro-hotplate for use in a gas sensor, comprising: a silicon substrate 1, a heat insulation layer 2, an insulation layer 3, a metal layer 4, a spacer ring 5, a Pad end 6 and a passivation layer 7;
the silicon substrate 1 adopts P-type silicon with the resistivity of 0.01-0.02 omega cm and the thickness of 380-420 mu m and the crystal orientation of <100 >;
the heat insulation layer 2 is arranged on the upper part of the silicon substrate 1, the heat insulation layer 2 is made of porous silicon, and the porosity of the porous silicon is 65% -70%;
the insulating layer 3 is arranged above the heat insulating layer 2, and the insulating layer 3 sequentially comprises a first silicon oxide layer 31, a silicon nitride layer 32 and a second silicon oxide layer 33 from bottom to top;
the metal layer 4 is arranged above the insulating layer 3, the metal layer 4 comprises a coplanar heating electrode 41 and a test electrode 42, the heating electrode 41 surrounds the test electrode 42 by adopting a serpentine structure, the test electrode 42 adopts a symmetrical comb-shaped interdigital electrode structure, the bending angle of the connecting section of the test electrode 42 and the Pad end 6 is 135 degrees, the width of the connecting part of the tail end of the test electrode 42 and the Pad end 6 is gradually increased, a separation ring 5 is arranged between the test electrode 42 and the heating electrode 41, and the separation ring 5 is made of silicon nitride;
a passivation layer 7 is disposed under the silicon substrate 1.
The technical scheme in the embodiment of the application at least has the following technical effects or advantages:
1. compared with a suspended structure, the MEMS micro-hotplate has good structural stability, does not need a suspended heating area process and is low in manufacturing difficulty, so that the stability and the practicability of the MEMS micro-hotplate are enhanced;
2. the insulating layer of the MEMS micro-hotplate is of a silicon oxide-silicon nitride-silicon oxide composite structure, and the composite structure improves the mechanical strength and the cold and hot impact resistance of the device;
3. the heating electrode and the testing electrode of the MEMS micro-hotplate adopt coplanar structures, so that the influence of parasitic parameters on the device is avoided; meanwhile, the heating area and the testing area are mutually independent, so that short circuit caused by coating of the gas sensitive material is avoided;
4. the test electrodes and the connecting sections which are symmetrically designed are bent at 135 degrees in the micro-thermal plate, so that electromagnetic interference and signal loss to test signals are reduced.
Example 2:
as shown in fig. 4, a method for preparing the MEMS micro-hotplate includes the following steps:
s1: p-type silicon substrate with crystal orientation <100> is prepared.
Firstly, placing the silicon wafer into a concentration H 2 SO 4 And H 2 O 2 Cleaning the mixed solution to remove organic pollutants on the surface; after washing by deionized water, continuously adding mixed solution of HF and deionized water to remove the surface oxide layer; respectively carrying out ultrasonic cleaning in acetone and ethanol solution after washing by deionized water; finally, the mixture is put into absolute ethyl alcohol for standby.
S2: and preparing porous silicon on the surface of the silicon substrate by adopting electrochemical corrosion to form a heat insulation layer.
Applying a certain current density to a silicon wafer in a mixed solution of hydrofluoric acid and ethanol to obtain porous silicon, wherein the current density is 60mA/cm in the example 2 The etching is performed for 30 minutes under the condition that the etching depth is about 70 mu m, and the redundant porous silicon can be etched by KOH solution.
S3: and depositing a passivation layer on the back surface of the silicon substrate by using a thermal oxidation method.
The insulating layer is a composite structure of silicon oxide-silicon nitride-silicon oxide, wherein the silicon oxide is prepared by LPCVD, and the silicon nitride is prepared by PECVD. The thickness of the composite structure of silicon oxide-silicon nitride-silicon oxide of the insulating layer is 11000A, and the thickness ratio of each layer is 3:5:3.
S4: and forming photoresist patterns by adopting a photoetching and etching mode, and then depositing metal on the insulating layer by magnetron sputtering to form a metal layer.
Stripping the redundant photoresist and metal by using a solution such as acetone; the metal layer comprises a heating electrode and a testing electrode, the heating electrode and the testing electrode are sputtered by adopting metal Pt, and the thickness is 3000+/-300A.
S5: and depositing silicon nitride above the metal layer, and forming an isolating ring between the heating electrode and the test electrode of the metal layer after photoetching and etching.
The spacer ring is about 6000-8000A thick and is prepared by PECVD.
S6: a thickened electrode was formed at Pad of the metal layer using PVD sputtering.
And (3) re-sputtering a layer of metal thickened electrode (Au) at the Pad position to serve as a bonding Pad, namely, the Pad end comprises a lower layer of metal Pt and an upper layer of metal Au. The thickness of the electrode is 4000+/-400A, and the sputtering method is magnetron sputtering.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (10)
1. A MEMS micro-hotplate, comprising:
a silicon substrate;
the heat insulation layer is arranged at the upper part of the silicon substrate, and is made of porous silicon;
the insulating layer is arranged above the heat insulating layer and comprises a first silicon oxide layer, a silicon nitride layer and a second silicon oxide layer from bottom to top in sequence;
the metal layer is arranged above the insulating layer and comprises a coplanar heating electrode and a test electrode, the test electrode is surrounded by the heating electrode, and an isolating ring is arranged between the test electrode and the heating electrode.
2. A MEMS micro-hotplate according to claim 1, wherein: the silicon substrate is P-type silicon with resistivity of 0.01-0.02 omega cm and thickness of 380-420 mu m and crystal orientation of <100>.
3. A MEMS micro-hotplate according to claim 1, wherein: the porosity of the porous silicon is 65% -70%.
4. A MEMS micro-hotplate according to claim 1, wherein: the thickness of the insulating layer is 11000A, and the thickness ratio of the first silicon oxide layer to the second silicon nitride layer to the second silicon oxide layer is 3:5:3.
5. A MEMS micro-hotplate according to claim 1, wherein: the heating electrode adopts a serpentine structure to surround the test electrode, the test electrode adopts a symmetrical comb-shaped interdigital electrode structure, and the bending angle of the test electrode and the Pad end connecting section is 135 degrees.
6. A MEMS micro-hotplate as claimed in claim 5, wherein: and the width of the joint of the tail end of the test electrode and the Pad end is gradually increased.
7. A MEMS micro-hotplate according to claim 1, wherein: the isolating ring is made of silicon nitride.
8. A MEMS micro-hotplate according to claim 1, wherein: and a passivation layer is arranged below the silicon substrate.
9. A method of producing a MEMS micro-hotplate as claimed in any of claims 1 to 8, comprising the steps of:
s1: preparing the silicon substrate;
s2: preparing porous silicon on the surface of the silicon substrate by adopting electrochemical corrosion to form the heat insulation layer;
s3: depositing a thermal insulating layer over the insulating layer using a chemical vapor deposition method;
s4: forming a photoresist pattern by adopting a photoetching combined etching mode, and depositing metal on the insulating layer by magnetron sputtering to form the metal layer;
s5: depositing silicon nitride above the metal layer, and forming the isolating ring between the heating electrode and the test electrode of the metal layer after photoetching and etching;
s6: a PVD sputter is used to thicken the electrode at Pad on the metal layer.
10. The method according to claim 9, wherein in step S2, the porous silicon is prepared as follows: at a current density of 60mA/cm 2 Is etched in a mixed solution of hydrofluoric acid and ethanol for 30 minutes.
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