A MEMS thermopile structure and a method of manufacturing the same

Abstract

The application discloses a MEMS thermoelectric structure and a preparation method thereof, and belongs to the technical field of microelectronic mechanical systems. The MEMS thermoelectric structure is characterized by comprising a substrate, a support film I and a support film II arranged in one step, and a plurality of thermocouple strip groups arranged in a radial manner from a hot end to a cold end on the support film II. The thermocouple strip group is in a curve shape and comprises a second thermocouple strip, an insulating interlayer and a first thermocouple strip arranged in sequence from top to bottom. The structure formed by the support film II, the electrode and the thermocouple strip group is covered with an infrared absorption layer and a passivation layer. The second thermocouple strip and the electrode are made of the same material. The end of the second thermocouple strip extends downward to be connected with the end of the first thermocouple strip to form a cold end of a thermoelectric pile, and the head end is connected with the head end of the adjacent first thermocouple strip to form a hot end of the thermoelectric pile. The ends of the first thermocouple strip and the second thermocouple strip of a group of thermocouple strips are connected with two electrodes respectively. The response rate, linearity, stability and other sensing performances of the MEMS thermoelectric pile temperature sensor are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a MEMS thermopile structure and a preparation method thereof. Background Art

[0002] In temperature monitoring applications such as healthcare, industry, and smart homes, MEMS thermopile temperature sensors, which use the Seebeck effect to convert temperature changes caused by infrared radiation into a voltage output, are widely studied due to their low cost, high accuracy, and wide monitoring range. As the number of thermopile pixel arrays increases and the size of the sensitive elements continues to shrink, there is an urgent need to improve the responsivity of thermopile sensors.

[0003] Responsivity of thermopile sensor The calculation formula can be expressed as:

[0004]

[0005] In the formula is the incident infrared radiation power, is the thermopile output voltage. When the test conditions remain unchanged, constant; and They are the Seebeck coefficients of two thermocouple materials, which are related to the materials and batch preparation process and are relatively difficult to change; is the number of thermopile thermocouple pairs, is the temperature difference between the hot and cold ends of the thermopile. 、 Can effectively increase the thermopile output voltage , thereby enhancing the response rate of the thermopile temperature sensor Therefore, the current research direction of MEMS thermopiles is mainly focused on improving the logarithmic and temperature difference .

[0006] The traditional layout of thermocouple strips includes classic four-terminal structure, "X" four-terminal structure, square radiation structure, circular radiation structure, etc. However, the classic four-terminal structure has low space utilization, and the center and edge corner areas are usually wasted, resulting in the number of thermocouple strip pairs. Smaller; the edge hot end temperature of the "X" type four-end structure is relatively low, so the temperature difference The output needs to be improved; the square radiation structure thermocouple strip has uneven length and uneven cold end temperature, resulting in poor linearity and long-term stability. The traditional circular radiation structure thermocouple strip has a small length between the hot and cold ends and low thermal resistance, and the cold end duty cycle is low, resulting in temperature difference. Small, output performance is limited.

[0007] The traditional thermocouple strip has a constant cross-sectional shape, which limits the space utilization and the improvement of the overall electrical conductivity, thereby hindering the further enhancement of the sensor output performance.

[0008] In addition, the two kinds of thermocouple materials of the traditional thermoelectric pile are usually prepared on the same layer of support film, that is, a single-layer thermoelectric pile structure, and the number N of thermocouple strips is low. The number N of thermocouple strips can be effectively increased by preparing a double-layer thermoelectric pile structure, so as to improve the output voltage of the thermoelectric pile. At present, the structure of the double-layer thermoelectric pile generally adopts the thermocouple strip formed by P-type polycrystalline silicon and N-type polycrystalline silicon and uses aluminum or other metals as the interconnecting wire, which requires that a first polycrystalline silicon layer, an insulating interlayer and a second polycrystalline silicon layer be prepared and doped with ions respectively, and then each film layer is patterned, and finally the metal interconnecting wire is prepared for connection. The structure process is complex and the cost is high.

[0009] In view of the above, it is necessary to provide a MEMS thermoelectric pile structure and a preparation method thereof, which optimizes the layout structure of the thermocouple strip and prepares a MEMS thermoelectric pile temperature sensor with low cost, high precision and high response rate. SUMMARY

[0010] In view of the above, it is necessary to provide a MEMS thermoelectric pile structure and a preparation method thereof, which optimizes the layout structure of the thermocouple strip and prepares a MEMS thermoelectric pile temperature sensor with low cost, high precision and high response rate.

[0011] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0012] In the first aspect, the present application provides a MEMS thermoelectric pile structure, comprising a substrate, a support film I and a support film II are sequentially arranged on the substrate, an electrode and a plurality of thermocouple strip groups arranged in a radial manner from a hot end to a cold end are arranged on the support film II; the thermocouple strip group is in a curve shape and comprises a second thermocouple strip, an insulating interlayer and a first thermocouple strip arranged in sequence from top to bottom; the structure composed of the support film II, the electrode and the thermocouple strip is covered with an infrared absorption layer and a passivation layer; the materials of the second thermocouple strip and the electrode are the same;

[0013] The end of the second thermocouple strip extends downward to connect with the end of the first thermocouple strip to form a cold end of the thermoelectric pile, and the head end is connected with the head end of the adjacent first thermocouple strip in the clockwise or counterclockwise direction through a series of wires to form a hot end of the thermoelectric pile; wherein the ends of the first thermocouple strip and the second thermocouple strip in a group of thermocouple strip groups are connected with two electrodes respectively.

[0014] Furthermore, the first thermocouple bar and the second thermocouple bar have the same shape, both of which are C-shaped or S-shaped.

[0015] Furthermore, the composite support membrane composed of the support membrane I and the support membrane II is circular with consistent radiant heat diffusion.

[0016] Furthermore, the first thermocouple strip and the second thermocouple strip have equal longitudinal cross-sections or variable longitudinal cross-sections in the length direction.

[0017] Furthermore, the vertical spatial layout of the first thermocouple strip and the second thermocouple strip overlaps or offsets.

[0018] Furthermore, the substrate is etched with a thermal isolation cavity extending to the support membrane I.

[0019] Furthermore, the composite support membrane composed of the support membrane I and the support membrane II is a fully closed membrane or an open membrane with grooves opened at intervals along the thermocouple strips.

[0020] Furthermore, the material of the first thermocouple bar is doped polysilicon or metal; the material of the second thermocouple bar is Al, Au, Ag or Ni; the material of the electrode is Al, Au, Ag or Ni, and the series wire and the second thermocouple bar are made of the same material.

[0021] Furthermore, the support film I and the support film II are silicon oxide films or silicon nitride films; and the infrared absorption layer and the passivation layer are silicon nitride films.

[0022] In a second aspect, the present invention provides a method for preparing a MEMS thermopile structure.

[0023] The following steps are involved:

[0024] S1, sequentially preparing a layer of support film I and a layer of support film II on a substrate;

[0025] S2, preparing a polysilicon thin film on the support film II; ion implanting doped polysilicon to form doped polysilicon and activating the polysilicon; and patterning the doped polysilicon by photolithography for the first time to form a plurality of first thermocouple strips;

[0026] S3, preparing a layer of insulating dielectric film on the surface of the structure obtained in step S2, and patterning the insulating dielectric film by photolithography for a second time to form an insulating interlayer;

[0027] S4, performing a third photolithographic patterning on the surface of the structure obtained in step S3, and preparing a layer of metal, which is then peeled off to form a second thermocouple bar, a series conductor, and an electrode; and performing an annealing process to form an ohmic contact at the connection between the first thermocouple bar and the second thermocouple bar;

[0028] S5, preparing a silicon nitride film as an infrared absorption layer and a passivation layer on the surface of the structure obtained in step S4, performing a fourth photolithography patterning, and etching to expose the electrodes;

[0029] S6. Etch the thermal isolation cavity on the back side of the substrate until the support film I, and cut to obtain the MEMS thermopile chip.

[0030] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0031] The present invention uses a curved design to shorten the spacing between adjacent thermocouple strips at the cold end of the radially arranged thermocouple strips, thereby improving the space utilization of the thermocouple strips and increasing the thermal resistance of the thermocouple strips. This increases the temperature difference between the hot and cold ends of the thermocouple strips, improves the output performance of the thermopile, and achieves the effect of enhancing the electrical performance of the MEMS thermopile temperature sensor. Compared with traditional single-layer MEMS thermopiles, the MEMS thermopile design with double-layer thermocouple strips can double the number of thermocouple strips while maintaining the same sensitive element area and process conditions, thereby doubling the output voltage after the series connection, thereby effectively improving the response rate of the infrared thermopile temperature sensor. In addition, the second thermocouple material is the same metal material as the series wires and electrodes, such as Al, Au, Ag, Ni, etc., which allows the metal thermocouple strips, series wires, and metal electrodes to be prepared simultaneously, greatly simplifying the preparation process of the double-layer MEMS thermopile and reducing its preparation cost while ensuring its electrical performance. This MEMS thermopile structure not only optimizes the circular radial thermocouple strip layout and improves the space utilization of the thermocouple strips, but also facilitates the miniaturization and high performance of the device.

[0032] Furthermore, the composite support membrane adopts a circular structure, which is consistent with the central heat conduction law, and can ensure the uniformity of the cold end temperature of multiple thermocouple strips, thereby improving the linearity and stability of the voltage signal output by the MEMS thermopile sensor.

[0033] Furthermore, the variable cross-section thermocouple strip design can effectively improve the electrical conductivity and increase the infrared light reflection at the cold end to reduce the impact of infrared radiation on the cold end, thereby improving the sensor output.

[0034] The present invention provides a method for preparing a MEMS thermopile structure. By patterning, a second thermocouple strip, series wires, and electrodes are formed on the same layer of metal film, thereby simplifying the preparation process of a double-layer MEMS thermopile and reducing its preparation cost while ensuring its electrical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A three-dimensional schematic diagram of the C-shaped arc structure of the MEMS thermopile of the present invention;

[0036] Figure 2A cross-sectional view of a MEMS thermocouple structure of the present application;

[0037] Figure 3 A top view of a MEMS thermocouple C-shaped arc structure of the present application;

[0038] Figure 4 A top view of a MEMS thermocouple S-shaped arc structure of the present application;

[0039] Figure 5 A partial enlarged view of a cold end of a MEMS thermocouple C-shaped arc structure of the present application;

[0040] Figure 6 A partial enlarged view of a hot end of a MEMS thermocouple C-shaped arc structure of the present application;

[0041] Figure 7 A bottom view of a MEMS thermocouple structure of the present application;

[0042] Figure 8 A top view of a MEMS thermocouple offset double-layer structure of the present application;

[0043] Figure 9 A top view of a MEMS thermocouple slotted composite support film structure of the present application;

[0044] Figure 10 A bottom view of a MEMS thermocouple slotted composite support film structure of the present application;

[0045] Figure 11 A cross-sectional view of a process for preparing a composite support film of the present application;

[0046] Figure 12 A cross-sectional view of a process for preparing a P-type polysilicon thermocouple strip of the present application;

[0047] Figure 13 A cross-sectional view of a process for preparing a silicon oxide insulating interlayer of the present application;

[0048] Figure 14 A cross-sectional view of a process for simultaneously preparing an Al metal thermocouple strip and an electrode of the present application;

[0049] Figure 15 A cross-sectional view of a process for preparing a silicon nitride infrared absorption layer and a passivation layer of the present application;

[0050] Figure 16 A cross-sectional view of a process for etching an exposed Al metal electrode of the present application;

[0051] Figure 17 A cross-sectional view of a process for releasing a composite support film layer by deep silicon etching on the back of the present application.

[0052] Numbers in the figure: 1-substrate, 2-support film I, 3-support film II, 4-first thermocouple bar, 5-insulating interlayer, 6-second thermocouple bar, 7-infrared absorption layer and passivation layer, 8-electrode, 81-positive electrode, 82-negative electrode, 9-series wire, 23-slot. DETAILED DESCRIPTION

[0053] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0055] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be another element centered thereon. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be another element centered thereon at the same time. The terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc. used herein indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0057] Example 1

[0058] Reference Figures 1 to 7 This embodiment provides a MEMS thermopile structure, which includes a substrate 1, a support film I 2, a support film II 3, a first thermocouple strip 4, an insulating interlayer 5, a second thermocouple strip 6, an infrared absorption layer and a passivation layer 7, electrodes 8, and a series conductor 9. The electrodes 8 include a positive electrode 81 and a negative electrode 82.

[0059] Wherein, the substrate 1 as the base, the substrate 1 on the support film Ⅰ2 and support film Ⅱ3 deposited in turn to constitute the composite support film. The first thermocouple strip 4 made of a plurality of first thermocouple material preparation on the support film Ⅱ3, its layout is based on the circular radial diffusion distribution. The first thermocouple strip 4 on the preparation of a layer of insulating interlayer 5, the insulating interlayer 5 both ends have corresponding gap. The second thermocouple strip 6 along the track of the first thermocouple strip 4 is prepared on the insulating interlayer 5, which is located directly above the first thermocouple strip 4, the first thermocouple strip 4 and the second thermocouple strip 6 between the electrical isolation with insulating interlayer, the first thermocouple strip 4, the insulating interlayer 5 and the second thermocouple strip 6 above the thermocouple strip group.

[0060] The second thermocouple strip 6 end extends downward, and is connected with the end of the second thermocouple strip 4 through the end gap of the insulating interlayer 5, the first end of the second thermocouple strip 6 is connected with the first end of the series wire 9, the second end of the series wire 9 is connected with the first end of the first thermocouple strip 4 along the clockwise or counterclockwise direction adjacent through the head gap of the insulating interlayer 5, the first thermocouple strip 4 and the second thermocouple strip 6 of two kinds of materials are connected respectively to form the series connection of the thermocouple strip. The positive electrode 81 is connected with the first thermocouple strip 4 of one group of thermocouple strips, and the negative electrode 82 is connected with the second thermocouple strip 6 of the same group of thermocouple strips. The surface of the thermoelectric pile is prepared with a layer of material film as the infrared absorption layer and the passivation layer 7. The substrate is deep silicon etching heat isolation cavity until the support film Ⅰ2.

[0061] The substrate 1 is N type silicon wafer with thickness of 400 μm, and has circular heat isolation cavity consistent with the heat diffusion law, and the composite support film layer is released and suspended.

[0062] The support film Ⅰ2 is silicon oxide film, the support film Ⅱ3 is silicon nitride film, the first thermocouple strip 4 is P type polysilicon doped with B ions, the second thermocouple strip 6 is Al metal, the insulating interlayer 5 is silicon oxide film, the infrared absorption layer and the passivation layer 7 are silicon nitride film, and the electrode 8 and the series wire 9 are made of the same material as the second thermocouple strip 6.

[0063] Reference Figure 3 The thermocouple strip group is evenly diffused in the radial direction from the hot end to the cold end, and the thermocouple strip is C-shaped curved, so as to shorten the spacing between the thermocouple strips at the cold end, thereby improving the duty cycle of the thermocouple strip.

[0064] Reference Figures 4-5 The first thermocouple strip 4 is prepared on the support film Ⅱ3, and the second thermocouple strip 6 is connected with the first thermocouple strip 4 through the end gap of the silicon oxide insulating interlayer 5. In addition, the positive electrode 81 is connected with one group of first silicon thermocouple strips 4, the negative electrode 82 is connected with the second thermocouple strip 6 of the same group of thermocouple strips, and the ends of the first silicon thermocouple strip 4 and the second thermocouple strip 6 in the thermocouple strip group are not connected.

[0065] refer to Figure 6 The second thermocouple strip 6 is vertically connected to the adjacent second thermocouple strip 4 through the gap at the other end of the silicon oxide insulating interlayer 5 to form the cold end of the thermopile. The Al metal thermocouple strip 6 is connected to the adjacent P-type polysilicon thermocouple strip 4 via a series conductor 9 to form the hot end of the thermopile. The thermocouple strips made of the two materials are connected end to end so that all the thermocouple strips are connected in series, thus forming a double-layer thermocouple strip structure.

[0066] The longitudinal sections of the first thermocouple bar 4 and the second thermocouple bar 6 are of equal or variable cross-section in the longitudinal direction, for example, the cross-section gradually increases from the hot end to the cold end. Figure 2 A 200 nm thick silicon nitride film is prepared on the surface of the thermopile as an infrared absorption layer and a passivation layer 7.

[0067] refer to Figure 7 , the suspended composite support membrane is a circular shape consistent with the radiative heat diffusion.

[0068] The working principle of a MEMS thermopile temperature sensor provided in this example is as follows:

[0069] When the MEMS thermopile temperature sensor of this example is operating, the infrared radiation emitted by the object to be measured irradiates the thermopile sensitive element, is absorbed by the silicon nitride infrared absorption layer, and is converted into heat. The heat diffuses from the hot end of the thermopile to the cold end, and is dissipated through the silicon substrate at the bottom of the cold end, thereby forming a temperature difference between the hot and cold ends. The design of the thermocouple strip can extend the thermal resistance of the thermocouple strip, thereby increasing the temperature difference between the hot and cold ends. According to the Seebeck effect, this temperature difference will generate a thermoelectric electromotive force within the thermocouple material. The multiple thermocouple strips are connected in series to form a thermopile, which outputs a voltage signal through the Al metal electrode. This realizes the signal conversion of light-heat-electricity of the MEMS thermopile temperature sensor.

[0070] Example 2

[0071] refer to Figure 2 and Figure 4 This embodiment provides another MEMS thermopile structure. The difference between this embodiment and embodiment 1 lies in the different bending shapes of the thermocouple bars. In this embodiment, the first thermocouple bar 4 and the second thermocouple bar 6 are bent in an S-shape, which shortens the spacing between adjacent thermocouple bars at the cold end, increases the duty cycle and thermal resistance of the thermocouple bars, and increases the temperature difference between the hot and cold ends to improve the electrical output performance of the MEMS thermopile.

[0072] Example 3

[0073] refer to Figure 2 and Figure 8This embodiment provides another MEMS thermopile structure. The difference between this embodiment and embodiment 1 is that the first thermocouple bar 4 and the second thermocouple bar 6 are offset in the vertical space. In this embodiment, the first thermocouple bar 4 and the second thermocouple bar 6 are offset and electrically isolated by an insulating interlayer 5, thereby increasing the number of thermocouple bar pairs and improving the density of the thermocouple bars, thereby enhancing the electrical output performance of the MEMS thermopile.

[0074] Example 4

[0075] refer to Figure 2 、 Figure 9 and Figure 10 This embodiment provides another MEMS thermopile structure. The difference between this embodiment and Example 1 lies in the composite support membrane. In this embodiment, the composite support membrane is an open membrane with slots along the intervals between the thermocouple strips. That is, the composite support membrane is provided with a plurality of slots 23 evenly arranged along the circumferential direction. The slots 23 can reduce the heat conduction path from the hot end of the thermopile to the cold end, thereby increasing the temperature difference between the hot and cold ends of the thermopile and enhancing the electrical output performance of the MEMS thermopile.

[0076] Example 5

[0077] refer to Figures 11-17 This embodiment provides a method for preparing a MEMS thermopile infrared temperature sensor, which includes the following steps:

[0078] S1. Reference Figure 11 , prepare a crystal <100> A silicon wafer is used as a silicon substrate 1, a silicon dioxide film is deposited on the surface of the silicon wafer by thermal oxidation or LPCVD as a support film I2, and a silicon nitride film is deposited on the silicon dioxide film by low pressure chemical vapor deposition (LPCVD) as a support film II3 to form a composite support film;

[0079] S2. Reference Figure 12 , using LPCVD to deposit a layer of polysilicon film on the surface of the silicon nitride film, and then performing B ion implantation and annealing activation on the polysilicon film to form a P-type polysilicon film;

[0080] S3, patterning the P-type polysilicon by photolithography for the first time, using inductively coupled plasma etching (ICP) to form a P-type polysilicon thermocouple bar, i.e., the first thermocouple bar 4, and removing the residual photoresist by wet method using acetone and alcohol solution;

[0081] S4. References Figure 13A silicon oxide film is deposited on the first thermocouple bar 4 by plasma enhanced chemical vapor deposition (PECVD), the silicon oxide film is patterned by a second photolithography process, the silicon oxide film is wet-etched by etching or a buffered oxide etchant (BOE) to form a silicon oxide insulating interlayer 5, and residual photoresist is wet-removed by using acetone and an alcohol solution;

[0082] S5. Reference Figure 14 , an Al metal thermocouple bar 6, an Al metal electrode 8, and a series conductor 9 are prepared by a lift-off process: a third photolithographic patterning is performed on the silicon oxide insulating interlayer 5, a layer of Al metal film is sputtered or deposited, and a second thermocouple bar 6, a series conductor 9, and an electrode 8 are formed by wet stripping using an acetone and alcohol solution;

[0083] S6, using an annealing process to form an ohmic contact between the second thermocouple bar 6 and the first thermocouple bar 4;

[0084] S7, Reference Figure 15 , using PECVD to deposit a layer of silicon nitride film on the surface of the thermopile as an infrared absorption layer and passivation layer 7;

[0085] S8, Reference Figure 16 , performing a fourth photolithographic patterning on the silicon nitride infrared absorption layer and the passivation layer 7, ICP etching the exposed electrode 8, and removing the residual photoresist by wet method using acetone and alcohol solution;

[0086] S9, Reference Figure 17 The back of the silicon wafer is patterned for the fifth time using photolithography. The thermal isolation cavity is etched by ICP deep silicon etching until the silicon dioxide layer 2 of the upper composite support film is reached. The front side is protected with a 6-8 μm thick photoresist. Finally, the wet stripping method using acetone and alcohol solution is used.

[0087] S10. Obtain MEMS thermopile structure chip by invisible laser cutting.

[0088] The term "consisting of" when describing a combination should include the identified elements, ingredients, components, or steps as well as other elements, ingredients, components, or steps that do not materially affect the basic novel characteristic of the combination. The use of the terms "comprising" or "including" to describe a combination of elements, ingredients, components, or steps herein also contemplates embodiments consisting essentially of these elements, ingredients, components, or steps. The use of the term "may" herein is intended to indicate that any of the attributes described as "may" be optional.

[0089] Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure of "a" or "an" to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0090] It should be understood that the above description is for illustrative purposes only and is not intended to be limiting. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of completeness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the preceding claims is not a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A MEMS thermopile structure, characterized in that: The invention comprises a substrate (1), wherein a support film I (2) and a support film II (3) are sequentially arranged on the substrate (1), and an electrode (8) and a plurality of thermocouple strip groups arranged radially from the hot end to the cold end are arranged on the support film II (3); the thermocouple strip group is curved and comprises a second thermocouple strip (6), an insulating interlayer (5) and a first thermocouple strip (4) sequentially arranged from top to bottom; the structure composed of the support film II (3), the electrode (8) and the thermocouple strips is covered with an infrared absorption layer and a passivation layer (7); the second thermocouple strip (6) and the electrode (8) are made of the same material; The end of the second thermocouple bar (6) extends downward and is connected to the end of the first thermocouple bar (4) to form a cold end of the thermopile, and the head end is connected to the head end of the first thermocouple bar (4) adjacent in a clockwise or counterclockwise direction through a series conductor (9) to form a hot end of the thermopile; wherein the ends of the first thermocouple bar (4) and the second thermocouple bar (6) in a group of thermocouple bars are respectively connected to two electrodes (8).

2. A MEMS thermopile structure according to claim 1, characterized in that: The first thermocouple strip (4) and the second thermocouple strip (6) have the same shape, both being C-shaped or S-shaped.

3. The MEMS thermopile structure according to claim 1, characterized in that: The composite support membrane composed of the support membrane I (2) and the support membrane II (3) is circular with consistent radiant heat diffusion.

4. The MEMS thermopile structure according to claim 1, characterized in that: The first thermocouple strip (4) and the second thermocouple strip (6) have equal longitudinal cross-sections or variable longitudinal cross-sections in the length direction.

5. The MEMS thermopile structure according to claim 1, characterized in that: The vertical spatial layout of the first thermocouple strip (4) and the second thermocouple strip (6) overlaps or is offset.

6. The MEMS thermopile structure according to claim 1, characterized in that: The substrate (1) is etched with a thermal isolation cavity to the support membrane I (2).

7. The MEMS thermopile structure according to claim 1, characterized in that: The composite support membrane composed of the support membrane I (2) and the support membrane II (3) is a fully closed membrane or an open membrane with grooves opened at intervals along the thermocouple strips.

8. The MEMS thermopile structure according to claim 1, characterized in that: The material of the first thermocouple bar (4) is doped polysilicon or metal; the material of the second thermocouple bar (6) is Al, Au, Ag or Ni; the material of the electrode (8) is Al, Au, Ag or Ni, and the material of the series conductor (9) and the second thermocouple bar (6) is the same.

9. The MEMS thermopile structure according to claim 1, characterized in that: The support film I (2) and the support film II (3) are silicon oxide films or silicon nitride films; the infrared absorption layer and the passivation layer (7) are silicon nitride films.

10. The method for preparing a MEMS thermopile structure according to claim 1, characterized in that: The following steps are involved: S1. sequentially preparing a layer of support film I (2) and a layer of support film II (3) on a substrate (1); S2, preparing a polysilicon film on the support film II (3); ion implanting doped polysilicon to form doped polysilicon and activating it; first photolithographically patterning the doped polysilicon to form a plurality of first thermocouple strips (4); S3, preparing a layer of insulating dielectric film on the surface of the structure obtained in step S2, and patterning the insulating dielectric film by photolithography for a second time to form an insulating interlayer (5); S4, the surface of the structure obtained in step S3 is patterned for the third time by photolithography, and a layer of metal is prepared, which is peeled off to form a second thermocouple bar (6), a series conductor (9) and an electrode (8); an annealing process is performed to form an ohmic contact between the first thermocouple bar (4) and the second thermocouple bar (6); S5, preparing a silicon nitride film as an infrared absorption layer and passivation layer (7) on the surface of the structure obtained in step S4, performing a fourth photolithography patterning, and etching to expose the electrode (8); S6. Etching the thermal isolation cavity on the back side of the substrate (1) up to the support film I (2), and cutting to obtain the MEMS thermopile chip.

Images