MEMS thermopile structure and preparation method thereof

Abstract

The invention discloses an MEMS (Micro Electro Mechanical System) thermopile structure and a preparation method thereof, and belongs to the technical field of micro electro mechanical systems, the MEMS thermopile structure is characterized by comprising a substrate, a support film I and a support film II which are arranged in one step, and the support film II is provided with an electrode and a plurality of thermocouple strip groups which are radially arranged from a hot end to a cold end; the thermocouple strip group is curved and comprises a second thermocouple strip, an insulating interlayer and a first thermocouple strip which are sequentially arranged from bottom to top; a structure formed by the support film II, the electrode and the thermocouple strip 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 tail end of the second thermocouple strip extends downwards and is connected with the tail end of the first thermocouple strip to form a cold end of the thermopile, and the head end is connected with the head end of the adjacent first thermocouple strip to form a hot end of the thermopile; and the tail ends of the first thermocouple strip and the second thermocouple strip of the group of thermocouple strips are respectively connected with the two electrodes. The sensing performance such as the response rate, the linearity and the stability of the MEMS thermopile temperature sensor is 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 the field of temperature monitoring such as medical, industrial and smart home, MEMS thermopile temperature sensors convert temperature changes caused by infrared radiation into voltage signal output based on the Seebeck effect. They 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 sensitive elements continues to shrink, there is an urgent need to improve the response rate of thermopile sensitive elements.

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

[0004] 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 .

[0005] Traditional thermocouple strip layouts include classic four-terminal structure, "X"-shaped 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 four corner areas are usually wasted, resulting in the number of thermocouple strip pairs. Small; 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 a temperature difference Small, output performance is limited.

[0006] The cross-sectional shape of traditional thermocouple strips remains unchanged, which limits the space utilization and the improvement of overall conductivity, thus hindering the further enhancement of sensor output performance.

[0007] In addition, the two thermocouple materials of the traditional thermopile are usually prepared on the same support film, that is, a single-layer thermopile structure, and the number of thermocouple strips N is relatively low. By preparing a double-layer thermopile structure, the number of thermocouple strips N can be effectively increased, thereby increasing the output voltage of the thermopile. At present, the structure of the double-layer thermopile generally uses thermocouple strips formed by P-type polysilicon and N-type polysilicon and uses metals such as aluminum as interconnecting wires. It requires first preparing the first polysilicon layer, insulating interlayer, and second polysilicon layer and doping them with ions respectively, and then patterning each film layer, and finally preparing metal interconnecting wires for connection. Its structural process is complex and the cost is high.

[0008] In view of the above, it is necessary to provide a MEMS thermopile structure and a preparation method thereof, optimize the layout structure of the thermocouple strips, and prepare a low-cost, high-precision and high-response MEMS thermopile temperature sensor. Summary of the invention

[0009] In view of the problems of low space utilization rate of the above-mentioned traditional thermocouple strip layout, uneven cold end temperature, small temperature difference between the cold end and the hot end, and poor process compatibility of PN junction devices, which lead to low response rate, poor linearity, high cost and other problems of MEMS thermopile temperature sensors, the present invention provides a MEMS thermopile structure and a preparation method thereof, which improves the sensing performance of the MEMS thermopile temperature sensor, such as response rate, linearity, and stability. At the same time, its preparation process has good compatibility and can be mass-produced at low cost.

[0010] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present invention provides a MEMS thermopile structure, comprising a substrate, on which a support film I and a support film II are sequentially arranged, on which an electrode and a plurality of thermocouple strip groups arranged radially from a hot end to a cold end are arranged; the thermocouple strip group is in a curved shape, comprising a second thermocouple strip, an insulating interlayer and a first thermocouple strip sequentially arranged from bottom to top; 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 second thermocouple strip and the electrode are made of the same material; The end of the second thermocouple bar extends downward and is connected to the end of the first thermocouple bar to form a cold end of the thermopile, and the head end is connected to the head end of the first thermocouple bar adjacent in a clockwise or counterclockwise direction through a series wire to form a hot end of the thermopile; wherein the ends of the first thermocouple bar and the second thermocouple bar in a group of thermocouple bars are respectively connected to two electrodes.

[0011] Furthermore, the first thermocouple bar and the second thermocouple bar have the same shape, both of which are C-shaped or S-shaped. Furthermore, the composite support membrane composed of the support membrane I and the support membrane II is a circle with consistent radiation heat diffusion.

[0012] Furthermore, the first thermocouple strip and the second thermocouple strip have equal longitudinal cross-sections or variable longitudinal cross-sections in the length direction.

[0013] Furthermore, the vertical spatial layout of the first thermocouple strip and the second thermocouple strip overlaps or offsets.

[0014] Furthermore, the substrate is etched with a thermal isolation cavity extending to the support membrane I.

[0015] 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 along the intervals between the thermocouple strips.

[0016] 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. Furthermore, the support film I and the support film II are silicon oxide films or silicon nitride films; the infrared absorption layer and the passivation layer are silicon nitride films.

[0017] In a second aspect, the present invention provides a method for preparing a MEMS thermopile structure. The following steps are involved: S1, sequentially preparing a support film I and a support film II on a substrate; S2, preparing a polysilicon film on the support film II; ion implanting doped polysilicon to form doped polysilicon and activating it; photolithography patterning the doped polysilicon for the first time to form a plurality of first thermocouple strips; 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; S4, performing photolithography patterning for the third time on the surface of the structure obtained in step S3, and preparing a layer of metal, which is peeled off to form a second thermocouple bar, a series conductor and an electrode; and performing an annealing process to form an ohmic contact between the first thermocouple bar and the second thermocouple bar at the connection; S5, preparing a layer of 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 electrode; 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.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects: The invention shortens the spacing between adjacent thermocouple strips at the cold end of the radially arranged thermocouple strips through a bending design, improves the space utilization rate of the thermocouple strips, and increases the thermal resistance of the thermocouple strips, thereby increasing the temperature difference between the hot and cold ends of the thermocouple strips, improving the output performance of the thermopile, and achieving the effect of enhancing the electrical performance of the MEMS thermopile temperature sensor; compared with the traditional single-layer MEMS thermopile, the MEMS thermopile design of the double-layer thermocouple strips can double the number of thermocouple strips under the condition that the sensitive element area and process conditions remain unchanged, so that the output voltage after the series connection is doubled, thereby effectively improving the response rate of the infrared thermopile temperature sensor; in addition, the second thermocouple material is a metal material such as Al, Au, Ag, Ni, etc. that is the same as the series wire and electrode, so that the metal thermocouple strips, the series wire and the metal electrode can be prepared at the same time, which greatly simplifies the preparation process of the double-layer MEMS thermopile and reduces its preparation cost on the basis of ensuring its electrical performance; the MEMS thermopile structure can not only optimize the layout of the circular radial thermocouple strips and improve the space utilization rate of the thermocouple strips, but also is more conducive to realizing the miniaturization and high performance of the device.

[0019] Furthermore, the composite support film 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.

[0020] Furthermore, the variable cross-section thermocouple strip design can effectively improve the conductivity and increase the infrared light reflection at the cold end to reduce the influence of infrared radiation on the cold end, thereby improving the sensor output.

[0021] The present invention provides a method for preparing a MEMS thermopile structure, which forms a second thermocouple strip, a series wire and an electrode on the same layer of metal film through patterning, simplifies the preparation process of a double-layer MEMS thermopile, and reduces its preparation cost while ensuring its electrical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A three-dimensional schematic diagram of the C-shaped arc structure of the MEMS thermopile of the present invention; Figure 2 It is a cross-sectional schematic diagram of the MEMS thermopile structure of the present invention; Figure 3 A top view of the C-shaped arc structure of the MEMS thermopile of the present invention; Figure 4 A top view of the S-shaped arc structure of the MEMS thermopile of the present invention; Figure 5 It is a partial enlarged view of the cold end of the C-shaped arc structure of the MEMS thermopile of the present invention; Figure 6It is a partial enlarged view of the hot end of the C-shaped arc structure of the MEMS thermopile of the present invention; Figure 7 A bottom view of the MEMS thermopile structure of the present invention; Figure 8 A top view of the MEMS thermopile offset double-layer structure of the present invention; Fig. 9 A top view of the MEMS thermopile slotted composite support membrane structure of the present invention; Fig.10 A bottom view of the MEMS thermopile slotted composite support membrane structure of the present invention; Fig.11 This is a schematic cross-sectional diagram of the process for preparing a composite support membrane according to the present invention; Fig.12 A schematic cross-sectional view of the process for preparing a P-type polysilicon thermocouple strip according to the present invention; Fig.13 This is a cross-sectional schematic diagram of the process for preparing a silicon oxide insulating interlayer according to the present invention; Fig.14 This is a schematic cross-sectional view of the process for simultaneously preparing an Al metal thermocouple bar and an electrode according to the present invention; Fig.15 A schematic cross-sectional diagram of the process for preparing a silicon nitride infrared absorption layer and a passivation layer according to the present invention; Fig.16 It is a cross-sectional schematic diagram of the process of etching a bare Al metal electrode according to the present invention; Fig.17 It is a cross-sectional schematic diagram of the process of releasing the composite support film layer by deep silicon etching on the back side of the present invention.

[0023] Numbers in the figure: 1-substrate, 2-support film I, 3-support film II, 4-first thermocouple strip, 5-insulating interlayer, 6-second thermocouple strip, 7-infrared absorption layer and passivation layer, 8-electrode, 81-positive electrode, 82-negative electrode, 9-series wire, 23-slot. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments 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 creative work should fall within the scope of protection of the present invention.

[0026] 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, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] Example 1 Reference Figures 1 to 7 The present embodiment provides a MEMS thermopile structure, which includes a substrate 1, a support film I2, a support film II3, a first thermocouple strip 4, an insulating interlayer 5, a second thermocouple strip 6, an infrared absorption layer and a passivation layer 7, an electrode 8, and a series wire 9. The electrode 8 includes a positive electrode 81 and a negative electrode 82.

[0029] Among them, the substrate 1 is used as the base, and the support film I2 and the support film II3 are sequentially deposited on the substrate 1 to form a composite support film. A plurality of first thermocouple strips 4 composed of a first thermocouple material are prepared on the support film II3, and their layout is based on a circular radial diffusion distribution. An insulating interlayer 5 is prepared on the first thermocouple strip 4, and corresponding gaps are left at both ends of the insulating interlayer 5. A second thermocouple strip 6 composed of a second thermocouple material is prepared on the insulating interlayer 5 along the trajectory of the first thermocouple strip 4, and is located directly above the first thermocouple strip 4. The first thermocouple strip 4 and the second thermocouple strip 6 are electrically isolated by an insulating interlayer, and the first thermocouple strip 4, the insulating interlayer 5 and the second thermocouple strip 6 above it form a thermocouple strip group.

[0030] The end of the second thermocouple bar 6 extends downward and is vertically connected to the end of the second thermocouple bar 4 through the end gap of the insulating interlayer 5. The head end of the second thermocouple bar 6 is connected to the first end of the series conductor 9. The second end of the series conductor 9 is connected to the head end of the first thermocouple bar 4 adjacent in the clockwise or counterclockwise direction through the head end gap of the insulating interlayer 5. The first thermocouple bar 4 and the second thermocouple bar 6 of the two materials are connected head to tail to form a series of thermocouple bars. The positive electrode 81 is connected to the first thermocouple bar 4 of one group of thermocouple bars, and the negative electrode 82 is connected to the second thermocouple bar 6 of the same group of thermocouple bars. A layer of material film is prepared on the surface of the thermopile as an infrared absorption layer and a passivation layer 7. The substrate is deep silicon-etched to form a thermal isolation cavity until the support film I2.

[0031] The substrate 1 is an N-type silicon wafer with a thickness of 400 μm and has a circular thermal isolation cavity in accordance with the heat diffusion law, and its composite support film layer is released and suspended.

[0032] The support film I2 is a silicon oxide film, and the support film II3 is a silicon nitride film; the material of the first thermocouple bar 4 is P-type polysilicon doped with B ions, and the material of the second thermocouple bar 6 is Al metal; the insulating interlayer 5 is a silicon oxide film; the infrared absorption layer and the passivation layer 7 are silicon nitride films; the materials of the electrode 8 and the series conductor 9 are the same as those of the second thermocouple bar 6.

[0033] refer to Figure 3 The thermocouple strip group spreads evenly from the hot end to the cold end in a radial shape, and the thermocouple strips are bent in a C shape, shortening the spacing between the thermocouple strips at the cold end, thereby increasing the duty cycle of the thermocouple strips.

[0034] refer to Figures 4 and 5 , the first thermocouple bar 4 is prepared on the support film II3, and the second thermocouple bar 6 is vertically connected to the first thermocouple bar 4 through the gap at one end of the silicon oxide insulating interlayer 5; in addition, the positive electrode 81 is connected to one group of first silicon thermocouple bars 4, and the negative electrode 82 is connected to the second thermocouple bar 6 of the same group of thermocouple bars, and the ends of the first silicon thermocouple bar 4 and the second thermocouple bar 6 in this thermocouple bar group are not connected.

[0035] refer to Figure 6 The second thermocouple bar 6 is vertically connected to the adjacent second thermocouple bar 4 through the gap at the other end of the silicon oxide insulating interlayer 5 to form the cold end of the thermopile, and the Al metal thermocouple bar 6 is connected to the adjacent P-type polysilicon thermocouple bar 4 through the series conductor 9 to form the hot end of the thermopile. The thermocouple bars of the two materials are connected head to tail respectively so that all the thermocouple bars are connected in series, thereby forming a double-layer thermocouple bar structure.

[0036] The longitudinal sections of the first thermocouple strip 4 and the second thermocouple strip 6 are of equal cross-section or variable cross-section in the length direction, for example, the cross-section gradually increases from the hot end to the cold end. Figure 2A 200 nm thick silicon nitride film is prepared on the surface of the thermopile as an infrared absorption layer and a passivation layer 7.

[0037] refer to Figure 7 , the suspended composite support membrane is a circular shape consistent with the radiative heat diffusion.

[0038] The working principle of a MEMS thermopile temperature sensor provided in this example is as follows: When the MEMS thermopile temperature sensor of this example is working, 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 converted into heat. The heat diffuses from the hot end of the thermopile to the cold end, and dissipates through the bottom silicon substrate at the cold end, thereby forming a temperature difference between the hot end and the cold end. 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, the temperature difference will generate a thermoelectric electromotive force in the thermocouple material. The multiple thermocouple strips are connected in series to form a thermopile, and a voltage signal is output through the Al metal electrode. Thereby, the MEMS thermopile temperature sensor uses light-heat-electricity signal conversion.

[0039] Example 2 refer to Figure 2 and Figure 4 This embodiment provides another MEMS thermopile structure. The difference between this embodiment and embodiment 1 is that the bending shape of the thermocouple strips is different. In this embodiment, the first thermocouple strip 4 and the second thermocouple strip 6 are bent in an S shape, shortening the distance between adjacent thermocouple strips at the cold end, increasing the duty cycle and thermal resistance of the thermocouple strips, and increasing the temperature difference between the hot and cold ends to improve the electrical output performance of the MEMS thermopile.

[0040] Example 3 refer to Figure 2 and Figure 8 This 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.

[0041] Example 4 refer to Figure 2 , Fig. 9 and Fig.10This embodiment provides another MEMS thermopile structure. The difference between this embodiment and embodiment 1 is that the composite support film is different. In this embodiment, the composite support film is an open film with grooves along the interval positions of the thermocouple strips, that is, the composite support film is provided with a plurality of grooves 23 evenly arranged along the circumferential direction. The grooves 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 to enhance the electrical output performance of the MEMS thermopile.

[0042] Example 5 refer to Figures 11 to 17 This embodiment provides a method for preparing a MEMS thermopile infrared temperature sensor, which includes the following steps: S1. References Fig.11 , prepare a crystal <100> A silicon wafer is used as a silicon substrate 1, a layer of silicon dioxide film is deposited on the surface of the silicon wafer by thermal oxidation or LPCVD as a support film Ⅰ2, and a layer of 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; S2. Reference Fig.12 , using LPCVD to deposit a layer of polysilicon film on the surface of the silicon nitride film, and implanting B ions into the polysilicon film and annealing to activate it, to form a P-type polysilicon film; 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; S4. References Fig.13 , depositing a silicon oxide film on the first thermocouple bar 4 by plasma enhanced chemical vapor deposition (PECVD), patterning the silicon oxide film by a second photolithography, etching or wet etching with a buffered oxide etchant (BOE) to form a silicon oxide insulating interlayer 5, and removing residual photoresist by wet method with acetone and alcohol solution; S5. Reference Fig.14 , using a stripping process to prepare an Al metal thermocouple bar 6, an Al metal electrode 8 and a series conductor 9: performing a third photolithography patterning on the silicon oxide insulating interlayer 5, sputtering or depositing a layer of Al metal film, and using acetone and alcohol solution wet stripping to form a second thermocouple bar 6, a series conductor 9 and an electrode 8; S6, using an annealing process to form an ohmic contact between the second thermocouple bar 6 and the first thermocouple bar 4 at the connection; S7, Reference Fig.15 , using PECVD to deposit a layer of silicon nitride film on the surface of the thermopile as an infrared absorption layer and a passivation layer 7; S8. Reference Fig.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; S9. Reference Fig.17 , the fifth photolithography patterning is performed on the back of the silicon wafer, and the thermal isolation cavity is etched by ICP deep silicon until the silicon dioxide layer 2 of the upper composite support film. The front side is protected with a 6-8 μm thick photoresist, and finally the acetone and alcohol solution are used for wet degumming; S10. Obtain MEMS thermopile structure chip by invisible laser cutting.

[0043] The term "consisting of" describing a combination shall include the identified elements, ingredients, parts or steps and other elements, ingredients, parts or steps that do not substantially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe a combination of elements, ingredients, parts or steps herein also contemplates embodiments that consist essentially of these elements, ingredients, parts or steps. By using the term "may", it is intended to illustrate that any of the attributes described that "may" be included are optional.

[0044] 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 "one" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0045] It should be understood that the above description is for illustration and not for limitation. 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 foregoing claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, 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 in the foregoing claims is not intended to be a waiver of such subject matter, nor should it be considered that the applicant has not considered 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), on which a support film I (2) and a support film II (3) are arranged in sequence, and on which an electrode (8) and a plurality of thermocouple strip groups arranged radially from a hot end to a cold end are arranged; the thermocouple strip groups are in a curved shape, and comprise a second thermocouple strip (6), an insulating interlayer (5) and a first thermocouple strip (4) arranged in sequence from bottom to top; 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. A 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 radiation heat diffusion.

4. A 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. A MEMS thermopile structure according to claim 1, characterized in that: The substrate (1) is etched with a thermal isolation cavity to the support film 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 along the intervals between 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) is the same as that of the second thermocouple bar (6).

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; photolithography patterning the doped polysilicon for the first time 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 by photolithography for the third time, 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 so that the first thermocouple bar (4) and the second thermocouple bar (6) form an ohmic contact at the connection point; S5, preparing a silicon nitride film as an infrared absorption layer and a 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 a thermal isolation cavity on the back side of the substrate (1) until reaching the support film I (2), and cutting to obtain a MEMS thermopile chip.

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