MEMS thermal flow sensor

Abstract

The invention provides an MEMS (Micro Electro Mechanical System) thermal flow sensor. 100 gt; the inclined edge corrosion holes extending in the crystal orientation are combined with the vertical corrosion holes. 100 gt; when the beveled edge corrosion hole in the crystal direction is corroded by an alkaline solution, the corrosion rate of the crystal face of the substrate (100) is far greater than that of the crystal face of the substrate (111), so that the beveled edge corrosion hole can completely corrode downwards along the thickness direction of the substrate to remove the substrate, thereby improving a hill-like structure at the center of the heat-insulating film, reducing heat loss towards the direction of the substrate, and improving the heat-insulating performance of the heat-insulating film. The vertical corrosion holes can also prevent heat from being transferred to the substrate in the horizontal direction, and heat loss is reduced; meanwhile, the bevel edge corrosion holes can hinder transverse temperature conduction, the multiple sub-film parts obtained through division can be located in different temperature fields, and due to the fact that the distances between the hot end of the thermopile and the heating element are different, the sensitivity to different measuring range flow is different. Therefore, different measuring range test requirements can be realized through different distances between the hot ends of the thermopiles at different sub-film parts and the heating element.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a MEMS thermal flow sensor. Background Art

[0002] In recent years, as humans have fully entered the era of intelligent information technology, the demand for information measurement and control has become increasingly high. Among them, the measurement and control of gas flow is of great significance in the fields of industry, medicine, bioengineering, etc. Among them, MEMS thermal flow sensors have been widely used due to their small size, high precision, low power consumption, and fast response speed. For example, in the automotive field, the effective combustion of fuel is ensured by controlling the flow of the engine intake; in the medical field, there is a demand for high-precision control of oxygen flow in traditional Chinese medicine household ventilators, oxygen concentrators, etc.

[0003] The working principle of the thermal flow sensor with thermopile structure is to use the Seebeck effect to determine the fluid flow rate by measuring the temperature changes of the upper and lower ends of the thermopiles on both sides of the middle heating element when the fluid passes through. At present, conventional MEMS thermal flow sensors have problems such as single range and low heat exchange efficiency between the heating element and the fluid. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a MEMS thermal flow sensor for solving at least one technical problem of the prior art MEMS thermal flow sensor, such as single measuring range and low heat exchange efficiency between the heating element and the fluid.

[0005] To achieve the above objectives and other related objectives, the present invention provides a MEMS thermal flow sensor, the MEMS thermal flow sensor comprising:

[0006] (100) a single crystal silicon substrate having a groove, wherein the groove is opened on the upper surface of the substrate;

[0007] A heat-insulating film, covering the groove and connected to the substrate, wherein the heat-insulating film and the substrate together form a heat-insulating cavity;

[0008] At least two vertical corrosion holes penetrating the thermal insulation film and extending in the vertical direction, all of the vertical corrosion holes are arranged in sequence in the horizontal direction and divide the thermal insulation film into three regions: an upstream film portion, a central film portion, and a downstream film portion, wherein the upstream film portion and the downstream film portion have the same size and are symmetrical about the central film portion;

[0009] The upstream thin film portion and the downstream thin film portion are respectively penetrated and along the substrate <100> A beveled etching hole extending in the crystal direction, wherein the beveled etching hole arranged in the upstream thin film portion is arranged mirror-symmetrically or 180° rotationally symmetrically with the beveled etching hole arranged in the downstream thin film portion, and the beveled etching hole divides the thin film portion where it is located into a plurality of sub-thin film portions;

[0010] A plurality of thermopiles are arranged on the sub-thin film portion, and all the thermopiles arranged on the sub-thin film portion of the upstream thin film portion are connected in series, and all the thermopiles arranged on the sub-thin film portion of the downstream thin film portion are connected in series;

[0011] A heating element is disposed on the central film portion and extends in a vertical direction;

[0012] Wherein, the horizontal direction is the <110> crystal direction, the vertical direction is the Crystal direction.

[0013] Optionally, the upstream film portion and the downstream film portion are each provided with one of the beveled-edge corrosion holes or two of the beveled-edge corrosion holes, and when the upstream film portion and the downstream film portion are each provided with two of the beveled-edge corrosion holes, the two beveled-edge corrosion holes are vertically arranged or parallelly arranged.

[0014] Optionally, a heating element metal wire and a thermopile series metal wire are also included, and both pass through the central film portion on both sides of the heating element in a vertical direction.

[0015] Optionally, a radiator is further included, which is arranged above the heating element and is used to dissipate heat from the heating element.

[0016] Furthermore, the heat sink is a sheet of metal, or the heat sink is composed of a plurality of horizontal metal strips arranged in a vertical direction, or the heat sink is composed of a plurality of inclined metal strips arranged in a vertical direction.

[0017] Optionally, the cold end of the thermopile is located on the substrate, so that the cold end of the thermopile is in full contact with the substrate.

[0018] Optionally, a temperature-sensitive resistor is further included, which is arranged on the outside of at least one cold end of the thermopile.

[0019] Optionally, the thermopile is configured to be at least one of the following three types: in the first type, the thermopile is arranged in series along the horizontal direction with a plurality of vertical thermocouple bars, the cold end of the thermopile is located on the substrate, and the hot end is adjacent to the bevel corrosion hole; in the second type, the thermopile is arranged in series along the horizontal direction with a plurality of thermocouple bars, the thermocouple bars are parallel to the bevel corrosion hole, the cold end of the thermopile is located on the substrate, and the hot end is parallel to the heating element; in the third type, the thermopile is arranged in series along the vertical direction with a plurality of horizontal thermocouple bars, the cold end of the thermopile is located on the substrate, and the hot end is adjacent to the bevel corrosion hole; all the thermopiles are configured to be at least one of the three types.

[0020] Furthermore, the thermocouple bars in the thermopile are a combination of any two of P-type doped polysilicon thermocouple bars, N-type doped polysilicon thermocouple bars and metal thermocouple bars.

[0021] Optionally, the thermocouple strips in the thermopile in a combined form are vertically stacked along the thickness direction of the (100) plane of the substrate or are laid flat along the (100) plane of the substrate.

[0022] As described above, the MEMS thermal flow sensor of the present invention is provided along the substrate <100> The beveled etching holes extending in the crystal direction combined with the vertical etching holes can effectively release the thermal insulation film. Generally, when releasing the thermal insulation film, the substrate needs to be deeply etched. When etching the substrate, the closer to the center, the smaller the etching rate, so there will be a hill-like structure in the center. The beveled etching holes are set in the thermal insulation film area. Since their direction is along the substrate, <100> In terms of crystal orientation, when an alkaline solution is used for etching, the etching rate of the crystal plane of the substrate (100) is much greater than the etching rate of the crystal plane of the substrate (111), so the beveled etching hole can be completely etched downward along the thickness direction of the substrate to remove the substrate, thereby improving the hill-like structure at the center of the thermal insulation film, improving the conformality of the thermal insulation cavity, reducing heat loss in the direction of the substrate, and improving measurement accuracy. The vertical etching hole can also hinder the transfer of heat to the substrate in the horizontal direction, reducing heat loss and further improving measurement accuracy. At the same time, the beveled etching hole can hinder the lateral conduction of temperature, so that the multiple sub-thin film parts obtained by dividing it can be in different temperature fields, and because the distance between the hot end of the thermopile and the heating element is different, the sensitivity to different range flow rates is different, so that different range test requirements can be realized by the different distances between the hot end of the thermopile and the heating element in different sub-thin film parts, thereby achieving multi-range measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram showing the cross-sectional structure of the MEMS thermal flow sensor substrate of the present invention.

[0024] Figure 2Shown is a schematic diagram of the global three-dimensional structure of the MEMS thermal flow sensor of the present invention.

[0025] Figure 3 Shown is a schematic cross-sectional view of the three-dimensional structure of the MEMS thermal flow sensor of the present invention.

[0026] Figure 4 and Figure 5 A schematic top view of the structure of the first example of the positional relationship between the vertical corrosion holes, the oblique corrosion holes, etc. in the MEMS thermal flow sensor of the present invention is shown.

[0027] Figure 6 A second exemplary top view structural diagram showing the positional relationship of vertical corrosion holes, oblique corrosion holes, etc. in the MEMS thermal flow sensor of the present invention is shown.

[0028] Figure 7 A schematic top view of the structure of a third example of the positional relationship of vertical corrosion holes, oblique corrosion holes, etc. in the MEMS thermal flow sensor of the present invention is shown.

[0029] Figure 8 A schematic diagram of a top view of a fourth example of the positional relationship of vertical corrosion holes, oblique corrosion holes, etc. in the MEMS thermal flow sensor of the present invention is shown.

[0030] Fig. 9 A schematic top view of a first exemplary structure of a MEMS thermal flow sensor of the present invention is shown.

[0031] Fig.10 A schematic diagram of a top view of a second example of the MEMS thermal flow sensor of the present invention is shown.

[0032] Fig.11 Display as Fig.10 A partial enlarged schematic diagram of the central film part.

[0033] Fig.12 It is a schematic top view of a first exemplary structure of a thermopile in a MEMS thermal flow sensor of the present invention.

[0034] Fig.13 A second exemplary top view structural diagram of a thermopile in a MEMS thermal flow sensor of the present invention is shown.

[0035] Fig.14 A schematic top view of a third exemplary structure of a thermopile in a MEMS thermal flow sensor of the present invention is shown.

[0036] Fig.15 A schematic top view of a fourth exemplary structure of a thermopile in a MEMS thermal flow sensor of the present invention is shown.

[0037] Fig.16 A schematic top view of a third example of the MEMS thermal flow sensor of the present invention is shown.

[0038] Fig.17 A schematic top view of a fourth example of the MEMS thermal flow sensor of the present invention is shown.

[0039] Fig.18 A fifth exemplary top view structural diagram of the MEMS thermal flow sensor of the present invention is shown.

[0040] Fig.19 A sixth exemplary schematic top view of the structure of the MEMS thermal flow sensor of the present invention is shown.

[0041] Fig. 20 It is a schematic top view of the seventh example structure of the MEMS thermal flow sensor of the present invention.

[0042] Fig.21 It is a schematic top view of an eighth example of the structure of the MEMS thermal flow sensor of the present invention.

[0043] Figure 22 to Figure 28 The schematic diagram of the cross-sectional structure corresponding to each step in the process of preparing the first example of the MEMS thermal flow sensor is shown, wherein the schematic diagram of the cross-sectional structure corresponding to each step is along the Fig. 9 The cross-section view in the AA direction, that is, from the vertical direction <110> Crystalline to horizontal direction <110> The cutting method of crystal direction.

[0044] Component number description

[0045] 1 Substrate

[0046] 11 Groove

[0047] 12 Thermal insulation film

[0048] 120 Upstream Film Division

[0049] 121 Central Film Department

[0050] 122 Downstream Film Division

[0051] 123 Sub-Film Department

[0052] 13 Insulation cavity

[0053] 14 Vertical corrosion holes

[0054] 15 Beveled edge corrosion hole

[0055] 16 Thermopile

[0056] 160 Cold end

[0057] 161 Hot End

[0058] 162 Thermocouple Strip

[0059] 163 Polysilicon Thermocouple Strip

[0060] 164 Metal Thermocouple Strip

[0061] 17 Heating element

[0062] 18 Radiator

[0063] 19 Metal Wire

[0064] 190 Heating element wire

[0065] 191 Thermopile Series Metal Wires

[0066] 192 Thermopile lead wire

[0067] 193 Thermistor Metal Wire

[0068] 20 Thermistor

[0069] 21 Lead pad

[0070] 22 First insulation layer

[0071] 23 Second insulation layer

[0072] 24 Polysilicon layer

[0073] 25 Third insulation layer

[0074] 26 Ohm contact hole

[0075] 27 Metal Layer

[0076] 28 Passivation layer DETAILED DESCRIPTION

[0077] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0078] See also Figures 1 to 28 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0079] Embodiment 1

[0080] like Figures 1 to 8 As shown, the present invention provides a MEMS thermal flow sensor, comprising:

[0081] like Figure 1 As shown, a (100)-plane single crystal silicon substrate 1 has a groove 11, and the groove 11 is opened on the upper surface of the substrate 1;

[0082] like Figure 3 As shown, the heat-insulating film 12 covers the groove 11 and is connected to the substrate 1. The heat-insulating film 12 and the substrate 1 together form a heat-insulating cavity 13;

[0083] like Figure 2 and Figures 4 to 8 As shown, at least two vertical corrosion holes 14 penetrate the thermal insulation film 12 and extend along the vertical direction Y. All the vertical corrosion holes 14 are arranged in sequence along the horizontal direction X and divide the thermal insulation film 12 into three areas in sequence, such as Figure 4 , Fig. 20 and Fig.21 As shown: an upstream thin film portion 120, a central thin film portion 121 and a downstream thin film portion 122, wherein the upstream thin film portion 120 and the downstream thin film portion 122 have the same size and are symmetrical about the central thin film portion 121, wherein a horizontal direction X is defined along the substrate 1 <110> Crystal direction, based on the properties of silicon materials, the vertical direction Y belongs to the lining

[0084] Bottom 1 <110> Negative direction of crystal

[0085] like Figures 4 to 8 As shown, the upstream thin film portion 120 and the downstream thin film portion 122 are respectively penetrated and along the substrate 1 <100> The beveled etching holes 15 extending in the crystal direction, and the beveled etching holes 15 arranged in the upstream thin film portion 120 and the beveled etching holes 15 arranged in the downstream thin film portion 122 are arranged in a mirror-symmetrical manner (such as Figures 4 to 7 ) or 180° rotational symmetry (as shown Figure 8 As shown), the beveled etching hole 15 is arranged to divide the film portion where it is located into a plurality of sub-film portions 123, for example, Figure 4 The beveled etched hole 15 divides the upstream thin film portion 120 into two sub-thin film portions 123, and also divides the downstream thin film portion 122 into two sub-thin film portions 123. Figures 6 to 8 The bevel etched hole 15 is divided into three sub-thin film portions 123;

[0086] like Figure 2As shown, a plurality of thermopiles 16 are disposed on the sub-thin film portion 123, and all the thermopiles 16 disposed on the sub-thin film portion 123 of the upstream thin film portion 120 are connected in series, and all the thermopiles 16 disposed on the sub-thin film portion 123 of the downstream thin film portion 122 are connected in series;

[0087] like Figure 2 As shown, the heating element 17 is disposed on the central film portion 121 and extends along the vertical direction Y.

[0088] Specifically, in this embodiment, the heating element 17 can be a heating resistor, and the material selected is a semiconductor material, a metal material or other material suitable for preparing a heating element; in addition, the structure of the heating element 17 is not specifically limited and is set according to actual needs.

[0089] Specifically, the number of the vertical corrosion holes 14 is at least two, such as Fig. 20 and Fig.21 As shown, two vertical etching holes 14 are provided at the center of the thermal insulation film 12, so as to divide the thermal insulation film 12 into three regions: an upstream film portion 120, a central film portion 121, and a downstream film portion 122. In addition, if the size allows, four vertical etching holes 14 may also be provided, such as Figure 4 , Fig. 9 , Fig.10 , Fig.16 , Fig.17 , Fig.18 , Fig.19 As shown, two vertical corrosion holes 14 are set at the center of the thermal insulation film 12, and two vertical corrosion holes 14 are set on both sides of the thermal insulation film 12, and the thermal insulation film 12 is also divided into three areas: an upstream film part 120, a central film part 121 and a downstream film part 122.

[0090] The thermopile 16 is located on both sides of the heating element 17, i.e., the upstream and downstream positions, and is mirror-symmetrical or 180° rotationally symmetrical, forming two independent thermopile detection circuits, respectively, in the upstream and downstream. When the heating element 17 is heated by an electric current, a steady-state temperature curve will be formed around the heating element 17. Through the symmetry of the two independent thermopile detection circuits, when no gas (medium) passes through the heating element 17 at normal temperature, the heating element 17 applies an electric load to generate heat, and the temperature fields generated by the two independent thermopile detection circuits in the upstream and downstream are symmetrical, so the two independent thermopile detection circuits in the upstream and downstream sense the same potential difference, so that the two independent thermopile detection circuits in the upstream and downstream cannot sense the temperature difference between the upstream and downstream thermopile detection circuits; when there is gas (medium) passing through, the heat in the upstream decreases and the heat in the downstream increases, and the corresponding thermopile generates different potential differences, so that the two independent thermopile detection circuits in the upstream and downstream sense the temperature difference between the upstream and downstream thermopile detection circuits, and the temperature difference is used for flow sensing.

[0091] In this embodiment, by setting <100> The beveled etching hole 15 extending in the crystal direction is combined with the vertical etching hole 14 to effectively release the thermal insulation film 12. Generally, when releasing the thermal insulation film 12, it is necessary to deeply etch the substrate 1, such as to a depth of 100 μm. When etching the substrate 1, the closer to the center, the smaller the etching rate, so there will be a hill-like structure in the center. The beveled etching hole 15 is set in the thermal insulation film area. Since its direction is along the substrate <100> Crystal direction, when etching with alkaline solution, the etching rate of the crystal plane of the substrate (100) is much greater than the etching rate of the crystal plane of the substrate (111), so the bevel etching hole 15 can be completely etched downward along the thickness direction of the substrate until the substrate is removed, thereby improving the hill-like structure at the center of the thermal insulation film, improving the conformality of the thermal insulation cavity, reducing heat loss in the direction of the substrate, and improving measurement accuracy. The vertical etching hole 14 can also hinder the transfer of heat to the substrate in the horizontal direction, reducing heat loss and further improving measurement accuracy. At the same time, the bevel etching hole 15 can hinder the lateral conduction of temperature, so that the multiple sub-thin film parts 123 obtained by dividing it can be in different temperature fields, and because the distance between the hot end of the thermopile and the heating element is different, the sensitivity to different range flow rates is different, so that different range test requirements can be achieved through the different distances between the hot end of the thermopile and the heating element in different sub-thin film parts 123, achieving multi-range measurement. Fig. 9For example, a beveled etched hole 15 is provided in each of the upstream thin film portion 120 and the downstream thin film portion 122, and the respective thin film portions are divided into two sub-thin film portions 123. Among the thermopiles on the two sub-thin film portions 123 in the upstream thin film portion 120, the inner thermopiles have a hot end closer to the heating element 17, and can be used to measure a larger flow rate of the fluid, while the outer thermopiles have a hot end farther from the heating element 17, and can be used to measure a smaller range of the fluid flow. Specifically, the range can be adjusted by changing the distance from the thermopiles hot end to the heating element as needed.

[0092] like Figure 5 As shown, in practice, the width W1 of the central thin film portion 121 should not be too wide, which may lead to incomplete removal of the substrate below the central thin film portion 121 and increase heat loss; nor should it be too narrow, which may reduce mechanical stability and easily break the film. Figure 5 Taking the four vertical corrosion holes 14 as an example, the distance W1 between the two vertical corrosion holes 14 in the middle position of the thermal insulation film 12 (i.e., the width of the central film portion 121) and the width W2 of the two vertical corrosion holes 14 determine the distance relationship between the thermopile and the heating element. At the same time, the positions of all vertical corrosion holes 14 and bevel corrosion holes 15 in the thermal insulation film 12 and the widths W2 and W3 of all vertical corrosion holes 14 and the width of the bevel corrosion holes 15 determine the size relationship of the cavity below.

[0093] The number of beveled edge corrosion holes can be selected according to different measurement range requirements and the size of the heat insulation cavity. In practice, two measurement ranges (large range, small range) or three measurement ranges (large range, medium range, small range) are generally selected, so it is better that the upstream film portion 120 and the downstream film portion 122 are each provided with one beveled edge corrosion hole 15 or two beveled edge corrosion holes 15, and when the upstream film portion 120 and the downstream film portion 122 are each provided with two beveled edge corrosion holes 15, the two beveled edge corrosion holes 15 are vertically arranged, such as Figure 6 and Figure 7 As shown or parallel settings as Figure 8 As shown. Fig. 9 , Fig.10 , Fig.16 , Fig.17 and Fig.18 As shown, when the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with one of the beveled corrosion holes 15, the thin film portions where they are located are respectively divided into two sub-thin film portions 123, and each sub-thin film portion 123 is provided with two thermopiles 16, so that two ranges of flow measurement can be achieved, ports 2 and 4 achieve small range measurement, and ports 3 and 4 achieve large range measurement; Figures 19 to 21As shown, when the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with two of the beveled corrosion holes 15, the thin film portions where they are located are divided into three sub-thin film portions 123, each sub-thin film portion 123 is provided with three thermopiles 16, so that flow measurement in three ranges can be realized.

[0094] like Figure 2 and Fig. 9 As shown, the flow sensor also includes a metal wire 19 to realize the circuit lead-out of each structure in the flow sensor, for example, a heating element metal wire 190, a thermopile series metal wire 191, a thermopile lead-out metal wire 192, a temperature-sensitive resistor metal wire 193, etc. Preferably, the heating element metal wire 190 and the thermopile series metal wire 191 can be arranged to pass through the vertical direction Y of the central thin film portion 121 on both sides of the heating element 17. Being arranged on both sides of the heating element 17 can ensure the uniformity of heating and improve the mechanical stability of the central thin film portion 121. Other metal wires can be optionally arranged on the substrate.

[0095] like Fig.10 As shown in FIG. 1 , as a preferred example, a heat sink 18 may be provided on the heating element 17 to further enhance the heat exchange rate between the heat and the surface of the fluid and improve the measurement accuracy. The specific form of the heat sink 18 is not limited here, as long as it can improve the heat exchange efficiency, for example, it can be a sheet of metal covering the heating element 17, such as Fig.11 As shown, a plurality of horizontal metal strips may be arranged in a vertical direction on the heating element 17, or a plurality of metal strips may be arranged obliquely on the heating element 17, etc., depending on actual needs.

[0096] As a preferred example, the cold end 160 of the thermopile 16 can be set on the substrate 1 so that the cold end 160 of the thermopile 16 is in full contact with the substrate 1, so as to increase the heat dissipation performance of the cold end, increase the temperature difference between the cold and hot ends, shorten the response time of the sensor, and increase the measuring range.

[0097] like Figure 2 As shown, the flow sensor may also be provided with a thermistor 20, which is provided outside at least one of the thermopile cold ends 160. The ambient temperature can be directly measured and compensated by the thermistor 20, thereby eliminating the influence of gas temperature fluctuation on the measurement result and improving the detection accuracy.

[0098] According to the number and position of the bevel corrosion holes 15, the thermopile 16 may include various types. Fig.12 and Fig.14As shown, the thermopile 16 is composed of a plurality of thermocouple strips 162 in a vertical direction Y arranged in series along a horizontal direction X. The cold end 160 of the thermopile 16 is located on the substrate 1, and the hot end 161 is adjacent to the bevel etched hole 15. Fig.13 As shown, the thermopile 16 is arranged in series with a plurality of thermocouple strips 162 in a horizontal direction, the thermocouple strips 162 are parallel to the bevel etched hole 15, the cold end 160 of the thermopile 16 is located on the substrate 1, and the hot end 161 is parallel to the heating element 17; Fig.15 As shown, the thermopile 16 is arranged in series along the vertical direction Y with a plurality of thermocouple bars 162 in the horizontal direction X. The cold end 160 of the thermopile 16 is located on the substrate 1 , and the hot end 161 is adjacent to the bevel corrosion hole 15 .

[0099] The thermopile 16 can be selected from at least one of the above three types according to actual needs. When the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with one oblique edge corrosion hole 15, as shown in FIG. Fig. 9 As shown, the four thermopiles 16 can all be used as Fig.12 The thermopile type shown; Fig.16 As shown, the four thermopiles 16 may also be used as Fig.13 The thermopile type shown; Fig.17 and Fig.18 As shown, the four thermopiles 16 may also be Fig.12 and Fig.13 When the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with two oblique-edge corrosion holes 15, as Fig.19 As shown, the six thermopiles can be used as follows Fig.12 and Fig.14 The thermopile type shown; Fig. 20 As shown, the six thermopiles 16 may also be Fig.12 and Fig.15 Combination of two thermopile types, such as Fig.21 As shown, the six thermopiles 16 may also be Fig.13 and Fig.15 Combination of two thermopile types. It can also be a combination of other thermopile types, which is actually set according to different shapes of the sub-thin film portion 123, and is not excessively limited here.

[0100] The material of the thermocouple strip 162 in the thermopile 16 can be selected from conventional materials suitable for use as thermocouples, such as a common polysilicon-metal combination with a large difference in Seebeck coefficients. The polysilicon can be selected as P-type doped or N-type doped polysilicon, or a P-type doped polysilicon-N-type doped polysilicon combination. The P-type doped ions can be P-type ions such as boron ions, and the N-type doped ions can be N-type ions such as phosphorus ions. The metal can be selected as aluminum metal or other metals. When the combination of the thermocouple strip 162 is selected as a polysilicon-metal combination, the heating element 17 can also be selected as a heating element of polysilicon material, and the polysilicon can be selected as P-type doped or N-type doped polysilicon. In this preparation process, the polysilicon thermocouple strip 162 and the heating element 17 can be prepared at the same time, that is, the same doping elements, dosage, concentration and other parameters are used, and annealing and etching are performed simultaneously to make them have electrical properties. Of course, doping under different conditions can also be performed in batches according to the actual design.

[0101] The two thermocouple strips 162 in the thermopile 16 can be arranged in a conventional manner, for example, vertically stacked along the thickness direction of the (100) plane of the substrate 1, as shown in FIG. Figures 12 to 15 As shown, the two thermocouple strips 162 are connected via VIA, or are laid flat along the (100) surface of the substrate 1, that is, arranged in the same plane, but other methods may also be used, which are selected according to actual needs.

[0102] Embodiment 2

[0103] This embodiment provides a method for preparing a MEMS thermal flow sensor, which can be used to prepare the above-mentioned MEMS thermal flow sensor, but the preparation method of the above-mentioned MEMS thermal flow sensor is not limited thereto, and other feasible preparation methods can also be used to prepare the above-mentioned MEMS thermal flow sensor.

[0104] The preparation method of this embodiment is described in detail below in conjunction with the specific drawings. It should be noted here that the preparation method of this embodiment is mainly for Fig. 9 The structure of the MEMS thermal flow sensor is described, wherein the two thermocouple strips in the thermopile in a combined form adopt a polysilicon-metal combination with a large difference in Seebeck coefficients, and are arranged in a vertically stacked manner along the thickness direction.

[0105] like Fig. 22 As shown, firstly, step S1 is performed to select a (100)-surface single crystal silicon wafer as the substrate 1 , and to sequentially form a first insulating layer 22 and a second insulating layer 23 on the surface of the substrate 1 .

[0106] The first insulating layer 22 is a silicon oxide film formed by a thermal oxidation process, and the second insulating layer 23 is a silicon nitride film formed by a LPCVD process. The first insulating layer 22 and the second insulating layer 23 serve as a supporting film structure of the device.

[0107] like Fig.23 As shown, step S2 is then performed to deposit polysilicon on the supporting membrane structure and perform P-type ion implantation, such as B ion implantation, and anneal to repair lattice damage to obtain a P-type ion-doped polysilicon layer 24.

[0108] Of course, N-type ion implantation, such as phosphorus ion implantation, can also be performed, and annealing can be performed to repair lattice damage to obtain N-type ion-doped polysilicon layer 24. In addition, in order to reduce contact resistance and make it easier to form ohmic contact later, secondary heavy doping can be performed at the place that needs to be connected to the metal later to form a heavy doped area.

[0109] like Fig.24 As shown, step S3 is then performed to pattern the polysilicon layer 24 using photolithography and etching processes to obtain the polysilicon thermocouple strip 163 and the heating element 17 .

[0110] like Fig.25 As shown, step S4 is then performed, using a third insulating layer 25, such as a silicon oxide insulating layer, to fill the patterned polysilicon layer 24 and cover the polysilicon layer 24 with a preset thickness, and then forming an ohmic contact hole 26 penetrating the third insulating layer 25 at a preset position of the third insulating layer 25. Here, the ohmic contact hole 26 is formed at the cold end and the hot end to achieve subsequent electrical connection with the metal thermocouple bar 164.

[0111] like Fig.25 As shown, step S5 is then performed to form a metal layer 27 on the third insulating layer 25 and the metal layer 27 fills the ohmic contact hole 26, such as an aluminum metal layer, and then the metal layer 27 is patterned to obtain structures such as the metal thermocouple bar 164, the metal wire 19, the heat sink 18 and the lead pad 21, and ohmic contact annealing is performed to form an ohmic contact between the polysilicon thermocouple bar 163 and the metal thermocouple bar 164.

[0112] like Fig.26 As shown, step S6 is then performed to form a passivation layer 28 on the surface of the above structure to protect the entire structure. The passivation layer 28 can be a stacked structure of silicon oxide and silicon nitride, and the lead pad 21 is exposed in turn, and the vertical etching hole 14 and the bevel etching hole 15 are prepared.

[0113] like Fig. 27 and Fig.28As shown, step S7 is finally performed, using an alkaline etching solution, such as TMAH, KOH, etc., and etching the substrate 1 based on the vertical etching hole 14 and the oblique etching hole 15 to obtain a heat-insulating cavity 13; then the first insulating layer 22 and the second insulating layer 23 on the back of the device are removed. Finally, a MEMS thermal flow sensor is obtained.

[0114] In summary, the present invention provides a MEMS thermal flow sensor, by setting <100> The beveled etching holes extending in the crystal direction combined with the vertical etching holes can effectively release the thermal insulation film. Generally, when releasing the thermal insulation film, the substrate needs to be deeply etched. When etching the substrate, the closer to the center, the smaller the etching rate, so there will be a hill-like structure in the center. The beveled etching holes are set in the thermal insulation film area. Since their direction is along the substrate, <100> In the crystal direction, when an alkaline solution is used for etching, the etching rate of the crystal plane of the substrate (100) is much greater than the etching rate of the crystal plane of the substrate (111), so the beveled etching hole can be completely etched downward along the thickness direction of the substrate to remove the substrate, thereby improving the hill-like structure at the center of the thermal insulation film, improving the conformality of the thermal insulation cavity, reducing the heat loss in the direction of the substrate, and improving the measurement accuracy. The vertical etching hole can also hinder the heat transfer to the substrate in the horizontal direction, reducing the heat loss and further improving the measurement accuracy; at the same time, the beveled etching hole can hinder the lateral conduction of temperature, so that the multiple sub-film parts obtained by dividing it can be in different temperature fields, and because the distance between the hot end of the thermopile and the heating element is different, the sensitivity to different range flow is different, so that different range test requirements can be achieved through the different distances between the hot end of the thermopile and the heating element in different sub-film parts, and multi-range measurement can be achieved. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0115] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A MEMS thermal flow sensor, characterized in that: The MEMS thermal flow sensor comprises: (100) a single crystal silicon substrate having a groove, wherein the groove is opened on the upper surface of the substrate; A heat-insulating film, covering the groove and connected to the substrate, wherein the heat-insulating film and the substrate together form a heat-insulating cavity; At least two vertical corrosion holes penetrating the thermal insulation film and extending in the vertical direction, all of the vertical corrosion holes are arranged in sequence in the horizontal direction and divide the thermal insulation film into three regions: an upstream film portion, a central film portion, and a downstream film portion, wherein the upstream film portion and the downstream film portion have the same size and are symmetrical about the central film portion; The upstream thin film portion and the downstream thin film portion are respectively penetrated and along the substrate <100> A beveled etching hole extending in the crystal direction, wherein the beveled etching hole arranged in the upstream thin film portion is arranged mirror-symmetrically or 180° rotationally symmetrically with the beveled etching hole arranged in the downstream thin film portion, and the beveled etching hole divides the thin film portion where it is located into a plurality of sub-thin film portions; A plurality of thermopiles are arranged on the sub-thin film portion, and all the thermopiles arranged on the sub-thin film portion of the upstream thin film portion are connected in series, and all the thermopiles arranged on the sub-thin film portion of the downstream thin film portion are connected in series; A heating element is disposed on the central film portion and extends in a vertical direction; Wherein, the horizontal direction is the <110> crystal direction, the vertical direction is the Crystal direction.

2. The MEMS thermal flow sensor according to claim 1, characterized in that: The upstream thin film portion and the downstream thin film portion are each provided with one beveled edge corrosion hole or two beveled edge corrosion holes, and when the upstream thin film portion and the downstream thin film portion are each provided with two beveled edge corrosion holes, the two beveled edge corrosion holes are vertically arranged or parallel arranged.

3. The MEMS thermal flow sensor according to claim 1, characterized in that: It also includes a heating element metal wire and a thermopile series metal wire, and both of them pass through the central film portion on both sides of the heating element in a vertical direction.

4. The MEMS thermal flow sensor according to claim 1, characterized in that: It also includes a radiator, which is arranged above the heating element and is used to dissipate heat from the heating element.

5. The MEMS thermal flow sensor according to claim 4, characterized in that: The heat sink is a sheet of metal, or the heat sink is composed of a plurality of horizontal metal strips arranged in a vertical direction, or the heat sink is composed of a plurality of inclined metal strips arranged in a vertical direction.

6. The MEMS thermal flow sensor according to claim 1, characterized in that: The cold end of the thermopile is located on the substrate, so that the cold end of the thermopile is in full contact with the substrate.

7. The MEMS thermal flow sensor according to claim 1, characterized in that: It also includes a temperature-sensitive resistor, which is arranged on the outside of at least one cold end of the thermopile.

8. The MEMS thermal flow sensor according to claim 1, characterized in that: The thermopile is configured to be at least one of the following three types: In the first type, the thermopile is composed of a plurality of vertical thermocouple strips arranged in series in a horizontal direction, the cold end of the thermopile is located on the substrate, and the hot end is adjacent to the bevel etched hole; In the second form, the thermopile is arranged in series with a plurality of thermocouple strips in a horizontal direction, the thermocouple strips are parallel to the beveled etched holes, the cold end of the thermopile is located on the substrate, and the hot end is parallel to the heating element; In the third type, the thermopile is arranged in series in a vertical direction with a plurality of horizontal thermocouple strips, the cold end of the thermopile is located on the substrate, and the hot end is adjacent to the bevel corrosion hole; all the thermopiles are arranged in at least one of the three types.

9. The MEMS thermal flow sensor according to claim 1 or 8, characterized in that: The thermocouple strips in the thermopile are a combination of any two of P-type doped polysilicon thermocouple strips, N-type doped polysilicon thermocouple strips and metal thermocouple strips.

10. The MEMS thermal flow sensor according to claim 9, characterized in that: The thermocouple strips in the thermopile in a combined form are vertically stacked along the thickness direction of the (100) plane of the substrate or are laid flat along the (100) plane of the substrate.

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