Glass substrate micro hot plate and preparation method thereof

Abstract

The invention discloses a micro hot plate with a glass substrate. The micro hot plate comprises the glass substrate; the heating electrode layer is adhered to the surface of the glass substrate through an adhesion layer; the insulating layer covers the surface of the electrode layer; wherein heat insulation holes are formed in the surface of the glass substrate; a cavity is formed in the back surface of the glass substrate; the cavity keeps the thickness of the substrate to be 5-100 [mu] m, the diameter of the cavity in the horizontal direction is 300-2000 [mu] m, and the depth of the cavity in the vertical direction is 200-600 [mu] m.

Description

Technical Field

[0001] This application relates to the technical field of micro hotplates, and particularly to a glass substrate micro hotplate and a preparation method thereof. Background Art

[0002] A micro hotplate (MHP) is a commonly used heating component in microelectromechanical systems (MEMS), and is widely applied to micro-devices such as micro gas sensors, micro thermal flow meters, micro infrared detectors, and barometers. The micro hotplate is an essential core component for the above micro-devices, especially for types such as catalytic combustion type, semiconductor type, and thermal conductivity type. As a miniaturized platform for carrying gas-sensitive materials, providing reaction heat sources, and measuring gas-sensitive effects, the micro hotplate not only brings the possibility of miniaturization to gas sensors, but also determines the performance (including power consumption, sensitivity, response time, temperature range, mechanical strength, etc.), volume, and cost of these gas sensors.

[0003] Generally, a single crystal silicon is used as the substrate material for the micro hotplate. Structurally, it includes a silicon substrate, a silicon oxide or silicon nitride thin film layer, a heating electrode layer, a dielectric layer, a measuring electrode layer, and a back cavity. Among them, the silicon substrate is the main body material of the component. On the silicon substrate, a layer of silicon oxide or silicon nitride thin film is formed through oxidation or nitridation treatment for insulation, heat insulation, and supporting the micro hotplate and the sensitive materials on the micro hotplate. On the silicon oxide or silicon nitride thin film, a heating electrode layer is formed by physical vapor deposition technology, and on this basis, a layer of silicon oxide or silicon nitride thin film is continuously deposited by low-pressure chemical vapor deposition technology as a dielectric layer for insulation. A measuring electrode layer is continuously deposited on the dielectric layer.

[0004] Due to the material property of the high thermal conductivity of the silicon substrate in the current micro hotplate structure, it is necessary to completely etch away the silicon on the back of the silicon substrate to form a back cavity to suspend the entire micro hotplate structure. This results in low structural strength of this typical structure, and at the same time, the thermal stability of this structure is insufficient, and it is easy to deform or even break at high temperatures. To alleviate the problem of high-temperature deformation, some micro hotplates make the single-layer structure of the silicon oxide or silicon nitride thin film layer into a double-layer or multi-layer structure. Although this improves the mechanical stability at high temperatures, it increases the thickness of the thin film, and since the thermal conductivity of the silicon nitride material is relatively higher than that of silicon oxide, it instead increases the power consumption of the micro hotplate; moreover, due to its multi-layer structure, it increases the complexity of the process and reduces the processing efficiency; in addition, when making the multi-layer structure of the thin film layer, it is necessary to adjust the composition of each layer of material to achieve the purpose of thermal expansion matching, which further increases the development difficulty, development cost, and processing difficulty. Summary of the Invention

[0005] In order to solve the above problems existing in the art, this application aims to provide a glass substrate micro hotplate and a preparation method thereof.

[0006] According to one aspect of the present application, there is provided a glass substrate microhotplate, comprising:

[0007] A glass substrate;

[0008] A heating electrode layer adhered to the first surface of the glass substrate through a first adhesion layer;

[0009] An insulating layer covering the surface of the heating electrode layer;

[0010] Wherein, heat insulation holes are provided on the first surface of the glass substrate;

[0011] A cavity is provided on the second surface of the glass substrate;

[0012] The distance from the top of the cavity to the second surface is 5 - 100 μm, the diameter of the cavity in the horizontal direction is 300 - 2000 μm, and the depth of the cavity in the vertical direction is 200 - 600 μm.

[0013] According to some embodiments of the present application, the width of the heat insulation holes is 5 - 200 μm.

[0014] According to some embodiments of the present application, metal pads with leads are provided at both ends of the heating electrode layer.

[0015] According to some embodiments of the present application, the insulating layer material is selected from silicon oxide or silicon nitride.

[0016] According to some embodiments of the present application, the glass substrate material includes: fused quartz or borated glass.

[0017] According to another aspect of the present application, there is provided a method for preparing the above glass substrate microhotplate, comprising:

[0018] Performing photolithography on the first surface of the glass substrate, and then depositing a first adhesion layer;

[0019] Continuing to deposit a heating electrode layer on the surface of the first adhesion layer;

[0020] Covering an insulating layer on the surface of the heating electrode by chemical vapor deposition;

[0021] Etching a cavity on the second surface of the glass substrate;

[0022] Etching heat insulation holes on the second surface of the glass substrate.

[0023] Compared with the prior art, the present application at least includes the following beneficial effects:

[0024] This application provides a glass substrate micro-hotplate, which uses a glass substrate with low thermal conductivity, high insulation, and high strength. By taking advantage of the fact that the thermal conductivity of the glass substrate material is much lower than that of single-crystalline silicon, the fragile suspended thin-film structure that is necessary for traditional silicon substrate micro-hotplates to reduce heat dissipation can be avoided. At the same time, the non-conductive property of the glass substrate is utilized to eliminate the insulating layer under the metal heating electrodes of traditional silicon substrate micro-hotplates, reducing the number of thin film layers of the device.

[0025] For the glass substrate micro-hotplate of this application, a part of the etching and hollowing (manufacturing a back cavity) is performed from the back of the substrate, and heat insulation holes are set at the same time, so that the heat capacity and heat conduction efficiency of the substrate are greatly reduced, thereby greatly reducing the power consumption. At the same time, for the micro-hotplate of this application, it is not necessary to completely etch through the substrate, and a part of the substrate can be retained to ensure the strength of the device; this application can adjust the thickness of the micro-hotplate according to different temperature, power consumption, and mechanical strength requirements. For traditional silicon substrate micro-hotplates, whether silicon-based thin films are directly grown on the substrate or other non-silicon-based thin film materials, such as ceramics, etc., are deposited, the core heating area can only completely etch away the substrate under the heating area, making the thin film suspended to form an adiabatic structure, resulting in very low strength. Brief Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of the glass substrate micro-hotplate of the exemplary embodiment of this application;

[0027] Figure 2 It is a schematic diagram of the process flow plan of the exemplary embodiment of this application;

[0028] Figure 3 It is a schematic structural diagram of the process flow of the exemplary embodiment of this application;

[0029] Figure 4 It is a sample of the heat insulation hole of the glass substrate micro-hotplate of this application;

[0030] Figure 5 It is a schematic structural diagram of the micro-hotplate of Comparative Example 1 of this application;

[0031] Figure 6 It is a schematic structural diagram of the silicon substrate micro-hotplate of Comparative Example 2 of this application;

[0032] Figure 7 It is a schematic structural diagram of the silicon substrate micro-hotplate of Comparative Example 3 of this application;

[0033] Figure 8 It is a schematic structural diagram of the glass substrate micro-hotplate without heat insulation holes of Comparative Example 4 of this application;

[0034] Figure 9 It is a schematic diagram of the width of the heat insulation hole of the glass substrate micro-hotplate of this application;

[0035] Figure 10 This is the graph showing the relationship between the power of the glass substrate micro-hotplate of the present application and the width of the heat insulation holes;

[0036] Figure 11 This is the graph showing the relationship between the power of the glass substrate micro-hotplate of the present application and the diameter of the cavity. Detailed implementation manners

[0037] Next, the technical solutions of the present application will be clearly and completely described in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present application.

[0038] It should be particularly noted that similar replacements and modifications made to the present application are obvious to those skilled in the art, and they are all regarded as included in the present application. Relevant personnel can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present application to implement and apply the technology of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0039] Unless otherwise specified in the present application, all are carried out according to conventional conditions or conditions recommended by the manufacturer. For the raw materials or excipients used, and for the reagents or instruments used without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0040] The following is a detailed description of the present application.

[0041] The current micro-hotplate structure has the following problems:

[0042] Low structural strength. The high thermal conductivity of silicon has led to the common structure of current silicon-based micro-hotplates, that is, the suspended thin film structure, that is, the silicon substrate is etched away by wet etching or other processes on the back of the silicon substrate on which a silicon nitride or silicon dioxide thin film has been grown or deposited, leaving only the above-mentioned grown or deposited silicon oxide or silicon nitride thin film. The thickness of this thin film is usually only 1μm. Such a thin structure makes it extremely easy for the thin film structure to be damaged under pressure during the process of transferring gas-sensitive materials in the subsequent processing of gas sensors; when the device is vibrating or impacted during operation, the fixed support beam structure formed by this thin film and the gas-sensitive material will output the vibration-coupled strain signal to form noise interference, and it is easier to damage the thin film structure. The quartz glass substrate has higher strength, and because it has a lower thermal conductivity compared with silicon materials, this allows the suspended thin film to be made thicker, and has a higher design freedom in the trade-off between power consumption and mechanical structure.

[0043] High temperature instability. The silicon oxide and silicon nitride film of the silicon-based electrode has poor heat resistance due to its thin film and small grain size. And the film will obviously have a mismatch in thermal expansion coefficient at high temperature, which will lead to an increase in film stress when working at high temperature. This situation is more obvious when there are more film layers, and adjusting the thermal expansion coordination of multi-layer film materials is a method that will reduce the yield and increase the cost. Therefore, it is difficult for silicon-based thin film micro-hotplates to work under high temperature conditions for a long time, but many practical examples of micro-hotplates require that they can work under a temperature of 400°C, such as methane gas detection, which causes the multi-layer silicon-based film of the micro-hotplate to collapse and burn out at high temperature, so the high temperature stability is poor. This application uses a fused quartz glass substrate with low thermal conductivity and high insulation, deliberately avoiding the fragile suspended film structure of the traditional silicon-based micro-hotplate for reducing heat dissipation; secondly, because the suspended structure of the glass quartz substrate is originally a part of the substrate, this means that the thermal expansion coefficient of the suspended structure and the substrate are consistent, so it is difficult to produce the stress increase caused by the mismatch of thermal expansion coefficients that the above-mentioned silicon-based micro-hotplate will produce under high temperature conditions.

[0044] There are many process steps. In order to meet the requirements of thermal insulation, mechanical strength of the structure and thermal stability at high temperatures, silicon-based micro-hotplates need to undergo multiple photolithography, oxidation and nitridation growth, chemical vapor deposition, physical vapor deposition, etching and release processes, which results in a whole set of process loads for gas sensors based on micro-hotplates, increases the risk of device processing failure, and also increases the production R&D cycle, risk and cost. The use of quartz glass substrates takes advantage of the non-conductive properties of quartz glass substrates, eliminates the insulating layer under the metal electrode of traditional silicon-based micro-hotplates, and reduces the number of thin film layers of the device.

[0045] In order to solve the above technical problems existing in the art, the present application provides a glass substrate micro-hotplate and a preparation method thereof.

[0046] Take the quartz glass substrate micro hotplate as an example: it includes three parts: substrate design, structural design and process design of the quartz glass substrate micro hotplate.

[0047] The substrate design is mainly the choice of substrate material, and a glass substrate is used as a substitute for a silicon substrate. Since glass substrates generally have low thermal conductivity, insulation, and high temperature resistance, this application does not have strict restrictions on the specific composition of the glass substrate. A fused quartz glass substrate or other glass materials such as boronized glass can be used. However, it should be noted that the use of glass substrates to prepare the micro-hotplate described in this patent should be covered by this patent.

[0048] According to some embodiments of the present application, fused silica glass is used as the substrate. The strength of the material itself is comparable to that of the silicon substrate, meeting the requirements of the MEMS process and devices for the substrate strength, while the thermal conductivity is two orders of magnitude lower than that of silicon. Generally, the thermal conductivity of silicon is 149 W / (m·K), and that of fused silica glass is 0.55 W / (m·K). Using a fused silica glass substrate can effectively reduce the heat conduction of the device to the environment and thus reduce the power consumption of the device; and it is non-conductive, has good insulation, and there is no need to additionally add an insulating layer under the metal electrode. At the same time, the fused silica glass substrate is compatible with the standard MEMS surface process for patterning metal electrodes. Generally, to ensure the yield of microfabrication, the thickness of the commonly used fused silica glass substrate is 200 - 700 μm. In addition, to reduce the power consumption of the micro-hotplate, heat-insulating holes are made in the remaining part of the micro-hotplate substrate, reducing the heat loss channels and the heat loss.

[0049] The basic structure of the fused silica glass substrate micro-hotplate of the present application is as Figure 1 shown.

[0050] Among them, (11) is the fused silica glass substrate, and (12) and (13) together form the metal electrode for heating. Among them, (12) is the adhesion layer and (13) is the main body layer. The method used is evaporation or sputtering to pattern the pattern of the heating electrode on the upper surface of the (11) fused silica glass substrate in sequence. There are metal pads with leads at both ends of each electrode.

[0051] (14) is the insulating layer covering the heating electrode. The material thereof can be silicon oxide, silicon nitride, and the processing method can be chemical vapor deposition, physical vapor deposition. Generally, the electrode thickness is in the order of hundreds of nanometers to ensure covering the heating electrode layer to achieve the insulating effect.

[0052] The fused silica glass substrate micro-hotplate of the present application may further include a metal electrode for detection, which includes an adhesion layer and a main body layer. The method used is evaporation or sputtering to pattern the pattern of the heating electrode on the upper surface of the insulating layer in sequence. There are metal pads with leads at both ends of each electrode.

[0053] The back surface of the fused silica glass substrate of the present application is microfabricated to significantly reduce the heat capacity and reduce the heat conduction efficiency. The method for reducing the heat capacity and preventing heat conduction is to etch a cavity on the back surface of the substrate and under the projection of the heating electrode, and continue to etch the remaining part of the quartz substrate with the cavity formed to form heat-insulating grooves or even holes.

[0054] Among them, the method of etching the cavity can be wet etching, sandblasting etching, laser etching, etc. The cavity part formed by etching away the substrate is (15). The method of etching the groove and hole can be laser etching, and the etched part of the groove or hole is (16). It should be noted that the cavity (15) is characterized in that it is not necessary to completely etch away the entire substrate, but a part of the thickness can be retained (the etched and retained thickness can be determined according to the power consumption requirements of the device. Usually, the retained thickness is 5 - 100 μm, that is, the metal electrode above the cavity of the present application together with the remaining etched substrate material does not have to form a completely suspended thin film structure (a thin film usually refers to a planar structure with a thickness of less than 10 μm). This is entirely because the quartz glass substrate has a thermal conductivity two orders of magnitude lower than that of the silicon substrate. However, this does not mean that the quartz glass substrate can only be used to fabricate a relatively thick suspended structure. According to requirements such as temperature and power consumption, the cavity can also be made deeper to form a suspended thin film structure of the substrate. The diameter and depth of the cavity (15) in the present application are in the order of hundreds of micrometers. Usually, the diameter in the horizontal direction is 300 to 2000 micrometers, and the depth in the vertical direction is 200 to 600 micrometers. As Figure 11 shown, it is a graph showing the relationship between the power of the glass substrate micro - hotplate of the present application and the cavity diameter.

[0055] Similar to conventional micro - processing, on one glass substrate wafer, multiple micro - hotplate units can be fabricated, and after dicing, multiple micro - hotplates are formed. The dimensional parameters between these units can be exactly the same or different. The pattern of the electrodes within the unit can be designed according to actual needs and has no direct relationship with the above - mentioned structure.

[0056] The glass substrate micro - hotplate processing technology of the present application only needs to achieve two purposes: one is to pattern and deposit metal electrodes and insulating layers on the front side of the substrate; the other is to reduce the heat capacity of the quartz substrate. Therefore, the process generally includes three core steps:

[0057] The first step is to lithograph and deposit the adhesion layer of the metal electrode, and the typical material is titanium.

[0058] The second step is to deposit the main layer of the metal electrode, and the generally selected materials are platinum and tungsten.

[0059] The third step is to process the cavity and heat - insulating holes on the back side of the substrate, so as to reduce the heat capacity and hinder the heat conduction. Specifically, the method of laser etching is used to process cavities, grooves or holes on the back side of the substrate.

[0060] The schematic diagram of the heat - insulating holes of the glass substrate micro - hotplate of the present application is as Figure 9 shown. Assuming the width of the heat - insulating hole is D, the required power when heated to the same temperature is as Figure 10As shown. It can be seen that the heat insulation holes play an obvious role in reducing power consumption, and their width is 5 - 200 μm. In different implementation cases, there can be different specific processes for the above overall process, and the sequence of steps can be adjusted according to actual processing conditions. For example, back etching can be done first, and then electrode patterning deposition on the front side. Similarly, in different implementation cases, the design of the processed microhotplate can be adjusted according to requirements such as mechanical strength, temperature, power consumption, and working scenarios. For example, in the application of this microhotplate in a gas sensor, the heating electrode and the measuring electrode can be deposited on the same plane. In this case, the electrodes can use the same electrode resistance to achieve measurement and heating functions according to different requirements, or two or more electrode resistances can be used; another example is that multiple heating / measuring structures can be designed in the same microhotplate device to achieve the purpose of measuring multiple gases with one device. In addition, during the process of obtaining a usable microhotplate, necessary conventional process steps such as annealing, dicing, and packaging are also required. Annealing can be high-temperature heating annealing or electrification aging annealing, which are not the key points protected by this patent.

[0061] Compared with various commercially available or publicly reported silicon-based microhotplates, the devices and methods of this application mainly have four advantages.

[0062] First, the mechanical strength of the device is higher. This application utilizes the low thermal conductivity of the substrate material, enabling the device to reduce its dependence on the suspended thin-film heat insulation structure. Only partial etching of the back side of the substrate and heat insulation hole treatment are required to achieve low power consumption. There is no separate thin-film structure in the finished device, and mechanical structure collapse will not occur during the transfer of gas-sensitive materials, device vibration, and impact, resulting in device failure and damage.

[0063] Second, the high-temperature performance of the device is better. The core heating area of this application is only composed of high-temperature-resistant quartz glass material and metal electrodes with an adhesion layer and also high-temperature-resistant. It will not burn or collapse during high-temperature operation, has thermal shock resistance, and avoids the high-temperature failure problem caused by the mismatch of thermal parameters between layers in the multi-layer thin films in the heating area of traditional silicon microhotplates.

[0064] Third, the processing technology is simpler. This application only needs to process metal electrodes and insulating layers on the front side of the substrate and remove some materials on the back side. Therefore, if the designs of the two microhotplates are the same, once a quartz glass substrate is selected, compared with the usual silicon-based microhotplates, at least the process steps of depositing thin-film layers will be reduced anyway. Therefore, this application reduces process steps and difficulty, making the processing and production process simple, with low cost, short cycle, and low risk.

[0065] Fourth, the power consumption is lower. On the one hand, the present application utilizes the low thermal conductivity and high mechanical strength of the base material to etch the back of the base to form a cavity, reducing the heat dissipation path of the micro-hotplate, decreasing the heat loss rate of the micro-hotplate, and reducing the power consumption of the micro-hotplate. On the other hand, after etching to form a cavity, the present application designs heat insulation holes in the remaining base part, further reducing the heat loss of the micro-hotplate and reducing the power consumption of the micro-hotplate.

[0066] In addition, the method of the present application is compatible with the main MEMS surface processes and bulk processes in the current industry, and the processing and preparation conditions are relatively easy to obtain, reducing the processing threshold of the micro-hotplate.

[0067] Example 1

[0068] For the glass substrate micro-hotplate of the present application, its process flow chart is as Figure 3 shown, and the preparation steps are as follows:

[0069] ① Prepare a quartz glass sheet with a thickness of 500 μm as the substrate, clean it, and spin-coat photoresist on the front of the substrate.

[0070] ② Use photolithography technology to pattern the photoresist, and its pattern is the heating electrode pattern to be processed.

[0071] ③ Use sputtering or evaporation technology to deposit Ti as an adhesion layer with a thickness of 20 nm with the photoresist as a mask; deposit Pt as the main layer of the heating electrode with a thickness of 150 nm.

[0072] ④ Remove the photoresist, leaving the patterned heating electrode made of Pt / Ti. The method of removing the glue is to soak it in acetone and ultrasonicate it. After replacing acetone with isopropanol multiple times, rinse it with a large amount of deionized water and dry it with nitrogen.

[0073] ⑤ Use methods such as PECVD or LPCVD to deposit a silicon oxide insulating layer on the front with a thickness of 600

[0074] nm. Subsequently, spin-coat photoresist on the silicon oxide, use RIE technology to dry-etch the exposed silicon oxide not covered by the photoresist, and then use the method of first dry-etching and then wet-etching (acetone) to remove the photoresist mask, leaving the silicon oxide insulating layer covering the heating area, and the size of the heating area is 500 μm × 500 μm.

[0075] ⑥ Use laser processing method to make the back cavity of the micro-hotplate, and finally make the etching depth of the back cavity reach 495 μm, leaving 5 μm thickness as the support structure. The opening size of its back cavity is 2 mm × 2

[0076] mm. Use laser processing technology to process heat insulation holes on the back of the support layer, and the etching depth is 5 μm to penetrate the support layer immediately. The pattern of its holes is as Figure 4As shown in Sample 1, the trapezoidal hole has a height of 50 μm, an upper base size of 460 μm, and a lower base size of 560 μm.

[0077] Example 2

[0078] The glass substrate micro-hotplate of the present application is prepared in substantially the same manner as in Example 1, with the differences as follows:

[0079] The back cavity of the micro-hotplate is fabricated using a laser processing method, and finally the back cavity reaches an etching depth of 490 μm, leaving a 10-μm thickness as a support structure. The opening size of the back cavity is 2 mm × 2 mm. The heat-insulating holes are processed on the back of the support layer using a laser processing technique, and the etching depth is 10 μm to penetrate the support layer immediately. The pattern of the holes is as Figure 4 shown in Sample 1, the trapezoidal hole has a height of 100 μm, an upper base size of 460 μm, and a lower base size of 660 μm.

[0080] Example 3

[0081] The glass substrate micro-hotplate of the present application is prepared in substantially the same manner as in Example 1, with the differences as follows:

[0082] The substrate material is a borated glass substrate.

[0083] The back cavity of the micro-hotplate is fabricated using a laser processing method, and finally the back cavity reaches an etching depth of 495 μm, leaving a 5-μm thickness as a support layer. The opening size of the back cavity is 2 mm × 2 mm. The heat-insulating holes are processed on the back of the support layer using a laser processing technique, and the etching depth is 5 μm to penetrate the support layer immediately. The pattern of the holes is as Figure 4 shown in Sample 2, the a parameter of the elliptical hole is 250 μm, and the b parameter is 50 μm.

[0084] Example 4

[0085] The glass substrate micro-hotplate of the present application is prepared in substantially the same manner as in Example 1, with the differences as follows:

[0086] The substrate material is a borated glass substrate.

[0087] The back cavity of the micro-hotplate is fabricated using a laser processing method, and finally the back cavity reaches an etching depth of 475 μm, leaving a 25-μm thickness as a support layer. The opening size of the back cavity is 2 mm × 2 mm. The heat-insulating holes are processed on the back of the support layer using a laser processing technique, and the etching depth is 25 μm to penetrate the support layer immediately. The pattern of the holes is as Figure 4 shown in Sample 1, and the width of the heat-insulating hole is 100 μm.

[0088] Comparative Example 1

[0089] A glass substrate micro-hotplate prepared by a certain prior art, the structure of the micro-hotplate is as Figure 5 shown, and the preparation method includes:

[0090] A 6-inch fused silica wafer with a thickness of 500 microns is used as the substrate, and a photoresist is coated on the surface of the quartz glass substrate; the photoresist is exposed and patterned;

[0091] The adhesion layer is sputtered, and the adhesion layer is a titanium metal layer with a thickness of 50 nanometers.

[0092] The electrode layer is sputtered, and the electrode layer is a platinum metal layer with a thickness of 400 nanometers.

[0093] Lift-off is performed to obtain the patterned first electrode unit and second electrode unit;

[0094] A photoresist is coated and patterned on the side of the quartz glass substrate facing away from the adhesion layer;

[0095] An isotropic wet etching is performed on the quartz glass substrate using a mixed solution of hydrofluoric acid and hydrochloric acid as the etching solution to obtain a cavity with a depth of 580 microns.

[0096] Comparative Example 2

[0097] A typical silicon substrate micro-hotplate, as Figure 6 shown.

[0098] Its structure: 61 is the silicon substrate, 62 is the deposited thin film whose function is insulation and support, 63 is the micro-hotplate heating electrode, 64 is the insulating layer, and 65 is the back cavity. The first feature is that the thin film 62 is deposited on the front surface of the silicon substrate, and the second feature is that the silicon substrate is etched clean (until the thin film 62) to fabricate the back cavity 65.

[0099] Comparative Example 3

[0100] A silicon substrate micro-hotplate, as Figure 7 shown.

[0101] The feature of this case is that the back cavity is fabricated on the front surface of the substrate, and its processing method is the conventional wet method commonly used in the art. However, its process is highly complex. After depositing multiple layers of thin films, windows are opened for wet etching to form a cavity as shown in Figure 7 75.

[0102] Comparative Example 4

[0103] The glass substrate micro-hotplate of this application is prepared in substantially the same manner as in Example 1, except that: no etching heat insulation holes are made.

[0104] Experimental Example

[0105] The temperature of the micro - hotplate under different heating voltages is measured by using the method for measuring surface infrared emissivity. The specific measurement method is as follows: Under room temperature and dry conditions, heating voltages from 0V to 15V (with a voltage increase gradient of 0.5V) are sequentially applied to the heating electrodes of the 3D quartz - glass - substrate MEMS micro - hotplate with a substrate thickness of 500μm until 500°C. After continuously working at each working point for at least 5 minutes until the surface temperature of the micro - hotplate stabilizes, an external infrared thermal imager (German inferatech infrared thermal imager, VCHD head880) is used to measure and record the heating voltage, current, and the average surface temperature of the heating target area of the micro - hotplate after temperature stabilization, and forward and reverse cyclic voltage - temperature curves are obtained. During the measurement, the surface emissivity settings of the infrared thermal imager all adopt the measured values. The test results are as follows in the table:

[0106] Power consumption (mW) Example 1 23.1 Example 2 25.5 Example 3 23.5 Example 4 30.1 Comparative Example 1 90.5 Comparative Example 2 35.9 Comparative Example 3 37.9 Comparative Example 4 33.3

[0107] According to the above comparison, the micro - hotplate structure disclosed in this application is as Figure 1 shown. Its cavity is close to a cuboid. Obviously, the thickness of the support layer area will be relatively uniform. The part of the back cavity close to the front of the substrate can be regarded as a plane, and the remaining support structure of the processed back cavity can be thinner than the "dome" - shaped back cavity, which is more conducive to reducing the power of the micro - hotplate. In addition, heat - insulating holes are designed in the heating area, using air as a heat barrier, reducing the heat - loss path, which is beneficial to reducing the power of the micro - hotplate. The power of Comparative Example 4 without heat - insulating holes is significantly higher than that of the micro - hotplate with heat - insulating holes in this application.

[0108] For the micro - hotplate in Comparative Example 1, its back cavity is close to a hemispherical shape, and the structure close to the front of the substrate is an arc surface. This leads to a problem that it is difficult to make the substrate support structure thin, and the support structure becomes thicker as it is farther from the center. The thickening of the support structure directly leads to an increase in heat loss, making it difficult to reduce the power of the micro - hotplate further.

[0109] In Comparative Example 2, the method of etching the back cavity is generally divided into two types: wet etching and dry etching. The side of the back cavity made by wet etching will form an inclined angle with the bottom surface, which directly limits the area of the upper bottom surface of the back cavity; dry etching not only produces inclined surfaces, but also has extremely high costs and is accompanied by a large amount of time costs required for processing. In contrast, the back cavity etched by laser is close to a cuboid, that is, it has more nearly vertical inclined surfaces, which means that the area of the upper bottom surface of the back cavity and the size of the window of the lower bottom surface of the back cavity are closer, which is beneficial to making enough suspended parts (i.e., support parts) to prevent heat loss.

[0110] The micro hotplate of Comparative Example 3 causes the front film structure to be highly fragile for two reasons: First, the films deposited for support and insulation are relatively thin, generally less than 1 μm; Second, due to the window opening, its support structure is inherently fragile and is easily damaged when subjected to low-frequency resonance or a large force. In addition, this micro hotplate has another defect, that is, it is difficult to make the cavity relatively deep, which will cause heat to be conducted through the air in the cavity to the silicon with higher thermal conductivity below and be lost. The thermal conductivities of silicon and quartz glass differ too much. Once the silicon material contacts the edge of the high-temperature region of the micro hotplate temperature field, the heat loss will be very serious.

[0111] The descriptions of the above embodiments are only used to help understand the method and its core idea of the present application. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A glass substrate microhotplate, characterized in that, Comprising: A glass substrate; A heating electrode layer adhered to the first surface of the glass substrate through a first adhesion layer; An insulating layer covering the surface of the heating electrode layer; Wherein, heat insulation holes are provided on the first surface of the glass substrate; A cavity is provided on the second surface of the glass substrate; The distance from the top of the cavity to the second surface is 5 - 100 μm, the diameter of the cavity in the horizontal direction is 300 - 2000 μm, and the depth in the vertical direction is 200 - 600 μm.

2. The glass substrate micro-hotplate according to claim 1, wherein The width of the heat insulation holes is 5 - 200 μm.

3. The glass substrate micro-hotplate according to claim 2, characterized in that, Metal pads with leads are provided at both ends of the heating electrode layer.

4. The glass substrate micro-hotplate according to claim 2, wherein, The insulating layer material is selected from silicon oxide or silicon nitride.

5. The glass substrate micro hotplate according to claim 1, wherein, The glass substrate material includes: fused quartz or borated glass.

6. A method for preparing the glass substrate micro-hotplate according to any one of claims 1-5, characterized in that, Comprising: Performing photolithography on the first surface of the glass substrate, and then depositing a first adhesion layer; Volume number: 220889CI Continuing to deposit a heating electrode layer on the surface of the first adhesion layer; Covering an insulating layer on the heating electrode by chemical vapor deposition; Etching to form a cavity on the second surface of the glass substrate; Etching to form heat insulation holes on the second surface of the glass substrate.

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