Low-power-consumption micro hot plate applied to MEMS gas sensor

Abstract

The invention relates to the technical field of sensors, in particular to a low-power-consumption micro hot plate applied to an MEMS gas sensor. Comprising a substrate as well as a cantilever supporting layer, a heating layer, an insulating layer and a detection layer which are sequentially stacked upwards from the substrate, and the heating layer comprises a heating wire and two heating electrodes; the heating wire comprises a first semi-spiral heating wire and a second semi-spiral heating wire, the semi-spiral heating wire comprises a plurality of arc-shaped heating wires, and the arc-shaped heating wires are arranged according to a concentric arc and are connected in series; the second semi-spiral heating wire is in central symmetry with the first semi-spiral heating wire; by arranging the heating wire into the double-spiral annular structure, when the heating layer with the structure is used for heating, the temperature distribution is more uniform, and the area of a high-temperature area is larger; according to the invention, the width of the cantilever beam is optimized, the heat conduction loss is reduced, the energy required for reaching the working temperature is reduced, the low power consumption requirement of portable equipment is met, and the endurance of the equipment is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, and particularly to a low-power micro-hotplate applied to a MEMS gas sensor. BACKGROUND

[0002] With the advancement of technology, people's demand for improving the quality of life and security is constantly increasing, which promotes the expansion of the gas sensor market. In the exploration of this field, the types and functions of gas sensors are constantly enriched and improved. The development of microelectronic manufacturing technology has promoted the wider application of micro-electro-mechanical system (MEMS) technology in metal-oxide-semiconductor (MOS) gas sensors. Gas sensors based on MEMS technology have become the focus of global gas sensor research due to their small size, low energy consumption, rapid response, high sensitivity, and good stability.

[0003] In the architecture of a gas sensor, the gas-sensitive material of the gas sensor often relies on a heating component, which we call a micro-hotplate, to function properly. The micro-hotplate serves as a load and a heater for the gas-sensitive material. The uniformity of the micro-hotplate's temperature during operation has a significant impact on the detection performance of the gas-sensitive material, including its sensitivity, selectivity, and reliability. At the same time, the overall power consumption of the sensor is also a key factor in its commercial application.

[0004] The application of gas sensors in national security and improving the quality of life for the public is becoming increasingly important. With the advancement of micro-electro-mechanical system (MEMS) technology, MEMS-based gas sensors have become a research hotspot due to their great potential, which has promoted the development of gas sensors towards smaller, more integrated, and smarter directions. However, despite some progress, MEMS-based gas sensors still face some challenges and technical problems:

[0005] The uneven heat distribution problem. The geometry and heating structure of the micro-hotplate directly affect the distribution of heat, which can cause local overheating or cold spots. In the existing technology, the heating electrode and the interdigital electrode can be located in the same layer or in different layers. When the heating electrode and the interdigital electrode are located in the same layer, the heating electrode is on the outside and the interdigital electrode is on the inside, forming a surrounding state, i.e. the interdigital electrode is surrounded by the heating electrode. The heat generated by the heating electrode is mainly transmitted to the interdigital electrode and the gas sensitive material through conduction. Because the heating electrode is in a surrounding state, the heat conduction path may not be uniform, causing uneven heating of different parts of the gas sensitive material. For example, the edge part near the heating electrode may heat up faster and have a higher temperature, while the center part heats up relatively slowly, affecting the overall performance of the gas sensitive material and the sensitivity of the sensor. When the heating electrode and the interdigital electrode are located in different layers, the heating electrode is located below the interdigital electrode, and an insulating layer is provided between the heating electrode and the interdigital electrode. When the heating electrode and the interdigital electrode are located in different layers, the heating electrode is in a long rectangular structure, such as the structure of the heating electrode disclosed in the Chinese invention patent application No. 202310575318.1, entitled "Simple planar structure micro-hotplate gas sensor and preparation method thereof". Due to the asymmetry of the shape and the edge effect, this traditional rectangular or linear heater is prone to form a temperature gradient at the edges and corners of the heating plate. This asymmetric heat transfer can cause uneven heating. For example, in some gas sensors that work in high temperature environments for a long time, the temperature at the edge area may be 50-100℃ higher than that at the center area. This local overheating can change the physical and chemical properties of the gas sensitive material, such as the phase change of some metal oxide gas sensitive materials at high temperature, which can reduce their adsorption and reaction capacity to gas, ultimately affecting the sensitivity of the sensor.

[0006] Therefore, solving the uneven heating, improving the thermal performance and reducing the power consumption are important challenges in the current gas sensor technology field. SUMMARY

[0007] The present application provides a low-power micro-hotplate applied to a MEMS gas sensor to solve the problems of uneven heating and high power consumption in the existing MEMS gas sensor.

[0008] To achieve the above functions, the technical solution provided by the present application is:

[0009] A low-power micro-hotplate applied to a MEMS gas sensor, comprising a substrate and a cantilever support layer, a heating layer, an insulating layer and a detection layer stacked in order from the substrate upwards, characterized in that the heating layer comprises a heating wire and two heating electrodes.

[0010] The heating wire comprises a first half-spiral heating wire and a second half-spiral heating wire, the first half-spiral heating wire comprises a plurality of arc-shaped heating wires, and the plurality of arc-shaped heating wires are arranged in concentric arcs and connected in series; the second half-spiral heating wire is centrally symmetric to the first half-spiral heating wire;

[0011] The terminal end of the arc-shaped heating wire located at the innermost layer in the first half-spiral heating wire is electrically connected with the terminal end of the arc-shaped heating wire located at the innermost layer in the second half-spiral heating wire.

[0012] The terminal end of the arc-shaped heating wire located at the innermost layer in the first half-spiral heating wire is electrically connected with the terminal end of the arc-shaped heating wire located at the innermost layer in the second half-spiral heating wire.

[0013] Preferably, the plurality of arc-shaped heating wires in the first half-spiral heating wire are arranged at equal intervals.

[0014] Preferably, the thickness of the arc-shaped heating wire is 100 nm, the line width is 10 μm, and the distance between adjacent two arc-shaped heating wires is 10 μm.

[0015] Preferably, the cantilever support layer comprises a cantilever platform and a cantilever beam connected with the cantilever platform, the cantilever platform is erected above the cavity of the substrate through the cantilever beam; and the cantilever platform is circular.

[0016] Preferably, the detection layer comprises an interdigital electrode and a pair of detection electrodes electrically connected with the interdigital electrode.

[0017] Preferably, the thickness of the cantilever platform and the cantilever beam is 550 nm, and the width of the cantilever beam is 27 μm.

[0018] Preferably, the thickness of the interdigital electrode is 200 nm, the line width is 10 μm, and the distance between adjacent two parallel electrodes is 10 μm.

[0019] Preferably, the cantilever support layer is silicon dioxide or silicon nitride.

[0020] The insulating layer is silicon dioxide or silicon nitride.

[0021] The present application has the following beneficial effects:

[0022] 1、The heating wire comprises a first half-spiral heating wire and a second half-spiral heating wire, the first half-spiral heating wire comprises a plurality of arc-shaped heating wires, and the plurality of arc-shaped heating wires are arranged in concentric arcs and connected in series; the second half-spiral heating wire is centrally symmetric to the first half-spiral heating wire, forming a double-spiral ring structure; when the heating layer of the double-spiral ring structure is heated, the temperature distribution is more uniform, and the high-temperature area is larger;

[0023] 2. Optimize the width of the cantilever beam to reduce heat conduction loss, reduce the energy required to reach the operating temperature, meet the low power consumption requirements of portable devices, and extend the device's battery life. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the micro-hot plate in this embodiment;

[0025] Figure 2 for Figure 1 A schematic diagram of the decomposition process;

[0026] Figure 3 This is a schematic diagram of the heating wire in this embodiment;

[0027] Figure 4 This is a schematic diagram of a serpentine heating wire for comparison.

[0028] Figure 5 This is a three-dimensional temperature distribution diagram of the micro-hot plate in this embodiment. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1 To be continued Figure 5 The present invention will be further described as follows:

[0030] like Figure 1 and Figure 2 The invention illustrates a low-power micro-hotplate for MEMS gas sensors, comprising a substrate 1 on which a cantilever support layer 2, a heating layer 3, an insulating layer 4, and a detection layer 5 are sequentially constructed. This invention selects 1mm × 1mm × 0.4mm single-crystal silicon as the substrate 1 material, based on the requirements of MEMS manufacturing processes for the substrate 1 material. Single-crystal silicon has mature microfabrication technology in the MEMS field, exhibits stable physical and chemical properties, and excellent mechanical properties, providing good support for subsequent structural construction.

[0031] The cantilever support layer 2 serves to provide suspended support for the heating layer 3, the insulation layer 4, and the detection layer 5.

[0032] The function of heating layer 3 is to heat the entire suspended part by electricity.

[0033] The function of insulating layer 4 is to electrically insulate heating layer 3 and detection layer 5.

[0034] The function of detection layer 5: The middle part of detection layer 5 is the interdigitated electrode. When in use, the interdigitated electrode is coated with a gas-sensitive material, which electrically connects the two interdigitated electrodes.

[0035] like Figure 2As shown, the cantilever support layer 2 comprises a cantilever platform 21 and a cantilever beam 22 connected to the cantilever platform 21, the cantilever platform 21 is erected above the cavity of the substrate 1 through the cantilever beam 22; the cantilever platform 21 is circular. In this embodiment, we adopt the design of four cantilever beams. The materials of the cantilever support layer 2 and the intermediate insulating layer 4 are selected from materials with good physical and chemical stability and insulating properties, such as silicon dioxide and silicon nitride, which not only provide excellent insulating properties and chemical stability, but also maintain structural integrity during thermal cycling, which helps to further improve the uniformity of heating.

[0036] The cantilever support layer 2 can be realized by different deposition processes or etching processes during preparation. If a deposition process is used, a thicker film may require a longer deposition time or multiple deposition operations; and in the etching process, different thicknesses of the film have different requirements for the selection of etchants and etching time parameters. In this embodiment, the thickness of the cantilever platform 21 and the cantilever beam 22 is 550 nm, and the width of the cantilever beam 22 is 27 μm.

[0037] As shown in Figure 2 and Figure 3 , the heating layer 3 comprises a heating wire 32 and a pair of heating electrodes 31 electrically connected to both ends of the heating wire 32. As shown in Figure 3 , the heating wire 32 comprises a first half-spiral heating wire 321 and a second half-spiral heating wire 322, the first half-spiral heating wire 321 comprises a plurality of arc-shaped heating wires 320, the plurality of arc-shaped heating wires 320 are arranged in concentric arcs and connected in series, that is, the ends of the adjacent two arc-shaped heating wires 320 are sequentially electrically connected to form a spiral annular structure; the second half-spiral heating wire 322 is symmetrically arranged with the first half-spiral heating wire 321; the end of the arc-shaped heating wire 320 located in the innermost layer of the first half-spiral heating wire 321 is electrically connected to the end of the arc-shaped heating wire 320 located in the innermost layer of the second half-spiral heating wire 322; the first end of the arc-shaped heating wire 320 located in the outermost layer of the first half-spiral heating wire 321 and the first end of the arc-shaped heating wire 320 located in the outermost layer of the second half-spiral heating wire 322 are respectively electrically connected to one of the two heating electrodes 31.

[0038] The spiral annular structure formed by the first half-spiral heating wire 321 and the second half-spiral heating wire 322 is wound in the same horizontal plane, and finally forms a circular heating area with a double spiral annular structure. In this embodiment, the radius of the circular heating area is 120 μm, the thickness of the heating wire 32 is 100 nm, the line width is 10 μm, and the distance between the adjacent two arc-shaped heating wires 320 is 10 μm. In this embodiment, the plurality of arc-shaped heating wires 320 in the first half-spiral heating wire 321 and the second half-spiral heating wire 322 are arranged at equal intervals.

[0039] The double-helix annular heating wire 32 has unique advantages. Compared with traditional rectangular, linear, or meandering heating wires, the double-helix annular heating wire 32 can achieve a more uniform heat conduction path on the micro-heating plate. During heating, heat transfer within the double-helix annular structure is more even, reducing uneven heat accumulation or loss caused by the structural shape. Figure 5 The three-dimensional temperature distribution diagram of the micro-heatplate in this embodiment shows that the edge effect of the double-helix ring structure is relatively small, and heat does not tend to concentrate as easily as in the corners of a rectangular structure, resulting in a smaller temperature gradient across the entire heating area. This uniform temperature distribution is crucial for the gas-sensitive material on the micro-heatplate, as its performance is highly sensitive to temperature uniformity. Uniform temperature ensures that the gas-sensitive material maintains stable responsiveness throughout the entire working area, improving the sensitivity and accuracy of the gas sensor, reducing measurement errors caused by temperature non-uniformity, and thus enhancing the performance of the micro-heatplate as a core component of the gas sensor. Figure 5 The central region of the micro-hotplate, as shown, contains the heating zone, which reaches its highest temperature of approximately 450°C. In contrast, the edge of substrate 1 has the lowest temperature, approximately 23°C, which is very close to the set ambient air temperature of 20°C. This phenomenon indicates that substrate 1 dissipates a significant amount of heat through convection with the surrounding air when the micro-hotplate is operating, preventing the entire gas sensor from overheating and thus protecting the internal components of the gas sensor.

[0040] In this embodiment, the thickness of the interdigitated electrodes is 200 nm, the linewidth is 10 μm, and the distance between two adjacent parallel electrodes is 10 μm.

[0041] Under otherwise identical conditions, we will use the micro-hot plate with the heating wire of the present invention and the... Figure 4 The micro-hot plate with the meandering heating wire shown is used for heating. The performance parameters of the device, as tested, are as follows:

[0042] Table 1: Performance parameters of different micro-hot plates

[0043] Research object Heater shape Vin (V) TP (°C) Q (pm 2 / °C) Power consumption (mW) 1 Double helix ring 6 445.065 3567.5 81.036 2 Meander shape 5.8 438.786 2091.1 79.740

[0044] In Table 1, the area factor Q is the ratio of the area ΔS to ΔT within the working area where the temperature is within the range of TP-ΔT, where ΔT represents the temperature difference from the peak temperature.

[0045] Q = ΔS / ΔT;

[0046] In the experimental setup, the temperature standard for all isotherms was set to TP-ΔT, and the area defined by the isotherm was ΔS. A larger Q value indicates that the device can provide a larger, more uniformly heated area.

[0047] From the comparison of the above performance parameters, we can draw the following conclusions:

[0048] (1) Temperature uniformity

[0049] The temperature variation in the effective area of the micro-hotplate with double spiral annular heater design is about ±1%, while the temperature fluctuation in the effective working area of the meander-shaped heater is maintained within ±3%. The more subtle temperature variation of the double spiral annular heater indicates a more uniform temperature distribution.

[0050] (2) Isothermal zone coverage area

[0051] The double spiral annular heater has a larger isothermal zone coverage area, with an area factor Q value of 3567.5 μm 2 / ℃, while the Q value of the meander-shaped heater is 2091.1 μm 2 / ℃. The larger isothermal zone coverage area means that a more uniform temperature environment can be provided in the heating area, which is beneficial to the stability of the gas-sensitive material performance and improves the sensitivity and accuracy of the gas sensor.

[0052] In summary, through the comparison of isothermal lines, the double spiral annular heater performs better in terms of temperature uniformity and isothermal zone coverage area, so the results are better.

[0053] The width of the cantilever beam 22 is a key structural parameter that significantly affects the power consumption performance of the micro-hotplate. The following table shows the relationship between the width of the cantilever beam 22 and the power consumption:

[0054] Table 2: Relationship between cantilever beam 22 width and power consumption

[0055] Cantilever beam width (μm) Power consumption (mW) 27 80.916 42 86.132 17 80.916

[0056] The width of the cantilever beam 22 is influenced by various factors, such as specific application scenarios, structural design requirements, and the load it bears. In some practical applications, the width of the cantilever beam can range from a few millimeters to tens of millimeters or even wider. As shown in Table 2, although the micro-hotplate with a cantilever beam width of 27 μm has the same power consumption as the micro-hotplate with a cantilever beam width of 17 μm, the former has better performance in terms of structural stability.

[0057] From the above table and data, it can be seen that by reasonably adjusting the width of the cantilever beam, the micro-hotplate can effectively reduce its power consumption and improve its performance. For example, when the width of the cantilever beam is adjusted from 42 μm to 27 μm, the power consumption decreases from 86.132 mW to 80.916 mW, which indicates the positive effect of the invention on performance improvement in structural design optimization.

[0058] The following comprehensive comparison table is obtained:

[0059] Table 3: Performance indicators

[0060] Performance index Before improvement After improvement Temperature uniformity (temperature gradient, °C / um) 50 10 Power consumption (mW) 100 65 Stress concentration area (um 2 )]]> 10 3

[0061] This table reflects the advantages of the invention from three aspects.

[0062] First, in terms of temperature uniformity, the temperature gradient is reduced from 50℃ / um to 10℃ / um, making the gas sensitive material reaction more stable, improving the sensor sensitivity and precision, and optimizing the heating effect.

[0063] Second, in terms of power consumption, it is reduced from 100mW to 65mW, reducing energy consumption, which is of great significance to portable devices, can prolong the use time, reduce the cost, and meet the environmental protection concept.

[0064] Third, the stress concentration area is reduced from 10um 2 to 3um 2 , optimizing the micro-hotplate structure, improving mechanical stability, reducing deformation and damage risk, prolonging service life, and ensuring stable gas sensor performance, good electrode contact, and unaffected heating effect. In summary, the patent has obvious advantages in improving performance, energy saving and enhancing stability.

[0065] The above examples are only preferred examples of the invention, and are not intended to limit the scope of the invention. Any equivalent changes or modifications made in accordance with the structure, features and principles described in the patent application scope of the invention shall be included in the patent application scope of the invention.

Claims

1. A low-power micro-hot plate for use in MEMS gas sensors, comprising a substrate and a cantilever support layer, a heating layer, an insulating layer, and a detection layer stacked sequentially from the substrate upwards, characterized in that: The heating layer includes a heating wire and two heating electrodes; The heating wire includes a first semi-spiral heating wire and a second semi-spiral heating wire. The first semi-spiral heating wire includes multiple arc-shaped heating wires, which are arranged in concentric arcs and connected in series. The second semi-spiral heating wire is symmetrical to the first semi-spiral heating wire. The end of the innermost arc-shaped heating wire in the first semi-spiral heating wire is electrically connected to the end of the innermost arc-shaped heating wire in the second semi-spiral heating wire. The first end of the outermost arc-shaped heating wire in the first half-spiral heating wire and the first end of the outermost arc-shaped heating wire in the second half-spiral heating wire are respectively electrically connected to one of the two heating electrodes.

2. The low-power micro-hot plate for MEMS gas sensors as described in claim 1, characterized in that: The multiple arc-shaped heating wires in the first semi-spiral heating wire are arranged at equal intervals.

3. The low-power micro-hot plate for MEMS gas sensors as described in claim 1, characterized in that: The thickness of the arc-shaped heating wire is 100 nm, the line width is 10 μm, and the distance between two adjacent arc-shaped heating wires is 10 μm.

4. The low-power micro-hot plate for MEMS gas sensors as described in claim 1, characterized in that: The cantilever support layer includes a cantilever platform and a cantilever beam connected to the cantilever platform. The cantilever platform is mounted above the cavity of the substrate via the cantilever beam. The cantilever platform is circular.

5. The low-power micro-hot plate for MEMS gas sensors as described in claim 2, characterized in that: The detection layer includes interdigitated electrodes and a pair of detection electrodes electrically connected to the interdigitated electrodes.

6. The low-power micro-hot plate for MEMS gas sensors as described in claim 4, characterized in that: The thickness of the cantilever platform and the cantilever beam is 550 nm, and the width of the cantilever beam is 27 μm.

7. The low-power micro-hot plate for MEMS gas sensors as described in claim 5, characterized in that: The interdigitated electrodes have a thickness of 200 nm, a linewidth of 10 μm, and a distance of 10 μm between two adjacent parallel electrodes.

8. The low-power micro-hot plate for MEMS gas sensors as described in any one of claims 1 to 7, characterized in that: The cantilever support layer is silicon dioxide or silicon nitride; The insulating layer is silicon dioxide or silicon nitride.

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