Thermal conductivity type gas sensor chip and gas concentration measuring method

Abstract

The invention provides a heat conduction type gas sensor chip and a gas concentration measuring method. The heat conduction type gas sensor chip comprises a sensing unit and a driving integrated circuit, the sensing unit comprises at least two cavities and heaters correspondingly suspended above the cavities, at least two heat dissipation areas with different heat conductivity are formed, and at least one temperature sensor is arranged on the surface of each heat dissipation area; and a mixed signal circuit system in the integrated driving circuit controls the heater and generates a target gas concentration signal according to the temperature signal of the temperature sensor. Through the structural design of the sensor chip and the synergistic effect of circuit integration and an intelligent algorithm, accurate measurement of the concentration of a target gas is realized, and meanwhile, the gas sensor chip has the capability of parallel detection of multiple gas components, so that the technical problems of insufficient anti-interference capability, relatively high power consumption and low integration degree of an existing gas sensor chip in a complex environment are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas detection, and in particular to a thermal conductivity type gas sensor chip and a gas concentration measurement method. BACKGROUND

[0002] In the field of gas detection, traditional thermal conductivity type gas sensors have been widely used in many scenes such as industrial production and environmental monitoring due to their simple principle and fast response. However, with the increasing complexity of the detection environment and the upgrading of application requirements, traditional thermal conductivity type gas sensors face the problem of insufficient anti-interference ability.

[0003] In actual detection environment, there are common interference factors such as humidity and background gas, which makes the traditional thermal conductivity type gas sensor unable to effectively distinguish the thermal response difference between the target gas and the interference gas, resulting in deviation of the measurement result and significant decrease of the precision. Moreover, the problem of steady-state thermal drift cannot be ignored, and in the long-term working process, the thermal accumulation effect causes the baseline of the traditional thermal conductivity type gas sensor to drift, making it difficult to guarantee the detection stability. Frequent calibration not only increases the maintenance cost, but also affects the reliability and continuity of the data. In addition, the complex structure of the discrete components of the traditional thermal conductivity type gas sensor makes it difficult to balance the integration and power consumption, and it is difficult to realize system-on-chip integration, which cannot meet the development trend of miniaturization and portability of modern detection equipment. At the same time, the high power consumption also limits its application in low-power scenarios.

[0004] The design of single thermal conductivity structure makes it difficult to detect multiple gases, and it is difficult to identify multiple gas components in parallel and needs to rely on complex calibration process, which is low in efficiency and high in cost. The existing traditional thermal conductivity type gas sensor uses a single thermistor or simple temperature compensation scheme, which cannot meet the high-precision detection requirements in complex environments.

[0005] Therefore, it is urgent to develop a new thermal conductivity gas sensor based on integrated design, multi-dimensional signal fusion and intelligent algorithm, which will bring new breakthroughs and development opportunities to the field of gas detection. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a thermal conductivity type gas sensor chip and a gas concentration measurement method.

[0007] To solve the above problems, the application provides a thermal conduction type gas sensor chip, which comprises a sensitive unit and an integrated driving circuit; the sensitive unit comprises at least two cavities and a heater corresponding to each cavity; at least one of the cavity depth, cavity material, surface covering superstructure radiation area and heating mode of the heater of the two cavities of the sensitive unit is configured to be different, so as to form two heat dissipation areas with different heating capacities; the surface of each heat dissipation area is provided with at least one temperature sensor, which is used for measuring the temperature of the heat dissipation area and outputting a temperature signal; the integrated driving circuit comprises a mixed signal circuit system, which is used for controlling the heater and generating a target gas concentration signal according to the temperature signal of the temperature sensor.

[0008] In some embodiments, the two cavities correspond to the heaters, each of which is independently selected from one of a polysilicon heater and a metal heater, so as to form two heat dissipation areas with different heating capacities.

[0009] In some embodiments, the heating frequency and amplitude of the two cavities corresponding to the heaters are independently configured to be different in the following ranges: the frequency range is 1 Hz-1 kHz, the pulse width range is 1 ms-1 s, and the range amplitude is 0.1 V to 10 V, so as to form two heat dissipation areas with different heating capacities.

[0010] In some embodiments, the surface of the temperature sensor in one heat dissipation area is covered with a superstructure radiation area, so as to form a temperature gradient.

[0011] In some embodiments, the surfaces of the temperature sensors in two heat dissipation areas are covered with superstructure radiation areas with different structures, so as to form a temperature gradient.

[0012] In some embodiments, the two superstructure radiation areas include a composite layer with a metal content greater than or equal to 50% and a composite layer with a dielectric layer content greater than or equal to 60%.

[0013] In some embodiments, the temperature sensor is independently selected from one of a thermocouple sensor and a thermal resistance sensor.

[0014] In some embodiments, the mixed signal circuitry comprises a pulse drive circuit, a differential summation circuit, a programmable gain amplifier, and a digital signal processing unit; the pulse drive circuit is configured to generate a pulse signal to drive the heater, the differential summation circuit is configured to perform a difference summation operation on the temperature signals of the temperature sensors to reduce the influence of interfering gases, the programmable gain amplifier is configured to adjust the signal gain of each temperature sensor, and the digital signal processing unit is configured to coordinate the pulse drive circuit, adjust the gain of the programmable gain amplifier, perform frequency domain filtering to distinguish target gases and interfering gases, and perform dynamic weighting based on the temperature signals of each temperature sensor to generate a target gas concentration signal.

[0015] In some embodiments, the digital signal processing unit performs dynamic weighting based on the temperature signals of each temperature sensor to generate a target gas concentration signal, specifically including: performing mean filtering or Kalman filtering on the temperature signals output by the plurality of temperature sensors to suppress single-point noise; and using time-division excitation for different heaters to obtain thermal response differentiation characteristics of target gases and interfering gases, and separate target gases and interfering gases; the concentration signal of the target gas is S = ∑(α i ·T i ·k i )·f(P, T am ), where T i is the temperature signal output by the temperature sensor i, α i is the weight coefficient of the temperature sensor i, k i is the thermal conductivity of the heat dissipation area corresponding to the temperature sensor i, and f(P, T am ) is a pressure and temperature compensation function, P is the pressure of the gas atmosphere to be measured, and T am is the temperature of the gas atmosphere to be measured.

[0016] In some embodiments, the digital signal processing unit models the interfering gas, specifically including: constructing a gas feature vector based on the response difference of different temperature sensors, training a temperature response model of the interfering gas through a machine learning model, and generating a gain adjustment parameter table, which is used to distinguish target gases and interfering gases.

[0017] In some embodiments, a storage unit is further included, which is an on-chip memory or an off-chip memory, and is configured to pre-store at least two sets of gain adjustment parameter tables of different interfering gases, which can be dynamically called through a serial communication protocol interface.

[0018] In some embodiments, the pressure-temperature compensation function is obtained by simulation and training according to pressure values obtained by on-chip or off-chip pressure sensors and temperature values obtained by on-chip or off-chip temperature sensors.

[0019] In some embodiments, the digital signal processing unit further provides a self-calibration algorithm, specifically including: periodically inputting a target gas with a known concentration into the temperature sensors, correcting the weight coefficient and thermal conductivity of each temperature sensor according to the difference between the concentration of the target gas with the known concentration and the output concentration signal; performing cross-calibration using redundant temperature sensors in the temperature sensors, identifying temperature sensors that have drifted and eliminating the drift of individual temperature sensors.

[0020] In some embodiments, the mixed-signal circuit system further includes a multiplexer for simultaneously accessing the temperature signals of multiple heaters and an analog-to-digital converter for converting analog signals into digital signals.

[0021] In some embodiments, the multiplexer includes at least two analog input signals, and the analog-to-digital converter has at least 12 bits.

[0022] In some embodiments, the pulse driving circuit includes a pulse generator for generating a low pulse signal with a specific frequency and duty cycle and a power amplifier for amplifying the low power pulse signal generated by the pulse generator to drive the heater to work.

[0023] In some embodiments, the frequency domain filtering excites a thermal transient response in pulse mode, converts the temperature signal in the time domain into a frequency domain signal through fast Fourier transform, and distinguishes target gases and interfering gases according to the frequency range of the frequency domain signal.

[0024] To solve the above problems, the application also provides a gas concentration measurement method using the thermal conductivity gas sensor chip, including: controlling the heater to form a gradient thermal excitation mode in different heat dissipation areas; performing frequency domain filtering on the temperature signal output by the temperature sensor to distinguish target gases and interfering gases; adjusting the signal gain of different temperature sensors in real time, amplifying the temperature signal of each temperature sensor to reduce the influence of interfering gases; and generating a target gas concentration signal according to the temperature signal of each temperature sensor.

[0025] The technical scheme above comprises a sensitive unit and a driving integrated circuit, the sensitive unit comprises at least two cavities and a heater corresponding to each cavity and forming at least two heat dissipation areas with different heat conductivities, and the surface of each heat dissipation area is provided with at least one temperature sensor; the heater is controlled by the mixed signal circuit system in the integrated driving circuit, and a target gas concentration signal is generated according to the temperature signal of the temperature sensor. The structure design of the sensor, the circuit integration and the intelligent algorithm are cooperated to realize the accurate measurement of the target gas concentration, and the multi-gas component parallel detection capability is provided to solve the technical problems of the existing gas sensor chip, such as insufficient anti-interference capability, high power consumption and low integration degree in a complex environment.

[0026] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. The technology, method and equipment known to those skilled in the related art can not be discussed in detail, but should be regarded as part of the authorization description under appropriate circumstances. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0028] Figure 1 is a device structure top view of a thermal conductivity type gas sensor chip provided by an embodiment of the present application; Figure 2 is a cross-sectional view of the device structure of the thermal conductivity type gas sensor chip along CC' provided by an embodiment of the present application.

[0029] Figure 3 is an on-chip signal processing schematic diagram of the thermal conductivity type gas sensor chip provided by an embodiment of the present application; Figure 4 is a flow chart of a gas concentration measurement method using the thermal conductivity type gas sensor chip provided by an embodiment of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] Figure 1 is a device structure top view of a thermal conductivity gas sensor chip provided by an embodiment of the present application. As shown in Figure 1 , the thermal conductivity gas sensor chip comprises a sensing unit 11 and an integrated driving circuit (not labeled).

[0032] The sensing unit 11, as shown in the dashed box in Figure 1 , comprises at least two cavities and a heater 13 corresponding suspended above each cavity, at least one of the cavity depth, cavity composition material, surface coverage superstructure radiation zone, and heating mode of the heater 11 of the two cavities of the sensing unit 11 is configured to be different, thereby forming two heat dissipation regions 14 with different heating capabilities.

[0033] The surface of each of the heat dissipation regions 14 is provided with at least one temperature sensor 12 for measuring the temperature of the heat dissipation region 14 and outputting a temperature signal.

[0034] The integrated driving circuit comprises a mixed signal circuit system for controlling the heater 13 and generating a target gas concentration signal according to the temperature signal of the temperature sensor 12.

[0035] In this embodiment, the sensing unit 11 is formed on a CMOS substrate, and a standard CMOS process is used to deposit multiple metal layers and dielectric layers on a silicon wafer to form the CMOS substrate. Specifically, the metal layer is three layers, including an aluminum layer and a tungsten layer, and the dielectric layer includes a silicon oxide layer and a silicon nitride layer.

[0036] The cavities of the sensing unit and the structures on the cavities are formed as suspended structures, which are multi-layer composite suspended films or cantilever beam structures. The suspended structures are formed on the CMOS substrate by photolithography and etching processes. In this embodiment, the suspended structure is a cantilever beam structure.

[0037] The surface of each of the heat dissipation regions 14 is provided with at least one temperature sensor 12 for measuring the temperature of the heat dissipation region 14 and outputting a temperature signal.

[0038] The heater 13 is used to heat the heat dissipation region 14 to form a gradient heat excitation mode for different heat dissipation regions 14, and the heating frequency and amplitude of the heater 13 are controlled by pulse driving mode.

[0039] The mixed signal circuit system is used to drive the heater 13 and generate a target gas concentration signal according to the temperature signal of the temperature sensor 12.

[0040] As shown in Figure 1As shown, the sensitive unit 11 includes two heat dissipation regions 14, namely a first heat dissipation region A and a second heat dissipation region B, and the thermal conductivity of the first heat dissipation region A is greater than or equal to twice the thermal conductivity of the second heat dissipation region B.

[0041] In the embodiment, the cavity depth and the surface coverage of the superstructure radiation zone of the first heat dissipation region A and the second heat dissipation region B are different.

[0042] Figure 2 is a cross-sectional view of the device structure of the thermal conduction type gas sensor chip along CC' according to an embodiment of the present application. In order to specifically describe the thermal conduction type gas sensor chip, the first heat dissipation region A and the second heat dissipation region B are shown in the figure. Figure 1 Compared with the prior art, Figure 2 a metal connecting structure is added.

[0043] The cavity surface covers different superstructure radiation zones to form two heat dissipation regions 14 with different heating capacities.

[0044] In the embodiment, the surface of the temperature sensor 12 in one of the heat dissipation regions 14 is covered with a superstructure radiation zone to form a temperature gradient. As shown, Figure 2 the left part of the first heat dissipation region A is a superstructure radiation zone, and the thickness of the superstructure radiation zone is obviously greater than the thickness of the right part of the first heat dissipation region A.

[0045] Specifically, the thickness of the first heat dissipation region A is 1-3 μm, and the thickness of the second heat dissipation region B is 2-8 μm.

[0046] The different cavity depths of the cavities are configured to form two heat dissipation regions 14 with different heating capacities, for example, Figure 2 In the embodiment, the cavity depth h1 of the first heat dissipation region A is obviously greater than the cavity depth h2 of the second heat dissipation region B.

[0047] Different cavity material compositions are configured to form two heat dissipation regions 14 with different heating capacities. Figure 1 In the embodiment, the cavity material compositions of the first heat dissipation region A and the second heat dissipation region B are different. The first heat dissipation region A is a composite layer with a metal content greater than or equal to 50%, and the second heat dissipation region B is a composite layer with a dielectric layer content greater than or equal to 60%. Moreover, the first heat dissipation region A and the second heat dissipation region B are thermally isolated.

[0048] The heat dissipation capacity of the heat dissipation region 14 can be configured according to different target gases. Moreover, the temperature sensor 12 outputs the temperature signal corresponding to the heat dissipation region 14, respectively.

[0049] In some embodiments, the surfaces of the temperature sensors 12 in the two heat dissipation regions 14 are covered with superstructure radiation regions of different structures to form a temperature gradient. Furthermore, one of the two superstructure radiation regions includes a composite layer with a metal content greater than or equal to 50%, and the other includes a composite layer with a dielectric layer content greater than or equal to 60%.

[0050] Each of the temperature sensors 12 is independently selected from either a resistive sensor or a thermopile sensor. The resistive sensor is composed of a polycrystalline silicon resistor, and its temperature is reflected by changes in resistance. The thermopile sensor is composed of a thermocouple formed by aluminum and polycrystalline silicon connected in series, or a thermocouple formed by p-type and n-type polycrystalline silicon connected in series. The output voltage of the thermopile sensor is proportional to the temperature difference between the hot and cold ends of the thermopile.

[0051] like Figure 1 As shown, the first temperature sensor R is integrated on the first heat dissipation partition A. 11 Second temperature sensor R 12 The second heat dissipation partition B integrates a third temperature sensor TS1. The first temperature sensor R... 11 and the second temperature sensor R 12 The sensors are resistive sensors with resistance values ​​of 1000Ω and 2000Ω respectively. The third temperature sensor TS1 is a thermopile sensor, which is composed of thermocouples formed by p-type polycrystalline silicon and n-type polycrystalline silicon connected in series, specifically, it consists of 20 pairs of thermocouples connected in series.

[0052] At least one heater 13 is suspended above each cavity of each of the heat dissipation areas 14, meaning that each heat dissipation area 14 is thermally coupled to at least one heater 13. Each heater 13 is independently selected from polycrystalline silicon heaters and metal heaters.

[0053] In this embodiment, each of the heat dissipation areas 14 includes one cavity. Accordingly, as... Figure 1 As shown, the first heat dissipation zone A is thermally coupled to the first heater H1, and the second heat dissipation zone B is thermally coupled to the second heater H2. Both the first heater H1 and the second heater H2 are metal heaters. The first heater H1 is made of aluminum and is formed on the aluminum layer of the CMOS substrate, with a resistance of 50Ω. The second heater H2 is made of tungsten and is formed on the tungsten layer of the CMOS substrate 11, with a resistance of 200Ω.

[0054] The heating mode of the heater 13 is configured differently to form two heat dissipation areas 14 with different heat generation capabilities. Specifically, the heating frequency and amplitude of the heater 13 corresponding to the two cavities are independently configured differently in the following ranges: frequency range 1Hz-1kHz, pulse width range 1ms-1s, range amplitude 0.1V to 10V.

[0055] The mixed signal circuit system is used to control the heater 13 and generate a target gas concentration signal according to the temperature signal of the temperature sensor 12. The mixed signal circuit system is integrated on the right edge of the CMOS substrate.

[0056] Figure 3 It is an on-chip signal processing schematic diagram of a thermal conductivity gas sensor chip provided by an embodiment of the present application.

[0057] As shown in Figure 3 The mixed signal circuit system includes a pulse driving circuit 31, a differential summation circuit 32, a programmable gain amplifier 33, and a digital signal processing unit 34. The pulse driving circuit 31 is used to generate a pulse signal to drive the heater 13. The differential summation circuit 32 performs differential summation operation on the temperature signal of each temperature sensor 12 to reduce the influence of interfering gases. The programmable gain amplifier 33 is used to adjust the signal gain of each temperature sensor 12. The digital signal processing unit 34 is used to coordinate the pulse driving circuit 31, adjust the gain of the programmable gain amplifier 33, perform frequency domain filtering to distinguish target gases and interfering gases, and perform dynamic weighting based on the temperature signal of each temperature sensor 12 to generate a target gas concentration signal.

[0058] As shown in Figure 3 The pulse driving circuit 31 includes a pulse generator and a power amplifier. The pulse generator is used to generate a low pulse signal with a specific frequency and duty cycle. Specifically, the frequency of the pulse generator ranges from 1Hz to 1kHz. By adjusting the pulse frequency, duty cycle, and amplitude, the average heating power of the heating resistor of the heater 13 can be accurately controlled, thereby achieving low-power operation. The power amplifier is used to amplify the low-power pulse signal generated by the pulse generator to drive the heater to work.

[0059] The differential summation circuit 32 can accurately weight and sum or difference multiple input signals while suppressing common-mode interference, and is a key circuit for connecting sensors, measurement devices, and control systems in analog signal processing.

[0060] The gain adjustment range of the programmable gain amplifier (PGA) 33 is 1-1000 times. In this embodiment, the gain adjustment range of the programmable gain amplifier 33 is 1-100 times. The signals of different temperature sensors 12 are amplified by the programmable gain amplifier 33, the gain ratio is adjusted in real time, the gain of the target gas is increased, the gain of the interference gas is reduced, and the sensitivity of the output response to the interference gas is minimized.

[0061] As shown in Figure 3 The mixed signal circuit system further includes a multiplexer 35 and an analog-to-digital converter 36. The multiplexer 35 is used to access the temperature signals of multiple heaters 13 at the same time, and the analog-to-digital converter 36 is used to convert analog signals into digital signals. Among them, the multiplexer 35 includes at least two analog input signals, for example, Figure 3 The multiplexer 35 in the above embodiment includes three analog input signals, and each analog input signal corresponds to the temperature signal of one temperature sensor 12. The number of bits of the analog-to-digital converter 36 is at least 12 bits.

[0062] The digital signal processing unit 34 includes a digital signal processor (DSP). The digital signal processing unit 34 performs coordination of the pulse driving circuit 31, adjustment of the gain of the programmable gain amplifier 33, frequency domain filtering, and dynamic weighting based on a preset algorithm through the digital signal processor.

[0063] The frequency domain filtering excites a thermal transient response in the pulse mode, converts the time domain temperature signal into a frequency domain signal through fast Fourier transform, and distinguishes the target gas and the interference gas according to the frequency range of the frequency domain signal. Fast Fourier transform (FFT) is a high-efficiency calculation algorithm of discrete Fourier transform (DFT).

[0064] In this embodiment, the digital signal processing unit 34 performs the frequency domain filtering and identifies the intermediate frequency component in the frequency domain signal as the target gas and the low frequency component in the frequency signal as the interference gas.

[0065] The digital signal processing unit 34 generates a target gas concentration signal based on the dynamic weighting of the temperature signals of each temperature sensor 12, which specifically includes the following steps: (1) Perform mean filtering or Kalman filtering on the temperature signals output by the plurality of temperature sensors 12 to suppress single-point noise. Single-point noise is a transient abnormal value caused by various disturbances, which can cause signal distortion. Suppressing single-point noise can make the signal more stable and provide reliable data for subsequent analysis. Among them, the mean filtering takes the average value of the signals at multiple consecutive times, smooths the transient fluctuations, and is suitable for scenes with stable noise; Kalman filtering predicts the signal trend through a mathematical model and dynamically corrects the error with the measured value, which is suitable for scenes where the signal changes dynamically over time, such as real-time temperature fluctuations.

[0066] (2) Time-sharing excitation is used for different heaters to obtain the differential characteristics of the thermal response of the target gas and the interfering gas, and separate the target gas and the interfering gas.

[0067] The target gas and the interfering gas have different thermal physical properties (such as specific heat capacity and thermal conductivity), and their response laws under different heating conditions are different. By time-sharing excitation (for example, the first heater H1 and the second heater H2 work alternately), the temperature signals of each temperature sensor 12 are collected in different time periods, and the differential temperature response of the target gas and the interfering gas can be obtained, and then the target gas and the interfering gas can be separated according to the response characteristics of the target gas.

[0068] In this embodiment, the digital signal processing unit 34 models the interfering gas. This includes: constructing a gas feature vector based on the response differences of different temperature sensors 12, training a temperature response model of the interfering gas through a machine learning model, and generating a gain adjustment parameter table for distinguishing the target gas and the interfering gas. The machine learning model used in this embodiment is a pre-trained neural network model.

[0069] Specifically, the response signals of different temperature sensors 12 are numerized and then form a feature vector in a certain order. The data used for training the model can be obtained by passing different concentrations of interfering gas through the temperature sensor 12 to obtain the response data, and then forming a training data set. Through the gain adjustment parameter table, the gain adjustment parameter can be quickly obtained, so as to more efficiently adjust the signal gain of each temperature sensor 12 and offset the influence of the interfering gas.

[0070] In this embodiment, the thermal conductivity type gas sensor chip further includes a storage unit 37, which is an on-chip memory or an off-chip memory. The storage unit 37 is used to pre-store at least two sets of gain adjustment parameter tables of different interfering gases, and the gain adjustment parameter table can be dynamically called through a serial communication protocol interface. Among them, the serial communication protocol is an Inter-Integrated Circuit (I2C) protocol.

[0071] On-chip Memory refers to the memory integrated on the processor chip; while the off-chip memory (such as EEPROM) is an external storage device independent of the chip, used to store small amount of data that needs to be frequently modified.

[0072] In the present embodiment, the gain adjustment parameter table of the interference gas is pre-stored in the off-chip EEPROM, which is an independent electrically erasable memory with non-volatile characteristics, suitable for scenarios that require frequent data updates. Its storage capacity is small, but it supports local erasing operation, and its durability can reach hundreds of thousands of erasing cycles.

[0073] (3) The concentration signal of the target gas is S = Σ (α i ·T i ·k i )·f(P, T am ), wherein T i is the temperature signal output by the temperature sensor i, α i is the weight coefficient of the temperature sensor i, k i is the thermal conductivity of the heat dissipation area corresponding to the temperature sensor i, f (P, T am ) is a pressure temperature compensation function, P is the pressure of the gas atmosphere to be measured, and T am is the temperature of the gas atmosphere to be measured.

[0074] The calculation method of the concentration signal of the target gas is an extended weighted difference algorithm, wherein the weight coefficient of the temperature sensor can be positive or negative. In the present embodiment, the weight coefficient of the temperature sensor sensitive to the target gas is larger, and the weight coefficient of the temperature sensor sensitive to the interference gas is smaller.

[0075] The pressure temperature compensation function is used to correct the interference caused by environmental factors such as pressure or temperature, wherein the pressure temperature compensation function is obtained according to the simulation and training of pressure value and temperature value, the pressure value is obtained by on-chip or off-chip pressure sensor, and the temperature value is obtained by on-chip or off-chip temperature sensor.

[0076] During long-term operation, thermal accumulation effect can easily cause the baseline of the thermal conductivity type gas sensor chip to drift, accordingly, the digital signal processing unit 34 also provides a self-calibration algorithm, which specifically includes: 1) periodically introduce a target gas of known concentration to the temperature sensors 12, and correct the weight coefficient and thermal conductivity of each temperature sensor 12 according to the difference between the concentration of the target gas of known concentration and the output concentration signal.

[0077] In most cases, the above step of correction involving each temperature sensor 12 can be used to periodically correct the overall drift of the thermal conductivity gas sensor chip.

[0078] 2) perform cross-calibration using redundant temperature sensors in the temperature sensors 12, identify the temperature sensor that has drifted, and eliminate the drift of the individual temperature sensor.

[0079] The redundant temperature sensors refer to multiple sensors in the temperature sensors 12 that are functionally identical or similar. The cross-calibration refers to finding the temperature sensor 12 that has drifted by comparing the response of an individual redundant temperature sensor with that of other redundant temperature sensors.

[0080] The above technical solution sets at least two cavities on the sensitive unit, and a heater corresponding to each cavity is suspended above each cavity to form at least two heat dissipation regions with different thermal conductivities. At least one temperature sensor is arranged on the surface of each heat dissipation region. The heater is used to heat the heat dissipation region to form a gradient thermal excitation mode for different heat dissipation regions. The digital signal processing unit coordinates the pulse driving circuit, adjusts the gain of the programmable gain amplifier, performs frequency domain filtering to distinguish target gas and interfering gas, and performs dynamic weighting based on the temperature signals of each temperature sensor to generate a target gas concentration signal. The structure design of the sensor, the integration of the circuit, and the intelligent algorithm work together to realize accurate measurement of the target gas concentration. At the same time, it has the ability to detect multiple gas components in parallel, to solve the technical problems of insufficient anti-interference ability, high power consumption, and low integration level of existing gas sensor chips in complex environments.

[0081] Based on the same inventive concept, the present application also provides a gas concentration measurement method using the thermal conductivity gas sensor chip.

[0082] Figure 4 is a flowchart of a gas concentration measurement method using the thermal conductivity gas sensor chip provided by an embodiment of the present application.

[0083] As Figure 1As shown, the heat conduction type gas sensor chip includes a sensitive unit 11 and an integrated driving circuit. The sensitive unit 11 includes at least two cavities and a heater 13 corresponding to each cavity. At least one of the cavity depth, cavity material composition, surface coverage superstructure radiation zone, and heating mode of the heater 11 of the two cavities of the sensitive unit 11 is configured to be different, thereby forming two heat dissipation regions 14 with different heating capacities.

[0084] The surface of each heat dissipation region 14 is provided with at least one temperature sensor 12 for measuring the temperature of the heat dissipation region 14 and outputting a temperature signal. The integrated driving circuit includes a mixed signal circuit system for controlling the heater 13 and generating a target gas concentration signal according to the temperature signal of the temperature sensor 12.

[0085] As shown in the figure, Figure 4 The gas concentration measurement method includes: step S41, controlling the heater to form a gradient heat excitation mode in different heat dissipation regions; step S42, performing frequency domain filtering on the temperature signal output by the temperature sensor to distinguish target gas and interfering gas; step S43, adjusting the signal gain of different temperature sensors in real time, and reducing the influence of interfering gas by amplifying the temperature signal output by different temperature sensors respectively; step S44, generating a target gas concentration signal according to the temperature signal of each temperature sensor.

[0086] Referring to Figures 1 to 3 , in this embodiment, the mixed signal circuit system includes a pulse driving circuit 31, a difference summation circuit 32, a programmable gain amplifier 33, and a digital signal processing unit 34. The gas concentration measurement method specifically includes: In step S41, the heating frequency and amplitude of the heater 13 are controlled by pulse driving to form a gradient heat excitation mode in different heat dissipation regions.

[0087] In this embodiment, the target gas is carbon dioxide gas, and the interfering gas is water vapor. The sensitive unit 11 forms two heat dissipation regions 14 with different heating capacities, which are the first heat dissipation region A and the second heat dissipation region B, respectively. The first heat dissipation region A is integrated with a first temperature sensor R 11 and a second temperature sensor R 12 , and the second heat dissipation region B is integrated with a third temperature sensor TS1. The first heat dissipation region A is thermally coupled to a first heater H1, and the second heat dissipation region B is thermally coupled to a second heater H2.

[0088] In step S41, the pulse driving mode controls different heaters 13 by time-sharing excitation, for example, the first heater H1 is pulse-driven at a frequency of 10 Hz, a pulse width of 50 ms, and an amplitude of 2 V, and the second heater H2 is pulse-driven at a frequency of 50 Hz, a pulse width of 5 ms, and an amplitude of 3 V, so that the first heater H1 and the second heater H2 work alternately, so that the first heat dissipation partition A becomes a high-temperature zone (about 70°C), and the second heat dissipation partition B becomes a low-temperature zone (about 50°C), and the first heat dissipation partition A and the second heat dissipation partition B form a thermal gradient of 20°C.

[0089] The first temperature sensor R 11 , the second temperature sensor R 12 , and the third temperature sensor TS1 acquire temperature signals T 11 , T 12 , T2 by multiplexing.

[0090] In step S42, the digital signal processing unit 34 performs frequency domain filtering on the temperature signals output by the temperature sensors 12 to distinguish target gases and interference gases.

[0091] Step S42 converts the time domain temperature signals into frequency domain signals by performing fast Fourier transform on the temperature signals, and distinguishes target gases and interference gases according to different frequencies. Specifically, the frequency domain signals in the frequency band of 10-100 Hz are extracted as target gases, and the frequency domain signals in the frequency band below 10 Hz are extracted as interference gases.

[0092] In step S43, the digital signal processing unit 34 adjusts the gain of the programmable gain amplifier 33 in real time to amplify the temperature signals output by different temperature sensors 12 and perform difference operation on the temperature signals of each temperature sensor 12 by the difference summation circuit 32, for reducing the influence of interference gases.

[0093] In step S43, adjusting the gain of the programmable gain amplifier 33 can suppress the influence of interference gases. In this embodiment, the resistance signal (voltage about 50 mV) of the heater of the first heat dissipation partition A is amplified by 10 times, and the thermocouple signal (voltage about 100 mV) of the heater of the second heat dissipation partition B is amplified by 10 times, and after difference summation by the difference summation circuit 32, ΔV=500 mV is obtained, which amplifies the signal of the target gas and further suppresses the influence of the interference gas on the output concentration of the target gas.

[0094] In step S44, the digital signal processing unit 34 generates a target gas concentration signal based on the temperature signals of each temperature sensor 12.

[0095] wherein the concentration signal of the target gas is S = ∑(α i ·T i ·k i )·f(P, T am ), wherein T i is the temperature signal output by the temperature sensor i, α i is the weight coefficient of the temperature sensor i, k i is the thermal conductivity of the heat dissipation area corresponding to the temperature sensor i, and f(P, T am ) is a pressure temperature compensation function. The pressure temperature compensation function f(P, T am ) is calculated by reading the pressure value of the on-chip pressure sensor at 100 kPa and the temperature value of the on-chip temperature sensor at 25℃, P is the pressure of the gas atmosphere to be measured, and T am is the temperature of the gas atmosphere to be measured.

[0096] The digital signal processing unit 34 models the interference gas, trains a temperature response model of the interference gas based on a pre-trained neural network model, generates a gain adjustment parameter table, and further eliminates the interference of the interference gas.

[0097] It should be noted that, in this document, relational terms such as“first” and“second”, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between or among the entities or actions. Moreover, the terms“comprises”,“comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Embodiments of the present disclosure are described in related manner, and the same or similar parts between different embodiments are cross-referenced, and each embodiment focuses on the differences from other embodiments.

[0098] The above only describes the preferred embodiments of the present disclosure, and is not intended to limit the protection scope of the present disclosure. It should be noted that, for those skilled in the art, without departing from the principles of the present disclosure, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present disclosure.

Claims

1. A thermal conductivity gas sensor chip, comprising a sensing unit and an integrated driving circuit, characterized in that, include: The sensitive unit includes at least two cavities and a heater suspended above each cavity. The two cavities of the sensitive unit are configured to have different cavity depths, cavity material compositions, surface covering superstructure radiation regions, and heating methods of the heaters, thereby forming two heat dissipation areas with different heat generation capabilities. At least one temperature sensor is provided on the surface of each heat dissipation area, and the temperature sensor is used to measure the temperature of the heat dissipation area and output a temperature signal. The integrated drive circuit includes a mixed-signal circuit system for controlling the heater and generating a target gas concentration signal based on the temperature signal from the temperature sensor.

2. The thermal conductivity gas sensor chip according to claim 1, characterized in that, The heaters corresponding to the two cavities are each independently selected from either polycrystalline silicon heaters or metal heaters, so as to form two heat dissipation areas with different heating capacities.

3. The thermal conductivity gas sensor chip according to claim 1, characterized in that, The heating frequencies and amplitudes of the heaters corresponding to the two cavities are independently configured to be different within the following ranges: frequency range 1Hz-1kHz, pulse width range 1ms-1s, and amplitude range 0.1V to 10V, so as to form two heat dissipation areas with different heating capacities.

4. The thermal conductivity gas sensor chip according to claim 1, characterized in that, The surface of the temperature sensor in one of the heat dissipation areas is covered with a superstructure radiation region to form a temperature gradient.

5. The thermal conductivity gas sensor chip according to claim 1, characterized in that, The surfaces of the temperature sensors in the two heat dissipation areas are covered with superstructure radiation regions of different structures to form a temperature gradient.

6. The thermal conductivity gas sensor chip according to claim 5, characterized in that, The two superstructure radiation regions include a composite layer with a metal content of 50% or more and a composite layer with a dielectric content of 60% or more.

7. The thermal conductivity gas sensor chip according to claim 1, characterized in that, Each temperature sensor is independently selected from either a thermopile sensor or a thermal resistance sensor.

8. The thermal conductivity gas sensor chip according to claim 1, characterized in that, The mixed-signal circuit system includes a pulse driving circuit, a differential summation circuit, a programmable gain amplifier, and a digital signal processing unit. The pulse drive circuit generates pulse signals to drive the heater. The differential summation circuit performs a difference summation operation based on the temperature signals from each of the temperature sensors to reduce the influence of interfering gases. The programmable gain amplifier adjusts the signal gain of each of the temperature sensors. The digital signal processing unit coordinates the pulse drive circuit, adjusts the gain of the programmable gain amplifier, performs frequency domain filtering to distinguish between target gas and interfering gas, and performs dynamic weighting based on the temperature signals from each of the temperature sensors to generate a target gas concentration signal.

9. The thermal conductivity gas sensor chip according to claim 8, characterized in that, The digital signal processing unit performs dynamic weighting to generate a target gas concentration signal based on the temperature signals from each of the temperature sensors, specifically including: Mean filtering or Kalman filtering is performed on the temperature signals output by the multiple temperature sensors to suppress single-point noise; By applying time-division excitation to different heaters, the thermal response differences between the target gas and the interfering gas are obtained, and the target gas and the interfering gas are separated. The concentration signal of the target gas is S = Σ(α) i ·T i ·k i )·f(P, T am ), where T i α is the temperature signal output by temperature sensor i. i k is the weighting coefficient for temperature sensor i. i Let f(P, T) be the thermal conductivity of the heat dissipation area corresponding to temperature sensor i. am ) is the pressure-temperature compensation function, P is the atmospheric pressure of the gas to be measured, and T is the pressure-temperature compensation function. am The temperature of the gas atmosphere to be measured is 1.

10. The thermal conductivity gas sensor chip according to claim 9, characterized in that, The digital signal processing unit models the interfering gas, specifically including: A gas feature vector is constructed based on the response differences of different temperature sensors. A temperature response model of the interfering gas is trained using a machine learning model to generate a gain adjustment parameter table, which is used to distinguish between the target gas and the interfering gas.

11. The thermal conductivity gas sensor chip according to claim 10, characterized in that, It also includes a storage unit, which is an on-chip memory or an off-chip memory. The storage unit is used to pre-store at least two sets of gain adjustment parameter tables for different interfering gases. The gain adjustment parameter tables can be dynamically called through a serial communication protocol interface.

12. The thermal conductivity gas sensor chip according to claim 9, characterized in that, The pressure-temperature compensation function is obtained based on the simulation and training of pressure and temperature values. The pressure value is obtained through an on-chip or off-chip pressure sensor, and the temperature value is obtained through an on-chip or off-chip temperature sensor.

13. The thermal conductivity gas sensor chip according to claim 9, characterized in that, The digital signal processing unit also provides a self-calibration algorithm, specifically including: A target gas of known concentration is periodically introduced into the temperature sensor, and the weighting coefficient and thermal conductivity of each temperature sensor are corrected based on the difference between the concentration of the target gas of known concentration and the output concentration signal. Cross-calibration is performed using redundant temperature sensors in the temperature sensor suite to identify drifting temperature sensors and eliminate the drift effects of individual temperature sensors.

14. The thermal conductivity gas sensor chip according to claim 8, characterized in that, The mixed-signal circuit system also includes a multiplexer and an analog-to-digital converter. The multiplexer is used to simultaneously receive temperature signals from multiple heaters, and the analog-to-digital converter is used to convert analog signals into digital signals.

15. The thermal conductivity gas sensor chip according to claim 14, characterized in that, The multiplexer includes at least two analog input signals, and the analog-to-digital converter has at least 12 bits.

16. The thermal conductivity gas sensor chip according to claim 8, characterized in that, The pulse drive circuit includes a pulse generator and a power amplifier. The pulse generator is used to generate a low pulse signal with a specific frequency and duty cycle, and the power amplifier is used to amplify the low-power pulse signal generated by the pulse generator to drive the heater to work.

17. The thermal conductivity gas sensor chip according to claim 8, characterized in that, The frequency domain filter excites the thermal transient response in pulse mode, and converts the temperature signal in the time domain into a frequency domain signal through fast Fourier transform, distinguishing the target gas and the interfering gas based on the frequency range of the frequency domain signal.

18. A method for measuring gas concentration using a thermal conductivity gas sensor chip according to any one of claims 1 to 17, characterized in that, include: The heater is controlled to form a gradient thermal excitation mode in different heat dissipation areas; Frequency domain filtering is performed on the temperature signal output by the temperature sensor to distinguish between the target gas and the interfering gas; The signal gain of different temperature sensors is adjusted in real time, and the temperature signals output by different temperature sensors are amplified to reduce the influence of interfering gases. A target gas concentration signal is generated based on the temperature signals from each of the temperature sensors.

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