A MEMS differential thermal analysis sensor and a DTA / DSC testing method

Abstract

The application provides a MEMS differential thermal analysis sensor and a DTA / DSC testing method, the sensor comprising a detection thermocouple, a reference thermocouple, an ambient resistance and a shielding ring, wherein the detection thermocouple and the reference thermocouple each comprise a single crystal silicon substrate, a heat insulation cavity, a plurality of single crystal silicon thermocouple pairs and a supporting film, the heat insulation cavity is located in the single crystal silicon substrate, the plurality of single crystal silicon thermocouple pairs are connected in series and are supported by the supporting film to be suspended above the heat insulation cavity to achieve thermal isolation, and the single crystal silicon thermocouple pair comprises an N-type single crystal silicon thermocouple and a P-type single crystal silicon thermocouple connected in series, the temperature and power sensitivity of the sensor are significantly improved, reach 28 mV / K and 100 V / W, and the noise equivalent temperature difference and the noise equivalent power reach 0.5 mK or 0.2 muW. Based on the output signal of the sensor, differential thermal analysis testing and differential scanning calorimetry testing on physical or chemical processes of material heat absorption and release can be realized, the sample consumption is small, and the testing precision is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-electro-mechanical system and thermal sensing, and relates to a MEMS differential thermal analysis sensor and a DTA / DSC testing method. BACKGROUND

[0002] Differential thermal analysis (DTA) technology is an analysis technology widely used in the fields of physics, chemistry, geology, metallurgy, petroleum, chemical industry and the like. It is based on the physical (such as crystal transformation, sublimation, evaporation, melting and the like), chemical changes (oxidation and reduction, decomposition, dehydration and dissociation and the like) that a substance often accompanies with endothermic or exothermic effect at a certain temperature during heating or cooling, through program-controlled temperature rise (or drop), the temperature (ΔT) between the sample and the reference when the above-mentioned endothermic or exothermic occurs is measured, and then the characteristic temperature (such as crystal transformation temperature, melting point, glass transition temperature and the like) of the physical or chemical change is obtained. On the basis of differential thermal analysis, through establishing a closed loop compensation, the heat supply (ΔQ) is compensated or reduced by the system when the endothermic or exothermic occurs, so that the temperature between the sample and the reference is kept consistent, and then the differential scanning calorimetry (DSC) technology is developed. The DSC technology can not only measure the characteristic temperature of the above-mentioned endothermic or exothermic change, but also quantitatively analyze the endothermic or exothermic value through heat compensation.

[0003] No matter the DTA or the DSC technology, the core of the differential thermal analyzer is a pair of sensing elements for monitoring the temperature (or heat) change, which outputs the differential electric signal between the sample and the reference with the temperature change. Therefore, the sensitivity and noise of the element to the temperature (or heat) greatly determine the analysis ability of the DTA and the DSC. The traditional differential thermal analysis core sensing element is two thermocouples (nickel-chromium alloy or platinum-rhodium alloy and platinum wire are welded in series), through the program-controlled temperature rise of the two crucibles (i.e. the sample and the reference), the test result is obtained according to the differential electric signal of the two thermocouples, but the program-controlled temperature rise rate and the temperature difference (or heat) resolution of the traditional differential thermal analyzer are relatively limited, high-precision test cannot be realized, and the size of the instrument is large, which may also be limited in application occasions. With the continuous development of MEMS technology, the differential analysis sensor gradually develops towards chip type with small size, high precision, rapid temperature rise and drop, thereby expanding the application field and improving the test performance.

[0004] Therefore, how to provide a MEMS differential thermal analysis sensor and a DTA / DSC testing method to realize the differential thermal analysis test or differential scanning calorimetry test with small size, rapid response, high precision and high sensitivity becomes an important technical problem to be solved by the person skilled in the art.

[0005] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely describing the technical scheme of the present application and facilitating the understanding of the skilled in the art. The above technical scheme cannot be considered as known to the skilled in the art only because it is described in the background of the present application. SUMMARY

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present application is to provide a MEMS differential thermal analysis sensor and a DTA / DSC testing method, which are used to solve the problems that the program heating rate and the temperature difference (or heat) resolution of the differential thermal analyzer in the prior art are relatively limited, the fast response, high precision and high sensitivity testing cannot be realized, and the size of the instrument is large, and the application occasion may also be limited.

[0007] To achieve the above-mentioned purpose and other related purposes, the present application provides a MEMS differential thermal analysis sensor, comprising an adjacent reference thermocouple and a detection thermocouple, wherein the reference thermocouple and the detection thermocouple each comprise the following structure:

[0008] a single crystal silicon substrate;

[0009] a heat insulation cavity located in the single crystal silicon substrate

[0010] a plurality of single crystal silicon thermocouple pairs in series and suspended above the heat insulation cavity, wherein the single crystal silicon thermocouple pairs comprise N-type single crystal silicon thermocouples and P-type single crystal silicon thermocouples, one end of the plurality of single crystal silicon thermocouple pairs after being connected in series as a hot end, and the other end of the plurality of single crystal silicon thermocouple pairs after being connected in series as a cold end;

[0011] a support film located above the single crystal silicon thermocouple pairs to support the single crystal silicon thermocouple pairs, wherein the hot end is located in the center region of the support film, and the cold end is located in the edge region of the support film.

[0012] Optionally, it further comprises a shielding ring located on the upper surface of the sensor and surrounding the reference thermocouple and the detection thermocouple.

[0013] Optionally, it further comprises an environmental resistance located on the upper surface of the sensor and between the reference thermocouple and the detection thermocouple.

[0014] Optionally, the reference thermocouple and the detection thermocouple each further comprise a heater located above the single crystal silicon thermocouple pairs and uniformly distributed around the hot end.

[0015] Optionally, the reference thermocouple and the detection thermocouple each further comprise an electrode structure, the electrode structure comprising a thermocouple heating electrode and a thermocouple output electrode, the thermocouple heating electrode being electrically connected to the heater, and the thermocouple output electrode being electrically connected to the single-crystal silicon thermocouple pair.

[0016] Optionally, the single-crystal silicon thermocouple pair comprises at least one of a straight line type, a broken line type, and a curved line type.

[0017] Optionally, the diameter of the support film ranges from 0.1 mm to 2 mm, and the number of the single-crystal silicon thermocouple pairs ranges from 2 to 400.

[0018] Optionally, the sensor is used for at least one of a differential thermal analysis test and a differential scanning calorimetry test.

[0019] The present application also provides a DTA test method, comprising the following steps:

[0020] providing the MEMS differential thermal analysis sensor as described above;

[0021] placing a sample to be tested in the middle of the detection thermocouple, the sample to be tested covering the heater of the detection thermocouple;

[0022] heating the hot end of the reference thermocouple and the hot end of the detection thermocouple simultaneously by the heater, the sample to be tested on the detection thermocouple being heated at the same time, and the heating process being stopped when the sample to be tested completes the heat absorption and release process;

[0023] obtaining the characteristic temperature of the sample to be tested when the heat absorption and release process occurs based on the output signal of the sensor during the heating process.

[0024] The present application also provides a DSC test method, comprising the following steps:

[0025] providing the MEMS differential thermal analysis sensor as described above;

[0026] placing a sample to be tested in the middle of the detection thermocouple, the sample to be tested covering the heater of the detection thermocouple;

[0027] heating the hot end of the reference thermocouple and the hot end of the detection thermocouple simultaneously by the heater, the sample to be tested on the detection thermocouple being heated at the same time, and the heating process being stopped when the sample to be tested completes the heat absorption and release process;

[0028] Since the temperature of the detection thermocouple changes due to the heat absorption and release of the sample to be tested, the heater of the detection thermocouple additionally compensates for the heating power to heat the detection thermocouple to the same temperature as the reference thermocouple.

[0029] Based on the output signal of the additional compensation power of the sensor during the temperature rising process, the characteristic temperature and the heat value of the sample under test during the heat absorption and release can be obtained.

[0030] As described above, the MEMS differential thermal analysis sensor of the present application is composed of a pair of thermocouples (reference thermocouple and detection thermocouple), each of which includes a single crystal silicon thermocouple pair. By differentiating the thermoelectric power signal of the temperature difference between the reference thermocouple and the detection thermocouple, a response curve linearly related to the temperature of the thermocouple is obtained, which can sensitively detect the temperature of the thermocouple. The noise of the sensor is relatively small, and the temperature sensitivity and power sensitivity are significantly improved compared with the corresponding sensitivity of the differential thermal analysis instrument in the prior art. The noise equivalent temperature difference and the noise equivalent power can reach the level of mk or μW. Moreover, the sensor structure is obtained by fabricating the reference thermocouple and the detection thermocouple on a single crystal silicon substrate, so that the sensor has good mechanical stability, batch manufacturing consistency and low cost. The test method of the MEMS differential thermal analysis sensor of the present application analyzes the physical (or chemical) process of material heat absorption and release by the output signal of the sensor, realizes differential thermal analysis test or differential scanning calorimetry test, and the test method is simple and easy to implement, the sample consumption is small, and high precision and high accuracy test can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A top view of the MEMS differential thermal analysis sensor of the present application is shown.

[0032] Figure 2 A response curve between the temperature of a single thermocouple in the MEMS differential thermal analysis sensor of the present application and the output potential difference is shown.

[0033] Figure 3 A data graph of the differential thermal analysis test of the MEMS differential thermal analysis sensor of the present application is shown.

[0034] ELEMENT NUMBER EXPLANATION

[0035] 1 reference thermocouple

[0036] 2 detection thermocouple

[0037] 21 single crystal silicon substrate

[0038] 22 heat insulation cavity

[0039] 23 single crystal silicon thermocouple pair

[0040] 24 support film

[0041] 25 heater

[0042] 26 thermocouple heating electrode

[0043] 27 thermoelectric pile output electrode

[0044] 3 shielding ring

[0045] 4 ambient resistance DETAILED DESCRIPTION

[0046] The present application is herein described, by way of example only, with the assistance of the accompanying drawings detailed description. As will be realized by those skilled in the art, the application is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the application. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

[0047] Reference will now be made to the drawings, wherein: Figures 1 to 3 It is to be understood that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the application, for which reference should be made to the appended claims. Moreover, the drawings are not necessarily drawn to scale, and that, although the application has been described in connection with particular embodiments thereof, it will be understood that the application is capable of further modifications. These and other changes can be made to the application in light of the above-detailed description. Other and different embodiments can be devised without departing from the spirit and scope of the application.

[0048] The inventor found in practical work that, as introduced in the background art, the conventional differential thermal analyzer all has defects, with the increasing demand for high-precision temperature measurement, it is urgent to further improve the measurement ability of MEMS thermoelectric pile to small temperature difference. According to the working principle of thermoelectric pile-Seebeck effect, the corresponding relationship between output electromotive force and temperature difference can be expressed as Uout=N(αA-αB)ΔT, where αA and αB are the Seebeck coefficients of two materials, and N is the number of thermocouples. Therefore, to improve the temperature measurement performance of MEMS thermoelectric pile, we can start from the following aspects: selecting high Seebeck coefficient materials to form thermocouples, effectively increasing the number of thermocouples arranged on the thermoelectric pile device through structural design, while meeting the miniaturization of the device and the feasibility of manufacturing process, and obtaining high-precision thermoelectric pile.

[0049] Embodiment one

[0050] The embodiment provides a differential quantity heat type MEMS gas sensor, please refer to Figure 1 , which is a top view schematic diagram of the sensor, including an adjacent reference thermoelectric pile 1 and a detection thermoelectric pile 2, the reference thermoelectric pile 1 and the detection thermoelectric pile 2 both include the following structures: a single crystal silicon substrate 21, a heat insulation cavity 22, a plurality of single crystal silicon thermocouple pairs 23 and a support film 24;

[0051] The heat insulation cavity 22 is located in the single crystal silicon substrate 21; a plurality of the single crystal silicon thermocouple pairs 23 are connected in series and suspended above the heat insulation cavity 22, the single crystal silicon thermocouple pair 23 includes an N-type single crystal silicon thermocouple and a P-type single crystal silicon thermocouple, one end of the plurality of the single crystal silicon thermocouple pairs 23 after being connected in series serves as a hot end, and the other end of the plurality of the single crystal silicon thermocouple pairs 23 after being connected in series serves as a cold end; the support film 24 is located above the single crystal silicon thermocouple pair 23 to support the single crystal silicon thermocouple pair 23, the hot end is located in a central region of the support film 24, and the cold end is located in an edge region of the support film 24.

[0052] Specifically, the single crystal silicon substrate 21 includes opposite front and back surfaces, the heat insulation cavity 22, the single crystal silicon thermocouple pair 23, and the support film 24 are processed based on the front surface of the single crystal silicon substrate 21, the single crystal silicon thermocouple pair 23 manufactured based on the single crystal silicon substrate 21 has structural and performance consistency, and the reference thermopile 1 and the detection thermopile 2 can be manufactured based on the same substrate or connected to form a whole after being manufactured respectively.

[0053] Specifically, the heat insulation cavity 22 is located in the single crystal silicon substrate 21, a top surface of the heat insulation cavity 22 is lower than the front surface of the single crystal silicon substrate 21, and a bottom surface of the heat insulation cavity 22 is higher than the back surface of the single crystal silicon substrate 21, that is, the heat insulation cavity 22 is manufactured by single-sided processing technology based on the front surface of the single crystal silicon substrate 21, without forming by double-sided etching technology from the back surface of the single crystal silicon substrate 21, thereby effectively reducing the manufacturing process difficulty and cost of the thermopile device, and the heat insulation cavity 22 can reduce heat loss along the substrate, thereby improving the performance of the device. In addition, in the manufacturing process of the sensor, the heat insulation cavity 22 is obtained by wet etching, anisotropic etching is realized based on the selection of etchant, and finally the heat insulation cavity 22 similar to a regular hexagon with a narrow upper part and a wide lower part is formed. In the etching process of the heat insulation cavity 22, by controlling etching parameters, the heat insulation cavities of the reference thermopile 1 and the detection thermopile 2 can be arranged at intervals or communicated with each other.

[0054] Specifically, the single crystal silicon thermocouple pair 23 includes an N-type single crystal silicon thermocouple and a P-type single crystal silicon thermocouple, the N-type single crystal silicon thermocouple and the P-type single crystal silicon thermocouple are connected by a metal interconnection structure (not shown in the figure). Figure 1The plurality of single-crystal silicon thermocouple pairs 23 are connected in series through the metal interconnection structure, one end of the plurality of single-crystal silicon thermocouple pairs 23 is a hot end, the metal interconnection structure corresponding to the position of the hot end is a hot end metal interconnection structure, and the other end of the plurality of single-crystal silicon thermocouple pairs 23 is a cold end, the metal interconnection structure corresponding to the position of the cold end is a cold end metal interconnection structure, wherein the cold end metal interconnection structure and the hot end metal interconnection structure each include a plurality of metal blocks arranged at intervals, each metal block is connected in series with an N-type single-crystal silicon thermocouple and a P-type single-crystal silicon thermocouple.

[0055] As an example, the single-crystal silicon thermocouple pair 23 includes at least one of a straight line type, a broken line type, and a curved line type, and preferably, the lengths of the single-crystal silicon thermocouple pairs 23 are equal. In this embodiment, the single-crystal silicon thermocouple pairs 23 are all of the broken line type. Compared with other arrangement modes, this arrangement mode can significantly increase the number of single-crystal silicon thermocouple pairs 23 in a unit area, improve the area utilization and integration, improve the thermal resistance, balance the thermal resistance thermal noise, and finally maintain the resolution ability of a small temperature difference (mK level), thereby significantly improving the working performance of the thermoelectric device. In other embodiments, the single-crystal silicon thermocouple pairs 23 are of the straight line type. Compared with the broken line type, the straight line type of thermocouple can further reduce the manufacturing difficulty, increase the manufacturing yield, and thus reduce the cost under the premise of meeting the test requirements.

[0056] Specifically, the support film 24 is located above the single-crystal silicon thermocouple pairs 23 to support the single-crystal silicon thermocouple pairs 23, the hot end is located in the central region of the support film 24, and the cold end is located in the edge region of the support film 24. The support film 24 functions to support the plurality of single-crystal silicon thermocouple pairs 23, so that they can be suspended above the heat insulation cavity 22, thereby reducing the interference of heat dissipation on the test results.

[0057] As an example, the diameter of the support film 24 ranges from 0.1 mm to 2 mm, and the number of the single-crystal silicon thermocouple pairs 23 ranges from 2 to 400. It should be noted that the shape of the support film 24 may vary due to different manufacturing processes, and may be circular, polygonal, or irregular. Here, the diameter is a parameter when the support film is idealized as approximately circular. In the present embodiment, the shape of the support film 24 is a regular hexagon, and the diameter is the length of the diagonal. When the support film is in other shapes, the diameter is the maximum distance between any two points on the support film, with the line connecting the two points passing through the geometric center of the support film. The number of the single-crystal silicon thermocouple pairs 23 is set based on the actual application and manufacturing feasibility through parameters such as shape and arrangement density, and is preferably 30 to 80, which can meet the needs of miniaturization while meeting the testing performance of higher testing accuracy. In the present embodiment, the number of the single-crystal silicon thermocouple pairs 23 of the reference thermopile 1 and the detection thermopile 2 is 54, and the diameter of the support film 24 is about 640 μm.

[0058] As an example, the reference thermopile 1 and the detection thermopile 2 further include a heater 25, which is located above the single-crystal silicon thermocouple pairs 23 and uniformly distributed around the hot end. The heater 25 functions to apply a voltage signal to the thermopile, thereby controlling the operating temperature of the thermopile. In the present embodiment, the shape of the heater 25 is similar to a gear-like structure, which can be more uniformly and closely distributed around the hot end, so that the hot end can be quickly and uniformly heated.

[0059] As an example, the reference thermopile 1 and the detection thermopile 2 further include an electrode structure, which includes a thermopile heating electrode 26 and a thermopile output electrode 27. The thermopile output electrode 27 is electrically connected to the single-crystal silicon thermocouple pairs 23, and the thermopile heating electrode 26 is electrically connected to the heater 25. The thermopile heating electrode 26 functions as an input electrode to input a voltage signal to the thermopile, so as to generate a temperature difference between the cold end and the hot end of the thermopile. The thermopile output electrode 27 functions as an output electrode to output a thermoelectric potential difference signal accumulated in the plurality of single-crystal silicon thermocouple pairs 23 connected in series in the thermopile.

[0060] As an example, the materials of the heater 25, the electrode structure, and the metal interconnection structure include at least one of Cr, Pt, and Au. The above structures can be single-layer or multi-layer structures. In the present embodiment, the above structures are all multi-layer structures, and specifically, the structures are Cr / Pt / Au laminated structures, and the thicknesses of the corresponding layers are 40 nm, 100 nm, and 300 nm, respectively.

[0061] As an example, the detection thermopile 2 and the reference thermopile 1 each further include a release hole 28, which is located at the center of the support film 24 and is used to release the support film 24. Figure 1The release hole is vertically through the support film 24 and communicates with the heat insulation cavity 22. The release hole can accelerate the formation of the heat insulation cavity 22 when the sensor is manufactured, thereby reducing the manufacturing time of the sensor.

[0062] As an example, the sensor further comprises a shielding ring 3 located on the upper surface of the sensor and surrounding the reference thermocouple 1 and the detection thermocouple 2. The shielding ring 3 is used to eliminate the accumulation of thermocouple surface charge, reduce noise, and improve performance.

[0063] As an example, the sensor further comprises an ambient resistance 4 located on the upper surface of the sensor and between the reference thermocouple 1 and the detection thermocouple 2. The ambient resistance 4 is mainly used as a real-time calibration of the thermocouple temperature with respect to the ambient reference temperature. Accordingly, the sensor further comprises an ambient resistance electrode (not shown) electrically connected to the ambient resistance 4. Figure 1

[0064] As an example, the MEMS differential thermal analysis sensor can be used to perform at least one of a differential thermal analysis test and a differential scanning calorimetry test.

[0065] In particular, the working principle of the sensor is as follows: the sensor mainly comprises a reference thermocouple and a detection thermocouple, and the upper surface of each thermocouple integrates a plurality of pairs of p-type and n-type doped monocrystalline silicon thermocouples. Based on the Seebeck effect, when there is a small amount of heat (or a small temperature difference (mK level)), a thermoelectric potential will be generated between the cold end and the hot end of the pair of monocrystalline silicon thermocouples. When tens of pairs of thermocouples are connected in series, the thermoelectric potential is U=N(αA-αB)ΔT, where αA and αB are the Seebeck coefficients of p-type and n-type doped monocrystalline silicon, and N is the number of thermocouples. In actual application, the heater of the reference thermocouple and the heater of the detection thermocouple are used to apply voltage signals to the reference thermocouple and the detection thermocouple, respectively, to control the working temperature of the two thermocouples. When the center of the heater of the detection thermocouple (hot end) generates heat changes (i.e., temperature changes) due to infrared radiation, environmental conditions (such as flow rate), surface material heat absorption and release, etc., the cold end of the detection thermocouple is close to room temperature due to its location at the edge of the device, thereby generating a small thermoelectric potential between the two ends (cold end and hot end) of the pair of monocrystalline silicon thermocouples of the detection thermocouple. The small thermoelectric potential gradually accumulates on the series-connected pairs of monocrystalline silicon thermocouples, and finally generates a significant electromotive force Uout between the input electrode (thermocouple heating electrode) and the output electrode (thermocouple output electrode) of the detection thermocouple and outputs it. Compared with the output signal of the reference thermocouple, the detection function is realized.

[0066] ​Specifically, the output signals of the sensor include the output signal of the reference thermocouple (i.e. the voltage V s between the input and output electrodes of the reference thermocouple), the output signal of the detection thermocouple (i.e. the voltage V r between the input and output electrodes of the detection thermocouple), and the differential signal (V diff = V s -V r ) between the reference thermocouple and the detection thermocouple. The output signal of a single thermocouple is used to indicate the real-time temperature of the thermocouple. The differential signal is used to analyze the slight temperature change of the measured sample caused by heat absorption and release by detecting the temperature difference between the detection thermocouple and the reference thermocouple. The differential output can eliminate common-mode noise caused by environmental interference, highlight the temperature change caused by heat absorption and release of the measured sample, and avoid interference of other factors on the test results.

[0067] Please refer to Figure 2 , which shows the response curve between the temperature of a single thermocouple (metal interconnection layer at the hot end) of the MEMS differential thermal analysis sensor of the embodiment and the output potential difference. As can be seen from the curve in Figure 2 , the output voltage V out of a single thermocouple (i.e. V s or V r during testing) has a linear relationship with the temperature of the thermocouple. The slope of the dashed line in the figure is the temperature response sensitivity (S u = 28 mV / K) of the sensor. At the same time, since the temperature (T) of the thermocouple is provided by the output power of the heater, recording the linear relationship between the output power of the heater and the temperature of the thermocouple can convert the temperature response sensitivity of the thermocouple into the power response sensitivity, i.e. S p = 100 V / W.

[0068] The relevant functional parameters of the sensor are generally obtained by theoretical calculation, including thermal noise voltage, noise equivalent temperature difference, and noise equivalent power. The thermal noise will be generated at a certain temperature and resistance, and the thermal noise belongs to the local oscillator noise of the device and cannot be avoided or eliminated. The noise equivalent temperature difference is the minimum temperature that can be detected by the sensor. The noise equivalent power is the minimum power that can be detected by the sensor. The smaller the values of the above three parameters, the more stable the performance of the sensor and the higher the detection accuracy. The thermal noise voltage of the sensor of the embodiment is wherein Boltzmann constant k B = 1.38 × 10 -23 J / K, temperature T = 300 K, resistance R = 540 kΩ, and frequency bandwidth f = 400 Hz. Usually, the thermal noise voltage is 8 times (i.e. δu pp = 8 δu rms) to estimate the noise equivalent temperature difference δT pp = δu pp / S u = 0.52 mK, and the noise equivalent power δp pp = δu pp / S p = 0.17 μW.

[0069] The MEMS differential thermal analysis sensor of the embodiment is composed of a pair of thermocouples (a reference thermocouple and a detection thermocouple), each of which includes a single-crystal silicon thermocouple pair. By differentiating the output thermoelectric power signals between the reference thermocouple and the detection thermocouple, a response curve linearly related to the temperature of the thermocouple is obtained, which enables sensitive detection of the temperature of the thermocouple. The sensor has relatively small noise, and the temperature sensitivity and power sensitivity are significantly improved compared with the corresponding sensitivity of the differential thermal analysis instrument in the prior art. The noise equivalent temperature difference and the noise equivalent power can reach the level of mk or μW. Moreover, since the reference thermocouple and the detection thermocouple are fabricated on a single-crystal silicon substrate to obtain the sensor structure, the sensor simultaneously has good mechanical stability, batch manufacturing consistency, and low cost.

[0070] Embodiment Two

[0071] The embodiment provides a DTA test method based on the MEMS differential thermal analysis sensor in Embodiment One. The principle of the analysis test is differential thermal analysis (DTA) test, which includes the following steps:

[0072] Providing the MEMS differential thermal analysis sensor as described in Embodiment One;

[0073] Placing a sample to be tested in the middle of the detection thermocouple, and the sample to be tested covers the heater of the detection thermocouple;

[0074] Raising the temperature of the hot end of the reference thermocouple and the hot end of the detection thermocouple simultaneously through the heater, and the sample to be tested on the detection thermocouple is heated accordingly. The heating process is stopped when the sample to be tested completes the heat absorption and release process;

[0075] Obtaining the characteristic temperature of the sample to be tested when the heat absorption and release process occurs based on the output signal of the sensor during the heating process.

[0076] As an example, the heat absorption and release process can be caused by physical processes such as crystal transformation, sublimation, evaporation, melting, etc., or by chemical changes such as oxidation and reduction, decomposition, dehydration, and dissociation, etc.

[0077] Specifically, taking the melting point of indium as an example, the theoretical value of the melting point of indium is 156.6℃, when the sensor is used for differential thermal analysis (DTA) analysis, the sample (indium) to be detected is placed on the detection thermocouple, the reference thermocouple is used as a control without placing materials, a programmed temperature signal is applied to the positive and negative electrodes of the reference thermocouple and the detection thermocouple to simultaneously heat the two thermocouples, when the melting point of the sample to be detected placed on the detection thermocouple is reached, the melting of the sample to be detected will absorb heat, so that the difference between the output signals of the two thermocouples will obtain a sudden change in the electric signal, and the direction is negative (representing heat absorption), and the temperature corresponding to the mutation corresponds to the melting point of the sample to be detected.

[0078] Referring to Figure 3 , which shows the differential thermal analysis test data diagram of the embodiment, it can be seen that in the programmed temperature process, the differential output of the two thermocouples of the sensor is close to 0 at the beginning, that is, the temperatures of the reference thermocouple and the detection thermocouple remain basically the same during the heating process, until the melting point of indium is approached, the detection thermocouple absorbs heat due to the melting of the indium placed thereon, resulting in a significant jump peak in the differential signal, downward, representing heat absorption during melting. Through analysis of the mutation peak, the temperature at this point corresponds to 156.8℃, which is basically consistent with the melting point of indium, and the experimental results verify that the MEMS differential analysis sensor of the embodiment can be used for analysis of the physical (or chemical) process of material heat absorption and release.

[0079] The test method of the MEMS differential thermal analysis sensor of the embodiment analyzes the physical (or chemical) process of material heat absorption and release through the output signal of the sensor, realizes differential thermal analysis test, the test method is simple and easy to realize, the sample consumption is small, and high-precision and high-accuracy test can be realized.

[0080] Embodiment three

[0081] The application also provides a DSC test method based on the MEMS differential thermal analysis sensor in embodiment one, and the difference between embodiment one and the embodiment is that the principle of analysis and test in embodiment one is differential thermal analysis (DTA) test, while the principle of analysis and test in the embodiment is differential scanning calorimetry (DSC) test, comprising the following steps:

[0082] providing the MEMS differential thermal analysis sensor as described in embodiment one;

[0083] placing the sample to be detected in the middle of the detection thermocouple, and the sample to be detected covers the heater of the detection thermocouple;

[0084] The heating of the hot end of the reference thermoelectric pile and the hot end of the detection thermoelectric pile is simultaneously performed by the heater, and the sample to be measured on the detection thermoelectric pile is heated, and the heating process is stopped when the sample to be measured completes the endothermic and exothermic process.

[0085] The temperature of the detection thermoelectric pile changes due to the endothermic and exothermic process of the sample to be measured, and the heater of the detection thermoelectric pile additionally compensates the heating power to heat the detection thermoelectric pile to the same temperature as the reference thermoelectric pile.

[0086] Based on the output signal of the sensor during the heating process, the characteristic temperature and the endothermic and exothermic heat value of the sample to be measured can be obtained.

[0087] As an example, the endothermic and exothermic process can be caused by physical processes such as crystal transformation, sublimation, evaporation, melting, etc., or caused by chemical changes such as oxidation and reduction, decomposition, dehydration and dissociation, etc.

[0088] Specifically, taking the heat absorbed by the sample to be measured when melting as an example, when the sensor is used for differential scanning calorimetry (DSC) analysis, the sample to be measured (metal indium) is placed on the detection thermoelectric pile, and the reference thermoelectric pile is used as a control without placing materials. The positive and negative electrodes of the reference thermoelectric pile and the detection thermoelectric pile are used to apply a programmed temperature signal to heat the two thermoelectric piles at the same time, and the temperatures of the two thermoelectric piles are kept the same during the heating process, i.e. s r When the sample to be measured melts, the heat of the detection thermoelectric pile is partially absorbed, causing the temperature to decrease. At this time, the heater of the detection thermoelectric pile will additionally output a part of the heating power (dQ / dt) to compensate for the heat loss caused by the endothermic process, so that the temperature of the detection thermoelectric pile returns to the same temperature as the reference thermoelectric pile. The additional compensation heat of the heater of the detection thermoelectric pile (relative to the environment reference) during the melting of the sample to be measured can be used to quantitatively determine the heat absorbed during the melting process.

[0089] The test method of the MEMS differential thermal analysis sensor of the embodiment can analyze the physical (or chemical) process of the endothermic and exothermic process of the material by analyzing the output signal of the sensor, realize differential scanning calorimetry analysis test, the test method is simple and easy to realize, the sample consumption is small, and high precision and high accuracy test can be realized.

[0090] ​In summary, the MEMS differential thermal analysis sensor of the present application is composed of a pair of thermocouples (reference thermocouple and detection thermocouple), each of which includes a single crystal silicon thermocouple, and the difference between the thermoelectric power signals of the reference thermocouple and the detection thermocouple is obtained, and the response curve between the temperature of the thermocouple and the temperature of the thermocouple is linear, which can be used to detect the temperature of the thermocouple. The sensor has relatively small noise, and the temperature sensitivity and power sensitivity are significantly improved compared with the corresponding sensitivity of the differential thermal analyzer in the prior art, and the noise equivalent temperature difference and the noise equivalent power can reach the level of mk or μW, and since the reference thermocouple and the detection thermocouple are made on the single crystal silicon substrate to obtain the sensor structure, the thermocouple device has good mechanical stability, batch manufacturing consistency and low cost. The test method of the MEMS differential thermal analysis sensor of the present application analyzes the physical (or chemical) process of the material heat absorption and release of the output signal of the sensor, realizes the differential thermal analysis test or the differential scanning calorimetry test, the test method is simple and easy to realize, the sample consumption is small, and high precision and high accuracy test can be realized. Therefore, the present application effectively overcomes the shortcomings of the prior art and has high industrial utilization value.

[0091] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea of the present application should be covered by the claims of the present application.

Claims

1. A DTA / DSC testing method characterized by, The method comprises the following steps: providing a MEMS differential thermal analysis sensor comprising an adjacent reference thermocouple and a detection thermocouple, each of the reference thermocouple and the detection thermocouple comprising the following structure, a single crystal silicon substrate; a thermal insulation cavity in the single crystal silicon substrate; a plurality of single crystal silicon thermocouple pairs in series and suspended above the thermal insulation cavity, the single crystal silicon thermocouple pairs comprising N-type single crystal silicon thermocouples and P-type single crystal silicon thermocouples, one end of the single crystal silicon thermocouple pairs in series serving as a hot end, and the other end of the single crystal silicon thermocouple pairs in series serving as a cold end; a support film above the single crystal silicon thermocouple pairs to support the single crystal silicon thermocouple pairs, the hot end being in a central region of the support film, and the cold end being in an edge region of the support film; placing a sample to be tested in the middle of the detection thermocouple, the sample to be tested covering the heater of the detection thermocouple; simultaneously heating the hot end of the reference thermocouple and the hot end of the detection thermocouple by the heater, the sample to be tested on the detection thermocouple being heated, and the heating process being stopped when the sample to be tested completes the heat absorption and release process; obtaining the characteristic temperature of the sample to be tested when the heat absorption and release process occurs based on the output signal of the sensor during the heating process; due to the heat absorption and release of the sample to be tested, the temperature of the detection thermocouple changes, and the heater of the detection thermocouple additionally compensates for the heating power to heat the detection thermocouple to keep the temperature of the detection thermocouple the same as the temperature of the reference thermocouple; based on the output signal of the sensor during the heating process, the characteristic temperature and the heat absorption and release heat value of the sample to be tested when the heat absorption and release occur can be obtained.

2. The method of claim 1, wherein, The MEMS differential thermal analysis sensor further comprises a shielding ring on the upper surface of the sensor and surrounding the reference thermocouple and the detection thermocouple.

3. The method of claim 1, wherein, The MEMS differential thermal analysis sensor further comprises an environmental resistor on the upper surface of the sensor and between the reference thermocouple and the detection thermocouple.

4. The method of claim 1, wherein, Each of the reference thermocouple and the detection thermocouple further comprises a heater above the single crystal silicon thermocouple pairs and uniformly distributed around the hot end.

5. The method of claim 4, wherein, Each of the reference thermocouple and the detection thermocouple further comprises an electrode structure comprising a thermocouple heating electrode and a thermocouple output electrode, the thermocouple heating electrode being electrically connected to the heater, and the thermocouple output electrode being electrically connected to the single crystal silicon thermocouple pairs.

6. The method of claim 1, wherein, The single crystal silicon thermocouple pairs comprise at least one of a straight line type, a broken line type, and a curved line type.

7. The method of claim 1, wherein, The diameter of the support film ranges from 0.1 mm to 2 mm, and the number of the single crystal silicon thermocouple pairs ranges from 2 pairs to 400 pairs.

8. The method of claim 1, wherein, The sensor is used for at least one of differential thermal analysis testing and differential scanning calorimetry testing.

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