CN116297647A - MEMS differential thermal analysis sensor and DTA/DSC testing method - Google Patents
MEMS differential thermal analysis sensor and DTA/DSC testing method Download PDFInfo
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- CN116297647A CN116297647A CN202211574791.XA CN202211574791A CN116297647A CN 116297647 A CN116297647 A CN 116297647A CN 202211574791 A CN202211574791 A CN 202211574791A CN 116297647 A CN116297647 A CN 116297647A
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Abstract
The invention provides a MEMS differential thermal analysis sensor and a DTA/DSC testing method, the sensor comprises a detection thermopile, a reference thermopile, an environmental resistor and a shielding ring, the detection thermopile and the reference thermopile comprise a monocrystalline silicon substrate, a heat insulation cavity, a plurality of monocrystalline silicon thermocouple pairs and a support film, wherein the heat insulation cavity is positioned in the monocrystalline silicon substrate, the monocrystalline silicon thermocouple pairs are connected in series and supported by the support film to be suspended above the heat insulation cavity for realizing heat insulation, the monocrystalline silicon thermocouple pairs comprise N-type monocrystalline silicon thermocouple and P-type monocrystalline silicon thermocouple which are connected in series, the temperature and power sensitivity of the sensor is obviously improved to 28mV/K and 100V/W, and the noise equivalent temperature difference and the noise equivalent power reach 0.5mK or 0.2 mu W. Based on the output signal of the sensor, differential thermal analysis test and differential scanning calorimetric analysis test can be carried out on the physical or chemical process of heat absorption and release of materials, the sample consumption is small, and the test precision is high.
Description
Technical Field
The invention belongs to the technical field of micro-electro-mechanical systems and thermal sensing, and relates to a MEMS differential thermal analysis sensor and a DTA/DSC testing method.
Background
Differential thermal analysis (Differential Thermal Analysis, DTA for short) technology is an analysis technology widely applied in the fields of physics, chemistry, geology, metallurgy, petroleum, chemical industry and the like. The method is based on physical (such as crystal form conversion, sublimation, evaporation, melting and the like) and chemical changes (oxidation reduction, decomposition, dehydration, dissociation and the like) of substances which are often accompanied by endothermic or exothermic effects at a certain specific temperature in the heating or cooling process, and the temperature (delta T) between a sample and a reference when the endothermic or exothermic heat occurs is measured by controlling the temperature rise (or the temperature drop) through a program, so that the characteristic temperature (such as the crystallization conversion temperature, the melting point, the vitrification temperature and the like) of the physical and chemical changes is obtained. Based on differential thermal analysis, differential scanning calorimetric (Differential Scanning Calorimetry, abbreviated as DSC) techniques have been developed by creating closed loop compensation, compensating by the system or reducing the heat supply (Δq) as the heat of absorption occurs, so that the temperature between the sample and the reference remains consistent. The DSC technology can not only measure the characteristic temperature of the change of the heat absorption and release, but also quantitatively analyze the heat absorption and release value through heat compensation.
The core of the differential thermal analyzer, whether DTA or DSC technology, is a pair of sensing elements that monitor temperature (or thermal) changes, outputting differential electrical signals between the sample and a reference as a function of temperature. Thus, the sensitivity of the element to temperature (or heat), noise, determines to a large extent the analytical capabilities of DTA and DSC. The traditional differential thermal analysis core sensing element is formed by welding two thermocouples (nickel-chromium alloy or platinum-rhodium alloy and platinum wire in series), the temperature of the two crucibles (namely a sample and a reference) is programmed, and the test result is obtained by analyzing the differential electric signals of the two thermocouples, but the temperature programming rate and the temperature difference (or heat) resolution of the traditional differential thermal analyzer are limited, the high-precision test cannot be realized, the instrument size is large, and the application occasion may be limited. With the continuous development of MEMS technology, the differential analysis sensor gradually develops to a miniaturized, high-precision and rapid temperature rise and reduction chip type, thereby expanding the application field and improving the test performance.
Therefore, how to provide a MEMS differential thermal analysis sensor and a DTA/DSC test method to achieve a miniaturized, fast-response, high-precision and high-sensitivity differential thermal analysis test or differential calorimetric analysis test is an important technical problem to be solved by those skilled in the art.
It should be noted that the foregoing description of the background art is only for the purpose of facilitating a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. The above-described solutions are not considered to be known to the person skilled in the art simply because they are set forth in the background section of the present application.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention is directed to a MEMS differential thermal analysis sensor and a DTA/DSC test method, which are used to solve the problems that in the prior art, the temperature programming rate and the temperature difference (or heat) resolution of the differential thermal analyzer are limited, the test with rapid response, high precision and high sensitivity cannot be achieved, the instrument size is large, and the application occasion may be limited.
To achieve the above and other related objects, the present invention provides a MEMS differential thermal analysis sensor, comprising a reference thermopile and a detection thermopile adjacent to each other, each of the reference thermopile and the detection thermopile comprising the following structures:
a monocrystalline silicon substrate;
a heat insulation cavity which is positioned in the monocrystalline silicon substrate
The plurality of monocrystalline silicon thermocouple pairs are connected in series and suspended above the heat insulation cavity, the monocrystalline silicon thermocouple pairs comprise N-type monocrystalline silicon thermocouples and P-type monocrystalline silicon thermocouples, one ends of the monocrystalline silicon thermocouple pairs after being connected in series are used as hot ends, and the other ends of the monocrystalline silicon thermocouple pairs after being connected in series are used as cold ends;
and the support film is positioned above the monocrystalline silicon thermocouple pair to support the monocrystalline silicon thermocouple pair, the hot end is positioned in the central area of the support film, and the cold end is positioned in the edge area of the support film.
Optionally, a shielding ring is also included, the shielding ring being located on an upper surface of the sensor and surrounding the reference thermopile and the detection thermopile.
Optionally, an environmental resistor is also included, the environmental resistor being located on an upper surface of the sensor and between the reference thermopile and the sense thermopile.
Optionally, the reference thermopile and the detection thermopile further comprise heaters, and the heaters are located above the monocrystalline silicon thermocouple pairs and uniformly distributed around the hot end.
Optionally, the reference thermopile and the detection thermopile each further comprise an electrode structure, the electrode structure comprises a thermopile heating electrode and a thermopile output electrode, the thermopile heating electrode is electrically connected with the heater, and the thermopile output electrode is electrically connected with the monocrystalline silicon thermocouple pair.
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.
Optionally, the diameter of the support film ranges from 0.1mm to 2mm, and the number of the monocrystalline silicon thermocouple pairs ranges from 2 pairs to 400 pairs.
Optionally, the sensor is for performing at least one of a differential thermal analysis test and a differential scanning calorimetric analysis test.
The invention also provides a DTA test method, which comprises the following steps:
providing a MEMS differential thermal analysis sensor as described above;
placing a sample to be detected in the middle of the detection thermopile, wherein the sample to be detected covers a heater of the detection thermopile;
heating the hot end of the reference thermopile and the hot end of the detection thermopile simultaneously by a heater, heating a sample to be detected on the detection thermopile along with the heating, and stopping the heating process until the sample to be detected finishes the heat absorption and release process;
and obtaining the characteristic temperature of the sample to be detected when the heat absorption and release process occurs based on the output signal of the sensor in the heating process.
The invention also provides a DSC testing method, which comprises the following steps:
providing a MEMS differential thermal analysis sensor as described above;
placing a sample to be detected in the middle of the detection thermopile, wherein the sample to be detected covers a heater of the detection thermopile;
heating the hot end of the reference thermopile and the hot end of the detection thermopile simultaneously by a heater, heating a sample to be detected on the detection thermopile along with the heating, and stopping the heating process until the sample to be detected finishes the heat absorption and release process;
the temperature of the detection thermopile changes due to the heat absorption of the sample to be detected, and the temperature of the detection thermopile is always kept the same as the temperature of the reference thermopile by additionally compensating the heating power of the heater of the detection thermopile;
based on the output signal of the sensor for additionally compensating the power in the heating process, the characteristic temperature and the heat absorption and release heat value of the sample to be detected when heat absorption and release occur can be obtained.
As described above, the MEMS differential thermal analysis sensor of the invention is composed of a pair of thermopiles (reference thermopile and detection thermopile), each thermopile comprises a monocrystalline silicon thermocouple pair, and the temperature of the thermopiles can be sensitively detected by differentiating the thermoelectric potential signals of the thermopiles between the reference thermopiles and the detection thermopiles to obtain a response curve which is in linear relation with the temperature of the thermopiles, the noise of the sensor is relatively small, the temperature sensitivity and the power sensitivity are obviously improved compared with the corresponding sensitivity of the differential thermal analyzer in the prior art, the noise equivalent temperature difference and the noise equivalent power can reach mk or mu W level, and the sensor structure is obtained by manufacturing the reference thermopiles and the detection thermopiles on a monocrystalline silicon substrate, so that the sensor has good mechanical stability, batch manufacturing consistency and low cost. According to the testing method of the MEMS differential thermal analysis sensor, disclosed by the invention, the physical (or chemical) process of heat absorption and release of the material is analyzed by the output signal of the sensor, so that the differential thermal analysis test or differential scanning calorimetric analysis test is realized, the testing method is simple and easy to realize, the sample consumption is small, and the high-precision and high-accuracy test can be realized.
Drawings
FIG. 1 shows a schematic top view of a MEMS differential thermal analysis sensor of the present invention.
FIG. 2 shows a response curve between individual thermopile temperature and output potential difference in a MEMS differential thermal analysis sensor of the present invention.
FIG. 3 is a graph showing data from differential thermal analysis testing performed by the MEMS differential thermal analysis sensor of the present invention.
Description of element reference numerals
1. Reference thermopile
2. Detecting thermopiles
21. Monocrystalline silicon substrate
22. Heat insulation cavity
23. Monocrystalline silicon thermocouple pair
24. Support film
25. Heater
26. Thermopile heating electrode
27. Thermopile output electrode
3. Shielding ring
4. Environmental resistance
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.
Please refer to fig. 1 to 3. It should be noted that, the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
The inventor finds that, as introduced in the background art, the traditional differential thermal analyzer has defects, and along with the increasing requirement of high-precision temperature measurement, the capability of the MEMS thermopile for measuring the micro temperature difference needs to be further improved. According to the working principle of the thermopile, the Seebeck effect, the correspondence between the output electromotive force and the temperature difference can be expressed as uout=n (αa- αb) Δt, where αa and αb are Seebeck coefficients of two materials, and N is the number of thermocouples. Therefore, the temperature measurement performance of the MEMS thermopile is improved, the thermopile with high temperature measurement precision can be obtained by selecting a material with high Seebeck coefficient to form a thermocouple, effectively increasing the thermal even number arranged on the thermopile device through structural design and the like, and simultaneously meeting the miniaturization of the device and the feasibility of a manufacturing process.
Example 1
The present embodiment provides a differential calorimetric MEMS gas sensor, referring to fig. 1, which is a schematic top view of the sensor, and includes a reference thermopile 1 and a detection thermopile 2 adjacent to each other, where the reference thermopile 1 and the detection thermopile 2 each include the following structures: a monocrystalline silicon substrate 21, a heat-insulating cavity 22, a plurality of monocrystalline silicon thermocouple pairs 23 and a support film 24;
the heat insulation cavity 22 is positioned in the monocrystalline silicon substrate 21; the monocrystalline silicon thermocouple pair 23 is connected in series and is suspended above the heat insulation cavity 22, the monocrystalline silicon thermocouple pair 23 comprises an N-type monocrystalline silicon thermocouple and a P-type monocrystalline silicon thermocouple, one end of the monocrystalline silicon thermocouple pair 23 after being connected in series is used as a hot end, and the other end of the monocrystalline silicon thermocouple pair 23 after being connected in series is used as a cold end; the support film 24 is located above the monocrystalline silicon thermocouple pair 23 to support the monocrystalline 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.
Specifically, the monocrystalline silicon substrate 21 includes a front surface and a back surface that are disposed opposite to each other, the structures of the heat insulation cavity 22, the monocrystalline silicon thermocouple pair 23, the support film 24, and the like are all obtained by processing the front surface of the monocrystalline silicon substrate 21, and the monocrystalline silicon thermocouple pair 23 that is manufactured based on the monocrystalline silicon substrate 21 has structural and performance consistency, where the reference thermopile 1 and the detection thermopile 2 may be manufactured based on the same substrate, or may be connected into a whole after being manufactured separately.
Specifically, the heat-insulating cavity 22 is located in the monocrystalline silicon substrate 21, the top surface of the heat-insulating cavity 22 is lower than the front surface of the monocrystalline silicon substrate 21, and the bottom surface of the heat-insulating cavity 22 is higher than the back surface of the monocrystalline silicon substrate 21, namely, in the process of manufacturing the thermopile device, the heat-insulating cavity 22 is manufactured by a single-sided processing technology based on the front surface of the monocrystalline silicon substrate 21, and is not required to be formed by a double-sided alignment technology from the back surface of the monocrystalline silicon substrate 21, so that the manufacturing technology difficulty and cost of the thermopile device are effectively reduced, and the heat dissipation of the heat-insulating cavity 22 along the substrate can be reduced, thereby improving the performance of the device. In addition, in the manufacturing process of the sensor, the heat-insulating cavity 22 is obtained through wet etching, anisotropic etching is realized based on the selection of corrosive agents, finally the heat-insulating cavity 22 similar to a regular hexagon with narrow upper part and wide lower part is formed, and in the etching process of the heat-insulating cavity 22, the heat-insulating cavity of the reference thermopile 1 and the heat-insulating cavity of the detection thermopile 2 can be arranged at intervals or are mutually communicated through controlling etching parameters.
Specifically, the pair of monocrystalline silicon thermocouples 23 includes an N-type monocrystalline silicon thermocouple and a P-type monocrystalline silicon thermocouple, the N-type monocrystalline silicon thermocouple and the P-type monocrystalline silicon thermocouple are connected in series through a metal interconnection structure (not shown in fig. 1), the plurality of monocrystalline silicon thermocouples 23 are also connected in series through the metal interconnection structure, one end of the finally formed plurality of monocrystalline silicon thermocouple pairs 23 is used as a hot end, the metal interconnection structure corresponding to the position of the hot end is a hot end metal interconnection structure, the opposite end of the plurality of monocrystalline silicon thermocouples 23 is used as 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, and each metal block is connected with one N-type monocrystalline silicon thermocouple and one P-type monocrystalline silicon thermocouple in series.
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 pair 23 are equal. In this embodiment, the single crystal silicon thermocouple pairs 23 are all broken lines, and compared with other arrangement modes, the arrangement mode can obviously increase the number of the single crystal silicon thermocouple pairs 23 in unit area, improve the area utilization rate and the integration level, improve the thermal resistance, balance the thermal resistance and the thermal noise, and finally can keep the resolution capability of a small temperature difference (mK level), thereby obviously improving the working performance of the thermopile device. In other embodiments, the pair of monocrystalline silicon thermocouples 23 is linear, and compared with the folded line type, the linear thermocouple arrangement can further reduce the manufacturing difficulty and increase the manufacturing yield on the premise of meeting the test requirement, thereby reducing the cost.
Specifically, the support film 24 is located above the monocrystalline silicon thermocouple pair 23 to support the monocrystalline silicon thermocouple pair 23, the hot end is located in a central area of the support film 24, and the cold end is located in an edge area of the support film 24. The supporting film 24 is used for supporting the monocrystalline silicon thermocouple pairs 23, so that the monocrystalline silicon thermocouple pairs can be suspended above the heat insulation cavity 22, and the interference of heat dissipation on test results is reduced.
By way of example, the diameter of the support film 24 is in the range of 0.1mm to 2mm, and the number of the monocrystalline silicon thermocouple pairs 23 is in the range of 2 pairs to 400 pairs. It should be noted that, in practice, the shape of the support film 24 may be circular, polygonal or irregular due to different manufacturing processes, and the term "diameter" here refers to a parameter when the support film is idealized to be approximately circular, and in this embodiment, the shape of the support film 24 is approximately regular hexagon, and the diameter at this time is the diagonal length of the support film 24. In other shapes of the support film, the so-called diameter is the maximum distance between any two points on the support film when the line passes through the geometric center of the support film. The number of the monocrystalline silicon thermocouple pairs 23 is reasonably set based on practical application occasions and manufacturing feasibility through parameters such as shape setting, arrangement density and the like, and is preferably 30-80 pairs, so that the miniaturization requirement can be met under the condition of meeting the test performance of higher test precision. The number of the single crystal silicon thermocouple pairs 23 of the reference thermopile 1 and the detection thermopile 2 in this embodiment is 54 pairs, and the diameter of the support film 24 is about 640 μm.
As an example, the reference thermopile 1 and the detection thermopile 2 further comprise a heater 25, and the heater 25 is located above the monocrystalline silicon thermocouple pair 23 and uniformly distributed around the hot end. The heater 25 functions to apply a voltage signal to the thermopile to control the operating temperature of the thermopile. In this embodiment, the heater 25 has a shape similar to a gear, and can be uniformly and more closely distributed around the hot end, so that the hot end can be heated quickly and uniformly.
As an example, the reference thermopile 1 and the detection thermopile 2 further comprise electrode structures comprising a thermopile heating electrode 26 and a thermopile output electrode 27, the thermopile output electrode 27 being electrically connected to the monocrystalline silicon thermocouple pair 23, the thermopile heating electrode 26 being electrically connected to the heater 25. Wherein the thermopile heating electrode 26 is used 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, and the thermopile output electrode 27 is used as an output electrode to output the temperature difference potential difference signal accumulated in the plurality of monocrystalline silicon thermocouple pairs 23 connected in series in the thermopile.
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, and the above structures may be single-layer or multi-layer structures, in this embodiment, the above structures are all multi-layer structures, specifically, cr/Pt/Au stack structures, and the thicknesses of the corresponding layers are 40nm, 100nm, and 300nm, respectively.
As an example, the detection thermopile 2 and the reference thermopile 1 each further comprise a release hole (not identified in fig. 1) which communicates with the insulating cavity 22 vertically through the support membrane 24. The release holes enable the formation of the insulating cavity 22 to be accelerated when the sensor is being manufactured, thereby reducing the manufacturing time of the sensor.
As an example, the sensor further comprises a shielding ring 3, the shielding ring 3 is located on the upper surface of the sensor and surrounds the reference thermopile 1 and the detection thermopile 2, and the shielding ring 3 is used for eliminating the accumulation of surface charges of the thermopile, reducing noise and improving performance.
As an example, the sensor further comprises an ambient resistance 4, said ambient resistance 4 being located at the upper surface of the sensor and between the reference thermopile 1 and the detection thermopile 2. The ambient resistor 4 is mainly used as an ambient reference temperature for calibrating the temperature of the thermopile in real time. Correspondingly, the sensor further comprises an ambient resistance electrode (not identified in fig. 1) electrically connected to said ambient resistance 4.
As an example, the MEMS differential thermal analysis sensor may be used to perform at least one of a differential thermal analysis test and a differential scanning calorimeter thermal analysis test.
Specifically, the working principle of the sensor is as follows: the sensor mainly comprises reference thermopiles and detection thermopiles, wherein a plurality of pairs of p-type and N-type doped monocrystalline silicon thermocouples are integrated on the upper surface of each thermopile, based on the Seebeck effect, when tiny heat (or tiny temperature difference (mK level)) exists, a thermoelectric potential is generated between the cold end and the hot end of each monocrystalline silicon thermocouple pair, when tens pairs of thermocouples are connected in series, the thermoelectric potential is U=N (alpha A-alpha B) delta T, wherein alpha A and alpha B are Seebeck coefficients of p-type and N-type doped monocrystalline silicon, and N is the number of the thermocouples. In practical application, voltage signals are respectively applied to the reference thermopile and the detection thermopile through the heater of the reference thermopile and the heater of the detection thermopile to respectively control the working temperatures of the two thermopiles, when the center (hot end) of the heater of the detection thermopile generates infrared radiation, changes of environmental conditions (such as flow rate), heat absorption and release of surface materials and the like, heat change (namely temperature change) is correspondingly generated, the cold end of the detection thermopile is positioned at the edge of the device, the temperature is close to room temperature, so that tiny thermoelectric electromotive force generated between two ends (cold end and hot end) of a monocrystalline silicon thermocouple pair of the detection thermopile is gradually accumulated on the monocrystalline silicon thermocouple pair connected in series, and finally, an obvious electromotive force Uout is generated between an input electrode (thermopile heating electrode) and an output electrode (thermopile output electrode) of the detection thermopile and is compared with the output signal of the reference thermopile, and thus the detection function is realized.
Specifically, the output signal of the sensor comprises the output signal of the reference thermopile (i.e., the voltage V between the reference thermopile input electrode and the output electrode s ) An output signal of the detection thermopile (i.e. a voltage V between the detection thermopile input electrode and output electrode r ) And a differential signal (V) between the reference thermopile and the sense thermopile diff ＝V s -V r ) The output signal of the single thermopile is used for indicating the real-time temperature of the thermopile, the differential signal is used for analyzing the tiny temperature change of a tested sample caused by heat absorption and heat release by detecting the temperature difference between the detection thermopile and the reference thermopile, common mode noise caused by environmental interference can be eliminated by differential output, the temperature change caused by heat absorption and heat release of the tested sample is highlighted, and the interference of other factors on a test result is avoided.
Referring to FIG. 2, a response curve between the temperature and the output potential difference of a single thermopile (hot side metal interconnection layer) of the MEMS differential thermal analysis sensor according to the present embodiment is shown, and as can be seen from the curve in FIG. 2, the output voltage V of the single thermopile out (i.e., V at test) s Or V r ) Is in linear relation with the temperature of the thermopile, and the slope of the dotted line in the figure is the temperature response sensitivity of the sensor (S u =28 mV/K). At the same time, since the temperature (T) of the thermopile is provided by the output power of the heater, the linear relation between the output power of the heater and the temperature of the thermopile is recorded, i.e. the temperature response sensitivity of the thermopile can be converted into the power response sensitivity, i.e. S p ＝100V/W。
The related functional parameters of the sensor are generally obtained by theoretical calculation, and comprise thermal noise voltage, noise equivalent temperature difference and noise equivalent power, wherein thermal noise is generated at a certain temperature and resistance, and the thermal noise belongs to local oscillation noise of a device and cannot be avoided or eliminated; the noise equivalent temperature difference is the minimum temperature that the sensor can detectA degree; the noise equivalent power is the minimum power which can be detected by the sensor, and the smaller the numerical value of the three parameters is, the more stable the performance and the higher the detection precision of the sensor are proved. Thermal noise voltage of the sensor of the present embodiment
Wherein Boltzmann constant k B ＝1.38×10 -23 J/K, temperature t=300K, resistance r=540 kΩ, frequency bandwidth f=400 Hz; typically at a thermal noise voltage of 8 times (i.e. δu pp ＝8δu rms ) To estimate the noise equivalent temperature difference delta T pp ＝δu pp /S u =0.52 mK, and noise equivalent power δp pp ＝δu pp /S p ＝0.17μW。
The MEMS differential thermal analysis sensor of the embodiment consists of a pair of thermopiles (reference thermopiles and detection thermopiles), each thermopile comprises a monocrystalline silicon thermocouple pair, a response curve which is in linear relation with the temperature of the thermopiles is obtained by differentiating the output thermoelectric potential signals between the reference thermopiles and the detection thermopiles, the temperature of the thermopiles can be sensitively detected, the noise of the sensor is relatively small, the temperature sensitivity and the power sensitivity are obviously improved compared with the corresponding sensitivity of a differential thermal analyzer in the prior art, the noise equivalent temperature difference and the noise equivalent power can reach mk or mu W levels, and the reference thermopiles and the detection thermopiles are manufactured on a monocrystalline silicon substrate to obtain the sensor structure, so that the sensor has good mechanical stability, batch manufacturing consistency and low cost.
Example two
The present embodiment provides a DTA test method, which is based on the MEMS differential thermal analysis sensor in the first embodiment, and the principle of the analysis test is Differential Thermal Analysis (DTA) test, and includes the following steps:
providing a MEMS differential thermal analysis sensor as described in embodiment one;
placing a sample to be detected in the middle of the detection thermopile, wherein the sample to be detected covers a heater of the detection thermopile;
the hot end of the reference thermopile and the hot end of the detection thermopile are heated simultaneously through the heater, a sample to be detected on the detection thermopile is heated along with the heating, and the heating process is stopped when the sample to be detected completes the heat absorption and release process;
and obtaining the characteristic temperature of the sample to be detected when the heat absorption and release process occurs based on the output signal of the sensor in the heating process.
As an example, the endothermic and exothermic processes may be caused by physical processes such as crystal form conversion, sublimation, evaporation, melting, etc., or may be caused by chemical changes such as oxidation-reduction, decomposition, dehydration, dissociation, etc.
Specifically, taking the melting point of the test metal indium as an example, the theoretical melting point value of the metal indium is 156.6 ℃, when the sensor is adopted for Differential Thermal Analysis (DTA) analysis, a sample to be tested (metal indium) is placed on the test thermopile, the reference thermopile is used as a reference non-placed material, the temperature programming signals are applied to the reference thermopile and the positive and negative electrodes of the test thermopile to enable the two thermopiles to be heated simultaneously, when the melting point of the sample to be tested placed on the test thermopile is reached, as the melting point of the sample to be tested absorbs heat, the difference of the output signals of the two thermopiles can obtain a sudden change electric signal, the direction is negative (representing the heat absorption), and the corresponding temperature of the sudden change part and the melting point of the corresponding sample to be tested.
Referring to fig. 3, which shows a graph of differential thermal analysis test data of the present embodiment, it can be seen by DTA analysis that during temperature programming, the differential output of two thermopiles of the sensor is initially close to 0, i.e., the temperature of the reference thermopile and the temperature of the detection thermopile remain substantially consistent throughout the temperature programming process until the temperature of the reference thermopile is close to the melting point of indium, and the detection thermopile has a distinct jump peak due to the melting endotherm of indium disposed thereon, with the direction being downward, representing the melting endotherm. The temperature corresponding to 156.8 ℃ is obtained by analyzing the abrupt peak, the temperature is basically consistent with the melting point of the metal indium, and the experimental result proves that the MEMS differential analysis sensor of the embodiment can be used for physical (or chemical) process analysis of heat absorption and release of materials.
According to the testing method of the MEMS differential thermal analysis sensor, the differential thermal analysis test is realized by analyzing the physical (or chemical) process of heat absorption and release of the material by the output signal of the sensor, the testing method is simple and easy to realize, the sample consumption is small, and the high-precision and high-accuracy test can be realized.
Example III
The present invention also provides a DSC test method, which is based on the MEMS differential thermal analysis sensor in the first embodiment, and differs from the first embodiment in that the principle of the analysis test in the first embodiment is a Differential Thermal Analysis (DTA) test, and the principle of the analysis test in the present embodiment is a differential scanning calorimeter analysis (DSC) test, and includes the following steps:
providing a MEMS differential thermal analysis sensor as described in embodiment one;
placing a sample to be detected in the middle of the detection thermopile, wherein the sample to be detected covers a heater of the detection thermopile;
the hot end of the reference thermopile and the hot end of the detection thermopile are heated simultaneously through the heater, a sample to be detected on the detection thermopile is heated along with the heating, and the heating process is stopped when the sample to be detected completes the heat absorption and release process;
the temperature of the detection thermopile changes due to the heat absorption of the sample to be detected, and the temperature of the detection thermopile is always kept the same as the temperature of the reference thermopile by additionally compensating the heating power of the heater of the detection thermopile;
based on the output signal of the sensor for additionally compensating the power in the heating process, the characteristic temperature and the heat absorption and release heat value of the sample to be detected when heat absorption and release occur can be obtained.
As an example, the endothermic and exothermic processes may be caused by physical processes such as crystal form conversion, sublimation, evaporation, melting, etc., or may be caused by chemical changes such as oxidation-reduction, decomposition, dehydration, dissociation, etc.
Specifically, taking the heat required to be absorbed when the sample to be tested is melted as an example, when the sensor is adopted to perform differential scanningDuring the analysis of calorimetric measurement (DSC), a sample (metal indium) to be measured is placed on a detection thermopile, a reference thermopile is used as a reference, no material is placed, a temperature programming signal is applied to the reference thermopile and the positive electrode and the negative electrode of the detection thermopile to enable the two thermopiles to be heated simultaneously, and the two thermopiles are kept at the same temperature all the time in the heating process, namely V s ＝V r . When the sample to be measured is melted, the heat of the detection thermopile is partially absorbed, so that the temperature of the detection thermopile is reduced, and at the moment, the heater of the detection thermopile can additionally output a part of heating power (dQ/dt) to compensate the heat loss generated by heat absorption, so that the temperature of the detection thermopile is restored to be the same as the temperature of the reference thermopile. The heat required to be absorbed by the melting can be quantified by the additional compensation heat (relative to the environmental reference) of the heater of the heating thermopile when the sample to be measured is melted.
According to the testing method of the MEMS differential thermal analysis sensor, the physical (or chemical) process of heat absorption and release of the material is analyzed by the output signal of the sensor, so that differential scanning calorimetric analysis testing is realized, the testing method is simple and easy to realize, the sample consumption is small, and testing with high precision and high accuracy can be realized.
In summary, the MEMS differential thermal analysis sensor of the present invention is composed of a pair of thermopiles (reference thermopile and detection thermopile), each of which includes a monocrystalline silicon thermocouple, and the temperature of the thermopiles can be sensitively detected by differentiating the thermoelectromotive force signals of the thermopiles between the reference thermopiles and the detection thermopiles to obtain a response curve having a linear relationship with the temperature of the thermopiles, and the noise of the sensor is relatively small, the temperature sensitivity and the 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 mk or μw levels. According to the testing method of the MEMS differential thermal analysis sensor, disclosed by the invention, the physical (or chemical) process of heat absorption and release of the material is analyzed by the output signal of the sensor, so that the differential thermal analysis test or differential scanning calorimetric analysis test is realized, the testing method is simple and easy to realize, the sample consumption is small, and the high-precision and high-accuracy test can be realized. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (10)
1. A MEMS differential thermal analysis sensor comprising a reference thermopile and a sense thermopile in close proximity, the reference thermopile and the sense thermopile each comprising the structure:
a monocrystalline silicon substrate;
a heat insulation cavity which is positioned in the monocrystalline silicon substrate
The plurality of monocrystalline silicon thermocouple pairs are connected in series and suspended above the heat insulation cavity, the monocrystalline silicon thermocouple pairs comprise N-type monocrystalline silicon thermocouples and P-type monocrystalline silicon thermocouples, one ends of the monocrystalline silicon thermocouple pairs after being connected in series are used as hot ends, and the other ends of the monocrystalline silicon thermocouple pairs after being connected in series are used as cold ends;
and the support film is positioned above the monocrystalline silicon thermocouple pair to support the monocrystalline silicon thermocouple pair, the hot end is positioned in the central area of the support film, and the cold end is positioned in the edge area of the support film.
2. The MEMS differential thermal analysis sensor of claim 1, wherein: the sensor also comprises a shielding ring, wherein the shielding ring is positioned on the upper surface of the sensor and surrounds the reference thermopile and the detection thermopile.
3. The MEMS differential thermal analysis sensor of claim 1, wherein: the sensor also comprises an environmental resistor, wherein the environmental resistor is positioned on the upper surface of the sensor and is positioned between the reference thermopile and the detection thermopile.
4. The MEMS differential thermal analysis sensor of claim 1, wherein: the reference thermopile and the detection thermopile also comprise heaters, and the heaters are positioned above the monocrystalline silicon thermocouple pairs and uniformly distributed around the hot end.
5. The MEMS thermopile device of claim 4, wherein: the reference thermopile and the detection thermopile also comprise electrode structures, each electrode structure comprises a thermopile heating electrode and a thermopile output electrode, the thermopile heating electrodes are electrically connected with the heater, and the thermopile output electrodes are electrically connected with the monocrystalline silicon thermocouple pairs.
6. The MEMS differential thermal analysis sensor of claim 1, wherein: the monocrystalline silicon thermocouple pair comprises at least one of a linear type, a broken line type and a curved type.
7. The MEMS differential thermal analysis sensor of claim 1, wherein: the diameter of the supporting film ranges from 0.1mm to 2mm, and the number of the monocrystalline silicon thermocouple pairs ranges from 2 pairs to 400 pairs.
8. The MEMS differential thermal analysis sensor of claim 1, wherein: the sensor is used for performing at least one of a differential thermal analysis test and a differential scanning calorimetric analysis test.
9. A DTA test method comprising the steps of:
providing a MEMS differential thermal analysis sensor as claimed in any one of claims 1 to 8;
placing a sample to be detected in the middle of the detection thermopile, wherein the sample to be detected covers a heater of the detection thermopile;
heating the hot end of the reference thermopile and the hot end of the detection thermopile simultaneously by a heater, heating a sample to be detected on the detection thermopile along with the heating, and stopping the heating process until the sample to be detected finishes the heat absorption and release process;
and obtaining the characteristic temperature of the sample to be detected when the heat absorption and release process occurs based on the output signal of the sensor in the heating process.
10. A DSC testing method, comprising the steps of:
providing a MEMS differential thermal analysis sensor as claimed in any one of claims 1 to 8;
placing a sample to be detected in the middle of the detection thermopile, wherein the sample to be detected covers a heater of the detection thermopile;
heating the hot end of the reference thermopile and the hot end of the detection thermopile simultaneously by a heater, heating a sample to be detected on the detection thermopile along with the heating, and stopping the heating process until the sample to be detected finishes the heat absorption and release process;
the temperature of the detection thermopile changes due to the heat absorption of the sample to be detected, and the temperature of the detection thermopile is always kept the same as the temperature of the reference thermopile by additionally compensating the heating power of the heater of the detection thermopile;
based on the output signal of the sensor for additionally compensating the power in the heating process, the characteristic temperature and the heat absorption and release heat value of the sample to be detected when heat absorption and release occur can be obtained.
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