TW202146864A - Thermistor and microbolometer based on the thermistor formed by sequentially forming a first aluminum nitride film, a vanadium oxide film, and a second aluminum nitride film on a substrate - Google Patents

Abstract

A thermistor is a three-layer stack structure formed by sequentially forming a first aluminum nitride film, a vanadium oxide film, and a second aluminum nitride film on a substrate. The first aluminum nitride film on the bottom layer has high thermal conductivity and excellent temperature uniformity, and can be a basis for the growth of vanadium oxide film. The vanadium oxide film on the middle layer is used as a heat-sensitive reaction layer, has a higher temperature resistivity, a faster reaction speed and a lower process temperature and provides a wide temperature measurement range. The second aluminum nitride film on the top layer is used as a passivation layer and provides excellent thermal conductivity, temperature uniformity and protection. Furthermore, fabricating the three-layer stack structure in a micro-floating bridge structure of the microbolometer can improve the temperature uniformity and increase the 10 to 17 μm far-infrared wavelength absorption efficiency.

Description

Thermistor and microbolometer based on the thermistor

The invention belongs to the technical field of semiconductors, and particularly relates to a thermistor and a microbolometer based on the thermistor.

Thermistor is a resistor that is extremely sensitive to temperature changes. Using its sensitivity to temperature, it has been widely used in temperature measurement, temperature control, temperature compensation, barometric pressure measurement, meteorological detection, overload protection and so on.

The thermistor-based microbolometer is an infrared detector that has developed very rapidly in recent years. It is mainly completed through the micro-pontoon structure. The basic principle is that the light absorbing layer of the micro-pontoon structure absorbs the external infrared radiation energy. A change occurs, resulting in a change in the resistance value of the thermistor, and the required information is obtained by detecting this change. In the micro-pontoon structure, the thermistor as the core has a great influence on the sensitivity of the microbolometer. At present, the most commonly used thermistor materials are polysilicon films or transition metal oxide films. Among them, vanadium oxide is one of the transition metal oxides, which has the advantages of high temperature resistivity, fast reaction speed, low process temperature and wide temperature measurement range, which can meet the requirements of high-performance micro-radiant heat Calculate the demand. However, the growth conditions of vanadium oxide thin films are not easy to control, and the resistance uniformity and thermal stability are often poor, resulting in unstable output signals, which affects product performance and is not conducive to the development of high-performance microbolometers.

Therefore, the above-mentioned prior art still has room for improvement and development.

In view of this, in view of the deficiencies in the prior art, the main purpose of the present invention is to provide a thermistor and a microbolometer based on the thermistor, which are sequentially stacked on a substrate to form a first aluminum nitride film, a vanadium oxide film and The second aluminum nitride film, based on the excellent thermal conductivity of aluminum nitride, can effectively improve the shortcomings of thermistor uniformity and poor thermal stability, so as to meet the needs of high-performance microbolometers.

In order to achieve the above object, the present invention provides a thermistor, wherein a substrate, a first aluminum nitride film, a vanadium oxide film and a second aluminum nitride film are stacked in sequence. Among them, the first aluminum nitride film has high thermal conductivity and can be the growth basis of the vanadium oxide film; the vanadium oxide film, as a heat-sensitive reaction layer, has a higher temperature resistance coefficient, a faster reaction speed, and a lower process temperature And provide a wide temperature measurement range; and the second aluminum nitride film acts as a passivation layer, and provides thermal conductivity, temperature uniformity and protection.

In addition, the present invention also provides a microbolometer, comprising a micro pontoon structure, the micro pontoon structure is located above a substrate, an air gap layer is formed between the micro pontoon structure and the substrate, and sequentially includes a second nitride layer from top to bottom Aluminum thin film, vanadium monoxide thin film and a first aluminum nitride thin film. Among them, the first aluminum nitride film is used as the support layer of the micro-floating bridge structure, which has the characteristics of being able to withstand about 440 MPa stress and good stability, and can be the growth basis of the vanadium oxide film. In addition, it also has high thermal conductivity, which can improve the temperature uniformity of the micro-floating bridge structure; as a heat-sensitive reaction layer, the vanadium oxide film has a higher temperature resistance coefficient, a faster reaction speed, a lower process temperature and provides a wide range of Temperature measurement range; while the second aluminum nitride film is used as a passivation layer to provide thermal conductivity and temperature uniformity, and can also absorb infrared energy of specific wavelengths.

Compared with the prior art, the present invention disposes the vanadium oxide film between the first aluminum nitride film and the second aluminum nitride film. Since the aluminum nitride film has high thermal conductivity and high heat transfer efficiency, it can provide Better temperature uniformity helps to improve the resistance uniformity and thermal stability of the thermistor, and in the micro-floating bridge structure, the aluminum nitride film can improve the absorption efficiency of the thermistor at the wavelength of 10 ~ 17μm at the same time. And according to Wein's displacement law of radiant heat: λ _m × T=2898μm·K, the thermistor structure of the aluminum nitride/vanadium oxide/aluminum nitride three-layer film of the present invention can enhance high-performance micro-radiant heat The meter measures the efficiency at a temperature of 17 ~ - 102 ℃.

The following describes in detail with specific embodiments, when it is easier to understand the purpose, technical content, characteristics and effects of the present invention.

Please refer to FIG. 1 , which shows the thermistor 100 provided by the first embodiment of the present invention. The thermistor 100 of the present embodiment is formed on a substrate 10 with a three-layer stack structure 20 of an aluminum nitride film/vanadium oxide film/aluminum nitride film, and the three-layer stack structure 20 includes a first aluminum nitride film 21. A vanadium oxide film 22 and a second aluminum nitride film 23.

In this embodiment, the substrate 10 is a silicon substrate; in practical applications, the material of the substrate 10 can be selected from one of single crystal silicon, single crystal germanium, titanium dioxide, silicon nitride, titanium nitride, glass, sapphire and metal element.

The bottom layer of the three-layer stack structure 20 is a first aluminum nitride film 21 . The first aluminum nitride film 21 is used as a buffer layer between the substrate 10 and the vanadium oxide film 22 , and can also be used as a vanadium oxide film. 22 growth basis, in addition, due to the high thermal conductivity of aluminum nitride material, the response speed and temperature uniformity of the thermistor can be increased.

The middle layer of the three-layer stack structure 20 is a vanadium oxide film 22, and the vanadium oxide film 22 is used as a heat-sensitive reaction layer. Temperature resistance coefficient (TCR), faster response speed, lower process temperature and provide a wide temperature measurement range. The vanadium oxide thin film 22 can be a pure phase monoclinic crystal phase or a tetragonal crystal phase, and the thickness of the vanadium oxide thin film 22 is preferably 100-300 nm, and the vanadium oxide thin film 22 is pure vanadium oxide or vanadium oxide doped with other elements.

The top layer of the three-layer stack structure 20 is a second aluminum nitride film 23, which is used as a passivation layer, and can provide high thermal conductivity and uniform temperature, and can achieve protection. The thicknesses of the first aluminum nitride film 21 and the second aluminum nitride film 23 are preferably 200-500 nm.

Please refer to FIG. 2, which shows the temperature resistance characteristic curve of the thermistor 100 provided by the first embodiment of the present invention. As shown in the figure, the sheet resistance value of the thermistor decreases as the temperature rises (negative temperature resistance characteristic), and it changes in a quadratic polynomial relationship. In this embodiment, the temperature resistance characteristic curve equation of the thermistor can be expressed as y = 0.019x ² - 3.5745x + 219.05, R ² = 0.9995, y represents the sheet resistance value of the thermistor, x represents the measurement temperature, R Representing the curvature of the temperature resistance characteristic curve, the sheet resistance value of the thermistor at 25 ℃ is 141.56 KΩ.

The thermistor 100 of this embodiment can be fabricated by sequentially depositing the first aluminum nitride film 21 , the vanadium oxide film 22 and the second aluminum nitride film 23 on the substrate 10 .

Please refer to FIG. 3 , which is a schematic cross-sectional structure diagram of the thermistor 200 provided by the second embodiment of the present invention. Different from the first embodiment, the thermistor 200 of this embodiment partially hollows out the substrate 10 , and can be fabricated by sequentially depositing the first aluminum nitride film 21 , the vanadium oxide film 22 and the second film on the substrate 10 . The aluminum nitride film 23 is then etched on the backside of the substrate 10 to form a plurality of holes 11 , and the hole-type thermistor 200 is completed, which can reduce the thermal capacity of the substrate 10 and increase the thermal sensitivity of the thermistor 200 .

Please refer to FIG. 4 , which is a schematic cross-sectional structure diagram of the microbolometer 300 provided by the third embodiment of the present invention. Different from the first and second embodiments, the microbolometer 300 of this embodiment uses the above three-layer stack structure to be suspended above the substrate 10 by using two supporting feet 30 . The polymer material is coated, and then the first aluminum nitride film 21 , the vanadium oxide film 22 and the second aluminum nitride film 23 are deposited in sequence, and then the polymer material is removed to form a connection between the three-layer stack structure 20 and the substrate 10 . Support the feet 30 to complete the pontoon-type microbolometer 300 .

Please refer to FIG. 5, which is a schematic cross-sectional structure diagram of the microbolometer 500 provided by the fourth embodiment of the present invention. The microbolometer 500 of this embodiment includes a micro-pontoon structure 50 , the micro-pontoon structure 50 is suspended above the substrate 10 , and a gap layer 60 is formed between the micro-pontoon structure 50 and the substrate 10 , and the micro-pontoon structure 50 has a A three-layer stack structure 20 of aluminum nitride film/vanadium oxide film/aluminum nitride film, the three-layer stack structure 20 includes a second aluminum nitride film 23, a vanadium oxide film 22 and a first nitrogen film from top to bottom Aluminum foil 21. The three-layer stack structure 20 of the micro-floating bridge structure 50 of this embodiment has been described in detail in the above-mentioned embodiments, and for the sake of brevity, it will not be repeated here. Meanwhile, those skilled in the art can also understand the specific structure of the microbolometer 500 and its deformation, which will not be repeated here.

To further illustrate the effects that the thermistor of the present invention can achieve when applied to a microbolometer. In the three-layer stack structure of thermistor, the first aluminum nitride film on the bottom layer is used as the support layer of the micro-floating bridge structure, which has the ability to withstand about 400 MPa stress, good stability, and can also be used as vanadium oxide. The growth basis of the film, and aluminum nitride material can be used to have high thermal conductivity, which can improve the temperature uniformity of the micro-floating bridge structure. The vanadium oxide film in the middle layer is used as a heat sensitive reaction layer, which has a higher temperature resistance coefficient, a faster response speed, a lower process temperature and a wide temperature measurement range. The second aluminum nitride film on the top layer is used as a passivation layer, which can provide thermal conductivity and temperature uniformity, and can improve the absorption efficiency of infrared rays with a wavelength of 10 ~ 17 μm.

In the present invention, the aluminum nitride film can simultaneously improve the absorption efficiency of the microbolometer in the infrared wavelength range of 10 ~ 17μm, and according to Wein's displacement law of radiant heat: λ _m × T=2898μm·K, the nitrogen of the present invention The thermistor structure of aluminum oxide/vanadium oxide/aluminum nitride three-layer film can enhance the temperature measurement efficiency of high-performance microbolometers at 17 ~ -102 ℃.

Table 1 Optical and thermal properties of aluminum nitride, silicon nitride and silicon Aluminum Nitride Film Silicon nitride film Silicon substrate Thermal conductivity (W/mK) ~170 ~20 ~150 Thermal expansion coefficient (10 ^-6 /℃) ~2.5 ~1.5 ~4 Dispersion Low (peak 14μm) High (peak 11μm) * Refractive index change Low (n=1.6-0.8) High (n=1.8-3.0) *

To further illustrate, it is known that the silicon nitride film can also be used as the base material of the thermal film, the thermistor of the present invention is to set the vanadium oxide film between the two aluminum nitride films, as can be seen from the above Table 1 The excellent properties of aluminum nitride films compared to silicon nitride films are as follows: 1. The aluminum nitride film has a high thermal conductivity, and its heat transfer efficiency is high. 2. The thermal expansion coefficient of the aluminum nitride film and the silicon substrate is closer to that of the silicon nitride film and the silicon substrate, and the aluminum nitride film is less likely to fall off due to thermal stress. 3. The dispersion phenomenon of silicon nitride film in the wavelength range of 6 ~ 12μm is higher than that of aluminum nitride film, and obvious dispersion phenomenon occurs in the wavelength of 11 μm, which is not conducive to spectrum detection. 4. For thermal detectors, the thermal conductivity (reaction speed) of the aluminum nitride film and the light absorption efficiency of the vanadium oxide film at a wavelength of 10 ~ 17μm are better than those of the silicon nitride film.

It must be noted that, in the three-layer stack structure of the thermistor of the present invention, the first aluminum nitride film on the bottom layer must be limited to the minimum temperature and the electrical properties of vanadium oxide that do not affect other film layers, and the first aluminum nitride film on the top layer must be limited. The process temperature of the aluminum nitride film must not affect the characteristics of the vanadium oxide film. The vanadium oxide film is a thermally reactive layer, which can exhibit a higher temperature resistivity.

To sum up, according to the thermistor and the microbolometer based on the thermistor provided by the present invention, the thermistor is formed on the substrate with three layers of aluminum nitride film/vanadium oxide film/aluminum nitride film The stacked structure helps to improve the radiant heat detection, resistance uniformity and thermal stability of the thermistor. This three-layer stacked structure can be further applied to the micro-floating bridge structure of the microbolometer, which can improve the temperature uniformity and specific wavelength. The high light absorption efficiency can meet the needs of high-performance microbolometers, thereby improving product value and industrial competitiveness.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of various changes or replacements thereof within the technical scope disclosed by the present invention. , these should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

100, 200: thermistor 10: Substrate 11: Holes 20: Three-layer stacked structure 21: The first aluminum nitride film 22: Vanadium oxide film 23: The second aluminum nitride film 30: Support feet 300, 500: Microbolometer 50: Micro pontoon structure 60: empty gap layer

FIG. 1 is a schematic cross-sectional structure diagram of the thermistor provided by the first embodiment of the present invention. FIG. 2 is a temperature resistance characteristic curve of the thermistor provided by the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional structure diagram of the thermistor provided by the second embodiment of the present invention. FIG. 4 is a schematic cross-sectional structure diagram of the microbolometer provided by the third embodiment of the present invention. FIG. 5 is a schematic cross-sectional structure diagram of the microbolometer provided by the fourth embodiment of the present invention.

100: Thermistor

10: Substrate

20: Three-layer stacked structure

21: The first aluminum nitride film

22: Vanadium oxide film

23: The second aluminum nitride film

Claims (12)

A thermistor comprising: a substrate; a first aluminum nitride film disposed above the substrate; The vanadium monoxide film is disposed on the first aluminum nitride film; and A second aluminum nitride film is disposed on the vanadium oxide film. The thermistor according to claim 1, wherein the substrate is one of single crystal silicon, single crystal germanium, titanium dioxide, silicon nitride, titanium nitride, glass, sapphire and metal element. The thermistor according to claim 1, wherein the structural formula of the vanadium oxide film is VOx, wherein x is 1.0-2.5. The thermistor according to claim 1, wherein the vanadium oxide thin film is a pure monoclinic or tetragonal phase. The thermistor as claimed in claim 1, wherein the thickness of the vanadium oxide film is 100-300 nm. The thermistor according to claim 1, wherein the thickness of the first aluminum nitride film and the second aluminum nitride film is 200-500 nm. A microbolometer includes a micro pontoon structure, an air gap layer is formed between the micro pontoon structure and a substrate, and the micro pontoon structure includes: a first aluminum nitride film disposed above the substrate; The vanadium monoxide film is disposed on the first aluminum nitride film; and A second aluminum nitride film is disposed on the vanadium oxide film. The microbolometer according to claim 7, wherein the substrate is one of single crystal silicon, single crystal germanium, titanium dioxide, silicon nitride, titanium nitride, glass, sapphire and metal element. The microbolometer according to claim 7, wherein the structural formula of the vanadium oxide film is VOx, wherein x is 1.0-2.5. The microbolometer according to claim 7, wherein the vanadium oxide thin film is a pure monoclinic or tetragonal crystal phase. The microbolometer as claimed in claim 7, wherein the thickness of the vanadium oxide film is 100-300 nm. The microbolometer according to claim 7, wherein the thickness of the first aluminum nitride film and the second aluminum nitride film is 200-500 nm.

Images