JPH0587643A - Thermometer for extremely low temperature - Google Patents

Abstract

PURPOSE:To realize a resistance thermometer for extremely low temp. capable of measuring temp. with high accuracy by constituting a finely crystallized semiconductor membrane of an amorphous silicon semiconductor membrane resistor composed of a fine crystal phase with a specific fine crystallization degree or more and showing a resistance value having a conductive characteristic almost proportional to the rise to the beta-th power of temp. CONSTITUTION:A thermometer for extremely low temp. is equipped with an insulating substrate, the finely crystallized semiconductor membrane 2 accumulated on the insulating substrate and a pair of the ohmic electrodes 3a, 3b respectively being in contact with the finely crystallized semiconductor membrane and provided so as to provide a predetermined distance therebetween. The finely crystallized semiconductor membrane is an amorphous silicon semiconductor membrane resistor composed of a fine crystal phase with a fine crystallization degree of 20% or more and showing a resistance value having a conductive characteristic almost proportional to the rise to the beta-th power of temp. Simple R=alphaTbeta is formed in the relation between temp. T and resistance R and a resistance thermometer for extremely low temp. capable of measuring temp. with high accuracy by performing relatively easy correction in a magnetic field at extremely temp. is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermometer for measuring temperature in a cryogenic region with high accuracy, particularly a cryostat operated under cryogenic conditions, a superconducting electromagnet for a fusion reactor, M
It is used to measure cryogenic temperatures such as HD power generation, superconducting power transmission, and ultra-high speed magnetic levitation trains.

[0002]

2. Description of the Related Art For measuring the temperature in an extremely low temperature range, a resistance temperature detector utilizing a change in resistance value of a semiconductor or a metal is used. This resistance thermometer is small and easy to use. In particular, the germanium thermometer has the characteristic of high temperature detection sensitivity (hereinafter also referred to as detection sensitivity or detection voltage). Heavily depends on. In addition, "Experimental Techn
issues in Low-Temperature
Physics (by GUY K. WHITE) OX
FORD SCIENCE PUBLICATION
S, 1979 Third Edition ",
As shown in FIG. 5, the relational expression between the resistance value R and the temperature T is complicated, and there is a large variation in individual characteristics. Therefore, in practice, individual calibration is required, so that there is a problem that the cost becomes high. It was

It is said that the above-mentioned problems are caused by carrier degeneracy due to high-concentration doping and hopping conduction, and those having small temperature dependency of temperature detection sensitivity have not been developed yet. The same applies when a silicon semiconductor is used. In other words, both have low detection sensitivity,
Further, the temperature dependency of the temperature detection sensitivity is large, and therefore the measurement temperature range is narrow, and a circuit for correcting the nonlinearity is required.

Next, when measuring a low temperature or a very low temperature using a resistance temperature detector, only the resistance temperature resistor is exposed to a low temperature or a very low temperature, and the reference resistance body is often kept at a room temperature. In such a case, a thermoelectromotive force due to noise generated on the wiring or a temperature difference between the wirings is easily generated, which leads to deterioration of measurement accuracy.

[0005]

However, as shown in FIG. 5, none of the conventional resistance thermometers for cryogenic temperatures has a simple relational expression for the relationship between the temperature T and the resistance R, so that there are relatively many. It was necessary to calibrate at temperature. Therefore, a simple relational expression holds in the relation between the temperature T and the resistance R, which does not require calibration at many temperatures,
Further, it is an object of the present invention to realize an extremely low temperature resistance thermometer capable of highly accurate measurement by performing relatively simple correction in a magnetic field under extremely low temperature.

[0006] In addition to the above, it is a resistance thermometer for cryogenic temperature, which has high-speed response, is easy to miniaturize and thin, and can integrate a resistance temperature detector and a reference resistor.
Further, it is an object of the present invention to realize a resistance thermometer for extremely low temperature of a resistance value changing type which also has a capability of being used in a low temperature region.

[0007]

In view of the above points, in the present invention, a "temperature-sensitive device" by the same applicant (Japanese Patent Laid-Open No. 58-17).
No. 0001) and "temperature sensitive device" (Japanese Patent Application No. 2-750).
No. 94), and the plasma CV
The conduction characteristics of the amorphous silicon thin film deposited on the insulating substrate by using the D method or the photo-CVD method are the microcrystallinity, that is, the microcrystals contained in the amorphous material measured by the X-ray diffraction method or the laser Raman spectroscopy method. Note that different experimental facts were obtained depending on the occupancy in the phase.

That is, plasma C is formed on the ceramic substrate.
It has been discovered by the inventor that the relational expression between the resistance R and the temperature T of the resistor formed of the microcrystalline silicon thin film deposited by using the VD method can be simply expressed and that the resistance change due to the magnetic field is extremely small. Take advantage of the phenomenon. FIG. 4 is a diagram showing the temperature (T) dependence of the resistance R of the microcrystallized silicon thin film resistors having different microcrystallinity. In the figure, solid lines (a-1), (a-2), and (a-3) indicate p-type microcrystalline silicon thin film resistors having microcrystallinity of 15%, 20%, and 60%, respectively. In addition, the solid line (b) shows a microcrystallinity of 65.
% N-type microcrystalline silicon thin film resistor. That is, as shown in FIG. 4, the relationship between the resistance R and the temperature T of the microcrystallized silicon thin film resistor having a microcrystallinity of 20% or more can be given by the following equation.

[0009]

[Equation 1]

Here, α and β are experimentally obtained, and are given by β = −0.28 in the solid line (a-3) and β = −1.06 in the solid line (b) of FIG. 3, for example. By using the amorphous silicon thin film deposited by using the plasma CVD method etc. in the detection part of the resistance temperature detector, the detection temperature is high, the response speed is high, and the resistance temperature for cryogenic temperature can be downsized and integrated. Realize the total.

[0011]

Function: Resistance R and temperature T of the microcrystalline silicon thin film resistor
The relation of can be expressed by a simple relational expression as shown in Expression (1). Therefore, by measuring the respective resistance values R1 and R2 at the temperature T1 and the temperature T2 and substituting those values into the equation (1), α and β in the equation (1) are uniquely determined. Therefore, by measuring the resistance value R of the calibrated resistor, the temperature T to be measured can be easily obtained by using the equation (1). Further, since ΔR / R is always constant, ΔT / T is also always constant. Therefore, the detection sensitivity does not deteriorate even at an extremely low temperature, and therefore the temperature can be measured with high accuracy over a wide range.

[0012]

1 and 2 are views showing the construction of an embodiment of a temperature sensing device according to the present invention. FIG. 1 is a plan view thereof, and FIG.
1 shows a sectional view taken along line XY of FIG. 1 and 2
In FIG. 1, 1 is an insulating substrate, 2 is an n-type (p-type) amorphous silicon-germanium thin film that is a microcrystalline semiconductor thin film, 3a and 3b are a pair of ohmic electrodes (also simply referred to as electrodes), and 4a and 4b are a pair of ohmic electrodes. Indicates a lead wire.

Next, a method of manufacturing the temperature sensitive device according to the present invention will be described. As the material of the insulating substrate 1, a surface of a heat-resistant insulator, a conductor plate or a semiconductor plate having similar properties is used for the silicon dioxide (Si
O ₂₎ film or a silicon nitride (Si ₃ N ₄₎ is preferably those covered with film, for example a glass plate, an alumina plate, a quartz plate, a fused quartz glass plate, quartz plate, poly Creamy de film, metal plate or the surface of a semiconductor An insulating thin film (for example, a silicon dioxide thin film or a silicon nitride thin film formed by the CVD method) is used. In particular, a glass plate or an alumina plate having a linear expansion coefficient close to that of an amorphous silicon thin film is preferable. The substrate made of these materials is thoroughly washed with an organic solvent or the like, and then instantaneously dried in a clean atmosphere.

Next, plasma CVD is performed using a mixed gas of silane (SiH ₄ ) or (silane + hydrogen (H ₂ )).
Amorphous silicon thin film (also referred to as amorphous silicon thin film resistor) 2 is deposited by using a photolithography method or an optical CVD method. In this case, it is desirable that the conductivity of the amorphous silicon thin film resistor is larger, and normally σ = 1 S · cm ^−1.
The above is used.

As an example of deposition conditions using the plasma CVD method, discharge pressure is 0.1 to 10 Torr, discharge power density is 0.01 to 10 W / cm ² (discharge current is 1 to 100 m).
A / cm ² , discharge voltage 500 to 800 V, electrode interval 1.
5 to 3 cm), a substrate temperature of 150 to 500 ° C., silane / hydrogen = 0.003 to 1, diborane / silane = 10 to 250.
0 ppm, phosphine / silane = 10 to 2500 pp
m. As the amorphous silicon thin film deposited under these conditions, it is easy to obtain a film having a conductivity σ of 20 S · cm ⁻¹ or more and a maximum of 100 S · cm ⁻¹ .

As a method of increasing the conductivity of the amorphous silicon thin film, a method of increasing the discharge current or a method of increasing the proportion of the doping gas is generally used.
As a method of controlling the microcrystallinity, a method disclosed by the same inventor (“amorphous silicon thin film conductor containing microcrystal phase” (Japanese Patent Laid-Open No. 62-158320)), that is, microcrystallinity Depends on the magnitude of the discharge power density, so a method of controlling the discharge power density based on this relationship was used. Alternatively, thermal annealing or laser annealing may be used.

Next, a metal film for electrodes (for example, NiCr 500 Å / Au) is formed by using a vacuum evaporation method.
1000 Å) is deposited. Further, the unnecessary portion is removed by using the photo etching technique, and the electrode pair 3
a, 3b and the amorphous silicon thin film resistor 2 are formed. The shape of the amorphous silicon thin film resistor 2 is determined in consideration of the conductivity, the film thickness and the output impedance of the amorphous silicon thin film. If the length of the amorphous silicon thin film is L and the width is W, it is usually L /
W is set to 1/10 to 10.

Next, a protective film is deposited on the surface of the insulating substrate. As the protective film, a silicon dioxide film formed by the CVD method,
A silicon nitride film and a polymide resin are used. The protective film on the electrode pad portion is removed by using a photo etching technique. Finally, the lead wires 4 for extraction are attached to the electrodes 3a and 3b.
Complete with a and b attached. The lead wire is formed by a beam lead method or by wire bonding an Au wire, an Au ribbon wire, or the like.

In the manufacturing method described above, the semiconductor thin film resistor and the electrode pair are formed by the photo-etching technique, but can be formed by a method using a metal mask. In this case, a method of covering an unnecessary portion with a metal mask is used when depositing an amorphous semiconductor thin film or when depositing an electrode metal thin film using a vacuum evaporation method.

FIG. 3 is a diagram showing an example of the temperature (T) dependence of the resistance R of the amorphous silicon thin film resistor manufactured by the above-described method. The relationship between the resistance R and the temperature T is as shown in equation (1). It can be given by a simple relational expression. Where α,
β is obtained experimentally, and β = − in the solid line (a-3), for example.
Given at 0.28. Therefore, by measuring the respective resistance values R1 and R2 at the temperature T1 and the temperature T2 and substituting those values into the equation (1), α and β in the equation (1) are uniquely determined. Therefore, by measuring the resistance value R of the calibrated resistor, the temperature T to be measured can be easily obtained with high accuracy by using the equation (1).

FIG. 4 shows a plan view of another embodiment according to the present invention. In FIG. 4, 11 is an insulating substrate, and 12a and 1
2b is a pair of amorphous silicon thin films deposited to form opposite sides of the resistance bridge, 13a and 13
b is a pair of tantalum nitride thin film resistors 14a, 14b, 1 deposited so as to form opposite sides of the resistance bridge.
4c and 14d are amorphous silicon thin films 12a and 1
2b of two ohmic electrodes facing each other for connecting 2b and each tantalum nitride thin film resistor 13a, 13b,
Reference numerals 15b, 15c, and 15d denote lead wires provided on the respective ohmic electrodes.

When a constant pressure Vin is applied between the ohmic electrodes 14a and 14c, the ohmic electrodes 14b and 14d are
The detection voltage Vout between varies depending on the ambient temperature and is given by the equation (2).

[0023]

[Equation 2]

Here, A is a coefficient determined by the shape and the like. For example, if the input voltage Vin is 10 mV, the rate of change of the detection voltage Vout is -15 μv / ° C. The cryogenic thermometer according to the present invention shown in FIG. 4 is obtained by depositing an amorphous semiconductor thin film on an insulating substrate at the stage of the method for manufacturing the cryogenic thermometer according to the present invention shown in FIGS. 1 and 2. It can be configured by adding a step of depositing a thin film resistor using a sputtering method or a plasma CVD method before or after the step of performing. In this case, a photoetching technique, a metal mask technique, or the like is used for patterning the thin film resistor.

As the above-mentioned cryogenic thermometer of the present invention, an ultra-small one within 1 mm square can be formed, and alumina or the like having a large thermal conductivity is used as the insulating substrate,
A response speed of 10 msec or less is realized. Moreover, it has been confirmed that the change in resistivity in a magnetic field of several Gauss is 1% or less.

[0026]

According to the present invention, the microcrystallized semiconductor thin film constituting the thermometer for cryogenic use has a microcrystallinity of 20% or more, and has a negative electric resistance when the specific resistance and the temperature are logarithmically taken. Since the amorphous silicon thin film having a temperature coefficient is used, the detection sensitivity is large and the temperature dependence of the detection sensitivity is small. Therefore, it was possible to realize a cryogenic thermometer in which the correction circuit is unnecessary or can be simply constructed. Furthermore, a cryogenic thermometer having the following unique effects could be realized. (1) Less susceptible to magnetic field. (2) Since the shape is as small as 1 mm square or less, the size can be reduced.
Further, by using an alumina substrate having a high thermal conductivity as the substrate, a high response speed of 10 msec or less is obtained. (3) The detection temperature range is as wide as 1.4K to 300K. (4) By integrating and miniaturizing the measuring resistor and the tantalum nitride thin film having a small temperature coefficient, the temperature can be measured with high accuracy by eliminating wiring noise. (5) By using a semiconductor process, the reproducibility is good and mass production is possible, so that the cost is low.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a cryogenic thermometer according to the present invention.

FIG. 2 is a diagram showing a cross-sectional view taken along line XY of FIG.

FIG. 3 is a diagram showing a relationship between resistance of an amorphous silicon thin film resistor and temperature.

FIG. 4 is a view showing another embodiment of the cryogenic thermometer according to the present invention.

FIG. 5 is a diagram showing a relationship between resistance R and temperature T of a conventional cryogenic thermometer.

[Explanation of symbols]

 1 Insulating substrate. 2 Amorphous silicon semiconductor thin film. 3a, 3b Ohmic electrodes. 4a, 4b Lead wire. 11 Insulating substrate. 12a, 12b Amorphous silicon semiconductor thin film. 13a, 13b Tantalum nitride thin film resistors. 14a, 14b, 14c, 14d ohmic electrodes. 15a, 15b, 15c, 15d Lead wire.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Atsushi Hiraoka 5-10-10 Minamiazabu, Minato-ku, Tokyo Anritsu Co., Ltd. (72) Koichi Nara 1-4-1 Umezono, Tsukuba-shi, Ibaraki Industrial Technology Institute of Metrology (72) Inventor Masahiro Okaji 1-4-1, Umezono, Tsukuba-shi, Ibaraki Industrial Technology Institute (72) Inventor Hideyuki Kato 1-4-1 Umezono, Tsukuba-shi, Ibaraki Industrial Technology Institute Metrology Institute

Claims (1)

[Claims] 1. An insulating substrate (1), a microcrystalline semiconductor thin film (2) deposited on the insulating substrate, and a microcrystalline semiconductor thin film, which are in contact with each other and are provided at a predetermined distance. In a temperature sensitive device including a pair of ohmic electrodes (3a, 3b), the microcrystallized semiconductor thin film has a microcrystallinity of 20%.
A cryogenic thermometer, which is an amorphous silicon semiconductor thin film resistor having the above-mentioned microcrystalline phase and having a conduction characteristic whose resistance value is approximately proportional to the βth power of temperature.