JPS63266801A - Manufacture of thin film thermistor - Google Patents

Abstract

PURPOSE:To reject crystallizations and O<-2> defects in a thin film and to obtain a thin film thermistor which is high in stability, accuracy, and reliability, by using specific thermistor materials consisting mainly of transition metals to form the thin film on a substrate which is heated at a constant temperature or above and performing heat treatment of this film. CONSTITUTION:Oxide, carbonate, oxalate of Mn, Co, Fe are used as starting materials of thermistor materials, and materials obtained by firing them or finely pulverizing them into 100mu or less are used as target materials. Their sputtering reaction products are stuck on a substrate which is made of glass, alumina, or the like and heated at 300 deg.C or above so as to form a thin film. Subsequently heat treatment of this film is performed in an atmosphere of an oxidizing gas to reject crystallizations and O<-2> defects in the thin film so that a thin film thermistor of high stability can be manufactured.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a thin film temperature-sensitive thermistor.

[Conventional technology]

Thermistors are used for temperature compensation, temperature measurement, and
It is a semiconductor device that is widely used for applications such as control.

Conventional thermistors are manufactured using transition metal oxides such as Mn, Ni, Go, Fe, etc. in an electric furnace using a ceramic method.
Ceramics are mainly made of ceramics sintered at 00°C, and their electrical properties are largely controlled by their sintering conditions, such as maximum firing temperature, holding time, cooling rate, purity and particle size of raw material powder, and therefore the reproducibility of properties is poor. Therefore, sufficient control is required in the preparation of raw materials and in the ceramic manufacturing process.

Furthermore, the resistance value, which is one of the important electrical characteristics of a thermistor, depends on the specific resistance of the material and the shape. The resistance value near room temperature is 104 to 1 for the beat type bulk thermistor.
07 [Ω], and about 102 to 104 [Ω] for the disk type.

[Problem that the invention seeks to solve]

Incidentally, thin film technology has rapidly advanced in connection with space exploration and the development of semiconductor devices such as VLSI.

By using this thin film technology, it is possible to obtain a thermistor that is highly accurate and lightweight compared to conventional leak-type thermistors, and is useful for temperature compensation, temperature measurement, control, liquid level detection, flow rate measurement, etc. In addition, it can be applied to attitude control of artificial satellites using infrared detection, and high-precision measurement control of radiation thermometers, etc. Thin-film thermistors are manufactured using a different method than bulk-type thermistors, so they are different from bulk-type thermistors. An electric conduction mechanism is considered.The material used in this example has a spinel structure and exhibits ferromagnetism, so it is expected to be applied as a temperature and magneto-optical sensor.

There are two types of thin film thermistors: thick film type and thin film type. The thick film type is manufactured using screen printing technology, and the thin film type is manufactured using sputtering or vacuum evaporation method.

In general, the advantage of thinning a thermistor is that it has a smaller heat capacity, so it has faster response speed and higher accuracy, and is known to be more reliable than thermistors made by sintering. .

An object of the present invention is to provide a highly stable, highly accurate, and highly reliable thin film thermistor.

[Means for solving the problems] The present invention uses a thermistor material mainly composed of transition metals as a starting material, and targets a sintered body of the material or a powder pulverized to 100μ or less, which is heated to 300°C or higher. A thin film is formed by adhering a sputtering reaction product on a substrate such as glass or alumina, and then heat treatment is performed in an oxidizing gas atmosphere to crystallize the thin film and remove O-2 defects. This is a method for manufacturing a characteristic thin film thermistor.

[Example〕 Examples of the present invention are shown below.

In the present invention, Mn is basically the same as in the prior art.

Co, Fe oxides, carbonates, oxalates are used as starting materials for thermistor materials, their fired bodies or finely pulverized materials of 100μ or less are used as target materials, and a thin film of the transition metal substance is deposited on a substrate using a sputtering device. It forms the The substrate on which the thin film has been formed is then heat treated, and electrodes are attached to it to complete the thermistor.

The materials used, equipment, and manufacturing conditions for the manufacturing process according to the present invention are shown below.

(a) Target material The composition ratio of the target used in the present invention is Mn:Co:F
The composition ratio is e=10:38.5:51.5 [moQ%].

The target was sintered at 1250° C. and then ground in an alumina mortar to a size of 100 μm or less. The powder was sealed in a quartz glass Petri dish [80φ] and placed in a sputtering device.

The raw materials used were subjected to X-ray diffraction using a Geiger Miniflex manufactured by Rigaku Denki, and the results are shown in FIG. 1(b). Furthermore, the results of elemental analysis using a fully automatic industrial fluorescent X-ray apparatus manufactured by Rigaku Denki are shown in FIG.

(b) When Ar ions in the Pelger sputtering device are accelerated by high frequency and irradiated onto a target, atoms and molecules on the target surface collide elastically and inelastically. As a result, atoms and molecules on the target surface evaporate.

Sputter deposition is the process of depositing this sputter-evaporated target material onto a substrate to form a thin film. Sputter deposition is characterized in that it is possible to form thin films even with materials that are difficult to vacuum evaporate, such as high melting point materials and alloys.

In the examples, a two-pole high frequency sputtering device was used.

In this case, an impedance matching circuit was inserted between the back-wave power source and the electrodes so that power could be introduced without loss. Furthermore, a capacitor was connected in series between the impedance matching circuit and the target electrode, so that a negative potential bias was induced even in the conductive target. This potential is approximately the peak value (approximately J2 times the actual value) of the high frequency applied voltage.

In this sputtering apparatus, the density of the ion current flowing into the target is given by t, where i is the density of the ion current flowing into the target. Here, C is the unit capacitance between the plasma and the target, and dV/dt is the time change in the target surface potential. As shown in equation (1), by increasing dV/dt, in other words, by using power at a higher frequency, the ion current increases and sputtering occurs more effectively.

However, if the frequency is too high, it becomes difficult to supply power to the target, so the industrially assigned frequency of 13.56 CM) Iz) is usually used. In high-frequency discharge, electrons in the discharge space move back and forth between electrodes due to the high-frequency electric field. As a result, electron collision becomes effective and approximately 1O-3
Sputtering is possible even at a gas pressure as low as TOrr.

The sputtering equipment used in the present invention is 5PF manufactured by Nikkei Anelva.
-210.

Its rating is shown below.

Frequency 13.56 (MHz) Output 1 [kII
l) MAx (c) Substrate material In forming a thin film, the selection of the substrate as well as the conditions for forming the thin film are important. This substrate is roughly classified into three types: glass, ceramic, and single crystal.

Glass and ceramic substrates are used for forming amorphous or polycrystalline films, and single crystal substrates are used for epitaxial growth of single crystal thin films. In the present invention, an alumina substrate was used in consideration of thermal distortion of the substrate. Table 1 summarizes the thermal characteristics of the substrate and thermistor material used in the present invention.

(Leaving space below) Table 1 Characteristics of each substrate (d) Sputtering conditions The most important sputtering condition is the substrate temperature, but in the example, a substrate heater was not used, but the radiant heat of the press sputtering caused the substrate to heat up. Sputtering was performed while taking time to raise the temperature to 300°C.

Ar gas, which has good sputtering efficiency, was used as the sputtering gas.

Table 2 shows the sputtering conditions.

FIG. 3 shows the amount of adhesion when the high frequency input is constant at 600 V and the sputtering time is used as a parameter.

The weight was measured using a balance AE-163 manufactured by Metra.

The measurement accuracy is I x 10-5 g. The adhesion amount of the thermistor was 0.54 (mg/h).

(e) Heat treatment conditions Although the target material used in the present invention is an oxide, Ar gas was used as the sputtering gas during sputtering, so it is thought that the thin film had 0-2 defects. o""" gas was introduced into the electric furnace at a rate of 0.5 u/min to crystallize the thin film and
I tried to remove the defects.

ω Heat treatment results X-ray diffraction and X-ray fluorescence analysis were performed on the heat-treated samples. The thin film thermistor before heat treatment was in an amorphous state, and no peak from the reflective surface was observed in X-ray diffraction, but after heat treatment, the peak from the (311) plane was observed as shown in Figure 1(a). appeared. (3
11) The lattice constant a□ obtained from the plane was found to be a□=8.33 from equation (2).

The lattice constant 82 obtained from the (311) plane of the main fired powder chart is 8.38 (human), indicating that the composition of the target material and the composition of the thin film are equal. FIG. 4 shows the tendency for the intensity of fluorescent X-rays to increase as a result of heat treatment.

(2) Electrode structure The electrode structure was an opposing and comb-shaped electrode structure as shown in FIGS. 5(a) and 5(b).

(3) Counter electrode (FIG. 5(a)) Silver-palladium was formed on the entire alumina substrate 1 by screen printing, and heat-treated at 950° C. for 50 minutes.

As the fired silver, C-416 fired silver made by Sumitomo Metal was used. The thickness of the lower electrode 2 after firing is approximately 2 (1). On this electrode 2, a thermistor thin film 3 was sputtered using a 20 x 20 (mm") stainless steel mask. As the upper electrode 4, Aρ was used. A counter electrode was formed by vacuum evaporation using a 1fiX16 (mm") mask. In order to increase the apparent resistance value, the measurement sample was diced so that the electrode area was 1 (mm2).

(ii) Comb-shaped electrode (Fig. 5(b)) alumina substrate 1
On top of the sample on which the thermistor thin film 12 was directly sputter-deposited on the thermistor 1, an Afl electrode 13 was vacuum-deposited using a stainless steel mask of 5×5 [mm2] with an interval of 1 (mm) to form a comb-shaped electrode.Characteristics of the obtained thermistor The following tests were conducted regarding:

■ Temperature characteristics of thin film thermistor resistance The resistance characteristics of thin film thermistors are determined using the constant current method (0.1 μA at 20°C) to reduce the influence of Joule heat.

(1 μA constant at 100° C.). 6th
The figure shows the temperature dependence of the resistance of the thin film thermistor shown in FIG. 5(a). Table 3 shows the B constant resistivity ρ and resistance R determined from this characteristic.

Table 3: B constant x resistivity ρ of thin film thermistor T = 25°C The resistance of the thin film thermistor can be selected in the range of about 10 -3 to 108 [Ω] by changing the electrode structure. By the way, the bulk type thermistor is 104 in the beat type.
~107 [Ω], and 1 to 10'Ω for the disc type.

The wide resistivity range of temperature sensitive materials in thin film thermistors makes it easy to select the type of heat sensitive material.

(i) Observation of lit film thermistor by ESCA and identification of compositional variations Figures 7(a) and (b) show surface observations of the thin film thermistor obtained by the method of the present invention. 400W -6h
The sample (Fig. 7(a)) sputtered with
It was found that the grain growth was better than that of the sample (Fig. 7(b)). FIG. 8 and Table 4 show the results of X-ray quantitative analysis of the thin film thermistor. As a result, regarding the composition of the starting material and the sputtered thin film, Mn was almost constant, but Fe and Go had a composition deviation of about 9%. Although this variation in composition causes a difference in the B constant and ρ, it is considered to be within a range that poses no problem for the stability of the thermistor's temperature characteristics based on bulk thermistor measurements, and this composition is extremely stable in terms of crystal chemistry. It can be understood that it is a thermistor material.

Although the compositional fluctuation causes a difference in the B constant and the value of ρ, it is considered to be within a range that poses no problem for the stability of the temperature characteristics of the thermistor (based on the measurement results of the bulk thermistor). This composition can be said to be a crystal-chemically stable two-mister material.

Table 4 Quantitative Analysis Results [Effects of the Invention] As described above, the present invention has the effect of increasing the accuracy and reliability, which are characteristics of thin film thermistors, and providing a highly stable thermistor.

[Brief explanation of drawings]

Figures 1 (a) and (b) are diagrams showing X-ray diffraction charts using Geiger miniflex for the thin film thermistor and thermistor raw material according to the present invention, and Figure 2 shows the elemental analysis results of the thermistor raw material using fluorescent X-rays. figure,
FIG. 3 is a diagram showing the relationship between sputtering time and thermistor deposition amount, FIG. 4 is a diagram showing the intensity change of fluorescent X-rays for the thermistor raw material and the thermistor before and after heat treatment,
Figure 5(a). (b) is a diagram showing the electrode structure, Figure 6 is a diagram showing the temperature dependence of the resistance of a thin film thermistor, and Figures 7 (a) and (b).
8 is an enlarged microscopic photograph of the surface of the thin film thermistor obtained according to the present invention, and FIG. 8 is a diagram showing the results of X-ray quantitative analysis of the thin film thermistor. ■, 11... Alumina substrate 2... Lower electrode 3
．． 12... Passermister thin film 4... Upper electrode 13
...Aluminum electrode patent applicant Oizumi Seisakusho Co., Ltd. Same as above 1) Positive part = 15- (α) Figure 5 Temperature + X1O-3 ('C) Resistance - temperature stability Figure 6 Procedure amendment ( method)

Claims (1)

[Claims] (1) Sputtering reaction using a thermistor material mainly made of transition metals as a starting material, using a sintered body of the material or a powder finely pulverized to less than 100μ as a target, on a substrate of glass, alumina, etc. heated to 300°C or higher. A method for producing a thin film thermistor, comprising forming a thin film by adhering a product, and then performing a heat treatment in an oxidizing gas atmosphere to crystallize the thin film and remove O^-^2 defects. .