JPH0350801A - Thin film resistor for strain gauge - Google Patents

Abstract

PURPOSE:To improve sensitivity, a mechanical strength, a strain resistance characteristic and a resistance temperature characteristic by specifying composition rates of Fe, oxygen and metals or semiconductors and a film thickness and by forming a thin film by a physical evaporation method or a chemical evaporation method. CONSTITUTION:The content of Fe is 60 to 98 atom % and the content of oxygen is in the range of 2 to 30 atom % or preferably 15 to 25%. As to metals, Al, titanium, tantalum, zirconium, indium, etc., are used. As for semiconductors, Si, germanium, boron, etc., are used. The contents of the metals and the semiconductors are preferably in the range of 0 to 10atom%. Excellent properties cannot be obtained unless Fe, oxygen and the metals or the semiconductors are not distributed uniformly substantially in the order of microns or less. A film thickness is 0.01mum or above and preferably 10mum or below so as to prevent breakdown of a film due to an internal stress. For forming the thin film, any of an ion plating method, a sputtering method, an evaporation method and a CVD method or a CVD method such as a plasma CVD method may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film resistor for strain gauges that utilizes changes in electrical resistance due to strain.

[Conventional technology and problems]

Conventionally, thin film resistors for strain dage have been broadly divided into two types: those that utilize a metal or alloy strain resistance variable (H), and those that utilize the piezoresistance effect of a semiconductor (Sensor Technology Vol. 1). 5, No, 7, 49 (1
985)). The former (e.g. nickel (Ni), chromium (C)
r) Alloy) has a small resistance temperature coefficient, so the fluctuation in output due to temperature is small, and the strain resistance characteristics are excellent in linearity. However, there was a drawback that the ratio of resistance change to strain, that is, the gauge factor was low. As a result, since the former has a low gauge factor, the strain gauge has a small S/N ratio and requires a highly sensitive amplifier, making it difficult to miniaturize the strain gauge. On the other hand, the latter (for example, silicon (Si)) has a high gauge factor, but has the drawbacks of a large resistance temperature coefficient and poor linearity of strain resistance characteristics.

As a result, the latter requires an amplifier and a temperature compensation circuit to improve the linearity of the strain gauge output, resulting in a complicated control system. Furthermore, the latter had a lower breaking strength than the former, making it unsuitable for high-pressure strain gauges.

That is, conventionally, there has been no thin film resistor for strain gauges that has high sensitivity and excellent mechanical strength. In particular, it has been considered difficult to develop thin film resistors for strain gauges that are highly sensitive and have good strain resistance characteristics, resistance temperature characteristics, and mechanical strength.

[Background of the invention]

Under these circumstances, the inventors of the present invention have made extensive efforts to solve the above problems. The present inventors used sputtering to combine iron (Fe), oxygen, and metal aluminum (Aj
It has been found that a thin film mixed with 2) has a gauge factor (k=5 to 7, normal metals are 1.5 to 3) that cannot be obtained with normal metals and alloys.

Therefore, it has been found that a highly sensitive strain gauge material can be obtained by using a thin film resistor containing Fe, oxygen, and metal as a strain gauge material. In addition, the inventor discovered that oxygen, which is an additive to Fe, and metals such as A1 act to make the crystal grains of Fe finer, making it possible to control the mean free path of conduction electrons in Fe, and as a result, the resistance We thought that the temperature coefficient could be lowered.

[Objective of the Invention] The present invention provides a thin film resistor for strain gauges with high sensitivity and improved mechanical strength, as well as a thin film resistor for strain gauges with excellent strain resistance characteristics and resistance temperature characteristics. With the goal.

[Description of the first invention] The first invention (the invention described in the claims) is based on Fe60 formed by a physical vapor deposition method or a chemical vapor deposition method.
~98 atomic%, oxygen 2-30 atomic%, metal or semiconductor 0
A thin film with a uniform distribution of ~10 atomic % and a film thickness of 0
．． The present invention relates to a thin film resistor for a strain gauge, characterized in that the thickness is 01 to 10 μm.

The thin film resistor for strain gauges according to the first invention exhibits a high gauge factor of 5 or more compared to conventional metal or alloy strain gauges. In addition, the linearity of strain resistance is superior to that of semiconductor strain gauges such as Si, and the temperature coefficient of resistance is ±100 ppm/
'C or less. Furthermore, even when kept at a temperature of around 120°C for a long time, the rate of change in resistance hardly changes, showing excellent high-temperature durability.

Furthermore, it maintains a strength close to that of conventional metal resistors, and exhibits significantly higher strength than semiconductor-based resistors such as Si. The reason for such excellent characteristics is not clearly clarified, but the reason for the low temperature coefficient of resistance is that oxygen and metal act as scatterers that impede the flow of conduction electrons in Fe, and the average conduction electrons in Fe are small. This is thought to be due to the fact that the free path is controlled and the structure is extremely fine due to the addition of metals such as AA and semiconductors such as Si. Furthermore, it is presumed that the high temperature strength is poor because the mixing state of Fe and the additive elements is uniform.

Therefore, by using the thin film resistor according to the present invention, it is possible to apply it to pressure sensors, load cells, etc. that have a high gauge factor and excellent high-temperature durability.

[Description of the Second Invention] Hereinafter, an invention that further embodies the first invention (referred to as the second invention) will be described in detail.

The content of Fe constituting the thin film resistor is 60 to 98 atomic %, and the content of oxygen is 2 to 30 atomic %.

Outside these ranges, it is difficult to obtain a high gauge factor. It is preferably 15 to 25%. In addition, the metal is Al,
Titanium (Ti), Kuntal (Ta), Zirconium (Z)
r), indium (In), etc., and semiconductors include Si,
Germanium (Ge), boron (B), etc. are used. The content of gold and semiconductor is 0 to 10 atomic% in order to maintain a high gauge factor and obtain good strain resistance characteristics and resistance temperature characteristics.
A range of is desirable. Good properties cannot be obtained unless Fe, oxygen, and metals or semiconductors are substantially uniformly distributed at least on the order of μm.

The film thickness is desirably 0.018 m or more in order to form a continuous film and obtain stable strain resistance characteristics, and 10 μm or less in order to prevent destruction due to internal stress of the film.

The method for manufacturing the thin film resistor according to the second aspect of the present invention may use any of the PVD methods or CVD methods, such as the ion blasting method, the sputtering method, the vapor deposition method, and the plasma CVD method, which are commonly used for forming thin films. However, in order to make the mixed state of Fe, oxygen, and metal or semiconductor dense and uniform, sputtering method or vapor deposition method is preferable. In addition, in order to make the mixed state of Fe, oxygen and metal or semiconductor m-uniform, after forming the thin film, it was heated at 200 to 500 °C for 1
Heat treatment may be performed for about 2 hours. In order to include oxygen in the thin film resistor, oxygen must be included in the processing atmosphere for sputtering or the like.

The film has particularly excellent properties when the oxygen content is 15 to 25a.
In order to include 15 at % or more of oxygen in the film, it is necessary to actively add oxygen to the atmosphere as an impurity in an amount greater than the amount of oxygen contained in the atmosphere.

However, even if the atmosphere does not contain oxygen, ACT
If a metal such as i or a semiconductor such as Si is sputtered in the form of an oxide, an oxygen amount of up to 30 at % can be included in the thin film.

〔Example〕

Example 1 FIG. 1 shows a strain gauge manufactured according to this example.

The thin film resistor was formed by a dual simultaneous sputtering method. First, a Corning 0313 glass substrate 1 was subjected to trichlene boiling cleaning and acetone ultrasonic cleaning, and after drying, it was placed in a sputtering device through a strain gauge SUS mask, and the device was evacuated to 5×10 −6 Torr. Next, Ar gas was introduced into the above device at 5X10-3T.
Introduced orr and DC300WSAff on Fe target
RF 150W (13,56MH
A power of z) was applied and sputtering was performed for 6 minutes.

The composition of the strain gauge film 2, which is a resistor manufactured in this way, was investigated by EPMA and XPS, and the thickness was investigated using a stylus-type film thickness meter.
)-4 at% AA film thickness was 0.20 μm (Table).

The substrate on which the strain gauge film was formed was taken out into the atmosphere, an electrode mask was attached, and then a power of 250 W DC was applied to the Au target in the same manner as above in the sputtering equipment, sputtering was performed for 1 minute, and the Au electrode was removed. A film 3 with a thickness of 0.1 μm was formed. Furthermore, 300°C, l in the atmosphere
After heat treatment for hr, lead wire 1 was soldered to the Au electrode. A characteristic evaluation test was conducted using the strain gauge thus manufactured.

Characteristics as a strain gauge were evaluated by strain resistance characteristics, resistance temperature characteristics, and high temperature storage tests. FIG. 3 shows the relationship between strain and resistance change rate of the strain gauge manufactured according to this example. The gauge factor was determined from the slope of the straight line showing the relationship between strain and resistance change rate. Resistance temperature characteristics are -30°C
By changing the temperature from 120°C to 120°C, the temperature coefficient of resistance TC
R (ppm 7°C) was measured. In addition, the high temperature storage test
Resistance change rate ΔR after being left at 1200C for 500 hours (
%) was measured. The evaluation results are shown in the table.

Examples 2 to 4 Strain gauge films were formed in the same manner as in Example 1, except that the composition of the film was 81 and the composition of oxygen was changed. The table shows the composition and thickness of the strain gauge film.

Next, electrodes and lead wires were attached in the same manner as in Example 1, and the same evaluation test as in Example 1 was conducted, and the evaluation results are shown in the table.

Comparative Example Similar to Example 1, the composition was changed to Fe-16at%0-13at%Aj2 and Fe-
24at%0-LLat%Si thin film resistor and conventionally used strain gauge materials N+Cr and S
i was formed as a strain gauge film on a glass substrate. The table shows the composition and film thickness. Next, in the same manner as in Example 1, the electrode
A strain gauge was manufactured by attaching a Riet wire, and the same evaluation test as in Example 1 was conducted. The evaluation results are shown in the table. Also,
Figure 3 shows the strain resistance characteristics of the NiCr alloy.

As can be seen from the evaluation table, the strain gauge films composed of Fe and oxygen, Fe, oxygen and Al, and Fe, oxygen and Si according to Examples 1 to 4 are superior to the NiCr alloy of the comparative example. ,3
~4.2 times the gauge factor. That is, it is clear that the strain gauge of this embodiment has several times better sensitivity than the conventional metal resistance type strain gauge. Furthermore, Comparative Example 5.6 in which 13 at % and 5 illat % of Al were added to Fe and oxygen had an inferior temperature coefficient of resistance. This is due to the effect that in the strain gauge of this example, a thin film having a high gauge factor and a small temperature coefficient of resistance is formed by mixing appropriate amounts of Fe with oxygen and Al or Fe with oxygen and Si. It is something.

Furthermore, as shown in the table, Fe and oxygen and Fe and oxygen and A! , a strain gauge made of Fe, oxygen, and Si is
It is clear that the resistance-temperature characteristics and high-temperature durability are poor compared to the Si strain gauge of the comparative example. This is achieved by mixing appropriate amounts of oxygen and Aβ or Si in Fe.
This is thought to be because the mean free path of conduction electrons in Fe became shorter and the temperature coefficient of resistance became smaller. Also, Fe
The thin film was stable even when left at high temperatures because the mixed state of oxygen, A1, or Si was uniform. Furthermore, from FIG. 3, it is clear that the strain gauge manufactured according to this example has significantly improved strain sensitivity while maintaining linearity.

Furthermore, the strain gauges according to Examples 1 and 2 had significantly superior strength compared to strain gauges made of semiconductors such as Si.

[Brief explanation of drawings]

Fig. 1 is a plan view of a strain gauge used in an example of the present invention, Fig. 2 is a cross-sectional view of the strain gage, and Fig. 3 shows the relationship between strain and resistance change rate in Example ① and Comparative Example 1. This is a diagram.

Claims (1)

[Claims] A thin film formed by a physical vapor deposition method or a chemical vapor deposition method, in which 60 to 98 atom% of iron, 2 to 30 atom% of oxygen, and 0 to 10 atom% of a metal or semiconductor are uniformly distributed,
A thin film resistor for a strain gauge, having a film thickness of 0.01 to 10 μm.