JPH0526751A - Pressure sensor - Google Patents

Abstract

PURPOSE:To obtain a stable output with a high sensitivity even at a high- temperature region by forming an SAW oscillator consisting of a piezoelectric ceramic (AIN) thin film on a surface of a diaphragm which is formed on a sapphire substrate. CONSTITUTION:A diaphragm 3 is formed on a recessed portion 2 which is machined to a sapphire substrate 1 and an AIN thin film on it is subjected to CVD or sputtering, thus forming tooth-shaped delay linear SAW oscillators 4a and 4b. When a liquid is led to a pressure-introduction chamber and a pressure is applied to the diaphragm 3, an oscillation frequency of the oscillators 4a and 4b changes due to the distortion, thus enabling the output to be input to feedback amplifiers 5a and 5b through connection pads 6a and 6b for detecting frequency and then to be output as a pressure signal from an operation device 7. Sapphire with a high melting temperature is used as the substrate 1, and at the same time a piezoelectric ceramic is used as the oscillators 4a and 4b and Pt or a silicide or a nitride with a high melt-point metal is used as a lead wire, thus obtaining a stable output even at a high temperature near 800 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor using a sapphire substrate, and more particularly to a pressure sensor with improved performance in a high temperature range (700 ° C. or higher).

[0002]

2. Description of the Related Art Conventionally, as a high temperature pressure sensor using a diaphragm, as shown in FIG. 3, a Si thin film 22 is epitaxially grown on a diaphragm 21 formed on a sapphire substrate 20, and a piezoresistive element ( (Not shown) is formed to measure the pressure from the change in electrical resistance that changes in association with the strain of the diaphragm 21. References Transducer 87 P316 Silicon on Sappire The key Tecnology for High Temperature Piezorestive Pressure Transducers As shown in FIG. 4, a SAW oscillator 32 is formed on a diaphragm 31 formed on a quartz substrate 30. The elastic constant and density of the diaphragm surface change. SAW oscillator 3 with it
The propagation velocity of 2 changes. When the strain spreads in the SAW propagation direction, the oscillation frequency changes, so the difference in the oscillation frequency is detected and the strength of the pressure applied to the diaphragm 31 is measured. References 1980 IEEE Published ULTRASONICS SYMPOSIOM P696 ~
P701 PROGRESS IN THE DEVELOPMENT OF SAW RESONATOR PRESSURE TRANSDUCERS

[0003]

It has been reported that the pressure sensor utilizing the piezo effect on the Si thin film on sapphire could measure up to 425 ° C. Also,
The sensor has reported the measurement results at -50 to + 100 ° C, but since the Curie point of the crystal is 573 ° C, there is a problem that it cannot be used at a high temperature of 700 ° C or higher.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a pressure sensor capable of obtaining a stable output with high sensitivity even at a high temperature near 800 ° C. To aim.

[0005]

In order to solve the above problems, the present invention is a SA in which a diaphragm is formed on a sapphire substrate and an AlN thin film is formed on the surface of the diaphragm.
The W oscillating means is formed.

[0006]

Function: The melting point of sapphire is 2030 ° C, and it is also an excellent elastic material. In addition, piezoelectric ceramics such as Al
The maximum operating temperature of N is 1800 ℃, and the Curie point is approximately 1.
Since it is as high as 200 ° C, there is no performance deterioration at high temperatures (600 to 1000 ° C).

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing an embodiment of the present invention. The sapphire substrate 1 has a recess 2 formed by machining and a diaphragm 3 formed on the surface thereof. The diaphragm may be processed by using a CO ₂ laser or the like to fuse the membrane (diaphragm thin portion) to the sapphire frame with holes. Reference numerals 4a and 4b are delay linear SAW oscillators, and an AlN (aluminum nitride ... Piezoelectric ceramic) thin film is formed by a method such as CVD or sputtering. The SAW oscillator has a known shape such as a comb shape,
The formation positions of the diaphragm are set at the central part (tensile stress) and the peripheral part (compressive stress) where the bending stress of the diaphragm is remarkable, and the polarity is reversed and the difference in the output of the oscillator is detected to detect external temperature fluctuations and power supply voltage. Offset the effects of changes over time.

In this case, the SAW oscillator is a sapphire R
It is formed on the surface (0112), and the excitation electrode is formed on the AlN thin film to form an interdigital transformer (IDT).
As the electrode material, Pt, which has heat resistance (800 to 900 ° C.), a refractory metal silicide, a nitride, or the like is used. Reference numeral 5a denotes an oscillator 4 arranged around the diaphragm.
A feedback amplifier for detecting the frequency by inputting the output of a through the connection pad 6a, and a feedback 5b for inputting the output of the oscillator 4b arranged at the center of the diaphragm through the connection pad 6b. Amplifier. Reference numeral 7 is an arithmetic unit for inputting the frequency output from the feedback amplifiers 5a and 5b and outputting it as a pressure signal.

Reference numeral 9 denotes Al formed on the sapphire substrate 1 outside the region (frame portion) where the diaphragm 3 is formed.
This SAW oscillator consists of N thin films, and this SAW oscillator functions as a thermometer by making the film thickness different from the oscillator on the diaphragm. The temperature dependence of the oscillation frequency itself of the SAW oscillator is, for example, that of Al ₂ O ₃ [1
When an AlN film is formed on the [100] plane, kH to 3.75 ... k; Wave number, H; AlN film thickness has almost no temperature dependency, and if the film thickness is increased, the frequency is related to temperature. Is known to change (1982 IEEE published 340-1982 ULTRASONICS SYMP
OSIOM).

Reference numeral 10 is an amplifier which outputs a temperature signal at a frequency based on the signal from the oscillator 9. FIG. 2 is a sectional view showing a state in which the pressure sensor of the present invention is incorporated in the case 11. Here, the sapphire substrate 1 is fixed to a second sapphire substrate 13 having a through hole 12 and then assembled into the case 11. The through-hole 13 is arranged substantially at the center of the diaphragm to form a pressure introducing chamber 14, and the measurement fluid is introduced through the through-hole 13. Reference numerals 15 and 16 denote support members, and a pressure sensor is sandwiched between the support members 15 and 16 and fixed to the case 11. An electric signal from the pressure sensor is connected to a super heat resistant cable 17 made of an alloy of Au and silicide, for example. Reference numeral 18 is a holding member for guiding the super heat resistant cable to the outside, and is supported by a bush 19 made of a material such as Au.

In the above structure, first, the frequency of the SAW oscillator in the standard state (for example, zero state) is detected. Next, when the fluid is guided to the pressure introducing chamber and pressure is applied to the diaphragm and the diaphragm is distorted in association with the pressure, the oscillation frequency of the SAW oscillator changes, so the applied pressure can be known. In this case, in the present invention, sapphire having a high melting temperature is used as the substrate, piezoelectric ceramics is used as the SAW oscillator, and Pt or a refractory metal silicide or nitride is used as the lead wire. It is possible to obtain a stable output.

[0012]

According to the pressure sensor of the present invention as described in detail with reference to the embodiments, the sapphire substrate on which the diaphragm is formed and the AlN (piezoelectric ceramic) thin film formed on the surface of the diaphragm are formed. SAW
Since the oscillating means is formed, it is possible to obtain a stable output with high sensitivity even at a high temperature.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a pressure sensor of the present invention.

FIG. 2 is a cross-sectional view showing a state in which the pressure sensor of the present invention is incorporated in a case.

FIG. 3 is a configuration perspective view showing a conventional example.

FIG. 4 is a configuration perspective view showing another conventional example.

[Explanation of symbols]

1 sapphire substrate 2 recess 3 diaphragm 4 SAW oscillator 5 Feedback amplifier 6 connection pad 7 arithmetic unit 9 Heat-resistant wiring (contact part) 10 amplifier 11 cases 12 Second sapphire substrate 13 through holes 14 Pressure introduction chamber 16 spaces 17 Super heat resistant cable 18 Hermetically sealed part 19 bush

Claims (2)

[Claims] 1. A SA having a diaphragm formed on a sapphire substrate and an AlN thin film formed on the surface of the diaphragm.
A pressure sensor comprising W oscillating means. 2. The pressure sensor according to claim 1, further comprising temperature detecting means made of an AlN thin film provided on the sapphire substrate outside the region where the diaphragm is formed.