JPS63298130A - Pressure sensor - Google Patents

Abstract

PURPOSE:To make a pressure sensor compact and to make the characteristics of an element excellent, in the electrostatic capacitor type pressure sensor, by using light sensitive glass as an insulating substrate, and forming a minute hole in the light sensitive glass. CONSTITUTION:Ultraviolet rays are projected only on the circular part of light sensitive glass 8. Heat treatment is performed, and the circular part, which is to become a minute hole 12, is developed. A lower fixed electrode 9 and an insulating film 10 are formed on the glass. Thereafter, poly alpha-methyl styrene, which is a thermally decomposing material, is spin-coated so as to form a pattern. A diaphragm 11 comprising a nickel film is formed on the poly alpha-methyl styrene. Thereafter, the rear surface of the glass is dipped in the solution of diluted fluoric acid. Only the exposed circular part is etched, and the minute hole 12 is formed. The poly alpha-methyl styrene, which is decomposed by heating, is removed from the minute hole 12. Thus, a pressure sensor is made compact, and the characteristics of the element become excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a pressure sensor that detects pressure changes in an atmosphere as changes in capacitance.

<Prior Art> Piezoresistive and capacitive pressure sensors have been mainly researched and developed as sensors for measuring pressure in an atmosphere. Piezoresistive pressure sensors change their resistance when a thin film of metal or semiconductor material is distorted by pressure.
It utilizes the so-called piezoresistance effect, and currently there are many silicon diaphragm pressure sensors on the market.

On the other hand, a capacitive pressure sensor is composed of a pair of electrodes facing each other with a specific space in between, and it is possible to detect changes in the capacitance between the pair of electrodes when the distance between the electrodes changes due to pressure. This is the pressure sensor used. A capacitance pressure sensor has a simple measurement principle, is easy to manufacture, and has the characteristics that a change in capacitance is easily converted into a change in digital output, and a measurement circuit is simple.

Regarding capacitive pressure sensors with these characteristics,
The element structure and manufacturing method of currently manufactured sensors are as follows:
For example, as shown in Japanese Patent Application Laid-Open No. 59-214727, electrodes are formed on a ceramic thin film diaphragm and a ceramic substrate, respectively, and then these ceramic plates are bonded together via a spacer.

<Problems to be Solved by the Invention> Conventionally produced capacitive pressure sensors have a large shape of several α angles, and also require adhesive (fusing agent) to connect the ceramic diaphragm and ceramic substrate via a spacer. Since the diaphragm and the substrate are bonded together, it is difficult to accurately control the distance between the diaphragm and the substrate, and furthermore, it is difficult to mass-produce sensors by batch processing. The present invention aims to provide a capacitive pressure sensor that can be miniaturized and further manufactured at low cost and with good reproducibility through batch processing.
．． This is the purpose.

<Summary of the Invention> The reasons why it is difficult to fabricate a conventional capacitive one-type pressure sensor at low cost through batch processing with good reproducibility include the fact that the fabrication process includes an adhesion step and the element size is large. . In the manufacturing process, adhesion is used to form a pair of electrodes for measuring capacitance with a certain distance apart. This makes it possible to extend out to form a pair of electrodes.

Furthermore, one reason why the conventional capacitive pressure sensor has a large shape is that the distance between the pair of electrodes becomes large.

That is, as the electrode spacing increases, the capacitance between the electrodes decreases, making measurement difficult, so the electrode area must be increased, and the element shape therefore becomes larger. In the present invention, the distance between the electrodes is reduced and it is possible to form a pair of electrodes with good reproducibility in a semiconductor process.

As mentioned above, the method of forming a pair of electrodes with a minute gap between them is the most important technique for manufacturing capacitive pressure sensors. It is possible to manufacture the device using a semiconductor process using a chemical or thermally decomposable substance.

A sublimable or thermally decomposable substance is coated on an insulating substrate on which a lower electrode has been formed in advance, and after patterned into a specific shape using photolithography, an upper electrode and an upper electrode are coated on the patterned sublimable or thermally decomposable substance. A metal film is formed. Next, the sublimable or thermally decomposable substance is removed from the micropores by heating in a vacuum, thereby forming a pair of electrodes separated by a specific distance, thereby forming a ferrosensor. Here, the specific spacing is determined by the thickness of the patterned film, which can be manufactured to a thickness of several μm with high precision, so that the characteristics of the capacitive pressure sensor can be made uniform. .

When fabricating capacitive pressure sensors using sublimable or thermally decomposable materials, the insulating substrate must have micropores in order for the patterned materials to be removed by vacuum heating. .

Generally, methods using ultrasonic processing, etching, etc. are known as methods for forming pores in a substrate. The ultrasonic machining method uses abrasive grains and ultrasonic vibration, but it is difficult to form pores with a diameter of less than 1 mm, and has the disadvantage of poor workability. On the other hand, in the etching method, when ordinary glass is etched with an aqueous hydrofluoric acid solution, it is difficult to make a hole when the substrate is thicker than 1 nm. Since the etching proceeds in the same direction, the etching becomes non-uniform in the depth direction of the glass, making it impossible to form micropores. but,
By using photosensitive glass as a substrate and exposing and heat-treating the photosensitive glass, it is possible to form micropores with a minimum diameter of several 10 μm by utilizing the fact that the exposed portions are selectively etched. It is.

FIG. 2 shows a basic element structure of a capacitive pressure sensor manufactured by bonding a ceramic substrate and a ceramic diaphragm with low-melting glass.

After forming a lower fixed electrode (3) on a ceramic substrate (1) having pores (2), a spacer (4) made of low melting point glass is entirely formed by screen printing or the like. Next, the ceramic diaphragm (5) having the upper movable electrode (6) is heat-bonded to produce a capacitive pressure sensor.

In the capacitive pressure sensor manufactured in this manner, the spacer has a thickness of several tens of micrometers, and the element size is several square meters. However, since it is difficult to control the thickness of the spacer, device characteristics are non-uniform and mass production is difficult due to batch processing.

<Example> As an example of the present invention, a first element structure diagram of a capacitive pressure sensor manufactured using a sublimable or thermally decomposable substance is shown.
As shown in the figure. Using a photosensitive glass (8) photomask, only the circular part with a diameter of about 800 μm was irradiated with ultraviolet rays.
Heat treatment is performed twice at 00° C. to form circular portions that will become micropores. Next, a lower fixed electrode (9) and an insulating film (2) are formed on the photosensitive glass (8) by vapor deposition or sputtering, and then poly α-methylstyrene, which is a thermally decomposable substance, is spin-coded. Patterned into a specific shape using photolithography technology. Furthermore, patterned polyα
- After forming a diaphragm or upper movable electrode α1) consisting of 73 islands of nickel film on methylstyrene by electroless plating, the back side of the photosensitive glass (8) is immersed in a diluted hydrofluoric acid solution, and the exposed circular part is Only etching is performed to form micropores a2.

Next, the substrate is heated in a vacuum to decompose the polyα-methylstyrene, and the polyα-methylstyrene is removed from the micropores (A) to produce the capacitive pressure sensor shown in FIG. .

The capacitive pressure sensor fabricated in this way is 13...
・The distance between the lead wire lower fixed electrode (9) and upper fixed electrode 0D is poly α
- It is defined by the film thickness of methylstyrene, and the film thickness is as thin as several micrometers and can be manufactured with good reproducibility, so there is little variation in capacitive pressure sensors, and it is possible to produce large plates by batch processing.

<Example> As described above, a pressure sensor in which a photosensitive glass is used and micropores are formed can be miniaturized, and furthermore, it can be mass-produced with good reproducibility of device characteristics by batch processing.

[Brief explanation of drawings]

FIG. 1 is a structural sectional view showing an embodiment of the capacitive pressure sensor of the present invention. FIG. 2 is a sectional view showing the basic configuration of a conventional capacitive pressure sensor. DESCRIPTION OF SYMBOLS 1... Ceramic substrate, 2... Pore, 3... Lower fixed electrode, 4... Spacer, 5... Ceramic diaphragm, 6... Upper movable electrode, 7... Lead wire, 8... Photosensitive glass substrate, 9... Lower fixed electrode,
10... Insulating film, 11... Metal film diaphragm, 1
2...Minor hole, agent: Takeshi Sugiyama (and 1 other person), Figure 1, Figure 2

Claims (1)

[Claims] 1. In a capacitive pressure sensor in which an upper movable electrode or diaphragm is formed through a cavity in an insulating substrate on which a lower fixed electrode is formed, the insulating substrate is made of photosensitive glass and micropores are formed. A capacitive pressure sensor characterized by: