JPH0795002B2 - Sensor element - Google Patents

Description

The present invention relates to a sensor element having at least two sensitive films for reference and detection, and more particularly to a humidity, gas or infrared sensor.

<Conventional Technology and Its Problems> FIG. 3 shows a structural cross-sectional view of a conventional thermistor humidity sensor. This has a structure in which a thermistor bead (7) is supported by lead wires (8) from both sides, and the thermistor bead (7) is used when the heat dissipation state of the thermistor bead (7) changes due to humidity change in the air. ), The temperature change is detected as a resistance change. A material having a large resistance temperature coefficient is used for the thermistor to improve the sensitivity. Also, to prevent the amount of heat generated from the thermistor bead (7) from escaping through the lead wire (8), the lead wire (8)
An extremely fine platinum wire is used for. Since the resistance change of the thermistor due to the humidity change is generally small, it is necessary to cancel the influence of the power supply voltage change and the ambient temperature change. For that purpose, two thermistors for reference and detection are provided, and the thermistor for reference is a bite (9) containing dry air.
In addition, the thermistor for detection is housed in an ale (9 ') having a small hole so that it can be exposed to the outside air.

However, the iron bag package has a drawback that it requires a lot of labor for assembling, the cost is high, and the package is inevitably large.

<Objects of the Invention> The present invention has been made in view of the above points, and provides a small and low-priced sensor element in which a reference sensitive film is covered with a shield without using a bag package for obtaining hermetic sealing. The purpose is to provide.

<Example> A perspective view of a sensor element according to an embodiment of the present invention is shown in FIG. 1 (A), and a structural sectional view thereof is shown in FIG. 1 (B).

A pair of penetrations by anisotropic etching of silicon using EPW (ethylenediamine-pyrocatechol-water) etc. for the insulating film (2) made of SiO ₂ sputtered film or thermal oxidation deposited on the silicon substrate (1) A groove is engraved, and the strip-shaped portion sandwiched by the groove serves as a bridge (3). A sensitive film (4) made of a thin film thermistor material is superposed on it. The silicon substrate (1) has a hollow portion in which the through hole and the portion below the bridge (3) are removed by the above etching. Therefore, the bridge (3) is supported at both ends. Although not shown here, a pair of comb-shaped electrodes for detecting the impedance of the sensitive film (4) are vapor-deposited on the upper or lower part of the sensitive film (4). The bridge (3) is provided so as to reduce the heat capacity of the sensitive film (4) and prevent the amount of heat generated from the sensitive film (4) from easily escaping to the substrate (1). Used. The bridges (3) are arranged side by side at two positions on the substrate (1), and the same sensitive film (5) is placed on the other bridge (3). That is, at least two sensitive films (4) and (5) of the same kind are formed on the same substrate (1).
They are juxtaposed in some places. The first sensitive film (4) is exposed to the outside world, and the state of heat dissipation from the sensitive film (4) changes due to, for example, changes in humidity in the air, and the impedance of the sensitive film (4) changes.

On the other hand, the shield (6) having a recess formed by half-etching the silicon of the rectangular parallelepiped from one side is formed on the substrate (1) on which the second sensitive film (5) is mounted using a low melting point glass adhesive. The second sensitive film (5) is hermetically sealed in the substrate (1) and the shield (6) by being bonded to the upper surface of (1), and is not affected by the change of humidity in the external environment. When the outside air temperature fluctuates, the impedance of the first sensitive film (4) changes, but the impedance of the second sensitive film (5) also changes, so that temperature compensation is performed and the two sensitive films (4). It is possible to accurately detect the external humidity from the output difference of (5). In this case, it is possible to reduce the heat capacity of the entire element by using a small shield (6) as in the present embodiment rather than by sealing with iron as in the conventional example, and it is possible to reduce the sensitivity of both sensitive films ( 4) The tracking response of (5) becomes faster.

In the sensor element of the above embodiment, the insulating film (2) and the sensitive films (4) and (5) are formed on the substrate (1) and the shield (6) is formed.
Since batch processing can be performed on a wafer-by-wafer basis consistently up to the etching and bonding, it is suitable for mass production and can be manufactured at low cost. In addition, the small size has an advantage of low power consumption. It is also possible to use III-V group compound semiconductors such as gallium arsenide as the substrate and the shield in addition to the group IV element such as silicon, and electric field application bonding can be used as the bonding method between the substrate and the shield. Further, the shape of the insulating film (2) may be a cantilever (3 ') as shown in FIG. 2 or may be a diaphragm. FIG. 2 is a sectional view of the configuration of a sensor element showing another embodiment of the present invention, in which the same symbols as those in FIG. Besides, a gas sensor can be obtained by the same principle. When gas species selectivity is required, it is possible to provide a gas selective permeable membrane on the sensitive membrane or in a vent hole of the package, or to separate the gas species by a column such as used in gas chromatography. The reference sealed gas may be appropriately selected depending on the type of detection gas and may be vacuum.

Further, the sensor element in which gold black or the like is deposited on the sensitive film can be applied as an infrared sensor. In this case, unlike the humidity sensor, the sensitive film is not heated, and the temperature rise of the sensitive film due to infrared irradiation is detected.

Since silicon transmits infrared rays, it is necessary to form an infrared reflection film on the reference sensitive portion when it is used as a shield.

It is also possible to form a humidity / gas composite sensor by providing a plurality of sensitive films on the same substrate.

<Effects of the Invention> The sensor element of the present invention is suitable for mass production because it can consistently perform batch processing on a wafer-by-wafer basis, including formation of an insulating film or a sensitive film on a substrate, etching of a shield, and bonding with a substrate. It can be manufactured inexpensively. In addition, the sensor element is small, so it is highly practical, and the reference sensitive part is hermetically sealed with a small, integrally molded shield made of the same material as the substrate, which significantly reduces the heat capacity. It has the advantages of being capable of following changes in the outside temperature, having high accuracy, and low power consumption.

[Brief description of drawings]

FIG. 1 (A) is a perspective view of a sensor element showing one embodiment of the present invention, and FIG. 1 (B) is a structural sectional view taken along the line AA ′. FIG. 2 is a structural sectional view of a sensor element showing another embodiment of the present invention in which the insulating film has a cantilever shape. FIG. 3 is a structural sectional view of a conventional thermistor humidity sensor. 1 ... Substrate, 2 ... Insulating film, 3 ... Bridge, 3 '...
Cantilever, 4 ... First sensitive film, 5 ... Second sensitive film, 6 ... Shield, 7 ... Thermistor bead, 8 ... Lead wire, 9 ...

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaya Kabagawa 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Co., Ltd. (72) Hiroki Tabuchi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (56) Reference JP-A-57-178419 (JP, A) JP-A-60-167388 (JP, A) US Patent 4177667 (US, A) US Patent 4337658 (US, A) US Patent 4343768 (US, A)

Claims (2)

[Claims] 1. Two sensitive films placed on an insulating support processed in a bridge shape, a cantilever shape, or a diaphragm shape in which a part of a substrate is anisotropically etched, are arranged in parallel,
The first sensitive film is exposed to the outside world, and the impedance changes in accordance with the change in the detected amount, and the integrally molded shield processed to have a void is fixed to the substrate.
The sensitive film of (1) is hermetically sealed by the shield, and at this time, the substrate and the shield are made of the same material selected from silicon or III-V group compound semiconductors. 2. The sensor element according to claim 1, wherein the detected amount is water vapor, gas, or infrared rays.