JPS62124454A - Hetero junction type gas sensor - Google Patents

Abstract

PURPOSE:To obtain a good sensing characteristic for a combustible gas by providing many gas introducing holes by etching to the joint surface of an n-type oxide semiconductor and p-type oxide semiconductor in such a manner that the gas contacts said surface. CONSTITUTION:The joint part is made of an Li-doped NiO film having 1mum thickness as the p-type oxide semiconductor 1 and a ZnO film having 2mum thickness as the n-type oxide semiconductor to a 1mmX2mm size and the gas introducing holes 3 sized 10mum square and 2mum depth are formed at 15mum pitch thereto by reactive ion etching from above the semiconductor 1. A positive bias voltage is impressed to such element in the forward direction of a diode formed of the semiconductors 1 and 2 to operate the same. The combustible gas reacts with gaseous oxygen adsorbed to the joint part when the gas arrives at the joint part of the semiconductors 1 and 2 through the holes 3. The electrostatic potential in the joint part is then changed and the current flowing in the joint part changes. As a result, the concn. of the cmbustible gas is known from the current flowing in the joint part.

Description

DETAILED DESCRIPTION OF THE INVENTION (First field of application in the industry) The present invention relates to a gas sensor that is small in size, has low power consumption, and is highly sensitive.

(Prior Art and Problems to be Solved by the Invention) Conventional gas sensors are broadly classified into electrical resistance type and non-electrical resistance type, as shown in Table 1. Currently, most of the commercially available devices are electrical resistance type, in which the element is made of an n-type compound semiconductor material such as S''O2+ ZnO, and the gas concentration is determined from the electrical resistance value. The major disadvantage of electrical resistance type gas sensor elements is that they operate only at a cylinder temperature of around 400°C, which consumes a lot of power, which prevents integration with sensors with other functions or control integration paths. It is the cause.

The non-resistance type is a method that uses the work function of a semiconductor through gas adsorption or reaction, either directly or indirectly, for gas detection. Specifically, it uses a metal/semiconductor junction diode and a gold maple gate film. There was MO8FET seven sensors/
Semiconductor junction diode sensor is Pd/CdS ff
Initially, elements using Pt/Ti1t, Pt/Ti1t, etc. have been proposed, but these are Pd, T
i' (H2 gas passing through is the main sensing gas. Also, the companion MO8FET sensor using a metal gate film is 5iFE
Due to the heat resistance of T, the operating temperature is limited to about 150°C, so it is limited to highly reactive gases such as H2 and CO, and there are still problems with the one-foot response characteristics (Reference 1).
).

An example of a full application of heterojunctions for oxide semiconductors is a humidity sensor (Reference 2). An oxide semiconductor is a sintered body in which the entire layer is carefully alternated, and an ionic current is generated when moisture enters between the sintered particles. Although the sensitivity is excellent, there are problems with stability.

(Means for determining the problem) The purpose of the invention is to provide all kinds of flammable gas sensors with new structures that eliminate the structural defect in which heterojunctions of oxide semiconductors are used only for unstable humidity sensors. There is a thing called VC.

In a gas sensor using a heterojunction of an oxide semiconductor, it is most important to provide a large number of gas inlet holes by etching in the gills where gas comes into contact with the junction surface of the n-type oxide semiconductor and the pW chloride conductor. Main characteristics. It differs from conventional technology in that it can stably and highly sensitively sense various flammable gases (and humidity).

Next, an example will be described.

FIG. 1 is a diagram illustrating a first embodiment of the present invention,
(a) is a plan view, and (b) is a cross-sectional view. In the figure 1
is a p-type oxide semiconductor (Lii-doped NiO), Z
u n-type oxide semiconductor (ZnO), 3 is a gas introduction hole formed by reactive ion etching, 4 is a lead wire, 5
is an electrode that forms an ohmic contact with a p-type oxide semiconductor, 6 is an St substrate, 7 is a heater, 8 is an electrode that forms an ohmic contact with an n-type oxide semiconductor, and 9 is a SiQ thermal oxide film (Stow). show.

To operate this, a positive bias voltage is applied in the forward direction of the diode formed by the p-type oxide semiconductor 1 and the n-type oxide semiconductor 2. ``When the flammable gas passes through the gas introduction hole 3 and reaches the junction between the p-type oxide semiconductor 1 and the n-type oxide semiconductor 2, it is adsorbed to the junction and reacts with friendly oxygen gas, increasing the electrostatic potential of the junction. changes, causing a change in the current flowing through the junction. As a result, the concentration of combustible gas can be determined from the current flowing through the joint. A junction was made with a dimension of 1×2# using a 1 μm thick Li mira-doped 7jNiO@ as the p-type oxide semiconductor 1 and a 2 μm-thick ZnO film as the n-type oxide semiconductor 2. Reactive ion etching 10μm square 2μm deep gas introduction hole 3'
It is manufactured with a pitch of 15 μm.

Fig. 2 shows the sensing characteristics of combustible gas by this element.

(The element temperature is 100°C.) In the figure, ■. is the device current in the atmosphere, and d is the device current in the gas atmosphere.

Because the structure includes this L-shaped gas inlet hole and a heater that heats the entire joint, the 9-heterojunction can now sense flammable gas, whereas conventionally only humidity was sensed unstablely. Natsu9.

[Embodiment 2] FIG. 3 is a diagram illustrating a second embodiment of the present invention,
10 has 5iCht of 10 μm on the surface is a friend direction (100
) is the space of a diaphragm produced by anisotropic etching with a mixture of ethylenediamine and pyrocatechol. 11 is an integrated circuit that controls calculations for the output of the element, temperature conditions of the heater, etc. .Other symbols are the same as those in Fig. 1.As the n-type oxide semiconductor 2, an ALf-doped ZnO1, a Liff1-doped ZnO, a Liff1-doped fc, and a CuOf, respectively. Manufactured with dimensions of 1+m x 1.5m.

Thereafter, gas introduction holes of 5 μm square are provided at a pitch of 10 μm from the upper surface of the n-type oxide semiconductor. The heater 7 and the element above it are formed in a diamond slam with a distance of 10 μm above the space.
The integrated circuit 11 is supported only by the 5iO1 film, and has a structure in which heat from the heater is difficult to transfer to the integrated circuit 11.

With this structure, the heater temperature can be raised, and in combination with the effect of the gas introduction hole, combustible gas can be sensed with high sensitivity. Figure 4 shows the results. Engineering here. is the device current in the atmosphere, and ■ is the device current in the gas atmosphere. As is clear from these results, there has been an improvement in that a heterojunction sensor, which has conventionally been used only as a humidity sensor, can now be used as a combustible gas sensor.

(Effects of the Invention) According to the above-described method, in the gas sensor of the present invention, a large number of gas introduction holes are provided deep into the pn junction between an n-type oxide semiconductor and a p-type oxide semiconductor, and Since the structure is heated with a heater, H2, CO, methane, ethane, and globan are used.

This has the effect of providing good sensing characteristics for flammable gases such as isopropylene.

[Brief explanation of drawings]

Figure 1 is a first embodiment showing the features of the present invention, (a) is a top view, (b) is a sectional view, the second factor is data showing the effect of the first embodiment, and Figure 3 is a top view. Embodiment 2 is shown in which (a) is a top view, (b) is a front view, and FIG. 4 is data showing the effects of the second embodiment. 1...p-type oxide semiconductor 2...nW# compound semiconductor 3...gas introduction hole 4...lead wire 5...p-type Oxide semicircular ohmic electrode 6.
...Si substrate 7 ... Heater 8 ... N-type oxide semiconductor ohmic electrode 9
...Thermal oxidation of Sin, film lO...Diaphragm space 11...Integrated circuit references (1) Takayama, Sakai; Center Technology vol. 1.4, m13
p 39-43 (1984) (2) Nakamura, Ikejiri, Miyayama, Kawamoto, Yanagita; Journal of the Chemical Society of Japan 1
985 (6) P1154-1159 patent applicant
Nippon Denki Denwa Co., Ltd. Fig. 1 9-1-da 1\MA Ei Otsu 510 February 5 self Fig. 2 Fig. 3]] (b) Fig. 4 Bare hand 5 bi/'L ('C)

Claims (1)

[Claims] In a pn junction consisting of an n-type oxide semiconductor and a p-type oxide semiconductor, a large number of gas introduction holes extending from one of the oxide semiconductors to a deep position through the junction, and a heater that heats the junction A heterojunction gas sensor comprising: