JPS63101740A - Vertical fet type gas sensor - Google Patents

Abstract

PURPOSE:To achieve a higher sensitivity with the element temperature raised up to about 400 deg.C, by arranging two electrodes on and beneath an oxide semiconductor film as source and drain and gate electrodes on both sides of an upper electrode to form an FET construction in which current flows vertically. CONSTITUTION:A band-shaped drain electrode 4 is provided on an insulating substrate 8 comprising aluminum oxide, a ZnO layer 6 is laminated at the thickness of 1-20mum thereon as an oxide semiconductor film ohmic connected to the drain electrode 4 and an insulation layer 2 made of SiO2 is laminated on the ZnO layer 6 at the thickness of 10-100nm. Then, a band-shaped source electrode 3 is provided on the insulation layer 2 almost parallel with the drain electrode 4 and a gate electrode film 1 comprising one kind of metal selected from among Pd, Pt, Rh, Ir, Ru, Os, Au and Re is formed on both sides of the source electrode 3 at the thickness of 5-100nm. A heater 9 for heating elements is provided beneath the insulating substrate 8 to heat semiconductor elements.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a compact size, low power consumption, and high sensitivity.
The present invention also relates to a vertical field-effect transistor type gas sensor that has high-speed response and long-term stability.

[Conventional technology]

Conventional gas sensors are mainly composed of oxide semiconductors as shown in Table 1, and their measurement principles are roughly divided into two types: electrical resistance type and non-electrical resistance type. Most of the devices currently in practical use are electrical resistance type. These are 5
This is a method in which powder of oxide semiconductors such as n02 and ZnO is made into devices using a sintering method, and gas concentration is detected from changes in electrical resistance. , depending on whether it extends to the inside.
It can be further classified into surface control type or bulk control type.

The major disadvantage of these low-resistance diffused elements is that they only operate at high temperatures of around 400°C, which generates a lot of heat and consumes a lot of power, and it is difficult to integrate them with sensors with other functions or integrated circuits for control. It is.

The operating principle of a non-electrical resistance type gas sensor is to use changes in the work function of a metal electrode due to gas adsorption or reaction, directly or indirectly, for gas detection.More specifically, it uses a MOSFET! There are gas sensors and metal semiconductor junction diode type sensors. FIG. 4(,) shows the structure of the MO8FET type gas sensor and its operating status. Figure 4 (&
), 1 is a dart electrode, 2 is an insulating layer made of 5102, 3 is a source electrode, 4 is a drain electrode, and 5 is a semiconductor current channel. As an example, the detection mechanism for H2 gas in the case where e-) the metal is Pd is as follows.

H2 gas is adsorbed and dissociated on the surface of Pd to become atomic hydrogen Ha. H1 atoms reach the Pd-8102 interface by diffusion and are polarized there to form a dipole layer and generate an interfacial potential. As a result, as shown in the graph of Figure 4(b), the FET
The threshold gate voltage vG, which is the basic characteristic of , is displaced by ΔV. By measuring this ΔV, the H2 degree can be observed. The major disadvantages of this MO8FET type gas sensor are that the operating temperature is limited to 150°C or less because the FET is composed of 81, the detectable gas is limited to highly reactive H2 gas and CO gas, and the current is 81
Since it flows parallel to the interface between and 5102, it is affected by defects at the interface.

On the other hand, metal-semiconductor junction diode gas sensors detect changes in the work function of metal electrodes due to gas adsorption as changes in the potential barrier at the junction interface, and although their sensitivity is high, due to their operating principle, the detection current is directly applied to the gas detection electrode. It has the disadvantage that it is highly unstable because of the flow of water.

[Problem that the invention seeks to solve]

The present invention is a longitudinal field effect transistor type gas sensor that solves the drawbacks of the conventional MO8FET type gas sensor using SS as a component, which is that the operating temperature is limited to 150°C or less and that it is affected by the interface state of 5t-sto2. The purpose is to provide a gas sensor.

[Means for solving problems]

In order to achieve the above object, the present invention provides a band-shaped lower electrode on an insulating substrate, laminates an oxide semiconductor film with a thickness of 1 to 20 μm and is ohmically connected to the lower electrode, A silicon oxide film with a thickness of ~1100 nm is laminated, and a band-shaped upper electrode is provided on the silicon oxide film at a position approximately parallel to the lower electrode, with a thickness of 5 to 10 nm on both sides of the upper electrode.
0 nm of Pd, Pt, Rh, Ir, Ru,
ff using one of the metals Oa, Au, and Re
-) It is characterized by a structure in which an electrode film is formed.

The conventional technology uses an oxide semiconductor film without using Sl.
Configuring ET and source, drain, ff-)
The difference is that the arrangement of each electrode is changed so that the current flows in the vertical direction, away from the dart electrodes and the semiconductor interface.

[Effect]

The present invention uses a silicon oxide semiconductor by the above means, and has a source and a drain disposed above and below, and a FE that allows current to flow in the vertical direction.
Since the T structure is used, the element temperature can be kept at 150°C or above 40°C.
It is possible to raise the temperature to about 0°C, achieving high sensitivity, and it is not affected by the semiconductor surface, making it possible to obtain stable characteristics over a long period of time.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

(Example 1) Figures 1(a) and 1(b) are diagrams for explaining the first embodiment of the present invention, and Figure 1(-) is a plan view, and Figure 1(-) is a plan view.
is a sectional view. 1 is a dirt electrode with 20 nm of Pd attached, 2 is an insulating layer of 5 to 2, 3 is a source electrode, 4 is a drain electrode, 6 is a ZnO layer, 1 is a depletion layer generated in the ZnO layer, 8 is an insulating substrate (oxidized aluminum substrate), 9
is an element heater for heating the element.

FIG. 2 shows an example of a drive circuit for operating this element. In FIG. 2, 11 is a constant current power supply, 12 is an amplifier, and 13 is an output terminal. To operate the device shown in FIGS. 1(1) and 1(b), a heater 9 is used to heat the device to 200° C., and a direct current of 10 μA is passed between the source electrode 3 and drain electrode 4. The potential difference vD generated between the source electrode 3 and the drain electrode 4 is approximately 1 V in the absence of flammable gas such as H2, 00.
There is no change over a long period of time, but when it comes into contact with flammable gases such as H2 and Co, the work function of Pd, which is the electrode 1, changes, the depletion layer 1 decreases, and the current increases. VD decreases.

FIG. 3 shows the temporal change in V with respect to CO gas when the device was heated to 200°C. The decrease in VD with increasing concentration of CO gas is extremely large, and the change occurs rapidly due to the high temperature of 200°C. As is clear from this result, the electron mobility of ZnO is 200 cm /%'・3eC and 1 of Sl
The electric resistance is too high in a horizontal FET structure as shown in Figure 4, which is smaller than 500 sub/Vsec, and the low temperature sensitivity below 150°C, which was a problem with conventional St. Regarding the point that it can only be used in a limited area, an improvement has been made to enable detection with high sensitivity by sandwiching the ZnO layer between upper and lower electrodes as mentioned in the first factor.

(Example 2) The f-) metal of the element in Example 1 was Pt other than Pd.
, Rh, Ir, Ru, Os, Au
, Re, and Ni are shown in Table 2. In Table 2, each gas concentration is 101,000 pp and the element temperature is 200°C. All platinum-based metals undergo a gas pressure reaction at 200°C and VD decreases from 1V. Ni is a base metal and does not react at all. As is clear from the above results, since the device of the present invention can be heated up to 200° C., gas detection can be performed using platinum-based metals other than Pd.

Table 2 [Effects of the Invention] As explained above, according to the present invention, two electrodes serving as a source and a drain are arranged above and below an oxide semiconductor film, and gate electrodes are provided on both sides of the upper electrode to conduct a current. Because it uses a FET structure that allows the flow to flow in the vertical direction, the element temperature can be kept at 150℃.
It is possible to raise the temperature up to about 400°C, and in addition to achieving high sensitivity, it has the advantage that it is not affected by the semiconductor surface and stable characteristics can be obtained over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, Fig. 2 is a drive circuit diagram of the first embodiment that best represents the features of the present invention, and Fig. 3 is a response to CO gas of the present invention. FIG. 4 is a diagram showing the configuration of a conventional MO8FET type gas sensor, which is characterized in that current flows in the horizontal direction, and a graph showing its characteristics. 1... f-) electrode, 2... insulating layer by 8102,
3... Source electrode, 4... Drain electrode, 5...
Semiconductor current channel, 6...ZnO layer, 7...Z
Depletion layer in nO layer, 8... Insulating substrate, 9... Heater for heating element. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 3 (a) (b) Figure 4
figure

Claims (1)

[Claims] A strip-shaped lower electrode is provided on an insulating substrate, a 1-20 μm thick oxide semiconductor film is layered ohmically connected to this lower electrode, a 10-100 nm thick silicon oxide film is layered on top of this oxide semiconductor film, and then this A band-shaped upper electrode is provided on the silicon oxide film at a position substantially parallel to the lower electrode, and on both sides of the upper electrode, Pd, Pt, Rh, Ir, R, with a thickness of 5 to 100 nm is provided.
A vertical field effect transistor type gas sensor characterized by a structure in which a gate electrode film is formed using one of the following metals: u, Os, Au, and Re.