JPS6133130B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a high performance hydrogen gas detection element.

Conventional gas detection semiconductor devices use polycrystals such as sintered bodies and thin films of oxide semiconductors, so it is impossible to control their crystal grain boundaries and impurities, and they lack reliability and compatibility. Furthermore, the gas detection mechanism in this element is unknown. This element is approximately
Since it exhibits practical sensitivity at 300°C, it was necessary to provide a heating section.

The purpose of this invention is to obtain a hydrogen gas detection element that can stably detect a small amount of hydrogen gas in a test gas at room temperature and is compatible with gas leak detectors, fire alarms, and gas concentration meters. .

To explain this invention based on the drawings, the first
In the figure, a crystal 1 of a semiconductor such as zinc oxide or tin oxide is subjected to surface treatment to remove processed layers, non-uniform layers, and dirt, and an insulating film 2 such as a silicon nitride film is deposited thereon. A hole is made in 2, and an ohmic contact electrode 3 such as an indium film and a metal thin film 4 whose work function changes due to hydrogen absorption such as a palladium thin film or a nickel thin film are deposited by vacuum evaporation. A conductive wire 5 and a conductive wire 6 are attached to the electrode 3 and the thin film 4 to obtain a diode. In this diode exposed to the test gas, the photocurrent, photovoltage, etc. that occur when photons with energy smaller than the current, voltage, resistance, capacitance, and bandgap of the semiconductor are incident from above or below the thin film 4. Measure.

By using the thin film 4 with a thickness of 10 to 100 nm, hydrogen adsorbed on its surface can quickly reach the metal-semiconductor interface, and the work function of the lower surface of the thin film 4 can be changed quickly, sensitively, and reversibly. As shown by Kurtin et al. in Physical Review Letters, Vol. 22, p. 1433, the high barrier in contact between semiconductors and metals where the difference in electronegativity between compound elements is 0.8 or more is Since the barrier height depends on the work function of the metal, when hydrogen gas in the test gas is absorbed by the thin film 4, the height of this barrier changes linearly with the amount of change in the work function of the thin film 4. As is well known, oxygen is one of the elements with the highest electronegativity, so semiconductors made of zinc oxide, tin oxide, and other metal oxides generally meet the above conditions for the difference in electronegativity between compound elements. When the semiconductor crystal 1 shown in FIG. 1 is a metal oxide, the device shown in FIG. 1 exhibits good characteristics as a hydrogen gas detection device. When the hydrogen gas concentration in the test gas is low, the amount of change is approximately proportional to the hydrogen gas concentration. Such a change in barrier height brings about a unique change in the current-voltage characteristics, capacitance-voltage characteristics, and photovoltage characteristics of the diode. Thus, by measuring the amount of change in any one of these characteristic values in the diode, the hydrogen gas concentration can be detected. In addition, the difference in electronegativity is 0.8
Even when using the above semiconductors, such as silicon or gallium arsenide, these semiconductors are subjected to appropriate treatment to form an extremely thin insulating film on the surface before depositing the metal thin film 4, thereby reducing the surface state density. The above effect is recognized. An example of this processing method is as follows. After chemically etching the silicon surface, it is exposed to an oxygen atmosphere at 400℃ for 10 minutes.

When a negative voltage is applied between conductive wire 6 and conductive wire 5 in a palladium thin film-n-type zinc oxide single crystal contact diode at room temperature exposed to air containing various concentrations of hydrogen gas, which is an embodiment of the present invention. In other words, when the conductor 6 is negatively biased with respect to the conductor 5, that is, when the conductor 6 is biased negatively, the current-voltage characteristics and the capacitance-voltage characteristics at the time of reverse bias are shown in Figs. 2 and 3, respectively. FIG. 4 shows the current-voltage characteristics when a voltage of 1 is applied, that is, when the conducting wire 6 is positively biased with respect to the conducting wire 5. Therefore, the current shown in FIG. 2 is the current flowing from the conducting wire 5 to the conducting wire 6, and the current shown in FIG. 4 is the current flowing from the conducting wire 6 to the conducting wire 5. Hydrogen gas can also be detected by applying a minute AC signal and measuring the resistance or capacitance of the diode.
Since increasing the element temperature increases the response speed and sensitivity of the element, the hydrogen gas detection characteristics can be improved by adding a heating section. Figure 5 shows the voltage of 1V applied to a palladium thin film-n-type zinc oxide single crystal contact diode, which is an embodiment of the present invention, at various device temperatures.
This shows the transient changes in the diode current when applying a reverse bias of , and changing the atmosphere of the device from normal air to air containing hydrogen, and when changing from air containing hydrogen to normal air. 6, 7, 8 and 9 respectively show forward current-voltage characteristics at room temperature for a palladium thin film-n-type silicon contact diode, which is an embodiment of the present invention;
Reverse current-voltage characteristics, capacitance-voltage characteristics, and when the device atmosphere is changed from normal air to air containing 0.05% _H2 at various temperatures and vice versa, when a forward bias of 0.1V is applied. Shows transient changes in diode current. The symbol % in the drawings represents the volume percentage of hydrogen gas.

By using the semiconductor crystal 1 with uniform donor and acceptor concentrations and few crystal defects, the diode's current-voltage characteristics, capacitance-voltage characteristics, and photovoltage characteristics exhibit good reproducibility, ensuring device compatibility. . Furthermore, the film 2 inactivates the semiconductor crystal surface against the atmosphere, thereby stabilizing the operation of the device.

As explained above, the present invention is effective in detecting hydrogen gas at room temperature with high sensitivity and high stability using a small and simple metal-semiconductor contact having compatibility and good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of the device according to the present invention, FIGS. 2, 4, 6, and 7 are current-voltage characteristics of the device, and FIGS. 3 and 8 are capacitance-voltage characteristics of the device. , FIG. 9 shows the temperature characteristics and transient response of the device. 1 is a semiconductor crystal, 2 is an insulating film, and 4 is a metal thin film.

Claims (1)

[Claims] 1 At different positions on one surface of the semiconductor crystal,
The metal thin film 4 whose work function changes due to hydrogen absorption and the ohmic contact electrode 3 are brought into contact with the semiconductor crystal 1, and the metal thin film 4 and the ohmic contact electrode 3 are used as terminals for detecting electrical characteristics. Characteristic hydrogen gas detection element.