JP2003270185A - Driving method of semiconductor gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption furthermore than hitherto. <P>SOLUTION: When shifting to a low temperature state for performing gas detection, which is, in this case, a period of about 50-400 ms (the keeping state at 100°C by 4.5 mW) after elapse of, for example, a period of minus 200-0 ms (the heating state up to about 450°C by 30 mW) for performing cleaning beforehand at the driving time of a heater of this semiconductor gas sensor, power supply to the sensor is stopped as long as, for example, 50 ms, to thereby reduce the power consumption as much as the time portion. Namely, the power consumption is increased hitherto because there is no suspension period. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low power consumption type semiconductor gas sensor, especially a method of driving the same, in consideration of battery driving.

[0002]

2. Description of the Related Art Generally, a gas sensor is used for an application such as a gas leak alarm, and a certain gas such as CO,
It is a device that is selectively sensitive to CH ₄ , C ₃ H ₈ , CH ₃ OH, etc., and due to its characteristics, high sensitivity, high selectivity, high responsiveness,
High reliability and low power consumption are essential. by the way,
Gas leak alarms that are widely used for household use include those for the purpose of detecting combustible gas for city gas and propane gas, those for detecting incomplete combustion gas of combustion equipment, or both. There are things that also have functions,
In both cases, the penetration rate is not so high due to cost and installation issues. Under these circumstances, in order to improve the penetration rate, it is desired to improve the installability, specifically, to be battery-powered and cordless.

In order to realize battery drive, low power consumption is the most important. Therefore, low power consumption is realized by performing intermittent driving in synchronization with the detection cycle.
As a concrete example, for example, a semiconductor C having a structure as shown in FIG.
The case of driving the O sensor will be described. It should be noted that the one shown in the figure has the outer periphery or both end portions of the thin film-like support film
A thin-film heater 3 is formed on a diaphragm-like support substrate which is supported by an i substrate 1, and has a thick outer peripheral portion or both end portions and a thin central portion, and the thin-film heater 3 is covered with an electric insulating film 4. An electrode 6 for a gas sensing film is formed thereon, and a gas sensing film 7 is further formed of a semiconductor thin film.

In such a semiconductor CO sensor, for example, an intermittent operation of 150 s is carried out. In order to detect CO gas, the sensor is first in a high state (high state: about 450).
The surface of the sensor is cleaned by heating for 200 ms at (° C.) to initialize the sensor. Then, the sensor is lowered to a low state (low state: 100 ° C. or lower), and the sensor resistance is measured after 400 ms, for example, to determine whether or not CO gas exceeds a predetermined gas concentration.

Therefore, as shown in FIG. 8, when the power is high, the heater is supplied with power of, for example, 30 mW, and when it is low, power is supplied with 4.5 mW. The actual temperature change at this time is shown in FIG. 30mW for the heater when high
Even if the power is turned on, it takes about 5
It takes 0mS time and power is from 30mW to 4.5mW
It shows that it takes about 100 mS for the temperature to stabilize even if the temperature is reduced to a low state by shifting to. The transient response characteristics of the sensor at this time are shown in FIG.
Shown in.

[0006]

However, there is still room for improvement in the above method. That is, an object of the present invention is to avoid unnecessary heating of the heater and further reduce power consumption.

[0007]

In order to solve such a problem, in the invention of claim 1, the semiconductor gas sensor is kept at a high temperature for a certain time for the purpose of cleaning, and then a low temperature for gas detection is used. The power supply to the heater that heats the sensor is temporarily cut off when shifting to the state. In the invention of claim 1, the period for temporarily cutting off the power supply is longer than half the response time of the heater, and the temperature of the sensor is detected by cutting off the power supply. It can be selected so that the time when the temperature becomes lower than the temperature is below a certain value (the invention of claim 2).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view for explaining a first embodiment of the present invention. As is clear from the figure, as compared with the case of FIG. 8, after the high state 200 mS,
The feature is that an off state of 50 mS is provided. In addition, each state of high, low and off,
A processing device is provided in a power conversion device (not shown) that uses a sensor battery as a power source, and the processing device causes the power conversion device to output a single pulse signal equivalent to 30 mW of power to the heater, or a plurality of minute pulse signals It is assumed that each of them is generated by an average power equivalent to 4.5 mW or is output in the same manner as in the conventional method such as stopping the output of the pulse signal.

FIG. 2 shows a temperature change of the sensor when driven as shown in FIG. As shown in FIG. 2, from high to l
It can be seen that the response speed to ow is shortened from 100 mS to 50 mS. The transient response characteristics of the sensor at this time are shown in FIG. Since the response is quicker than that of the conventional example of FIG. 10, the detection time after the end of high can be shortened accordingly.

FIG. 4 is an explanatory view for explaining the second embodiment of the present invention, which is characterized in that the off time is set to 150 mS. FIG. 5 shows the temperature change of the sensor when driven as in FIG. As shown in FIG. 5, from high to l
The difference is that when the temperature changes to ow, the temperature once falls below the steady temperature in the low state and then reaches the temperature in the low state. If the time when the sensor temperature becomes lower than the low set temperature (100 ° C. or less) becomes a certain fixed value (about 150 mS in this example) or more, problems occur in moisture resistance and stability, so this time is set to a certain value. It is desirable to keep it below a certain value.

FIG. 6 shows transient response characteristics of the sensor when driven as shown in FIG. Now, for example, 100 ppm,
Regarding the difference (or ratio) of the respective resistance values (concentrations) of 300 ppm and 500 ppm, comparing FIG. 6 with the conventional FIG. 10, the difference is small in FIG. 10, but the difference is slightly larger in FIG. There is. This indicates that the concentration gradient value is large and therefore the sensitivity is high.
That is, driving as shown in FIG. 4 can not only reduce power consumption but also improve sensitivity.

The present invention can be applied not only to the CO gas sensor described above but also to general semiconductor gas sensors.

[0013]

According to the present invention, the sensor (heater)
When driving the, the off state is provided between the high state and the low state, so that there is an advantage that the power consumption can be reduced and the quick detection can be performed. In particular, the sensitivity can be improved by the invention of claim 2.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining a first embodiment of the present invention.

FIG. 2 is a temperature change diagram of a sensor when driven as in FIG.

FIG. 3 is a transient response diagram of the sensor when driven as in FIG.

FIG. 4 is an explanatory diagram for explaining a second embodiment of the present invention.

FIG. 5 is a temperature change diagram of the sensor when driven as in FIG.

FIG. 6 is a transient response diagram of the sensor when driven as in FIG.

FIG. 7 is a cross-sectional view showing a general example of a semiconductor gas sensor.

FIG. 8 is a conventional sensor drive pattern diagram.

FIG. 9 is a temperature change diagram of the sensor when driven as in FIG.

FIG. 10 is a transient response diagram of the sensor when driven as in FIG.

[Explanation of symbols]

1 ... Si substrate (diaphragm), 2 ... Support layer, 3 ... Heater, 4 ... Insulating film, 5 ... Bonding layer, 6 ... Sensing film electrode, 7 ...
Sensitive membrane.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsumi Higaki             4-1-2 Hirano-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Within Osaka Gas Co., Ltd. (72) Inventor Hirokazu Sasaki             4-1-2 Hirano-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Within Osaka Gas Co., Ltd. (72) Inventor Hisao Onishi             4-1-2 Hirano-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Within Osaka Gas Co., Ltd. (72) Inventor Shinji Ogino             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Takuya Suzuki             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Ken Matsubara             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Kenji Kunihara             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Mitsuo Kobayashi             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 2G046 AA11 AA19 AA21 AA24 BA01                       BA09 BB02 BB04 BE03 DA05                       DB02 DB03 DB04 DB05 DC13                       DD01 DD03 EB06 FB02 FE31                       FE38 FE39 FE46                 2G060 AA01 AB08 AB17 AB18 AB21                       AE19 AF07 BA01 BB09 HB02                       HB03 HB05 HB06 HC07 HE02                       KA01

Claims (2)

[Claims] 1. When a semiconductor gas sensor is held at a high temperature for a certain period of time for the purpose of cleaning, and then a low temperature is set for gas detection, power is temporarily supplied to a heater for heating the sensor. A method for driving a semiconductor gas sensor, characterized in that the semiconductor gas sensor is shut off. 2. The period for which the power supply is temporarily cut off is longer than half the response time of the heater, and the temperature of the sensor is higher than the temperature for the purpose of detection due to the cutoff of the power supply. 2. The method for driving a semiconductor gas sensor according to claim 1, wherein the time for lowering is selected so as to be a certain value or less.