JP2000275201A - Gas sensor, manufacture thereof, and gas detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sensitively detect molodor gas such as hydrogen sulfide, ammonia by exposing metal oxide semiconductor in silicon compound vapor to deposit it thereon. SOLUTION: The film thickness of a metal oxide semiconductor film such as SnO2, In2O3, ZnO is set to be about 0.01-30 μm, silicon compound is stuck to it in gas phase, a gas sensor is used in the atmoshere containing silicon compound, and the silicon compound is decomposed by pulse heating. The concentration of silicon compound to be stuck is set to be about 10-1000 ppm (gas phase concentration), and the exposure time is set to be about 10 min-10 day. The width of heating pulse is about 5 msec-4 sec, the period is about 200 msec-300 sec, and the width of the heating pulse is set to be about 0.01-10% of the period. The range in which hydrogen sulfide, ammonia, or the derivative can be sensitively detected is the range after the sensor temperature is lowered under about room temperature +30 deg.C after completing the heating pulse, or during heating pulse, the range at the beginning of the pulse until the sensor temperature reaches about 100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to detection of an odorous gas using a metal oxide semiconductor gas sensor.

[0002]

2. Description of the Related Art It is known that a metal oxide semiconductor gas sensor is exposed to a vapor of an organic compound of silicon such as trimethylchlorosilane to obtain a hydrogen-selective sensor.
1-33142). By the way, attention has been paid to detection of odor, and ammonia and hydrogen sulfide are typical odor gases as is well known. Hydrogen sulfide also represents organic sulfur-containing malodorous substances such as thiol and thiophenol, and ammonia represents malodorous substances such as various amines. In general, the smell of hydrogen sulfide is stronger than the smell of ammonia. However, in the conventional metal oxide semiconductor gas sensor, the sensitivity to ammonia is too low with respect to the sensitivity to hydrogen sulfide, and the balance between the odor and the intensity is not balanced. Secondly, the sensitivity to gases such as ethanol is too high and hinders the detection of odors. The inventor of the present invention has found that when a pulse-driven gas sensor is treated with silicone vapor (silicon compound vapor), sensitization to malodorous gas such as hydrogen sulfide or ammonia occurs instead of sensitization to hydrogen. Reached.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to detect a malodorous gas such as hydrogen sulfide or ammonia with high sensitivity, particularly at a concentration of about 1 ppm, using a pulse-driven metal oxide semiconductor gas sensor.

[0004]

The present invention comprises a metal oxide semiconductor for gas detection and a heater, and the heater heats the metal oxide semiconductor periodically and in a pulsed manner. In the meantime, in the gas sensor in which the metal oxide semiconductor is left at a temperature around room temperature, the metal oxide semiconductor is exposed to a silicon compound, and the silicon compound is attached. I do.

According to the present invention, after assembling a metal oxide semiconductor for gas detection and a heater into a predetermined shape, the metal oxide semiconductor is exposed to a silicon compound to remove the silicon compound attached to the metal oxide semiconductor. And a method of manufacturing a gas sensor, which is decomposed by heat generated from the heater. Preferably,
The sensitivity to the malodorous substance is sensitized by exposing the metal oxide semiconductor to an atmosphere containing a vapor of an organic compound of silicon and decomposing the silicon compound attached to the metal oxide semiconductor by the heater.

The present invention also provides a gas sensor having a metal oxide semiconductor for gas detection and a heater, wherein the heater heats the metal oxide semiconductor periodically and in a pulsed manner. In the gas detection method in which the temperature of the metal oxide semiconductor is set to around room temperature between the pulse and the pulse, the metal oxide semiconductor is exposed to a silicon compound, and the silicon compound is attached to the metal oxide semiconductor. A gas sensor is used to detect an odor component from the resistance value of the metal oxide semiconductor near room temperature or at the beginning of a heating pulse. Preferably, the gas sensor is placed in an atmosphere containing the vapor of the silicon compound, and after the silicon compound attached to the metal oxide semiconductor is decomposed by the heat generated by the heater of the gas sensor, the odorous gas is detected.

[0007]

When the pulse-driven metal oxide semiconductor gas sensor is exposed to a silicon compound to cause the silicon compound to adhere thereto (hereinafter, this processing is referred to as silicone processing),
Instead of sensitization to hydrogen, sensitization to gases such as ammonia and hydrogen sulfide occurs. Preferably, the silicon compound is adhered to the gas sensor as vapor in principle, and the gas sensor is used in an atmosphere containing the vapor of the silicon compound under, for example, ordinary conditions, and the silicon compound adhered is decomposed by pulse heating. The state of the decomposed silicon compound is considered to be silica or a substance in the process of decomposing the silicon compound into silica. Silicon compounds to be attached are, for example, HMDS (hexamethyldisiloxane), SiH3Cl, SiHCl3, CH3SiCl
2, SiCl (CH3) 3, etc., and the processing concentration and processing time are, for example, (10 ppm to 1000 ppm) × (10 minutes to
1 hour) or (10 ppm x 100 ppm) x
(10 minutes to 10 days).

In the case of the pulse drive type, sensitization of hydrogen during the silicone treatment does not occur or occurs only slightly.
In the detection of odor, ammonia sensitivity and ethanol sensitivity are similar, and it is difficult to detect ammonia separately from ethanol. However, in the silicone treatment of the pulse-driven gas sensor, the ethanol sensitivity generally decreases. On the other hand, the silicone treatment causes a slight increase in hydrogen sulfide sensitivity and a marked increase in ammonia sensitivity. For these reasons, the detection of offensive odor becomes easy, and the sensitivity to the offensive odor gas according to the human sense of smell is obtained.

When a pulse-driven metal oxide semiconductor gas sensor is subjected to silicone treatment, sensitization is caused not to hydrogen but to ammonia or hydrogen sulfide, but the cause is unknown. When a pulse-driven gas sensor is subjected to silicone treatment, ammonia or ammonia is used under a weaker silicone treatment condition than when a hydrogen sensor is sensitized by a continuously heated gas sensor to a constant temperature (hereinafter, referred to as a continuously-driven gas sensor). Sensitization to hydrogen sulfide occurs. Whether the sensitization to hydrogen or the sensitization to hydrogen sulfide or ammonia occurs does not depend on the material, shape, or structure of the gas sensor, but depends on the difference in driving conditions between continuous driving and pulse driving.

In a pulse-driven gas sensor, sensitization to ammonia and hydrogen sulfide occurs during the heating pulse period and other periods. Here, in order to detect ammonia and hydrogen sulfide with high sensitivity, the temperature of the metal oxide semiconductor is changed at the beginning of the heating pulse after the metal oxide semiconductor is cooled to a temperature of room temperature + 30 ° C. or less after the end of the heating pulse. 1
It is preferable to use a signal in a time range of 00 ° C. or less. That is, within this range, the sensitivity to hydrogen sulfide and ammonia is high,
About 1 ppm of ammonia and less than 1 ppm of sulfided water can be detected.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing conditions of a gas sensor, sampling conditions of a sensor signal, and characteristics of a gas sensor will be described in this order. FIG.
In the gas sensor 1 of the embodiment, reference numeral 2 denotes a heat-resistant insulating substrate such as alumina, 4 denotes a heat insulating film such as a glass film, and the heat insulating film 4 is unnecessary when the substrate 2 is made of a heat insulating material such as glass. It is. 6 is a heater film such as a Pt film or a RuO2 film, and 8 is not necessarily an insulating film such as a glass film or a silica film, and 10 is a metal oxide semiconductor film such as a SnO2 film, an In2O3 film, or a ZnO film. The material of the metal oxide semiconductor film 10 is not limited, but is preferably SnO2, and the thickness is 0.01 to 30.
It is about μm.

The silicon compound is deposited on the gas sensor in a gas phase in principle, and the gas sensor is used under an ordinary atmosphere in an atmosphere containing the silicon compound, and the silicon compound attached to the metal oxide semiconductor is decomposed by pulse heating. The decomposition of the silicon compound may be performed not by pulse heating but by continuous heating by a heater of the gas sensor. The decomposition products are considered to be intermediate substances in the process of decomposing silica and the silicon compound attached to silica. The concentration of the silicon compound to be attached to the metal oxide semiconductor (concentration in the gas phase in ppm by volume) is, for example, 10 p
pm to 1000 ppm, and the exposure time is in the range of about 10 minutes to 10 days. In a combination of the exposure concentration and the exposure time, for example, (10 ppm to 1000 ppm) × (1
0 minutes to 1 hour) or (10 ppm x 100 pp)
m) × (10 minutes to 10 days). Exposure time x
The product of the exposure concentration is 100 ppm · min.
ppm / min is preferred.

The material of the metal oxide semiconductor of the gas sensor is arbitrary, and the structure is not limited to the one shown in FIG. A covered electrode or a coil-shaped heater / electrode covered with a metal oxide semiconductor in a bead shape may be used, except for the center electrode. Further, a heater film and a metal oxide semiconductor thin film may be formed on a bridge of a silica thin film or the like. Each of these sensors is small and can be pulsed.

The structure of the gas sensor may be of a pulse drive type, that is, a type in which the metal oxide semiconductor is left near room temperature for most of the period and is pulse-heated periodically. The width of the heating pulse is, for example, 5 ms to 4 seconds, and the cycle is 200 m.
Seconds to 300 seconds, and the width of the heating pulse is 0.1
It is set to about 01% to 10%, preferably about 0.02 to 5%. Further, the heating pulse in the pulse driving may be constituted by a group of fine sub-pulses by duty ratio control.

FIG. 2 shows sampling conditions. The operation cycle (pulse cycle) of the sensor is T1 and the pulse width is T2. The range in which hydrogen sulfide, ammonia, or their derivatives can be detected with high sensitivity,
Sensor temperature (temperature of metal oxide semiconductor film 10) is room temperature +
This is a section after the temperature has dropped to 30 ° C. or lower. In addition, the heating pulse is in a range until the sensor temperature reaches 100 ° C. at the beginning of the pulse. A typical sampling point is a point where the sensor temperature has dropped to almost room temperature immediately before the heating pulse or after the end of the heating pulse.

FIG. 3 shows the structure of a continuously driven gas sensor 11 used for comparison. 2 is a substrate of alumina or the like, 6 is a heater film, 10 is a metal oxide semiconductor film (SnO2 × 20 μm).
m). Here, the continuous driving refers to driving the metal oxide semiconductor film 10 with a constant temperature by applying a constant power to the heater film 6. The data of the continuously driven gas sensor is shown in FIGS.
19 and 20 show the characteristics without silicon treatment, and FIGS. 18 and 21 show the characteristics after silicon treatment. Silicon treatment conditions are HMD
At 1000 ppm × S for 40 minutes, the sensor was energized and heated to 400 ° C. during the silicon treatment.

In the data of FIGS. 4 to 21, the sensor of FIG. 1 was used as a pulse-driven gas sensor, and SnO 2 (about 20 μm thick) was used for the metal oxide semiconductor film. When the driving condition is a 1 second cycle, the heating pulse width is 14 ms, and the maximum temperature is over 300 ° C., the sensor temperature is about 70 ° C. 2.8 ms from the start of the heating pulse, and 16 m after the end of the heating pulse.
About 100 ° C in seconds, and room temperature + 88 msec after the end of the heating pulse
Room temperature is about 10 ° C., and 488 msec after the end of the heating pulse. When the pulse width is kept at 14 ms, the pulse cycle may be changed in a range of, for example, about 0.25 seconds to 60 seconds. The heating pulse width may be changed in a range of about 5 ms to 4 seconds. In this case, according to the change of the heating pulse width,
The heating cycle may be changed to about 200 ms to 300 seconds. The data in each figure is shown as a ratio to the resistance value in air except for FIGS.

The sensor shown in FIG. 3 was used as a comparatively continuously driven gas sensor, and SnO 2 having a thickness of about 20 μm was used as a metal oxide semiconductor. The results are shown in FIGS.

HMDS for silicone treatment (silicon treatment)
(Hexamethyldisiloxane) and the processing conditions are shown in FIG.
In the case of (1), the sensor was pulse-driven at a cycle of 1 second at HMDS 10 ppm × 40 minutes, and after the silicon treatment, the sensor was energized in air for 3 days, and then the characteristics were measured. 4 and 5
Is 3 sensors. FIG. 5 shows the comparative data of FIG. 4 and is the result of the sensor without silicone treatment. The sampling point in FIGS. 4 and 5 is 10 ms before the next heating pulse.

4 and 5, the sensitivity to hydrogen hardly increases and the sensitivity to ethanol decreases to about 1/10 due to the silicone treatment. On the other hand, the sensitivity to hydrogen sulfide is slightly increased, and the sensitivity to ammonia is significantly increased. Thus, silicon treatment with pulse heating resulted in an increase in hydrogen sulfide sensitivity and a sharp increase in ammonia sensitivity.

For comparison with FIGS. 4 and 5, FIGS. 18 and 19 show the characteristics of the continuously driven gas sensor of FIG. 3 when subjected to silicone treatment under the same conditions. FIG. 18 shows the characteristics after processing, and FIG. 19 shows the characteristics of the unprocessed sensor. Under these conditions, there is no increase in hydrogen sensitivity, no increase in hydrogen sulfide sensitivity, and no increase in ammonia sensitivity. In the silicon treatment under the condition that the sensitivity to ammonia or hydrogen sulfide is increased in the pulse-driven gas sensor, the characteristics of the continuously-driven gas sensor hardly change.

FIGS. 6 to 11 show that a pulse-driven gas sensor (FIG. 1) was energized for one day in 10 ppm of HMDS.
This is the characteristic after energizing in air for three days. 12 to 1
Reference numeral 7 denotes the characteristics of the above-described comparative sensor without silicone treatment. In each figure, the number of sensors is three, and the average value and the maximum and minimum ranges are shown. Sampling points are 10 ms before the heating pulse (SnO2 temperature is room temperature) in FIGS. 6 and 12, 2.8 ms after the start of the heating pulse (SnO2 temperature is about 70 ° C.) in FIGS. 14 is 14 ms after the start of the heating pulse (SnO2 temperature is slightly over 300 ° C.)
9 and 15 show 16 ms after the end of the heating pulse (about 100 ms).
10 and 88 are 88 ms after the end of the heating pulse (room temperature + 10 ° C.), and FIGS. 11 and 17 are 488 msec after the end of the heating pulse (room temperature).

In any case, by silicone treatment,
The hydrogen sulfide sensitivity increases slightly, and the ammonia sensitivity increases significantly. Hydrogen sensitivity does not change, CO sensitivity and ethanol sensitivity decrease. As a result, the sensitivity to sulfur-based compounds (hydrogen sulfide, mercaptan compounds, thiophenol compounds, etc.) and ammonia-based compounds (ammonia and amine-based compounds), which are the main components of malodor, is improved. The problem of low sensitivity to ammonia-based compounds can be solved. And the interference by CO and ethanol is eliminated.

In FIGS. 6 to 11, when the sensor temperature is high at the end of the pulse (FIG. 8) or immediately after the end of the pulse (FIG. 9), the sensitivity to hydrogen sulfide and ammonia is low. On the other hand, the sensitivity to hydrogen sulfide and ammonia is high at the beginning of the pulse (FIG. 7) or after cooling to near room temperature after the end of the pulse (FIGS. 6, 10 and 11). From these facts, the sampling is performed after the sensor temperature drops to room temperature + 30 ° C. or less after the end of the heating pulse, or when the sensor temperature is 10
It is preferable to carry out until the temperature reaches 0 ° C.

FIGS. 20 and 21 show that the continuous drive type gas sensor of FIG.
This shows the characteristics when energized for one minute. One sensor, FIG.
FIG. 21 shows the results without silicone treatment (silicon treatment).
Is the result after the treatment, and the gas concentration is 2000 ppm each. As is known in the prior art, hydrogen sensitivity is increased. As described above, it is a phenomenon peculiar to the pulse heating sensor that the sensitivity to the odorous gas is increased by the silicone treatment and the sensitivity to the interfering gas such as alcohol is decreased. In the embodiment, the shape of the pulse heating sensor is specified, but it is important to use conditions in which the metal oxide semiconductor is heated in a pulsed manner and is left near room temperature for most of the period. Therefore, the sensor to be used may be a pulse heating type sensor using a metal oxide semiconductor, and is not limited to the specific shape shown in FIG.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a gas sensor according to an embodiment.

FIG. 2 is a diagram showing driving timings of the gas sensor according to the embodiment.

FIG. 3 is a cross-sectional view of a continuously driven gas sensor used for comparison.

FIG. 4 is a characteristic diagram of the gas sensor after the silicone treatment. The treatment condition is HMDS 10 ppm × 40 minutes energization.

FIG. 5 is a characteristic diagram of a gas sensor without silicone treatment.

FIG. 6 is a graph showing gas concentration characteristics immediately before a heating pulse (10 ms before the next heating pulse) in the example, and the processing condition is HMDS 10 ppm × 1 day energization.

FIG. 7 is a diagram showing gas concentration characteristics at an initial stage (2.8 msec from the start of pulse heating) in a heating pulse in the embodiment.
Processing conditions are HMDS 10 ppm x 1 day

FIG. 8 is a diagram showing gas concentration characteristics at the end of a heating pulse (14 msec from the start of pulse heating) in the example, and the processing conditions were HMDS 10 ppm × 1 day energization.

FIG. 9 is a graph showing gas concentration characteristics 16 ms after the end of a heating pulse in the example, and the processing condition is HMDS 10p
pm x 1 day

FIG. 10 is a graph showing gas concentration characteristics 88 msec after the end of a heating pulse in the example, and the processing condition is HMDS 10p
pm x 1 day

FIG. 11 is a graph showing gas concentration characteristics 488 msec after the end of a heating pulse in the example.
ppm x 1 day

FIG. 12 is a graph showing gas concentration characteristics immediately before a heating pulse (10 ms before the next heating pulse) in a gas sensor without silicone treatment.

FIG. 13 is a diagram showing gas concentration characteristics at an initial stage (2.8 msec from the start of pulse heating) in a heating pulse in a gas sensor without silicone treatment.

FIG. 14 is a view showing gas concentration characteristics of a gas sensor without silicone treatment at the end of a heating pulse (14 msec from the start of pulse heating).

FIG. 15 is a graph showing gas concentration characteristics of a gas sensor without silicone treatment after 16 msec from the end of a heating pulse.

FIG. 16 is a view showing gas concentration characteristics of a gas sensor without silicone treatment after 88 msec from the end of a heating pulse.

FIG. 17 is a diagram showing gas concentration characteristics of a gas sensor without silicone treatment after 488 msec after the end of a heating pulse.

FIG. 18 is a view showing gas concentration characteristics after silicone treatment with a continuously driven gas sensor, and the treatment conditions are HMDS 1
0 ppm x 40 minutes

FIG. 19 is a graph showing gas concentration characteristics of a continuously driven gas sensor without silicone treatment.

FIG. 20 is a graph showing gas sensitivity of a continuously driven gas sensor without silicone treatment.

FIG. 21 is a view showing gas sensitivity after silicone treatment with a continuously driven gas sensor, and the treatment condition is HMDS 100
0 ppm x 40 minutes

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Substrate 4 Heat insulation film 6 Heater film 8 Insulation film 10 Metal oxide semiconductor film

Claims (5)

[Claims] 1. A semiconductor device comprising: a metal oxide semiconductor for detecting gas; and a heater.
In a gas sensor in which the metal oxide semiconductor is heated periodically and in a pulsed manner, and the pulse is left between the pulses, the metal oxide semiconductor is exposed to a silicon compound. A gas sensor to which a silicon compound is attached. 2. After assembling a metal oxide semiconductor for gas detection and a heater into a predetermined shape, exposing the metal oxide semiconductor to a silicon compound to remove the silicon compound attached to the metal oxide semiconductor into the heater. A method of manufacturing a gas sensor that decomposes due to heat generated from the gas. 3. The sensitivity to malodorous substances is increased by exposing the metal oxide semiconductor to an atmosphere containing a vapor of an organic compound of silicon and decomposing the silicon compound attached to the metal oxide semiconductor by the heater. Characterized by feeling,
A method for manufacturing the gas sensor according to claim 2. 4. Using a gas sensor provided with a metal oxide semiconductor for gas detection and a heater, the heater heats the metal oxide semiconductor periodically and in a pulsed manner,
In a gas detection method in which the temperature of the metal oxide semiconductor is set to around room temperature between the pulses, the metal oxide semiconductor is exposed to a silicon compound, and the silicon compound is attached to the metal oxide semiconductor. A gas detection method, comprising: detecting a malodorous component from the resistance value of the metal oxide semiconductor near room temperature or at an early stage of a heating pulse using the gas sensor. 5. A gas sensor is placed in an atmosphere containing a vapor of the silicon compound, and after the silicon compound attached to the metal oxide semiconductor is decomposed by heat generated by a heater of the gas sensor, an odor gas is detected. The gas detection method according to claim 4, wherein