JP7653866B2 - Gas sensor element and gas sensor including precious metal chalcogenide thin film - Google Patents

Description

The present invention relates to a gas sensor element used in a gas sensor that detects various chemical gases in a target atmosphere. More specifically, the present invention relates to a gas sensor element that uses a thin film of a transition metal chalcogenide, which is a semiconductor material, as a sensitive part for gas detection.

Various types of gas sensors are known for detecting various chemical gases in the atmosphere to be detected. Specifically, catalytic combustion gas sensors, electrochemical gas sensors, non-dispersive infrared absorption (NDIR) gas sensors, semiconductor gas sensors, etc. are known. These gas sensors are distinguished by their operating principles, and each has its own advantages. Among these gas sensors, semiconductor gas sensors are highly sensitive and capable of detecting trace amounts of gas, and are highly durable and have long-term stability, so they are installed in household gas alarms, etc. Furthermore, taking advantage of these characteristics, they are expected to be applied to medical diagnostic equipment for diagnosis by breath analysis.

A semiconductor gas sensor detects gas based on a change in resistance caused by a change in the electronic state when gas molecules to be detected are adsorbed to a sensitive part (semiconductor material). Here, oxide semiconductors such as tin oxide ( _SnO2 ) have been used as the semiconductor material for the sensitive part of semiconductor gas sensors (for example, Patent Document 1, etc.).

One problem with gas sensors that use oxide semiconductors as their sensitive parts is the need to heat the sensitive part. Semiconductor gas sensors that use oxide semiconductors as their sensitive parts cannot detect gas unless they are heated to around 200°C to 400°C. This heating requires an external power supply, which affects the energy costs of running the gas sensor as well as its ease of handling and portability. As mentioned above, gas sensors are used in a variety of fields, and so there is a demand for lighter and more cordless power sources, so the issue of power supply is significant.

In addition, a sensitive part made of an oxide semiconductor such as tin oxide can be manufactured by applying and sintering a paste containing oxide powder, but there is a limit to how thin it can be made even if the paste application method is improved. A thinner sensitive part is preferable in terms of power consumption as mentioned above, but it also contributes to the miniaturization of the gas sensor element. Therefore, it can be said that oxide semiconductors also have a limit to how small the element can be made.

In recent years, a transition metal chalcogenide thin film has been considered to be a useful semiconductor material for the sensing part of a semiconductor gas sensor. A transition metal chalcogenide is a compound of a metal from Group 3 to Group 11 of the transition metals and a chalcogen element other than oxygen. It is known that transition metal chalcogenides exhibit unique electrical properties and semiconductor properties depending on the type of transition metal. In the field of gas sensors, there are also known gas sensors that use graphene, MoS ₂ (molybdenum disulfide), WS ₂ (tungsten disulfide), and other transition metal chalcogenides as the sensing part (Patent Documents 2 and 3, etc.).

Gas sensors that use transition metal chalcogenide thin films as the sensing part are sensitive to various gases at room temperature, unlike oxide semiconductors, and therefore have no problems with power sources. Transition metal chalcogenides are substances in which transition metal atoms and chalcogen atoms are regularly arranged and bonded by ionic and/or covalent bonds, and are also called two-dimensional semiconductors. Transition metal chalcogenides can exhibit favorable semiconductor properties when made into a thin film, so they can also be used to thin the sensing part. Transition metal chalcogenides can also be easily made into thin films using various thin film formation processes such as physical vapor deposition (PVD) and chemical vapor deposition (CVD and ALD).

JP 2000-214119 A JP 2016-151558 A International Publication No. 2017/002854

However, because the semiconductor material transition metal chalcogenide is currently under research, there is still room for improvement in gas sensors that use this as a sensitive part. As mentioned above, transition metal chalcogenides that constitute gas sensor elements to date include _MoS2 and _WS2 , but these are not necessarily sufficient in terms of sensitivity and responsiveness.

The present invention was made against the background described above, and proposes a new transition metal chalcogenide suitable as the sensing part of a semiconductor gas sensor. It also provides a gas sensor element that is highly sensitive and responsive to a variety of detection gases, yet consumes low power and is highly reliable.

The present invention, which solves the above problems, is a gas sensor element that includes a substrate and a sensitive part for gas detection formed on the substrate, the sensitive part being made of a thin film of a chalcogenide compound of a precious metal.

As described above, the gas sensor element according to the present invention uses a thin film of transition metal chalcogenide with a precious metal as the central metal as the sensing part. Precious metal chalcogenide compounds are not unknown substances in themselves. The inventors have been researching precious metal chalcogenide compounds and have found that the compounds have suitable properties as optical semiconductors. Precious metal chalcogenides tend to have a band gap that is about 1 eV smaller than transition metal chalcogenides such as Mo and W. This is thought to enable the high mobility (carrier mobility), which is a characteristic of transition metal chalcogenides, to be more effectively exhibited. The present invention was made based on the findings of the inventors and the usefulness of precious metal chalcogenides as the sensing part of a gas sensor element. The configuration of the gas sensor element according to the present invention will be described below.

(A) Configuration of the gas sensor element according to the present invention (A-1) Substrate The substrate is a member for supporting a thin film made of a transition metal chalcogenide. The material of the substrate may be any material that can support a thin film made of a transition metal chalcogenide. Examples of the material include glass, quartz, silicon, ceramics, and metals. The shape and dimensions of the substrate are not particularly limited.

(A-2) Precious metal chalcogenide thin film Precious metal is a transition metal group consisting of Au (gold) and Ag (silver) plus platinum group metals Pt (platinum), Pd (palladium), Ru (ruthenium), Ir (iridium), Rh (rhodium), and Os (osmium). The precious metal of the precious metal chalcogenide applied in the present invention is preferably any one of Pt, Pd, Ru, and Ir. And, the chalcogen element of the precious metal chalcogenide applied in the present invention is preferably any one of S (sulfur) and Se (selenium). The preferred compounds of the precious metal chalcogenide in the present invention are PtS ₂ , PtSe ₂ , PdS ₂ , PdSe 2 , RuS ₂ , RuSe ₂ , IrS ₂ , Ir _{2 S 3} , and IrSe ₂ .

The preferred noble metal chalcogenides exemplified above generally have a stoichiometric composition in which the noble metal element and the chalcogen element are in an integer ratio. The noble metal chalcogenide constituting the thin film is optimally one that conforms to the above stoichiometric composition. However, the noble metal chalcogenide does not necessarily have to have a stoichiometric composition to function as the sensitive portion of the gas sensor element. For example, a thin film that partially or entirely contains a noble metal chalcogenide with chalcogen element deficiencies may also be used. This is because even noble metal chalcogenides that do not have such a stoichiometric composition can exhibit semiconductor behavior.

The sensitive portion of the gas sensor element according to the present invention is made of a thin film of the above-mentioned noble metal chalcogenide compound. The thickness of this thin film is preferably 0.5 nm to 500 nm. Furthermore, among the noble metal chalcogenides, noble metal chalcogenides such as PtS ₂ , PtSe ₂ , and PdSe ₂ , which are said to have a two-dimensional structure, have a band gap that changes depending on the number of layers, and may exhibit antimetallic properties when in a bulk state. The thin film of such noble metal chalcogenides having a two-dimensional structure is preferably 5 nm or less.

The thin film that will be the sensitive portion may be formed on the entire surface of the substrate, but it is sufficient that it is formed on the portion that will be the sensitive portion based on the design of the gas sensor element. The thin film may be formed on the entire surface of the sensitive portion, but may also be partially island-shaped. This is because even if the chalcogenide compound crystals are not a continuous film over the entire surface, the semiconductor properties can be exhibited by the interaction of the crystals scattered in an island shape. An island-shaped thin film is a thin film formed by a growth form based on the Volmer-Weber type. This is a state in which a three-dimensional island made of a precious metal chalcogenide is formed on the substrate. In other words, it shows a transitional state until the precious metal chalcogenide thin film is formed over the entire surface of the substrate. Including the case where this island-shaped thin film is formed, it is preferable that the coverage rate of the substrate of the precious metal chalcogenide thin film is 10% or more. The coverage rate is calculated by the ratio of the surface area of the precious metal chalcogenide thin film to the surface area of the surface of the substrate on which the thin film is formed.

(B) Manufacturing method of the gas sensor element according to the present invention The gas sensor element according to the present invention is manufactured by forming a precious metal chalcogenide thin film on the above-mentioned substrate. As a method for forming the precious metal chalcogenide thin film, in addition to a method in which a precious metal chalcogenide is directly produced on a substrate by various thin film formation processes, a method in which a precious metal thin film is first formed and then chalcogenized to form a precious metal chalcogenide thin film can also be applied.

In sputtering, a method for directly forming a precious metal chalcogenide on a substrate can be used to produce a precious metal chalcogenide thin film by reactive sputtering using a precious metal target. In addition, a precious metal chalcogenide can be produced by powder metallurgy or the like, and this can be used as a sputtering target to produce a precious metal chalcogenide thin film.

Furthermore, suitable thin film formation processes include chemical vapor deposition methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). Chemical vapor deposition can efficiently obtain a precious metal thin film of the desired thickness.

In the film formation process using chemical vapor deposition (CVD and ALD), a precious metal source gas, which is generated by vaporizing a raw material (precursor) of a precious metal compound that serves as a precious metal source, and a chalcogen source gas containing a chalcogen or chalcogenide compound that serves as a chalcogen element source, are supplied onto a substrate and reacted to deposit the precious metal chalcogen on the substrate to form a thin film.

Examples of precursors of noble metal compounds that can be used in the chemical vapor deposition method include organic platinum compounds such as dimethyl(N,N-dimethyl-3-butan-1-amine-N)platinum (DDAP), 1,5-hexadienedimethylplatinum (HDMP), (trimethyl)methylcyclopentadienylplatinum (MeCpPtMe ₃ ), and bis(acetylacetonato)platinum (Pt(acac) ₂ ). Examples of precursors of noble metal compounds that can be used in the chemical vapor deposition method include organic palladium compounds such as bis(hexafluoroacetylacetonato) (Pd(hfac) ₂ ), cyclopentadienylallylpalladium (CpPd(allyl)), and bis(methylallyl)palladium (Pd(Meallyl) ₂ ). For ruthenium, organic ruthenium compounds such as dicarbonyl-bis(5-methyl-2,4-hexanedionato)ruthenium, hexacarbonyl[methyl-(1-methylpropyl)-butene-aminato]diruthenium, dodecacarbonyltriruthenium (DCR) and the like can be used. For iridium, organic iridium compounds such as tris(acetylacetonato)iridium (Ir(acac) ₃ ) and (cyclohexadienyl)methylcyclopentadienyliridium ((MeCp)Ir(CHD)) can be used.

The precious metal raw material gas generated by vaporizing the above-mentioned precious metal compound is supplied to the reactor after appropriately merging with a carrier gas. An inert gas such as Ar is used as the carrier gas.

On the other hand, the chalcogen source gas can be obtained by heating solid chalcogen (S, Se, etc.) and vaporizing it by sublimation to obtain a source gas. In addition, as a chalcogen compound gas, a hydrogenated chalcogen gas (H ₂ S, H ₂ Se, etc.) can also be used as the chalcogen source gas.

When forming a film of a precious metal chalcogenide by chemical vapor deposition, a source gas is introduced into a reactor that contains a substrate. A one-zone heating system equipped only with a means for heating the substrate can be used as the reactor. In this case, there are no particular restrictions on the procedure for introducing the source gas. Both the precious metal source gas and the chalcogen source gas may be introduced into the reactor at the same time, or the precious metal source gas may be introduced first and then the chalcogen source gas.

A two-zone heating reactor can also be used as the reactor. A two-zone heating reactor is a reactor that has heating means at two locations: the position where the substrate is set and a specified position upstream of the substrate. In the two-zone system, chalcogen elements are placed at the heating position upstream of the substrate and heated and vaporized to generate chalcogen source gas. A precious metal source gas is then introduced into the reactor and supplied onto the substrate together with the chalcogen source gas.

A precious metal source gas and a chalcogen source gas are supplied onto the substrate, and the substrate is heated to cause the precious metal chalcogenide to precipitate and form a thin film. The heating temperature at this time is preferably 200°C or higher and 800°C or lower.

In addition to the direct process described above, thin films of precious metal chalcogenides can also be formed by chalcogenizing a thin film of a precious metal. This process is also known as the metal film reaction method, in which a thin film of a precious metal is formed on a substrate and then heat-treated in an atmosphere containing a chalcogen element to chalcogenize the precious metal.

In the metal film reaction method, the precious metal thin film can also be formed by sputtering or chemical vapor deposition (CVD, ALD). The above-mentioned precious metal compounds can also be used as the source gas (precious metal compound) for the chemical vapor deposition method. The formation of the precious metal thin film by the chemical vapor deposition method proceeds by the decomposition of the precious metal source gas (precious metal compound) on the substrate. At this time, a reaction gas can be supplied to the substrate surface to promote the decomposition of the metal compound in the source gas. The reaction gas used can be oxygen, hydrogen, etc., depending on the type of precious metal compound.

Then, the formed noble metal thin film is treated in a chalcogen atmosphere to generate a noble metal chalcogenide thin film. A gas of a chalcogen compound such as hydrogen sulfide (H ₂ S) can be used to form the chalcogen atmosphere. Also, the chalcogen atmosphere can be formed by vaporizing solid chalcogen such as solid sulfur. The chalcogenization of the noble metal thin film is preferably performed by heating the thin film in a chalcogen atmosphere. The heating temperature is preferably 500° C. or more and 1200° C. or less for the chalcogenization of a Pt thin film, 450° C. or more and 1100° C. or less for the chalcogenization of a Pd thin film, 800° C. or more and 1100° C. or less for the chalcogenization of an Ir thin film, and 600° C. or more and 1300° C. or less for the chalcogenization of a Ru thin film. At a temperature below the lower limit of the temperature range, the chalcogenization is insufficient, and at a temperature above the upper limit, the chalcogenide may decompose.

The sensitive portion of the gas sensor element is formed by forming a thin film of a precious metal chalcogenide on the substrate described above. In addition, by appropriately forming electrodes, etc., the gas sensor element according to the present invention can be manufactured.

The semiconductor gas sensor according to the present invention includes the above-mentioned gas sensor element. The gas sensor according to the present invention is capable of detecting various compound gases, such as carbon monoxide (CO), nitrogen dioxide ( _NO2 ), ammonia ( _NH3 ), volatile organic compounds (VOCs), etc. The present invention provides a highly sensitive and highly responsive gas sensor.

As described above, the gas sensor element for semiconductor gas sensors according to the present invention uses a noble metal chalcogenide, which has never been used before, as the sensitive portion. The gas sensor element according to the present invention is superior in sensitivity and responsiveness to various gases to conventional gas sensor elements that use transition metal chalcogenides such as _MoS2 as the sensitive portion.

FIG. 2 is a graph showing the response characteristics to NO ₂ gas of the gas sensor element (RuS ₂ ) manufactured in the first embodiment and the gas sensor elements (MoS ₂ , WS ₂ ) of Comparative Examples 1 and 2. FIG. 11 is a graph showing the response characteristics of the gas sensor element (RuS ₂ ) of the second embodiment to NH ₃ gas and CO gas. FIG. 13 is a graph showing the response characteristics of the gas sensor element (RuS _2-x ) of the third embodiment to NH ₃ gas and CO gas. FIG. 13 is a graph showing response characteristics of the gas sensor element (PtSe ₂ ) of the fourth embodiment to various gases.

First embodiment : Hereinafter, an embodiment of the present invention will be described. In this embodiment, a gas sensor element was manufactured using a _RuS2 thin film as a noble metal chalcogenide thin film as a sensitive part. Then, the response characteristics to _NO2 gas were evaluated.

[Manufacture of gas sensor element]
A _SiO2 glass substrate (dimensions: 20 x 20, thickness 1.5 mm) was prepared as the substrate, and a _RuS2 thin film was formed on this substrate by CVD. A one-zone reactor (reaction tube) was used for the film formation. The substrate was set in a reaction tube set in an electric furnace, and a precious metal source gas and a chalcogen source gas were introduced. Dicarbonyl-bis(5-methyl-2,4-hexanedionato)ruthenium(II) was used as the precious metal source. Ar gas was used as the carrier gas. _H2S was used as the chalcogen source gas.

The _RuS2 thin film was formed by introducing Ru source gas (including carrier gas), _H2S gas, and Ar gas as flow gas into the reaction tube. The flow gas was introduced together with each source gas to prevent the precursor, hydrogen sulfide, and by-products after the reaction from stagnation inside the reaction tube. The detailed film formation conditions are as follows. The thickness of the _RuS2 thin film formed on the substrate in this film formation process was 12 nm.
・Ru raw material heating temperature: 67℃
Ru source gas flow rate: 30 sccm
・Flow gas flow rate: 50sccm
_H2S gas flow rate: 10 sccm
・Substrate heating temperature: 600℃
Film formation time: 10 minutes

After forming a _RuS2 thin film on the substrate, a comb-shaped electrode was formed on the surface of the substrate to prepare a gas sensor element. The comb-shaped electrode was formed by patterning a Ti film (5 nm thick) and an Au film (40 nm thick) in this order on the surface of the substrate on which the _RuS2 thin film was formed.

Comparative Example 1 : As a comparative example for the gas sensor element ( _RuS2 thin film) of the first embodiment described above, a gas sensor element was manufactured in which a _MoS2 thin film, which is a known transition metal chalcogenide, was used as a sensitive portion.

The same substrate and film-forming apparatus as those in the first embodiment were used. Molybdenum pentachloride (MoCl ₅ ) was used as the molybdenum raw material. H ₂ S was used as the chalcogen raw material gas, and a MoS ₂ thin film was formed under the following conditions. In addition, in the formation of the MoS ₂ thin film, the Mo raw material gas and H ₂ S gas were introduced into the reaction tube at the same time.
・Mo raw material heating temperature: 90℃
Mo raw material gas flow rate: 7 sccm
・Flow gas flow rate: 7sccm
_H2S gas flow rate: 7 sccm
・Substrate heating temperature: 800℃
Film formation time: 10 minutes

The thickness of the _MoS2 thin film formed on the substrate in the film formation process was 1.5 nm. After film formation, a comb-shaped electrode was formed on the substrate in the same manner as in the first embodiment to form a gas sensor element.

Comparative Example 2 : In this comparative example, a gas sensor element was manufactured using a _WS2 thin film, a known transition metal chalcogenide, as the sensing part. The same substrate and film-forming device as those in the first embodiment and comparative example 1 were used to form the _WS2 thin film. Tungsten hexachloride ( _WCl6 ) was used as the W raw material. _H2S was used as the chalcogen raw material gas, and the _WS2 thin film was formed under the following conditions. In forming the _WS2 thin film, the W raw material gas and _H2S gas were also introduced into the reaction tube at the same time.
・W raw material heating temperature: 100℃
W source gas flow rate: 30 sccm
・Flow gas flow rate: 30sccm
_H2S gas flow rate: 30 sccm
・Substrate heating temperature: 800℃
Film formation time: 15 minutes

The thickness of the _WS2 thin film formed on the substrate in the film formation step was 1.6 nm. After film formation, comb-shaped electrodes were formed on the substrate in the same manner as in the first embodiment to form a gas sensor element.

[Evaluation of response characteristics of gas sensor element]
The response characteristics of the gas sensor elements of the first embodiment, comparative examples 1 and 2 prepared above were evaluated. In this evaluation test, a multimeter was connected to the gas sensor element sealed in a vacuum atmosphere, and a measurement gas containing a predetermined concentration of detection gas was introduced and sealed in the atmosphere while applying a bias voltage, and the change in the current value was measured. In the evaluation test, the gas sensor element was exposed to nitrogen gas for 20 minutes or more before the measurement, and then the measurement gas was introduced. The detection gas here was _NO2 , and the _NO2 concentration of the measurement gas was 10 ppm. The introduction time of the measurement gas was 1 hour, and after the measurement, the gas sensor element was exposed to nitrogen gas for 1 hour to return the current value to the baseline. In the characteristic evaluation, the time required for the measured current value (bias voltage 0.5 V) to reach 10% to 90% of the maximum value was taken as the response speed.

Regarding the evaluation results of the response characteristics, the measurement results of the gas sensor elements of the first embodiment ( _RuS2 thin film), Comparative Example 1 ( _MoS2 thin film), and Comparative Example 2 ( _WS2 thin film) are shown in Fig. 1. From Fig. 1, it was confirmed that the gas sensor element of this embodiment, which uses the _RuS2 thin film as the sensitive part, has a faster response speed than the gas sensor elements of Comparative Examples 1 and 2, which use the conventional transition metal chalcogenide thin film as the sensitive part.

Second embodiment : In this embodiment, the gas sensor element ( _RuS2 thin film) was evaluated for its response characteristics to the gases to be detected, _NH3 (concentration 10 ppm) and CO (concentration 500 ppm).

2 shows the response characteristics of the gas sensor element ( _RuS2 thin film) of this embodiment to each measurement gas. From this figure, it was confirmed that the gas sensor element of this embodiment can detect _NH3 and CO and has good response characteristics.

Third embodiment : In this embodiment, the conditions for forming the precious metal chalcogenide thin film (RuS ₂ ) in the first embodiment were changed to form a non-stoichiometric Ru chalcogenide thin film (RuS _2-x ), and the characteristics of the film were also investigated.

In the above-mentioned first embodiment of the method for forming a RuS ₂ thin film, the flow rate of the flow gas introduced together with the Ru source gas and the H ₂ S gas was set to 50 sccm to 100 sccm. As described above, the flow gas is introduced to suppress the retention of precursors and the like in the reaction tube, but by adjusting the flow rate of the flow gas, the reaction time of the precursors in the reactor can be adjusted to change the thin film composition. In this embodiment, the conditions other than the flow rate of the flow gas were the same as those in the first embodiment (RuS ₂ ). When the formed RuS _2-x thin film was analyzed by X-ray photoelectron spectroscopy, it was confirmed that it was a metal-rich Ru chalcogenide thin film (RuS _2-x : x = 0.6).

Then, similarly to the first embodiment, an interdigital electrode was formed to form a gas sensor element, and response characteristics of the gas sensor element were evaluated using NH ₃ (concentration: 10 ppm) and CO (concentration: 500 ppm) as measurement gases.

The results are shown in Figure 3. As can be seen from Figure 3, the Ru chalcogenide thin film that serves as the sensitive portion does not necessarily have to be of stoichiometric composition (RuS ₂ ) to function as a gas sensor element. Compared to the first embodiment, the response speed of the Ru chalcogenide thin film (RuS _2-x : x = 0.6) is longer for NH ₃ but shorter for CO. A preferred embodiment is to use a noble metal chalcogenide thin film of bistoichiometric composition, but even a metal-rich thin film like that of this embodiment can be used as a gas sensor element.

Fourth embodiment : In this embodiment, a gas sensor element was manufactured using a thin film of _PtSe2 as a precious metal chalcogenide as a sensitive part. Then, the response characteristics to various detection gases were evaluated.

[Manufacture of gas sensor element]
The same substrate as in the first embodiment was prepared, and a PtSe ₂ thin film was formed by the CVD method. In this embodiment, a two-zone CVD apparatus (hot wall type horizontal CVD apparatus) was used as the film formation apparatus. The substrate was set in the CVD apparatus, and 5 g of selenium powder was placed upstream of the substrate. In this CVD apparatus, the substrate temperature and the selenium powder temperature can be controlled separately. Before film formation, the inside of the reactor was purged with argon gas (200 sccm).

A platinum complex (dimethyl(N,N-dimethyl-3-butan-1-amine-N) platinum (DDAP)) was used as the Pt raw material, and this platinum complex was heated and vaporized and introduced into a reactor together with a carrier gas. The platinum complex vaporized on the substrate was decomposed, and platinum and selenium were reacted to precipitate PtSe ₂ to form a thin film. The film formation conditions were as follows. The thickness of the PtSe ₂ thin film formed on the substrate in this film formation process was 4 nm.
・Raw material heating temperature: 67℃
Carrier gas: Argon/10 sccm
Flow gas: Argon/200 sccm
Substrate temperature/selenium powder heating temperature: 400°C/220°C
Film formation time: 15 minutes

After forming a PtSe ₂ thin film on the substrate, a comb-shaped electrode was formed in the same manner as in the first embodiment to obtain a gas sensor element. For the gas sensor element of this embodiment, response characteristics were evaluated using NO ₂ (concentration 10 ppm), NH ₃ (concentration 10 ppm), and CO (concentration 10 ppm) as the measurement gas. The evaluation test method was the same as in the first embodiment, except that the measurement gas was introduced for 30 minutes and the bias voltage was -2 V.

FIG. 4 shows the response characteristics of the gas sensor element ( _PtSe2 thin film) of the second embodiment for each measurement gas. From this figure, it was confirmed that the gas sensor element of this embodiment can also detect _NO2 , _NH3 , and CO, and has good response characteristics. In addition, based on the evaluation results of _NO2 , in comparison with the gas sensor elements of Comparative Example 1 (MoS2 _thin film) and Comparative Example 2 ( _WS2 thin film), it can be seen that the gas sensor element of the second embodiment also has a superior response speed to these conventional gas sensor elements that use transition metal chalcogenides as the sensitive part.

The gas sensor element of the semiconductor gas sensor according to the present invention has a sensitive portion made of a thin film of a chalcogenide compound of a precious metal such as Pt, Pd, Ru, Ir, etc. The gas sensor element according to the present invention has excellent sensitivity and responsiveness to various detection gases. The semiconductor gas sensor according to the present invention is useful in many fields such as gas alarms and air purifier control units for home use and diagnostic equipment in the medical field.

Claims (3)

A gas sensor element including a substrate and a gas sensing portion formed on the substrate,
the sensitive portion is made of a thin film of a chalcogenide compound of a precious metal;
the noble metal chalcogenide compound is a Ru chalcogenide compound,
A gas sensor element characterized in that the chalcogen element of the chalcogenide compound of the noble metal is either S or Se . 2. The gas sensor element according to claim 1 , wherein the substrate is made of any one of glass, quartz, silicon, carbon, ceramics and metal. A gas sensor comprising the gas sensor element according to claim 1 or 2 .

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