JP4530034B2 - Gas sensor, gas detection module therefor, and gas measurement system using them - Google Patents

Description

  The present invention relates to a gas sensor, a gas detection module therefor, and a gas measurement system using the same, and more specifically, using a highly sensitive gas detection element that can be used in the semiconductor field, The present invention relates to an ultra-compact gas sensor that can be attached to a gas pipe, a gas detection module therefor, and a gas measurement system using the gas sensor or gas detection module.

  Fullerenes are a series of spherical carbon molecules consisting only of carbon atoms, and were discovered in 1985 by Kroto et al. (Kroto, HW; Heath, JR; O) in a cluster beam mass spectrometry spectrum by laser ablation of carbon. 'Brien, SC; Curl, RF; Smalley, RE Nature 1985, 318, 162.). Later, the existence of fullerene as the third crystalline carbon after diamond and graphite was clarified, and it was not until 1990 that the synthesis method for macro quantities (such as the arc discharge method for carbon electrodes) was established. (Kratschmer, W .; Fostiropoulos, K .; Huffman, DR Chem. Phys. Lett. 1990, 170, 167. and Kratschmer, W .; Lamb, LD; Fostiropoulos, K .; Huffman, DR Nature 1990, 347, 354.).

  Fullerenes have been pointed out to have optical, electrical, chemical, and mechanical properties from the beginning, and are highly sensitive sensitizers, n-type semiconductors, active oxygen scavengers. Applications such as micro bearings have been studied. However, since the discovery of carbon nanotubes (CNT) as a similar carbon nanomaterial in the mid-1990s, the attention of researchers has rather turned to this CNT. For this reason, it is difficult to say that the basic physical properties of fullerene are still accurately grasped even though 20 years have passed since the discovery, and further clarification is required.

  In addition, there are many types of fullerene-based materials (hereinafter also referred to as “fullerene-based materials”, details of which will be described later). Specifically, endohedral fullerenes and heterofullerenes (which constitute a fullerene skeleton). Examples include those in which some carbons are substituted with other atoms (for example, nitrogen)), norfullerenes (those in which a part of carbons constituting the fullerene skeleton is missing), chemically modified fullerenes, and fullerene polymers. Many of these materials have not even been established as a synthesis method, and many have unknown physical properties.

  One specific application example of such fullerene materials (hereinafter, used as a general term for fullerene and fullerene base material) is a gas detection element for a gas sensor (for example, Patent Document 1).

Patent Document 1 discloses a gas sensor using fullerenes having an oxygen content of 10 ¹⁴ pieces / cm ³ or less and a water content of 10 ¹⁶ pieces / cm ³ or less. The gas sensor according to Patent Document 1 has an initial conductance of about 0.1 (Ωcm) ⁻¹ , but becomes 2 × 10 ⁻⁹ (Ωcm) ⁻¹ by introducing oxygen at atmospheric pressure, Thereafter, it is shown that the oxygen is removed by heating in a nitrogen atmosphere to recover to about 0.1 (Ωcm) ⁻¹ before introducing oxygen.
It is described that the conductance almost returns to the original value, and the conductivity of fullerenes reversibly changes.
International Publication WO2007 / 029684 Pamphlet

  Since a gas sensor using such a material can be measured with high sensitivity, it can also be used for the purpose of detecting mixed gas in a semiconductor production line. However, on the other hand, it is not easy to make a sensor that is easily affected by the manufacturing process and measurement environment, and that can stably measure with high reproducibility.

  Therefore, an object of the present invention is to provide an ultra-compact gas sensor that can be installed in individual gas piping in a semiconductor manufacturing facility, and further to provide a gas measurement system using the gas sensor.

  The present inventor has studied in detail the characteristics of fullerene materials that are expected to be one of the constituent materials of gas sensing elements that can solve the above-mentioned problems, and has studied a sensor system that can make full use of these characteristics. It was. As a result, the following new findings were obtained.

  (A) It is well known that a member containing a fullerene material (for example, a vapor-deposited film of fullerene material) increases in resistivity (lowers conductivity) by gas adsorption, but if the amount of gas adsorption is sufficiently reduced The member containing the fullerene material exhibits the conductivity of the semiconductor region having good conductivity.

  (B) On the other hand, a member containing a fullerene material exhibits a dielectric property that undergoes dielectric polarization in a DC electric field. That is, the fullerene material can be defined as a semiconductor having dielectric properties.

(C) A gas sensor using a gas sensing element having a dielectric semiconductor whose conductivity varies due to the adsorption of gas, such as charging up due to dielectric properties when a DC voltage is applied. appear. Therefore, in order to use a dielectric semiconductor as a highly sensitive sensor, it is preferable to apply an AC voltage. By applying an AC voltage and measuring its electrical response, for example, conductance, a gas sensor having excellent stability can be realized.

  (D) Furthermore, if the capacitance part is electrically connected in series to the dielectric semiconductor and the real part of the complex capacitance is measured as an electrical response, the influence of noise during measurement can be reduced. Therefore, an ultra-sensitive gas sensor is realized.

  (E) Moreover, since the detection capability of the gas sensor can be adjusted by adjusting the added capacitance portion, it is possible to reduce the load of quality control in the manufacturing process of the gas detection element, and high sensitivity. It is possible to obtain a simple gas sensor with high productivity.

The present invention provided based on the above new findings is as follows.
(1) A gas detection element having a dielectric semiconductor, the conductivity of which varies according to the state of gas adsorption, a capacitance unit connected in series to the gas detection element, a gas detection element, and an electrostatic A pair of electrodes respectively connected to the ends of the electric element including the capacitance unit, and a capacitance of the capacitance unit larger than the capacitance of the gas detection element, the polarity being applied to the pair of electrodes A gas sensor that detects an adsorption state of a gas to a gas detection element from an electrical response of the gas sensor that changes according to a voltage that periodically changes including inversion.

  Here, the “dielectric semiconductor” is a semiconductor having a dielectric property, and when a voltage from the outside is applied, a predetermined capacitance is measured by dielectric polarization inside the material according to the generated electric field. In addition, it refers to a material whose predetermined conductance is measured by the movement of charge carriers according to an external voltage. Therefore, the equivalent circuit has a configuration in which a capacitor and a resistor are connected in parallel.

  “The conductivity changes according to the gas adsorption state” means that the conductivity of the gas detection element varies due to a qualitative and / or quantitative change in the gas adsorbed to the gas detection element. That means. The qualitative change includes not only the type of gas but also the degree of chemical interaction with the substance that constitutes the gas sensing element, such as a change from physical adsorption to chemical adsorption, It also includes a change in the adsorption location in the gas detection element, for example, a transition from surface adsorption to adsorption diffused inside.

  There may be one or more gases that cause a change in conductivity in the gas detection element, and there may be a gas that does not cause a change in conductivity even if it is adsorbed (hereinafter also referred to as “inert gas”). Further, the change in conductivity is preferably caused as a characteristic due to the dielectric semiconductor.

  “A periodically changing voltage including polarity reversal” is a voltage in which a predetermined waveform is repeatedly applied to at least one electrode of a pair of electrodes in a predetermined cycle, and the voltage waveform is the other electrode. It is a voltage having a case where a positive voltage and a case where a negative voltage is formed with respect to the potential. A typical example of such a voltage change is an AC voltage generated by a sine wave, but is not limited thereto, and the waveform may be a rectangular wave or a triangular wave. Further, the center voltage of the voltage waveform may be 0 V, or a positive or negative bias may be applied.

  “Electrical response” refers to all responses measurable by an electrical measuring means among responses by a gas sensor to application of a periodically changing voltage including polarity reversal. Therefore, the electrical parameter to be measured is not particularly limited, and a change in current may be measured as a response, or an admittance as an impedance or its inverse may be measured. Further, the complex capacitance of the gas sensor may be measured, or the complex conductance may be measured. Among them, it is preferable to measure the conductance with the applied voltage as an alternating current.

  Here, the “capacitance portion” is a separate electric element having a dielectric part, which is different from a capacitor having a gas sensing element including a dielectric semiconductor, and has an electric end portion thereof. A member whose predetermined capacitance is measured when a voltage is applied to. The form is arbitrary, and may be a form of a general capacitor as an electronic component, or a film-like body, a block-like body, or a linear shape having a structure in which a layer made of a dielectric material is sandwiched between two layers of a conductive material. It may be the body. In addition, a dipole such as an electric double layer or an electric barrier may constitute the capacitance portion. If the gas sensing element has a structure in which at least a part of the capacitance part is in direct contact with the gas sensing element, the gas sensor can be reduced in size, which is advantageous.

  The “electric element including the gas detection element and the capacitance part” may be connected to any other electric element as long as the gas detection element and the capacitance part are connected in series. For example, a resistance component may be further connected in series.

  Any electrical parameter may be used to measure the “electrical response” for the above gas sensor, but the real part in the complex capacitance (hereinafter “capacitance real part” or “capacitance”) with the applied voltage as the AC voltage. Or a conductance is preferably measured.

  “Gas sensing element capacitance” means that when the gas sensing element is made only of a dielectric semiconductor, the capacitance of the dielectric semiconductor directly becomes the capacitance of the gas sensing element, but the gas sensing element is a substance other than the dielectric semiconductor. When a dielectric such as ceramics is included, the capacitance of the dielectric semiconductor and the capacitance of the material are combined according to the component ratio.

  In this way, by making the capacitance of the capacitance part larger than the capacitance of the gas sensing element, when measuring the frequency dependence of the applied voltage for the real part of the complex capacitance, the conductivity of the gas sensing element is increased. Measurement with sensitivity is realized. If the capacitance of the capacitance part is 10 times or more of the capacitance of the gas sensing element, stable measurement is realized, and if it is 100 times or more, the quantitativeness of the measurement is also improved.

(2) The gas sensor according to the above (1) , wherein the capacitance section is configured by a plurality of members.
Here, the “member” means not only an independent component such as a commercially available capacitor but also an area having a different dielectric property because it is integrated with the gas detection element but has a different structure.

(3) A metal layer formed directly on the surface that forms the electrical end of the gas detection element, and a metal layer in which the metal of the metal layer is modified at the interface on the gas detection element side of the metal layer The gas sensor according to (1) or (2) , wherein the gas sensor has a modified layer, and the dielectric modified layer forms at least a part of the capacitance portion.

  The dielectric modification layer may be a metal surface oxidized, or a nitrided or carbonized one. In addition, those obtained by complex processing such as carbonitriding may be used. In addition to the dielectric modification layer, a dipole and / or an electrical barrier formed in the vicinity of the interface between the dielectric modification layer and the gas detection element may constitute the capacitance portion.

(4) modified dielectric layer, the above (3) by oxygen that has passed through the gas detection device the metal of the metal layer is an oxide film formed by oxidizing gas sensor according.
Here, the oxide film may be a natural oxide film that is normally oxidized spontaneously in the atmosphere, or may be an oxide film that is positively oxidized on the surface of the metal layer by heating in an atmosphere containing oxygen, for example.

(5) A dielectric layer directly formed on a surface forming at least one of the electrical ends of the gas detection element is provided, and the dielectric layer forms at least a part of the capacitance portion and is connected to the gas detection element. The gas sensor according to any one of (1) to (4) , wherein charge injection is prevented.

Examples of the material constituting the dielectric layer include oxides and the like, and preferably have a high dielectric constant. Examples of such a material include HfO ₂ -based materials. Further, it is preferable to have a thickness of 1 nm or more in order to prevent charge injection due to a tunneling phenomenon.

(6) The gas sensor according to any one of (1) to (5) , wherein the dielectric semiconductor is a fullerene material having a characteristic that conductivity is reduced by gas adsorption.

  The “fullerene material” is a general term for “fullerene” which is a hollow carbon cluster material, a material which can be synthesized using fullerene as a starting material, and a “fullerene base material” which is a material having the same basic structure as fullerene.

  As a gas detection element made of a fullerene material, a single crystal obtained by sublimating a fullerene material, a vapor-deposited film obtained by sublimating a fullerene material, an epitaxial film obtained by depositing a molecular beam of a fullerene material, a liquid containing a fullerene material Examples thereof include a film obtained by heating a body coating film to 200 ° C. or higher in a vacuum to remove the dispersion medium.

(7) The gas sensor according to any one of (1) to (5) , wherein the dielectric semiconductor is an organic semiconductor.

“Organic semiconductor” is an organic material exhibiting the characteristics of a semiconductor, among which one or a group selected from the group consisting of phthalocyanine, pentacene, anthracene, Alq ₃ , thiophene, aniline, polyaniline, polythiophene, and polyparaphenylene vinylene It is preferable that 2 or more types are included.

(8) The gas sensor according to any one of (1) to (5) , wherein the dielectric semiconductor is a carbon nanomaterial.

  The “carbon nanomaterial” is a material mainly composed of carbon and having a basic skeleton having a nano size, and a fullerene material is one of the carbon nanomaterials. Among carbon nanomaterials, it is preferable to include one or two or more selected from the group consisting of fullerene, endohedral fullerene and heterofullerene, carbon nanotube, peapod, carbon nanoonion, derivatives thereof, and polymers thereof.

(9) A gas detection element having a dielectric semiconductor, the conductivity of which changes according to the adsorption state of the gas, and a pair of electrodes connected to the gas detection element, the above (1) or (2) A gas detection module for use in the gas sensor according to claim 1, wherein a capacitance part is electrically connected in series to the gas detection module, and the gas sensor includes the gas detection module and the capacitance part. A gas sensor is characterized in that a periodically changing voltage including polarity reversal is applied to the target end, and the gas adsorption state can be detected from the electrical response of the gas sensor to the voltage application. Gas detection module.

(10) The gas sensor described in any one of (1) to (8) above, a power supply capable of applying a periodically changing voltage including polarity reversal at the electrical end of the gas sensor, and the power supply A gas measurement system comprising: a measurement unit that measures an electrical response of the gas sensor to a voltage applied by the gas sensor.

It is preferable that the power supply can change the frequency of the periodically changing voltage, and it is further preferable if the power supply can generate a voltage signal in which voltage changes at a plurality of frequencies are superimposed.
The measuring means may be integrated with the power source, and may have means for calculating a change in conductivity of the gas detection element from the measured electrical response, and further means for calculating the gas adsorption amount.

(11) An electric end of a gas sensor including the gas detection module described in (9) above, a capacitance unit connected in series to the gas detection module, and the gas detection module and the capacitance unit A gas measuring system comprising: a power source capable of applying a periodically changing voltage including polarity reversal; and a measuring means for measuring an electrical response of the gas sensor to a voltage applied by the power source.

  It is preferable that the power supply can change the frequency of the periodically changing voltage, and it is further preferable if the power supply can generate a voltage signal in which voltage changes at a plurality of frequencies are superimposed. Moreover, the electrostatic capacitance part may be integrated.

  The measuring means may be integrated with the power source and / or the capacitance unit, and means for calculating the change in the conductivity of the gas detection element from the measured electrical response, and further means for calculating the change in the gas adsorption amount You may have.

(12) The gas measurement system according to (10) or (11) , further including gas desorption means for desorbing the gas adsorbed on the gas sensor.

  Specific means for desorbing gas include heating with a heater, irradiation with an infrared lamp, laser irradiation, irradiation with high energy particles, etc., in order to reduce the partial pressure of the adsorbed gas around the gas detection element. For example, a vacuum exhaust device, a high purity inert gas supply device, and the like. Further, the gas sensor and the gas desorption means may be configured integrally.

(13) It further has a temperature measuring means for measuring the temperature of the gas sensor, and this temperature measuring means has the same configuration as the gas sensor and is sealed so that the gas detection element does not adsorb gas. The gas measurement system according to any one of (10) to (12) , which is a thing.

  Here, even if the temperature measuring means does not have the same configuration as the gas sensor, the change in conductivity with respect to the temperature change is substantially the same, and the change in conductivity in the gas sensor and the temperature measuring means It is possible to calculate only the change in conductivity due to gas adsorption by removing the influence of the change in conductivity due to the temperature change in the gas sensor by performing an appropriate calculation with the change in conductivity as an input. In other words, it can be said that they have substantially the same “same” configuration.

  The gas sensor comprising the gas detection element according to the present invention and a pair of electrodes applies a voltage that periodically changes and includes polarity reversal to the dielectric gas detection element. Phenomena that destabilize measurement such as charge-up that has occurred are unlikely to occur. For this reason, the measurement with the sensitivity which a gas detection element can achieve in principle can be performed stably.

  In addition, the gas sensor according to the present invention having a configuration in which the gas detection element and the capacitance unit are connected in series greatly increases the electrical response obtained when a periodically changing voltage including polarity inversion is applied. Is possible. Therefore, it is possible to detect the conductivity of the gas detection element with higher sensitivity. In particular, gas is detected with higher sensitivity by measuring the real part of the capacitance and conductance of the gas sensor as an electrical parameter for detecting the electrical response, and analyzing the profile data that measures the frequency dependence of the applied voltage. Is realized. Moreover, when at least a part of the capacitance part is integrated with the gas detection element, the load of quality control in the manufacture of the gas sensor is alleviated and a high quality gas sensor can be stably obtained. Is also realized.

  Hereinafter, representative embodiments according to the present invention will be described. However, the present invention is not limited to the following embodiments, and any modifications are included in the technical scope as long as they are not contrary to the spirit of the present invention. .

1. Fullerene Material As described above, “fullerene material” is a general term for “fullerene” and “fullerene base material”.

“Fullerene” is a hollow carbon cluster material represented by Cn (n = 60, 70, 76, 78...) And has a structure containing 12 5-membered rings and at least 20 6-membered rings. Have. Specifically, mention may be made of C ₆₀ and C _70.

The “fullerene base material” is a material that can be synthesized using the above-mentioned fullerene as a starting material, and a material having the same basic structure as fullerene, and includes the following substances.
The “encapsulated fullerene” is a carbon cluster material in which atoms or molecules other than carbon are confined in the hollow portion of the bowl-shaped fullerene. An atom or molecule confined in a fullerene molecule (cage) is called an inclusion target atom (molecule), and a trapped atom (molecule) is called an inclusion atom (molecule). The inclusion target atoms include all atoms defined by the periodic rule in principle, such as alkali atoms such as Li, Na, and K, lanthanoid atoms such as La, Ce, and further B, N, F, and Cl. Typical element atoms such as are exemplified. One molecule to be included is not particularly limited and may be any molecule, and H ₂ , N ₂ , A _3−x B _x N (x is an integer of 1 to 3, A and B are metal atoms, typical examples Is exemplified by Sc ₃ N), metal oxides, and the like.

“Heterofullerene” is one in which a part of carbon constituting the fullerene skeleton is substituted with another atom (for example, nitrogen). The number of substituted carbons is not particularly limited as long as it is 1 or more.
“Norfullerene” is one in which one or more carbons constituting the fullerene skeleton are missing, and the unbonded portion of the carbon on the fullerene skeleton caused by the lack of carbon is terminated by, for example, hydrogen. The number of missing carbons is not particularly limited, but is necessarily limited in order to maintain the fullerene skeleton, and usually about 5 is the upper limit.

  The “secofullerene” is one in which one or more carbon-carbon bonds constituting the fullerene skeleton are cleaved and each bond is bonded to, for example, hydrogen. The number of bond cleavages is not particularly limited, but is necessarily limited in order to maintain the fullerene skeleton, and usually about 10 is the upper limit.

  “Chemically modified fullerene” is a compound in which atoms or molecular residues are bonded to carbon constituting the fullerene skeleton. Typical examples of those in which atoms are bonded are hydrogenated fullerene, oxidized fullerene, and halogenated fullerene, and typical examples in which molecular residues are bonded include hydroxylated fullerene and PCBM (phenyl C61-butyric acid methyl ester).

The “fullerene polymer” is a polymer in which the same type of fullerene and the above-mentioned fullerene base material or chemically different types are combined.
“Mixed fullerene” is a mixture of a plurality of fullerenes and the above-mentioned fullerene base materials.

2. Dielectric Semiconductors (1) Dielectric Semiconductors “Dielectrics” are substances that generate dielectric polarization when a positive electric field is applied, but do not generate direct current (Source: “Ferroelectric Devices” by Kenji Uchino / Uchino) Kenji Translated / Ishii Takaaki Translated, Morikita Publishing Co., Ltd., published on August 25, 2005). Therefore, “dielectric” means a property that causes dielectric polarization when a positive electric field is applied, but does not produce a direct current.

  In addition, the term “semiconductor” refers to the generation of carriers that transfer charges to the conduction band or valence band due to the partial transition of electrons in the valence band to the conduction band beyond the forbidden band. A material that expresses.

  Therefore, a dielectric semiconductor (hereinafter referred to as a “dielectric semiconductor”) is dielectrically polarized inside a material in response to an electric field generated when an external voltage is applied, and charge carriers are externally applied. A material that moves in response to voltage.

  Here, the dielectric polarization is classified into electronic polarization, ion polarization, orientation polarization, and space charge polarization, and any of them may be used. The charge carriers may be electrons or holes, and atoms or molecules may be doped for the purpose of changing the generation of carriers or conductivity.

  Since the dielectric semiconductor has the characteristics as described above, the equivalent circuit has a configuration in which a capacitance component and a resistance component are arranged in parallel.

(2) Organic semiconductor Examples of such a dielectric semiconductor include organic semiconductors and carbon nanomaterials.

Organic semiconductors, which are organic materials that exhibit semiconductor characteristics, include perylenetetracarboxylic anhydride and derivatives thereof, perylenetetracarboxydiimide derivatives, naphthalenetetracarboxylic anhydride and derivatives thereof, naphthalenetetracarboxydiimide derivatives, and metal phthalocyanine derivatives. For example, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation) : BeBq _2), bis (2-methyl-8-quinolinolato) -4-phenylphenolato - aluminum (abbreviation: BAlq) and metal complex having a quinoline skeleton or a benzoquinoline skeleton may be exemplified. In addition, bis [2- (2-hydroxyphenyl) benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) benzothiazolate] zinc (abbreviation: Zn (BTZ) And metal complexes having an oxazole-based or thiazole-based ligand such as ₂ ). In addition to metal complexes, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis [5- (P-tert-butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4-phenyl-5- ( 4-biphenylyl) -1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2, Examples include 4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), and the like. In addition, a derivative having a molecular skeleton combining the above substances as a main chain may be used.

Among these organic semiconductors, the organic semiconductor is preferably composed of one or more selected from the group consisting of phthalocyanine, pentacene, anthracene, Alq ₃ , thiophene, aniline, polyaniline, polythiophene, and polyparaphenylene vinylene.

(3) Carbon nanomaterials Carbon nanomaterials mainly composed of carbon and having a basic skeleton of nano-size include carbon nanotubes, peapods, carbon nano-onions and their derivatives, and derivatives thereof in addition to the above fullerene materials. Examples are polymers.

3. Gas sensing element (1) Configuration The gas sensing element according to the present invention has the above-described dielectric semiconductor, and the electrical conductivity varies depending on the state of the adsorbed gas as a characteristic attributed to the dielectric semiconductor. is there. Typically, the electrical conductivity of a dielectric semiconductor changes due to gas adsorption. The change in the state of the adsorbed gas includes not only a quantitative change in the adsorbed gas but also a qualitative change. This qualitative change includes not only the type of gas but also the degree of chemical interaction with the substance that constitutes the gas sensing element, such as a change from physical adsorption to chemical adsorption, For example, the adsorption location in the detection element changes, for example, the transition from surface adsorption to adsorption diffused inside.

This characteristic will be explained using a C ₆₀ fullerene single crystal as an example. A single crystal of C ₆₀ fullerene (molecular density is 1.44 × 10 ²¹ / cm ³ ) is exposed to an atmosphere of room temperature 50% RH. According to the present inventors, the molecular density of water adsorbed on the single crystal is about 2 × 10 ²⁰ molecules / cm ³ in a saturated state, and one molecule of water can adsorb 7.6 molecules of fullerene. Investigation revealed. Further, the number of oxygen molecules adsorbed in the same environment is about 2 × 10 ¹⁸ molecules / cm ³ , which means that one molecule of oxygen is adsorbed to about 860 fullerenes. Therefore, the saturation, the adsorbed molecules was confirmed to have adsorbed to fullerenes therein not only the surface of the single crystal of C ₆₀ fullerene.

Thus a single crystal of C ₆₀ fullerene can be adsorbed very many molecules, has substantially the same adsorption characteristics of a deposited film of C ₆₀ fullerene. Therefore, as shown in Patent Document 1, a gas detection element made of a vapor deposition film of C ₆₀ fullerene can realize a change in conductivity of 10 ⁸ (Ωcm) ⁻¹ by gas adsorption.

Other fullerene materials behave similarly to C ₆₀ fullerenes, but the degree of change in conductivity depends on the type of fullerene material and the structure of fullerene material as a gas sensing element (for example, the bonding state with other fullerene materials). Varies depending on the type of gas to be adsorbed. For example, a case where oxygen is detected using a gas detection element made of C ₆₀ fullerene containing alkali metal-encapsulated fullerene (Li @ C ₆₀ ) will be described. The conductivity is higher than that of a gas detection element made only of C ₆₀ fullerene. because of the high, if the gas detection device the same measurement conditions and comprising only C ₆₀ fullerene, becomes the more current is obtained, more measurement sensitive is realized. This also, when measured at the same current, since the gas detection element also means that it is possible to miniaturize, to realize a compact sensor than for gas detection comprising only C ₆₀ fullerene be able to.

In addition, the carbon nanomaterial other than the fullerene material also changes (usually decreases) in electrical conductivity due to gas adsorption in the same manner as the fullerene material.
On the other hand, in a gas detection element including an organic semiconductor as a dielectric semiconductor, a layer having high conductivity is formed on the surface of the organic semiconductor due to adsorption of an electron donating gas, and the conductivity may increase.

  The gas detection element according to the present invention has such a dielectric semiconductor, and may contain any other material as long as its characteristics cause variation in conductivity due to gas adsorption. An insulating substance such as ceramics, for example, a conductive substance such as metal, or a substance having an intermediate conductivity may be included.

(2) Structure The structure of the gas detection element is a pair of electrical ends to which an AC voltage is applied by a periodic change in voltage including polarity reversal, typically a sine wave having a center voltage of 0 V, via electrodes or the like. And a dielectric semiconductor disposed between the electrical ends, and any structure as long as the gas to be measured can be adsorbed to the dielectric semiconductor disposed between the electrical ends. It doesn't matter. It may be a thin film, a block or a line.

(3) Manufacturing method A manufacturing method will not be restrict | limited especially if a gas detection element can exhibit the function as a dielectric semiconductor.

  If a gas detection element made of a fullerene material is described as an example, one of the preferable manufacturing methods is to sublimate the fullerene material by heating, and the gas detection element using a single crystal or a vapor deposition film obtained by sublimation is Has excellent properties. The heating method and heating temperature for sublimation may be appropriately set according to the target fullerene material, and specific heating methods include current heating, heating with an electron beam, heating by laser irradiation, and the like.

  Here, when a substance having a sublimation temperature equivalent to the sublimation temperature of the fullerene material, for example, copper phthalocyanine, is mixed in the crucible containing the fullerene material, a deposited film in which such materials are mixed at a predetermined ratio is obtained. Also in this case, since the sublimation process is adopted, it is possible to reduce the impurity concentration.

  In addition, an MBE film obtained by epitaxially growing a fullerene material as a molecular beam can provide a gas detection element having a crystal structure similar to that of a single crystal. Therefore, the gas detection element using this MBE film also has excellent characteristics.

  Alternatively, the gas detection element may be obtained as a sputtered film by sputtering using an inert gas such as argon instead of heating the fullerene material. In this case, the possibility that a component derived from a decomposition product or a sputtering gas is mixed is higher than that of the vapor deposition film, so that the purity is slightly lowered, but the productivity of the gas detection element is improved.

  In addition, a gas sensing element may be obtained by introducing a sublimated fullerene material into plasma and depositing a polymer of fullerene material in a film shape. In this case, however, some impurities are inevitably mixed.

  Instead of the dry process as described above, the fullerene material may be dissolved or dispersed in an appropriate medium to form a solution or dispersion, which is thinned using a technique such as spin coating, and then the medium is volatilized. In this case, it is possible to manufacture the gas detection element without using expensive vacuum equipment.

  In addition, the gas detection element may be manufactured as a pellet obtained by compressing and compressing a powdered fullerene material. At this time, if deaeration is simultaneously performed using a vacuum pump, it is possible to easily obtain a dense gas detection element.

  Note that the fullerene material contained in the gas detection element or a part thereof may be polymerized by irradiating the gas detection element obtained by the above-described method with light or an electron beam. Polymerization can improve the heat resistance of the gas detection element.

4). First Embodiment Hereinafter, a gas measurement system according to a first embodiment of the present invention will be described.

(1) Configuration FIG. 1 is a conceptual diagram showing a gas measurement system according to a first embodiment of the present invention.
As shown in FIG. 1, the gas measurement system 0100 according to the first embodiment measures a gas sensor 0101, a power supply 0102 capable of generating an alternating voltage of a plurality of frequencies, and an electrical response from the gas sensor. Measuring means 0103 and gas desorption means 0104 for desorbing the gas adsorbed by the gas sensor are provided.

  Hereinafter, the gas sensor will be described first, and then the principle of gas detection will be described, followed by the description of components other than the gas sensor.

(2) Structure of gas sensor (A) Outline A gas sensor according to the present invention includes a gas detection element, a capacitance part, and a pair of electrodes as minimum components, and includes the gas detection element and the capacitance part. A structure is provided in which a pair of electrodes are electrically connected to the electrical end of the electrical element.

  2A and 2B are conceptual views showing the structure of the gas sensor according to the first embodiment of the present invention, in which FIG. 2A is a top view, FIG. 2B is a cross-sectional view taken along the line AA in FIG. FIG. 4 is a cross-sectional view taken along the BB cross section in FIG.

The gas sensor 0200 according to the first embodiment includes the following components:
Ceramic heater 0201 which is a gas desorption means,
A first gold layer 0202 and a second gold layer 0206 formed on the ceramic heater 0201 at predetermined intervals,
Covering a portion of the first gold layer 0202 near the second gold layer 0206, it was formed on the ceramic heater 0201 and between the gold layers 0202 and 0206 at a portion near the first gold layer 0202. First aluminum layer 0203,
A portion on the first aluminum layer 0203 near the second gold layer 0206, and a first aluminum layer on the ceramic heater 0201 between the first aluminum layer 0203 and the second gold layer 0206 The gas sensing element 0204 formed near the portion 0203, the portion near the second gold layer 0206 on the opened upper surface of the gas sensing element 0204, and the first gold layer 0202 near the second gold layer 0206 And a second aluminum layer 0205 having a connecting portion formed so as to connect them.

Aluminum layers 0203 and 0205 have metal portions 0203a and 0205a, and oxide film portions 0203b and 0205b formed on the surface facing gas detection element 0204, respectively. Since the gas detection device 0204 according to this embodiment as described below is composed of C ₆₀ fullerenes, it is possible to the interior of the gas detection device oxygen passes, the oxygen oxidizes the metal surface of the aluminum layer As a result, this oxide film is formed.

Further, although details are not necessarily clear, a dielectric layer containing C ₆₀ fullerene is formed in the vicinity of the interface between the oxide film portions 0203 b and 0205 b and the gas sensing element 0204, which includes a dipole and / or an electrical barrier. is assumed. The dielectric layer and the oxide film portions 0203b and 0205b of the aluminum layer are integrated to form a capacitance portion of the gas sensor according to the present embodiment, and this is connected in series with the gas detection element 0204. It has become.

  Note that a natural oxide film is also formed on the upper surface portion of the second aluminum layer 0205, but this is not shown for convenience of explanation. In FIG. 2, the display enlargement ratio differs greatly (about 1000 times) between the stacking direction of each member and the in-plane direction perpendicular thereto, and the structure on the substrate 0201 is actually a thin film. Is. For this reason, in the connection part of the gas detection element 0204 and the second gold layer 0206 in the second aluminum layer 0205, the area of the part in contact with the gas detection element 0204 is the gas detection element of the second aluminum layer 0205. It is much smaller than the area of the part formed on 0204. Therefore, the electrical end of the gas sensing element 0204 is substantially the part that contacts the second aluminum layer 0205 formed on the gas sensing element 0204.

  The electric end of the electric element including the gas detection element 0204 and the electrostatic capacitance portion includes a surface of the oxide film portion 0203b of the first aluminum layer 0203 facing the metal portion 203a and an oxide film of the second aluminum layer 0205. This is a surface facing the metal portion 205a in the portion 0205b. Therefore, the electrodes of the gas sensor according to the present embodiment are the metal portion 203a of the first aluminum layer 0203 and the metal portion 205a of the second aluminum layer 0205. Note that the gold layers 0202 and 0206 are members (pad electrodes) for facilitating connection with the wiring member, and are not essential.

(B) Gas Detection Element The gas detection element 0204 according to the present embodiment is formed of a vapor deposition film of C ₆₀ fullerene that is one of dielectric semiconductors. As described above, since a gas such as oxygen can easily enter the C ₆₀ fullerene vapor deposition film, the adsorption region is not only the surface of the gas detection element 0204 but also the entire element.

For this reason, the electrical conductivity of the gas detection element 0204 according to the present embodiment can vary from 10 ⁻² (Ωcm) ⁻¹ or more to 10 ⁻¹⁰ (Ωcm) ⁻¹ or less in the range of 10 ⁸ (Ωcm) ⁻¹ or more. . On the other hand, since the relative dielectric constant of C ₆₀ fullerene is about 4 to 5, the capacitance is about 40 pF when the shape of the gas detection element 0204 is 1 mm ² in thickness and 1 μm in thickness. Since the gas sensing element that is assumed to be actually used has an area of 0.1 to 100 mm ² and a thickness of about 0.1 to ¹⁰ μm, in this case, the capacitance of the gas sensing element is about 1 pF to about 1 nF. It becomes the range.

(C) Capacitance part Since the gas detection element 0204 according to the present embodiment is made of a vapor deposition film of C ₆₀ fullerene, oxygen molecules can freely move inside the gas detection element 0204. Therefore, the surface facing the vapor deposition film in the aluminum layer 203 and 205 which are formed in direct contact with the deposited film of C ₆₀ fullerene, is oxidized by oxygen coming through the deposited film, the natural oxide film of aluminum (Al ₂ O ₃ ) is formed. In the gas sensor according to the present embodiment, this oxide film is one of the constituent members of the capacitance unit.

In this case, the thickness of the oxide film is about 0.1 to 10 nm, generally about 0.5 to 5 nm. For this reason, even if one electrical end of the gas detection element has an area of about 1 mm ² , a capacitance unit having a capacitance of about 1 to 100 nF is formed.

  As will be described later, the detection sensitivity can be increased as the capacitance of the capacitance section alone is larger. From this viewpoint, the thinner the oxide film, the better. On the other hand, the oxide film also has a function as a barrier layer that prevents charge injection from the electrode to the gas detection element. Charge injection is a cause of measurement instability, and this tendency becomes significant when the frequency of the voltage applied to the gas sensor is high. For this reason, it is preferable that the oxide film has a certain thickness. Therefore, a preferable oxide film thickness is 1 to 5 nm.

  Note that the preferred range of the thickness of the oxide film is that of an aluminum layer. Similarly, when a metal on which a natural oxide film is formed, such as titanium, is used, its dielectric constant is also a characteristic as a barrier layer. However, since the oxide film is different from the aluminum oxide film, the preferable range of the thickness of the oxide film naturally varies.

Further, as described above, a dielectric layer containing C ₆₀ fullerene is formed in the vicinity of the interface between the oxide film portions 0203 b and 0205 b and the gas detection element 0204. This point will be described with actual measurement results. Based on the characteristic evaluation result of the gas sensor according to the present embodiment, the capacitance existing at the interface between aluminum and the fullerene vapor deposition film was calculated by simulation from an equivalent circuit. Next, when the thickness was calculated on the assumption that this capacitance was caused by an aluminum oxide film, it was confirmed to correspond to 6 nm. However, when the thickness of the oxide film formed on the aluminum layer of the gas sensor was measured by a spectroscopic ellipso method (high-speed spectroscopic ellipsometer M-2000V manufactured by JAWoollam), it was 1.0 nm. That is, according to this result, it is assumed that the dielectric layer other than the oxide film as the electrostatic capacitance component is electrically equivalent to an oxide film of 5 nm, and is near the interface between the fullerene deposited film and the oxide film. Will exist.

(D) Electrode Since the electrode of the gas sensor according to the present invention is electrically connected to the electrical end of the electric element including the gas detection element and the capacitance part, in the present embodiment, the aluminum layer The metal parts 203a and 205a of 203 and 205 are shown.

Typical examples of the electrode include metals such as gold, aluminum, and copper, oxide-based conductive materials such as ITO and ZnO, and metallic carbon materials such as graphite and metallic SWCNT.
However, in the present embodiment, since a metal natural oxide film is used as a part of the capacitance portion, it is preferable to use a metal capable of forming a dense natural oxide film. Examples of the metal include titanium, chromium, nickel, niobium, and tantalum in addition to aluminum according to the present embodiment.

(3) Gas detection principle (A) Outline The gas sensor according to the present embodiment having the above-described configuration is represented as an equivalent circuit as shown in FIG. Here, C and R are each capacitance and resistance of the gas detection device, C _b is the capacitance of the capacitive element.

  In the gas measurement system according to the present embodiment, an AC voltage is applied to the gas sensor having the equivalent circuit shown in FIG. 3, and the electrical response is measured to measure the gas adsorption state on the gas detection element. Here, the “electrical response” refers to all responses that can be measured by the electric measuring means among the responses by the gas sensor to the application of an alternating voltage. Therefore, a change in current may be measured as a response, or an admittance as an impedance or its inverse may be measured. Further, the gas sensor may be measured as a complex capacitance, or the complex conductance may be measured.

  Thus, by measuring with an alternating voltage, the charge-up to the gas detection element which has dielectric property is prevented. For this reason, the phenomenon of reducing measurement accuracy such as drift is suppressed, and measurement with high accuracy is realized.

(B) Complex Capacitance Measurement Hereinafter, a case where a complex capacitance is measured will be described as a typical example. By measuring the complex capacitance, the influence of the electrical characteristics of each component in the gas sensor can be made independent. Specifically, it is realized that the two capacitance components and the resistance component shown in FIG. 3 are made independent of each other, and the fluctuation of the resistance component, that is, the fluctuation of the conductivity of the gas detection element is efficiently detected.

First, the admittance Y ^* is calculated for this circuit.

It becomes. Here, as described above, C is whereas a nF the order of pF, C _b are generally several tens nF order. Therefore, since C _b >> C,

It becomes.
Of the admittance Y ^* thus obtained, the real part, that is, the conductance component G, is extracted.

It becomes. Therefore, when the frequency dependence of the AC voltage of the conductance G is measured, the conductance G increases with an increase in frequency at a low frequency, but the conductivity of the gas detection element is substantially directly shown at a high frequency.

On the other hand, the relationship between the admittance Y ^{* of the} gas sensor and the complex capacitance C ^* (= C′−jC ″) is

It becomes. Therefore, the real part C ′ of the complex capacitance C ^* (hereinafter referred to as “capacitance C ′”) is

It becomes. Therefore, when the frequency dependence of the AC voltage of the capacitance C ′ is measured, at low frequency, 1 >> ω ² C _b CR ² and 1 >> ω ² C _b ² R ² , which is almost C _b , and high frequency Then, 1 << ω ² C _b CR ² and 1 << ω ² C _b ² R ² , resulting in C.

  FIG. 4 shows the capacitance C in the case where the environment of the gas detection element is maintained at a vacuum degree of 10 Pa (temperature: 200 ° C.), and R is made constant so as not to cause a change in the gas adsorption state to the gas detection element. It is a graph which shows the dependence with respect to applied AC voltage frequency. In FIG. 4, the circles are measured data, and the solid lines are the results of fitting using the equivalent circuit shown in FIG. 3.

As shown in FIG. 4, the following low frequency 200 Hz, the capacitance C 'is the capacitance unit what was C _b due to (aluminum oxide portion of) the gas detection device in the above high-frequency 100kHz ( reduced to the capacitance C due to C ₆₀ fullerene). The intermediate frequency band is a transition region, and the variation of the capacitance C ′ in the transition region has a maximum absolute value of the rate of change near the end of the region (near several hundred Hz and 10 kHz). There is a part.

  Here, when R is changed, the capacitance C ′ converges to a constant value when the frequency becomes low and high, and there is no change in the basic tendency of having a transition region in the middle. Moving.

  FIG. 5 is a graph showing a capacitance profile obtained by an equivalent circuit simulation of the gas sensor according to the present embodiment. When R is increased, the transition region profile is not changed, but the entire transition region is on the low frequency side. When R is reduced, it can be confirmed that the entire transition region moves to the high frequency side.

As described above, by measuring the capacitance C ′ of the gas sensor according to the present embodiment, when the gas is adsorbed to the gas detection element and the conductivity is lowered, it is possible to measure the change as the capacitance C ′. Wherein a change in the capacitance C 'is a upper limit generally C _b, the lower limit is C. Therefore, it is advantageous in measurement that C _b > C and the difference is large. If C _b / C is 10 or more, stable measurement is realized. If this ratio is 100 or more, particularly stable measurement is realized.

  Note that this capacitance C ′ or an electrical parameter obtained based on the capacitance C ′, for example, a relative dielectric constant ε ′ may be used at the stage of measurement or display. In addition, the gas detection element according to the present embodiment has a decrease in conductivity due to gas adsorption, but conversely, even if the conductivity increases due to gas adsorption, only the moving direction of the transition region is different. Therefore, it is possible to apply the present gas detection principle as it is.

(C) Specific Method of Measurement There are a plurality of specific methods for the measurement as follows.
a) Frequency Fixation First, if a capacitance C ′ is measured in a state where the capacitance C ′ is fixed in the transition region, for example, at the center of the transition region, with the gas not adsorbed, and fixed at that frequency. When the conductivity of the gas detection element decreases due to gas adsorption and the transition region moves to the low frequency side, the capacitance C ′ at that frequency decreases. Accordingly, it is possible to quantitatively measure the change in the gas adsorption amount as the change in the capacitance C ′.

  On the other hand, if the measurement is performed while fixing the frequency to the peak or valley value at which the rate of change is maximum or minimum within the transition region, the capacitance C ′ changes greatly even with a small amount of gas adsorption. Measurement suitable for the application is realized. Further, if measurement is performed at a frequency lower than the valley value on the lower frequency side of the transition region, the capacitance C ′ hardly changes when the gas adsorption amount is small, but changes greatly when the adsorption amount reaches a certain level. Measurement is realized. This measurement method can be applied to an application in which the degree of risk is managed step by step in combination with the previous measurement method for detecting a small amount. Specifically, when measuring at multiple frequencies and detecting an extremely small amount of gas leak by measuring at a frequency close to the valley value, an alarm is issued. It is conceivable to issue a signal for forcibly stopping the whole.

b) Capacitance Fixation In addition to the measurement of fixing the frequency of the applied voltage as described above, frequency modulation is performed so that a constant capacitance C ′ is always measured, and the resistance value of the resistance component of the gas detection element (from the frequency ( It is also conceivable to obtain the conductivity) and estimate the amount of gas adsorption based on the result.

c) Capacitance profile Alternatively, there is a method in which a frequency sweep is performed for each measurement and a frequency-dependent profile (hereinafter referred to as “capacitance profile”) of the capacitance C ′ as shown in FIG. In this case, this profile is analyzed to determine the resistance value (conductivity) of the resistance component of the gas detection element, and the amount of gas adsorption can be estimated based on the result. Although this measurement method increases the load on the power source and the measurement means, it is expected that the measurement accuracy will increase.

(D) Influence of temperature Depending on the gas detection element, the resistance value (conductivity) of the resistance component may vary depending not only on gas adsorption but also on the temperature of the gas detection element. The gas detection element according to the present embodiment also has a tendency for the conductivity to increase as the temperature increases. In this case, conductivity variation due to temperature may be prepared as back data in advance, and the contribution due to temperature variation may be removed from the obtained measurement result, or a reference sensor having a structure that does not adsorb gas May be installed in the vicinity of the gas sensor, and the difference from this reference sensor may be used as the measurement value. Here, the reference sensor has the same structure as the gas sensor, but the entire exposed portion of the gas detection element may be a material that does not allow gas to pass therethrough, for example, an organic material such as polyimide, or has a siloxane bond. If a material sealed with an inorganic material or a composite material of these materials is used, it can be made to function as a temperature sensor having the same temperature-sensitive characteristics as the gas sensor.
In addition, the ceramic heater may be operated at all times during the measurement to maintain a temperature at which the change in environmental temperature can be canceled although the gas can be adsorbed.

(E) Study of the equivalent circuit, where, if strictly examined electrical properties of the gas sensor according to the present embodiment, in addition to the capacitive component represented by C _b in the capacitance section composed of such as an oxide film There is a resistance component _Rb . Therefore, the equivalent circuit of the gas sensor according to the present embodiment should be accurately described as shown in FIG.

However, at high frequencies, the influence of the capacitance component Cb in the capacitance portion is dominant, and the influence of the resistance component _Rb is almost completely negligible. On the other hand, at a low frequency, although the value of the capacitance C ′ of the entire gas sensor is slightly increased, there is almost no influence on the profile of the transition region. Therefore, if measurement is performed focusing on this transition region, there is no influence of _Rb . Even when low frequency measurement is required, the effect can be eliminated by measuring the difference from the above-described reference sensor.

(4) Components other than the gas sensor Components other than the gas sensor of the gas measurement system according to the present embodiment will be described.
(A) Power source The power source is not particularly limited as long as an AC voltage can be generated. When measuring an AC applied frequency dependence profile with respect to an electrical response, such as a capacitance profile, it is necessary to be able to output frequencies of a plurality of applied voltages. At this time, a plurality of frequencies may be output by sweeping the frequency from a high frequency to a low frequency or vice versa, or a voltage on which the plurality of frequencies are superimposed is output at one time, and a Fourier transform or the like is performed in the measuring means. It is good also as profile data by performing frequency analysis by performing.

  In this embodiment, an alternating voltage by a sine wave is applied, but a voltage that periodically changes including a certain polarity inversion, that is, a predetermined waveform for at least one of a pair of electrodes is repeated at a predetermined period. If the voltage waveform is a voltage having a case where the voltage waveform is positive with respect to the potential of the other electrode and a case where the voltage waveform is negative, the voltage waveform may be a rectangular wave. A triangular wave may be used. Further, the center voltage of the voltage waveform may be 0 V, or a positive or negative bias may be applied.

Moreover, the maximum value of the absolute value of the voltage applied from a power supply will not be restrict | limited especially if it is less than the dielectric breakdown voltage of a gas detection element. Here, the breakdown voltage depends on the material and structure of the gas detection device, for example in the case of a gas detection device comprising a C ₆₀ fullerene is about 10V at 1μm thick. If this maximum value is excessively low, the influence of noise on the electrical response becomes large. Therefore, an appropriate value may be set in consideration of this influence. If gas detection device consisting of the above _{C 60} fullerene, it is preferable to measure the degree 20～100MV.

(B) Measuring means The measuring means is a so-called general LCR meter, as long as it can measure impedance and admittance. In this case, the capacitance C ′ may be separately calculated based on the output data. Of course, it is preferable if each component such as resistance, reactance, conductance, and susceptance can be output independently, or if complex conductance or complex capacitance can be output, and more preferable if capacitance C ′ can be directly output. Moreover, it is particularly preferable if it is integrated with a power source and can measure a desired profile at a time.

(C) Gas desorption means The gas desorption means is for removing the gas that changes the conductivity of the gas detection element from the gas detection element. In the gas measurement system according to the present embodiment, the ceramic heater that also serves as the substrate of the gas sensor corresponds to the gas desorption means. In the ceramic heater 0201 shown in FIG. 2, heater wires 0201a and 0201b are connected to a heater power source (not shown). When the heater power source is operated to heat the ceramic heater 0201, the gas detection element 0204 is heated by this heat, and as a result, the gas adsorbed on the gas detection element 0204 is desorbed.

  Thus, the simplest gas removal method is heating, and a ceramic heater is used as one means in this embodiment. Therefore, a carbon heater or a metal resistance heating body may be used as long as it can function as a gas desorption means. As long as the gas can be removed, an infrared lamp, a laser, or a means for causing high energy particles such as electrons to collide with the gas detection element 0204 may be used.

  In addition, gas desorption may be performed by reducing the partial pressure of the gas to be desorbed around the gas sensor. In this case, exhaust means such as rotary pumps, cryopumps, turbo molecular pumps, diffusion pumps, sublimation pumps, gas cylinders supplying inert gases such as high purity nitrogen and argon, and air supply means consisting of regulators are gases. Desorption means.

  Next, a start-up process and a regeneration process using a gas desorption means will be described.

a) Start-up process The gas measurement system according to the present embodiment starts measurement in a state in which the gas to be measured (hereinafter also referred to as “active substance”) is hardly adsorbed, and from a very small amount, sub ppm to ppb In some cases, it is also intended to detect gas at the ppt level. Therefore, before starting the measurement, it is preferable to execute a process of desorbing the active substance from the gas detection element as a start-up and adsorbing the inert substance if necessary. Specifically, the gas desorption means may be operated to perform exposure to a vacuum environment or an inert gas atmosphere such as high-purity nitrogen and / or heating.

  Before use, the gas detection element is covered with a cover layer or electrode so that it is isolated from the outside air, and when used, the cover layer is broken or removed, etc. May be exposed. In this case, the start-up process is to expose the gas detection element to the measurement environment without using the gas desorption means.

b) Regeneration Process In the gas detection element according to the present embodiment, the active substance exchanges electrons directly or indirectly with C ₆₀ fullerene to change the conductivity of the gas detection element. However, even if the active substance does not interact enough to form a strong chemical bond with the fullerene material, the change in the conductivity of the gas sensing element occurs, so the interaction between substances that affects the variation in the conductivity of the gas sensing element Most of them are reversible processes.

  Therefore, the conductivity of the gas sensing element, which has been reduced by the adsorption of the active substance, is similar to that in the start-up process described above, by operating the gas desorption means and exposing it to a vacuum environment or an inert gas atmosphere such as high purity nitrogen Or it is possible to return to a high level again by heating. Repeated use is realized by performing this regeneration process.

(D) Temperature measuring means The gas detecting element according to the present embodiment preferably has a temperature measuring means for measuring the temperature of the gas detecting element because the conductivity fluctuates even when the temperature changes. The temperature measuring means may be a known means such as a thermocouple, but has the same structure as the gas sensor according to the present embodiment and is further sealed so that the gas detection element does not adsorb gas. If the data from this temperature measuring means is used as reference data, it is preferable to accurately remove the influence of the temperature in the gas sensor.

(5) Gas Sensor Manufacturing Method Next, a gas sensor manufacturing method according to the present embodiment will be described.
Basically, gold, aluminum, C ₆₀ fullerene, and aluminum may be sequentially laminated on a ceramic heater that also serves as a substrate through an appropriate mask. After forming the layers, an atmosphere containing oxygen, by exposing approximately 1 hour, for example, in the atmosphere to form an oxide film at the interface between C ₆₀ fullerene deposited film of aluminum layer. It is the most convenient process manner to form such a natural oxide film, if necessary, an aluminum layer between the substrate and the C ₆₀ fullerene deposited film of a ceramic heater also serves for (203 in FIG. 2) is it may be actively oxidize the surface before performing the deposition of C ₆₀ fullerene.

(6) Gas sensor according to the detection target gas present embodiment, transfer of C ₆₀ fullerene and directly or indirectly electrons constituting the gas detection device, resulting in the adsorption change the conductivity of the gas detection element by Any substance can be used as a measurement target. Specifically, oxygen and moisture are typical. In addition, alcohols such as hydrogen and ethanol, aldehydes such as formaldehyde, ketones such as acetone, nitrogen-containing compounds such as ammonia and methylamine, and aromatic compounds such as benzene Examples include acidic substances such as NO _x and SO _x , and halogen-containing substances such as HCl and chlorine gas.

This detection target gas can be changed by the material constituting the gas detection element, and its sensitivity can also be controlled. For example, if the gas detection device comprising a C ₆₀ fullerene is a relatively low sensitivity had fullerene is chemically modified, endohedral and hetero fullerenes, the structure easily and chemical interaction with the detection target gas By making the material part or all of the material constituting the gas detection element, detection with high sensitivity is realized.

(7) Applications The gas sensor according to the present embodiment can be made smaller in size than a conventional sensor using a mass analyzer, for example, while having high sensitivity. Therefore, the gas measurement system including the gas sensor can be applied to various uses such as semiconductor manufacturing process use and fuel cell. As an example of these applications, a semiconductor manufacturing process application will be described below.

  The demand for reducing the gas contamination concentration in the semiconductor manufacturing process is particularly severe. For example, the concentration of oxygen and moisture in nitrogen gas is still less than 5 ppb, and in 2010, it is required to be less than 1 ppb. At present, analysis by an atmospheric pressure mass spectrometer is generally performed as an analysis method for such a trace amount of gaseous active substance, but since the apparatus is large, it is suitable for applications such as measuring individual pipes. Is not applicable and only the process chamber is being measured. However, when management at the ppt level is required, the time required for quality recovery when contamination occurs once becomes long in measurement using only the process chamber, and management of the lead time becomes difficult. Therefore, it is necessary to install a highly sensitive gas sensor in the individual piping to prevent contamination to the process chamber. For this reason, the development of an ultra-small and highly sensitive gas sensor is strongly demanded. Yes.

  The gas sensor according to the present embodiment is a small and highly sensitive sensor, and in principle it is possible to measure at the ppt level as well as the ppb order. Therefore, by installing the gas sensor according to the present invention in each of the individual pipes of the gas piping system in the semiconductor manufacturing apparatus, it is possible to meet the strict requirement for contamination management as described above.

(8) Modification of gas sensor according to first embodiment (A) Capacitance portion other than natural oxide film In the present embodiment, at the interface with the gas detection element of the metal layer directly formed on the gas detection element Although the spontaneously formed natural oxide film is used as a part of the capacitance portion, as described above, not the natural oxide film but an actively oxidized oxide film may be used. Further, the metal surface is modified by nitriding or carbonizing instead of oxidation, and a modified layer having dielectric properties on the metal surface (hereinafter referred to as “dielectrically modified layer” including a natural oxide film). ) May be formed.

  Alternatively, the metal layer is made of a material that does not substantially form a natural oxide film such as gold (hereinafter, a layer made of this material is referred to as an “inactive metal layer”), and a dielectric modification layer is formed. Alternatively, a member constituting the electrostatic capacity portion may be provided separately. The method is roughly divided into a case where it is formed integrally with the gas detection element and a case where it is formed separately from the gas detection element.

a) Integrated formation of dielectric additional layer When the electrostatic capacitance part is formed integrally with the gas detection element, there is an advantage that a small configuration can be maintained as a gas sensor. In this case, as shown in FIG. 7A, as in the case of the natural oxide film, a dielectric layer is provided between the gas detection element 0701 and the metal layer, that is, the inert metal layers 0704 and 0705. (Hereinafter referred to as “dielectric additional layer”) Inert metal layers 0707 and 0708 are directly formed on the electrical end of the gas sensing element 0706 as shown in FIG. And dielectric additional layers 0709 and 0710 thereon. In the former configuration, the inert metal layers 0704 and 0705 correspond to “electrodes” in the constituent elements of the gas sensor. In the latter configuration, the inert metal layer includes “gas detection element” and “capacitance portion”. Therefore, it is necessary to further form electrodes 0711 and 0712 at the electrical ends of the dielectric addition layers 0709 and 0710.

The material forming the dielectric additional layer is typically an insulating material such as SiO _2, and the higher the capacitance of the electrostatic capacity portion, the higher the detection sensitivity. For example, an HfO ₂ -based material It is preferable to use a high dielectric constant material such as BaO—R ₂ O ₃ —TiO ₂ based material. Moreover, since it preferably functions as a charge injection preventing layer for the gas detection element, it preferably has a thickness of 1 nm or more so as not to cause a tunneling phenomenon.

  When an inert metal layer is directly formed on the gas detection element, a metal such as gold constituting this layer diffuses into the gas detection element, and the electric field applied to the gas detection element becomes non-uniform. Or in the worst case, a short circuit occurs. Therefore, the configuration in which the dielectric additional layer is formed between the gas detection element and the inert metal layer is preferable because such a situation is unlikely to occur.

b) Connection of external capacitor When the capacitance part is formed separately from the gas detection element, as shown in FIG. 8, the inert metal layer 0802 is formed on both electrical ends of the gas detection element 0801. A basic configuration is a configuration in which 0803 is provided and a capacitor 0804 is connected in series thereto. At this time, the gas sensor refers to the whole 0805, and the inert metal layer 0803 on the side to which the capacitor is not connected and the electrode on the side not facing the gas detection element of the capacitor 0804 correspond to the “electrode” of the gas sensor. Become. In this configuration, the capacitor 0804 that forms the electrostatic capacity portion is not limited to the size of the gas detection element 0801, and thus there is an advantage that the degree of freedom in designing the electrostatic capacity portion is increased. For example, in applications where the presence or absence of gas is detected, a capacitor with a small capacitance is connected to pursue downsizing and cost reduction, and when high quantitative measurement capability is required, a capacitor with a large capacitance is connected to Just widen the range.

  In addition, when the natural oxide film is used as the electrostatic capacity portion, it is necessary to control the thickness of the oxide film in the manufacturing process, but in this configuration, a commercially available capacitor can be used. This process management item can be reduced.

(B) Combination of integrated formation and separate formation As a combination of the above two, in addition to the dielectric layer formed so as to be integrated with the gas sensing element, separate capacitors are connected in series. May be. At this time, the dielectric layer may be a dielectric modified layer or a dielectric additional layer. In FIG. 9, as an example, an electric element in which dielectric addition layers 0902 and 0903 are formed at both electrical ends of the gas detection element 0901 and an inert metal layer 0904 and 0905 are formed at both ends thereof. A gas sensor having a configuration in which a capacitor 0906 is connected in series is shown.

  Compared to the configuration shown in FIG. 8, this configuration is less likely to inject charges into the gas detection element, and more stable measurement is expected. However, in this case, the capacitance of the entire capacitance portion is more strongly affected by the smaller one of the capacitance of the dielectric additional layer and the capacitance of the capacitor. The meaning provided is virtually lost. Therefore, it is preferable to use a separate capacitor for adjustment by setting the ratio of both capacitances to about 0.1 to 10 times. For example, a laminate of a metal film-insulating film-metal film formed in another region on the substrate where the gas sensor is formed is used as an external capacitor, and its shape, in particular, the laminate is formed using means such as a laser. What is necessary is just to set it as the structure which can adjust the capacitance by changing the area of the film | membrane to comprise. When the capacitance of the integrated member is slightly different from the design, the shape of the separate capacitor is changed, for example, a part of the film is trimmed, and the capacitance of the entire capacitance portion is predetermined. Should be in the range.

  In addition, if a separate capacitor is capable of reversibly adjusting the capacitance, it is not necessary to adjust the capacitance of the integrated capacitor at the manufacturing stage. May be adjusted to a predetermined value. Such a configuration is suitable for applications where quantitativeness is strictly required.

(C) Other sensor structures In the gas sensor according to the present embodiment, the normal direction of the surface forming the two electrical ends of the gas detection element, that is, the main electric field direction of the gas detection element is relative to the substrate of the gas detection element. Although the structure substantially coincides with the stacking direction (stacked structure, sandwich structure), a structure other than this structure may be used.

  For example, the electric field direction may be substantially orthogonal to the stacking direction. An example of the structure in this case will be described. Two comb-shaped electrodes are formed on a substrate so that the comb-tooth portions of the electrodes are engaged with each other with a predetermined distance, and the surface of the electrode is subjected to dielectric modification. Forming a layer or a dielectric additive layer; Furthermore, the member which makes a gas detection element is laminated | stacked so that the end surface facing the said separation part in the comb-tooth part on the board | substrate which makes the separation part of the comb-tooth part may be covered. If it does so, it will become a gas sensor of the structure where the dielectric modification layer or dielectric addition layer formed in the end face of the above-mentioned comb tooth part serves as an electrostatic capacity part, and the electric field direction goes straight to the lamination direction.

  Since this structure exposes the gas detection element area in the gas detection element, that is, the gas detection element portion sandwiched between the capacitance parts, gas adsorption is performed quickly and responsive measurement is realized. There are advantages.

(D) Other Measurement Method In this embodiment, the complex capacitance of the gas sensor is measured. However, the measurement may be performed paying attention to another electrical response. For example, the conductance shown in the above equation (3) may be measured. FIG. 10 is a graph showing an applied AC frequency dependence profile (hereinafter referred to as “conductance profile”) of conductance obtained by simulation of the equivalent circuit shown in FIG. 3, and the resistance component R of the gas detection element. It shows how the profile fluctuates due to fluctuations. From this figure, the fluctuation of R can be read as a change in conductance at a high frequency of about 1 MHz, and the fluctuation of R can be measured by tracking a frequency indicating a predetermined conductance in a low frequency band of 100 Hz or less. It can be seen that it is. Further, it is possible to measure the variation of R by tracing the frequency forming the minimum value in the differential data of the profile.

4). Second Embodiment Subsequently, a gas measurement system according to a second embodiment of the present invention will be described.
(1) Configuration The basic configuration of the gas measurement system according to the second embodiment of the present invention is the same as the configuration of the gas measurement system according to the first embodiment shown in FIG. That is, the gas measurement system according to the second embodiment is also adsorbed to the gas sensor, a power source capable of generating an alternating voltage of a plurality of frequencies, a measurement unit that measures an electrical response from the gas sensor, and the gas sensor. Gas desorption means for desorbing the generated gas. The components other than the gas sensor are the same as those in the first embodiment.

(2) Gas sensor The gas sensor according to the present embodiment has a dielectric semiconductor, and a gas detection element whose conductivity changes according to the state of gas adsorbed as a characteristic attributed to the dielectric semiconductor, and the gas A pair of electrodes electrically connected to the sensing element. The characteristics required for the dielectric semiconductor are the same as those of the gas sensor according to the first embodiment. Also in this embodiment, the gas detection device consists of a deposited film of C ₆₀ fullerene, it may be used gas detection device consisting of another member.

  The specific configuration of the gas sensor according to the present embodiment is a configuration in which the aluminum layer in FIG. 2 is replaced with a gold layer that is an inert metal layer. For this reason, the element which comprises an electrostatic capacitance part, such as an oxide film, is not contained in the gas sensor which concerns on this embodiment. That is, the gas sensor according to the present embodiment includes the pair of inert metal layers as electrodes and a gas detection element sandwiched between the electrodes.

(3) Gas Detection Principle The gas sensor according to the present embodiment having the above configuration is as shown in FIG. 11 when expressed as an equivalent circuit. Here, C and R are the capacitance and resistance of the gas sensing element, respectively, and _Rb is the resistance of the inert metal layer forming the electrode.

  In the gas measurement system according to the present embodiment, an AC voltage is applied to the gas sensor having the equivalent circuit shown in FIG. 11, and the electrical response is measured to measure the gas adsorption state on the gas detection element. By measuring with an alternating voltage, the charge-up to the gas detection element which has dielectric property is prevented. For this reason, the phenomenon of reducing measurement accuracy such as drift is suppressed, and measurement with high accuracy is realized.

Hereinafter, a case where conductance is measured will be described as a typical example. First, the admittance Y ^* for this circuit is

It becomes. Here, although _Rb slightly changes depending on the metal material of the inert metal layer, the film forming method, and the like, since the thickness is usually 0.1 μm or less, it is clearly R >> _Rb . Therefore,

It becomes.
Of the admittance Y ^* thus obtained, the real part, that is, the conductance component G, is extracted.

It becomes. Therefore, when the frequency dependence of the AC voltage of the conductance G is measured, it becomes (1 / R) in the low frequency region, and the conductance G directly indicates the conductivity of the gas detection element, and in the high frequency region, it is shown in FIG. Show a tendency to increase. FIG. 12 shows a simulation result of the conductance profile calculated based on the equivalent circuit shown in FIG.

  Therefore, when the conductance is measured for the gas sensor of the present embodiment, the conductivity is directly measured up to a frequency equal to or lower than a predetermined frequency, and the influence of charge-up and the like is suppressed by the application of the AC voltage. More stable measurement is possible.

  In addition, since the frequency at which the conductance tends to increase from the almost constant value in the conductance profile depends on the conductivity of the gas sensing element, the conductance profile is measured over time, and the frequency indicating the maximum value in the differential data. It is also possible to measure the change in the conductivity of the gas detection element by tracing.

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples.
1. Example 1
First, the basic operation of the gas sensor according to the present invention will be described using Examples 1-1 to 1-4 and Comparative Example 1-1.

(1) Example 1-1
A glass substrate (30 mm × 30 mm, thickness 0.12 to 0.17 mm) was prepared and placed in a vacuum chamber having a degree of vacuum of 1 × 10 ⁻⁵ Pa and a residual oxygen concentration of 10 ¹¹ / cm ³ or less (10 ppb or less). . Then, a rectangular (20 mm × 4 mm) pattern for electrodes and a linear lead electrode pattern connected thereto were formed on the glass substrate by vapor deposition of Al. Its thickness was about 100 nm.

Next, the molybdenum boat filled with C ₆₀ fullerene (manufactured by Frontier Carbon Co., Ltd., product name Nanom purple) is heated while energizing while measuring the temperature, and is controlled within a range of 500 to 550 ° C. to sublimate C ₆₀ fullerene, A C ₆₀ fullerene film having a thickness of 2 μm was formed on the electrode Al pattern. Incidentally, the pattern by the C ₆₀ fullerene, and a rectangular pattern such as Al pattern thereunder is completely covered.

Subsequently, the C ₆₀ fullerene film, the tip of the electrode Al pattern and the same pattern was formed by evaporation of Al. Its thickness was about 200 nm. The lead electrode of this electrode was also formed by Al vapor deposition so as not to overlap with the lead electrode of the lower electrode.

The gas sensor thus obtained was taken out from the chamber and subjected to atmospheric exposure treatment in which it was left in the atmosphere for 2 hours, and then installed in the measurement chamber. The measurement chamber was maintained at a vacuum degree of 10 ⁻⁵ Pa, a residual oxygen concentration of 10 ⁹ / cm ³ or less (0.1 ppb or less), and an oxygen concentration of 10 ⁹ / cm ³ or less (0.1 ppb or less). Pure nitrogen (hereinafter abbreviated as “pure nitrogen”) was introduced until the total pressure reached 1 atm. And it supplies with electricity to the carbon heater made to contact | abut the surface on the opposite side to the surface which forms the film-forming area | region of the glass substrate of the gas sensor manufactured as mentioned above, and the surface temperature of a gas sensor is set to 280 +/- 10 degreeC. The gas sensor was started up by heating for 6 hours.

  After heating at 280 ° C for 6 hours, the amount of current applied to the carbon heater is adjusted to set the surface temperature of the gas sensor to 250 ° C, and then an impedance analyzer (Yokogawa, Hewlett-Packard Co. Terminals from a company (currently Agilent Technologies LF4192A type) were connected.

  Here, the vacuum chamber is provided with a gas introduction mechanism capable of switching a plurality of gas paths capable of mixing a plurality of gases at an arbitrary ratio, and a mass analyzer (API-500 manufactured by Japan API Corporation). Therefore, this mass analyzer can measure an arbitrary gas in the order of ppm even under atmospheric pressure. Therefore, a path for introducing pure nitrogen at 1 L / min by adjusting the gas introduction mechanism in advance and a gas having a total pressure of 1 atm in which 1 ppm of oxygen is added thereto (hereinafter abbreviated as “1 ppm oxygen-containing nitrogen”). The route to be introduced at 1 L / min can be switched.

  After connecting the terminal to the extraction electrode, the gas introduction mechanism was operated to introduce pure nitrogen into the chamber. After confirming that the pressure became 1 atm and a stable state was achieved, voltage application at 20 mV and 1 MHz was started on the extraction electrode, and impedance measurement was started in units of 1 minute. The relative permittivity of the gas sensor was calculated from the measured impedance, and the change was recorded over time.

  After the start of measurement, the gas path of the gas introduction mechanism was switched at a predetermined timing to expose the gas sensor installed in the chamber to 1 ppm oxygen-containing nitrogen. As a result, as shown in FIG. 13, a rapid decrease (40 → 30) in the relative permittivity was observed immediately after introducing 1 ppm oxygen-containing nitrogen, and thereafter the relative permittivity decreased while decreasing with time. It was confirmed that it decreased.

  120 minutes after the introduction of 1 ppm oxygen-containing nitrogen, when the gas path was switched to pure oxygen again, an increase in the dielectric constant that had been reduced to 22 was observed, and in one hour at 250 ° C., the test temperature of this example. It was confirmed that when the temperature was raised to about 38 and then increased to 280 ° C., the relative dielectric constant recovered to 40 at the start of measurement in 1 hour.

(2) Example 1-2
A gas sensor manufactured by the same manufacturing method as in Example 1-1 and subjected to the same heat treatment under vacuum as a start-up process is installed in the chamber, and gas is supplied through a gas path for supplying pure nitrogen at 1 L / min. Was introduced and the measurement of relative permittivity was started. Then, instead of the oxygen 1 ppm in Example 1-1, when switching to a gas path for supplying a gas having a total pressure of 1 atm added with 10 ppm of water (hereinafter abbreviated as “10 ppm water-containing nitrogen”) at 1 L / min, As shown in FIG. 14, a rapid decrease in the dielectric constant was observed as in Example 1-1 (145 → 127).

  When the measurement was continued thereafter, the decrease in the dielectric constant was saturated 15 minutes after the introduction of 10 ppm water-containing nitrogen, and almost stabilized at 120. Therefore, the dielectric constant increases rapidly when switching to the pure nitrogen path 25 minutes after the introduction of 10 ppm moisture-containing nitrogen, and is equivalent to the relative dielectric constant before the introduction of 10 ppm moisture nitrogen after 20 minutes from the introduction of pure nitrogen. Recovered to the level.

(3) Example 1-3
An experiment similar to Example 1-2 was performed with the surface temperature of the gas sensor at the time of measurement being 150 ° C.

  The result is shown in FIG. In order to easily compare the effect with the case of 250 ° C., normalization was performed by setting the relative dielectric constant at the beginning of measurement to 100%. The solid line in FIG. 15 is the result when the temperature is 150 ° C., and the broken line indicates the result when the temperature is 250 ° C. As shown in FIG. 15, the general tendency of a rapid decrease in the relative permittivity and a decrease in the amount of decrease per unit time with time was the same as in Example 1-2, but the relative permittivity is Saturation occurred at about 92% at the start of measurement, and the time until the decrease in relative permittivity became saturated was as long as about 2 hours. Compared to the case of 250 ° C., the decrease in relative permittivity was ½, and the time until saturation was 8 times.

  Further, when switching to the pure nitrogen path 130 minutes after the introduction of 10 ppm water-containing nitrogen, the relative dielectric constant gradually increased as compared to Example 1-1, and at the start of measurement even after 100 minutes had passed since the introduction of pure nitrogen. It recovered only to about 93% with respect to the relative dielectric constant. However, when the temperature was raised to 300 ° C., the original relative dielectric constant was recovered in 1 hour.

(4) Example 1-4
A glass substrate (30 mm × 30 mm, thickness 0.12 to 0.17 mm) is prepared and placed in a vacuum chamber having a degree of vacuum of 1 × 10 ⁻⁵ Pa and a residual oxygen concentration of 10 ¹¹ / cm ³ or less (10 ppb or less). A rectangular (20 mm × 4 mm) pattern for electrodes and a linear lead electrode pattern connected thereto were formed on the glass substrate by vapor deposition of Al, and the thickness was about 100 nm.

Then, Li containing C ₆₀ fullerene containing mixture (Ideal Star Inc., product name 001A, the weight ratio of the total mixture of endohedral: 5%) were electrically heated while the temperature measurement molybdenum boat filled, 550-600 sublime range control to the Li containing _{C 60} fullerene containing a mixture of ° C., to form a fullerene mixture containing Li containing _{C 60} in a thickness of 2μm on said electrode for Al pattern. In addition, the pattern by a fullerene mixture was made into the rectangular pattern that the Al pattern under it was covered completely.

Subsequently, C on the ₆₀ fullerene film, ahead of the same pattern as the electrode Al pattern was formed by evaporation of Al. At this time, a similar extraction electrode was also formed by Al vapor deposition so as not to overlap with the extraction electrode of the lower electrode. Its thickness was about 200 nm.

  The gas sensor manufactured as described above was subjected to the same atmospheric exposure treatment and start-up treatment as in Example 1-1, and after the surface temperature of the gas sensor was set to 250 ° C., pure nitrogen was introduced at 1 L / min. Measurement of relative permittivity started.

After confirming that the measurement environment was stable and the relative dielectric constant was stable at about 52, introduction of 1 ppm oxygen-containing nitrogen at 1 L / min was started as in Example 1-1. Then, as shown by the solid line in FIG. 16, a rapid decrease in the relative dielectric constant was measured, and after 5 minutes from the introduction, the relative dielectric constant became about 30, and then the decrease rate decreased, but the nitrogen content of 1 ppm oxygen was reduced. The dielectric constant became 20 120 minutes after the start of introduction. Comparing this behavior as C ₆₀ only result of the gas sensor by the gas sensing device fabricated in (Figure 16 dashed lines), but differs in that the dielectric constant of the pre-measurement start is increased, the oxygen adsorption relative dielectric constant of 20 It is common in terms of degree. Therefore, it was confirmed that the improved oxygen detection sensitivity by the addition of Li containing C _60.

  Thereafter, when pure nitrogen was introduced by switching the gas path, the relative dielectric constant immediately started to rise, and after 1 hour from the switching, the relative dielectric constant recovered to almost the same level as the relative dielectric constant at the start of measurement. Thereafter, when the amount of current supplied to the carbon heater was increased and the temperature of the gas sensor surface was set to 280 ° C., the relative dielectric constant at the start of measurement was restored after 1 hour.

(5) Comparative Example 1-1
A glass substrate (30 mm × 30 mm, thickness 0.12 to 0.17 mm) is prepared and placed in a vacuum chamber having a degree of vacuum of 1 × 10 ⁻⁵ Pa and a residual oxygen concentration of 10 ⁹ / cm ³ or less (0.1 ppb or less). installed. Then, two rectangular patterns (20 mm × 2 mm) for electrodes are formed on the glass substrate so that the distance between the electrodes is 2 mm, and a linear lead electrode pattern connected to each electrode is deposited by Au. Formed by. The thickness of the formed Au electrode was about 100 nm.

Next, the molybdenum boat filled with C ₆₀ fullerene (manufactured by Frontier Carbon Co., Ltd., product name Nanom purple) is heated while energizing while measuring the temperature, and is controlled within a range of 500 to 550 ° C. to sublimate C ₆₀ fullerene, to form a C ₆₀ fullerene film having a thickness of 2μm above on the two electrode Au pattern and their inter-electrode region.

Subsequently, the degree of vacuum ¹⁰ -5 Pa, the chamber maintained residual oxygen concentration ¹⁰ 9 / cm ³ or less (0.1 ppb or less), the oxygen concentration ¹⁰ 9 / cm ³ or less by Ti getter pump (0.1 ppb or less) High purity nitrogen (hereinafter abbreviated as “pure nitrogen”) was introduced until the total pressure reached 1 atm. And it supplies with electricity to the carbon heater made to contact | abut the surface on the opposite side to the surface which forms the film-forming area | region of the glass substrate of the gas sensor manufactured as mentioned above, and the surface temperature of a gas sensor is set to 280 +/- 10 degreeC. The gas sensor was started up by heating for 6 hours.

  After heating at 280 ° C for 6 hours, adjust the amount of electricity to the carbon heater, set the surface temperature of the gas sensor to 250 ° C, connect the terminal from the impedance analyzer and apply DC voltage (20V) Measurement of resistivity of gas sensor started.

  After measuring the resistivity in pure nitrogen, the oxygen added to pure nitrogen was increased stepwise, and the state where the variation in resistivity was stabilized was measured as the resistivity of the added oxygen concentration. As a result, as shown in FIG. The oxygen concentration dependence of resistivity was observed. In FIG. 17, ◯ is the measurement result, and the solid line is an approximate straight line.

  Thus, although high linearity was observed and it was confirmed that the sensor had the basic performance required as a sensor, the time required for the stability of the resistivity was about 2 hours, and after exposure to oxygen of 1000 ppb, Even when the gas sensor was heated to 280 ° C., the original state was not recovered unless 20 hours had passed.

  Moreover, although the same measurement was performed also about the water | moisture content, the fluctuation | variation of resistance value like the case of oxygen was not measured.

2. Example 2
Next, a configuration that can be taken by the gas sensor according to the present invention, particularly a configuration in the case where the configuration of the capacitance section is different, will be described using the second embodiment. In the following examples, it is used that the gas sensing element made of a C ₆₀ fullerene vapor-deposited film has a reduced conductivity even when the temperature is lowered so that the conductivity is lowered when the gas is adsorbed. Then, the gas adsorption state was simulated by changing the temperature, and the measurement result of the gas sensor when the configuration of the capacitance part was different was verified.

(1) Example 2-1
Alumina substrate (30 mm × 30 mm, thickness 0.12 to 0.17 mm) polished to a surface roughness Ra of 20 nm or less, and a gold vapor deposition film as an electrode pad in advance at predetermined positions (two locations) Was prepared and placed in a vacuum chamber for Al vapor deposition with a degree of vacuum of 3 × 10 ⁻⁵ Pa. A rectangular (4 mm × 6 mm) pattern for electrodes and a linear lead electrode pattern connected thereto were formed on the polished surface of the ceramic substrate by vapor deposition of Al. The deposition rate was about 1.5 Å / s, and the thickness of the deposited film was about 50 nm. In addition, it electrically connected by forming a part of extraction electrode on one gold electrode pad.

Next, the Al-deposited substrate was placed in a vacuum chamber for fullerene deposition having a degree of vacuum of 1 × 10 ⁻⁴ Pa and a residual oxygen concentration of 10 ⁹ / cm ³ or less (1 ppb or less). The air release time from the Al deposition chamber was 20 minutes or less. Then, a molybdenum boat filled with C ₆₀ fullerene (manufactured by Frontier Carbon Co., Ltd., product name Nanom purple) was heated while energized while measuring the temperature, and was controlled within a range of 500 to 550 ° C. to sublimate C ₆₀ fullerene. Thus, C ₆₀ fullerene was deposited on the Al pattern for electrodes at a film formation rate of about 3 to 4 liters / s to form a C ₆₀ fullerene film having a thickness of 1.4 μm. Incidentally, the pattern by the C ₆₀ fullerene, and a rectangular pattern as under the Al pattern thereof (excluding the extraction electrode portion.) Is completely covered.

Subsequently, a substrate which the C ₆₀ fullerene film was formed was again placed in Al deposition chamber above. At this time, the open time to the atmosphere was 20 minutes. Then, on the C ₆₀ fullerene film, a pattern (2 mm × 5 mm) in a narrower range than the previous electrode Al pattern was formed by deposition of Al. The film formation rate was the same as the previous Al deposition, and the thickness was about 50 nm. Further, in this vapor deposition, the lead electrode of this electrode was formed by Al vapor deposition so as not to overlap the lead electrode of the lower electrode, and a part thereof was on the gold electrode pad.

The substrate was removed from the chamber and allowed to stand in the atmosphere (25 ° C., 60% RH) for 24 hours to form a natural oxide film on the Al deposited film. The capacitance of the electrostatic capacitance part including the natural oxide film was about 15 nF. Thus, a gas sensor having an effective electrode area of 10 mm ² was obtained.

  The gas sensor was taken out from the Al deposition chamber and placed in a measurement chamber maintained at a vacuum degree of 10 Pa. Subsequently, a carbon heater in contact with the surface of the gas sensor opposite to the surface forming the ceramic substrate is energized and heated for 24 hours so that the surface temperature of the gas sensor becomes 200 ± 10 ° C. And started up the gas sensor.

  After the start-up process is completed, the surface temperature of the gas sensor is maintained at approximately 200 ° C., and power is applied to the two extraction electrodes from a power source that can arbitrarily change the frequency of the applied voltage in the range from 0.01 Hz to 10 MHz. The terminal was connected. And the wiring from the terminal of the power supply which can change an applied frequency from 0.01 Hz to 10 MHz was connected to this extraction electrode, maintaining an applied voltage at 50 mV, and the impedance was measured. The capacitance of the gas sensor was calculated from the measured impedance, and the capacitance profile when the surface temperature of the gas sensor was 200 ° C. was obtained.

  Subsequently, the carbon heater was adjusted to lower the surface temperature of the gas sensor to 180 ° C., and after confirming that the temperature was stable at this temperature, impedance measurement was performed while changing the frequency to obtain the capacitance profile.

Thus, the capacitance profile was measured several times while the surface temperature of the gas sensor was lowered to 25 ° C.
The result is shown in FIG. The points in FIG. 18 are actually measured values, and the solid line is the result of fitting based on the equivalent circuit shown in FIG. The profile indicated by reference numeral 1301 is a measurement result at 200 ° C., and the profiles indicated by reference numerals 1302 to 1310 are 180 ° C., 160 ° C., 140 ° C., 120 ° C., 100 ° C., 80 ° C., 60 ° C., and 40 ° C., respectively. And 25 ° C. measurement results.

As shown in FIG. 18, at any temperature, the capacitance profile was low at high frequencies and high at low frequencies, with a transition region approximately 10 ³ Hz wide in the middle. This transition region is located on the higher frequency side as the temperature is higher and the conductivity is higher. At 200 ° C., the center of the transition region is approximately 10 kHz. On the other hand, at 25 ° C., the center of the transition region was about 0.2 Hz based on the decrease in conductivity. From this result, it was confirmed that the change in conductivity of the gas sensing element can be measured as the change in capacitance profile. When the above measurement results are fitted on the assumption that the equivalent circuit of the gas sensor according to the present embodiment is the circuit described in FIG. 6, the conductivity of the gas detection element is about 10 ⁻¹¹ (Ωcm) ⁻¹ to about 10 ^−. It was estimated to change in the range of ⁶ (Ωcm) ⁻¹ .

Therefore, when the gas is adsorbed, the same change in conductivity occurs, and it was confirmed that the adsorption amount can be estimated from the capacitance profile.
As a general tendency of the profile, the capacitance on the low frequency side increased as the temperature increased. As a result of simulation, it was estimated that the capacitance of the electrostatic capacitance portion increased when the temperature was high. Specifically, what was about 15 nF at 25 ° C. was calculated to increase to about 35 nF at 200 ° C.

The reason why the capacitance increases in this way is not clear, but elements other than the natural oxide film constituting the capacitance portion, for example, a highly dielectric region formed in the vicinity of the interface with the natural oxide film of the gas sensing element is the temperature. It is considered that this is measured as a change in capacitance.
There was also a tendency for the capacitance to gradually increase on the low frequency side of the transition region. This is due to the fact that the resistance component included in the capacitance portion also varies with temperature.

(2) Example 2-2
In the manufacturing method of Example 2-1, a gas sensor was manufactured by the same manufacturing method except that the vapor deposition material was changed from Al to Au, and a similar start-up process was performed. After the start-up process is completed, the surface temperature of the gas sensor is maintained at approximately 200 ° C., and power is applied to the two extraction electrodes from a power source that can arbitrarily change the frequency of the applied voltage in the range from 0.01 Hz to 10 MHz. The terminal was connected. And the wiring from the terminal of the power supply which can change an applied frequency from 0.01 Hz to 10 MHz was connected to this extraction electrode, maintaining an applied voltage at 50 mV, and the impedance was measured. The conductance of the gas sensor was calculated from the measured impedance, and the conductance profile when the surface temperature of the gas sensor was 200 ° C. was obtained. Thereafter, similar to Example 2-1, a plurality of conductance profiles were measured while cooling the surface temperature of the gas sensor.

  The result is shown in FIG. The profile indicated by reference numeral 1401 is a measurement result at 200 ° C., and the profiles indicated by reference numerals 1402 to 1410 are 180 ° C., 160 ° C., 140 ° C., 120 ° C., 100 ° C., 80 ° C., 60 ° C., and 40 ° C., respectively. And 24 ° C. measurement results.

  As shown in FIG. 19, at any temperature, the conductance profile tended to be flat at low frequencies and increased at high frequencies. Moreover, the frequency which started to increase was so low that temperature was low, ie, the electrical conductivity of the gas detection element was low.

(3) Example 2-3
A gas sensor was manufactured by the same manufacturing method as that of Example 2-2, and a similar start-up process was performed. After the start-up process is completed, with the surface temperature of the gas sensor maintained at approximately 210 ° C., terminals from the power source that can arbitrarily change the frequency of the applied voltage in the range from 5 Hz to 5 MHz are provided at the two extraction electrodes. Connected. And the wiring from the terminal of the power supply which can change an applied frequency from 0.01 Hz to 10 MHz was connected to this extraction electrode, maintaining an applied voltage at 50 mV, and the impedance was measured. The capacitance of the gas sensor was calculated from the measured impedance, and the capacitance profile when the surface temperature of the gas sensor was 210 ° C. was obtained. The results are indicated by black circles (●) in FIG.

  Next, a 1 nF (1000 pF) commercially available capacitor was interposed between the extraction electrode and the power supply terminal, and the surface temperature of the gas sensor was maintained at 210 ° C. to obtain a capacitance profile. The result is indicated by a triangle (Δ) in FIG.

  Subsequently, the 1 nF (1000 pF) capacitor was replaced with a 10 nF (10000 pF) commercially available capacitor, and the surface temperature of the gas sensor was similarly maintained at 210 ° C. to obtain a capacitance profile. The result is indicated by a diamond (◇) in FIG.

  As shown in FIG. 20, when no capacitor is interposed, the capacitance profile is almost flat and does not change. However, when a 1 nF capacitor is interposed, the capacitance increases in the low frequency region, and the transition region extends from 2 kHz to 50 kHz. Measured. Further, when a 10 nF capacitor was interposed, the capacitance in the low frequency region was further increased, and the transition region was measured from 20 Hz to 50 kHz.

  As a result, it is possible to obtain a capacitance profile by providing an external capacitor even with an electrical element having a simple structure in which electrodes made of an inert metal layer are formed at both electrical ends of the gas sensing element. It was confirmed that the capacitance profile can be arbitrarily adjusted by using an external capacitor.

It is a conceptual diagram which shows the gas measurement system which concerns on 1st embodiment of this invention. It is a conceptual diagram which shows the structure of the gas sensor which concerns on 1st embodiment of this invention, (a) is a top view, (b) is sectional drawing in the AA cross section in (a), (c) is (a). It is sectional drawing in BB cross section in. It is a partial circuit diagram showing an equivalent circuit of the gas sensor according to the first embodiment of the present invention. It is a graph which shows an example of the capacitance profile obtained by the gas measurement system which concerns on 1st embodiment of this invention, and its fitting result. It is a graph which shows the capacitance profile obtained by simulation of the equivalent circuit of the gas sensor which concerns on 1st embodiment of this invention. It is a partial circuit diagram showing an equivalent circuit when the gas sensor according to the first embodiment of the present invention is strictly interpreted. It is a figure which shows notionally the structure of the modification (when forming the electrostatic capacitance part containing a dielectric addition layer integrally with a gas detection element) of the gas sensor which concerns on 1st embodiment of this invention, (a ) Shows a case where a dielectric additional layer is formed between the gas sensing element and the inert metal layer, and (b) shows that an inert metal layer is directly formed on the gas sensing element, and further, a dielectric additional layer is formed at both ends thereof. The case where it forms is shown. It is a figure which shows notionally the structure of the modification (when forming an electrostatic capacitance part separately from a gas detection element) of the gas sensor which concerns on 1st embodiment of this invention. It is a figure which shows notionally the structure of the modification (combination of integral formation and separate body formation) of the gas sensor which concerns on 1st embodiment of this invention. It is a graph which shows the conductance profile obtained by simulation of the equivalent circuit of the gas sensor which concerns on 1st embodiment of this invention. It is a partial circuit diagram which shows the equivalent circuit of the gas sensor which concerns on 2nd embodiment of this invention. It is a graph which shows the conductance profile obtained by simulation of the equivalent circuit of the gas sensor which concerns on 2nd embodiment of this invention. It is a graph which shows the measurement result of oxygen in 250 ° C by the gas sensor concerning Example 1-1. It is a graph which shows the measurement result of the water | moisture content in 250 degreeC by the gas sensor which concerns on Example 1-2. It is a graph which shows the measurement result of the water | moisture content in 150 degreeC by the gas sensor which concerns on Example 1-3. It is a graph which shows the measurement result of oxygen in 250 ° C by the gas sensor concerning Example 1-4. 6 is a graph showing the measurement results of oxygen at 250 ° C. by the gas sensor according to Comparative Example 1. It is a graph which shows the measurement result (circle mark) of the capacitance profile in each temperature by the gas sensor which concerns on Example 2-1, and the fitting result (solid line) with respect to these. It is a graph which shows the measurement result of the conductance profile in each temperature by the gas sensor which concerns on Example 2-2. It is a graph which shows the measurement result of a capacitance profile when the gas sensor which concerns on Example 2-3 as it is, and when an external capacitor of 1 nF and 10 nF is connected.

Claims (13)

A gas sensing element having a dielectric semiconductor, the conductivity of which varies depending on the state of gas adsorption;
A capacitance unit connected in series to the gas sensing element;
A pair of electrodes respectively connected to electrical ends of electrical elements including the gas sensing element and the capacitance part;
The capacitance of the capacitance unit is a gas sensor larger than the capacitance of the gas sensing element,
That the electrical response of the gas sensor changes depending on the voltage periodically changes include inversion applied to the pair of electrodes, and detects the adsorption state of gas into the gas detection device Characteristic gas sensor.   The gas sensor according to claim 1, wherein the capacitance unit is configured by a plurality of members.   A metal layer formed directly on a surface forming at least one of the electrical ends of the gas detection element, and the metal of the metal layer is modified at an interface portion of the metal layer on the gas detection element side The gas sensor according to claim 1, further comprising a dielectric modification layer, wherein the dielectric modification layer forms at least a part of the capacitance portion.   The gas sensor according to claim 3, wherein the dielectric modification layer is an oxide film formed by oxidizing the metal of the metal layer by oxygen that has passed through the gas detection element.   A dielectric layer formed directly on a surface forming at least one of the electrical ends of the gas sensing element, wherein the dielectric layer forms at least a part of the capacitance part and is connected to the gas sensing element; The gas sensor according to claim 1, wherein charge injection is prevented.   The gas sensor according to any one of claims 1 to 5, wherein the dielectric semiconductor is a fullerene material having a characteristic that conductivity is reduced by gas adsorption.   The gas sensor according to claim 1, wherein the dielectric semiconductor is an organic semiconductor.   The gas sensor according to claim 1, wherein the dielectric semiconductor is a carbon nanomaterial. The gas sensor according to claim 1, comprising: a gas detection element having a dielectric semiconductor, the conductivity of which varies depending on a gas adsorption state; and a pair of electrodes connected to the gas detection element. A gas detection module used,
Connect the capacitance part electrically in series with the gas detection module,
Applying a periodically changing voltage including polarity reversal to the electrical end of the gas sensor including the gas detection module and the capacitance unit,
A gas detection module for a gas sensor, wherein an adsorption state of a gas to the gas detection element can be detected from an electrical response of the gas sensor to the voltage application.   A gas sensor according to any one of claims 1 to 8, a power source capable of applying a periodically changing voltage including polarity reversal at an electrical end of the gas sensor, and a voltage applied by the power source A gas measurement system comprising: a measurement unit that measures an electrical response of the gas sensor.   A polarity at an electrical end of a gas sensor including the gas detection module according to claim 9, a capacitance unit connected in series to the gas detection module, and the gas detection module and the capacitance unit. A gas measurement system comprising: a power source capable of applying a periodically changing voltage including inversion; and a measuring means for measuring an electrical response of the gas sensor to a voltage applied by the power source.   The gas measurement system according to claim 10 or 11, further comprising gas desorption means for desorbing the gas adsorbed on the dielectric semiconductor.   Further comprising a temperature measuring means for measuring the temperature of the gas sensor, the temperature measuring means having the same configuration as the gas sensor and sealed so that the gas detection element does not adsorb gas. The gas measurement system according to any one of claims 10 to 12.

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