JP2007271577A - Sensor head and gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor head and a gas sensor having a wide dynamic range for hydrogen gas detection, high sensitivity and high-speed response, wherein output fluctuation does not occur being influenced by a using environment. <P>SOLUTION: This sensor head is equipped with a container 64, 65, 66 transmissible selectively only by hydrogen gas, having sealability to gases other than the hydrogen gas; a three-dimensional substrate 40 having a curved surface for defining a circulation band enabling multiple circulation of a collimated surface acoustic wave; an electric sound transducer element positioned on the circulation band of the three-dimensional substrate 40, for exciting the surface acoustic wave along the circulation band; and a sensitive film 25 at least a part of which exists on at least a part of the circulation band of the three-dimensional substrate 40, to be reacted with hydrogen gas molecules. The sensor head includes hydrogen gas detection parts 25, 27, 40 stored inside the container 64, 65, 66. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sensor head for detecting leakage and measuring the concentration of hydrogen gas in the atmosphere, a gas phase chemical process, or an environment using hydrogen gas, and a hydrogen gas sensor using the sensor head.

As a solution to today's global energy and environmental problems, high energy efficient and clean hydrogen energy utilization systems such as fuel cells are expected. However, hydrogen (H ₂ ) has a lower ignition temperature (530 ° C.), lower ignition energy (0.02 mJ), and a wider explosion limit (4) than methane (CH ₄ ), which is the main component of natural gas. ˜75%) and high combustion rate (2.65 m / s). Therefore, for the spread of hydrogen energy, a sensor device for hydrogen gas leak detection and concentration measurement for managing the safety of production, transportation, and use of hydrogen is indispensable.

  Currently, hydrogen gas sensors are used in special fields such as oil refining, semiconductor factories, and space industry rockets, but in the future, fuel cell vehicles, industrial stationary fuel cells, and household stationary fuel cells will become widespread. At the same time, the demand for hydrogen gas sensors is expected to increase significantly.

  The performance required for this hydrogen gas sensor is, for example, high sensitivity (0.1% -10%), low operating temperature (-30 ° C to 80 ° C), and stability in the case of a hydrogen leak or leak sensor. High selectivity for hydrogen gas, fast response speed (<1 s), and low cost. However, none of the contact combustion sensors, semiconductor sensors, and surface acoustic wave sensors that are currently on the market satisfy the above performance.

  In the contact combustion type sensor, since the hydrogen concentration is measured from the calorific value when the gas burns using the oxidation catalyst, it reacts with all combustible gases other than hydrogen and has a high operating temperature.

A semiconductor sensor using an adsorption phenomenon measures a hydrogen concentration from a change in electrical conductivity when hydrogen molecules are adsorbed on the surface of a metal oxide semiconductor such as tin oxide (SnO ₂ ). This method has a high response speed and can detect a hydrogen concentration of several tens of ppm. However, the sensor output is saturated as the hydrogen concentration increases, so it is limited to the measurement on the low concentration side (up to 0.2%). The If a platinum film is formed on the SnO ₂ surface as a catalyst, the output of the sensor is higher than that of other combustible gases, but is still affected by carbon monoxide and other combustible gases.

  Therefore, in recent years, various types of sensors such as semiconductor type, optical type, surface acoustic wave type, thermoelectric type, and electrochemical type are competing for higher performance. Among them, in the semiconductor type, optical type, and surface acoustic wave type, a palladium (Pd) or palladium alloy film having a characteristic of selectively absorbing and releasing hydrogen is formed on the sensor surface, thereby preventing hydrogen gas. It is said to have selectivity.

However, in 1996, it has been reported that other gases such as carbon monoxide (CO) or nitrogen monoxide (NO) other than hydrogen also have a characteristic change of the film itself (see Non-Patent Document 1). ).
V. I. Anisimkin and five others, “REAL TIME CHARACTERIZATION OF ELASTIC VARIATIONS IN PALLADIUM FILMS PRODUCED BY HYDROGEN ADSORPTION, American Institute of Electronics and Electrical Engineers (IEEE) Ultrasonic Symposium (ULTRASONICS SYMPOSIUM ), P293, 1996

  As can be seen from the above explanation, fuel cell vehicles that require high safety in the living environment of the general atmosphere, hydrogen stations that use high-pressure and high-concentration hydrogen gas, or hydrogen gas from natural gas in high-temperature and high-humidity conditions. In the fields of industrial stationary fuel cells or household stationary fuel cells that purify and convert energy into hydrogen, leakage of hydrogen gas can be detected under the influence of high temperature and high humidity and other gases, or hydrogen gas Therefore, a sensor head and a gas sensor that can detect the concentration of gas are desired.

  The present invention provides a sensor head having a wide dynamic range for hydrogen gas detection, high sensitivity, high speed response, and no fluctuation in output due to the influence of the use environment such as high temperature and high humidity and the presence of other gases. An object of the present invention is to provide a gas sensor using a sensor head.

  In order to achieve the above object, the first aspect of the present invention is (i) a container that selectively transmits only hydrogen gas and has a sealing property against gas other than hydrogen gas, and (b) collimated elasticity. A three-dimensional substrate having a curved surface defining a circumferential band in which surface waves can circulate multiple times, an electroacoustic transducer disposed on the circumferential band of the three-dimensional substrate, and exciting a surface acoustic wave along the circumferential band, at least a part of which The gist of the present invention is that the sensor head includes a hydrogen gas detection unit that is provided in at least a part of the circumference of the three-dimensional substrate, includes a sensitive film that reacts with hydrogen gas molecules, and is housed inside the container. Here, the “surface acoustic wave” includes all the elastic waves that are concentrated and propagate along the surface of the substrate. For example, pseudo Sezawa waves (leakage Sezawa waves) propagating while slightly leaking energy to the substrate, SH waves, and Love waves that can propagate through a film provided on the surface are included. The “circular band in which collimated surface acoustic waves can circulate multiple times” refers to the case where the widths of the circular bands are parallel, and the surface acoustic waves circulate with the narrowest width. The “three-dimensional substrate” has a first curvature in the first main direction along the center line of the orbital belt, and a second curvature in the second main direction orthogonal to the first main direction. It is preferable to have. However, the first curvature and the second curvature are not necessarily equal. The first curvature defined in the first main direction does not necessarily have a constant radius of curvature, but the curvature must have the same sign in any direction at least at every point on the propagation path. The second curvature defined in the second main direction does not necessarily have a constant radius of curvature. When viewed in a cross-sectional view along the second main direction, the second curvature is microscopic in the vicinity of the center line of the orbital zone. Can tolerate topologies that form a flat outer surface. That is, in the topology where the radius of curvature is infinite near the centerline of the orbital band, but the radius of curvature decreases continuously or stepwise as it moves away from the centerline of the orbital band along the second main direction. good. Just like a topology in which the end of the circumference of the abacus ball is cylindrical, or two cones are connected to each other at the bottom, and the end of the circumference that becomes the maximum diameter of the connection is made cylindrical Such a topology may be used.

  As a simple case, if a true sphere is considered as the “three-dimensional substrate”, the width of the orbital band is determined by the radius of the sphere and the wavelength of the surface acoustic wave. The wave number parameter defined by the ratio of the circumference of the sphere (true sphere) and the wavelength of the surface acoustic wave (or the product of the surface wave number and the radius of the sphere) and the width of the orbital zone and the radius of the sphere There is an approximately constant relationship between the collimating angles defined by the ratio. For example, in a 10 mm diameter crystal sphere, at a frequency of 45 MHz, the wave number parameter is 438, the collimating angle is about 8 °, and the width of the orbital band is about 7/100 of the diameter.

  As the “electroacoustic transducer for exciting the surface acoustic wave along the circulation band”, interdigital electrodes of an alternite phase array may be used. The longitudinal direction of the fingers of the interdigital electrode is orthogonal to the direction of the circular band, but the circular band needs to include the entire longitudinal direction of the interdigital electrode. In such a topology, the three-dimensional substrate may have a beer barrel shape or the like, or may have a bowl shape or a rugby ball type.

  As described above, a surface acoustic wave element that circulates on a closed curved surface other than a true sphere can be configured under certain conditions. Even on a curved surface other than a true sphere, a surface acoustic wave that is generated at one point and spreads in a ring shape can return to the same point after one round, but the return time differs depending on the propagation path on the curved surface, and the waveform is a time axis. Since it spreads above, the precision as a sensor which measures the change of propagation time or a circumference resonance frequency will fall. For this reason, a true sphere is most preferable as the topology of the “three-dimensional substrate” used in the sensor head according to the first aspect of the present invention.

  In any case, the “three-dimensional substrate” does not have to be a solid block, and may be a three-dimensional shape having a hollow portion (hollow portion) or a three-dimensional shape having an outer surface formed by a shell having a certain thickness. good. Therefore, the orbital band may be defined on the outer peripheral side surface of the three-dimensional substrate, or may be defined on the inner wall side surface of the hollow portion of the three-dimensional substrate.

  The surface acoustic wave propagating through the orbital band of the three-dimensional substrate used in the sensor head according to the first aspect of the present invention does not diffract and circulates multiple times. For example, according to the measurement result using a crystal ball having a diameter of 10 mm, the multiple rounds range from 300 rounds to 500 rounds. This shows that even if a smaller sphere having a diameter of 1 mm is used, the propagation distance is equivalent to an effective length of 900 mm in 300 laps. Compared with a conventional planar type (two-dimensional structure) surface acoustic wave element, the propagation distance is about two orders of magnitude longer. This means that in the propagation delay time measurement, the time resolution is improved by about two orders of magnitude compared to the conventional case, and the sensitivity is improved.

  The sensitive film used in the sensor head according to the first aspect of the present invention reacts with hydrogen gas molecules, that is, causes adsorption, occlusion, chemical reaction or catalytic chemical reaction of hydrogen gas molecules, and thereby the surface acoustic wave thereof. A material that changes the propagation characteristics is selected. For example, if hydrogen gas molecules are adsorbed on the sensitive film, the propagation speed of the surface acoustic wave is slowed and the damping factor of the vibration amplitude is increased due to the mass effect of the gas molecules. Alternatively, when the hydrogen gas molecule reacts with the sensitive film and changes to another compound, the elastic characteristics change, resulting in a difference in the surface acoustic wave propagation characteristics. The propagation characteristics of the surface acoustic wave also change due to a temperature change caused by the reaction between the hydrogen gas molecules and the sensitive film or a chemical reaction using the sensitive film as a catalyst. Therefore, the presence / absence, concentration, etc. of hydrogen gas molecules can be measured by detecting delay times, frequency changes, amplitudes, and output waveforms of multiple rounds of surface acoustic waves.

  The thickness of the sensitive film used in the sensor head according to the first aspect of the present invention is preferably 100 nm or less. Since the surface acoustic wave only needs to circulate around the sensitive film, the required amount of sensitive film is very small, and the cost can be greatly reduced by reducing the thickness of the sensitive film. Especially in the case of occlusion type sensitive membranes, the diffusion of hydrogen gas molecules into the sensitive membrane determines the response time, so the response time is shortened by making the sensitive membrane thinner, providing a more practical sensor. Because it can. Of course, if the thickness is the same, the sensitivity can be dramatically improved, and a sensitivity that could not be detected in the past can be obtained. In this case, the lower limit is a monomolecular layer, but usually it is preferably about 3 molecular layers or more. Furthermore, by making the sensitive film 100 nm or less, it is possible to realize a structure that is strong against repeated expansion and contraction of the film due to changes in external temperature and temperature of reaction heat of the film itself, and physical crystal structure changes due to chemical reaction and atomic absorption. .

  The thickness of the sensitive film is preferably 1/500 or less of the wavelength of the surface acoustic wave. More preferably, the thickness of the sensitive film should be 1/1000 or less of the wavelength of the surface acoustic wave.

Further, as the sensitive film for detecting hydrogen gas (H ₂ ), a film containing palladium (Pd) is suitable. “Pd-containing film” means a single Pd film, titanium / palladium (Ti—Pd), nickel / palladium (Ni—Pd), magnesium / palladium (Mg—Pd), gold / palladium (Au—Pd). ), Silver / palladium (Ag—Pd), or a palladium alloy film such as gold / silver / palladium (Au—Ag—Pd). Palladium absorbs 935 times its own volume of hydrogen. There may be an expensive material such as a sensitive film containing Pd. For example, if a sensitive film is formed on a part of the sphere surface, the cost can be reduced.

Various hydrogen storage alloy films may be used as a sensitive film for detecting hydrogen gas (H ₂ ). Hydrogen storage alloys are classified into AB ₅ type alloys, AB ₂ type alloys, etc. depending on the atomic ratio of A and B. As elements of the A site, magnesium (Mg), titanium (Ti), zirconium (Zr), vanadium ( V), metals belonging to Group 2A to 5A such as rare earth metals, and B site elements are composed of metals belonging to Group 6A to 8 such as iron (Fe) and nickel (Ni). AB ₂ type alloy is an alloy that becomes B-site element 2 with respect to A-site element 1, and is well known based on alloys of transition elements such as Ti, manganese (Mn), Zr, and Ni. ing. The crystal has a hexagonal base structure called Laves phase. The hydrogen density is high and the capacity can be increased, but the higher the capacity, the more difficult the activation is. On the other hand, the AB ₅ type alloy is a B site such as a transition element (Ni, cobalt (Co), aluminum (Al), etc.) having a catalytic effect on the element 1 of the A site such as rare earth elements, niobium (Nb), Zr and the like. This is based on an alloy containing the element 5, and is easy to hydrogenate from the initial stage, but it is difficult because it contains rare earth elements and cobalt, but a sensitive film is formed on part of the sphere surface. If you do it, you can make it cheaper.

In addition, Ti—Fe-based, V-based, Mg alloy, Ca-based alloy, and the like are also hydrogen storage alloy films and can be used as a sensitive film for detecting hydrogen gas (H ₂ ). The Ti—Fe-based hydrogen storage alloy film is based on a Ti—Fe-based which forms a body-centered cubic intermetallic compound having a relatively large number of voids. The V-based hydrogen storage alloy film is a body-centered cubic alloy having a relatively large number of voids based on V because V reacts efficiently with hydrogen. The hydrogen storage alloy film of Mg alloy stores as much as 7.6 wt% of hydrogen, but since magnesium hydride is relatively stable, an alloy with a catalyst element that destabilizes this is effective. The Ca-based alloy hydrogen storage alloy film is mainly made of an alloy of calcium and a transition element (such as nickel) having a strong affinity for hydrogen.

Further, as a sensitive film for detecting hydrogen gas (H ₂ ), it is possible to use a metal thin film having gas absorption Kettering properties such as titanium (Ti).

  In the second aspect of the present invention, (a) a container that selectively transmits only hydrogen gas and has a sealing property against a gas other than hydrogen gas, and (b) collimated surface acoustic waves can circulate multiple times. A three-dimensional substrate having a curved surface defining a loop, an electroacoustic transducer disposed on the loop of the three-dimensional substrate, and exciting a surface acoustic wave along the loop, at least a part of the loop of the three-dimensional substrate A hydrogen gas detection unit that is provided at least in part and includes a sensitive film that reacts with hydrogen gas molecules, and is housed inside the container; and (c) a high frequency generation unit that supplies a high frequency electrical signal to the electroacoustic transducer. (D) The gist of the present invention is a gas sensor including a detection / output unit for measuring a high-frequency signal related to propagation characteristics of surface acoustic waves from an electroacoustic transducer.

According to a second aspect of the present invention, there is provided a high-frequency generator for applying a high-frequency signal to the interdigital electrode constituting the electroacoustic transducer of the hydrogen gas detector described in the first aspect, and an elastic surface from the electroacoustic transducer. It has a detection / output unit that measures high-frequency signals related to wave propagation characteristics. The detection / output unit detects a high-frequency signal received from the electroacoustic transducer and measures the propagation characteristics of surface acoustic waves such as delay time, frequency, or amplitude, and changes in the propagation characteristics of hydrogen gas molecules. It has presence / absence and an output unit for converting and displaying the density. In the gas sensor according to the second aspect of the present invention having such a configuration, if hydrogen gas molecules are adsorbed to the sensitive film, the propagation speed of the surface acoustic wave becomes slow due to the mass effect of the gas molecules, and the vibration amplitude The attenuation factor of the is also increased. Alternatively, when the hydrogen gas molecule reacts with the sensitive film and changes to another compound, the elastic characteristics change, resulting in a difference in the surface acoustic wave propagation characteristics. The surface acoustic wave propagation characteristics also change depending on the temperature change caused by the reaction between the hydrogen gas molecules and the sensitive film, or the chemical reaction using the sensitive film as a catalyst. By detecting the output waveform, the presence or concentration of hydrogen gas molecules can be measured.

  According to the gas sensor of the second aspect of the present invention, an effective propagation length that is two orders of magnitude longer than that of a conventional planar surface acoustic wave element can be realized by using the multiple circulation phenomenon of surface acoustic waves. Therefore, the time resolution can be increased by two digits or more, and the sensitivity of the gas sensor can be increased. Further, as described in the first embodiment, particularly in the case of an occlusion type sensitive film, the diffusion of hydrogen gas molecules into the sensitive film determines the response time, so that the response can be achieved by making the sensitive film thin. Time can be shortened and more practical sensors can be supplied. Further, by making the sensitive film thin, it is possible to make the structure strong against repeated expansion and contraction of the film due to external temperature change and temperature change of reaction heat of the film itself, and physical crystal structure change due to chemical reaction and atomic absorption.

  In the second aspect of the present invention, it is preferable that the high-frequency generator and the detection / output unit be integrated on the three-dimensional substrate because the gas sensor can be miniaturized.

  According to the present invention, the sensor head has a wide dynamic range for hydrogen gas detection, high sensitivity, high-speed response, and does not fluctuate in output due to the influence of the use environment such as high temperature and high humidity and the presence of other gases. And a gas sensor using this sensor head can be provided.

  Next, first to fourth embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The first to fourth embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the component parts. The material, shape, structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the technical scope described in the claims.

(First embodiment)
As shown in FIGS. 1 and 2, the sensor head according to the first embodiment of the present invention is a container (64, 64) that selectively permeates only hydrogen gas and has sealing properties against gases other than hydrogen gas. 65, 66) and a three-dimensional substrate 40 having a curved surface that defines a circumferential band in which collimated surface acoustic waves can circulate multiple times. An electroacoustic transducer to be excited, and at least part of which is present in at least part of the circumference of the three-dimensional substrate 40 and includes a sensitive film 25 that reacts with hydrogen gas molecules, and the interior of the container (64, 65, 66). And a hydrogen gas detector (25, 27, 40) housed in the container.

  As shown in FIGS. 1 and 2, the container (64, 65, 66) includes a container body (64, 65) including a mounting substrate (package substrate) 64 on which the three-dimensional substrate 40 is mounted, and selective hydrogen gas permeation. And a package upper cover 66 including a filter. The package upper lid 66 includes a mesh structure substrate 662 and a hydrogen permeable film 661 on the mesh structure substrate 662. The hydrogen permeable film 661 may be made of palladium (Pd), a palladium alloy thin film, or a hydrogen storage alloy film. The mesh structure substrate 662 may be formed by opening a rectangular through hole as shown in FIGS. 1 and 2 by using a reactive ion etching (RIE) or the like on a semiconductor substrate such as silicon (Si). For example, if anisotropic etching by RIE is performed using an etching mask formed in a lithography process using a Si (100) surface, through holes surrounded by the (100) surface as shown in FIGS. 1 and 2 are formed. It can be formed in a matrix.

  Further, the package upper lid 66 includes a micro heater 665 embedded in the mesh structure substrate 662. The microheater 665 is a resistance wire heater made of a metal such as Al, tungsten (W), molybdenum (Mo), etc., and an etching mask formed in a lithography process is used to form a groove by RIE, and a vacuum is formed inside the groove. If embedded by vapor deposition or sputtering, a meander-line resistance wire heater as shown in FIGS. 1 and 2 can be formed. By heating and raising the temperature of the hydrogen permeable membrane 661 to a predetermined temperature with the microheater 665, the package upper lid 66 functions as a selective hydrogen gas permeable filter, and hydrogen is selectively introduced into the container. be able to. Although the heating temperature depends on the material constituting the hydrogen permeable membrane 661, the Pd film may be heated to a low temperature of about 300 ° C. to 500 ° C., and the Pd alloy film may be heated to a low temperature of 100 ° C. or more.

  As shown in FIG. 3, the hydrogen gas detection unit (21, 27, 40) includes a three-dimensional substrate 40 having a curved surface defining a circulation zone B in which a collimated surface acoustic wave can circulate multiple times, and the three-dimensional substrate. The electroacoustic transducer 21 is located on the orbital zone B 40 and excites surface acoustic waves along the orbital zone B, and is present in almost the entire region of the orbital zone B of the three-dimensional substrate 40 and reacts with hydrogen gas molecules. The sensitive film 25 is provided.

A homogeneous material sphere 40 made of a piezoelectric crystal is used as the three-dimensional substrate 40. As the homogeneous material sphere 40, for example, a single crystal sphere such as quartz, LiNbO ₃ , LiTaO ₃ , piezoelectric ceramic (PZT), bismuth germanium oxide (Bi ₁₂ GeO ₂₀ ), or langasite (La ₃ Ga ₅ SiO ₁₄ ) is employed. Is possible. A sensitive film 25 is provided on almost the entire surface of the homogeneous material sphere 40. Further, as shown in FIG. 3, an opening of the sensitive film 25 that exposes a part of the surface of the homogeneous material sphere 40 exists in a part of the homogeneous material sphere 40 on the equator, and the inside of the opening is inside. Interdigital electrodes 21 are arranged. Here, the “equator” means a line passing through the center of the homogeneous material sphere 40 shown in FIG. 3A and intersecting the surface of the homogeneous material sphere 40 with a plane orthogonal to the crystal direction of the arrow A.

  In the case of a single crystal crystal sphere such as the homogeneous material sphere 40, the route around which the surface acoustic wave circulates is limited to the orbital zone B. For example, if one of the trigonal crystal axes is set in the direction of arrow A shown in FIG. 3A, a surface acoustic wave circulates in a belt-like circulation band B having a certain width around the equator. From the propagation characteristics of surface acoustic waves, it is desirable to take the Z axis of the homogeneous material sphere 40 in the direction of arrow A.

  The interdigital electrode 21 is a so-called alternite phase array, which excites a surface acoustic wave by piezoelectrically converting a high-frequency electric signal supplied from a high-frequency generator 22 via a switch unit 23. Further, the interdigital electrode 21 also has a function of converting a surface acoustic wave that has circulated around the belt-like orbital band B on the equator into a piezoelectric wave and converting it into a high-frequency electric signal again. The high frequency electrical signal converted into the high frequency electrical signal again by the interdigital electrode 21 is supplied to the detection / output unit 24 via the switch unit 23 and detected by the detection / output unit 24. The switch unit 23 switches between the high frequency generation unit 22 and the detection / output unit 24. A high-frequency electrical signal from the high-frequency generator 22 is supplied to the interdigital electrode 21, and after the interdigital electrode 21 sends out the surface acoustic wave, the surface acoustic wave of the predetermined number of turns (n-th turn: n ≧ 1) is generated. Before returning, the signal path from the interdigital electrode 21 is switched to the detection / output unit 24. Of course, a directional coupling circuit or the like from the high frequency generator 22 to the interdigital electrode 21 and from the interdigital electrode 21 to the detection / output unit 24 may be used.

As the interdigital electrode 21 constituting the alternite phase array, for example, a metal film such as aluminum (Al) or gold (Au) can be employed. In order to increase the number of multiple turns in the orbital zone B on the equator, a light metal with a small mass effect on the surface acoustic wave is desirable as the material of the interdigital electrode 21, and a thinner metal film is preferable. desirable. Separate interdigital electrodes may be provided on the transmitting side and the receiving side. However, in the element in which the surface acoustic wave circulates on the equator of the homogeneous material sphere 40, the surface acoustic wave returns, so one interdigital electrode It is effective to share 21 by time division.

As shown in FIG. 3 (a), the interdigital electrode 21 used to excite and receive the surface acoustic wave has a longitudinal direction perpendicular to the equator direction on the surface of the homogeneous material sphere 40. good. The length of the interdigital electrode 21 is determined by the velocity of the surface acoustic wave, the radius of the homogeneous material sphere 40, and the like, and by designing to an optimum value, the surface acoustic wave having a certain width can be circulated in multiple rounds.

When the length of the interdigital electrode 21 is shorter than the optimum value, the width of the surface acoustic wave becomes maximum when it circulates by 90 ° in angle, and returns to the original width at the next 90 ° lap, and this is repeated thereafter. On the other hand, when the length of the interdigital electrode 21 is longer than the optimum value, the width of the surface acoustic wave is minimized when it circulates by 90 ° in angle, and returns to the original width at the next 90 ° lap, and so on. . Therefore, the length of the interdigital electrode 21 may be designed by a desired propagation path. The repetition period of the interdigital electrode 21 constituting the alternite phase array is designed so as to obtain a desired frequency characteristic from the velocity of the surface acoustic wave and the radius of the homogeneous material sphere 40. The shorter the repetition period, the higher the resonance frequency for the surface acoustic wave, and the higher the efficiency of interaction with the surface, the higher the sensitivity. The greater the number of repetitions, the narrower the resonance width and the higher the Q value.

The sensitivity as the hydrogen gas detection unit depends on the material and structure of the sensitive film 25 formed on the surface of the homogeneous material sphere 40. The sensitive film 25 needs to change the elastic surface propagation characteristics by contacting with hydrogen gas. For example, gas may be adsorbed on the surface, and the propagation speed of the surface acoustic wave may be slowed by the mass effect, or the propagation intensity may be attenuated by the mass effect. Alternatively, the gas may be occluded in the sensitive film 25, and the mechanical rigidity of the thin film may be changed to change the propagation speed and attenuation of the surface acoustic wave. Furthermore, it may cause an endothermic or exothermic reaction by reacting with a gas and affect the propagation speed and attenuation of the surface acoustic wave. It is desirable that the sensitive film 25 is a material that selectively reacts only with a specific gas and that causes a reversible reaction.

For example, as such a sensitive film 25, palladium (Pd), a palladium alloy thin film, another hydrogen storage alloy film, or titanium that stores hydrogen (H ₂ ) and forms a hydride to change mechanical properties. A metal thin film having gas absorption Kettering properties such as (Ti) is preferable.

In the hydrogen gas detection unit according to the first embodiment, after a surface acoustic wave is transmitted from the interdigital electrode 21, the propagation characteristics such as delay time and amplitude of the surface acoustic wave after a specific number of rounds are measured. By doing so, it is possible to measure the adsorbed or occluded state of hydrogen gas molecules, and the presence or concentration of hydrogen gas molecules.

As shown in FIGS. 1 and 2, the container body (64, 65) has a package sidewall (65) whose bottom is connected to the periphery of the mounting substrate (package substrate) 64 and whose top is connected to the periphery of the package upper lid 66. The three-dimensional substrate 40 is mounted on a parallel plate-shaped mounting substrate 64 using a plurality of metal bumps 50a, 50b,... As the conductive connecting members 50a, 50b, and the present invention. The sensor head according to the first embodiment is configured. The package side wall 65 functions as a spacer that adjusts the distance between the package upper lid 66 and the mounting substrate (package substrate) 64 in consideration of the diameter of the hydrogen gas detector.

The mounting substrate (package substrate) 64 and the package side wall 65, or the package side wall 65 and the package upper lid 66 are bonded to each other with, for example, an adhesive having heat resistance at high temperature and high sealing performance so as to keep confidentiality. The The mounting substrate (package substrate) 64 and the package side wall 65, and the package side wall 65 and the package upper lid 66 may be bonded at high temperature using an alloy adhesive layer, or may be bonded using a low melting glass material or the like. You may do it.

More specifically, a plurality of internal mounting wires 61a, 61b,... Are patterned on the mounting substrate 64, and a plurality of metals are formed on the plurality of internal mounting wires 61a, 61b,. A hydrogen gas detector is mounted using the bumps 50a, 50b,. The plurality of metal bumps 50a, 50b,... Are solder balls, gold (Au) bumps, silver (Ag) bumps, copper (Cu) bumps, nickel / gold (Ni-Au) bumps, or nickel / gold. / Indium (Ni-Au-In) bumps can be used. As the solder balls, eutectic solder of tin (Sn): lead (Pb) = 6: 4 having a diameter of 100 μm to 250 μm and a height of 50 μm to 200 μm can be used. Alternatively, Sn: Pb = 5: 95 solder may be used. It is used and can be bonded by a combination of thermocompression bonding and ultrasonic vibration or heat melting.

As the material of the mounting substrate 64, inorganic materials such as various organic synthetic resins, ceramics, and glass can be used. As the organic resin material, phenol resin, polyester resin, epoxy resin, polyimide resin, fluororesin, etc. can be used, and the base material used as a core when making a plate is paper, glass cloth, glass base Materials are used. A common inorganic substrate material is ceramic. In addition, glass is used when a metal substrate or a transparent substrate is required to enhance heat dissipation characteristics. As the material for the ceramic substrate, alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), beryllia (BeO), aluminum nitride (AlN), silicon nitride (SiC), or the like can be used. Further, a metal base substrate (metal insulating substrate) in which a polyimide resin plate having high heat resistance is laminated on a metal such as iron or copper may be used. As the plurality of internal mounting wirings 61a, 61b,..., Metal thin films such as gold, copper, and aluminum can be used.

In the homogeneous material sphere 40, since the circumferential band B of the surface acoustic wave is limited to the vicinity of the equator, a plurality of metal bumps 50a, 50b,... 40 may be fixed. A metal pad (bonding pad) for attaching the plurality of metal bumps 50a, 50b,... Is installed avoiding the circumferential band B of the surface acoustic wave.

  As shown in FIG. 1, a plurality of via plugs 62a, 62b are provided inside a mounting substrate (package substrate) 64 so as to be electrically connected to a plurality of internal mounting wirings 61a, 61b,. , ... are embedded. The plurality of external mounting wirings 63a are electrically connected to the plurality of via plugs 62a, 62b,..., Respectively, so as to enable connection to the external circuit of the container (64, 65, 66). , 63b,... Are provided on the back surface of the mounting substrate (package substrate) 64.

1 and 2, the high frequency generator and the detection / output circuit are not particularly shown, but the high frequency generator and the detection / output unit include a plurality of external mounting wires 63a, 63b,... -You may arrange | position outside a container (64, 65, 66) so that it may connect via.

Further, in the sensor head according to the first embodiment, it is preferable to flow hydrogen gas, which is a gas to be measured, in parallel with the surface of the mounting substrate 64.

The gas sensor using the sensor head according to the first embodiment has, for example, the detection / output unit 24 having a resolution of 1 ns (0.1%) when the propagation length is about 3 mm and 1 μs. In this case, if measurement is performed with a resolution of 1 ns after 100 μs, a resolution of 10 ppm, which is 1/100 of the conventional one, can be measured.

  As described above, according to the first embodiment, the detection range (dynamic range) of hydrogen gas is wide from 10 [ppm] to 100%, has high-speed response, and is in a high temperature and high humidity or other gas. It is possible to provide a sensor head and a gas sensor whose output does not fluctuate even in the presence of.

<First Modification>
As shown in FIG. 4, the hydrogen gas detection unit of the sensor head according to the first modification of the first embodiment of the present invention has a curved surface that defines an orbital band B in which a collimated surface acoustic wave can circulate multiple times. Of the three-dimensional substrate 40, the electroacoustic transducer 21 that is located on the orbital band B of the three-dimensional substrate 40 and excites a surface acoustic wave along the orbital band B, and the orbital band B of the three-dimensional substrate 40. And a sensitive film 26 that reacts with hydrogen gas molecules present in part. The three-dimensional substrate 40 is a homogeneous material sphere 40 similar to that of the first embodiment, but the point that the sensitive film 26 is provided only on a part of the homogeneous material sphere 40 is different from the first embodiment. Is different. And the interdigital electrode 21 as the electroacoustic transducer 21 is arrange | positioned in a part on the equator of the homogeneous material ball | bowl 40 in which the sensitive film | membrane 26 does not exist.

That is, in the hydrogen gas detection unit according to the first modification of the first embodiment, the sensitive film 26 is provided only on a portion of the surface of the homogeneous material sphere 40 that is located on the opposite side of the interdigital electrode 21. . As the homogeneous material sphere 40, a single crystal sphere such as quartz, LiNbO ₃ , LiTaO ₃ or the like similar to the hydrogen gas detection unit according to the first embodiment can be adopted, but the first sphere of the first embodiment is used. In the hydrogen gas detection unit according to the modification, a case of a crystal ball having a diameter of 10 mm will be described. The sensitive film 26 was a Pd film, and was formed into a circular region having a diameter of about 6 mm on the surface band of the surface acoustic wave by vacuum deposition to a thickness of 20 nm. Since Pd selectively absorbs only hydrogen and forms a hydrogen alloy, it is a highly selective hydrogen gas sensor. Further, since Pd can be formed only on the upper surface of the spherical surface acoustic wave element by vacuum deposition after the interdigital electrode 21 is formed and assembled, it is easy to manufacture.

When the sensitive film 26 is expensive as a material such as Pd, if the sensitive film 26 is formed on a part of the sphere surface as shown in FIG. 4, the required amount of the sensitive film 26 is very small, and the cost is reduced. Can be greatly reduced. Therefore, the industrial value of the hydrogen gas detection unit according to the first modification of the first embodiment is very high.

Here, reference is made to the limit sensitivity to hydrogen of the gas sensor according to the first modification of the first embodiment. In order to evaluate the response time to hydrogen, a wavelet transform using a Gabor function having excellent time and frequency resolution as a mother wavelet is applied to the waveform of the 41st round, and the times 403.040 s to 403. A time at which the real part of the wavelet transform is maximized during 060 s was obtained and used as a delay time. The measurement sampling time was 0.5 ns, but when wavelet analysis was interpolated at a time interval of 0.025 ns, a significant change was seen at a resolution of 0.025 ns. On the other hand, since the total delay time is 403 μs, the relative time accuracy is 0.025 / 403000 = 60 ppb. This corresponds to 30 ppm in terms of hydrogen gas concentration. This means that if the number of laps is set to 300 laps, hydrogen concentration accuracy in the ppm range can be achieved. Conversely, if the Pd film is made thinner while maintaining the same sensitivity, the response time can be further shortened. Such extreme measurement accuracy is made possible by the super multi-turn by non-diffracting propagation, which is a characteristic characteristic of the surface acoustic wave of the homogeneous material sphere 40.

  Currently available hydrogen gas sensors are of catalytic combustion type and semiconductor type. The catalytic combustion method also responds to combustible gases other than hydrogen, and there is a problem in selectivity. The catalytic combustion method can be used only at a high concentration and the semiconductor method can be used only at a low concentration, and cannot be used over a wide concentration range. As described above, in a hydrogen gas sensor using a planar surface acoustic wave element, response time is a problem. Therefore, conventionally, there has not been a hydrogen gas sensor that satisfies all of selectivity, sensitivity and dynamic range, response time, etc., but the gas sensor according to the first modification of the first embodiment is very selective. It is an excellent hydrogen gas sensor in all respects, having excellent sensitivity in ppm, dynamic range up to 100%, and response time within 4 seconds at room temperature and within 2 seconds at 130 ° C.

<Second Modification>
As shown in FIG. 5, the hydrogen gas detection unit of the sensor head according to the second modification of the first embodiment of the present invention is configured such that a piezoelectric material is applied to at least a part of a homogeneous material sphere 40 made of a homogeneous material having elastic properties. A conductive thin film 41 is formed. Since the piezoelectric thin film 41 is formed on the surface, unlike the first embodiment and the first modified example, the homogeneous material sphere 40 may be a substance having no piezoelectricity (non-piezoelectric substance). For this reason, as a material of the homogeneous material sphere 40, a glass material such as an amorphous material such as borosilicate glass or quartz glass can be employed. As the piezoelectric thin film 41, cadmium sulfide (CdS), zinc oxide (ZnO), zinc sulfide (ZnS), aluminum nitride (AlN), or the like can be used. These thin films can be formed by a known sputtering method, vacuum deposition method, or the like. Then, it may be deposited on the surface of the homogeneous material sphere 40.

A sensitive film 25 is provided on the surfaces of the homogeneous material sphere 40 and the piezoelectric thin film 41. The piezoelectric thin film 41 only needs to be in the vicinity of the interdigital electrode 21 used for exciting and receiving surface acoustic waves. A surface acoustic wave cannot be excited by the interdigital electrode 21 directly on the surface of the non-piezoelectric material. This is because the crystal is not distorted even when an electric field is applied. Therefore, if there is at least the piezoelectric thin film 41 in the vicinity of the interdigital electrode 21, such as directly under the interdigital electrode 21, it is possible to excite and receive the surface acoustic wave. The high frequency generation unit 22, the switch unit 23, and the detection / output unit 24 are the same as those of the gas sensor according to the first embodiment, and redundant description is omitted.

FIG. 5B shows a cross-sectional structure of the hydrogen gas detection unit according to the second modification of the first embodiment shown in FIG. The design of the interdigital electrode 21 is not different from that of the hydrogen gas detection unit according to the first embodiment. In the cross-sectional view shown in FIG. 5B, the interdigital electrode 21 is formed on the piezoelectric thin film 41. However, the position of the interdigital electrode 21 is not limited to this. It may be between the piezoelectric thin films 41 or may be structured such that the upper and lower sides of the piezoelectric thin film 41 are sandwiched between a pair of interdigital electrodes 21. In any case, the circumferential band B of the surface acoustic wave becomes a direction perpendicular to the longitudinal direction of the interdigital electrode 21, and an arbitrary direction can be selected.

  The sensitivity of the hydrogen gas detection unit is determined by the material and structure of the sensitive film 25 formed on the surface of the homogeneous material sphere 40. The sensitive film 25 needs to change the elastic surface propagation characteristics by contacting with hydrogen gas. For example, gas may be adsorbed on the surface, and the propagation speed of the surface acoustic wave may be slowed by the mass effect, or the propagation intensity may be attenuated by the mass effect. Alternatively, the gas may be occluded in the sensitive film 25, and the mechanical rigidity of the thin film may be changed to change the propagation speed and attenuation of the surface acoustic wave. Furthermore, it may cause an endothermic or exothermic reaction by reacting with a gas and affect the propagation speed and attenuation of the surface acoustic wave. The sensitive film 25 is desirably made of a material that selectively reacts only with a specific gas and that causes a reversible reaction.

<Third Modification>
The hydrogen gas detector of the sensor head according to the third modification of the first embodiment of the present invention has a sensitive film 25 formed only in the circumferential band B of the surface acoustic wave as shown in FIG. Is a feature. A piezoelectric thin film 41 is formed on at least a part of a homogeneous material sphere 40 made of a homogeneous material having elastic characteristics. The piezoelectric thin film 41 is only in the vicinity of the interdigital electrode 21 used for exciting and receiving surface acoustic waves. There is a circumferential band B of surface acoustic waves perpendicular to the longitudinal direction of the interdigital electrode 21. The high-frequency generator 22, the switch 23, and the detection / output unit 24 are the same as those in the gas sensor according to the first embodiment, the first modification, and the second modification, and redundant description is omitted.

In the hydrogen gas detection unit according to the third modification of the first embodiment, the sensitive film 25 is formed only in the vicinity of the circumferential band B of the surface acoustic wave. While it is necessary to pattern the sensitive film 25, the surface without the sensitive film 25 can be used for other purposes.

When the sensitive film 25 is expensive as a material such as Pd, if the sensitive film 25 is formed only in the orbital zone B as shown in FIG. 6, the required amount of the sensitive film 25 is very small, and the cost is reduced. It can be greatly reduced. Therefore, the industrial value of the hydrogen gas detection unit according to the third modification of the first embodiment is very high.

<Fourth Modification>
As shown in FIG. 7, the hydrogen gas detection unit of the sensor head according to the fourth modification of the first embodiment of the present invention includes a high-frequency generation unit 82, a switch unit 83, and a detection / output unit 84, which are homogeneous material balls. A schematic structure example integrated on the surface of 40 is shown. The piezoelectric thin film 41 is formed on at least a part of the homogeneous material sphere 40 as in FIG. The piezoelectric thin film 41 is present only in the vicinity of the interdigital electrode 21 used to excite and receive the surface acoustic wave, and there is a circumferential band B of the surface acoustic wave perpendicular to the longitudinal direction of the interdigital electrode 21. Since the sensitive film 25 is formed only in the vicinity of the circumferential band B of the surface acoustic wave, other circuits can be formed in other regions.

The homogeneous material sphere 40 shown in FIG. 7 is preferably a silicon sphere 40 having an oxide film formed on the surface. After the uniformity of the surface acoustic wave propagation is approximately secured by the oxide film, the oxide film is removed except for the region where the sensitive film 25 is formed, so that the spherical semiconductor is formed in the region that does not contribute to the surface acoustic wave propagation. Depending on the manufacturing technology, circuits such as the high-frequency generator 82, the switch unit 83, the detection / output unit 84, and other high-frequency circuits and integrated circuits can be formed, and the gas sensor can be downsized.

Of course, a glass material such as borosilicate glass or quartz glass is used as the homogeneous material sphere 40, a polycrystalline silicon thin film or an amorphous silicon thin film is deposited on a portion where a high frequency circuit or an integrated circuit is formed, and a thin film transistor is integrated thereon. You can also. A polycrystalline silicon thin film or an amorphous thin film may be used after being single-crystallized by heat treatment or laser annealing. It goes without saying that the method of forming a new thin film can also be applied to a hydrogen gas detection unit using the homogeneous material sphere 40.

As shown in FIG. 7, the hydrogen gas detection unit according to the fourth modification includes a temperature sensor 42 on the homogeneous material sphere 40. A piezoelectric thin film 41 is formed on at least a part of the homogeneous material sphere 40. The piezoelectric thin film 41 is present only in the vicinity of the interdigital electrode 21 used to excite and receive the surface acoustic wave, and there is a circumferential band B of the surface acoustic wave perpendicular to the longitudinal direction of the interdigital electrode 21. Since the sensitive film 25 is formed only in the vicinity of the circumferential band B of the surface acoustic wave, other circuits can be formed in other regions.

In the hydrogen gas detection unit according to the fourth modification, a temperature sensor 42 is provided at a location outside the orbital band B of the surface acoustic wave. As the temperature sensor 42, for example, a thermocouple type or a semiconductor type is used. Since the temperature sensor 42 is provided at a position very close to the circumferential band B of the surface acoustic wave, the accuracy of temperature calibration is high.

As shown in FIG. 7, when a circuit such as the high-frequency generator 82 and the detection / output unit 64 is integrated on the homogeneous material sphere 40, a direct measurement result can be obtained. 1 to the metal pad (bonding pad) shown in FIG. 1 can be omitted.

(Second Embodiment)
As shown in FIG. 8, the gas sensor according to the second embodiment of the present invention is disposed on the mounting substrate 64 on which the three-dimensional substrate 40 is mounted, and the electroacoustic transducer (not shown). A semiconductor chip 91 mounted with a high-frequency generator for supplying a high-frequency electrical signal; a semiconductor chip 92 mounted on a mounting substrate 64 for measuring a high-frequency signal related to the propagation characteristics of surface acoustic waves from an electroacoustic transducer; The first internal mounting wiring 61a disposed on the surface of the mounting substrate 64 and electrically connected to the high frequency generation unit mounting semiconductor chip 91, and the detection / output unit mounting semiconductor chip disposed on the surface of the mounting substrate 64 The second internal mounting wiring 61b that is electrically connected to 92, the first internal mounting wiring 61a and the second internal mounting wiring 61b, and the electroacoustic transducer are electrically connected to each other. Conductive connector 50a to be connected, and a 50b.

  As described above, in the gas sensor according to the second embodiment of the present invention, the high frequency generation unit and the detection / detection unit are located at positions different from the hydrogen gas detection unit (25, 27, 40) on the mounting substrate (package substrate) 64. The output units are integrated on the high frequency generation unit mounting semiconductor chip 91 and the detection / output unit mounting semiconductor chip 92, respectively, and mounted on a mounting substrate (package substrate) 64 as a hybrid integrated circuit.

In FIG. 8, the electroacoustic transducer is not shown, but the hydrogen gas detection unit according to the first embodiment and its modification already described with reference to FIGS. 3, 4, 5, and 6. It can be easily understood from the structure of That is, the gas sensor according to the second embodiment includes any one of the hydrogen gas detectors illustrated in FIGS. 3, 4, 5 and 6 described in the first embodiment on a mounting plate 64 having a parallel plate shape. The mounting body (assembly) is mounted using the metal bumps 50a, 50b,... As the conductive connection bodies 50a, 50b,. More specifically, the internal mounting wires 61a, 61b,... Are patterned on the mounting substrate 64, and the metal bumps 50a, 50b,. The hydrogen gas detection unit according to the first embodiment described with reference to FIGS. 3, 4, 5, and 6 and its modification is mounted.

In the homogeneous material sphere 40, since the orbital band B of the surface acoustic wave is limited to the vicinity of the equator, the metal bumps 50a, 50b,... It doesn't matter. The metal pads (bonding pads) for attaching the metal bumps 50a, 50b,... Are installed avoiding the circumferential band B of the surface acoustic wave. However, power is supplied to the interdigital electrode from the high frequency generating portion mounting semiconductor chip 91 disposed on the mounting substrate 64 side, and a high frequency electrical signal is disposed from the interdigital electrode on the mounting substrate 64 side. In order to supply to 92, the electrode wiring 27 is extended from the interdigital electrode, and a metal pad (bonding pad) is provided at the end of the electrode wiring 27.

The first internal mounting wiring 61a is electrically connected to the high frequency generation unit mounting semiconductor chip 91, and the second internal mounting wiring 61b is electrically connected to the detection / output unit mounting semiconductor chip 92. Then, the metal bumps 50a, 50b,... As the conductive connectors 50a, 50b,... Are respectively connected to the first and second internal mounting wirings 61b and the electroacoustic transducers ( (Not shown) are electrically connected. In this manner, a system-on-package in which the high-frequency generating unit mounting semiconductor chip 91 and the detection / output unit mounting semiconductor chip 92 are formed on the mounting substrate 64 can be configured.

  According to the second embodiment, as in the first embodiment, the hydrogen gas detection range (dynamic range) is as wide as 10 ppm to 100%, has high-speed response, and has a high temperature and high temperature. It is possible to provide a gas sensor whose output does not fluctuate even in the presence of humidity or other gases.

(Third embodiment)
As shown in FIG. 9, the sensor head according to the third embodiment of the present invention is a container (64, 65, 66) that selectively transmits only hydrogen gas and has sealing properties against gases other than hydrogen gas. 3) the three-dimensional substrate 40 and the three-dimensional substrate 40 having a curved surface that defines a circular band in which the collimated surface acoustic wave can circulate multiple times, and excite the surface acoustic wave along the circular band. An electroacoustic transducer, at least part of which is present in at least part of the circumference of the three-dimensional substrate 40, includes a sensitive film 25 that reacts with hydrogen gas molecules, and is accommodated inside a container (64, 65, 66). And a hydrogen gas detector (25, 27, 40).

As shown in FIG. 9, the container (64, 65, 66) includes a container body (64, 65) including a mounting substrate (package substrate) 64 on which the three-dimensional substrate 40 is mounted, and a selective hydrogen gas permeation filter. And a package upper lid 66. The package upper cover 66 includes a mesh structure substrate 662, a hydrogen permeable film 661 on the mesh structure substrate 662, and a hydrogen permeable insulating film sandwiched between the mesh structure substrate 662 and the hydrogen permeable film 661. 663. The hydrogen permeable film 661 may be made of Pd, a Pd alloy thin film, or a hydrogen storage alloy film. The mesh structure substrate 662 may be formed by opening a rectangular through hole as shown in FIG. 9 by using a semiconductor substrate such as Si using RIE or the like. For example, if anisotropic etching by RIE is performed using an etching mask formed in a lithography process using a Si (100) surface, through holes surrounded by the (100) surface as shown in FIG. Can be formed. As the hydrogen permeable insulating film 663, a silicon oxide film (SiO ₂ ), a silicon nitride film (SiN), or the like can be used. As for the hydrogen permeability of the silicon oxide film (SiO ₂ ) and the silicon nitride film (SiN), a desired value can be obtained by controlling the denseness of the film quality according to the CVD conditions and selecting the film thickness. More specifically, inorganic insulating materials such as silicon monoxide (SiOC, SiOF) to which carbon or fluorine is added, hydrogen silsesquioxane polymer (HSQ), organic silica, porous HSQ, benzocyclobutene (BCB) In addition, a low dielectric constant insulating film such as an insulating film obtained by making these materials porous can be used as the hydrogen permeable insulating film 663.

  Further, the package upper lid 66 includes a micro heater 665 embedded in the hydrogen permeable insulating film 663. The micro heater 665 is a resistance wire heater made of a metal such as Al, W, or Mo. For example, after depositing a lower hydrogen permeable insulating film by a CVD method or the like, using an etching mask formed in a lithography process, a meander line-shaped damascene groove portion is formed by RIE, and then a metal film such as Al, W, or Mo is formed. When deposited by vacuum evaporation, sputtering, or the like, and further planarized by chemical mechanical polishing (CMP), a metal film to be a microheater 665 is embedded in the damascene trench. Thereafter, by depositing an upper hydrogen permeable insulating film thereon by a CVD method or the like, the hydrogen permeable insulating film 663 in which the meander line-shaped microheater 665 is embedded can be formed. By heating and raising the temperature of the hydrogen permeable membrane 661 to a predetermined temperature with the microheater 665, the package upper lid 66 functions as a selective hydrogen gas permeable filter, and hydrogen is selectively introduced into the container. As described above, the sensor head according to the first embodiment can be used.

  Others are substantially the same as the structure of the sensor head according to the first and second embodiments, and therefore, a duplicate description is omitted.

  According to the third embodiment, similarly to the first and second embodiments, the hydrogen gas detection range (dynamic range) is wide from 10 [ppm] to 100%, and has a high-speed response, In addition, it is possible to provide a sensor head and a gas sensor whose output does not fluctuate even under high temperature and high humidity or in the presence of other gases.

(Fourth embodiment)
In the sensor head according to the third embodiment, a structure in which a porous insulating film or an insulating film having poor density is used as the hydrogen permeable insulating film 663 is exemplified. In the case of a dense silicon oxide film (SiO ₂ ) or silicon nitride film (SiN), hydrogen permeability is negligible above a certain thickness.

  As shown in FIG. 10, the sensor head according to the fourth embodiment of the present invention is a container (64, 65, 66) that selectively transmits only hydrogen gas and has sealing properties against gases other than hydrogen gas. 3) the three-dimensional substrate 40 and the three-dimensional substrate 40 having a curved surface that defines a circular band in which the collimated surface acoustic wave can circulate multiple times, and excite the surface acoustic wave along the circular band. An electroacoustic transducer, at least part of which is present in at least part of the circumference of the three-dimensional substrate 40, includes a sensitive film 25 that reacts with hydrogen gas molecules, and is accommodated inside a container (64, 65, 66). And a hydrogen gas detector (25, 27, 40), and the container (64, 65, 66) includes a container body (64, 65) including a mounting substrate (package substrate) 64 on which the three-dimensional substrate 40 is mounted. Selective hydrogen gas permeation fill In that it has a package upper lid 66 provided with is similar to the sensor head according to the first to third embodiments.

  However, as shown in FIG. 10, the package upper lid 66 is sandwiched between the mesh structure substrate 662, the hydrogen permeable film 661 on the mesh structure substrate 662, and the mesh structure substrate 662 and the hydrogen permeable film 661. And an insulating film 668 having a mesh structure. The through holes of the mesh structure substrate 662 are formed continuously with the through holes constituting the mesh of the insulating film 668. That is, a mesh structure is formed by rectangular holes that continuously penetrate the insulating film 668 and the mesh structure substrate 662. Similar to the sensor heads according to the first to third embodiments, the hydrogen permeable film 661 may be made of Pd, a Pd alloy thin film, or a hydrogen storage alloy film.

The mesh structure substrate 662 may be formed by opening a rectangular through hole as shown in FIG. 10 using RIE or the like for a semiconductor substrate such as Si. For example, if anisotropic etching by RIE is performed using an etching mask formed by a lithography process using a Si (100) surface, through holes surrounded by the (100) surface as shown in FIG. Can be formed. The insulating film 668 has a high density such as a silicon oxide film (SiO ₂ ) thermal oxide film or a stoichiometric silicon nitride film (Si ₃ N ₄ ) formed at a high temperature and has a barrier property against hydrogen permeation. An insulating film can be used.

  Further, the package upper lid 66 includes a micro heater 665 embedded in an insulating film 668 having a mesh structure. The micro heater 665 is a resistance wire heater made of a metal such as Al, W, or Mo. For example, after depositing a lower hydrogen permeable insulating film by a CVD method or the like, using an etching mask formed in a lithography process, a meander line-shaped damascene groove portion is formed by RIE, and then a metal film such as Al, W, or Mo is formed. When deposited by vacuum evaporation, sputtering, or the like, and further planarized by chemical mechanical polishing (CMP), a metal film to be a microheater 665 is embedded in the damascene trench. Thereafter, if an upper hydrogen permeable insulating film is deposited thereon by a CVD method or the like, an insulating film 668 having a mesh structure in which a meander line-shaped microheater 665 is embedded can be formed. In order to process the insulating film 668 into a mesh structure, through holes can be formed in a matrix by performing etching such as RIE, magnetron plasma etching, or ion milling using an etching mask such as a photoresist film formed in a lithography process. . The mesh structure substrate 662 and the insulating film 668 can be bonded by a bonding method or the like.

  By heating and raising the temperature of the hydrogen permeable membrane 661 to a predetermined temperature with the microheater 665, the package upper lid 66 functions as a selective hydrogen gas permeable filter, and hydrogen is selectively introduced into the container. What can be done is the same as described for the sensor heads according to the first to third embodiments, and redundant description is omitted.

  According to the fourth embodiment, similarly to the first and second embodiments, the hydrogen gas detection range (dynamic range) is as wide as 10 [ppm] to 100%, and has high-speed response, In addition, it is possible to provide a sensor head and a gas sensor whose output does not fluctuate even under high temperature and high humidity or in the presence of other gases.

(Other embodiments)
As described above, the present invention has been described according to the first to fourth embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, schematic structural examples, and operation techniques will be apparent to those skilled in the art.

  For example, as a container for storing the hydrogen gas detection unit of the present invention, it is possible to apply a technique such as a ceramic DIP package or a can-type package, which is exemplified in FIGS. 1, 2, 8, and 9. The structure need not be limited. Accordingly, in FIG. 1, a plurality of external plugs 62 a, 62 b,... Are electrically connected to each other so as to allow connection with an external circuit of the container (64, 65, 66). The mounting wirings 63a, 63b,... Exemplify the structure provided on the back surface of the mounting substrate (package substrate) 64. However, as shown in FIG. 11, a plurality of external mounting wirings (pins) 67l to 67n. , 67p to 67w may be provided on the side wall of the package base 68 provided with the mounting substrate, and connected to the internal mounting wiring via the embedded wiring.

  Alternatively, as shown in FIG. 12, gas introduction pipes 72a and 73a, gas introduction valves 71a, gas exhaust pipes 72b and 73b, and gas exhaust valves 71b are provided on the package side wall 69, and after the hydrogen gas is detected, the gas introduction valves 71a and 71a and The gas exhaust valve 71b may be opened, and a purge gas such as Ar may be introduced into the container so that the surface of the hydrogen gas detector can be purged.

When the purge is completed, the gas introduction valve 71a and the gas exhaust valve 71b are closed to provide a mode of use in which hydrogen gas is detected.

  In the description of the hydrogen gas detectors according to the first to fourth embodiments already described, the case where the homogeneous material sphere 40 is used as the “three-dimensional substrate” is illustrated, but the three-dimensional substrate is true. If the accuracy of the sensor is not limited to a sphere, a beer barrel shape or the like, or a bowl shape or a rugby ball shape may be used. In other words, the “three-dimensional substrate” of the present invention has a first curvature in the first main direction along the center line of the orbital belt and in the second main direction orthogonal to the first main direction. If the second curvature is provided in the vicinity of the orbital band, the collimated surface acoustic wave can be circulated multiple times. The width of the orbital band having the second curvature is determined by the second main direction, the radius of curvature, and the surface acoustic wave wavelength. For example, if the radius of curvature in the second main direction is about 5 mm, the width of the orbital band is about 7/50 of the radius of curvature in the second main direction at a frequency of 45 MHz.

  For this reason, there may exist a topology in which the collimated surface acoustic wave can circulate multiple times, even if it has a polyhedron shape or the like, far away in the second main direction outside the width of the orbital band.

  Furthermore, the structure of the hydrogen gas detection unit according to the first to fourth embodiments has been described with respect to a three-dimensional structure in real space. However, in the elastic tensor space, the elastic constant and the like are gradually changed, and A structure equivalent to a curved surface may be realized. For example, an effect similar to that of a spherical surface can be realized even if the elastic characteristics are gradually changed along the second main direction as the distance from the center of the orbital zone increases.

  As described above, the present invention naturally includes a hydrogen gas detection unit and the like according to various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is typical sectional drawing for demonstrating the structure of the sensor head which concerns on the 1st Embodiment of this invention. It is a typical bird's-eye view for demonstrating the structure of the sensor head which concerns on the 1st Embodiment of this invention. FIG. 3A is a schematic bird's-eye view for explaining the structure of the hydrogen gas detector used in the sensor head according to the first embodiment of the present invention, and FIG. It is an equator sectional view seen from a plane that cuts the center of the orbital band of the surface acoustic wave having the structure shown in FIG. It is an equator sectional view explaining the structure of the hydrogen gas detection part used for the sensor head which concerns on the 1st modification of the 1st Embodiment of this invention. FIG. 5A is a schematic bird's-eye view for explaining the structure of the hydrogen gas detection unit used in the sensor head according to the second modification of the first embodiment of the present invention, and FIG. FIG. 6 is an equatorial cross-sectional view of the surface acoustic wave having the structure shown in FIG. It is a typical bird's-eye view for demonstrating the structure of the hydrogen gas detection part used for the sensor head which concerns on the 3rd modification of the 1st Embodiment of this invention. It is a typical bird's-eye view for demonstrating the structure of the hydrogen gas detection part used for the sensor head which concerns on the 4th modification of the 1st Embodiment of this invention. It is a typical bird's-eye view for demonstrating the structure of the gas sensor which concerns on the 2nd Embodiment of this invention. It is typical sectional drawing for demonstrating the structure of the sensor head which concerns on the 3rd Embodiment of this invention. It is typical sectional drawing for demonstrating the structure of the sensor head which concerns on the 4th Embodiment of this invention. It is a typical bird's-eye view for demonstrating the structure of the gas sensor which concerns on other embodiment of this invention. It is typical sectional drawing for demonstrating the structure of the sensor head which concerns on other embodiment of this invention.

Explanation of symbols

15 ... sensitive film 21 ... interdigital electrode (electroacoustic transducer)
22, 82 ... high frequency generator 23, 83 ... switch part 24, 84 ... detection / output part 25, 26 ... sensitive film 27 ... electrode wiring 40 ... homogeneous material ball (three-dimensional substrate)
41 ... Piezoelectric thin film 42 ... Temperature sensor 50a, 50b ... Conductive connector (metal bump)
61a, 61b ... internal mounting wiring 62a, 62b ... via plug 63a, 63b ... external mounting wiring 64 ... mounting substrate 65 ... package side wall 66 ... package top cover 68 ... package base 69 ... package side wall 71a ... gas introduction valve 71b ... gas exhaust valve 72a 73a ... Gas introduction pipes 72b, 73b ... Gas exhaust pipes 91 ... High frequency generator mounting semiconductor chip 92 ... Detection / output section mounting semiconductor chip 661 ... Hydrogen permeable film 662 ... Mesh structure substrate 663 ... Hydrogen permeable insulating film 665 ... Micro heater 668 ... Insulating film

Claims (12)

A container that selectively permeates only hydrogen gas and has a sealing property against a gas other than hydrogen gas;
A three-dimensional substrate having a curved surface that defines a circular band in which a collimated surface acoustic wave can circulate multiple times, and an electric located on the circular band of the three-dimensional substrate to excite the surface acoustic wave along the circular band An acoustic conversion element, a hydrogen gas detection unit that is at least partially present in at least a part of the circumference of the three-dimensional substrate and includes a sensitive film that reacts with hydrogen gas molecules; A sensor head comprising: The container
A container body including a mounting substrate on which the three-dimensional substrate is mounted;
The sensor head according to claim 1, further comprising: a package upper cover including a selective hydrogen gas permeable filter. The package top lid is
A mesh structure substrate;
The sensor head according to claim 2, further comprising: a hydrogen permeable film on the mesh structure substrate.   The sensor head according to claim 3, wherein the upper lid of the package further includes a micro heater embedded in the mesh structure substrate. The package top lid is
A hydrogen permeable insulating film sandwiched between the mesh structure substrate and the hydrogen permeable film;
The sensor head according to claim 3, further comprising a micro heater embedded in the hydrogen permeable insulating film.   6. The package body according to claim 2, further comprising a package side wall having a bottom connected to a peripheral portion of the mounting substrate and a top connected to a peripheral portion of the package upper lid. The sensor head described. A container that selectively permeates only hydrogen gas and has a sealing property against a gas other than hydrogen gas;
A three-dimensional substrate having a curved surface that defines a circular band in which a collimated surface acoustic wave can circulate multiple times, and an electric located on the circular band of the three-dimensional substrate to excite the surface acoustic wave along the circular band An acoustic conversion element, at least part of which is present in at least part of the circumference of the three-dimensional substrate, and a sensitive film that reacts with hydrogen gas molecules, and a hydrogen gas detector housed in the container;
A high frequency generator for supplying a high frequency electrical signal to the electroacoustic transducer;
A gas sensor comprising: a detection / output unit that measures a high-frequency signal related to a propagation characteristic of the surface acoustic wave from the electroacoustic transducer. The gas sensor according to claim 7, wherein the high-frequency generator and the detection / output unit are integrated on the three-dimensional substrate. The container
A container body including a mounting substrate on which the three-dimensional substrate is mounted;
The gas sensor according to claim 7, further comprising: a package upper cover including a selective hydrogen gas permeation filter.   The gas sensor according to claim 9, wherein the high-frequency generation unit and the detection / output unit are mounted on the mounting substrate at a position different from the hydrogen gas detection unit on the mounting substrate. A plurality of internal mounting wirings disposed on the top surface of the mounting substrate and electrically connected to the hydrogen gas detection unit;
A plurality of via plugs embedded in the mounting substrate and electrically connected to the plurality of internal mounting wirings;
The gas sensor according to claim 9, further comprising: a plurality of external mounting wirings that are respectively electrically connected to the plurality of via plugs and enable connection to an external circuit of the container. The gas sensor according to claim 11, wherein the high-frequency generation unit and the detection / output unit are arranged outside the container via the plurality of external mounting wirings.

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