WO2022137565A1 - Detection element, gas detection system, and method for manufacturing detection element - Google Patents

Abstract

This detection element comprises: a vibrator; a substrate layer; and a sensitive film. The substrate layer has, on the surface thereof, needle-like projections that are provided above the vibrator. The sensitive film covers at least a portion of the needle-like projections, and adsorbs gas molecules.

Description

Detection element, gas detection system and manufacturing method of detection element

The present invention relates to a detection element using an FBAR (Film Bulk Acoustic Resonator, hereinafter referred to as a piezoelectric thin film resonator) or the like, a gas detection system, and a method for manufacturing the detection element.

The piezoelectric thin film resonator is a resonator in the GHz band used for filters, duplexers, etc. of mobile communication equipment. There is a gas detection device that applies a sensitive film to which a specific gas is adsorbed on a crystal oscillator, a surface acoustic wave resonator, and a piezoelectric thin film resonator, and detects a frequency change corresponding to the mass change.

In Patent Document 1, a gas molecule detection element provided with a gas molecule selection material having gas discrimination as a sensitive film on a surface elastic wave resonator is used, and an anti-resonance frequency or a resonance frequency is used by using a mass change due to gas molecule adsorption. It is described that the substance is detected by the displacement difference of.

Patent Document 2 describes a stress sensor in which a sensitive film is provided on a diaphragm having an uneven shape and a sensitive film having an uneven shape is formed. It is described that the sensitivity is improved by providing unevenness on the sensitive film.

Japanese Unexamined Patent Publication No. 2005-331326. Japanese Unexamined Patent Publication No. 2017-181435

In the detection element, the sensitivity can be improved by increasing the surface area of the sensitive film. For example, in a detection element using a surface acoustic wave resonator, it is conceivable to provide an uneven shape on the surface of any one of the upper electrode, the lower electrode, and the piezoelectric film, which is the interface of the sensitive film. However, in such a configuration, the Q value deteriorates due to the influence on the crystal growth direction of the piezoelectric film, and the thickness of the electrode film becomes non-uniform in the plane, so that it is unnecessary other than resonance and antiresonance. Peaks occur and sensitivity deteriorates.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a detection element capable of high-sensitivity detection, a gas detection system, and a method for manufacturing the detection element.

The detection element according to one embodiment of the present invention includes a vibrator, a base layer, and a sensitive film.
The base layer is provided on the vibrator and has a needle-shaped protrusion on the surface.
The sensitive membrane covers at least a part of the needle-shaped protrusion and adsorbs gas molecules.

According to such a configuration, the surface area of the sensitive film can be increased, and the detection sensitivity of the detection element can be improved.

The needle-shaped protrusion may be formed by crystal growth.
The underlayer includes a first region having a thin film and a second region having the needle-shaped protrusions located on the first region, the first region and the second region. It may be composed of the same material as the main component.
The first region and the second region may be integrated.
The material may be aluminum oxide.

The vibrator has a piezoelectric film and a first electrode and a second electrode facing each other with at least a part of the piezoelectric film interposed therebetween, and the sensitive film is the first electrode of the first electrode. The electrode and the second electrode may be provided at least in a part of the resonance region facing the piezoelectric film with the piezoelectric film interposed therebetween, via the base layer.

The oscillator has a substrate, a piezoelectric film provided on the substrate, and a laminated film including the first electrode and the second electrode, and the substrate and the laminated film are in contact with each other. A protective layer covering the site may be further provided.
According to such a configuration, the invasion of moisture between the substrate and the laminated film can be suppressed by the protective layer, and the moisture resistance of the detection element is improved.

The oscillator may be a piezoelectric thin film resonator, a surface acoustic wave resonator, or a crystal oscillator.

The gas detection system according to one embodiment of the present invention includes a detection element and a detection circuit.
The detection element is a sensitive film that covers at least a part of the oscillator, the base layer provided on the oscillator and having needle-shaped protrusions on the surface, and the needle-shaped protrusions, and adsorbs gas molecules. And.
The detection circuit detects the gas based on the fluctuation amount of the resonance frequency output by the detection element.

In the method for manufacturing a detection element according to one embodiment of the present invention, a vibrator on which a base film is formed is heat-treated under conditions of a relative humidity of 95% RH or higher and a temperature of 95 ° C. or higher, and the base film is applied to the surface thereof. Change to a base layer with needle-shaped protrusions.

According to the present invention, high-sensitivity detection is possible.

It is a top view which shows the structure of the detection element which concerns on 1st Embodiment of this invention. It is sectional drawing which shows typically the cross section cut by the line II-II of FIG. It is a flow chart (the 1) which shows the manufacturing method of the detection element which concerns on 1st Embodiment. It is a flow chart (the 2) which shows the manufacturing method of the detection element which concerns on 1st Embodiment. It is a flow chart (No. 3) which shows the manufacturing method of the detection element which concerns on 1st Embodiment. It is a top view which shows the structure of the detection element which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows typically the cross section cut by the VII-VII line of FIG. It is a flow chart (the 1) which shows the manufacturing method of the detection element which concerns on 2nd Embodiment. It is a flow chart (the 2) which shows the manufacturing method of the detection element which concerns on 2nd Embodiment. It is a flow chart (No. 3) which shows the manufacturing method of the detection element which concerns on 2nd Embodiment. It is a flow chart (the 4) which shows the manufacturing method of the detection element which concerns on 2nd Embodiment. It is a flow chart (No. 5) which shows the manufacturing method of the detection element which concerns on 2nd Embodiment. It is a flow chart (No. 6) which shows the manufacturing method of the detection element which concerns on 2nd Embodiment. A cross-sectional view schematically showing a cross section of a base layer constituting a part of the detection element according to the first and second embodiments, and a state in which a sensitive film is formed in a second region of the base layer are schematically shown. It is sectional drawing which shows. It is a schematic schematic diagram which shows the structure of the gas detection system which includes the detection element which concerns on 1st or 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the first and second embodiments, an example in which a piezoelectric thin film resonator is used as the vibrator will be given. The piezoelectric thin film resonator is a resonator using a bulk wave propagating in the piezoelectric film in the thickness direction, and a vibrating portion forming a resonance region described later in the resonator constitutes a resonator.
In the specification, when the detection element and each component of the detection element are viewed from the thickness direction of the substrate, it is referred to as a plan view.

<Detection element>
[First Embodiment]
(Overall configuration of detection element)
1 and 2 are diagrams showing the configuration of the detection element of the present embodiment. 1 is a plan view, and FIG. 2 is a sectional view taken along line II-II in FIG.
As shown in FIGS. 1 and 2, the detection element 10 includes a substrate 1, a piezoelectric film 4, an upper electrode 3 as a first electrode, a lower electrode 2 as a second electrode, and a base layer 6. It has a sensitive film 5, metal layers 7a and 7b, and an insertion film 8. The lower electrode 2 and the upper electrode 3 are arranged so as to face each other with at least a part of the piezoelectric film 4 interposed therebetween. A laminated film 70 in which the lower electrode 2, the piezoelectric film 4, and the upper electrode 3 are laminated is provided on the substrate 1. The detection element 10 has a piezoelectric thin film resonator 11 as an oscillator, and a base layer 6 and a sensitive film 5 provided on the piezoelectric thin film resonator 11. The piezoelectric thin film resonator 11 has a substrate 1 and a laminated film 70.

(Explanation of each configuration)
((substrate))
As the substrate 1, for example, a silicon (Si) substrate can be used. As the substrate 1, in addition to the silicon substrate, a quartz substrate, a glass substrate, a ceramic substrate, a lithium tantalate (LiTaO ₃ (LT)) substrate, a lithium niobate (LiNbO ₃ (LN)) substrate, or a gallium arsenide (GaAs) substrate. Etc. can be used.

((Lower electrode))
For example, as shown in FIG. 1, the lower electrode 2 is formed on the substrate 1 in a predetermined shape. The lower electrode 2 has aluminum (Al), copper (Cu), chromium (Cr), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), ruthenium (Ru), rhodium (Rh), and the like. Alternatively, it is composed of a metal monolayer film of iridium (Ir) or a laminated film selected from these. Here, an example of using a laminated film in which a lower layer using Cr and an upper layer using Ru are laminated on the lower electrode 2 will be given.

((Piezoelectric membrane))
The piezoelectric film 4 is formed on the substrate 1 in a predetermined shape so as to cover a part of the lower electrode 2. To. The piezoelectric film 4 is composed of, for example, a piezoelectric body containing aluminum nitride (AlN) having an axis in the (002) direction as a main component. In addition to aluminum nitride, zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), and the like can be used for the piezoelectric film 4. Further, for example, the piezoelectric film 4 may contain aluminum nitride as a main component and may contain other elements for improving resonance characteristics or piezoelectricity. For example, by using scandium (Sc) as an additive element, the effective electromechanical coupling coefficient can be improved.

((Upper electrode))
The upper electrode 3 is formed on the piezoelectric film 4 in a predetermined shape so as to cover at least a part of the piezoelectric film 4. The upper electrode 3 is composed of a single-layer film of the metal material listed in the lower electrode 2 or a laminated film thereof. Here, an example of using a laminated film in which a lower layer using Ru and an upper layer using Cr are laminated on the upper electrode 3 will be given.

((Resonance region))
The detection element 10 has a resonance region 30. The resonance region 30 refers to a region where the lower electrode 2 and the upper electrode 3 face each other with the piezoelectric film 4 interposed therebetween. In the resonance region 30, a gap 32 is provided between the substrate 1 and the lower electrode 2. In the present embodiment, in the resonance region 30, the piezoelectric film 4, the lower electrode 2, and the upper electrode 3 are convex curved surface portions that form a gap 32 between the substrate 1 and the lower electrode 2. The planar shape of the convex curved surface of the upper electrode 3 corresponding to the resonance region 30 is, for example, an elliptical shape having a major axis of 270 μm and a minor axis of 180 μm. The resonance region 30 is a region that resonates in the thickness longitudinal vibration mode when a voltage signal having a predetermined frequency is input between the lower electrode 2 and the upper electrode 3. The vibrating portion forming the resonance region 30 constitutes the oscillator. The resonance frequency of the resonance region 30 is not particularly limited, and is typically a frequency in the GHz band.

The planar shape of the resonance region 30 may be formed into another shape such as a circular shape or a polygonal shape. In particular, by making the planar shape of the resonance region 30 an ellipse or a polygonal shape, it is possible to suppress the occurrence of a vibration mode propagating in the lateral direction as compared with the case where the planar shape of the resonance region 30 is a quadrangle (square or rectangular). It is possible to prevent deterioration of the resonance characteristics.

In the resonance region 30, the void 32 is a dome-shaped bulge formed between the flat upper surface of the substrate 1 and the lower electrode 2. The dome-shaped bulge is, for example, a bulge having a shape in which the height of the void 32 is low around the void 32 and the height of the void 32 is higher toward the inside of the void 32. The lower electrode 2 is formed with an introduction path (not shown) for etching the sacrificial layer 9 described later. The sacrificial layer is a layer for forming the void 32. The vicinity of the tip of the introduction path is not covered with the piezoelectric film 4, and the lower electrode has a hole 31 at the tip of the introduction path. The hole 31 is an introduction port for introducing an etchant when forming the void 32.

The formation position of the hole portion 31 is not particularly limited, but is preferably provided in the vicinity of the resonance region 30. After the void 32 is formed, the hole 31 is closed with an appropriate material. As a result, the communication of the void 32 with the outside air can be cut off, so that deterioration of the resonance characteristic due to the invading gas into the void 32 can be prevented. The material that closes the hole 31 is not particularly limited, and the hole 31 may be closed by a part of the sensitive film 5.
Further, instead of the void 32, an acoustic reflection layer that reflects elastic waves propagating in the longitudinal direction of the piezoelectric film may be used.

((Sensitive membrane))
The sensitive film 5 adsorbs gas molecules. When the gas contains an odorant, the sensitive membrane adsorbs the odorant contained in the gas.
The sensitive film 5 is made of a material capable of adsorbing gas molecules to be detected. The material constituting the sensitive film can be arbitrarily selected depending on the type of gas to be detected, and typically, an organic polymer film, an organic small molecule film, an organic dye film, an inorganic film or the like can be used. More specifically, the sensitive film 5 includes, but is not limited to, a cellulosic resin, a fluororesin, an acrylic resin, or a conductive polymer.

Examples of the organic polymer material include polystyrene, polymethyl methacrylate, 6-nylon, cellulose acetate, poly-9,9-dioctirefluorene, polyvinyl alcohol, polyvinylcarbazole, polyethylene oxide, polyvinyl chloride, and poly-p-. Homopolymers having a single structure such as phenylene ether sulfone, poly-1-butene, polybutadiene, polyphenylmethylsilane, polycaprolactone, polybisphenoxyphosphazene, polypropylene, and copolymers that are copolymers of two or more homopolymers. Can be used as a blended polymer or the like in which the above is mixed.

For example, as organic low molecular weight materials, tris (8-quinolinolato) aluminum (Alq3), naphthyldiamine (α-NPD), BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), CBP (4,4'-N, N'-dicarbazole-biphenyl), copper phthalocyanine, fullerene, pentacene, anthracene, thiophene, Ir (ppy (2-phenylpyridinato)) 3, triazinethiol derivative, dioctylfluorene derivative, tetracontane, parylene Etc. can be used.

For example, examples of the inorganic material include aluminum oxide, titania, vanadium pentoxide, tungsten oxide, lithium fluoride, magnesium fluoride, aluminum, gold, silver, tin, indium-thin oxide (ITO), sodium chloride, magnesium chloride and the like. Can be used.

The sensitive film 5 is selectively provided in the resonance region 30. In the present embodiment, the sensitive film 5 is provided in the resonance region 30 of the upper electrode 3, and is provided on the upper electrode 3 at a portion corresponding to the resonance region 30 via the base layer 6. The portion corresponding to the resonance region 30 refers to the surface of the elliptical dome portion of the upper electrode 3, and the sensitive film 5 is provided on the convex curved surface portion of the upper electrode 3 via the base layer 6. The resonance region 30 is formed in an elliptical shape having the same major axis and minor axis as the dome portion. The thickness of the sensitive film 5 is not particularly limited, and is, for example, 250 μm.

The sensitive film 5 is formed on the upper electrode 2 via the base layer 6. The base layer 6 is a layer having needle-shaped protrusions on its surface, and the sensitive film 5 is formed in a state of substantially following the shape of the needle-shaped protrusions of the base layer 6. Therefore, the sensitive film 5 has a plurality of irregularities due to the needle-shaped protrusions 621 of the base layer 6. The base layer 6 and the sensitive film 5 will be described later.
As a method for forming the sensitive film 5, a method of dissolving the material of the sensitive film in a solvent and applying it by a spray coat, a vapor deposition method, a sputtering method or a CVD (Chemical Vapor Deposition) method can be used.

((Metal layer))
The metal layer 7a is provided on the lower electrode 2. The metal layer 7b is provided on the upper electrode 3. Each of the metal layers 7a and 7b is in contact with the lower electrode 2 and the upper electrode 3, respectively, and functions as wiring and / or a pad. The metal layers 7a and 7b are, for example, Au layers. An underlayer such as a Ti layer or a W layer may be provided under the Au layer.

((Insert membrane))
The insertion membrane 8 is inserted into the piezoelectric membrane 4. The insertion film 8 is provided, for example, substantially in the center of the piezoelectric film 4 in the film thickness direction. The insertion film 8 may be provided in the outer peripheral region in the resonance region 30 where the lower electrode 2 and the upper electrode 3 face each other with the piezoelectric film 4 interposed therebetween, or may be provided in the region surrounding the resonance region 30.
As the insertion film 8, it is preferable to use a material having a Young's modulus smaller than that of the piezoelectric film 4, such as Al, Au, Cu, Ti, Pt, Ta, Cr or silicon oxide (SiO ₂ ). This makes it possible to improve the Q value of the detection element 10.

((Underground layer))
FIG. 14A is an enlarged schematic view of the base layer 6. The base layer 106 of the second embodiment, which will be described later, has the same configuration.
The base layer 6 is provided on the upper electrode 3. As shown in FIG. 14A, the base layer 6 includes a thin film-shaped first region 61 located on the upper electrode 3 side and a needle-shaped second region 62 located on the surface side of the base layer 6. Have.
The first region 61 has a thin film 611. The second region 62 is located on the first region 61 and has a plurality of needle-shaped protrusions 621. The plurality of needle-shaped protrusions 621 are formed irregularly in length and direction.

The base layer 6 having the needle-shaped protrusions 621 on the surface can be formed by heat-treating an alumina (Al ₂ O ₃ ) film having a uniform film thickness under high humidity. By heat treatment under high humidity, needle-shaped protrusions 621 grow crystals from the surface of the base film 60 using alumina. As a result, the base film 60 changes into the base layer 6 in which the thin film-shaped first region 61 and the second region 62 having the needle-shaped protrusions 621 are integrated, and the base film 60 changes to the first region 61. The needle-shaped protrusion 621 is firmly fixed and held by the thin film 611.

In the base layer 6, both the first region 61 and the second region 62 contain alumina as a main component, and the crystal structure of alumina is different. The crystal structure of the first region 61 is α-Al ₂ O ₃ , and the crystal structure of the second region 62 is γ-Al ₂ O ₃ .
The main component means the component having the largest amount. The main component of the first or second region allows impurities other than the main component to be intentionally or unintentionally contained in the first or second region. For example, the first or second region contains oxygen and aluminum in a total of 50 atomic% or more, more preferably 80 atomic% or more, respectively.
The processing conditions of the base film 60 in the manufacture of the base layer 6 will be described in the method of manufacturing the detection element described later.

The sensitive film 5 is formed on the base layer 6. More specifically, it is formed so as to cover at least a part of the second region 62 of the base layer 6.
A morphological example of the sensitive film 5 formed on the base layer 6 will be described with reference to FIGS. 14 (b) and 14 (c).
The sensitive membrane 5 has a first sensitive membrane region 51 and a second sensitive membrane region 52. The first sensitive film region 51 is formed on the thin film 611 of the first region 61. The second sensitive membrane region 52 is formed on the needle-shaped protrusion 621 of the second region 62.
14 (b) and 14 (c) schematically show a state in which the first sensitive film region 51 is formed on the thin film 611 and the second sensitive film region 52 is formed on the needle-shaped protrusion 621. It is a figure shown. In the figure, the sensitive film 5 is schematically formed so as to cover the entire surface of the needle-shaped protrusions 621, but the plurality of needle-shaped protrusions 621 are formed in irregular directions. Therefore, the needle-shaped protrusion 621 may have a portion where the sensitive film 5 is not formed. The same applies to the base layer 106 of the second embodiment described later.

In the example shown in FIG. 14B, the first sensitive film region 51 constituting a part of the sensitive film 5 is formed on the thin film 611. The second sensitive film region 52, which constitutes a part of the sensitive film 5, has a needle-shaped protrusion 621 so that the needle-shaped protrusion 621 is buried in the sensitive film 5 and the surface of the sensitive film 5 is not flat. It is formed to cover at least a part of.
As a result, the formed second sensitive film region 52 has a shape substantially following the needle-like shape of the protrusion 621 of the second region 62, and the sensitive film 5 has irregularities. As a result, the surface area of the sensitive film 5 can be increased as compared with the case where the sensitive film 5 is a flat film.

As shown in FIG. 14 (c), the sensitive film may be infiltrated and formed so as to fill the root portion of the needle-shaped protrusion 621 of the second region 62 of the base layer 6. Therefore, the thickness of the first sensitive film region 51 formed on the thin film 611 is thicker than that of the form shown in FIG. 14 (b). The second sensitive film region 52 includes at least one of the tip portions of the needle-shaped protrusions 621 so that the tip portion of the needle-shaped protrusions 621 is buried in the sensitive membrane 5 and the surface of the sensitive membrane 5 is not flat. It suffices if it is formed so as to cover the portion.
As a result, the formed second sensitive film region 52 has a shape that substantially resembles a part or most of the needle-like shape of the second region 62, and the sensitive film 5 has irregularities. As a result, the surface area of the sensitive film 5 can be increased as compared with the case where the sensitive film 5 is a flat film.

As described above, in the detection element 10 of the present embodiment, the surface area of the sensitive film 5 can be increased, and the detection element with improved detection sensitivity can be obtained.
Further, in the detection element 10 of the present embodiment, the upper electrode 3 is not provided with irregularities, and an underlayer 6 having a needle-shaped protrusion 621 on the surface is provided between the upper electrode 3 and the sensitive film 5, and the underlayer is provided. By forming the sensitive film 5 on the 6, the surface area of the sensitive film 5 is increased. As a result, there is no deterioration of the Q value caused by the unevenness of the electrode or unnecessary peaks other than resonance and antiresonance due to the non-uniform thickness of the electrode, and the Q value is good and the detection sensitivity. The detection element 10 has a high value.

((Other configurations))
As another configuration constituting the detection element 1, a frequency adjustment film may be provided on the upper electrode 2. The resonance frequency may be adjusted by adjusting the film thickness of the frequency adjusting film. The frequency adjusting film may be made of silicon oxide (SiO ₂ ), silicon nitride (SiN), aluminum nitride (AlN), Cr or the like. The frequency adjusting film may function as a passivation film.
In this embodiment, the piezoelectric thin film resonator is applied to the detection element for detecting gas. In the gas detection system using the detection element, the gas is detected by using the change in the resonance frequency, so that the resonance frequency can be adjusted by the detection circuit. Therefore, the frequency adjustment film is not always necessary.

(Dimensional example of each configuration)
A dimensional example in the case of a piezoelectric thin film resonator having a resonance frequency of 2.4 GHz is given, but the material and dimensions are not limited to those described here. The film thickness of each configuration can be appropriately set in order to obtain desired resonance characteristics.
The lower electrode 2 is configured by laminating, for example, a lower layer using Cr and an upper layer using Ru. The film thickness of the lower layer is 70 nm. The film thickness of the upper layer is 166 nm.
The film thickness of the piezoelectric film using AlN is 996 nm.
The film thickness of the insertion film 8 using SiO ₂ is 107 nm.
The upper electrode 3 is configured by laminating a lower layer using Ru and an upper layer using Cr. The film thickness of the lower layer is 166 nm. The film thickness of the upper layer is 55 nm.

The film thickness of the thin film 611 of the first region 61 of the base layer 6 containing Al ₂ O ₃ as a main component is, for example, 10 nm to 100 nm, and here, as an example, it is 50 nm.
The length of the needle-shaped protrusion 621 of the second region 62 of the base layer 6 containing Al ₂ O ₃ as a main component is, for example, 1 nm to 300 nm, and here, as an example, 100 nm. The width of the protrusion 621 is, for example, 1 nm to 500 nm, and here, as an example, 5 nm. The aspect ratio of the protrusion 621 is 2: 1 to 10: 1.
The length and width of the protrusion 621 show average values. Based on the observation image when observing the cross section of the base layer 6 with a scanning electron microscope or the like, the average value of each of the length and width of 20 protrusions 621 arbitrarily selected in one visual field is calculated as the protrusion. Let it be the average length and the average width in 621. The maximum ferret diameter is adopted as the length of the protrusion 621, and the minimum ferret diameter is adopted as the width of the protrusion 621. The aspect ratio is a value obtained by dividing the average length by the average width.
Further, the surface of the first region 61 on the side where the protrusion 621 of the thin film 611 is located is not a flat surface. Based on the observation image when observing the cross section of the base layer 6 with a scanning electron microscope or the like, the average value of the film thicknesses at 20 points arbitrarily set in one visual field is set as the film thickness of the first region 61. ..

The sensitive film 5 is formed with a film thickness of, for example, 100 nm or less, for example, 10 nm to 100 nm, and here, as an example, it is 20 nm.
The film thickness of the sensitive film 5 can be measured by preparing a film thickness monitor at the time of film formation of the actual device and measuring the film thickness monitor by a stylus type, a non-contact type, or an electric resistance type. The same applies to cross-section analysis.

(Example of manufacturing method of detection element)
An example of a manufacturing method of the detection element 10 will be described with reference to the manufacturing flow charts of FIGS. 3 to 5.
As shown in FIG. 3A, the sacrificial layer 9 for forming the void 32 is formed on the substrate 1 having the flat main surface. The thickness of the sacrificial layer 9 is, for example, 10 to 100 nm, and is selected from materials that can be easily dissolved in an etching solution or an etching gas such as MgO, ZnO, Ge, or SiO ₂ . The sacrificial layer 9 is formed by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method. The sacrificial layer 9 may be formed by a lift-off method.
In a plan view, the planar shape of the sacrificial layer 9 is a shape corresponding to the planar shape of the void 32, and includes, for example, a region that becomes a resonance region 30.

Next, as shown in FIG. 3B, the lower electrode 2 is formed on the sacrificial layer 9 and the substrate 1. The lower electrode 2 has a laminated structure in which, for example, a lower layer using Cr and an upper layer using Ru are laminated. The lower electrode 2 is formed by patterning a film formed by, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method into a desired shape using a photolithography technique and an etching technique. The lower electrode 2 may be formed by a lift-off method.

Next, as shown in FIG. 3C, the piezoelectric film 4a is formed on the lower electrode 2 and the substrate 1. The piezoelectric film 4a is formed into a film by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method.
Next, as shown in FIG. 3D, an insertion film 8 using SiO ₂ patterned in a desired shape is formed on the piezoelectric film 4. For example, the insertion film 8 is formed by patterning a film formed by a sputtering method, a vacuum vapor deposition method, or a CVD method into a desired shape using a photolithography technique and an etching technique.

Next, as shown in FIG. 3 (e), the piezoelectric film 4b is formed on the insertion film 8 and the piezoelectric film 4a. The piezoelectric film 4b is formed into a film by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method. The piezoelectric film 4 is composed of the piezoelectric film 4a and the piezoelectric film 4b.

Next, as shown in FIG. 4A, the upper electrode 3 is formed on the piezoelectric film 4. The upper electrode 3 has a laminated structure in which, for example, a lower layer using Ru and an upper layer using Cr are laminated. The upper electrode 3 is formed by patterning a film formed by, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method into a desired shape using a photolithography technique and an etching technique. The upper electrode 3 may be formed by a lift-off method.

Next, a mask layer (not shown) having a desired shape is formed on the upper electrode 3 and the piezoelectric film 4. The mask layer is, for example, a photoresist, and is formed by using a photolithography method. Using the mask layer as a mask, a part of the piezoelectric film 4 is removed by using an etching method. Then, the mask layer is removed by an organic cleaning method or an ashing method. As a result, as shown in FIG. 4B, a part of the lower electrode 2 is exposed.
When forming the frequency adjusting film, for example, it is formed after removing the mask layer.

Next, as shown in FIG. 4C, a base film 60 using alumina patterned in a desired shape is formed on the upper electrode 3. The undercoat film 60 is formed by patterning a film formed by, for example, a sputtering method, a CVD method, or an ALD (Atomic Layer Deposition) method into a desired shape using a photolithography technique and an etching technique. The base film 60 may be formed by a lift-off method.
The undercoat film 60 is formed with a film thickness of, for example, 100 nm.
From the viewpoint of maintaining good resonance characteristics of the manufactured detection element 10, the undercoat film 60 is preferably formed with a film thickness of, for example, 30 nm or less. From the viewpoint of efficiently performing needle-like crystallization of the outermost surface of the undercoat film 60 by heat treatment under high humidity, which will be described later, the undercoat film 60 is preferably formed with a film thickness of, for example, 100 nm or less.

Next, as shown in FIG. 4D, the metal layers 7a and 7b patterned in a desired shape are formed in contact with the lower electrode 2 and the upper electrode 3, respectively. The metal layers 7a and 7b are formed by patterning a film formed by a sputtering method, a vacuum vapor deposition method, or a CVD method into a desired shape using a photolithography technique and an etching technique. The metal layers 7a and 7b may be formed by a lift-off method.

Next, as shown in FIG. 5A, the etchant of the sacrificial layer 9 is introduced into the sacrificial layer 9 under the lower electrode 2 via the hole 31 (see FIG. 1) and the introduction path (not shown). .. As a result, the sacrificial layer 9 is removed and the void 32 is formed.
The medium for etching the sacrificial layer 9 is preferably a medium that does not etch the material constituting the resonator other than the sacrificial layer 9. In particular, the etching medium is preferably a medium in which the lower electrode 2 with which the etching medium is in contact is not etched. The pressure of the laminated film 70 is set so as to be a compressive stress. As a result, when the sacrificial layer 9 is removed, the laminated film 70 swells on the opposite side of the substrate 1 so as to be separated from the substrate 1. A void 32 having a dome-shaped bulge is formed between the lower electrode 2 and the substrate 1.

Next, the surface of the undercoat film 60 is needle-shaped crystallized by heat treatment under high humidity. As a result, as shown in FIG. 14A, the base film 60 is formed on the base layer 6 including the first region 61 having the thin film 611 and the second region 62 having the needle-shaped protrusions 621. Change.

It was confirmed that the surface of the undercoat film 60 using alumina can be needle-like crystallized by treating under the following conditions.
The heat treatment under high humidity can be performed in the chamber (treatment chamber).
It is preferable that the treatment chamber temperature is 95 ° C. or higher and the relative humidity is 95% RH or higher. As a result, the surface of the undercoat film 60 using alumina can be crystallized in a needle shape. Although it has been confirmed that alumina is needle-shaped crystallized by performing the treatment under the above conditions, there is a possibility of needle-like crystallization under different conditions, and the treatment is not limited to the above treatment conditions.
Under conditions where the relative humidity is 95% RH or higher, needle-like crystallization does not occur at temperatures below 95 ° C. Needle-like crystallization tends to proceed when the temperature is raised, and the upper limit of the temperature is not particularly limited. However, if the temperature is higher than 150 ° C., it is difficult to control the humidity in the treatment chamber. Therefore, from the viewpoint of controlling the relative humidity in the treatment humidity to 95% RH or more, the temperature is preferably 150 ° C. or lower.
If the relative humidity is less than 95% RH under the condition that the temperature is 95 ° C. or higher, needle-like crystallization does not occur. Needle-like crystallization tends to proceed when the humidity is increased, and the upper limit of the humidity is not particularly limited.
Further, the treatment time varies depending on the film thickness of the base film 60. For example, in the case of the base film 60 having a film thickness of 100 nm, it takes 60 minutes. With time, the length of the needle-shaped protrusion 621 can be adjusted, in other words, the degree of growth of the needle-shaped crystal can be adjusted. The film thickness of the base film 60 before the treatment and the film thickness of the base layer 6 after the treatment are substantially the same. From the viewpoint of fixing and holding the needle-shaped protrusion 621 by the thin film 611, the film thickness of the thin film 611 is preferably about 30 to 90% of the film thickness of the base layer 6.
Further, although the gauge pressure is set to 0 MPa or more here, the gauge pressure is not particularly limited. When the gauge pressure is increased, the formation of needle-shaped protrusions tends to proceed.
The length, thickness, and orientation (extending direction) of the needle-shaped protrusion 621 formed are irregular.

The crystal structure of the base film 60 using alumina before the heat treatment under high humidity is α-Al ₂ O ₃ . Due to the heat treatment under high humidity, only the surface of the base film 60 changes its crystal structure from α-Al ₂ O ₃ to γ-Al ₂ O ₃ and becomes needle-like crystals. In the base layer 6, the crystal structure of the first region 61 having the thin film 611 is α-Al ₂ O ₃ , and the crystal structure of the second region 62 having the needle-shaped protrusions 621 is γ-Al ₂ O ₃ . Is.

Next, as shown in FIG. 5C, a sensitive film 5 is formed on the base layer 6. As a film forming method of the sensitive film 5, for example, a method of spray-applying a sensitive film material dissolved in a solvent, a vacuum vapor deposition method, a sputtering method, or a CVD method can be used. Since the sensitive film 5 is provided on the base layer 6 whose surface has a needle-like shape, the surface area of the sensitive film 5 can be increased as compared with the case where a flat sensitive film is formed. This improves the detection sensitivity of the detection element 10.

In the above description of the method for manufacturing the detection element 10, the process of manufacturing one detection element has been described for convenience. Typically, after forming a lower electrode, a piezoelectric film, an upper electrode, an underlayer, a metal layer, and a sensitive film corresponding to a plurality of detection elements on one substrate, the substrate is cut into individual detection elements. Manufactured by separation.

Here, instead of alumina, it is conceivable to use carbon nanotubes, which are needle-shaped crystals having a diameter of nanometer size and are composed of only carbon, for example, as the base layer of the sensitive film.
However, since the formation of carbon nanotubes is generally performed under high temperature conditions of about 600 ° C., the lower electrode and the upper electrode tend to deteriorate. On the other hand, since the underlayer layer containing alumina as a main component mentioned in the above-described embodiment can be formed under a temperature condition of about 95 ° C. to 150 ° C., deterioration of the lower electrode and the upper electrode due to high temperature treatment Can be maintained, and the performance of the detection element can be maintained satisfactorily. As described above, it is particularly preferable to use alumina as the base layer.

[Second Embodiment]
The detection element according to the second embodiment is different from the detection element according to the first embodiment in that it has a stepped portion on the peripheral edge of the substrate and a protective layer is formed. Hereinafter, configurations different from those of the first embodiment will be mainly described, and similar configurations may be designated by the same reference numerals and description thereof may be omitted. Further, the manufacturing method will be mainly described with respect to the steps different from the manufacturing method of the detection element 10 of the first embodiment, and the description of the same steps will be simplified.

(Overall configuration of detection element)
6 and 7 are diagrams showing the configuration of the detection element of the present embodiment. 6 is a plan view, and FIG. 7 is a sectional view taken along line VII-VII in FIG.
As shown in FIGS. 6 and 7, the detection element 110 includes a substrate 101, a piezoelectric film 4, an upper electrode 3 as a first electrode, a lower electrode 2 as a second electrode, and a base layer 106. It has a sensitive film 5, electrode layers 7a and 7b, an insertion film 8, and a protective layer 20. The lower electrode 2 and the upper electrode 3 are arranged so as to face each other with at least a part of the piezoelectric film 4 interposed therebetween. The laminated film 70 in which the lower electrode 2, the piezoelectric film 4, and the upper electrode 3 are laminated is provided on the substrate 101. The detection element 110 has a piezoelectric thin film resonator 111 as an oscillator, an underlayer 106 provided on the piezoelectric thin film resonator 111, and a sensitive film 5. The piezoelectric thin film resonator 111 has a substrate 101 and a laminated film 70.

As shown in FIGS. 6 and 7, the detection element 110 of the present embodiment has a stepped portion 210 on the peripheral edge of the main surface 110a of the substrate as compared with the detection element 10 of the first embodiment, and is protected. The main difference is that it has a layer 20.

((substrate))
As the substrate 101, for example, a silicon (Si) substrate can be used. As the substrate 101, in addition to the silicon substrate, a quartz substrate, a glass substrate, a ceramic substrate, lithium tantalate (LiTaO ₃ (LT)), lithium niobate (LiNbO ₃ (LN)), a gallium arsenide (GaAs) substrate, or the like can be used. Can be used.
The peripheral edge of the main surface 101a on the side of the substrate 101 on which the laminated film 70 is formed is relatively thin and has a stepped portion 210.

((Protective layer))
As shown in FIG. 7, the protective layer 20 is formed so as to cover a portion where the substrate 101 and the laminated film 70 are in contact with each other. More specifically, as shown in the portion surrounded by the broken line ellipse A in FIG. 7, the protective layer 20 is formed on the side surface of the laminated film 70 near the portion where the substrate 101 and the laminated film 70 are in contact, and the main surface 101a of the substrate 101. The side surface 101b of the substrate 1 is covered with a continuous shape.
By providing the protective layer 20 so as to cover the portion where the substrate 101 and the laminated film 70 are in contact with each other in this way, it is possible to suppress the intrusion of moisture into the interface between the substrate 101 and the laminated film 70, and the detection element 110 can be prevented. Moisture resistance can be improved.

Here, when the piezoelectric thin-film resonator is used as a filter for distinguishing and passing electrical signals in a required frequency band, the piezoelectric thin-film resonator is packaged, but when used as a detection element for detecting gas as in the present embodiment. Is not packaged. Therefore, for example, moisture easily penetrates between the substrate 101 and the laminated film 70 due to a capillary phenomenon.
On the other hand, in the present embodiment, by providing the protective layer 20 so as to cover the portion where the substrate 101 and the laminated film 70 are in contact with each other, it is possible to suppress the intrusion of moisture into the interface between the substrate 101 and the laminated film 70. can.
When water penetrates between the substrate 101 and the laminated film 70, the water is adsorbed on the laminated film 70. More specifically, water is adsorbed on the piezoelectric film 4, the upper electrode 3, and the lower electrode 2 constituting the laminated film 70. As a result, the mass of the laminated film 70 increases by the mass of the water molecules, the resonance frequency decreases, and the Q value decreases. On the other hand, in the present embodiment, the Q value can be prevented from decreasing by providing the protective layer 20.

Further, the protective layer 20 of the present embodiment is formed so as to cover the portion where the substrate 101 and the laminated film 70 are in contact with each other, and also to cover the side surface of the laminated film 70. As shown in FIGS. 6 and 7, the protective layer 20 is formed so as to cover the entire laminated film 70 other than the region where the electrode layers 7a and 7b are formed, and covers the side surface of the laminated film 70.
By forming the protective layer 20 so as to cover the side surface of the laminated film 70 in this way, the invasion of water from the side surface of the laminated film 70 to the interface where two different configurations such as the piezoelectric film and the electrode are in contact is suppressed. Will be done. Thereby, the moisture resistance of the detection element 110 can be further improved.

The protective layer 20 is made of, for example, alumina. Alumina is moisture resistant and, for example, exhibits higher moisture resistance than silicon oxide. For the evaluation of moisture resistance, various insulating films (aluminum oxide, silicon oxide, silicon nitride, silicon oxide, DLC (diamond-like carbon)) are formed on a silicon substrate, and high temperature using D2O (heavy water) is used. In a moist environment (85 ° C., 95% RH), the amount of D2O invaded into the membrane after being left for 27 hours is evaluated by using D-SIMS (Dynamic mode Secondary Ion Mass Spectrometry) to evaluate the D atom concentration in the depth direction. did. Then, the D concentration in the depth direction is fitted using Fick's law, and the diffusion coefficient is obtained from the fitting line. It was judged that the smaller the diffusion coefficient, the more difficult it is for moisture to diffuse, and the higher the moisture resistance is.
As described above, by using alumina, which is a humidity resistant film, for the protective layer 20, the moisture resistance of the detection element 1110 can be improved.

The protective layer 20 can be formed, for example, in the same process as the film formation of the undercoat film 160 using alumina, which will be described later. The protective layer 20 may be formed by forming a film in a process different from the film forming step of the undercoat film 160, and the material is not limited to alumina, and for example, silicon nitride, silicon oxide, DLC and the like are the main components. An inorganic insulator film or the like may be used.
As described above, by providing the protective layer 20, it is possible to suppress the intrusion of moisture from the side surface of the laminated film 70 constituting the piezoelectric thin film resonator and the intrusion of moisture into the interface between the substrate 101 and the laminated film 70. The moisture resistance of the detection element 110 can be improved.

(Example of manufacturing method of detection element)
An example of a manufacturing method of the detection element 110 will be described with reference to the manufacturing flow charts of FIGS. 8 to 13.
In the following description, an example will be given in which each configuration corresponding to a plurality of detection elements is formed on one substrate, and then the substrate is cut and separated into a plurality of detection elements.

As shown in FIG. 8A, a sacrificial layer 9 for forming the void 32 is formed on the substrate 101 ′ having a flat main surface.
Next, as shown in FIG. 8B, the lower electrode 2 is formed on the sacrificial layer 9 and the substrate 101'.
Next, as shown in FIG. 8C, the piezoelectric film 4a is formed on the lower electrode 2 and the substrate 101'.
Next, as shown in FIG. 9A, an insertion film 8 using SiO ₂ patterned in a predetermined shape is formed on the piezoelectric film 4.
Next, as shown in FIG. 9B, the piezoelectric film 4b is formed on the insertion film 8 and the piezoelectric film 4a. The piezoelectric film 4 is composed of the piezoelectric film 4a and the piezoelectric film 4b.

Next, as shown in FIG. 10A, the upper electrode 3 is formed on the piezoelectric film 4.
Next, a mask layer (not shown) having a desired shape is formed on the upper electrode 3 and the piezoelectric film 4. Using the mask layer as a mask, a part of the piezoelectric film 4 is removed by using an etching method. After that, the mask layer is removed. As a result, a part of the lower electrode 2 is exposed.
Next, as shown in FIG. 10B, the metal layers 7a and 7b patterned in a desired shape are formed in contact with the lower electrode 2 and the upper electrode 3, respectively.

Next, as shown in FIG. 11A, the recess 21 is formed by half-dicing the substrate 101'using, for example, a dicing plate. Reference numeral 101 is attached to the substrate on which the recess 21 is formed. The recess 21 is formed in a groove shape on the substrate 101 so as to partition each detection element.
The recess 21 may be formed by an etching method or a blast method in addition to the half dicing treatment using a dicing plate.

Next, as shown in FIG. 11B, the undercoat film 160 and the protective layer 20 using alumina patterned in a desired shape are formed. Here, the undercoat film 160, which is needle-like crystallized by heat treatment under high humidity in a subsequent step and changes to the underlayer layer 6, and the protective layer 20 which is not acicularly crystallized will be described separately. The protective layer 20 is a film formed in the same film forming process.
As shown in FIG. 11B, the undercoat film 160 and the protective layer 20 are formed in a region other than the regions where the electrode layers 7a and 7b are formed in a plan view.
The base film 160 is formed on the upper electrode 3 on which the electrode layer 7b is not formed.
The protective layer 20 is formed on the side surface of the laminated film 70 and the surface of the substrate 101 where the substrate 101 is exposed. The exposed surface of the substrate 110 includes not only the main surface 101a of the substrate 101 but also the inner surface of the recess 21, and the protective layer 20 is also formed on the side surface 101b corresponding to the inner surface of the recess 21 of the substrate 101. ..

The undercoat film 160 and the protective layer 20 using alumina are formed by patterning a film formed by, for example, a sputtering method, a CVD method or an ALD (Atomic Layer Deposition) method into a desired shape by using a photolithography technique and an etching technique. It is formed by etching. The base film 160 and the protective layer 20 may be formed by a lift-off method.
From the viewpoint of maintaining good resonance characteristics of the manufactured detection element 110, the undercoat film 160 is preferably formed with a film thickness of, for example, 30 nm or less. From the viewpoint of efficiently performing needle-like crystallization of the outermost surface of the base film 60 by the high temperature and high humidity treatment described later, the base film 160 is preferably formed with a film thickness of, for example, 100 nm or less.
From the viewpoint of moisture resistance, the protective layer 20 is preferably formed with a film thickness of, for example, 20 nm or more.
In the present embodiment, the undercoat film 160 and the protective layer 20 are simultaneously formed into a film, for example, to have a film thickness of 100 nm.

Next, as shown in FIG. 12 (a), the etchant of the sacrificial layer 9 is introduced into the sacrificial layer 9 under the lower electrode 2 via the hole 31 (see FIG. 6) and the introduction path (not shown). .. As a result, the sacrificial layer 9 is removed and the void 32 is formed.

Next, as shown in FIG. 12B, the protective film 24 is formed on the entire surface of the substrate 101 including the laminated film 70, the electrode layers 7a and 7b, excluding the region where the undercoat film 160 is formed.
Next, the surface of the base film 160 exposed by heat treatment under high humidity is crystallized in a needle shape, and then the protective film 24 is removed. As a result, as shown in FIGS. 13 (a) and 14 (a), the base film 160 includes a first region 61 having a thin film 611 and a second region 62 having a needle-shaped protrusion 621. It becomes the stratum 106. On the other hand, the protective layer 20 covered with the protective film 24 is not needle-shaped crystallized.
The heat treatment conditions under high humidity are the same as those in the first embodiment.

Next, as shown in FIG. 13B, after the sensitive film 5 is formed on the base layer 106, a groove penetrating the substrate 101 is formed in the recess 21. The groove is formed by, for example, full dicing using a dicing blade. As a result, the substrate 101 is divided and separated into a plurality of detection elements 110.
Since the sensitive film 5 is provided on the base layer 106 having the needle-shaped protrusions 621 on the surface, the surface area of the sensitive film 5 can be increased. This improves the detection sensitivity of the detection element 110.

<Configuration of gas detection system>
FIG. 15 is a diagram schematically showing the configuration of a gas detection system using the above-mentioned detection element 10 or detection element 110.
As shown in FIG. 15, the gas detection system 100 includes a gas sensor device (hereinafter referred to as a sensor device) 50 and an information processing unit 40. The sensor device 50 and the information processing unit 40 are connected to each other so as to be able to communicate with each other wirelessly or by wire. The sensor device 50 and the information processing unit 40 are connected to each other so as to be capable of wireless communication using, for example, a communication standard of BLE (Bluetooth (registered trademark) Low Energy).

The sensor device 50 has one or more, typically a plurality of detection elements 10 (or detection elements 110), and an oscillation circuit 53. The correspondence between the detection element 10 (or the detection element 110) and the oscillation circuit 53 may be one-to-one or one-to-many such as one-to-two.

The resonance frequency of the detection element 10 (or the detection element 110) fluctuates due to the sensitive film adsorbing gas molecules. When the oscillation circuit 53 inputs a voltage signal having a predetermined frequency between the upper electrode and the lower electrode, the detection element 10 (or the detection element 110) resonates at a predetermined resonance frequency. The resonance frequency of the detection element 10 (or the detection element 110) is not particularly limited, and for example, the sensor device 50 in the several GHz band detects the fluctuation amount of the resonance frequency of the detection element 10 (or the detection element 110). The sensor device 50 wirelessly transmits the fluctuation amount of the resonance frequency to the information processing unit 40.
The sensor device 50 detects the gas and further measures the composition and concentration of the gas. When the gas contains an odor, the sensor device 50 detects the odor and further measures the composition and concentration of the gas. An odor is an aggregate of multiple types of odorous substances. That is, the odor substance corresponds to a constituent component (odor component) of the odor. Based on the detection result of the sensor device 50, the type of odor, which is an aggregate of each odorous substance, can be determined.
When the sensor device 50 includes a plurality of detection elements 10 (or detection elements 110), the sensitive film of each detection element 10 (or detection element 110) is manufactured of different materials having the selectivity of the gas molecule to be adsorbed. .. The sensitive films of the plurality of detection elements 10 (or detection elements 110) mainly adsorb different types of gas molecules.

The information processing unit 40 has a detection circuit 41.
The information processing unit 40 receives the fluctuation amount of the resonance frequency of the detection element 10 (or the detection element 110) from the sensor device 50.
The detection circuit 41 detects gas based on the fluctuation amount of the resonance frequency of the detection element 10 (or the detection element 110), measures the component and concentration of the gas, and generates a measured value.
The information processing unit 40 is typically a personal computer, a tablet computer, or the like. The information processing unit 40 may include a cloud server or the like.

Since the gas detection system 100 of the present embodiment includes the detection element 10 or 110 having a large surface area of the sensitive film and improved sensitivity, the gas detection accuracy can be improved.

<Other embodiments>
Although each embodiment of the present invention has been described above, the present technique is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present technique.
For example, in the above-described embodiment of the detection element, the detection element having an insertion film is given as an example, but the detection element may not have the insertion film.

Further, in the above-described embodiment, an example in which a piezoelectric thin film resonator is used as the vibrator is given, but the present invention can be applied to a detection element using a crystal oscillator or a surface acoustic wave resonator.

A QCM (Quartz Crystal Microbalance) detection element using a crystal oscillator has a sensitive film and a quartz crystal oscillator.
The crystal oscillator is, for example, an oscillator cut at a cut angle called AT cut, and has a thin plate shape. A first electrode and a second electrode in which a metal thin film is patterned into a predetermined shape are formed on one main surface of the crystal oscillator and the other main surface facing the main surface, respectively. The sensitive film is formed (coated) on one of the electrodes via the base layer. The base layer has the same structure as the base layer shown in the first and second embodiments described above, and has a first region having a thin film and a needle-shaped protrusion located on the first region. Has a second region and has. Since the sensitive film is formed on the base layer having a needle-like surface shape, the surface area of the sensitive film can be increased as compared with the case where the sensitive film is formed on the flat film.
In the QCM detection element, when the oscillation circuit inputs a voltage signal of a predetermined frequency between the first electrode and the second electrode, the crystal oscillator resonates at a predetermined resonance frequency. Gas is detected by the fluctuation of the resonance frequency due to the adsorption of gas molecules on the sensitive membrane.

A detection element using a surface acoustic wave resonator is configured by, for example, providing two sets of comb-shaped electrodes (first and second electrodes) on the surface of a piezoelectric substrate. When a high-frequency AC voltage is applied to this comb-shaped electrode, the piezoelectric substrate is distorted due to the piezoelectric effect, and surface waves are excited. This excited part constitutes the oscillator.
In a detection element using a surface acoustic wave resonator, a protective film is formed on the comb-shaped electrode so as to cover the comb-shaped electrode, and a sensitive film is formed (coated) on the base layer formed on the protective film. To. The base layer has the same structure as the base layer shown in the first and second embodiments described above, and has a first region having a thin film and needle-shaped protrusions located in the first region. It has a second region having. Since the sensitive film is formed on the base layer having a needle-like surface shape, the surface area of the sensitive film can be increased as compared with the case where the sensitive film is formed on the flat film.
In a detection element using a surface acoustic wave resonator, when a voltage signal having a predetermined frequency is input between the first electrode and the second electrode, the surface wave is excited. Gas is detected by utilizing the fluctuation of the frequency (resonance frequency) of the surface acoustic wave due to the adsorption of gas molecules on the sensitive membrane.

1, 101 ... Substrate 2 ... Lower electrode (second electrode)
3 ... Upper electrode (first electrode)
4 ... Piezoelectric film 5 ... Sensitive film 6, 106 ... Underlayer 61 ... First region 611 ... Thin film 62 ... Second region 621 ... Needle-shaped protrusions 10, 110 ... Detection element 11, 111 ... Piezoelectric thin film resonator (Vibrator)
41 ... Detection circuits 60, 160 ... Undercoat film 70 ... Laminated film 100 ... Gas detection system

Claims (10)

1. Oscillator and
   A base layer provided on the oscillator and having needle-shaped protrusions on the surface, and
   A detection element provided with a sensitive film that covers at least a part of the needle-shaped protrusion and adsorbs gas molecules.
2. The detection element according to claim 1.
   The needle-shaped protrusion is a detection element formed by crystal growth.
3. The detection element according to claim 1 or 2.
   The underlayer includes a first region having a thin film and a second region having the needle-like protrusions located on the first region.
   A detection element having the same material as the main component of the first region and the second region.
4. The detection element according to claim 3.
   A detection element in which the first region and the second region are integrated.
5. The detection element according to claim 3 or 4.
   The material is aluminum oxide.
6. The detection element according to any one of claims 1 to 5.
   The oscillator has a piezoelectric film and a first electrode and a second electrode facing each other with at least a part of the piezoelectric film interposed therebetween.
   The sensitive film is a detection element provided in at least a part of the resonance region of the first electrode, in which the first electrode and the second electrode face each other with the piezoelectric film interposed therebetween, via the base layer. ..
7. The detection element according to claim 6.
   The oscillator has a substrate and a piezoelectric film provided on the substrate, a laminated film including the first electrode and the second electrode.
   A detection element further comprising a protective layer that covers a portion where the substrate and the laminated film are in contact with each other.
8. The detection element according to any one of claims 1 to 7.
   The oscillator is a piezoelectric thin film resonator, a surface acoustic wave resonator, or a detection element that is a crystal oscillator.
9. Oscillator and
   A base layer provided on the oscillator and having needle-shaped protrusions on the surface, and
   A detection element comprising a sensitive film that covers at least a part of the needle-shaped protrusion and adsorbs gas molecules.
   A gas detection system including a detection circuit that detects the gas based on the fluctuation amount of the resonance frequency output by the detection element.
10. A detection element that heat-treats an oscillator on which a base film is formed under conditions of a relative humidity of 95% RH or higher and a temperature of 95 ° C. or higher to change the base film into a base layer having needle-shaped protrusions on the surface. Manufacturing method.

Images