Detection element, method of manufacturing the same, and detection system

Abstract

This detecting element comprises a substrate 10, a piezoelectric film 14 provided on the substrate, a lower electrode 12 and an upper electrode 16 opposing one another across at least a portion of the piezoelectric film, an insertion film 28 comprising a thin film portion 28b that is provided between the lower electrode and the upper electrode in a resonance region 50 defined by a region in which the lower electrode and the upper electrode face one another sandwiching at least a portion of the piezoelectric film, and that is provided inward of the resonance region in a plan view, and a thick film portion 28a which surrounds the thin film portion in a plan view, is provided in a peripheral edge of the resonance region, and is thicker than the thin film portion, and a sensitive film 24 provided in a region surrounded by a first step 23 which is provided on an upper surface of the upper electrode and which is defined by the thin film portion and the thick film portion, wherein a resonant frequency changes in accordance with a change in environment.　

Description

[Technical Field]

[0001] The present invention relates to a detection element, a manufacturing method thereof, and a detection system, and more particularly to a detection element having a resonator, a manufacturing method thereof, and a detection system. [Background technology]

[0002] Environmental sensors are known that detect environmental changes such as the concentration of specific atoms or molecules in a gas or liquid, temperature, or humidity by detecting changes in the mass of a sensitive film. A detection system is known in which a sensitive film is provided on the upper electrode of a piezoelectric thin film resonator, and environmental changes are detected based on changes in resonance frequency caused by changes in the mass of the sensitive film (see, for example, Patent Document 1). A piezoelectric thin film resonator has a structure in which a lower electrode and an upper electrode face each other, sandwiching a piezoelectric film. The region where the lower electrode and upper electrode face each other, sandwiching at least a portion of the piezoelectric film, is a resonance region in which elastic waves resonate. It is known to provide an insert film within the piezoelectric film of a piezoelectric thin film resonator (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-115927 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-139167 Summary of the Invention [Problem to be solved by the invention]

[0004] If the sensitive film is not formed stably, the characteristics of the resonator will not be stable. If a dam is formed using a protective film to surround the resonance region, as shown in Figure 17(b) of Patent Document 1, the manufacturing process will become complicated. Furthermore, when the detection element is operated, the characteristics of the resonator may not be stable.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to simplify the manufacturing process and stabilize the characteristics of the resonator. [Means for solving the problem]

[0006] The present invention is a detection element comprising: a substrate; a piezoelectric film provided on the substrate; a lower electrode and an upper electrode facing each other with at least a portion of the piezoelectric film sandwiched therebetween; an insertion membrane provided between the lower electrode and the upper electrode within a resonance region defined by the region where the lower electrode and the upper electrode face each other with at least a portion of the piezoelectric film sandwiched therebetween, the insertion membrane comprising: a thin film portion provided inside the resonance region in a planar view; and a thick film portion surrounding the thin film portion in a planar view and provided on the periphery of the resonance region and thicker than the thin film portion; and a sensitive membrane provided on the upper surface of the upper electrode in a region surrounded by a first step defined by the thin film portion and the thick film portion, wherein the resonance frequency changes with changes in the environment.

[0007] In the above configuration, the sign of the temperature coefficient of the elastic constant of the thin film portion may be opposite to the sign of the temperature coefficient of the elastic constant of the piezoelectric film.

[0008] In the above configuration, the thick film portion may include a film having a Young's modulus smaller than that of the piezoelectric film.

[0009] In the above configuration, the piezoelectric film may be mainly made of aluminum nitride film, and the insertion film may be mainly made of silicon oxide.

[0010] In the above configuration, the piezoelectric film may comprise a lower piezoelectric film provided on the lower electrode and an upper piezoelectric film provided on the lower piezoelectric film, and the insertion film may be configured to be provided between the lower piezoelectric film and the upper piezoelectric film.

[0011] In the above configuration, the thickness of the thick film portion may be 1.5 times or more the thickness of the thin film portion.

[0012] In the above configuration, the temperature frequency coefficient of the resonant frequency of the detection element may be set to be not less than −20 ppm / K and not more than 20 ppm / K.

[0013] In the above configuration, a second step is provided on the upper surface of the insertion film so that the upper surface of the thin film portion is recessed toward the front substrate more than the upper surface of the thick film portion, and a third step is provided on the upper surface of the piezoelectric film so that the upper surface of the piezoelectric film corresponding to the thin film portion is recessed toward the substrate more than the upper surface of the piezoelectric film corresponding to the thick film portion, and the first step is provided so that the upper surface of the upper electrode corresponding to the thin film portion is recessed toward the substrate more than the upper electrode corresponding to the thick film portion.

[0014] In the above configuration, the inclination of the first step may be gentler than the inclination of the second step.

[0015] The present invention is directed to a detection system that detects a change in the environment based on the detection element and a signal output from the detection element.

[0016] In the above configuration, a plurality of the detection elements may be provided, and the sensitive films of at least two of the plurality of detection elements may be formed from different materials.

[0017] The present invention provides a method for manufacturing a resonator, the method comprising: a step of fabricating a resonator including: a piezoelectric film provided on a substrate; a lower electrode and an upper electrode that face each other with at least a part of the piezoelectric film sandwiched therebetween; and an insertion film that is provided between the lower electrode and the upper electrode within a resonance region that is defined by a region where the lower electrode and the upper electrode face each other with at least a part of the piezoelectric film sandwiched therebetween, the insertion film including a thin film portion that is provided inside the resonance region and a thick film portion that surrounds the thin film portion in a plan view and is provided on the periphery of the resonance region and is thicker than the thin film portion; and forming a sensitive film whose mass changes with changes in the environment in an area surrounded by a step defined by the thin film portion and the thick film portion provided on the upper surface of the upper electrode.

[0018] In the above configuration, the step of forming the sensitive film may include a step of applying a solvent containing a sensitive agent. [Effects of the Invention]

[0019] The present invention aims to simplify the manufacturing process and stabilize the characteristics of the resonator. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1(a) is a plan view of a detection element according to Example 1, and FIG. 1(b) is a cross-sectional view taken along the line AA in FIG. 1(a). [Figure 2] 2(a) to 2(d) are cross-sectional views (part 1) illustrating a method for manufacturing the detection element according to the first embodiment. [Figure 3] 3(a) to 3(c) are cross-sectional views (part 2) illustrating a method for manufacturing the detection element according to the first embodiment. [Figure 4] 4(a) to 4(c) are cross-sectional views (part 3) illustrating a method for manufacturing the detection element according to the first embodiment. [Figure 5] Figures 5(a) to 5(c) are photographs of the sensitizer after application of each solution in Experiment 1, viewed from above. [Figure 6] 6(a) to 6(c) are diagrams showing the thickness of the sensitizer with respect to the position after application of each solvent in Example 1. FIG. [Figure 7] FIG. 7 is a diagram showing the Q value versus the thickness of the sensitive film in Experiment 2. [Figure 8] 8(a) to 8(c) are plan views of resonators A to C fabricated in Experiment 3. FIG. [Figure 9] 9(a) and 9(b) are diagrams showing the magnitude of impedance |Z| versus frequency for resonators A to C in Experiment 3. FIG. [Figure 10] FIG. 10 is a cross-sectional view showing the insertion membrane in Experiment 4. [Figure 11]11(a) and 11(b) are diagrams showing k2 and Qa, respectively, relative to the thickness Ta of the thick film portion 28a in Experiment 4. FIG. [Figure 12] FIG. 12 is a graph showing the TCF versus the thickness Tb of the thin film portion in Experiment 4. [Figure 13] FIG. 13 is a graph showing the change Δf in the resonant frequency with respect to time in Experiment 5. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing an example of steps in the piezoelectric film, the insertion film, the upper electrode, and the sensitive film in Example 1. As shown in FIG. [Figure 15] 15(a) and 15(b) are cross-sectional views of film bulk acoustic resonators according to first and second modifications of the first embodiment, respectively. [Figure 16] FIG. 16 is a functional block diagram of a detection system according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment will be described with reference to the drawings. [Example]

[0022] This is an example in which a piezoelectric thin film resonator is used as the detection element 112. Fig. 1(a) is a plan view of the detection element 112 according to the first embodiment, and Fig. 1(b) is a cross-sectional view taken along line AA of Fig. 1(a). The normal direction to the upper surface of the substrate 10 is the Z direction, the direction in which the lower electrode 12 is drawn out from the resonance region 50 is the X direction, and the direction perpendicular to the X direction among the planar directions is the Y direction.

[0023] As shown in FIGS. 1(a) and 1(b), in the detection element 112, a gap 30 having a dome-shaped bulge is formed between the flat upper surface of the substrate 10 and the lower electrode 12. The dome-shaped bulge is a bulge in which, for example, the height of the gap 30 is small at the periphery and increases toward the center of the gap 30. A piezoelectric film 14 is provided on the lower electrode 12. An upper electrode 16 is provided on the piezoelectric film 14. A resonance region 50 is defined by the region where the lower electrode 12 and the upper electrode 16 face each other, sandwiching at least a portion of the piezoelectric film 14. The resonance region 50 has an elliptical shape and is a region in which elastic waves, such as those in a thickness longitudinal vibration mode or a thickness shear vibration mode, resonate.

[0024] The piezoelectric film 14 includes a lower piezoelectric film 14a provided on the lower electrode 12 and an upper piezoelectric film 14b provided on the lower piezoelectric film 14a. An insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b in the resonance region 50. The lower piezoelectric film 14a and the upper piezoelectric film 14b have approximately the same thickness. Although the lower piezoelectric film 14a and the upper piezoelectric film 14b do not need to have the same thickness, making them the same will allow them to function better as the insertion film 28.

[0025] The insertion film 28 includes a thin film portion 28b and a thick film portion 28a. The thick film portion 28a is thicker than the thin film portion 28b. The thin film portion 28b is provided in an inner region 54 of the resonance region 50. The thick film portion 28a is provided in at least a portion of an outer peripheral region 52 of the resonance region 50. The inner region 54 is a region within the resonance region 50 that is located inside the resonance region 50 in a planar view. The outer peripheral region 52 is a region within the resonance region 50 that surrounds the inner region 54 and includes and is located along the outer periphery of the resonance region 50. In a planar view, the thick film portion 28a surrounds at least a portion of the outer periphery of the thin film portion 28b and is provided along the outer periphery of the resonance region 50, including the outer periphery of the resonance region 50. The planar shape of the thick film portion 28a is, for example, a ring shape or at least a portion of a ring. The thin film portion 28b has a substantially uniform thickness, and the thick film portion 28a has a substantially uniform thickness.

[0026] A recess 26 corresponding to the difference in film thickness between the thick film portion 28a and the thin film portion 28b is provided on the upper surface of the insertion film 28. A recess 27 defined by the recess 26 is formed on the upper surface of the piezoelectric film 14. A recess 22 defined by the recesses 26 and 27 is formed on the upper surface of the upper electrode 16. In other words, the recess 22 is an area surrounded by a step 23 defined by the thin film portion 28b and the thick film portion 28a. A sensitive film 24 is provided within the recess 27. The height of the step 23 is D1. The upper surface of the sensitive film 24 is approximately flat.

[0027] An insulating film may be provided between the upper electrode 16 and the sensitive film 24 as a protective film or a frequency adjustment film. A metal layer 20 is provided on the lower electrode 12 and the upper electrode 16 outside the resonance region 50. The metal layer 20 is, for example, a pad or wiring. The lower electrode 12 is provided with a hole 35 for etching the sacrificial layer. The hole 35 is connected to the gap 30.

[0028] Hereinafter, environmental changes refer to changes in the concentration, humidity, temperature, or light intensity of a specific substance in the gas or liquid surrounding the detection element 112. When specific atoms, molecules, or other substances in the gas or liquid are adsorbed onto the sensitive film 24, the mass of the sensitive film 24 increases, lowering the resonant frequency of the detection element. When the humidity around the sensitive film 24 increases, moisture is adsorbed onto the sensitive film 24, increasing the mass of the sensitive film 24 and lowering the resonant frequency of the detection element 112. When the temperature changes, the adsorption and desorption characteristics of the sensitive film 24 for specific atoms, molecules, or other substances change, resulting in a change in the mass of the sensitive film 24. Furthermore, when the temperature changes, the resonant frequency of the detection element changes due to the temperature characteristics of the sensitive film 24 and the piezoelectric thin film resonator. When light such as ultraviolet light is irradiated onto the sensitive film 24, the adsorption and desorption characteristics of the sensitive film 24 for specific atoms, molecules, or other substances change, resulting in a change in the mass of the sensitive film 24 and a change in the resonant frequency of the detection element. In this way, a change in the environment changes the resonant frequency of the detection element 112. The change in the resonant frequency of the detection element 112 can be used to detect a change in the environment.

[0029] The substrate 10 is, for example, a silicon substrate, a sapphire substrate, a quartz substrate, a glass substrate, a ceramic substrate, or a GaAs substrate. The lower electrode 12 and the upper electrode 16 are, for example, single-layer films of ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), iridium (Ir), or the like, or laminated films thereof. The lower electrode 12 is, for example, a chromium film and a ruthenium film from the substrate 10 side, and the upper electrode 16 is, for example, a ruthenium film and a chromium film from the piezoelectric film 14 side.

[0030] The piezoelectric film 14 may be, for example, an aluminum nitride (AlN) film, a zinc oxide (ZnO) film, a gallium nitride (GaN) film, a lead zirconate titanate (PZT) film, a lead titanate (PbTiO3) film, a lithium tantalate (LiTaO3) film, or a lithium niobate (LiNbO3) film. The piezoelectric film 14 is primarily composed of aluminum nitride (AlN) with its principal axis oriented in the (002) direction, and may contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 can be improved by adding scandium (Sc), a group 2 element or two elements, a group 12 element and a group 4 element, or two elements, a group 2 element or two elements, a group 12 element and a group 5 element, as additive elements. This improves the effective electromechanical coupling coefficient of the piezoelectric thin film resonator. Examples of group 2 elements include calcium (Ca), magnesium (Mg), and strontium (Sr), and examples of group 12 elements include zinc (Zn). The Group 4 element is, for example, titanium, zirconium (Zr), or hafnium (Hf). The Group 5 element is, for example, tantalum, niobium (Nb), or vanadium (V). Furthermore, the piezoelectric film 14 may be mainly composed of aluminum nitride and may also contain boron (B).

[0031] The thin film portion 28b of the insertion film 28 has a temperature coefficient of elastic constant with an opposite sign to that of the piezoelectric film 14. This allows the temperature coefficient of the resonant frequency, etc., to approach zero. The thin film portion 28b is, for example, a silicon oxide film or a silicon oxide film containing impurities such as fluorine. At least a portion of the thick film portion 28a of the insertion film 28 includes a film of a material with a smaller Young's modulus than the piezoelectric film 14, such as a silicon oxide film, an aluminum film, a titanium film, a chromium film, a ruthenium film, or a tungsten film. The metal layer 20 is, for example, a low-resistance film such as a gold film, a copper film, or an aluminum film. The protective film or frequency adjustment film is, for example, a silicon oxide film, a silicon nitride film, or an aluminum oxide film.

[0032] The sensitive film 24 may be, for example, an organic polymer film, an organic low-molecular-weight film, or an inorganic film. Examples of organic polymer materials that can be used include homopolymers having a single structure, such as polystyrene, polymethyl methacrylate, 6-nylon, cellulose acetate, poly-9,9-dioctylenefluorene, polyvinyl alcohol, polyvinylcarbazole, polyethylene oxide, polyvinyl chloride, poly-p-phenylene ether sulfone, poly-1-butene, polybutadiene, polyphenylmethylsilane, polycaprolactone, polybisphenoxyphosphazene, and polypropylene, copolymers that are copolymers of two or more homopolymers, and blend polymers that are mixtures of these.

[0033] For example, organic low molecular weight materials that can be used include 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, triazine thiol derivatives, dioctylfluorene derivatives, tetratetracontane, and parylene.

[0034] For example, inorganic materials that can be used include alumina, titania, vanadium pentoxide, tungsten oxide, lithium fluoride, magnesium fluoride, aluminum, gold, silver, tin, indium tin oxide (ITO), carbon nanotubes, sodium chloride, and magnesium chloride.

[0035] In the case of a detection element 112 using a piezoelectric thin film resonator with a resonant frequency of 2.4 GHz, the lower electrode 12 is a 70 nm thick chromium film and a 166 nm thick ruthenium film, from the substrate 10 side. The lower piezoelectric film 14a is a 498 nm thick aluminum nitride film, and the upper piezoelectric film 14b is a 498 nm thick aluminum nitride film. The insertion film 28 is a silicon oxide (SiO2) film, with the thin film portion 28b having a thickness of 73 nm and the thick film portion 28a having a thickness of 180 nm. The upper electrode 16 is a 166 nm thick ruthenium film and a 55 nm thick chromium film, from the piezoelectric film 14 side. The sensitive film 24 is, for example, a cellulose-based resin (cellulose acetate) having a thickness of 80 nm. A 70 nm thick silicon oxide film may be provided between the upper electrode 16 and the sensitive film 24 as a protective film or frequency adjustment film. The film thickness of each layer can be appropriately set to obtain the desired resonance characteristics.

[0036] [Manufacturing method of Example 1] 2(a) to 4(c) are cross-sectional views showing a manufacturing method of the detection element 112 according to the first embodiment. As shown in FIG. 2(a), a sacrificial layer 38 for forming a void is formed on a substrate 10 having a flat upper surface. The sacrificial layer 38 is, for example, a magnesium oxide (MgO) film, a zinc oxide (ZnO) film, a germanium (Ge) film, a silicon oxide (SiO2) film, or a phosphosilicate glass (PSG) film. The thickness of the sacrificial layer 38 is, for example, 10 to 100 nm. The sacrificial layer 38 is formed using a sputtering method, a vacuum deposition method, or a CVD (Chemical Vapor Deposition) method. The sacrificial layer 38 is then patterned into a desired shape using photolithography and etching techniques. The shape of the sacrificial layer 38 corresponds to the planar shape of the void 30 and includes, for example, a region that becomes the resonance region 50.

[0037] As shown in FIG. 2(b), a lower electrode 12 is formed on the sacrificial layer 38 and the substrate 10. The lower electrode 12 is formed by, for example, sputtering, vacuum deposition, or CVD. The lower electrode 12 is then patterned into a desired shape using photolithography and etching. The lower electrode 12 may also be formed by a lift-off method. As shown in FIG. 2(c), a lower piezoelectric film 14a is formed on the lower electrode 12 and the substrate 10 by, for example, sputtering, vacuum deposition, or CVD.

[0038] As shown in FIG. 2(d), an insertion film 28 is formed on the lower piezoelectric film 14a. The insertion film 28 is patterned into a desired shape using photolithography and etching. The insertion film 28 may be formed by lift-off. A method for forming the thick film portion 28a and the thin film portion 28b in the insertion film 28 will now be described. An insertion film having the thickness of the thick film portion 28a is formed on the lower piezoelectric film 14a using sputtering, vacuum deposition, or CVD. Then, the region of the insertion film that will become the thin film portion 28b is thinned using photolithography and etching. This forms the thick film portion 28a and the thin film portion 28b. Alternatively, a first insertion film having the thickness of the thin film portion 28b is formed on the lower piezoelectric film 14a using sputtering, vacuum deposition, or CVD. A second insertion film having the desired pattern is formed on the first insertion film using lift-off. The insertion film 28 formed with the first and second insertion films becomes the thick film portion 28a. The insertion membrane 28 where the first insertion membrane is formed but the second insertion membrane is not formed becomes a thin film portion 28b.

[0039] As shown in FIG. 3(a), an upper piezoelectric film 14b is formed on the lower piezoelectric film 14a and the insertion film 28. The upper piezoelectric film 14b is formed by, for example, sputtering, vacuum deposition, or CVD. The piezoelectric film 14 is formed from the lower piezoelectric film 14a and the upper piezoelectric film 14b. A recess 27 corresponding to the recess 26 of the insertion film 28 is formed on the top surface of the upper piezoelectric film 14b.

[0040] As shown in FIG. 3(b), an upper electrode 16 is formed on the upper piezoelectric film 14b. The upper electrode 16 is formed by, for example, sputtering, vacuum deposition, or CVD. The upper electrode 16 is patterned into a desired shape by, for example, photolithography and etching. The upper electrode 16 may also be formed by lift-off. A recess 22 surrounded by a step 23 is formed on the upper surface of the upper electrode 16, corresponding to the recess 26 on the upper surface of the insertion film 28 and the recess 26 on the upper surface of the upper piezoelectric film 14b. As shown in FIG. 3(c), the piezoelectric film 14 is patterned into a desired shape by, for example, photolithography and etching.

[0041] As shown in FIG. 4(a), a metal layer 20 is formed on the lower electrode 12 and upper electrode 16 outside the resonance region 50. The metal layer 20 is formed, for example, by sputtering or vacuum deposition and lift-off. As shown in FIG. 4(b), an etching solution is introduced into the sacrificial layer 38 below the lower electrode 12 through the hole 35 (see FIG. 1(a)). This removes the sacrificial layer 38. The medium used to etch the sacrificial layer 38 is preferably one that does not etch the materials constituting the resonator other than the sacrificial layer 38. In particular, the etching medium is preferably one that does not etch the lower electrode 12, which it comes into contact with. The stresses of the lower electrode 12, piezoelectric film 14, and upper electrode 16 are set to compressive stress. As a result, when the sacrificial layer 38 is removed, the lower electrode 12 bulges away from the substrate 10 on the opposite side. This forms a dome-shaped void 30 between the lower electrode 12 and the substrate 10.

[0042] As shown in FIG. 4(c), the sensitive film 24 is formed in the recess 22 on the upper surface of the upper electrode 16. The sensitive film 24 is formed, for example, by applying a solvent in which the material of the sensitive film 24 is dissolved, and then drying the solvent. Alternatively, the sensitive film 24 may be formed into a desired pattern using a sputtering method or a vacuum deposition method and a lift-off method. In this way, the detection element 112 according to Example 1 is manufactured.

[0043] [Experiment 1] The following experiment 1 was conducted assuming the formation of a sensitive film 24 on the upper electrode 16. A solvent was prepared by dissolving cellulose-based resin in 5 g of acetone. Approximately 2 μl (microliters) of the prepared solvent was applied to a glass slide using a micropipette to prepare a sensitive agent 25. The concentrations of cellulose-based resin in the solvent for each sample were 0.1 wt %, 0.5 wt %, and 1.0 wt %.

[0044] Figures 5(a) to 5(c) are photographs of the sensitizer 25 viewed from above after application of each solution in Experiment 1. As shown in Figures 5(a) to 5(c), the area of ​​the sensitizer 25 does not change much between 0.5 wt% and 1.0 wt%, but the area of ​​the sensitizer 25 in plan view increases at 0.1 wt%. Furthermore, at 0.1 wt%, the planar shape of the sensitizer 25 becomes distorted. The dimensions of the sensitizer 25 in the X and Y directions are denoted by Lx and Ly.

[0045] 6(a) to 6(c) are diagrams showing the thickness of the sensitizer 25 relative to the position after application of each solvent in Example 1. As shown in FIGS. 6(a) to 6(c), the thickness of the sensitizer 25 varies depending on the position. The thickness Tmax is the maximum film thickness at the edge of the sensitizer 25, and the thickness Tc of the sensitizer 25 at the center. In FIG. 6(a), Tmax = 0.35 μm and Tc = 0.05 μm. In FIG. 6(b), Tmax = 3.3 μm and Tc = 0.56 μm. In FIG. 6(c), Tmax = 5.40 μm and Tc = 1.03 μm. As such, the sensitizer 25 is thicker at the edge and thinner at the center. The thickness of the sensitizer 25 was measured at multiple locations for each sample.

[0046] Table 1 is a table summarizing the dimensions Lx, Ly, thickness Tmax and Tc of each sensor 25. Tmax and Tc indicate the range of measurement results at multiple locations. [Table 1]

[0047] As shown in Table 1, when an attempt is made to apply a thin layer of the sensitizer 25, the concentration of the sensitizer in the solution is lowered. However, if the concentration is low, the planar shape of the sensitizer 25 becomes distorted.

[0048] [Experiment 2] For Example 1, the Q value at the anti-resonance frequency was measured relative to the thickness of the sensitive film 24. The materials and dimensions of each layer were the same as those exemplified in Example 1 when the resonant frequency was 2.4 GHz.

[0049] Fig. 7 is a diagram showing the Q value versus the thickness of the sensitive film in Experiment 2. As shown in Fig. 7, the Q value Qa at the anti-resonance frequency decreases as the sensitive film 24 becomes thicker. The Qa of a piezoelectric thin film resonator with a sensitive film 24 that is 156 nm thick is less than half the Qa of a piezoelectric thin film resonator that does not have a sensitive film 24. The Qa of a piezoelectric thin film resonator with a sensitive film 24 that is 500 nm thick is nearly 0, and no resonance occurs.

[0050] 7, the thickness of the sensitive film 24 is preferably 500 nm or less, and more preferably 200 nm or less. However, if an attempt is made to form the sensitive film 24 thin, the planar shape of the sensitive film 24 will become distorted, as shown in FIGS. 5(a) to 6(c) and Table 1.

[0051] [Experiment 3] To investigate the effect of distortion of the planar shape of the sensitive film 24, a piezoelectric thin film resonator according to Comparative Example 1 was fabricated in which no recesses 22 were formed on the upper surface of the upper electrode 16. A sensitive film 24 was formed in the resonance region of Comparative Example 1. FIGS. 8(a) to 8(c) are plan views of resonators A to C fabricated in Experiment 3. The region of the sensitive film 24 is hatched. As shown in FIG. 8(a), in resonator A, the sensitive film 24 is not provided on the upper electrode 16. As shown in FIG. 8(b), in resonator B, the sensitive film 24 is provided in the resonance region 50 on the upper electrode 16. The sensitive film 24 is not provided in the region 58 on the extraction side of the resonance region 50, and the planar shape of the sensitive film 24 is distorted. As shown in FIG. 8(c), in resonator C, the sensitive film 24 is provided over the entire resonance region 50 on the upper electrode 16.

[0052] 9(a) and 9(b) are diagrams showing the magnitude of impedance |Z| versus frequency for resonators A to C in Experiment 3. FIG. 9(b) is an enlarged view of FIG. 9(a). As shown in FIGS. 9(a) and 9(b), compared to resonator A, resonators B and C have duller peaks at the anti-resonance frequency fa and the resonance frequency fr, and a lower Q value. In addition, the difference between the anti-resonance frequency fa and the resonance frequency fr is smaller, and the electromechanical coupling coefficient k 2 In this way, when the sensitive film 24 is provided, the Q value and the electromechanical coupling coefficient k2 decreases. In resonator B, a spurious response 56 is observed between fa and fr. On the other hand, in resonator C, no spurious response 56 is observed. In resonator B, the spurious response is thought to occur because the planar shape of the sensitive film 24 is distorted. If the spurious response 56 occurs, it may be mistakenly recognized as fr or fa when measuring fluctuations in the resonant frequency fr or anti-resonant frequency fa of the detection element. In Example 1, the sensitive film 24 is provided within the recess 22 on the top surface of the upper electrode 16, which prevents the planar shape of the sensitive film 24 from becoming distorted. This makes it possible to suppress the spurious response 56.

[0053] [Experiment 4] For Example 1, resonators were fabricated with different thicknesses of the insertion film 28. FIG. 10 is a cross-sectional view showing the insertion film in Experiment 4. As shown in FIG. 10, the thickness of the thick film portion 28a of the insertion film 28 was Ta, and the thickness of the thin film portion 28b was Tb. The thickness Td = Ta - Tb was fixed at 107 nm. The materials and dimensions of the other layers were the same as those exemplified for a piezoelectric thin film resonator with a resonant frequency of 2.4 GHz.

[0054] 11(a) and 11(b) show the relationship between the thickness Ta of the thick film portion 28a and the k 2 11(a), as the thickness Ta of the thick film portion 28a increases, the electromechanical coupling coefficient k 2 As shown in FIG. 11(b), as the thickness Ta increases, the Q value Qa of the anti-resonance frequency increases. In this way, by increasing the thickness Ta of the thick film portion 28a, it is possible to suppress the leakage of the acoustic wave outside the resonance region 50, and the Q value can be improved. However, the electromechanical coupling coefficient k 2 The electromechanical coupling coefficient k 2 When the difference between the resonance frequency fr and the anti-resonance frequency fa becomes small, the difference between the resonance frequency fr and the anti-resonance frequency fa becomes small. In a high frequency filter, if the difference between the resonance frequency fr and the anti-resonance frequency fa is small, the achievable bandwidth is limited, making it difficult to design the high frequency filter. For this reason, high frequency filters such as those in Patent Document 2 have an electromechanical coupling coefficient k 2In the case of a detection element, if the Q value is high, the k 2 Therefore, the thickness Ta can be increased.

[0055] FIG. 12 is a diagram showing the TCF versus the thickness Tb of the thin film portion in Experiment 4. The temperature coefficients of frequency (TCF) are the temperature coefficients of the resonant frequency. The temperature coefficient of the elastic constant of the piezoelectric film 14 is negative, while the temperature coefficient of the elastic constant of the thin film portion 28b is positive. Therefore, if the thin film portion 28b is not provided, the TCF is negative. Increasing the thickness Tb of the thin film portion 28b changes the TCF in the positive direction. By setting the thickness Tb to about 70 nm, the TCF can be made almost zero. Increasing the thickness Tb reduces the electromechanical coupling coefficient k 2 In high frequency filters, the electromechanical coupling coefficient k 2 Therefore, it is difficult to adopt a thickness Tb where the TCF is almost 0. In the detection element, the electromechanical coupling coefficient k 2 Since it is acceptable for the thickness Tb to decrease, the thickness Tb can be set so that the TCF is nearly zero.

[0056] [Experiment 5] FIG. 13 is a graph showing the change Δf in resonant frequency over time. The change Δf in resonant frequency after powering on the detection element was measured for Example 1 and Comparative Example 2. The materials and dimensions of Example 1 are the same as those exemplified for a piezoelectric thin film resonator with a resonant frequency of 2.4 GHz. The insertion film 28 is a silicon oxide film, with the thick film portion 28a having a thickness Ta of 180 nm and the thin film portion 28b having a thickness Tb of 73 nm. Comparative Example 1 is the same as Example 1 except that the thin film portion 28b is not provided.

[0057] As shown in FIG. 13 , in Comparative Example 2, Δf changes significantly after power-on, and it takes about 500 seconds for Δf to stabilize. Even after Δf stabilizes, there is a large frequency drift, and Δf remains unstable. In Example 1, Δf remains very stable immediately after power-on. In Comparative Example 2, the large change in Δf after power-on is thought to be due to the temperature increase caused by self-heating of the piezoelectric thin-film resonator upon power-on. It is thought that Δf remains unstable even after the element temperature of the piezoelectric thin-film resonator stabilizes due to small fluctuations in the environmental temperature. On the other hand, in Example 1, the provision of the thin-film portion 28b makes it possible to make the TCF nearly zero, and therefore Δf remains stable. Therefore, in Example 1, frequency changes due to element temperature and environmental temperature can be suppressed, allowing for more accurate measurement of the mass change of a substance, such as a specific atom or molecule, in a gas or liquid.

[0058] In a high-frequency filter, a slight change in the resonant frequency does not pose a problem as long as the temperature change in the passband is within an allowable range. Also, if the thin film portion 28b is made thicker to make the TCF 0, the electromechanical coupling coefficient k 2 This reduces the TCF, limiting the achievable bandwidth and making it difficult to design a high-frequency filter. For this reason, the TCF may not be set to 0. On the other hand, since the detection element detects environmental changes based on changes in the resonant frequency, even a slight change in the resonant frequency can be a problem. In addition, the electromechanical coupling coefficient k 2 A decrease in TCF does not pose as big a problem as in a high frequency filter. In the first embodiment, by providing the thin film portion 28b, the TCF can be made close to 0, and the resonance frequency can be stabilized.

[0059] According to Example 1, the thin film portion 28b of the insertion film 28 is provided in the center of the resonance region 50 in plan view, and the thick film portion 28a of the insertion film 28 is provided around the thin film portion 28b and on the periphery of the resonance region 50 in plan view. The sensitive film 24 is provided in a recess 22 (region) that is provided on the upper surface of the upper electrode 16 and surrounded by a step 23 (first step) defined by the thin film portion 28b and the thick film portion 28a. Because the sensitive film 24 is provided within the recess 22, even if the sensitive film 24 is made thin, the planar shape of the sensitive film 24 is distorted, which can prevent the generation of spurious signals 56 caused by the distortion of the planar shape of the sensitive film 24, as in resonator B in Experiment 3. Furthermore, the sensitive film 24 can be formed relatively flat. This allows the characteristics of the resonator to be stabilized. Furthermore, since the recess 22 is defined by the thin film portion 28b and the thick film portion 28a, the complicated manufacturing process of forming a dam as in Patent Document 1 is not necessary, and the manufacturing process can be simplified.

[0060] The sign of the temperature coefficient of the elastic constant of the thin film portion 28b is opposite to that of the piezoelectric film 14. This makes it possible to reduce the TCF, as shown in Figure 12 of Experiment 4. Therefore, as shown in Figure 13 of Experiment 5, when the detection element is operated, the characteristics of the resonator can be stabilized.

[0061] The thick film portion 28a includes a film having a Young's modulus smaller than that of the piezoelectric film 14. This improves the Q value, as shown in FIG. 11(b) of Experiment 3. As shown in FIG. 7 of Experiment 2, the Q value of the detection element is low due to the presence of the sensitive film 24. Therefore, it is preferable to provide the thick film portion 28a.

[0062] The piezoelectric film 14 is primarily composed of aluminum nitride, and the insertion film 28 is primarily composed of silicon oxide. The temperature coefficient of the elastic constant of silicon oxide is positive, while the temperature coefficient of the elastic constant of aluminum nitride is negative. Furthermore, the Young's modulus of silicon oxide is smaller than that of aluminum nitride. Therefore, the insertion film 28 can reduce the TCF and improve the Q value. Note that the term "primary component" allows for the intentional or unintentional inclusion of impurities. For example, the piezoelectric film 14 being primarily composed of aluminum nitride means that the sum of the O and Al concentrations in the piezoelectric film 14 is 50 atomic % or more or 80 atomic % or more, and the O concentration and the Al concentration are both 10 atomic % or more or 20 atomic % or more. The insertion film 28 being primarily composed of silicon oxide means, for example, that the sum of the O and Si concentrations in the insertion film 28 is 50 atomic % or more or 80 atomic % or more, and the O concentration and the Si concentration are both 10 atomic % or more or 20 atomic % or more.

[0063] The insertion film 28 may be provided between the lower electrode 12 and the piezoelectric film 14, or may be provided between the piezoelectric film 14 and the upper electrode 16. As in Example 1, by providing the insertion film 28 between the lower piezoelectric film 14a and the upper piezoelectric film 14b, the TCF can be reduced and the Q value can be increased even if the thicknesses Ta and Tb of the insertion film 28 are thin.

[0064] The thickness Ta of the thick film portion 28a is preferably 1.1 times or more, more preferably 1.5 times or more, and even more preferably 2 times or more, the thickness Tb of the thin film portion 28b. This allows a step 23 to be formed on the upper electrode 16, defined by the step Td between the thick film portion 28a and the thin film portion 28b. The height D1 of the step 23 is preferably 1 / 4 or more of the thickness Ta, more preferably 1 / 2 times or more of Ta. The difference between Ta and Tb is preferably 50 nm or more, more preferably 100 nm or more. The height D1 of the step 23 is preferably 50 nm or more, more preferably 100 nm or more. Ta is preferably 0.1 times or more, more preferably 0.2 times or more, and even more preferably 0.3 times or more the thickness of the piezoelectric film 14. A thick Ta makes it difficult to form the insertion film 28. Therefore, Ta is preferably 5 times or less than Tb, the difference between Ta and Tb is preferably 500 nm or less, and Ta is preferably 0.5 times or less the thickness of the piezoelectric film 14. It is preferable that D1 is four times or less than Tb and 500 nm or less. The width of the thick film portion 28a in the direction perpendicular to the outer periphery of the resonance region 50 is 0.3 to 2.5 times the wavelength of the elastic wave (twice the total thickness of the lower electrode 12, the piezoelectric film 14, and the upper electrode 16).

[0065] In high frequency filters, increasing the thickness Ta increases the electromechanical coupling coefficient k 2 If the thickness Ta is small, a step is not formed on the upper electrode as shown in the drawing of Patent Document 2. On the other hand, in the detection element, the electromechanical coupling coefficient k 2 Since a decrease in Ta is not as significant a problem as in a high-frequency filter, the thickness Ta can be increased. This allows the formation of a step 23 on the upper electrode 16. Therefore, the sensitive film 24 can be applied to the recess 22 formed in the resonance region 50 without misalignment. Furthermore, the presence of the step 23 in the resonance region 50 prevents the sensitive film 24 from moving out of the resonance region 50 and reduces the difference in film thickness between the center and outer periphery of the sensitive film 24. Therefore, it is possible to prevent the formation of spurious signals 56 caused by distortion of the planar shape of the sensitive film 24, as in resonator B in Experiment 3.

[0066] This section explains the problem of forming a dam using a protective film, as shown in Figure 17(b) of Patent Document 1. There are two methods for forming a dam using a protective film. In Method 1, a thick protective film is formed, and then the area on the protective film surrounded by the dam is etched. In Method 2, a thin protective film is formed, and then an additional protective film is formed in the area where the dam is to be formed. In both Methods 1 and 2, a mask layer is formed on the protective film using photolithography. Because the protective film is disposed on the upper electrode, the upper surface of the protective film has large irregularities. This reduces the accuracy of aligning the mask layer pattern used to form the dam. Furthermore, if the upper surface of the protective film has large irregularities, it is difficult for the mask layer to completely cover the irregularities on the upper surface of the protective film. As a result, the mask layer may become thin in the area where the mask layer should be formed, resulting in etching of the protective film. In addition, the mask layer may become thick in the area where an opening in the mask layer should be formed, resulting in the protective film not being etched. Furthermore, if the mask layer does not completely cover the protective film, etching residue or an etching solution may penetrate between the mask layer and the protective film during etching of the protective film.

[0067] 14 is an enlarged cross-sectional view showing an example of steps in the piezoelectric film, insertion film, upper electrode, and sensitive film in Example 1. As shown in FIG. 14, the upper surface of the lower piezoelectric film 14a is approximately flat. Note that, as shown in FIG. 1(b), the upper surface of the lower piezoelectric film 14a in the resonance region 50 is dome-shaped due to the dome-shaped cavity 30. However, while the width of the resonance region 50 is several tens to several hundreds of μm, the height of the cavity 30 is several μm, so the upper surface of the lower piezoelectric film 14a in the resonance region 50 is approximately flat.

[0068] As shown in Fig. 2(d), an insertion film 28 having a thick film portion 28a and a thin film portion 28b is formed on the lower piezoelectric film 14a. As a result, a step 26a (second step) is provided on the upper surface of the insertion film 28 so that the upper surface of the thin film portion 28b is recessed toward the substrate 10 relative to the upper surface of the thick film portion 28a, as shown in Fig. 14. The upper surface of the thin film portion 28b becomes the recess 26.

[0069] 3(a), the upper piezoelectric film 14b is formed on the insertion film 18. As a result, a step 27a (third step) is provided on the upper surface of the piezoelectric film 14, so that the upper surface of the piezoelectric film 14 corresponding to the thin film portion 28b is recessed toward the substrate 10 relative to the upper surface of the piezoelectric film 14 corresponding to the thick film portion 28a, as shown in FIG. 14. The region of the upper surface of the piezoelectric film 14 surrounded by the step 27a becomes the recess 27.

[0070] 3(b), an upper electrode 16 is formed on the piezoelectric film 14. As a result, a step 23 (first step) is provided on the upper surface of the upper electrode 16, so that the upper surface of the upper electrode 16 corresponding to the thin film portion 28b is recessed toward the substrate 10 more than the upper electrode 16 corresponding to the thick film portion 28a, as shown in FIG. 14. The region of the upper surface of the upper electrode 16 surrounded by the step 23 becomes a recess 22.

[0071] 4(c) and 14, the sensitive film 24 is formed in the recess 22 on the upper surface of the upper electrode 16. This prevents distortion from occurring in the planar shape of the sensitive film 24, thereby suppressing spurious responses.

[0072] When step 27a is formed on step 26a, the inclination of step 27a becomes gentler than the inclination of step 26a. That is, angle θ2 of the surface of step 27a relative to the bottom surface of recess 27 becomes smaller than angle θ1 of the surface of step 26a relative to the bottom surface of recess 26. When step 23 is formed on step 27a, the inclination of step 23 becomes gentler than the inclination of step 27a. That is, angle θ3 of the surface of step 23 relative to the bottom surface of recess 22 becomes smaller than angle θ2 of the surface of step 27a relative to the bottom surface of recess 27. In this way, the inclination of step 23 can be made gentler than the inclination of step 26a.

[0073] If the slope of the step 23 is steep (i.e., if the angle θ3 is close to 90°), voids and the like are likely to form in the sensitive film 24 near the step 23 in the recess 22 when a solvent containing the sensitive film 24 is applied to the recess 22 or when the sensitive film 24 is sputtered. Furthermore, if the slope of the step 23 is steep, uneven application occurs near the step 23 when the solvent containing the sensitive film 24 is applied to the recess 22, and the thickness of the sensitive film 24 is likely to vary. This results in non-uniform sensitivity of the sensitive film 24. In Example 1, the slope of the step 23 can be made gentler than the slope of the step 26a. This makes it possible to suppress the formation of voids near the step 23, variations in the thickness of the sensitive film 24, and the like. This makes it possible to make the sensitivity of the sensitive film 24 uniform.

[0074] As shown in FIG. 3( c), when the piezoelectric film 14 is patterned, the etching solution used to etch the piezoelectric film 14 may penetrate into the interface between the insertion film 28 and the upper piezoelectric film 14b and the interface between the upper piezoelectric film 14b and the upper electrode 16. In Example 1, a step 26a is provided on the upper surface of the insertion film 28, which prevents the etching solution from penetrating into the interface between the insertion film 28 and the upper piezoelectric film 14b. A step 27a is provided on the upper surface of the upper piezoelectric film 14b, which prevents the etching solution from penetrating into the interface between the upper piezoelectric film 14b and the upper electrode 16. Note that even in processes other than etching the piezoelectric film 14, the etching solution can be prevented from penetrating into the interface between the insertion film 28 and the upper piezoelectric film 14b and the interface between the upper piezoelectric film 14b and the upper electrode 16.

[0075] As shown in Fig. 2(c), the unevenness of the upper surface of the lower piezoelectric film 14a is small before the formation of the insertion film 28. This makes it possible to suppress the above-mentioned problem that occurs when the dam of the protective film shown in Fig. 17(b) of Patent Document 1 is formed due to the large unevenness of the upper surface of the protective film.

[0076] Table 2 is a table summarizing the film thickness and TCF when copper phthalocyanine (CuPc), an organic low molecular weight material, is used as the sensitive film 24 on the upper electrode 16 of the detection element. [Table 2]

[0077] As shown in Table 2, the thicker the sensitive film 24, the more negative the TCF becomes. Thus, the TCF of the sensing element varies depending on the material of the sensitive film 24 formed on the upper electrode 16. Therefore, it is necessary to adjust the thickness Tb of the thin film portion 28b so that the TCF of the sensitive film 24 approaches ±0. The thickness Tb of the thin film portion 28b is preferably set so that the TCF (temperature coefficient of frequency) of the resonant frequency of the sensing element is greater than or equal to -20 ppm / K and less than or equal to 20 ppm / K. This allows the resonator characteristics to be stabilized when the sensing element is operated, as shown in Figure 13 of Experiment 5. The TCF is more preferably greater than or equal to -10 ppm / K and less than or equal to 10 ppm / K, and even more preferably greater than or equal to -5 ppm / K and less than or equal to 5 ppm / K.

[0078] [Modification 1 of Example 1] Modifications 1 and 2 of Example 1 are examples in which the configuration of the void is changed. FIG. 15(a) is a cross-sectional view of a detection element according to Modification 1 of Example 1. As shown in FIG. 15(a), a recess is formed on the upper surface of the substrate 10. The lower electrode 12 is formed flat on the substrate 10. As a result, the void 30 is formed in the recess of the substrate 10. The void 30 is formed so as to include the resonance region 50. The other configurations are the same as those of Example 1, and therefore description thereof will be omitted. The void 30 may be formed so as to penetrate the substrate 10.

[0079] [Modification 2 of Example 1] FIG. 15(b) is a cross-sectional view of a detection element according to Modification 2 of Example 1. As shown in FIG. 15(b), an acoustic reflection film 31 is formed below the lower electrode 12 in the resonance region 50. The acoustic reflection film 31 is formed by alternating low-acoustic-impedance films 31a and high-acoustic-impedance films 31b. The thicknesses of the films 31a and 31b are, for example, approximately λ / 4 (λ is the wavelength of the elastic wave). The number of layers of the films 31a and 31b can be set arbitrarily. The acoustic reflection film 31 may be formed by stacking at least two types of layers with different acoustic properties with a gap between them. Furthermore, the substrate 10 may be one of the at least two types of layers with different acoustic properties of the acoustic reflection film 31. For example, the acoustic reflection film 31 may be configured by providing one layer of a film with different acoustic impedance in the substrate 10. The other configurations are the same as those in Example 1, and therefore a description thereof will be omitted.

[0080] As in Example 1 and its Modification 1, the piezoelectric thin film resonator used in the detection element may be an FBAR (Film Bulk Acoustic Resonator) in which a gap 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. Alternatively, as in Modification 2 of Example 1, the piezoelectric thin film resonator may be an SMR (Solidly Mounted Resonator) that includes an acoustic reflection film 31 that reflects elastic waves propagating through the piezoelectric film 14 below the lower electrode 12 in the resonance region 50. The acoustic reflection layer that includes the resonance region 50 may include the gap 30 or the acoustic reflection film 31.

[0081] Although the planar shape of the resonance region 50 has been described as an ellipse, the planar shape of the resonance region 50 may be any shape, such as a square or a polygonal shape such as a pentagon. [Example]

[0082] Example 2 is an example of a detection system including the detection elements of Example 1 and its modified examples. FIG. 16 is a block diagram showing the configuration of an odor detection device 100 according to this embodiment. As shown in FIG. 16, the odor detection device 100 includes an odor detection unit 110 and a control unit 120. The odor detection unit 110 includes a chamber 111, a detection element 112, a humidity sensor 113, a temperature sensor 114, a first pump 115, a second pump 116, and a filter 117. The chamber 111 houses the detection element 112, the humidity sensor 113, and the temperature sensor 114. The chamber 111 is provided with a first intake port 111a, a second intake port 111b, and an exhaust port 111c.

[0083] The detection element 112 is housed in the chamber 111 and detects odor components contained in the gas supplied into the chamber 111. The detection element 112 is a sensor that can detect odor components by adsorbing them, and as shown in Figures 1(a) and 1(b), has a configuration in which a sensitive film 24 for adsorbing the components to be detected is provided on the surface of the upper electrode 16. When an odor component is adsorbed on the surface of the sensitive film 24, the resonant frequency fluctuates (decreases) depending on the mass, making it possible to detect minute changes in mass.

[0084] The odor components detected by the detection element 112 are typically relatively heavy molecules in the air, such as polymer compounds, but are not particularly limited thereto. The odor components detected by the detection element 112 are not limited to those that can be detected by the human sense of smell, and may be any chemical species present in the gas.

[0085] As shown in Figure 16, the odor detection device 100 includes 16 detection elements 112, from channel 1 (ch1) to channel 16 (ch16). Each detection element 112 can have a different sensitive film 24, and each can adsorb a different odor component. That is, a plurality of detection elements 112 can be provided, and the sensitive films 24 of at least two of the plurality of detection elements 112 can be made of different materials. The number of detection elements 112 included in the odor detection device 100 is not particularly limited, as long as it is one or more.

[0086] The humidity sensor 113 and the temperature sensor 114 are housed in the chamber 111 and detect the humidity and temperature inside the chamber 111. The types of the humidity sensor 113 and the temperature sensor 114 are not particularly limited.

[0087] Next, the pumps will be described. The first pump 115 is connected to the first intake port 111a and delivers gas into the chamber 111 through the first intake port 111a. The first pump 115 may be, for example, a diaphragm pump, but may be another type of pump. The second pump 116 is connected to the second intake port 111b and delivers gas into the chamber 111 through the second intake port 111b. The second pump 116 may be, for example, a diaphragm pump, but may be another type of pump. Note that although the first pump 115 and the second pump 116 are used in FIG. 16, these pumps may be omitted.

[0088] Filter 117 is connected to second intake port 111b and removes odor components from the gas flowing into chamber 111 through second intake port 111b. Filter 117 is configured to be able to remove at least the odor components that are the detection targets of each detection element 112. Furthermore, filter 117 is preferably able to remove water molecules.

[0089] The control unit 120 is connected to the odor detection unit 110 and performs arithmetic processing on the output of the odor detection unit 110. As shown in FIG. 16, the control unit 120 includes an acquisition unit 121, a calculation unit 122, a determination unit 123, and a memory unit 124. As shown in FIG. 16, the acquisition unit 121 is connected to each detection element 112, humidity sensor 113, and temperature sensor 114, and acquires the output of each sensor. The connection between the acquisition unit 121 and each sensor may be wired or wireless. The acquisition unit 121 supplies the acquired output of each sensor to the calculation unit 122. The calculation unit 122 performs arithmetic processing using the output of each sensor supplied from the acquisition unit 121, and supplies the calculation result to the determination unit 123.

[0090] The determination unit 123 performs an odor component determination using the calculation results supplied from the calculation unit 122. The determination unit 123 can determine at least one of the presence or absence of an odor component, the concentration of the odor component, the type of odor, and the intensity of the odor. The determination unit 123 supplies the determination result and the measurement results by the odor detection unit 110 to the memory unit 124. The memory unit 124 stores the determination result by the determination unit 123 and the measurement results by the odor detection unit 110.

[0091] Each of the components of the control unit 120 described above is a functional configuration realized by cooperation between hardware such as a processor and memory and software, and the manner of realization is not particularly limited. That is, the control unit 120 may be realized by an information processing unit configured integrally with the odor detection unit 110, or may be realized by an information processing unit independent of the odor detection unit 110. Furthermore, each of the functional components of the control unit 120 may be realized by multiple information processing units connected via a network. The detection element may be the detection element of Variation 1 or 2 shown in Figures 15(a) and 15(b).

[0092] The detection system using the detection element 112 may be any detection system that detects changes in the environment based on the signal output by the detection element 112.

[0093] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0094] 10 Substrate 12 Lower electrode 14 Piezoelectric film 14a Lower piezoelectric film 14b Upper piezoelectric film 16 Upper electrode 22, 26, 27 recesses 23, 26a, 27a steps 24 Sensitive membrane 28 Insertion membrane 28a Thick film section 28b Thin Film Section

Claims

1. A substrate; a piezoelectric film provided on the substrate; a lower electrode and an upper electrode facing each other with at least a part of the piezoelectric film interposed therebetween; an insertion film including: a thin film portion provided between the lower electrode and the upper electrode in a resonance region defined by an area where the lower electrode and the upper electrode face each other, sandwiching at least a portion of the piezoelectric film, the thin film portion being provided inside the resonance region in a plan view; and a thick film portion that surrounds the thin film portion in a plan view and is provided on the periphery of the resonance region and is thicker than the thin film portion; a sensitive film provided in a region surrounded by a first step defined by the thin film portion and the thick film portion provided on the upper surface of the upper electrode; Equipped with A detection element whose resonant frequency changes with changes in the environment.

2. 2. The detection element according to claim 1, wherein the sign of the temperature coefficient of elastic constant of said thin film portion is opposite to the sign of the temperature coefficient of elastic constant of said piezoelectric film.

3. The detection element according to claim 2 , wherein the thick film portion includes a film having a Young's modulus smaller than that of the piezoelectric film.

4. 2. The detection element according to claim 1, wherein the piezoelectric film is mainly made of aluminum nitride, and the insertion film is mainly made of silicon oxide.

5. A detection element described in any one of claims 1 to 4, wherein the piezoelectric film comprises a lower piezoelectric film provided on the lower electrode and an upper piezoelectric film provided on the lower piezoelectric film, and the insertion film is provided between the lower piezoelectric film and the upper piezoelectric film.

6. The detection element according to claim 1 , wherein the thickness of the thick film portion is 1.5 times or more the thickness of the thin film portion.

7. 5. The detection element according to claim 1, wherein the temperature coefficient of the resonant frequency of the detection element is −20 ppm / K or more and 20 ppm / K or less.

8. a second step is provided on the upper surface of the insertion film so that the upper surface of the thin film portion is recessed toward the substrate more than the upper surface of the thick film portion; a third step is provided on the upper surface of the piezoelectric film so that the upper surface of the piezoelectric film corresponding to the thin film portion is recessed toward the substrate more than the upper surface of the piezoelectric film corresponding to the thick film portion; 5. The detection element according to claim 1, wherein the first step is provided so that the upper surface of the upper electrode corresponding to the thin film portion is recessed toward the substrate relative to the upper surface of the upper electrode corresponding to the thick film portion.

9. The detection element according to claim 8 , wherein the inclination of the first step is gentler than the inclination of the second step.

10. A detection element according to any one of claims 1 to 4; A detection system that detects a change in the environment based on a signal output by the detection element.

11. The detection system according to claim 10 , wherein a plurality of the detection elements are provided, and the sensitive films of at least two of the plurality of detection elements are formed from different materials.

12. a process for fabricating a resonator comprising: a piezoelectric film provided on a substrate; a lower electrode and an upper electrode facing each other with at least a portion of the piezoelectric film sandwiched therebetween; and an insertion film provided between the lower electrode and the upper electrode within a resonance region defined by a region where the lower electrode and the upper electrode face each other with at least a portion of the piezoelectric film sandwiched therebetween, the insertion film comprising a thin film portion provided inside the resonance region in a plan view; and a thick film portion surrounding the thin film portion in a plan view, provided on the periphery of the resonance region, and thicker than the thin film portion; forming a sensitive film whose mass changes in response to an environmental change in an area surrounded by a step defined by the thin film portion and the thick film portion provided on the upper surface of the upper electrode; A method for manufacturing a detection element comprising the steps of:

13. The method for manufacturing a detection element according to claim 12, wherein the step of forming the sensitive film includes a step of applying a solvent containing a sensitive agent.

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