Detection Device

Abstract

To provide a detection device capable of increasing a detection precision.SOLUTION: A detection device includes a piezoelectric part 21 having a piezoelectric layer 14, and a first electrode and a second electrode provided while sandwiching at least one portion of the piezoelectric layer, and a sensitive film 18 that is provided in a side opposite to the piezoelectric layer of the first electrode and causes mass to be changed by a change in the environment, and also includes a resonator 40 that corresponds to a change in the mass, and causes a change in at least one of a resonance frequency and an antiresonant frequency in an even-order vibration mode as a vibration mode of elastic waves capable of performing electric excitation differing from an odd-order mode after providing the sensitive film in the piezoelectric part when a frequency capable of performing electric excitation in the piezoelectric part in which the sensitive film is not provided is set to an odd-order mode of elastic waves, and a detector 45 for detecting a change in the environment on the basis of a change in at least the one frequency.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a detection device, for example, a detection device having a resonator with a sensitive membrane. [Background technology]

[0002] Environmental sensors are known that detect environmental changes by detecting changes in the mass of a sensitive film. A detection device 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 the resonant frequency caused by changes in the mass of the sensitive film (for example, Patent Document 1). In sensing in liquid, it is known that the Q value decreases when a sensitive film is grown on the resonator (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2005-533265 [Patent Document 2] Special Publication No. 2020-519886 Summary of the Invention [Problem to be solved by the invention]

[0004] When detecting environmental changes in a gas, it is preferable to use a thin sensitive film to prevent deterioration of the resonance characteristics of the resonator. However, if the sensitive film is made thinner, the surface area of ​​the sensitive film will decrease, and the sensitivity to environmental changes will decrease.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to improve detection sensitivity while suppressing deterioration of the resonance characteristics of a resonator. [Means for solving the problem]

[0006] The present invention provides a detection device comprising: a piezoelectric section including a piezoelectric layer and a first electrode and a second electrode sandwiching at least a portion of the piezoelectric layer; a sensitive membrane provided on the opposite side of the piezoelectric layer from the first electrode, the mass of which changes with changes in the environment; a resonator that responds to the change in mass, and when the frequency at which electrical excitation is possible in the piezoelectric section without the sensitive membrane is defined as an odd mode of elastic waves, after the sensitive membrane is provided on the piezoelectric section, at least one of the resonance frequency and anti-resonance frequency in an even mode, which is a vibration mode of elastic waves that can be electrically excited differently from the odd mode, changes; and a detector that detects changes in the environment based on changes in at least one of the frequencies.

[0007] In the above configuration, the even-order mode may be a second-order mode.

[0008] In the above configuration, the thickness of the sensitive film may be 0.2 to 1.0 times the thickness of the piezoelectric layer.

[0009] In the above configuration, the elastic stiffness C of the sensitive membrane 33 is the elastic stiffness C of the piezoelectric layer 33 The ratio can be set to 0.06 to 0.62 times.

[0010] In the above configuration, the density of the sensitive film may be 0.35 to 0.54 times the density of the piezoelectric layer.

[0011] In the above configuration, the piezoelectric layer is an aluminum nitride layer, the Young's modulus of the sensitive film is 20 GPa or more and 80 GPa or less, and the density of the sensitive film is 1.2 g / cm 3 or more and 1.7g / cm 3 The following configuration can be adopted.

[0012] In the above configuration, the piezoelectric layer is an aluminum nitride layer, and the sensitive film is Metal Phthalocyanine The main component can be a composition of

[0013] In the above configuration, the resonant frequency of the resonator in the even-order mode may be 0.85 to 1.15 times the resonant frequency of the resonator in the first-order mode from which the sensitive film is removed. [Effects of the Invention]

[0014] An object of the present invention is to improve detection sensitivity. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram illustrating a detection device according to a first embodiment. [Figure 2] FIG. 2(a) is a plan view of a resonator 40 according to the first embodiment, and FIG. 2(b) is a cross-sectional view taken along the line AA of FIG. 2(a). [Figure 3] 3(a) and 3(b) are diagrams showing the magnitude |Z| of impedance and the Q value with respect to frequency in Simulation 1. FIG. [Figure 4] 4(a) to 4(c) are diagrams showing impedance |Z| versus frequency in the experiment. [Figure 5] FIG. 5 is a diagram showing impedance |Z| versus frequency in the experiment. [Figure 6] 6(a) and 6(b) are diagrams showing the Q value versus frequency in the experiment. [Figure 7] FIG. 7(a) is a graph showing impedance |Z| versus frequency for a sample with T=450 nm in the experiment, and FIG. 7(b) is an enlarged view of FIG. 7(a). [Figure 8] 8(a) to 8(c) are diagrams showing displacement relative to position in the Z direction in simulation 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment will be described with reference to the drawings. [Example]

[0017] FIG. 1 is a block diagram showing a detection device according to a first embodiment. The detection device 100 includes an oscillation circuit 42 and a detector 45. The oscillation circuit 42 includes a resonator 40 and an amplifier 41, and oscillates at a resonance frequency or an anti-resonance frequency in an even mode of the resonator 40 to output an oscillation signal. A measuring device 44 measures the frequency of the oscillation signal. A calculator 46 detects environmental changes based on changes in the frequency of the oscillation signal measured by the measuring device 44. Examples of environmental changes include changes in the amount of a substance such as a specific atom or molecule in the gas, changes in the temperature of the environment, changes in humidity, etc. When a specific substance in the gas is the source of an odor, the detection device 100 functions as an odor sensor.

[0018] Fig. 2(a) is a plan view of the resonator 40 according to the first embodiment, and Fig. 2(b) is a cross-sectional view taken along line AA in Fig. 2(a). The normal direction to the top 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.

[0019] The structure of the resonator 40 will be described with reference to FIGS. 2(a) and 2(b). The substrate 10 has a thickness and is rectangular in plan view. A lower electrode 12 extends from the center of the substrate 10's flat upper surface to one end of the substrate 10 in the longitudinal direction (X direction). A piezoelectric layer 14 and an upper electrode 16 formed on the piezoelectric layer 14 extend from the center of the substrate 10's upper surface to the other end of the substrate in the longitudinal direction. 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 layer 14. The elliptical portion in FIG. 2(a) is the resonance region 50, and the piezoelectric layer 14 corresponding to this resonance region 50 is sandwiched between the lower electrode 12 and the upper electrode 16. A dome-shaped void 22 is formed between the substrate 10 and the lower electrode 12, corresponding to the resonance region 50. When a voltage is applied to the lower electrode 12 and the upper electrode 16, the piezoelectric layer 14 vibrates, and the provision of this gap 22 facilitates the vibration.

[0020] A protective film 17 is provided on the entire surface of the upper electrode 16. A sensitive film 18 is provided on the protective film 17 at least corresponding to the resonance region 50. The protective film 17 does not have to be provided. The sensitive film 18 has a thickness T, which will be described later. The sensitive film 18 is only required to be provided so as to include the resonance region 50 in a planar view. The sensitive film 18 may cover the resonance region 50 or may extend beyond the periphery of the resonance region 50. The lower electrode 12, piezoelectric layer 14, upper electrode 16, protective film 17, and sensitive film 18 in the resonance region 50 form a laminated film 20. Before the sensitive film 18 is provided, the lower electrode 12, piezoelectric layer 14, upper electrode 16, and protective film 17 form a piezoelectric portion 21. The laminated film 20 in the resonance region 50 resonates with elastic waves in a thickness longitudinal vibration mode or a thickness shear vibration mode, for example.

[0021] 2(a), the planar shape of the resonance region 50 is, for example, an ellipse. The hatched area in a grid pattern represents the planar shape of the resonance region 50. The planar shape of the resonance region 50 may also be a polygonal shape, such as a pentagon. In this embodiment, the resonator 40 is described as an FBAR (Film Bulk Acoustic Resonator) in which a gap 22 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50.

[0022] When a substance such as an atom or molecule in the gas is adsorbed onto the sensitive film 18, the mass of the sensitive film 18 increases. When the humidity around the sensitive film 18 increases, moisture is adsorbed onto the sensitive film 18, increasing the mass of the sensitive film 18. When the temperature changes, the adsorption characteristics of the film change, causing the mass of the sensitive film 18 to change. Thus, the mass of the sensitive film 18 changes due to changes in the concentration, humidity, and temperature of a specific substance in the gas surrounding the sensitive film 18. When the mass of the sensitive film 18 changes, the resonant frequency and antiresonant frequency of the piezoelectric thin film resonator also change. For example, when a specific substance is adsorbed onto the sensitive film 18, the mass of the sensitive film 18 increases. Examples of specific substances include acetone, ethanol, and toluene. This lowers the resonant frequency and antiresonant frequency of the resonator 40. When a specific substance is desorbed from the sensitive film 18, the mass of the sensitive film 18 decreases. This increases the resonant frequency and antiresonant frequency of the resonator 40.

[0023] 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, a single layer film of ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), or iridium (Ir), or a laminate film of multiple films selected from these. In this embodiment, both the lower electrode 12 and the upper electrode 16 are ruthenium films.

[0024] The piezoelectric layer 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 layer 14 is primarily composed of aluminum nitride (AlN) with its principal axis in the (002) direction (Z-axis direction), and may contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric layer 14 can be improved by adding scandium (Sc), a group 2 element or a group 12 element and a group 4 element, or a group 2 element or a group 12 element and a group 5 element as an additive element. This improves the 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 layer 14 may be mainly composed of aluminum nitride and may contain boron (B).

[0025] An insertion film may be provided on the piezoelectric layer 14 in the resonance region 50. For example, in FIG. 2(b), a lower piezoelectric layer having a thickness half that of the piezoelectric layer 14 is provided on the substrate 10. The insertion film is provided on the lower piezoelectric layer. Furthermore, an upper piezoelectric layer having a thickness half that of the piezoelectric layer 14 is provided on the insertion film. A resonator with such a structure can suppress the temperature dependence of the resonance frequency. The insertion film is, for example, a silicon oxide film. The insertion film is, for example, a film for suppressing the temperature dependence of the resonance frequency or a film for improving the Q value (Quality Factor) of the resonator.

[0026] The protective film 17 is a film that protects the surface of the upper electrode 16, and is, for example, an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film, or a metal film.

[0027] The sensitive film 18 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 multiple types selected from these.

[0028] For example, at least one of the following organic low molecular weight materials can be used: 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, parylene, etc.

[0029] For example, the inorganic material may be at least one of alumina, titania, vanadium pentoxide, tungsten oxide, lithium fluoride, magnesium fluoride, aluminum, gold, silver, tin, indium tin oxide (ITO), carbon nanotubes, sodium chloride, magnesium chloride, and the like.

[0030] The sensitive membrane 18 is Metal Phthalocyanine That's fine too. Metal Phthalocyanine Examples of the phthalocyanine include copper phthalocyanine (CuPc), fluorinated copper phthalocyanine (CuPcF8, CuPcF 16 ), cobalt phthalocyanine (CoPc), manganese phthalocyanine (MnPc), iron phthalocyanine (FePc), nickel phthalocyanine (NiPc), or the like can be used.

[0031] [Simulation 1] The response of the resonator 40 was simulated. The simulation was performed using a model in which the laminated film 20 was in the shape of a strip. The simulation conditions were as follows: Lower electrode 12: A chromium layer with a thickness of about 70 nm is provided on the substrate 10 side, and a ruthenium layer with a thickness of 166 nm is laminated thereon. Piezoelectric layer 14: Aluminum nitride layer with a thickness of 996 nm Upper electrode 16: A ruthenium layer with a thickness of 173 nm is provided on the piezoelectric layer 14 side, and a chromium layer with a thickness of 55 nm is laminated thereon. Protective film 17: The upper surface of the upper electrode 16 is covered with a silicon oxide layer having a thickness of 70 nm. Sensitive film 18: Copper phthalocyanine layers of varying thickness T

[0032] 3(a) and 3(b) are diagrams showing the magnitude |Z| of impedance and the Q value versus frequency in Simulation 1. The horizontal axis of FIG. 3(a) and FIG. 3(b) is frequency, the vertical axis of FIG. 3(a) is the absolute value of impedance, and the vertical axis of FIG. 3(b) is the Q value. The thickness T of the sensitive film 18 is changed in the range of 75 nm to 700 nm. As shown in FIG. 3(a), as the thickness T of the sensitive film 18 increases, the resonant frequency f r1 and anti-resonance frequency f a1 When the thickness T of the sensitive film 18 increases, the resonant frequency f r1 and anti-resonance frequency f a1 The difference between the peaks of the resonant frequency f r1 and anti-resonance frequency f a1 are the resonant frequency and anti-resonant frequency when the acoustic wave resonates in the first mode in the laminated film 20. As shown in FIG. 3(b), the Q value is r1 and anti-resonance frequency f a1 When the thickness T of the sensitive film 18 increases, the Q value decreases.

[0033] As shown in FIGS. 3(a) and 3(b), as the thickness T1 of the sensitive film 18 increases, the resonance in the first mode decreases, and the Q value decreases. This makes it difficult for the resonator 40 to resonate. On the other hand, as the sensitive film 18 becomes thinner, the number of sites in the sensitive film 18 that adsorb specific substances decreases. In addition, the surface roughness of the sensitive film 18 becomes smaller. As the sensitive film 18 becomes thinner, the number of sites in the sensitive film 18 that adsorb specific substances decreases, and therefore the change in mass of the sensitive film 18 due to environmental changes decreases. This reduces the detection sensitivity of the detection device 100 to environmental changes. The above-mentioned problems arise when attempting to oscillate and measure the resonator using the first mode.

[0034] [experiment] A resonator 40 was fabricated and the resonance response of the resonator 40 was measured. The fabrication conditions for the resonator 40, except for the sensitive film 18, were essentially the same as those in Simulation 1, although there were some manufacturing errors. Samples were fabricated with the thickness T of the sensitive film 18 set to 0 nm, 130 nm, 297 nm, 324 nm, and 506 nm. The thickness T was measured using a step gauge when the sensitive film 18 was fabricated.

[0035] Figures 4(a) to 4(c) are graphs showing impedance |Z| versus frequency in the experiment. The horizontal axis is frequency, and the vertical axis is the absolute value of impedance |Z|. In Figures 4(a) to 4(c), the thickness T of the sensitive film 18 was measured using a step gauge and was 297 nm, 324 nm, and 506 nm, respectively. T=0 nm in each graph represents the result measured before the sensitive film 18 was formed on the resonator.

[0036] As shown in FIG. 4(a), before the sensitive film 18 is formed, the resonant frequency f r1 and anti-resonance frequency f a1 After forming the sensitive film 18 with a thickness T=297 nm, a peak having a resonant frequency f r1 and anti-resonance frequency f a1 and a peak at the resonant frequency f r2 and anti-resonance frequency f a2 A peak having a resonant frequency f r1 and anti-resonance frequency f a1 is the resonance frequency f at T=0 nm r1 and anti-resonance frequency f a1 The resonant frequency f is lower than r2 and anti-resonance frequency f a2 is the resonance frequency f at T=0 nm r1 and anti-resonance frequency f a1 It is a higher frequency.

[0037] As shown in FIG. 4(b), the resonant frequency f r1 and anti-resonance frequency fa1 is the resonant frequency f of the sample with T = 297 nm in Figure 4(a). r1 and anti-resonance frequency f a1 The resonance frequency f at T = 324 nm shifts to a lower frequency. r2 and anti-resonance frequency f a2 is the resonance frequency f at T=297 nm r2 and anti-resonance frequency f a2 The resonant frequency f before the sensitive film 18 is formed is shifted to a lower frequency. r1 and anti-resonance frequency f a1 The resonant frequency f at T=324 nm approaches r2 Anti-resonance frequency f for |Z| a2 The Z ratio and Q value of |Z| are higher than those at T=297 nm.

[0038] As shown in FIG. 4(c), the resonant frequency f r2 and anti-resonance frequency f a2 is the resonance frequency f before the sensitive film 18 is formed (T=0 nm). r1 and anti-resonance frequency f a1 It is almost the same frequency.

[0039] As shown in Figures 4(a) to 4(c), in the samples with T = 297 nm and 324 nm, as the thickness T of the sensitive film 18 increases, the resonant frequency f r1 and anti-resonance frequency f a1 The peak of becomes smaller and shifts to lower frequencies. At T = 297 nm, the resonant frequency f r2 and anti-resonance frequency f a2 As in the samples with T=324 nm and 506 nm, when the thickness T of the sensitive film 18 increases, the resonant frequency f r2 and anti-resonance frequency f a2 The peak of becomes larger and shifts to a lower frequency, and the designed frequency before the sensitive film 18 is formed (i.e., the resonant frequency f r1 and anti-resonance frequency f a1 ) approaching.

[0040] FIG. 5 is a graph showing the impedance |Z| versus frequency in the experiment. The horizontal axis is frequency, and the vertical axis is the absolute value of the impedance |Z|. As shown in FIG. 5, in the sample with T=130 nm, the resonant frequency f r1 and anti-resonance frequency f a1 A large peak is observed at the resonance frequency f r2 and anti-resonance frequency f a2 No peak is observed below 2900 MHz.

[0041] Figures 6(a) and 6(b) show the Q value versus frequency in the experiment. Figure 6(b) is an enlarged view of Figure 6(a). The horizontal axis represents frequency, and the vertical axis represents the Q value. As shown in Figures 6(a) and 6(b), in the sample with T=130 nm, the resonant frequency f r1 and anti-resonance frequency f a1 A large Q-value peak is observed between the resonant frequency f r2 and anti-resonance frequency f a2 The peak Q value of the T=297 nm sample is much smaller than that of the T=130 nm sample. For the T=324 nm sample, the resonant frequency f r2 and anti-resonance frequency f a2 The peak Q value between T = 506 nm and T = 297 nm is larger than that of the sample with T = 297 nm. r2 and anti-resonance frequency f a2 The peak Q value between 100 nm and 120 nm is even larger than that of the sample with T=324 nm. Thus, the Q value in the second-order mode increases as the sensitive film 18 becomes thicker.

[0042] FIG. 7(a) is a diagram showing the impedance |Z| versus frequency for a sample with T=450 nm in the experiment, and FIG. 7(b) is an enlarged view of FIG. 7(a). The horizontal axis is frequency, and the vertical axis is the absolute value of impedance |Z|. FIG. 7(a) has a wider frequency range than FIG. 5. FIG. 7(b) enlarges the frequency range around 1400 MHz. T=0 nm shows the characteristics before the sensitive film 18 is formed. As shown in FIGS. 7(a) and 7(b), when T=450 nm, there is a small peak at 1400 MHz, and this peak corresponds to the resonant frequency f of the first mode. r1 and anti-resonance frequency f a1 The peak of the first mode resonance frequency f r1 and anti-resonance frequency f a1 The resonant frequency f has almost the same frequency as the peak of r2 and anti-resonance frequency f a2 is the resonant frequency of the second mode f r2 and anti-resonance frequency f a2 This is considered to be the peak.

[0043] [Simulation 2] To investigate why the Q value of the second-order mode increases as the sensitive film 18 becomes thicker, the displacement within the laminated film 20 in the first and second modes was simulated. The simulation conditions were the same as in Simulation 1. The thickness of the sensitive film 18 was kept constant, and the Young's modulus of the sensitive film 18 was changed to reproduce a state in which the thickness T of the sensitive film 18 was artificially changed.

[0044] 8(a) to 8(c) are diagrams showing displacement relative to position in the Z direction in Simulation 2. The vertical axis represents position in the Z direction, with the lower surface of the lower electrode 12 set at Z=0, and the horizontal axis represents displacement due to elastic waves. The circles + and - written above the lower electrode 12 and below the upper electrode 16 represent the positive and negative potentials generated by displacement of the elastic waves.

[0045] In FIG. 8(a), the sensitive film 18 is not provided. As shown in FIG. 8(a), in the first mode (fundamental wave mode), the thickness of the laminated film 20 corresponds to half the wavelength λ of the elastic wave. In the first mode resonance state, a state in which the lower electrode 12 is at a negative potential and the upper electrode 16 is at a positive potential, and a state in which the lower electrode 12 is at a positive potential and the upper electrode 16 is at a negative potential, are repeated over time. FIG. 8(a) shows the state in which the lower electrode 12 is at a negative potential and the upper electrode 16 is at a positive potential. This allows electrical excitation in the first mode.

[0046] In the second mode (second harmonic mode), the thickness of the laminated film 20 corresponds to the wavelength λ of the elastic wave. When the lower electrode 12 is at a positive potential, the upper electrode 16 is also at a positive potential. Thus, in the second mode, the lower electrode 12 and the upper electrode 16 are at approximately the same potential, so electrical excitation is not possible.

[0047] In Figures 8(b) and 8(c), a sensitive film 18 is provided on the upper electrode 16. The Young's modulus of the sensitive film 18 is smaller than that of the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16. As shown in Figure 8(b), when the sensitive film 18 is provided, the displacement of the elastic wave enters the sensitive film 18. Therefore, the thickness of the laminated film 20 including the sensitive film 18 corresponds to λ / 2 in the first-order mode and λ in the second-order mode. If the Young's modulus of the sensitive film 18 is smaller than that of the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16, the displacement of the elastic wave in the sensitive film 18 becomes larger, and the potential also changes significantly within the sensitive film 18. In Figure 8(b), the Young's modulus of the sensitive film 18 is not so low, so the potentials in the first and second-order modes of the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16 are almost the same as those in Figure 8(a). This allows electrical excitation in the first mode, but not in the second mode.

[0048] In FIG. 8(c), the Young's modulus of the sensitive film 18 is made smaller than in FIG. 8(b), and the sensitive film 18 is artificially thicker than the thickness T of the sensitive film 18 in FIG. 8(b). The displacement of the elastic wave enters the sensitive film 18 even more than in FIG. 8(b). In the first-order mode, a displacement of λ / 4 or more of the λ / 2 displacement occurs within the sensitive film 18. Therefore, the potential difference between the lower electrode 12 and the upper electrode 16 in the first-order mode is smaller than in FIG. 8(b). This is thought to result in a smaller resonance response in the first-order mode than in FIG. 8(b). In the second-order mode, a displacement of λ / 2 or more occurs within the sensitive film 18. Therefore, the lower electrode 12 has a positive potential and the upper electrode 16 has a negative potential. This enables electrical excitation in the second-order mode.

[0049] As described above, it is believed that when the sensitive film 18 is made thicker, the resonance response of the first mode becomes smaller and the resonance response of the second mode becomes larger.

[0050] According to the first embodiment, the resonator 40 includes a piezoelectric portion in which an upper electrode 16 (first electrode) and a lower electrode 12 (second electrode) sandwich at least a part of a piezoelectric layer 14, and a sensitive film 18 provided on the upper electrode 16 on the side opposite to the piezoelectric layer 14. The resonator 40 changes in resonance frequency f in the second mode in response to a change in the mass of the sensitive film 18. r2 and anti-resonance frequency f a2 The detector 45 detects a change in at least one of the resonant frequency f r2 and anti-resonance frequency f a2 A change in the environment is detected based on a change in at least one of the above. As a result, even if the sensitive film 18 is made thick, a resonance response with a high Q value can be obtained. Because the sensitive film 18 can be made thicker, the change in mass of the sensitive film 18 corresponding to the change in the environment can be made larger. As a result, the detection sensitivity of the detection device 100 to the change in the environment can be improved.

[0051] In the first embodiment, the resonance frequency f r2 and anti-resonance frequency f a2In the above example, in the even-order mode, if the sensitive film 18 is not provided, the potentials of the lower electrode 12 and the upper electrode 16 will be approximately the same, and almost no electrical excitation will occur. Increasing the thickness T of the sensitive film 18 increases the potential difference between the lower electrode 12 and the upper electrode 16, making electrical excitation in the even-order mode possible. In the fourth-order even-order mode, the thickness of the laminated film 20 is approximately 2λ, and in the sixth-order even-order mode, the thickness of the laminated film 20 is approximately 3λ. Thus, in the even-order mode, in the nth-order even-order mode, the thickness of the laminated film 20 is approximately n×λ / 2.

[0052] Also, the resonance frequency in the first mode is f r1 and anti-resonance frequency f a1 In the above example, excitation of odd-order modes is possible if the sensitive film 18 is not provided. In the third-order odd mode, the thickness of the laminated film 20 is approximately 3λ / 2, and in the fifth-order odd mode, the thickness of the laminated film 20 is approximately 5λ / 2. Thus, in the nth odd mode, the thickness of the laminated film 20 is approximately n×λ / 2. In the resonator 40, if the frequency at which electrical excitation is possible in the piezoelectric portion 21 before the sensitive film 18 is provided is defined as the odd mode of elastic waves, then after the sensitive film 18 is provided on the piezoelectric portion 21, the even mode, which is an elastic wave vibration mode that can be electrically excited, different from the odd mode, is achieved.

[0053] As shown in Figures 8(a) to 8(d), as the thickness T of the sensitive film 18 increases, the resonator 40 can be electrically excited in the second-order mode. As shown in Figure 5, it is believed that the resonator 40 resonates in the second-order mode when the thickness T of the sensitive film 18 is 200 nm or greater. The piezoelectric layer 14 is the thickest layer in the laminated film 20. Even when resonators 40 with various resonant frequencies are designed, the ratio of the thickness of the lower electrode 12 and the upper electrode 16 to the thickness of the piezoelectric layer 14 does not change significantly. Therefore, when the thickness T of the sensitive film 18 is normalized by the thickness of the piezoelectric layer 14, the thickness T of the sensitive film 18 is 200 nm, which is 0.2 times the thickness of the piezoelectric layer 14. Therefore, the thickness T of the sensitive film 18 is preferably 0.2 times or greater than the thickness of the piezoelectric layer 14. The thickness T of the sensitive film 18 is more preferably 0.3 times or greater than the thickness of the piezoelectric layer 14, and even more preferably 0.4 times or greater.

[0054] If the sensitive film 18 is thick, most of the displacement of the elastic wave will be within the sensitive film 18, resulting in a smaller resonant response. For example, if, when T = 506 nm, a displacement equivalent to λ / 2 of the λ standing wave in the second-order mode is displaced within the sensitive film 18, then, when T = 1000 nm, a displacement equivalent to 2λ / 3 will be displaced within the sensitive film 18, reducing the potential difference between the lower electrode 12 and the upper electrode 16. This is thought to result in a smaller resonant response. From this perspective, the thickness T of the sensitive film 18 is preferably 1 time or less, more preferably 0.7 times or less, and even more preferably 0.6 times or less, the thickness of the piezoelectric layer 14.

[0055] As the Young's modulus of the sensitive film 18 decreases, the displacement of the elastic wave becomes more likely to enter the sensitive film 18. The Young's modulus of the copper phthalocyanine used as the sensitive film 18 is 55 GPa and the Poisson's ratio is 0.35. Therefore, it is believed that the experimental results can be generalized if the sensitive film 18 has a resistance of 20 GPa to 80 GPa and a Poisson's ratio of 0.2 to 0.4. Since the aluminum nitride layer of the piezoelectric layer 14 is not isotropic, we will use elastic stiffness for our analysis. The piezoelectric layer 14 is a polycrystal oriented so that the Z-axis direction of the crystal orientation is in the Z direction in Figures 2(a) and 2(b). Therefore, the elastic stiffness C 33 The elastic stiffness C 33 The subscript 3 indicates the Z-axis direction of aluminum nitride. 33 is 280 GPa to 340 GPa, while the Young's modulus of the sensitive film 18 is 20 GPa to 80 GPa and the Poisson's ratio is 0.2 to 0.4. In this case, the elastic stiffness C 33 is the elastic stiffness C of the piezoelectric layer 14 33 It is believed that the results of the experiment can be generalized if the C of the sensitive film 18 is 0.06 to 0.62 times. 33 is the C of the piezoelectric layer 14 33 The range is preferably 0.1 to 0.5 times, and more preferably 0.2 to 0.4 times.

[0056] The density of the sensitive film 18 also relates to the displacement of the elastic wave. The density of copper phthalocyanine used as the sensitive film 18 is 1.5 g / cm 3 Therefore, the density of the sensitive film 18 is set to 1.2 g / cm 3 ~1.7g / cm 3 If so, we believe that the experimental results can be generalized. The density of the aluminum nitride layer of the piezoelectric layer 14 is 3.2 g / cm 3 ~3.4g / cm 3 Therefore, it is believed that the experimental results can be generalized if the density of the sensitive film 18 is 0.35 to 0.54 times the density of the piezoelectric layer 14. The density of the sensitive film 18 is preferably 0.4 to 0.5 times the density of the piezoelectric layer 14.

[0057] When the piezoelectric layer 14 is an aluminum nitride layer, the Young's modulus of the sensitive film 18 is preferably 20 GPa or more and 80 GPa or less, more preferably 30 GPa or more and 70 GPa or less, and even more preferably 50 GPa or more and 60 GPa or less. The density of the sensitive film 18 is 1.2 g / cm 3 or more and 1.7g / cm 3 Less than 1.3 g / cm is preferred 3 or more and 1.65g / cm 3 Less than 1.4 g / cm is preferred 3 or more and 1.6g / cm 3 The following is more preferred:

[0058] The piezoelectric layer 14 is an aluminum nitride layer, and the sensitive film 18 is Metal Phthalocyanine This allows the sensitive film 18 to have a Young's modulus and density comparable to those of copper phthalocyanine. This allows the results of the experiment to be more generalized. Metal Phthalocyanine The main component is that the sensitive film 18 is Metal Phthalocyanine The sensitive film 18 may intentionally or unintentionally contain impurities other than those mentioned above. Metal Phthalocyanine The proportion is, for example, 50% by weight or more or 80% by weight or more.

[0059] 1 adjusts the detector 45 using the resonance response in the first mode of the resonator 40 before providing the sensitive film 18. If the resonance frequency or anti-resonance frequency of the resonator 40 with the sensitive film 18 provided is significantly different from the resonance frequency or anti-resonance frequency of the resonator before providing the sensitive film 18, the detector 45 will need to be adjusted again. From this perspective, the resonance frequency in the even mode of the resonator 40 is preferably 0.85 to 1.15 times, more preferably 0.9 to 1.1 times, and even more preferably 0.95 to 1.05 times the resonance frequency in the first mode of the resonator 40 without the sensitive film 18.

[0060] In the past, the resonant frequency or anti-resonant frequency of the piezoelectric portion 21 of the resonator 40 changed when the sensitive film 18 was formed. As a result, the oscillator circuit 42 needed to be adjusted to oscillate at this changed resonant frequency. In this embodiment, the sensitive film 18 is formed on the piezoelectric portion 21 and oscillates in an even-order mode, so the resonant frequency or anti-resonant frequency of the piezoelectric portion 21 can be made closer to that before the sensitive film 18 was formed. This eliminates the need to adjust the oscillator circuit 42. Furthermore, the sensitive film 18 can be formed thick, which improves the sensitivity of the detection device 100.

[0061] 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]

[0062] 10 Substrate 12 Lower electrode 14 Piezoelectric layer 16 Upper electrode 17 Protective film 18 Sensitive membrane 20 Laminated Film 21 Piezoelectric part 22 void 40 resonator 42 Oscillator Circuit 44 Measuring instruments 45 detectors 46 Calculator 50 resonance area T Thickness

Claims

1. a piezoelectric portion including a piezoelectric layer and a first electrode and a second electrode sandwiching at least a portion of the piezoelectric layer; a sensitive film that is provided on the opposite side of the piezoelectric layer from the first electrode and whose mass changes in response to a change in the environment; a resonator in which, when a frequency at which electrical excitation is possible in the piezoelectric portion where the sensitive film is not provided is defined as an odd-order mode of an elastic wave, at least one of a resonance frequency and an anti-resonance frequency in an even-order mode, which is a vibration mode of an elastic wave that can be electrically excited different from the odd-order mode, changes in response to the change in mass, after the sensitive film is provided on the piezoelectric portion; a detector that detects a change in the environment based on a change in the at least one frequency; A detection device comprising:

2. 2. The detection device according to claim 1, wherein the even-order mode is a second-order mode.

3. 3. The detection device according to claim 2, wherein the thickness of the sensitive film is 0.2 times or more and 1.0 times or less the thickness of the piezoelectric layer.

4. The elastic stiffness C of the sensitive film ３３ is the elastic stiffness C of the piezoelectric layer ３３ 4. The detection device according to claim 3, wherein the value is 0.06 times or more and 0.62 times or less.

5. 5. The detection device according to claim 3, wherein the density of the sensitive film is 0.35 to 0.54 times the density of the piezoelectric layer.

6. The piezoelectric layer is an aluminum nitride layer, the Young's modulus of the sensitive film is 20 GPa or more and 80 GPa or less, and the density of the sensitive film is 1.2 g / cm ３ or more and 1.7 g / cm ３ 4. The detection device according to claim 3, wherein:

7. 4. The detection device according to claim 3, wherein the piezoelectric layer is an aluminum nitride layer, and the sensitive film is mainly composed of metal phthalocyanine.

8. 8. The detection device according to claim 1, wherein the resonant frequency in the even-order mode of the resonator is 0.85 to 1.15 times the resonant frequency in the first-order mode of the resonator from which the sensitive film is removed.

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