JP2020064014A - Sensor circuit - Google Patents

Abstract

To provide a sensor circuit having high output voltage.SOLUTION: A sensor circuit comprises: a resonator 12 for changing a resonance frequency and/or an anti-resonance frequency by changing the mass of a sensitive part; an oscillator 10 for outputting an oscillation signal S1 corresponding to the resonance frequency or the anti-resonance frequency; a frequency discriminator 16 for converting the change of the frequency of the oscillation signal S1 into the change of the amplitude thereof; and a wave detector 18 for outputting the amplitude voltage of the output signal S2 of the frequency discriminator 16.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sensor circuit, for example, a sensor circuit having a resonator.

  There is known an environmental sensor that detects a physical quantity such as a concentration of a specific atom or molecule in a gas or a liquid, temperature, or humidity by detecting a change in mass of a sensitive film. There is known a sensor circuit in which an elastic wave resonator having a sensitive film (a surface for detecting a substance) is used as a phase shifter to detect a substance by a phase shift amount of a reference oscillation signal (for example, Patent Document 1). A sensor circuit is known that detects a substance by a difference in resonance frequency between an elastic wave resonator having a sensitive film (a reactive film or a chemically interactive film that detects a substance) and a reference acoustic wave resonator. (For example, patent documents 2 and 3). A substance is detected by branching an oscillation signal output from an elastic wave resonator having a sensitive film into two signals whose phase difference changes in response to a change in the frequency of the oscillation signal and mixing the two signals. A sensor circuit is known (for example, Patent Document 4).

US Pat. No. 5,932,953 JP, 2004-226405, A International Publication No. 2007/005701 JP, 2018-115927, A

  In Patent Document 1, the elastic wave resonator having the sensitive film has a small Q value. For this reason, the amount of phase shift with respect to the mass change of the sensitive film becomes small, and the detection sensitivity decreases. In Patent Documents 2 and 3, two oscillators having elastic wave resonators are used, which increases the circuit scale. In Patent Document 4, the detection sensitivity is good, but the voltage of the output signal is low.

  The present invention has been made in view of the above problems, and an object thereof is to provide a sensor circuit having a high output voltage.

  The present invention includes a resonator having a resonance frequency and / or an anti-resonance frequency that changes when the mass of a sensitive section changes, and an oscillator that outputs an oscillation signal corresponding to the resonance frequency or the anti-resonance frequency; A sensor circuit comprising: a frequency discriminator that converts a change in frequency of a signal into a change in amplitude; and a detector that outputs an amplitude voltage of an output signal of the frequency discriminator.

  In the above configuration, the frequency discriminator includes a first acoustic wave resonator connected in series and / or a shunt between a terminal to which the oscillation signal is input and a terminal to which an output signal whose amplitude changes is output. Can be

  In the above configuration, the resonator may include a second acoustic wave resonator having the sensitive section.

  In the above configuration, the second acoustic wave resonator includes a first piezoelectric film, first and second electrodes sandwiching at least a part of the first piezoelectric film, and the first piezoelectric film of the second electrode. A sensitive film, which is provided on the opposite side and is the sensitive section, may be provided.

  In the above configuration, the frequency discriminator includes a first elastic wave resonator connected in series and / or a shunt between a terminal to which the oscillation signal is input and a terminal to which an output signal whose amplitude changes is output, The first acoustic wave resonator includes a second piezoelectric film made of the same material as the first piezoelectric film, and a third electrode and a fourth electrode sandwiching at least a part of the second piezoelectric film. be able to.

  In the above structure, the oscillator has a transistor having a control terminal, a first terminal, and a second terminal for outputting the oscillation signal, and one end is connected to the control terminal and the other end is connected to the first terminal. A first capacitor, a third acoustic wave resonator connected in parallel with the transistor between the second terminal and the first terminal, and the third acoustic wave resonator between the second terminal and the first terminal An inductor connected in series with the acoustic wave resonator; and a second capacitor connected in parallel with the third acoustic wave resonator and in series with the inductor between the second terminal and the first terminal, The second acoustic wave resonator may have one end connected to the control terminal and the other end connected to the second terminal.

  The present invention has an oscillator that outputs an oscillation signal, and a resonator that has a passage characteristic that changes when the mass of a sensitive section changes, and frequency discrimination that changes the amplitude of the oscillation signal in response to the change in the passage characteristic. And a detector that outputs an amplitude voltage of the output signal of the frequency discriminator.

  In the above configuration, the frequency discriminator is connected in series and / or a shunt between a terminal to which the oscillation signal is input and a terminal to which an output signal whose amplitude changes, and has one or a plurality of the sensitive sections. A configuration including the first acoustic wave resonator may be provided.

  In the above configuration, at least one of the one or more first acoustic wave resonators includes a first piezoelectric film, a first electrode and a second electrode sandwiching at least a part of the first piezoelectric film, and the second piezoelectric film. A sensitive film that is provided on the opposite side of the electrode from the first piezoelectric film and that is the sensitive section may be provided.

  In the above configuration, the oscillator includes a second elastic wave resonator, outputs an oscillation signal corresponding to a resonance frequency or an anti-resonance frequency of the second elastic wave resonator, and the second elastic wave resonator is A second piezoelectric film made of the same material as the first piezoelectric film and a third electrode and a fourth electrode sandwiching at least a part of the second piezoelectric film may be provided.

  According to the present invention, it is possible to provide a sensor circuit having a high output voltage.

FIG. 1 is a circuit diagram of a sensor circuit according to the first embodiment. FIG. 2A and FIG. 2B are diagrams showing the pass characteristic of the frequency discriminator in the first embodiment. FIG. 3 is a circuit diagram illustrating an example of the wave detector according to the first embodiment. FIG. 4 is a diagram showing the output level with respect to the input power of the detector in the first embodiment. 5A and 5B are circuit diagrams showing an example of the frequency discriminator in the first embodiment. FIG. 6A and FIG. 6B are diagrams showing the pass characteristic of the frequency discriminator in the first embodiment. 7A is a plan view showing an example of the resonator according to the first embodiment, and FIG. 7B is a sectional view taken along line AA of FIG. 7A. FIG. 8 is a circuit diagram illustrating an example of the oscillator according to the first embodiment. FIG. 9 is a circuit diagram showing another example of the oscillator according to the first embodiment. FIG. 10 is a diagram showing the reactance component with respect to the frequency of the resonator. FIG. 11 is a diagram showing reactance components with respect to frequencies of the resonator and the resonance circuit. 12A and 12B are circuit diagrams of the resonator and the resonance circuit, and FIG. 12C is a diagram showing reactance components with respect to frequencies of the resonator and the resonance circuit. FIG. 13 is a diagram illustrating phase noise of the oscillator according to the first embodiment. FIG. 14 is a block diagram showing the measurement system of the sensor circuit according to the first embodiment. FIG. 15A is a change in the oscillation spectrum of the oscillator when acetone is applied in Example 1, and FIG. 15B is a diagram showing the voltage of the output signal with respect to time. FIG. 16A is a diagram showing the amount of attenuation of the frequency discriminator with respect to the frequency in Example 1, and FIG. 16B is a diagram showing the phase change of the phase shifter with respect to the frequency in Comparative Example 1. FIG. 17 is a diagram showing the output voltage of the sensor circuit with respect to the oscillation frequency in Example 1 and Comparative Example 1. FIG. 18 is a block diagram of the sensor circuit according to the second embodiment. 19 (a) to 19 (d) are circuit diagrams of the frequency discriminator in the second embodiment. FIG. 20A and FIG. 20B are diagrams showing the attenuation amount with respect to the frequency of the frequency discriminator in the second embodiment. 21 (a) and 21 (b) is a figure which shows the attenuation amount with respect to the frequency of the frequency discriminator in Example 2. As shown in FIG. FIG. 22 is a plan view showing an example of the acoustic wave resonator according to the first and second embodiments. 23A and 23B are cross-sectional views taken along the lines AA and BB of FIG. 22, respectively.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a sensor circuit according to the first embodiment. The sensor circuit includes an oscillator 10, a frequency discriminator 16, and a detector 18.

  The oscillator 10 has a resonator 12 and an amplifier 14. In the resonator 12, the resonance frequency and / or the anti-resonance frequency changes according to the change in the mass of the sensitive section. The sensitive part is a part whose mass changes due to environmental changes. For example, when a specific atom or molecule in a gas or a liquid is adsorbed on the sensitive section, the mass of the sensitive section increases. Further, when the humidity of the atmosphere becomes high, moisture is adsorbed on the sensitive section and the mass of the sensitive section increases. When the temperature changes, the mass of the sensitive part changes. Further, when the sensitive part is irradiated with light such as ultraviolet rays, the mass of the sensitive part changes. The amplifier 14 functions as an oscillator and outputs an oscillation signal S1 corresponding to the resonance frequency or antiresonance frequency of the resonator.

  A frequency discriminator 16 converts a change in frequency of the oscillation signal S1 into a change in amplitude and outputs the signal as a signal S2. FIG. 2A and FIG. 2B are diagrams showing the pass characteristic of the frequency discriminator in the first embodiment. As shown in FIG. 2A, the frequency discriminator 16 is a notch filter. When the frequency of the oscillation signal S1 changes from f1 to f2, the power of the signal S2 changes from P1 to P2. As shown in FIG. 2B, the frequency discriminator 16 is a bandpass filter. When the frequency of the oscillation signal S1 changes from f1 to f2, the power of the signal S2 changes from P1 to P2. In this way, the frequency discriminator 16 converts a change in frequency of the oscillation signal S1 into a change in amplitude. The detector 18 converts a change in the amplitude of the signal S2 into a change in the voltage and outputs the signal S3.

[Example of detector]
FIG. 3 is a circuit diagram illustrating an example of the wave detector according to the first embodiment. As shown in FIG. 3, the terminal T1 is an input terminal to which the signal S2 is input, and the terminal T2 is an output terminal to which the signal S3 is output. A capacitor C3 and a diode D1 are connected in series between the terminals T1 and T2. The direction of connection of the diode D1 is the forward direction from the terminals T1 to T2. The resistor R1 is connected between the node between the capacitor C3 and the diode D1 and the ground. The capacitor C1 and the resistor R2 are connected in parallel between the terminal T2 and the ground. The capacitor C3 is for blocking direct current on the input side. The resistor R1 is for matching the input impedance. The capacitor C1 and the resistor R2 are for adjusting the detection accuracy.

The detection characteristic of the detector 18 was measured. The measurement conditions are as follows.
Resistance R1: 51Ω
Resistance R2: 1MΩ
Capacitor C1: 15pF
Capacitor C3: 15pF
Frequency of signal S2: 2.4 GHz

  FIG. 4 is a diagram showing the output level with respect to the input power of the detector in the first embodiment. As shown in FIG. 4, when the input power of the signal S2 increases, the output level of the signal S3 increases. When the input power of the signal S2 is -20 dBm, the output level of the signal S3 is 53 mV. When the input power of the signal S2 is 8 dBm, the output level of the signal S3 is about 3V. In this way, the detector 18 can convert the amplitude (that is, the envelope) of the signal S2 into a voltage level.

[Example of frequency discriminator]
5A and 5B are circuit diagrams showing an example of the frequency discriminator in the first embodiment. As shown in FIG. 5A, the terminal T1 is an input terminal to which the oscillation signal S1 is input, and the terminal T2 is an output terminal to which the signal S2 is output. In the frequency discriminator 16a, the resonator 15a is connected in series to the path between the terminals T1 and T2. One end of the resonator 15b is connected to the path between the terminals T1 and T2, and the other end is connected to the ground.

  As shown in FIG. 5B, in the frequency discriminator 16b, the resonators 15a and 15c are connected in series in the path between the terminal T1 and the terminal T2. One ends of the resonators 15b and 15d are connected to the path between the terminals T1 and T2, and the other ends are connected to the ground. It is preferable that the resonators 15a to 15d have large Q values in order to make the inclination of the amplitude with respect to the frequency steep. As the resonators 15a to 15d, elastic wave resonators or crystal resonators having a large Q value are used.

The resonators 15a to 15d are piezoelectric thin film resonators having aluminum nitride as a piezoelectric film, and the pass characteristics of the frequency discriminators 16a and 16b are simulated. FIG. 6A and FIG. 6B are diagrams showing the pass characteristic of the frequency discriminator in the first embodiment. In FIG. 6A, the resonance frequency fr and the anti-resonance frequency fa of each of the resonators 15a to 15d are set as follows.
15a, 15c: fr = 2.316 GHz, fa = 2.393 GHz
15b, 15d: fr = 2.393 GHz, fa = 2.470 GHz
By making the anti-resonance frequency fa of the resonators 15a and 15c and the anti-resonance frequency fa of the resonators 15b and 15d substantially the same, the one-stage and two-stage ladder type notch filters were formed.

  As shown in FIG. 6A, the one-stage ladder type frequency discriminator 16a can convert a frequency fluctuation of about 10 MHz into an amplitude fluctuation of about 35 dB. The two-stage ladder type frequency discriminator 16b can convert a frequency fluctuation of about 10 MHz into an amplitude fluctuation of about 60 dB. Thus, the frequency discriminator can be realized by using the ladder type notch filter. As the number of ladder stages increases, the slope of amplitude with respect to frequency becomes steeper.

In FIG. 6B, the resonance frequency fr and the anti-resonance frequency fa of the resonators 15a and 15b are set as follows.
15a: fr = 2.393 GHz, fa = 2.470 GHz
15b: fr = 2.431 GHz, fa = 2.447 GHz
A one-stage ladder type bandpass filter was formed by increasing the anti-resonance frequency fa of the resonator 15a by about 20 MHz higher than the anti-resonance frequency fa of the resonator 15b.

  As shown in FIG. 6B, the one-stage ladder type frequency discriminator 16a can convert a frequency fluctuation of about 10 MHz into an amplitude fluctuation of about 29.5 dB. As described above, the frequency discriminator can be realized by using the ladder type bandpass filter.

  In addition to the ladder type filter, the frequency discriminator 16 includes a circuit including only the resonator 15a connected in series between the terminals T1 and T2 and a circuit including only the resonator 15b shunt connected between the terminals T1 and T2. A circuit may be used. In order to increase the sensitivity of conversion from frequency fluctuation to amplitude fluctuation, it is preferable to connect the resonator in a ladder type.

[Example of resonator]
An example in which a piezoelectric thin film resonator is used as the resonator will be described. 7A is a plan view showing an example of the resonator according to the first embodiment, and FIG. 7B is a sectional view taken along line AA of FIG. 7A. As shown in FIGS. 7A and 7B, the piezoelectric film 42 is provided on the substrate 40. A lower electrode 41 and an upper electrode 43 are provided so as to sandwich the piezoelectric film 42. A space 46 is formed between the lower electrode 41 and the substrate 40. The resonance region 48 is a region where the lower electrode 41 and the upper electrode 43 face each other with at least a part of the piezoelectric film 42 sandwiched therebetween. In the resonance region 48, the lower electrode 41 and the upper electrode 43 excite elastic waves in the thickness extensional vibration mode in the piezoelectric film 42. A protective film 44 is provided on the substrate 40 so as to cover the lower electrode 41, the piezoelectric film 42, and the upper electrode 43. A sensitive film 45 is provided on the protective film 44. The sensitive film 45 includes a resonance region 48 in a plan view. An electrode 51 is provided on the lower surface of the substrate 40. A penetrating electrode 50 that penetrates the substrate 40 and the piezoelectric film 42 is provided. The through electrode 50 connects the lower electrode 41 and the upper electrode 43 to the electrode 51.

  When gas or liquid molecules are adsorbed on the sensitive film 45, the mass of the sensitive film 45 increases. Further, when the temperature or the humidity changes, the mass of the sensitive film 45 changes. As the mass of the sensitive film 45 in the resonance region 48 increases, the resonance frequency and anti-resonance frequency of the piezoelectric thin film resonator decrease.

  The substrate 40 is, for example, a sapphire substrate, an alumina substrate, a spinel substrate, or a silicon substrate. The lower electrode 41 and the upper electrode 43 are metal films such as ruthenium (Ru) films. The piezoelectric film 42 is, for example, an aluminum nitride (AlN) film, a zinc oxide (ZnO) film, a crystal layer, or the like. The protective film 44 is an insulating film such as a silicon oxide film or a silicon nitride film. The through electrode 50 and the electrode 51 are metal layers such as a gold (Au) layer or a copper (Cu) layer.

  The sensitive film 45 corresponds to a sensitive part. As the sensitive film 45, an organic polymer film, an organic low molecular film, an inorganic film or the like can be used. As a method for forming the sensitive film 45, a method of dissolving and coating the material of the sensitive film in a solvent, a vapor deposition method, a sputtering method or a CVD (Chemical Vapor Deposition) method can be used.

  Examples of the organic polymer material include polystyrene, polymethylmethacrylate, 6-nylon, cellulose acetate, poly-9,9-dioctylfluorene, polyvinyl alcohol, polyvinylcarbazole, polyethylene oxide, polyvinyl chloride, poly-p- Phenylene ether sulfone, poly-1-butene, polybutadiene, polyphenylmethylsilane, polycaprolactone, polybisphenoxyphosphazene, homopolymers having a single structure such as polypropylene, copolymers of two or more homopolymers, and these A blended polymer obtained by mixing

For example, organic low molecular weight materials 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 derivative, dioctylfluorene derivative, tetracontane, parylene Etc. can be used.

  For example, as the inorganic material, alumina, titania, vanadium pentoxide, tungsten oxide, lithium fluoride, magnesium fluoride, aluminum, gold, silver, tin, indium thin oxide (ITO), carbon nanotube, sodium chloride, chloride Magnesium or the like can be used.

  Instead of the void 46, an acoustic reflection film that reflects elastic waves propagating in the piezoelectric film 42 in the vertical direction can be used. The plane shape of the resonance region 48 may be a polygon such as a quadrangle or a pentagon other than the elliptical shape.

[Example of oscillator]
FIG. 8 is a circuit diagram illustrating an example of the oscillator according to the first embodiment. As shown in FIG. 8, the oscillator 10a includes a resonator 12, a transistor Q1, resistors R1 to R3, capacitors C1 to C3, and an inductor L1. The resonator 12 is connected between the base and collector of the transistor Q1. Resistors R1 and R2 provide the base bias. Resistor R3 supplies the emitter bias. The capacitors C1 and C2 are used for frequency adjustment and waveform improvement. The capacitor C4 increases the amplitude of the oscillation signal S1 output from the terminal T1. The capacitor C3 is a DC blocking capacitor.

  In the measurement and simulation described below, in the oscillator 10a, the resonator 12 is a piezoelectric thin film resonator including aluminum nitride as the piezoelectric film 42. The resistors R1 to R3 are 2 kΩ, 3 kΩ and 180 Ω, respectively. Capacitors C1 to C4 are 1 pF, 1.8 pF, 15 pF and 15 pF respectively, inductor L1 is 15 nH. The power supply voltage Vcc is 3.3V.

  FIG. 9 is a circuit diagram showing another example of the oscillator according to the first embodiment. As shown in FIG. 9, the oscillator 10b includes a resonator 12, transistors Q1 and Q2, resistors R1 to R5, capacitors C1 and C3 to C6, and an inductor L1. The resonator 11a, the capacitor C6, and the inductor L1 form the resonance circuit 11. The resonator 12 has a sensitive film, and the resonator 11a does not have a sensitive film. Compared to the oscillator 10a of FIG. 8, the transistors Q1 and Q2 are mainly cascode-connected, and the capacitor C2 between the collector and the emitter is changed to the resonance circuit 11.

  In the measurement and simulation described below, in the oscillator 10b, the resonators 12 and 11a are piezoelectric thin film resonators having aluminum nitride as the piezoelectric film 42. The resistors R1 to R5 are 1 kΩ, 1 kΩ, 790 Ω, 1 kΩ and 180 Ω, respectively. Capacitors C1, C3 to C6 are 7 pF, 15 pF, 3 pF, 7 pF and 3 pF, respectively, inductor L1 is 3 nH. The power supply voltage Vcc is 3.3V.

  The reason for providing the resonance circuit 11 will be described. The oscillators 10a and 10b are Pierce oscillators, and oscillate when the collector-base is inductive, the base-emitter is capacitive, and the emitter-collector is capacitive.

  FIG. 10 is a diagram showing the reactance component with respect to the frequency of the resonator. The range in which the reactance component is larger than 0 is inductive, and the range in which the reactance component is smaller than 0 is capacitive. A piezoelectric thin film resonator having the piezoelectric film 42 made of aluminum nitride was manufactured, and the measurement results of the resonator having the sensitive film 45 and the resonator having no sensitive film 45 were compared.

  As shown in FIG. 10, the resonator without the sensitive film 45 has a small inductive range A0 of 78 MHz. Therefore, if the piezoelectric thin film resonator without the sensitive film 45 is used for the resonator 12 of the oscillator 10a, the oscillator 10a oscillates in a narrow range and the phase noise is small.

  However, in the resonator having the sensitive film 45, the inductive range A1 is widened to 368 MHz. Furthermore, it becomes inductive even in the range A2 of 2.7 GHz or higher. Therefore, if the resonator having the sensitive film 45 is used as the resonator of the oscillator 10a, the oscillator 10a oscillates in a wide range and the phase noise deteriorates.

  FIG. 11 is a diagram showing reactance components with respect to frequencies of the resonator and the resonance circuit. In the oscillator 10b, the resonance circuit 11 is connected between the collector and the emitter, and the resonator 12 is connected between the collector and the base. It is the result of the simulation based on the measurement result of the resonator. As shown in FIG. 11, the range A1 in which the resonator 12 having the sensitive film is inductive is wide as 368 MHz. The range A3 in which the resonance circuit 11 is capacitive is 12 MHz. As a result, the oscillation range of the oscillator 10b becomes 12 MHz. Therefore, the phase noise does not deteriorate.

  12 (a) and 12 (b) are circuit diagrams of the resonator and the resonance circuit, and FIG. 12 (c) is a diagram showing reactance components with respect to frequencies of the resonator and the resonance circuit. As shown in FIG. 12A, the reactance component with respect to the frequency of the resonator 11a having no sensitive film connected in series between the terminals T1 and T2 was measured. As shown in FIG. 12B, the reactance component of the resonance circuit 11 in which the inductor L1 and the resonator 11a are connected in series between the terminals T1 and T2 and the capacitor C6 is connected in parallel to the resonator 11a is simulated.

  As shown in FIG. 12C, the resonator 11a alone is capacitive in a wide frequency range and inductive in a narrow range. Even if such a resonator 11a is used between the collector and the emitter of the oscillator 10b, the oscillating frequency range cannot be narrowed. The resonance circuit 11 can be inductive in a wide frequency range and capacitive in a narrow frequency range. The capacitance range can be adjusted by the capacitor C6 and the inductor L1.

  FIG. 13 is a diagram illustrating phase noise of the oscillator according to the first embodiment. The phase noise of the oscillators 10a and 10b was measured. As shown in FIG. 13, at a phase frequency of 1 MHz, the phase noise of the oscillator 10b is 20 dBc smaller than that of the oscillator 10a.

  As described above, in the oscillator 10b, by connecting the resonance circuit 11 between the collector and the emitter, the frequency range in which the collector-emitter is capacitive can be narrowed. As a result, even if the inductive frequency range of the resonator having the sensitive film 45 is wide, the oscillating frequency range can be narrowed. Thereby, phase noise can be suppressed.

[Measurement of sensor circuit]
A sensor circuit was prototyped. FIG. 14 is a block diagram showing the measuring system of the oscillator in the first embodiment. The oscillator 10b shown in FIG. 9 was used as the oscillator 10. Copper phthalocyanine was used for the sensitive film 45 of the resonator 12. As the frequency discriminator 16, the notch filter of the frequency discriminator 16b shown in FIG. The detector 18 shown in FIG. 3 was used as the detector 18. A buffer amplifier 60 that amplifies and impedance-converts the oscillation signal S1 and an amplifier 61 that amplifies the DC signal S3 are used. The microcomputer 62 converts the analog signal S3 amplified by the amplifier 61 into a digital signal and performs data processing. The personal computer 64 displays the data processing result.

  FIG. 15A is a change in the oscillation spectrum of the oscillator when acetone is applied in Example 1, and FIG. 15B is a diagram showing the voltage of the output signal with respect to time. Acetone was applied to the sensitive film 45. FIG. 15A shows changes in the spectrum of the output signal of the buffer amplifier 60 when acetone is applied. The frequency f1 indicates the oscillation frequency of the oscillation signal S1 before applying acetone, and the frequency f2 is the oscillation frequency of the oscillation signal S1 after applying acetone. By giving acetone, the oscillation frequency was lowered by 60 kHz. Further, the level of the output signal of the buffer amplifier 60 was lowered by 0.16 dB by supplying acetone.

  FIG. 15B shows the voltage change of the output signal of the amplifier 61 when acetone is instantaneously applied. When acetone is given, the voltage drops. After that, it returns to the original voltage. The fluctuation of the oscillation frequency of the oscillator 10 by applying acetone was about −60 kHz, the amplitude fluctuation of the signal S2 was about −0.16 dBm, and the voltage fluctuation of the signal S3 was about 5 mV.

  A difference from Comparative Example 1 referring to the sensor circuit of FIG. 1 of Patent Document 1 was simulated. FIG. 16A is a diagram showing the amount of attenuation of the frequency discriminator with respect to the frequency in Example 1, and FIG. 16B is a diagram showing the phase change of the phase shifter with respect to the frequency in Comparative Example 1. As shown by the arrow in FIG. 16A, in the first embodiment, when the frequency of the oscillation signal S1 changes by about 10 MHz, the amount of attenuation changes by about 20 dB. As shown by the arrow in FIG. 16B, in Comparative Example 1, when the frequency of the oscillation signal changes by about 10 MHz, the phase changes by about 123 °.

  FIG. 17 is a diagram showing the output voltage of the sensor circuit with respect to the oscillation frequency in Example 1 and Comparative Example 1. As shown by the arrow in FIG. 17, in Example 1, when the frequency of the oscillation signal changes by about 10 MHz, the output voltage changes by about 0.22V. In Comparative Example 1, when the frequency of the oscillation signal changes by about 10 MHz, the output voltage changes by about 0.33 mV.

  As described above, the output voltage in Example 1 can be increased by about 650 times as compared with Comparative Example 1. Further, in Comparative Example 1, the maximum phase difference is 180 °, so the output voltage range is narrow, but in Example 1, since the signal amplitude is detected, the voltage range can be increased. In Comparative Example 1, since the mixer uses the mixer, the fluctuation of the bias voltage causes a measurement error. However, in the first embodiment, since the bias voltage is not used for the frequency discriminator 16 and the detector 18, the fluctuation of the bias voltage hardly causes the measurement error. .

  According to the first embodiment, as shown in FIG. 1, the oscillator 10 includes the resonator 12 whose resonance frequency and / or anti-resonance frequency is changed by changing the mass of the sensitive part. The corresponding oscillation signal S1 is output. The frequency discriminator 16 converts a change in frequency of the oscillation signal S1 into a change in amplitude. The detector 18 outputs the amplitude voltage of the output signal of the frequency discriminator 16. Thereby, the output voltage can be increased.

  As shown in FIGS. 5A and 5B, the frequency discriminator 16 includes a series and / or a shunt between the terminal T1 to which the oscillation signal S1 is input and the terminal T2 to which an output signal whose amplitude changes is output. To the resonators 15a to 15d (first acoustic wave resonator) connected to. Thereby, the change in the oscillation frequency can be converted into the change in the amplitude. Further, by using an elastic wave resonator having a high Q value, it is possible to increase the sensitivity to frequency changes.

  The resonator 12 includes a piezoelectric thin film resonator (second acoustic wave resonator) having a sensitive section. As a result, the resonance frequency and / or the anti-resonance frequency of the resonator changes due to the change in the mass of the sensitive section.

  As shown in FIGS. 7A and 7B, the resonator 12 includes a piezoelectric film 42 (first piezoelectric film), a lower electrode 41 (first electrode) sandwiching at least a part of the piezoelectric film 42, and an upper portion. It has an electrode 43 (second electrode) and a sensitive film 45 which is provided on the opposite side of the upper electrode 43 from the piezoelectric film 42 layer and is a sensitive portion. As a result, the resonance frequency and / or the anti-resonance frequency of the resonator changes due to the change in the mass of the sensitive section.

  As shown in FIG. 9, the oscillator 10b includes transistors Q1 and Q2 having a base (control terminal), an emitter (first terminal), and a collector (second terminal) that outputs the oscillation signal S1. The capacitors C1 and C4 (first capacitors) have one end connected to the base and the other end connected to the emitter. This makes the base-emitter capacitive. The resonator 11a (third acoustic wave resonator) is connected in parallel with the transistors Q1 and Q2 between the collector and the emitter. The inductor L1 is connected in series with the resonator 11a between the collector and the emitter. The capacitor C6 (second capacitor) is connected between the collector and the emitter in parallel with the resonator 11a and in series with the inductor L1. The resonator 12 has one end connected to the base and the other end connected to the collector. As a result, even if the inductive frequency range of the resonator 12 having the sensitive section is wide, the capacitive frequency range of the resonant circuit 11 is narrow, so that phase noise can be suppressed.

  FIG. 18 is a block diagram of the sensor circuit according to the second embodiment. As shown in FIG. 18, the sensor circuit includes an oscillator 10d, a frequency discriminator 16d, and a detector 18.

  The oscillator 10d has a resonator 12d and an amplifier 14. The resonator 12d has no sensitive portion. The frequency discriminator 16d has a resonator having a sensitive section. The other circuits are the same as those in the first embodiment and the description thereof is omitted.

  19 (a) to 19 (d) are circuit diagrams of the frequency discriminator in the second embodiment. As shown in FIG. 19A, in the frequency discriminator 16e, the resonator 15b having the sensitive film 45 between the terminals T1 and T2 is connected to the shunt. As shown in FIG. 19B, in the frequency discriminator 16f, the resonator 15a having the sensitive film 45 is connected in series between the terminals T1 and T2.

  As shown in FIG. 19C, in the frequency discriminator 16g, the resonator 15a having the sensitive film 45 is connected in series between the terminals T1 and T2, and the resonator 15b having the sensitive film 45 is connected to the shunt. There is. As shown in FIG. 19D, in the frequency discriminator 16h, the resonators 15a and 15c having the sensitive film 45 are connected in series between the terminals T1 and T2, and the resonators 15b and 15d having the sensitive film 45 are shunted. It is connected to the.

  Thus, the frequency discriminator 16d includes one or more resonators 15a and 15c connected in series and / or one or more resonators 15b and 15d connected in shunt between the terminals T1 and T2. ing. At least one of the resonators 15a to 15d may be provided with the sensitive film 45.

  Acetone or ethanol was applied to the sensitive film 45 of the piezoelectric thin film resonator having the aluminum nitride film as the piezoelectric film 42, and the pass characteristic was measured. Using the measurement results, the pass characteristics of the frequency discriminators 16e to 16h were simulated.

  20 (a) to 21 (b) are diagrams showing the attenuation amount with respect to the frequency of the frequency discriminator in the second embodiment. “No odor” is the passage characteristic when acetone and ethanol are not applied to the sensitive film 45, “acetone” is the passage characteristic when acetone is applied to the sensitive film 45, and “ethanol” is ethanol provided to the sensitive film 45. It is a passage characteristic at time.

  As shown in FIG. 20 (a), in the frequency discriminator 16e, at a frequency of 2.375 GHz, the change in amplitude when acetone is applied is -1.13 dB, and the change in amplitude when ethanol is applied is -0. It is 0.34 dB. As shown in FIG. 20B, in the frequency discriminator 16f, at a frequency of 2.46 GHz, the change in amplitude when acetone is applied is −0.52 dB, and the change in amplitude when ethanol is applied is −0. It is .13 dB.

  In the frequency discriminators 16e and 16f, the resonance frequency fr and the anti-resonance frequency fa without the smell of the resonators 15a and 15b are 2363.0 MHz and 2472.8 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa when acetone is applied are 2370.6 MHz and 2468.2 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa when ethanol is given are 2366.8 MHz and 2472.2 MHz, respectively.

  As shown in FIG. 21 (a), in the frequency discriminator 16 g, at a frequency of 2.375 GHz, the change in amplitude when acetone is applied is −1.87 dB, and the change in amplitude when ethanol is applied is −0. It is 0.51 dB. As shown in FIG. 21B, in the frequency discriminator 16h, at a frequency of 2.375 GHz, the change in amplitude when acetone is applied is -4.04 dB, and the change in amplitude when ethanol is applied is -1. It is 0.05 dB.

  In the frequency discriminators 16g and 16h, the resonance frequency fr and the anti-resonance frequency fa without smell of the resonators 15a and 15c are 2279.6 MHz and 2387.8 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa when acetone is applied are 2286.3 MHz and 2383.4 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa when ethanol is given are 2282.3 MHz and 2387.6 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa without the smell of the resonators 15b and 15d are 2363.0 MHz and 2472.8 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa when acetone is applied are 2370.6 MHz and 2468.2 MHz, respectively. The resonance frequency fr and the anti-resonance frequency fa when ethanol is given are 2366.8 MHz and 2472.2 MHz, respectively.

  As described above, in the piezoelectric thin film resonator having the sensitive film 45, not only the resonance frequency and / or the anti-resonance frequency change but also the amount of attenuation changes when the mass of the sensitive film changes. Accordingly, the piezoelectric thin film resonator having the sensitive film 45 can be used as a frequency discriminator. As shown in FIGS. 20 (a) to 21 (b), the larger the number of resonator stages, the larger the amplitude changes.

  According to the second embodiment, the oscillator 10d outputs the oscillation signal S1 as shown in FIG. The frequency discriminator 16d has resonators 15a to 15d whose pass characteristics change due to a change in the mass of the sensitive section, and changes the amplitude of the oscillation signal S1 in response to the change in pass characteristics. The detector 18 outputs the amplitude voltage of the output signal S2 of the frequency discriminator 16d. Thereby, the output voltage can be increased.

  As shown in FIGS. 19A to 19D, the frequency discriminator 16d includes a series and / or shunt between the terminal T1 to which the oscillation signal S1 is input and the terminal T2 to which an output signal whose amplitude changes is output. And resonators 15a to 15d (one or a plurality of first acoustic wave resonators) connected to each other and having a sensitive portion. Thereby, the amplitude of the oscillation signal S1 can be changed.

  At least one of the resonators 15a to 15d includes a piezoelectric film 42 (first piezoelectric film), a lower electrode 41 (first electrode) and an upper electrode 43 (second electrode) that sandwich at least a part of the piezoelectric film 42, It is provided on the opposite side of the upper electrode 43 from the piezoelectric film 42, and has a sensitive film 45 as a sensitive portion. As a result, the passage characteristic of the resonator changes due to the change in the mass of the sensitive section.

  The oscillator 10d may be, for example, a PLL circuit or an atomic oscillator. A measurement error can be reduced by using an oscillator with high oscillation accuracy as the oscillator 10d.

[Example of resonator of Examples 1 and 2]
FIG. 22 is a plan view showing an example of the acoustic wave resonator according to the first and second embodiments. 23A and 23B are cross-sectional views taken along the lines AA and BB of FIG. 22, respectively. As shown in FIGS. 22 to 23B, acoustic wave resonators 54 and 56 are provided on the same substrate 40. The acoustic wave resonator 54 has the sensitive film 45 in the resonance region 48 on the protective film 44 and does not have the additional film 47. The acoustic wave resonator 56 has the additional film 47 in the resonance region 48 between the upper electrode 43 and the protective film 44, and does not have the sensitive film 45. The material and film thickness of the lower electrode 41, the piezoelectric film 42, and the upper electrode 43 are substantially the same in the acoustic wave resonators 54 and 56. Other configurations are the same as those in FIGS. 7A and 7B, and the description thereof will be omitted.

  In the first embodiment, the acoustic wave resonator 54 is used for the resonator 12 of the oscillator 10, and the acoustic wave resonator 56 is used for the resonators 15a to 15d of the frequency discriminator 16. In the second embodiment, the elastic wave resonator 54 is used for the resonators 15a to 15d of the frequency discriminator 16, and the elastic wave resonator 56 is used for the resonator 12d of the oscillator 10d.

  In the first embodiment, the acoustic wave resonator 56, which is the resonators 15 a to 15 d, includes the piezoelectric film 42 (second piezoelectric film) made of the same material as the piezoelectric film 42 of the acoustic wave resonator 54, which is the resonator 12. A lower electrode 41 (third electrode) and an upper electrode 43 (fourth electrode) sandwiching at least a part of the film 42.

  In the second embodiment, the elastic wave resonator 56 that is the resonator 12d includes a piezoelectric film 42 (second piezoelectric film) made of the same material as the piezoelectric film 42 of the elastic wave resonators 54 that are the resonators 15a to 15d. A lower electrode 41 (third electrode) and an upper electrode 43 (fourth electrode) sandwiching at least a part of the film 42.

  The acoustic wave resonators 54 and 56 are provided on the same substrate 40. Thereby, even if either of the acoustic wave resonators 54 and 56 generates heat, the temperatures of the acoustic wave resonators 54 and 56 can be made substantially the same. Further, by adjusting the masses of the sensitive film 45 and the additional film 47 in the resonance region 48 to the same degree, the resonance frequencies (or anti-resonance frequencies) of the acoustic wave resonators 54 and 56 can be adjusted to the same degree.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and alterations are possible within the scope of the gist of the present invention described in the claims. It can be changed.

10, 10a, 10b, 10d Oscillator 11a, 12, 12d, 15a-15d Resonator 14 Amplifier 16, 16a, 16b, 16d-16h Frequency discriminator 18 Detector 40 Substrate 41 Lower electrode 42 Piezoelectric film 43 Upper electrode 44 Protective film 45 Sensitive film 46 Void 48 Resonance region

Claims (10)

An oscillator that includes a resonator whose resonance frequency and / or anti-resonance frequency changes when the mass of the sensitive part changes, and which outputs an oscillation signal corresponding to the resonance frequency or the anti-resonance frequency;
A frequency discriminator that converts a change in frequency of the oscillation signal into a change in amplitude,
A detector that outputs the amplitude voltage of the output signal of the frequency discriminator,
And a sensor circuit.   The said frequency discriminator is equipped with the 1st elastic wave resonator connected in series and / or shunt between the terminal which the said oscillation signal inputs, and the terminal which outputs the output signal whose amplitude changes. Sensor circuit.   The sensor circuit according to claim 1, wherein the resonator includes a second acoustic wave resonator having the sensitive section. The second acoustic wave resonator includes
A first piezoelectric film,
A first electrode and a second electrode sandwiching at least a part of the first piezoelectric film;
A sensitive film which is provided on the side of the second electrode opposite to the first piezoelectric film and which is the sensitive section;
The sensor circuit according to claim 3, further comprising: The frequency discriminator includes a first acoustic wave resonator connected in series and / or a shunt between a terminal to which the oscillation signal is input and a terminal to which an output signal whose amplitude changes is output,
The first acoustic wave resonator is
A second piezoelectric film made of the same material as the first piezoelectric film;
A third electrode and a fourth electrode sandwiching at least a part of the second piezoelectric film,
The sensor circuit according to claim 4, further comprising: The oscillator is
A transistor having a control terminal, a first terminal, and a second terminal for outputting the oscillation signal;
A first capacitor having one end connected to the control terminal and the other end connected to the first terminal;
A third acoustic wave resonator connected in parallel with the transistor between the second terminal and the first terminal;
An inductor connected in series with the third acoustic wave resonator between the second terminal and the first terminal;
A second capacitor connected in parallel with the third acoustic wave resonator and in series with the inductor between the second terminal and the first terminal;
Have
The sensor circuit according to claim 3, wherein the second acoustic wave resonator has one end connected to the control terminal and the other end connected to the second terminal. An oscillator that outputs an oscillation signal,
A frequency discriminator that has a resonator whose pass characteristic changes as the mass of the sensitive part changes, and which changes the amplitude of the oscillation signal in response to the change of the pass characteristic;
A detector that outputs the amplitude voltage of the output signal of the frequency discriminator,
And a sensor circuit.   The frequency discriminator is connected in series and / or a shunt between a terminal for inputting the oscillation signal and a terminal for outputting an output signal whose amplitude changes, and has one or a plurality of first elastic waves having the sensitive section. The sensor circuit according to claim 7, comprising a resonator. At least one of the one or more first acoustic wave resonators is
A first piezoelectric film,
A first electrode and a second electrode sandwiching at least a part of the first piezoelectric film;
9. The sensor circuit according to claim 8, further comprising: a sensitive film which is provided on a side of the second electrode opposite to the first piezoelectric film and which is the sensitive section. The oscillator includes a second acoustic wave resonator, and outputs an oscillation signal corresponding to a resonance frequency or an anti-resonance frequency of the second acoustic wave resonator,
The second acoustic wave resonator includes
A second piezoelectric film made of the same material as the first piezoelectric film;
A third electrode and a fourth electrode sandwiching at least a part of the second piezoelectric film,
The sensor circuit according to claim 9, further comprising:

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