JP2016186442A - Sensor, detection system, and detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent false oscillation by allowing setting of an appropriate oscillation condition according to an environment in which a sensor is used, and obtain an oscillation state as stable as possible.SOLUTION: The sensor includes: a crystal resonator 2 having a sensing region with a detection target attached; a package 3 containing the crystal resonator 2 so that the sensing region is exposed; and an IC chip 4 oscillating the crystal resonator 2 and forming a voltage-controlling oscillation circuit controlling the oscillation frequency of the crystal resonator 2 based on a control voltage input to a control voltage input terminal 26, the IC chip 4 being contained in the package 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sensor suitable for detecting a trace amount of a specific substance contained in a gas or liquid as a detection target, a detection system including the sensor, and a detection method.

In recent years, for example, as a sensor for detecting a small amount of a specific substance in a liquid, a resonance frequency is changed by immersing a quartz vibrator, which is a piezoelectric vibrator, in a liquid and attaching the substance to the electrode surface of the quartz vibrator. A QCM (Quartz Crystal Microbalance) sensor that detects a very small amount of substance by using properties is used (for example, see Patent Document 1). This QCM sensor can detect a mass change of a substance of the order of 1 ng / cm ² .

  When such a crystal unit is immersed in a liquid, the effective resistance of the crystal unit increases, so that oscillation may become unstable and non-oscillate. For this reason, it has been proposed to configure the oscillation circuit with a feedback circuit including a plurality of amplifiers and a liquid crystal sensor (see, for example, Patent Document 2).

JP 2007-271449 A JP-A-11-163633

  There are various liquids in which the QCM sensor is immersed in order to detect a specific substance to be detected, which have different viscosities and densities. For this reason, under certain designed oscillation conditions, some liquids may not oscillate or may oscillate but the oscillation frequency may not be stable.

  Therefore, it is desired to set an appropriate oscillation condition according to the liquid in which the QCM sensor is immersed, that is, the environment in which the QCM sensor is used.

  The present invention has been made in view of the above points, and is capable of setting an appropriate oscillation condition according to the environment in which the sensor is used to prevent non-oscillation and as much as possible. An object of the present invention is to obtain a stable oscillation state.

  In order to achieve the above object, the present invention is configured as follows.

That is, the sensor of the present invention is a sensor including a piezoelectric vibrator having a sensing region to which a detection target adheres, and a package that houses the piezoelectric vibrator so that the sensing region of the piezoelectric vibrator is exposed. ,
A voltage-controlled oscillation circuit that oscillates the piezoelectric vibrator and controls the oscillation frequency of the piezoelectric vibrator based on an input control voltage, the voltage-controlled oscillation circuit being housed in the package It is.

  In a preferred embodiment of the sensor according to the present invention, the sensing region of the sensor is immersed in a liquid, and the control voltage is a constant voltage corresponding to the liquid.

  In another embodiment of the sensor of the present invention, the piezoelectric vibrator is a crystal vibrator in which excitation electrodes are respectively formed on both main surfaces of the crystal vibrating piece, and the sensing region is the both parts of the crystal vibrating piece. It includes a sensitive film formed on the excitation electrode on at least one main surface of the main surface.

  In still another embodiment of the sensor according to the present invention, the package includes an accommodation recess having a step portion, and the accommodation recess accommodates an IC chip constituting the voltage-controlled oscillation circuit, and the crystal oscillation. A piece is accommodated above the IC chip with its peripheral portion supported by the stepped portion, and a gap between the peripheral portion of the quartz crystal vibrating piece supported by the stepped portion and the peripheral wall of the receiving concave portion And sealed with a sealing material.

  In a preferred embodiment of the sensor of the present invention, the sensing region is provided on one side of the package in the longitudinal direction, and an external terminal connected to the IC chip is provided on the other end in the longitudinal direction.

  According to the sensor of the present invention, since the voltage control type oscillation circuit that controls the oscillation frequency of the piezoelectric vibrator constituting the sensing region is provided, by varying the control voltage input to the voltage control type oscillation circuit, The oscillation conditions such as the oscillation margin and load capacitance of the oscillation circuit can be varied. By inputting an appropriate control voltage in accordance with the environment in which the sensor is used, for example, various liquids having different viscosities and densities that immerse the sensing area of the sensor, an appropriate oscillation corresponding to the environment in which the sensor is used By setting conditions, it is possible to prevent non-oscillation and obtain a stable oscillation state.

  In addition, since the piezoelectric vibrator and the voltage control type oscillation circuit are accommodated in a single package, the transmission distance between the piezoelectric vibrator and the voltage control type oscillation circuit is shortened, and noise mixing and fluctuations are reduced. Therefore, the stability of oscillation can be improved and the measurement accuracy can be improved.

  Moreover, since the input control voltage is a constant voltage according to the liquid in which the sensing area of the sensor is immersed, by inputting a constant voltage according to the type of liquid with different viscosity, density, etc. as the control voltage Even when immersed in a liquid, non-oscillation can be prevented and the oscillation frequency can be stabilized.

  Further, the sensing region includes a sensitive film formed on at least one excitation electrode of both excitation electrodes respectively formed on both main surfaces of the crystal vibrating piece constituting the crystal resonator, and by this sensitive film, A detection target can be attached.

  Further, the periphery of the quartz crystal resonator element is supported by a stepped portion formed in the accommodating recess so that the sensing region is exposed, but between the periphery of the quartz crystal resonator element and the peripheral wall of the accommodating recess. However, since it is sealed by the sealing material, even if the sensing region is immersed in the liquid, the liquid can be prevented from entering the other main surface side of the quartz crystal vibrating piece. Thereby, the non-oscillation by the short circuit between the excitation electrodes of both the main surfaces of the crystal vibrating piece can be prevented.

  In addition, a sensing region is provided on one side in the longitudinal direction of the package, and an external terminal connected to the IC chip with an internal wiring is provided at the other end, so that the external terminal protrudes above the liquid level. Thus, the sensing area can be immersed in the liquid, and the liquid can be prevented from adhering to the external terminal.

  The detection system of the present invention includes a piezoelectric vibrator having a sensing region to which a detection target adheres, and voltage control that oscillates the piezoelectric vibrator and controls the oscillation frequency of the piezoelectric vibrator based on an input control voltage. And a control device for controlling the control voltage output to the sensor, the control device having a resonance frequency of the piezoelectric vibrator in a state where the control voltage is controlled to a constant voltage. The detection object is detected based on the change.

  In a preferred embodiment of the detection system of the present invention, the sensing area of the sensor is immersed in a liquid, and the control device outputs the constant voltage corresponding to the liquid to the sensor.

  In another embodiment of the detection system of the present invention, the control device determines the control voltage with the sensing region immersed in the liquid in order to determine the constant voltage according to the liquid. The oscillation output of the piezoelectric vibrator is measured when the voltage is lowered from a voltage high enough for the piezoelectric vibrator to oscillate.

  In still another embodiment of the detection system of the present invention, the piezoelectric vibrator is a crystal vibrator in which excitation electrodes are respectively formed on both main surfaces of the crystal vibrating piece, and the sensing region is the crystal vibrating piece. It includes a sensitive film formed on the excitation electrode on at least one of the main surfaces.

  According to the detection system of the present invention, it is possible to vary the oscillation conditions such as the oscillation margin and the load capacitance of the oscillation circuit by varying the control voltage input to the voltage-controlled oscillation circuit of the sensor. Appropriate oscillation conditions according to the liquid are set by outputting an appropriate control voltage to the sensor in accordance with the environment in which the sensor is used, for example, various liquids with different viscosities and densities that immerse the sensing area of the sensor. Thus, non-oscillation can be prevented and a stable oscillation state can be obtained, and the detection target can be detected in this stable oscillation state.

  In addition, in order to determine a constant voltage according to the liquid, the control device lowers the control voltage from a voltage that is sufficiently high for the piezoelectric vibrator to oscillate in a state where the sensing region is immersed in the liquid. Since the oscillation output of the piezoelectric vibrator at this time is measured, an appropriate constant voltage can be determined as the control voltage based on the measured oscillation output of the piezoelectric vibrator and the control voltage.

The detection method of the present invention includes a piezoelectric vibrator having a sensing region to which a detection target adheres, and voltage control for oscillating the piezoelectric vibrator and controlling the oscillation frequency of the piezoelectric vibrator based on an input control voltage. A method of detecting the detection object using a sensor including a type oscillation circuit,
A first step of inputting the control voltage high enough for the piezoelectric vibrator to oscillate to the sensor to oscillate the sensing region immersed in a liquid;
A second step of measuring an oscillation output of the piezoelectric vibrator when the control voltage is lowered from the sufficiently high control voltage in a state where the sensing region is immersed in the liquid;
A third step of determining a constant voltage corresponding to the liquid as a control voltage based on the oscillation output measured in the second step and the control voltage;
And a fourth step of inputting the constant voltage determined in the third step as a control voltage to the sensor and detecting the detection target based on a change in a resonance frequency of the piezoelectric vibrator. Yes.

  According to the detection method of the present invention, the oscillation condition such as the oscillation margin and load capacitance of the oscillation circuit can be varied by varying the control voltage input to the voltage-controlled oscillation circuit of the sensor. By inputting an appropriate constant voltage as a control voltage to the sensor according to the environment in which the sensing area of the sensor is immersed, such as various liquids with different viscosities and densities, etc., an appropriate oscillation condition according to the liquid can be obtained. By setting, it is possible to prevent non-oscillation and obtain a stable oscillation state.

  Then, with this constant voltage immersed in the sensing area in the liquid, the oscillation output of the piezoelectric vibrator is measured when the control voltage is lowered from a control voltage sufficiently high for the piezoelectric vibrator to oscillate. Can be determined.

  According to the present invention, since the voltage control type oscillation circuit for controlling the oscillation frequency of the piezoelectric vibrator is provided, the oscillation margin of the oscillation circuit and the load can be changed by varying the control voltage input to the voltage control type oscillation circuit. Oscillation conditions such as capacitance can be varied. Therefore, by inputting an appropriate control voltage according to the environment in which the sensor is used, for example, various liquids having different viscosities and densities in which the sensing area of the sensor is immersed, an appropriate oscillation according to the environment in which the sensor is used It is possible to set a condition to prevent non-oscillation and to detect a detection target as a stable oscillation state.

1A and 1B are views showing a QCM sensor according to an embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a longitudinal side view. FIG. 2 is an enlarged partial sectional view taken along the line CC of FIG. FIG. 3 is a configuration diagram of a voltage-controlled oscillation circuit. FIG. 4 is a diagram showing the relationship between the control voltage and the oscillation margin. FIG. 5 is a diagram showing the relationship between the control voltage and the load capacity. FIG. 6 is a diagram showing the relationship between the control voltage and the frequency change. FIG. 7 is a configuration diagram of a detection system according to an embodiment of the present invention. FIG. 8 is a diagram showing the relationship between the control voltage and the oscillation voltage in air and liquid.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1A and 1B are diagrams showing a sensor according to an embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a longitudinal side view. FIG. 2 is an enlarged cross-sectional view taken along line CC in FIG.

  The sensor of this embodiment is a QCM sensor 1 including a crystal resonator 2 that is a piezoelectric resonator as a sensor element. The QCM sensor 1 includes a package 3, and an AT-cut crystal resonator 2 is incorporated in the package 3 on the surface side.

  As shown in FIG. 2B, the package 3 has a three-layer structure of a lower layer 5, an intermediate layer 6, and an upper layer 7, and is formed by laminating and firing insulating sheets such as ceramics. The

  An intermediate layer 6 and an upper layer 7 constituting a frame portion are laminated on the upper surface of a flat lower layer 5 constituting the substrate portion.

  A regular octagonal through hole 7a is formed in the upper layer 7, and a regular octagonal through hole 6a smaller than the through hole of the upper layer 7 is formed in the intermediate layer 6. A housing recess 8 for housing is formed, and a step portion for supporting the peripheral portion of the circular crystal piece 9 of the crystal resonator 2 is formed. On this step portion, support protrusions (not shown) that support the crystal piece 9 are formed at a plurality of locations along the circumferential direction of the crystal piece 9.

  Excitation electrodes 10a and 10b are formed in a circular shape at the center of both the front and back surfaces of the crystal piece 9 of the crystal resonator 2.

  From each excitation electrode 10a, 10b, extraction electrodes 11a, 11b are formed toward the outer peripheral direction of the crystal piece 9 so as to be opposite to each other. The extraction electrode 11a on the front surface side of the crystal piece 9 goes around to the back surface side. These electrodes 10a, 10b; 11a, 11b are formed of a laminated film in which, for example, chromium (Cr) is used as a base layer, and gold (Au) or titanium (Ti) is stacked on the base layer. The electrodes 10a and 10b; 11a and 11b are not limited to the above-described film configuration, and may be a laminated film of three or more layers. For example, a three-layer structure in which chromium (Cr) is used as a base layer, gold (Au) or titanium (Ti) is stacked on the base layer, and gold (Au) is further stacked on the top layer may be used. The electrode material is not limited to these metals, and nickel (Ni) / silver (Ag) or other metals may be used.

  On the excitation electrode 10a on the surface side of the crystal piece 9, a sensitive film 16 having a function of capturing and adsorbing a specific substance to be detected is formed to constitute a sensing region exposed to the outside.

  Since the sensing area of the QCM sensor 1 is immersed in a liquid to detect a specific substance, when the excitation electrodes 10a and 10b on the front and back surfaces of the crystal piece 9 come into contact with the liquid, the crystal oscillator 2 is short-circuited. Cannot oscillate. Therefore, an insulating sealing material 15 is filled between the outer peripheral edge of the crystal piece 9 and the peripheral wall of the housing recess 8 of the package 3 in order to prevent liquid from entering the housing recess 8. Sealed.

  As the liquid in which the sensing area of the QCM sensor 1 is immersed, various liquids having different viscosities, densities, and the like are assumed depending on the detection target and the like.

  For this reason, under certain designed oscillation conditions, there are problems that some liquids do not oscillate or oscillate, but the oscillation frequency is not stable.

  For this reason, the QCM sensor 1 of this embodiment can oscillate even when immersed in various liquids, and in order to enable as stable oscillation as possible, the oscillation conditions are set according to the liquid to be immersed. It is configured so that it can be set.

  That is, the QCM sensor 1 of this embodiment incorporates an IC chip 4 that constitutes a voltage-controlled oscillation circuit that oscillates the crystal resonator 2 and controls its oscillation frequency in accordance with an input control voltage. . The IC chip 4 is mounted on the lower layer 5 of the housing recess 8 of the package 3.

  A voltage-controlled oscillation circuit constituted by the IC chip 4 is supplied with a control voltage having a constant voltage determined as described later in accordance with the liquid in which the sensing area of the QCM sensor 1 is immersed, and stable oscillation. Can be done.

  As shown in FIG. 2, connection electrodes 12 and 13 are formed on the stepped portion of the housing recess 8 of the package 3, that is, on the upper surface of the intermediate layer 6 so as to correspond to the extraction electrodes 11 a and 11 b of the crystal piece 9. The lead electrodes 11a and 11b of the crystal piece 9 are connected to the connection electrodes 12 and 13 via a conductive adhesive 14 using an epoxy resin or the like. Note that as the conductive adhesive 14, a resin other than an epoxy-based resin may be used.

  Each of the connection electrodes 12 and 13 is connected to electrode pads 35 and 36 on the upper surface of the lower layer 5 on which the IC chip 4 is mounted by internal wiring (not shown), and as shown in FIG. Are connected to crystal resonator connection terminals 22 and 23 (XT1, XT2) which are external terminals at respective corners on one end side.

  FIG. 3 is a diagram illustrating a configuration of a voltage controlled oscillation circuit configured by the IC chip 4.

  The voltage-controlled oscillation circuit of this embodiment includes a constant voltage power supply circuit 17 that supplies a constant voltage, an oscillation circuit unit 18, a level shift circuit 19, and an output buffer 20.

  The oscillation circuit unit 18 includes an inverting amplifier 21 having two transistors Tr1 and Tr2, a feedback resistor Rf, DC cut capacitors C1 and C2, variable capacitance diodes DV1 and DV2, bias resistors R1 and R2, and a crystal. A vibrator 2 and a resistor Rd are provided.

  A crystal resonator 2 and a feedback resistor Rf are connected in parallel between the input and output of the inverting amplifier 21, and fixed capacitors C1 and C2 are respectively connected between the input and output of the inverting amplifier 21 and the ground potential (reference potential). And series circuits of variable capacitance diodes DV1 and DV2.

  The control voltage Vc for changing the oscillation frequency is applied to the midpoint between the capacitors C1 and C2 and the variable capacitance diodes DV1 and DV2 connected in series via the bias resistors R1 and R2, respectively.

  In this voltage-controlled oscillation circuit, the control voltage Vc is varied to vary the capacitances of the variable capacitance diodes DV1 and DV2, and as a result, the oscillation frequency of the crystal resonator 2 is varied.

  In this voltage-controlled oscillation circuit, the crystal resonator connection terminals 22 and 23 (XT1, XT2), the ground terminal 24 (GND), the power supply terminal 25 (VCC), and the control voltage Vc are input as external terminals. The control voltage input terminal 26 (VC) and the output terminal 27 (OUT) are provided.

  These external terminals 22 to 27 are drawn out to the surface on one end side of the package 3 as shown in FIG.

  The voltage control type oscillation circuit is not limited to the above configuration, and any voltage control type oscillation circuit may be used as long as the oscillation frequency of the crystal resonator 2 can be controlled by the control voltage.

  The QCM sensor 1 of this embodiment is suitable for, for example, a chemical sensor or a biosensor that detects an organic compound or a biomolecule, and the sensing region in which the sensitive film 16 is formed is immersed in a liquid and used. The

  Since the QCM sensor 1 incorporates an IC chip 4 that constitutes a voltage controlled oscillation circuit, the oscillation margin and the load capacitance can be varied by the control voltage input to the voltage controlled oscillation circuit. The oscillation margin is the maximum equivalent resistance value that allows the crystal to oscillate, and the load capacitance indicates the circuit-side capacitance during oscillation.

  In this embodiment, an appropriate control voltage corresponding to the liquid is input to the control voltage input terminal 26 of the QCM sensor 1 so as to oscillate under an optimal oscillation condition in which the oscillation frequency is stabilized.

  FIG. 4 is a diagram showing the relationship between the control voltage Vc and the oscillation margin for the voltage-controlled crystal oscillation circuit, and shows each crystal oscillation circuit with oscillation frequencies of 25 MHz, 30 MHz, 35 MHz, and 40 MHz.

  As shown in FIG. 4, when the control voltage Vc is increased, the oscillation margin that is the limit value of the impedance of the oscillating crystal resonator is increased, and the oscillation limit in the liquid is increased, that is, the oscillation is easily performed.

  For example, when the oscillation frequency is 25 MHz, the control voltage Vc = 1.0V and the oscillation margin is −140Ω, whereas when the control voltage Vc = 4.0V, the oscillation margin is −633Ω.

  FIG. 5 is a diagram showing the relationship between the control voltage Vc and the load capacitance for the voltage controlled crystal oscillation circuit.

  Regardless of the oscillation frequency, the load capacitance is 5 pF at the control voltage Vc = 1.0 V, and 2.4 pF at the control voltage Vc = 4.0 V.

  As described above, when the control voltage Vc is increased, the load capacity is decreased and the stability of the oscillation frequency is decreased.

  FIG. 6 is a diagram showing the relationship between the control voltage Vc and the change in frequency (ΔF) for the voltage controlled crystal oscillation circuit. In FIG. 6, the fluctuation of the oscillation frequency with respect to the control voltage Vc is the fluctuation of the unintended load capacity of ± 0.5 pF with respect to the intended load capacity CL ± 0 pF, that is, the fluctuation of the load capacity CL ± 0.5 pF. It shows the change in oscillation frequency when assumed.

  When the control voltage Vc is large, for example, when Vc = 4.0V, the oscillation frequency changes by 151 ppm when the load capacitance CL fluctuates by ± 0.5 pF. On the other hand, when the control voltage Vc is small, for example, when Vc = 0.5V, the oscillation frequency changes by 32 ppm when the load capacitance CL fluctuates by ± 0.5 pF.

  Thus, the crystal oscillation frequency is determined by the load capacity, that is, the frequency stability is an unintended fluctuation of the load capacity (CL).

  When the control voltage Vc is reduced, as shown in FIG. 4, the oscillation margin is reduced, the oscillation limit in the liquid is reduced, and oscillation is difficult.

  On the other hand, when the control voltage Vc is reduced, as shown in FIG. 5, the load capacity is increased and the frequency stability of crystal oscillation is increased.

  In FIG. 6, in the state of the control voltage Vc = 0.5V, when the load capacitance CL fluctuates by ± 0.5 pF, the oscillation frequency changes by 32 ppm, with respect to 151 ppm which is the fluctuation when Vc = 4.0V. It will be within 21% fluctuation. That is, the lower the control voltage Vc, the higher the frequency stability.

  In consideration of this characteristic, the control voltage Vc that can be oscillated in the state with the highest frequency stability in the liquid among the conditions that oscillate in various liquids having different viscosities and densities, etc. Become.

  As described above, various liquids having different viscosities, specific gravity, and the like are assumed as the liquid in which the sensing region of the QCM sensor 1 is immersed, and in order to ensure that the QCM sensor 1 oscillates in the liquid, the design is performed. One set of oscillation conditions is not sufficient.

  In this embodiment, in order to surely oscillate, the characteristic of FIG. 4 in which the oscillation margin changes greatly depending on the value of the control voltage Vc of the voltage controlled oscillation circuit is used.

  Further, in order to oscillate under optimum oscillation conditions, it is necessary to appropriately select two parameters of oscillation, “drive level” and “load capacitance value”. The load capacitance value and the oscillation frequency stability are as shown in FIGS.

  The “drive level” is a product (power) of voltage and current applied when the QCM sensor oscillates, and is set to a value as small as possible so that oscillation can be sustained. When the value of the control voltage Vc decreases, the “drive level” also decreases. Therefore, it is important to set the value of the control voltage Vc to a small value for the “drive level”, that is, to lower the control voltage Vc. .

  In this embodiment, in order to predetermine a control voltage that can oscillate and is as low as possible in accordance with the liquid, the following is performed.

  That is, a sufficiently high control voltage that can oscillate even when immersed in a liquid, in this embodiment, a control voltage of 4.0 V is input to the QCM sensor 1 to oscillate, and in this oscillated state, the sensing region of the QCM sensor 1 is set. Immerse in liquid. Next, the oscillation voltage of the QCM sensor 1, specifically, the oscillation amplitude of the QCM sensor 1 is handled until the oscillation stops while the control voltage is gradually lowered from the sufficiently high control voltage of 4.0 V. Measure the oscillation voltage.

  Based on the relationship between the measured control voltage and the oscillation voltage, an appropriate control voltage corresponding to the liquid is determined. The sufficiently high control voltage is not limited to 4.0 V, and may be any control voltage that can oscillate while the sensing region of the QCM sensor 1 is immersed in a liquid. The sufficiently high control voltage is not necessarily applied before the sensing region of the QCM sensor 1 is immersed in the liquid, and is applied in a state where the sensing region of the QCM sensor 1 is immersed in the liquid. You may make it oscillate.

  In this embodiment, as will be described later, in the curve indicating the change in the oscillation voltage with respect to the control voltage, it corresponds to a tangent that has an inclination of about 50% with respect to the slope of the tangent of the curve immediately before the point where the oscillation stops. The control voltage to be determined is determined as an appropriate control voltage according to the liquid.

  An appropriate control voltage determined in advance in this way is input as a control voltage for the QCM sensor 1 to detect a specific substance to be detected, and measure the mass of the specific substance.

  Next, a detection system including the QCM sensor 1 will be described.

  FIG. 7 is a diagram showing a schematic configuration of the detection system of this embodiment.

  The detection system 28 of this embodiment includes the QCM sensor 1, the frequency counter 29, an AC voltmeter 30, a control device 31 composed of a personal computer or the like, and variable voltage first and second DC power sources 32 and 33. I have.

  The sensing area of the QCM sensor 1 is immersed in the liquid 38 of the constant temperature bath 37 with a stirring function.

  The frequency counter 29 measures the oscillation frequency of the oscillation output signal from the QCM sensor 1 and inputs frequency data to the control device 31.

  The AC voltmeter 30 measures the AC voltage (effective value) of the crystal resonator connection terminals 22 and 23 (XT 1 and XT 2) of the QCM sensor 1 and inputs it to the control device 31 as oscillation voltage data.

  The control device 31 sets an appropriate power supply voltage Vcc to the QCM sensor 1 via the second DC power supply 33, and controls on / off of the power supply voltage Vcc. Further, the control device 31 applies the control voltage Vc to the QCM sensor 1 via the first DC power supply 32.

  In this embodiment, when the sensing region of the QCM sensor 1 is immersed in the solvent solution before mixing the test solution in which the specific substance to be detected is mixed, for example, the electrolyte solution before mixing the test solution. An appropriate control voltage that oscillates reliably and obtains a stable oscillation state is determined in advance, and the determined appropriate control voltage is input to the QCM sensor 1 to obtain a stable oscillation state. A liquid to be tested is mixed, a specific substance to be detected is detected based on a frequency change from the frequency counter 29, and its mass or the like is measured by a predetermined parameter.

  Next, the procedure of the detection method by this detection system will be described in more detail.

  First, in the air, the power supply voltage Vcc is set and the power switch 34 is turned on to operate the QCM sensor 1, that is, oscillate. The control voltage Vc is set to a sufficiently high voltage that can oscillate while the sensing region of the QCM sensor 1 is immersed in a liquid, and is set to a maximum value of 4.0 V in this embodiment.

  Next, the sensing area of the QCM sensor 1 is immersed in the solvent liquid before mixing the test liquid.

  Next, while monitoring the oscillation voltage Vq and the oscillation frequency, the control voltage Vc is gradually lowered from 4.0V. At this time, the control voltage Vc and the oscillation voltage Vq are curves as shown in FIG.

  FIG. 8 shows changes in the oscillation voltage Vq when the control voltage Vc is gradually lowered from 4.0 V, and shows examples in the air and in the two types of liquids A and B. Yes.

  As shown in FIG. 8, when the sensing area of the QCM sensor 1 is immersed in the liquids A and B, and the control voltage Vc is gradually lowered from 4.0 V, the oscillation voltage Vq is gradually lowered to stop the oscillation. Oscillation stops at points PA and PB. In this way, the control voltage Vc is lowered to the oscillation stop point to grasp the lower limit value of the control voltage Vc.

  As shown in liquids A and B in FIG. 8, the oscillation stop points PA and PB differ depending on the types of liquids having different components, specific gravity, viscosity, and the like.

  In this embodiment, an appropriate control voltage Vc corresponding to the liquid is determined as follows. That is, the value of the control voltage Vc is preferably the lower limit value that oscillates as described above. However, when measuring the mass or the like of the specific substance, the specific substance is bonded and attached to the sensitive film 16 of the QCM sensor 1. In consideration of the deterioration of the oscillation condition due to the addition, it is necessary to take a margin in advance for the higher control voltage Vc.

  The margin is desirably a point where the slope of the fluctuation of the oscillation voltage Vq with respect to the control voltage Vc becomes gentle to about 50% when the oscillation is stopped. It is not limited to about 50% but may be larger or smaller than about 50%.

  For example, in the case of the liquid A, the control voltage VcA corresponding to the tangent line SA ′ having an inclination of 50% of the inclination of the tangent line SA immediately before the oscillation stop point PA is preferable, and in the example of the liquid B, immediately before the oscillation stop point PB. The control voltage VcB corresponding to the tangent line SB ′ having an inclination of 50% of the inclination of the tangent line SB is preferable. In this case, the margins up to the lower limit values for the liquids A and B are indicated by VcMA and VcMB, respectively.

  Determination of the appropriate control voltage Vc according to the liquid is calculated by the control device 31 based on the control voltage Vc and the input oscillation voltage Vq using the curve of FIG. 8 as described above. A curve as shown in FIG. 8 is displayed on the display unit of the control device 31, and the operator determines an appropriate control voltage Vc based on the display, and operates the operation unit of the control device 31 to perform an appropriate operation. A control voltage may be set.

  In the example of FIG. 8, the value of the control voltage VcB of the liquid B is not suitable for the value of the control voltage VcA of the liquid A. This is because the control voltage VcB is higher than the control voltage VcA and the load capacitance CL is small, so that the oscillation frequency is unstable.

  Next, the control device 31 inputs an appropriate constant voltage determined as described above to the QCM sensor 1 as the control voltage Vc.

  Then, after the oscillation frequency is stabilized, the test solution in which the specific substance to be detected is dissolved is mixed with the solvent solution, measurement by the control device 31 is started, and changes in the oscillation frequency are sequentially monitored. Based on the change in the oscillation frequency, the concentration of the specific substance is measured.

  That is, the specific substance in the mixed liquid in which the test liquid is mixed with the solvent liquid bonds and adheres to the sensitive film 16 of the QCM sensor 1, and the mass of the excitation electrode 10a increases. As the mass of the excitation electrode 10a increases, the resonance frequency of the crystal unit 2 decreases. By analyzing the decrease amount of the resonance frequency by the control device 31 via the frequency counter 29, the mass of the specific substance in the mixed liquid is calculated.

  In addition, after determining the appropriate control voltage Vc according to the kind of liquid as described above, when detecting a specific substance using the same liquid, the appropriate control voltage Vc already determined is controlled. You may enable it to set by operating the operation part of the apparatus 31. FIG.

[Other Embodiments]
Although the above embodiment is applied to detection of a specific substance in a liquid, it may be applied to detection of a specific substance in a gas.

  In the above embodiment, when the sensing area of the QCM sensor 1 is immersed in the liquid, the QCM sensor 1 is in an oscillating state, but is not necessarily in the oscillating state, and the sensing area of the QCM sensor 1 is immersed in the liquid. If it is not oscillating at the time, after the control voltage Vc is sufficiently increased and the QCM sensor 1 is oscillated, the control voltage is gradually decreased and an appropriate control voltage is determined as in the above embodiment. Good.

  The material of the QCM sensor package is not limited to ceramic, but may be glass, crystal, silicon, or the like.

  The piezoelectric vibrator is not limited to a flat plate shape, but an inverted mesa structure in which a recess is formed in the central portion of one surface or / and the other surface to increase the thickness around the central portion, or one surface or / and the other surface A piezoelectric vibrator having a mesa structure or the like in which the thickness of the outer peripheral portion of the surface is thinner than the thickness of the central portion may be used.

  The present invention may be applied to a flow cell type QCM sensor in which a flow path for allowing a sample solution to flow into and out of a sensing region of a crystal resonator is formed.

DESCRIPTION OF SYMBOLS 1 QCM sensor 2 Crystal oscillator 3 Package 4 IC chip 8 Receiving recessed part 9 Crystal piece 10a, 10b Excitation electrode 16 Sensing film | membrane 28 Detection system 29 Frequency counter 30 AC voltmeter 31 Control apparatus

Claims (10)

A sensor comprising: a piezoelectric vibrator having a sensing region to which a detection target is attached; and a package containing the piezoelectric vibrator so that the sensing region of the piezoelectric vibrator is exposed,
A voltage-controlled oscillation circuit that oscillates the piezoelectric vibrator and controls the oscillation frequency of the piezoelectric vibrator based on an input control voltage;
The voltage controlled oscillation circuit is housed in the package;
A sensor characterized by that. The sensing area of the sensor is immersed in a liquid,
The control voltage is a constant voltage according to the liquid;
The sensor according to claim 1. The piezoelectric vibrator is a crystal vibrator in which excitation electrodes are formed on both main surfaces of the crystal vibrating piece,
The sensing region includes a sensitive film formed on the excitation electrode on at least one main surface of the two main surfaces of the quartz crystal resonator element,
The sensor according to claim 1 or 2. The package includes an accommodation recess having a stepped portion,
An IC chip that constitutes the voltage-controlled oscillation circuit is accommodated in the accommodating recess, and the quartz crystal resonator element is accommodated above the IC chip in a state where a peripheral portion thereof is supported by the stepped portion,
The gap between the peripheral part of the quartz crystal vibrating piece supported by the step part and the peripheral wall of the housing recess is sealed with a sealing material,
The sensor according to claim 3. The sensing region is provided near one side of the package in the longitudinal direction, and an external terminal connected to the IC chip is provided at the other end in the longitudinal direction.
The sensor according to claim 4. A piezoelectric vibrator having a sensing region to which a detection target is attached; a sensor including a voltage-controlled oscillation circuit that oscillates the piezoelectric vibrator and controls an oscillation frequency of the piezoelectric vibrator based on an input control voltage; ,
A control device for controlling the control voltage output to the sensor,
The control device detects the detection target based on a change in a resonance frequency of the piezoelectric vibrator in a state where the control voltage is controlled to a constant voltage.
A detection system characterized by that. The sensing area of the sensor is immersed in a liquid,
The control device outputs the constant voltage corresponding to the liquid to the sensor;
The detection system according to claim 6. The control device determines the control voltage from a voltage high enough for the piezoelectric vibrator to oscillate in a state where the sensing region is immersed in the liquid in order to determine the constant voltage according to the liquid. Measure the oscillation output of the piezoelectric vibrator when lowered,
The detection system according to claim 7. The piezoelectric vibrator is a crystal vibrator in which excitation electrodes are formed on both main surfaces of the crystal vibrating piece,
The sensing region includes a sensitive film formed on the excitation electrode on at least one main surface of the two main surfaces of the quartz crystal resonator element,
The detection system according to claim 6. A sensor including a piezoelectric vibrator having a sensing region to which a detection target is attached, and a voltage-controlled oscillation circuit that oscillates the piezoelectric vibrator and controls the oscillation frequency of the piezoelectric vibrator based on an input control voltage. A method for detecting the detection object using:
A first step of inputting the control voltage high enough for the piezoelectric vibrator to oscillate to the sensor to oscillate the sensing region immersed in a liquid;
A second step of measuring an oscillation output of the piezoelectric vibrator when the control voltage is lowered from the sufficiently high control voltage in a state where the sensing region is immersed in the liquid;
A third step of determining a constant voltage corresponding to the liquid as a control voltage based on the oscillation output measured in the second step and the control voltage;
A fourth step of inputting the constant voltage determined in the third step as a control voltage to the sensor and detecting the detection object based on a change in a resonance frequency of the piezoelectric vibrator;
A detection method comprising:

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