JP2008180668A - Lamb wave type high-frequency sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Lamb wave type high-frequency sensor device having high detection sensitivity. <P>SOLUTION: The Lamb wave type high-frequency sensor device is provided with a piezoelectric substrate 11 having principle surfaces 14 and 15 in the front and back and an IDT electrode 12 formed in one principle surface 14 of the piezoelectric substrate 11 for exciting Lamb waves and constituted in such a way that the other principle surface 15 opposed to the one principle surface 14 of the piezoelectric substrate 11 may be a detection surface for detecting physical quantities. By using Lamb waves in this way, it is possible to achieve the Lamb wave type high-frequency sensor device 10 having high detection sensitivity and capable of operating at a frequency higher than those of a resonator using bulk waves or similar resonator using elastic surface waves of a conventional system. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a Lamb wave type high frequency sensor device using Lamb waves.

2. Description of the Related Art Conventionally, a high-frequency device that constitutes a high-frequency resonator and uses a bulk wave or a surface acoustic wave is known. Typical examples of the high-frequency resonator include a quartz AT-cut vibrator using a bulk wave, and a surface acoustic wave element using a surface acoustic wave such as a Rayleigh wave or an SH wave. Various sensors using these high-frequency devices have been developed.
For example, a plurality of AT-cut quartz resonators having electrodes on a quartz substrate as shown in Patent Document 1 are formed, and the components of the sample on the electrode surface are determined from changes in electrical characteristics such as the frequency and impedance of the quartz resonator. Multi-channel QCM sensor devices that detect and quantify are known.
Further, as shown in Patent Document 2, between a comb-shaped vibrating electrode (excitation-side IDT electrode) that excites a surface acoustic wave and a comb-shaped receiving electrode (receiving-side IDT electrode) that receives a propagated surface acoustic wave. 2. Description of the Related Art A gas sensor that detects a gas by providing a gas adsorber and changing a frequency by changing a propagation speed of a surface acoustic wave according to the mass of the gas adsorbed by the gas adsorber is known.

JP 2000-283905 A JP-A-8-68781

In such a high-frequency sensor device, the physical quantity is generally detected with high sensitivity by detecting the frequency. The higher the frequency, the larger the frequency change and the better the detection sensitivity.
In the QCM sensor device shown in Patent Document 1, since an AT-cut quartz crystal resonator is used, the frequency is determined by the thickness of the quartz substrate, the frequency is limited to about 40 to 60 MHz, and further frequency improvement is difficult. is there. For this reason, there is a limit in improving the detection sensitivity in the QCM sensor device.
In addition, the gas sensor using the surface acoustic wave shown in Patent Document 2 uses the surface acoustic wave, so the frequency can be increased compared to the AT vibrator and the detection sensitivity can be improved. Depending on the pitch of the IDT electrode, there is a limit to the miniaturization of the IDT electrode.
Further, in the above two examples of sensors, the surface on which the electrode is formed is used as a physical quantity detection surface, so that care should be taken in handling so as not to damage the electrode.

In recent years, in such a high-frequency sensor device, a high-frequency sensor device with higher detection sensitivity is required in order to detect a small amount of physical quantity and component.
In view of this, the present inventor has paid attention to a Lamb wave type high frequency sensor device using Lamb waves operating at a higher frequency than a resonator using a conventional bulk wave or a resonator using a surface acoustic wave.
The present invention has been made to solve the above problems, and an object of the present invention is to provide a Lamb wave type high frequency sensor device having high detection sensitivity and easy handling.

  In order to solve the above problems, a Lamb wave type high frequency sensor device of the present invention includes a piezoelectric substrate having main surfaces on the front and back sides, an IDT electrode for exciting a Lamb wave formed on one of the main surfaces of the piezoelectric substrate, and , And the other main surface opposite to one main surface of the piezoelectric substrate is a detection surface for detecting a physical quantity.

According to this configuration, in the Lamb wave type high frequency sensor device of the present invention, the IDT electrode is formed on one main surface of the piezoelectric substrate and excites the Lamb wave. Lamb waves are elastic waves propagating in a diagonal direction through a plate having a thickness of 5 wavelengths or less compared to the wavelength, and the phase velocity is high and the frequency can be increased. Thus, by using Lamb waves, it is possible to operate at a higher frequency than a resonator using a conventional bulk wave or a resonator using a surface acoustic wave, and a high-frequency sensor device with high detection sensitivity. Obtainable.
In addition, since the main surface of the back surface of the surface on which the IDT electrode is formed is a detection surface for detecting a physical quantity, a Lamb wave type high frequency sensor device that can be easily handled without damaging the IDT electrode in handling can be provided. .

  The Lamb wave type high frequency sensor device of the present invention includes a piezoelectric substrate having a main surface on both sides, an IDT electrode for exciting a Lamb wave formed on one of the main surfaces of the piezoelectric substrate, and one main surface of the piezoelectric substrate. And a sensitive film that reacts with a gas or a liquid formed on the other main surface facing the surface.

According to this configuration, in the Lamb wave type high frequency sensor device of the present invention, the IDT electrode is formed on one main surface of the piezoelectric substrate and excites the Lamb wave. Lamb waves are elastic waves propagating in a diagonal direction through a plate having a thickness of 5 wavelengths or less compared to the wavelength, and the phase velocity is high and the frequency can be increased. Thus, by using Lamb waves, it is possible to operate at a higher frequency than a resonator using a conventional bulk wave or a resonator using a surface acoustic wave, and a high-frequency sensor device with high detection sensitivity. Obtainable.
In addition, a sensitive film is formed on the back surface of the surface on which the IDT electrode is formed, and gas, components, etc. can be detected by adsorbing or reacting with the sensitive film.
In addition, since the main surface of the back surface of the surface on which the IDT electrode is formed is a detection surface, it is possible to provide a Lamb wave type high frequency sensor device that is easy to handle without damaging the IDT electrode in handling.

  The Lamb wave type high frequency sensor device of the present invention is formed at a position corresponding to the plurality of IDT electrodes on the other main surface of the piezoelectric substrate and the plurality of IDT electrodes formed on one main surface of the piezoelectric substrate. It is preferable that a plurality of the sensitive films are provided.

  According to this configuration, it is possible to provide a multi-channel Lamb wave type high frequency sensor device capable of detecting a plurality of gas and liquid components by appropriately selecting a sensitive film.

  In the Lamb wave type high frequency sensor device of the present invention, it is desirable that the plurality of sensitive films are formed of different types of sensitive films.

  According to this configuration, it is possible to provide a multi-channel Lamb wave type high frequency sensor device capable of detecting a plurality of gas and liquid components.

  In the Lamb wave type high frequency sensor device of the present invention, the piezoelectric substrate is preferably a quartz substrate.

  According to this configuration, since the piezoelectric substrate is formed of a quartz substrate, it is possible to provide a highly accurate Lamb wave type high frequency sensor device that is excellent in frequency temperature characteristics, which is a characteristic indicating the amount of change in frequency with respect to temperature. it can.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
(First embodiment)

FIG. 1 is a configuration diagram showing the configuration of a Lamb wave type high frequency sensor device of the present embodiment, FIG. 1 (a) is a schematic perspective view, and FIG. 1 (b) is an AA disconnection in FIG. 1 (a). FIG.
The Lamb wave type high frequency sensor device 10 is provided with an IDT (Interdigital Transducer) electrode 12 and a reflector 13 on a rectangular piezoelectric substrate 11 made of a quartz substrate. The piezoelectric substrate 11 has main surfaces 14 and 15 on the front and back, and an IDT electrode 12 and a reflector 13 are formed on one main surface 14. The IDT electrode 12 is formed of a metal material such as Al, and is configured such that Lamb waves can be excited by alternately inserting interdigitated electrodes 12a and 12b and applying a reverse-phase voltage to each of them. . Then, the reflector 13 is formed so as to sandwich the IDT electrode 12 from both sides, and the Lamb wave propagated from the IDT electrode 12 is reflected by the reflector 13, and energy is applied to the central portion of the piezoelectric substrate 11 on which the IDT electrode 12 is formed. Plays the role of confining. The reflector 13 is also made of a metal material such as Al, like the IDT electrode 12.
The distance between the cross finger electrode 12a and the cross finger electrode 12b in the IDT electrode 12 is formed at equal intervals with a pitch P, and the wavelength λ of the excited Lamb wave has a relationship of λ = 2P. The IDT electrode 12 is formed to have a predetermined thickness h. The thickness t of the piezoelectric substrate 11 is set to a thickness of 5 wavelengths (5λ) or less of Lamb waves.
Further, the other main surface 15 of the piezoelectric substrate 11 is in a state where the surface of the piezoelectric substrate 11 is exposed, and this main surface 15 is configured as a detection surface of the Lamb wave type high frequency sensor device 10.

Here, in order to facilitate understanding of the invention, a lamb wave type high frequency sensor device will be briefly described.
The Lamb wave is a bulk wave propagating in an oblique direction through a plate having a thickness of 5 wavelengths or less compared to the wavelength, and the Lamb wave type high frequency sensor device using the Lamb wave has a high phase velocity and a high frequency. be able to.
As described above, the frequency of the Lamb wave type high frequency sensor device depends on the thickness of the piezoelectric substrate as in the AT cut crystal resonator. FIG. 2 is a graph showing the relationship between the thickness of the quartz substrate and the resonance frequency in a Lamb wave type high frequency sensor device using a quartz substrate and an AT-cut quartz resonator. As can be seen from FIG. 2, the Lamb wave type high frequency sensor device can obtain a higher frequency than the AT cut quartz crystal resonator for the same quartz substrate thickness.

Next, a case where the Lamb wave type high frequency sensor device using Lamb waves is used as a film thickness sensor will be described. The film thickness sensor is equipped in a vacuum vapor deposition apparatus or a sputtering apparatus, and is used for detecting a film formation rate and a film thickness.
FIG. 3 is a schematic cross-sectional view showing a packaged Lamb wave type high frequency sensor device in which the Lamb wave type high frequency sensor device described in FIG. 1 is configured as a film thickness sensor.
The film thickness sensor 20 is packaged so that one main surface 14 on which the IDT electrode 12 and the reflector 13 of the Lamb wave type high frequency sensor device 10 are formed in the container 21 faces inward and the main surface 14 is protected. Yes. The film thickness sensor is configured such that the other main surface 15 of the Lamb wave type high frequency sensor device 10 is exposed. Although not shown, the container terminal and the IDT electrode 12 are connected by a metal wire or the like so as to be electrically connected to the IDT electrode 12. The container 21 can be electrically connected to the outside.

  Such a film thickness sensor 20 is provided in a film forming tank of a vacuum vapor deposition apparatus or a sputtering apparatus, and is installed so that the exposed main surface 15 faces the vapor deposition source and the sputtering target. When the film formation is started, a film forming material is deposited on the main surface 15 of the film thickness sensor 20, and a mass is added to the piezoelectric substrate 11, and the frequency of the excited Lamb wave type high frequency sensor device 10 is increased. It changes to be lower. By detecting the amount of change in frequency, the film formation rate and film thickness can be detected.

For example, FIG. 4 shows a standardized film thickness (in a film thickness sensor using an AT-cut quartz crystal resonator that is generally used and a film thickness sensor using a Lamb wave type high-frequency sensor device of the present embodiment ( Here, it is a graph showing the relationship between the film thickness H formed by dividing the film thickness H by the wavelength λ) H / λ and the amount of change in frequency.
According to FIG. 4, the film thickness sensor using the Lamb wave type high frequency sensor device has a larger amount of change in frequency for the same standardized film thickness than the film thickness sensor using the AT-cut crystal resonator. It can be seen that the film thickness detection sensitivity is high.

Further, FIG. 5 shows the frequency deviation and the formation of the normalized film thickness (here, the value obtained by dividing the film thickness H by the wavelength λ) H / λ = 0.01 (constant). It is a graph which shows the relationship with the density of the film | membrane material. It can be seen that the amount of change in the frequency deviation increases as the density of the deposited material increases. In this manner, the density of the deposited material can be obtained by detecting a change in frequency, and can be used as a density sensor.
Further, in the same manner, the mass of the deposited material can be obtained and can be used as a mass sensor, and can be used as a sensor for detecting various physical quantities.

As described above, in the Lamb wave type high frequency sensor device 10 of the present embodiment, the IDT electrode 12 is formed on one main surface 14 of the piezoelectric substrate 11 to excite the Lamb wave. Thus, by using Lamb waves, it is possible to operate at a higher frequency than a resonator using a conventional bulk wave or a resonator using a surface acoustic wave, and a Lamb wave type high frequency with high detection sensitivity. The sensor device 10 can be obtained.
In addition, since the main surface 15 on the back surface of the surface on which the IDT electrode 12 is formed is a detection surface for detecting a physical quantity, the lamb wave type high frequency sensor device 10 that is easy to handle without damaging the IDT electrode 12 in handling is provided. can do. Furthermore, after using as a sensor, it can be reused by washing the detection surface.
(Second Embodiment)

Next, as a second embodiment, a Lamb wave type high frequency sensor device in which a sensitive film for adsorbing or reacting a gas or liquid is provided on the other main surface of the Lamb wave type high frequency sensor device described in the first embodiment. Will be described.
6A and 6B are configuration diagrams showing the configuration of the Lamb wave type high-frequency sensor device of the present embodiment. FIG. 6A is a schematic perspective view, and FIG. 6B is a BB disconnection in FIG. FIG. In addition, about the structure similar to 1st Embodiment, a same sign is attached | subjected and demonstrated.
The Lamb wave type high frequency sensor device 30 is provided with an IDT electrode 12 and a reflector 13 on a rectangular piezoelectric substrate 11 made of a quartz substrate. The piezoelectric substrate 11 has main surfaces 14 and 15 on the front and back, and an IDT electrode 12 and a reflector 13 are formed on one main surface 14. The IDT electrode 12 is formed of a metal material such as Al, and is configured such that Lamb waves can be excited by alternately inserting interdigitated electrodes 12a and 12b and applying a reverse-phase voltage to each of them. . Then, the reflector 13 is formed so as to sandwich the IDT electrode 12 from both sides, and the Lamb wave propagated from the IDT electrode 12 is reflected by the reflector 13, and energy is applied to the central portion of the piezoelectric substrate 11 on which the IDT electrode 12 is formed. Plays the role of confining. The reflector 13 is also made of a metal material such as Al, like the IDT electrode 12.
The distance between the cross finger electrode 12a and the cross finger electrode 12b in the IDT electrode 12 is formed at equal intervals with a pitch P, and the wavelength λ of the excited Lamb wave has a relationship of λ = 2P. The IDT electrode 12 is formed to have a predetermined thickness h. The thickness t of the piezoelectric substrate 11 is set to a thickness equal to or less than 5 wavelengths (5λ) of Lamb waves.
A sensitive film 31 is formed on the other main surface 15 of the piezoelectric substrate 11, and this surface is configured as a detection surface of the Lamb wave type high frequency sensor device 30.
As the sensitive film 31, an allylamine film that adsorbs water vapor, a styrene film or a lecithin film that adsorbs ethanol gas, and the like are used, and are appropriately selected depending on the application.

Next, a case where a Lamb wave type high frequency sensor device using Lamb waves is used as a gas sensor will be described.
FIG. 7 is a schematic cross-sectional view showing a packaged Lamb wave type high frequency sensor device in which the Lamb wave type high frequency sensor device described in FIG. 6 is configured as a gas sensor.
The gas sensor 40 is packaged so that one main surface 14 on which the IDT electrode 12 and the reflector 13 of the Lamb wave type high frequency sensor device 30 are formed in the container 41 faces inward and the main surface 14 is protected. The gas sensor 40 is configured such that the sensitive film 31 formed on the other main surface 15 side of the Lamb wave type high frequency sensor device 30 is exposed. Although not shown, the container terminal and the IDT electrode 12 are connected by a metal wire or the like so as to be electrically connected to the IDT electrode 12. The container 21 can be electrically connected to the outside.

In such a gas sensor 40, when the gas comes into contact with the sensitive film 31, a specific gas is adsorbed and mass is added to the piezoelectric substrate 11, and the frequency of the excited Lamb wave type high frequency sensor device is sequentially lowered. It changes to become. This tendency is similar to the relationship between the film thickness and the amount of change in frequency described in the first embodiment, and the amount of gas can be detected by detecting the amount of change in frequency.
For example, when an allylamine film is used as the sensitive film 31, water vapor is adsorbed and the frequency of the Lamb wave type high frequency sensor device changes according to the amount of adsorption. From this, it can comprise as a humidity sensor which detects the water vapor | steam of gas.
Further, by forming a film that reacts with a liquid component on the sensitive film 31, it is possible to detect the liquid component. Furthermore, it is also possible to use it as a biosensor by configuring the sensitive membrane with a biological material.

As described above, in the Lamb wave type high frequency sensor device 30 of the present embodiment, the IDT electrode 12 is formed on one main surface 14 of the piezoelectric substrate 11 and excites the Lamb wave. Thus, by using Lamb waves, it is possible to operate at a higher frequency than a resonator using a conventional bulk wave or a resonator using a surface acoustic wave, and a high-frequency sensor device with high detection sensitivity. Obtainable.
In addition, a sensitive film 31 is formed on the back main surface 15 of the surface on which the IDT electrode 12 is formed, and gas, liquid components, etc. can be adsorbed or reacted to the sensitive film 31 to enable detection of gas, components, etc. To do.
Furthermore, since the main surface 15 on the back surface of the surface on which the IDT electrode 12 is formed is a detection surface, the Lamb wave type high frequency sensor device 30 that is easy to handle without damaging the IDT electrode 12 in handling can be provided. .
(Modification)

Next, a modification of the Lamb wave type high frequency sensor device of the second embodiment will be described.
FIG. 8 is a schematic explanatory view of a multi-channel sensor device in which a plurality of Lamb wave type high frequency sensor devices are provided on one piezoelectric substrate, FIG. 8 (a) is a plan view, FIG. 8 (b) is a bottom view, FIG.8 (c) is sectional drawing which follows CC disconnection of the figure (b).

The multichannel sensor device 50 includes a plurality of Lamb wave type high frequency sensor devices on a piezoelectric substrate 51 made of a quartz substrate.
Four sets of patterns each including the IDT electrode 52 and the reflector 53 are formed on the main surface 54 of the piezoelectric substrate 51. One crossing finger of the IDT electrode 52 is connected to the wiring 56 and connected to the external wiring on the input side. The other crossing finger is connected to the wiring 57 and connected to the output-side external wiring.
On the other main surface 55 side of the piezoelectric substrate 51, a recess 58 is provided at a position facing the IDT electrode 52 and the reflector 53. The recess 58 is formed by etching the piezoelectric substrate 51, and the substrate in the recess 58 is configured to have a predetermined thickness. The sensitive films 61a, 61b, 61c and 61d are formed in the recess 58.
The sensitive films 61a to 61d are provided with an allylamine film, a styrene film, a lecithin film, or the like, and configured to be able to detect corresponding to various gases.
Further, by forming a film that reacts with the liquid component on the sensitive films 61a to 61d, it is possible to detect the liquid component.

  As described above, by using the multi-channel sensor device 50 of the present modification, a multi-channel Lamb wave type high-frequency sensor device that can detect a plurality of gas and liquid components and is easy to handle with high sensitivity is provided. can do.

The piezoelectric substrate described in the first and second embodiments is formed of a quartz substrate.
FIG. 9 is a graph showing frequency temperature characteristics when a quartz substrate is used in a Lamb wave type high frequency sensor device and when a lithium tantalate (LT) substrate is used. As can be seen from this graph, by using a quartz substrate as a piezoelectric substrate for exciting Lamb waves, the amount of change in frequency with respect to temperature can be suppressed smaller than that of a lithium tantalate substrate, and frequency temperature characteristics can be improved. .
Thus, since the Lamb wave type high frequency sensor device of the first and second embodiments uses the quartz substrate, it is possible to provide a Lamb wave type high frequency sensor device having excellent frequency temperature characteristics and high accuracy. .

It is a block diagram which shows the structure of the Lamb wave type | mold high frequency sensor device in 1st Embodiment, (a) is a model perspective view, (b) is a schematic cross section along the AA disconnection of the same figure (a). The graph which shows the relationship between the thickness of the quartz substrate in a Lamb wave type high frequency sensor device using a quartz substrate, and an AT cut quartz crystal unit, and a resonance frequency. The schematic cross section which shows the packaged Lamb wave type | mold high frequency sensor device which comprised the Lamb wave type | mold high frequency sensor device as a film thickness sensor. The graph which shows the relationship between the film thickness formed into a film, and the variation | change_quantity of a frequency. The graph which shows the relationship between the frequency deviation and the density of the deposited material when the film thickness is constant. It is a block diagram which shows the structure of the Lamb wave type | mold high frequency sensor device in 2nd Embodiment, (a) is a model perspective view, (b) is a schematic cross section along the BB disconnection of the same figure (a). The schematic cross section which shows the packaged Lamb wave type | mold high frequency sensor device which comprised the Lamb wave type | mold high frequency sensor device as a gas sensor. It is a schematic explanatory drawing of a multichannel sensor device, showing a modification of the second embodiment, (a) is a plan view, (b) is a bottom view, and (c) is a CC disconnection in FIG. FIG. The graph which shows the frequency temperature characteristic when using the quartz substrate in a Lamb wave type high frequency sensor device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Lamb wave type high frequency sensor device, 11 ... Piezoelectric substrate, 12 ... IDT electrode, 13 ... Reflector, 14, 15 ... Main surface, 20 ... Film thickness sensor, 21 ... Container, 30 ... Lamb wave type high frequency sensor device, DESCRIPTION OF SYMBOLS 31 ... Sensitive membrane, 40 ... Gas sensor, 41 ... Container, 50 ... Multichannel sensor device, 51 ... Piezoelectric substrate, 52 ... IDT electrode, 53 ... Reflector, 54, 55 ... Main surface, 56, 57 ... Wiring, 61a, 61b, 61c, 61d ... Sensitive membrane.

Claims (5)

A piezoelectric substrate having a main surface on both sides;
An IDT electrode for exciting a Lamb wave formed on one of the principal surfaces of the piezoelectric substrate, and the other principal surface facing the one principal surface of the piezoelectric substrate is a detection surface for detecting a physical quantity Lamb wave type high frequency sensor device characterized by. A piezoelectric substrate having a main surface on both sides;
An IDT electrode for exciting a Lamb wave formed on one of the principal surfaces of the piezoelectric substrate;
A Lamb wave type high frequency sensor device comprising: a sensitive film that reacts with a gas or a liquid formed on the other main surface opposite to one main surface of the piezoelectric substrate. In the Lamb wave type high frequency sensor device according to claim 2,
A plurality of the IDT electrodes formed on one main surface of the piezoelectric substrate;
A Lamb wave type high frequency sensor device comprising: a plurality of the sensitive films formed on the other principal surface of the piezoelectric substrate at positions corresponding to the plurality of IDT electrodes. In the Lamb wave type high frequency sensor device according to claim 3,
A lamb wave type high frequency sensor device, wherein the plurality of sensitive films are formed of different types of sensitive films. In the Lamb wave type high frequency sensor device according to any one of claims 1 to 4,
A Lamb wave type high frequency sensor device, wherein the piezoelectric substrate is a quartz substrate.

Images