JP2007078428A - Surface acoustic wave sensor, and surface acoustic wave sensor system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave (SAW) sensor of a high Q-value, which can be small-sized, exhibits an excellent frequency temperature characteristic, and has high sensitivity, in particular, suitable for a liquid phase system. <P>SOLUTION: This SAW sensor 1 uses a piezoelectric substrate 1 of a rotary Y-cut quartz plate of which the cut face and the propagation direction of the SAW are formed into (0°, -64 to -49.3°, +90°, 90±5°)=(0°, 26 to 40.7°, 90±5°) in Eulerian angle display. IDTs 12, 13 are formed of an electrode film comprising Al or an alloy containing Al as a main component, on a surface of the piezoelectric substrate, and a film thickness H of the electrode film is set in 0.04<H/λ<0.12, where λ is a wavelength of the SAW. A receptor 5 for recognizing an objective substance is provided on a propagation face of the SAW. A pair of reflectors 15, 15 is provided further in both sides of the IDTs. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave sensor and a surface acoustic wave sensor system that use a surface acoustic wave (SAW) element as a transducer to detect a specific chemical substance and / or measure its physical properties. .

  Recently, particularly in technical fields such as biotechnology and medicine, a SAW sensor using a SAW element as a transducer has been developed to detect a chemical or physical change in a receptor that recognizes a chemical substance to be measured. (For example, refer nonpatent literatures 1 and 2.). In general, a SAW sensor has a receptor such as a detection substance reaction film on the SAW propagation surface of a piezoelectric substrate. When the target chemical substance is bound to the receptor and its weight changes, the SAW propagation speed changes. By measuring this as a change in oscillation frequency, the target substance and / or its physical properties can be detected with high accuracy. can do.

  For example, a SAW device is known in which a gas adsorber as a receptor is disposed on a piezoelectric substrate between an excitation electrode made of IDT (interdigital transducer) and a reception electrode (see, for example, Patent Document 1). In addition, an electrical short circuit, an electrical release, and a sample cell are provided on the SH-SAW (transverse surface acoustic wave) propagation surface of the piezoelectric substrate, and the SAW generated between the electrical short circuit and the electrical release when the same liquid is loaded. A surface acoustic wave biosensor that detects physical properties such as pH and conductivity from a change in propagation speed is known (see Patent Document 2). In addition, three SAW sensors each having a sensor cell between a transmitting electrode and a receiving electrode each made of IDT are arranged side by side on a single piezoelectric substrate, so that the dynamic quantity and the electric quantity of the measurement liquid can be measured simultaneously. A type of solution sensor system is known (see, for example, Patent Document 3).

  On the other hand, SAW devices widely used in electronic equipment such as communication / information equipment are generally required to be small in size, high Q value (resonance sharpness), and excellent frequency stability. As a SAW device that satisfies these requirements, there is a SAW device using an ST cut quartz substrate. The ST-cut quartz substrate is a quartz plate that is cut out using a plane (XZ ′ plane) obtained by rotating the XZ plane 42.75 ° counterclockwise from the crystal Z axis with the crystal X axis as the rotation axis. A SAW which is a (P + SV) wave called a Rayleigh wave propagating in the direction is used.

However, when a liquid is loaded on the SAW propagation surface, the Rayleigh wave is radiated into the liquid and attenuates, so that it cannot be used particularly for a liquid phase SAW sensor. Therefore, SH-SAW using 36 ° rotated Y-plate X-propagating LiTaO ₃ as a piezoelectric substrate is widely adopted as a liquid-phase SAW sensor (see, for example, Non-Patent Document 2). Since this piezoelectric substrate does not generate unnecessary SAW (spurious vibration such as longitudinal waves) other than the intended SAW and has a large electromechanical coupling coefficient, a highly sensitive sensor can be realized (for example, see Patent Document 3). .

  Also, the Euler is set so that the cut angle θ of the rotated Y-cut quartz plate is set in the vicinity of −50 ° rotated counterclockwise from the crystal Z axis, and the elastic wave propagation direction is perpendicular to the crystal X axis. 2. Description of the Related Art An acoustic wave device using a quartz crystal plate with an angle (0 °, θ + 90 °, 90 °) = (0 °, 40 °, 90 °) as a piezoelectric substrate is known (for example, Non-Patent Document 3 and Patent Document 4). reference). This acoustic wave element is characterized in that a surface traveling volume wave (SSBW) whose main component of displacement is parallel to the substrate surface (SH component) is excited by IDT and its vibration energy is confined immediately below the electrode.

  Further, when 800 ± 200 pairs of IDTs are formed on a piezoelectric substrate made of this rotated Y-cut quartz plate and the wavelength of the elastic wave excited by the IDT is λ, the electrode film thickness of the IDT is A multi-pair IDT type acoustic wave resonator having a wavelength of 2% λ or more, preferably 4% λ or less is known (see, for example, Patent Document 5). Thereby, without using a grating reflector, SAW energy can be confined only by reflection of IDT itself, and Q value can be raised.

Industrial Property General Information Center, “Patent Distribution Support Chart / Chemical 2 / Biosensor”, Invention Association of Japan, June 29, 2002, p. 3-5 and 16-18 Japan Society for the Promotion of Science Elastic Wave Device Technology 150th Edition, “Acoustic Wave Device Technology”, Ohmsha, August 20, 2004, p. 405-412 Meirion Lewis, “Surface Skimming Bulk Wave, SSBW”, IEEE Ultrasonics Symp. Proc., 1977, p. 744-752 JP-A-8-68781 JP-A-6-133759 Japanese Patent Laid-Open No. 9-80035 Japanese Examined Sho 62-016050 Japanese Patent Publication No. 01-034411

However, the 36 ° rotated Y-plate X propagation LiTaO ₃ has the following problems. First, as shown by the broken line in FIG. 10, there is a problem that the frequency variation with respect to the temperature is −20 ppm / ° C., which is very large. Therefore, noise due to temperature change is large, and the S / N ratio may be reduced. In order to solve this problem, difficult temperature management is required, for example, a special circuit for adjusting the oscillation frequency with respect to the operating temperature must be added.

Further, as shown in FIG. 11, there is a problem that the center frequency f ₀ has a frequency characteristic having a certain bandwidth, the transmission characteristic is broad, and the Q value is small. For this reason, the SAW sensor using this has a large so-called fluctuation of the measurement frequency, and there is a risk of reducing the measurement accuracy. Therefore, in order to ensure measurement accuracy, extra signal processing and data processing such as removal of the fluctuation component are required.

  On the other hand, as shown by the solid line in FIG. 10, the crystal has excellent frequency stability with respect to temperature, and temperature management is easy. However, the ST-cut quartz substrate is small in size and can realize a high Q value and excellent frequency stability. However, as described above, since the SAW used is a Rayleigh wave, it cannot be used for a liquid phase sensor. There is.

  In addition, the rotating Y-cut quartz plate described in Patent Documents 5 and 6 described above is a wave in which the SSBW wave basically goes under the substrate, so that an efficient energy confinement effect cannot be obtained. There is a problem that the reflection efficiency is poor. Therefore, it is difficult to realize a SAW device having a small size and a high Q value. In particular, the multi-pair IDT type SAW resonator described in Patent Document 6 has a problem that the device size becomes so large that the requirement for miniaturization cannot be satisfied because the number of IDT pairs necessary for obtaining a high Q value is very large. There is.

  Therefore, the present invention has been made in view of the above-described conventional problems, and its purpose is to be able to be miniaturized, exhibiting a high Q value and excellent frequency temperature characteristics, and particularly high sensitivity suitable for a liquid phase system. Another object of the present invention is to provide a multi-channel SAW sensor system having a single SAW sensor and a plurality of channels composed of such SAW sensors on a single piezoelectric substrate.

  As shown in FIG. 1, the inventors of the present application have a piezoelectric substrate made of a rotated Y-cut quartz plate and having a SAW propagation direction of 90 ± 5 ° with respect to the crystal X axis, and Al or A variety of experiments were conducted on SAW devices including an IDT made of an alloy containing Al as a main component and the SAW excited by the IDT being an SH wave, and normalized by the cut angle θ and the wavelength λ of the excited SAW. The relationship between the electrode thickness H / λ, Q value, and frequency temperature characteristics of the IDT was examined in detail. As a result, the cut angle θ of the rotated Y-cut quartz plate is set in the range of −64 ° <θ <−49.3 ° counterclockwise from the crystal Z axis, and the electrode film thickness H / λ is 0.04. By setting it in the range of <H / λ <0.12, the SAW device is focused on the substrate surface to improve the SAW reflection efficiency and provide a small SAW device with high Q value and excellent frequency stability. I found out that I could do it.

This invention is made | formed based on this knowledge of this inventor.
According to the present invention, in order to achieve the above object, the piezoelectric substrate, the IDT formed on the surface of the piezoelectric substrate, and the SAW excited by the IDT are fixed to the propagation surface to recognize the target substance. The piezoelectric substrate is a rotating Y-cut quartz plate, and the cut surface and SAW propagation direction are displayed in Euler angles (0 °, −64 to −49.3 ° + 90 °, 90 ± 5 °). ) = (0 °, 26-40.7 °, 90 ± 5 °), the IDT is formed of an electrode film made of Al or an alloy containing Al as a main component, and the electrode film A SAW sensor having a thickness H of 0.04 <H / λ <0.12 is provided where the wavelength of SAW is λ.

  By configuring the piezoelectric substrate and the IDT in this way, the SAW sensor of the present invention excites the SH wave, so that it can be used for a liquid phase sensor, and has good temperature characteristics and high Q. Since the value is obtained, the CI value can be suppressed low, and a sensor with high sensitivity and high measurement accuracy can be realized.

  In some embodiments, a pair of reflectors disposed on both sides of the IDT and the receiver along the SAW propagation direction further comprises a pair of reflectors to enhance the effect of confining SAW energy between them. Since the reflected wave from the end face of the piezoelectric substrate is reduced and the loss is reduced, the Q value is increased, the CI value is reduced, and more excellent resonance characteristics can be obtained, so that the sensitivity of the SAW sensor can be improved.

  In another embodiment, the SAW sensor IDT is a two-port resonator type in which the IDT includes an excitation IDT and a reception IDT, and the receptor is disposed between the excitation IDT and the reception IDT.

  In one embodiment, the IDT of the SAW sensor is a one-port resonator type consisting of one IDT having a pair of cross finger electrodes, and one IDT can be omitted as compared to the transversal type. It is possible to reduce the size and the manufacturing cost. In this case, the receptor can be placed between the electrode fingers of the interdigitated electrode, or can be placed between the IDT and one reflector.

  According to another aspect of the present invention, a plurality of the above-described SAW sensors of the present invention are provided, the SAW sensors are arranged in series and / or in parallel with respect to the propagation direction of the SAW, and each SAW sensor is a single unit. By providing them on a common piezoelectric substrate, a multi-channel SAW sensor system with improved sensitivity and measurement accuracy of each channel is provided. In particular, when the SAW sensor of each channel has a pair of reflectors, the effect of the SAW excited from the adjacent channel and the effect of the SAW reflected wave from the end face of the piezoelectric substrate are effectively obtained even if they are simultaneously oscillated. Can be eliminated.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
First, the SAW resonator constituting the SAW sensor of the present invention will be described. In this SAW resonator, as shown in FIG. 1, the cut angle θ of the rotated Y-cut quartz substrate is set in the vicinity of being rotated −64 to −49.3 ° counterclockwise from the crystal Z axis, and SAW propagation is performed. It is a quartz plate whose direction is substantially perpendicular to the crystal X axis (90 ± 5 °). The SAW excited in this piezoelectric substrate is an SH wave. The electrode material of IDT formed on the surface of the piezoelectric substrate is Al or an alloy containing Al as a main component. In this embodiment, the electrode film thickness H of the IDT is represented by a value H / λ normalized by the wavelength λ of the SAW excited thereby.

  The piezoelectric substrate shown in FIG. 1 uses a rotating Y-cut 90 ° X propagation quartz substrate (Euler angle display (0 °, 39 °, 90 °)) with a cut angle θ = −51 °, a resonance frequency of 315 MHz, and an electrode film A SAW resonator having a thickness H / λ of 0.06, a logarithm of IDT of 100, and further provided with 100 grating reflectors was fabricated, and its characteristics were measured. Further, along the SAW propagation direction, the electrode finger width with respect to the pitch of the electrode fingers constituting the IDT (= the width of the electrode fingers + the space between the electrode fingers) is defined as the line occupation ratio mr, and mr = 0.60 is set. did. As a comparative example, a conventional SAW resonator was manufactured using an ST cut quartz plate as a piezoelectric substrate and under the same design conditions, and various characteristics were measured.

  FIG. 2 shows their frequency temperature characteristics. As can be seen from the figure, the SAW resonator of the present invention has an apex temperature Tp of about 25 ° C., and the frequency variation due to temperature is about 0.6 times that of the conventional ST-cut quartz SAW resonator. It became small to the extent. Thus, in the present invention, excellent frequency stability can be obtained.

In general, what is important in the optimum design of the SAW resonator is that the frequency temperature characteristic is excellent, the Q is high, and the capacitance ratio γ is small, that is, the sensitivity (figure of merit = Q / γ) is large. The SAW resonator of the present invention had a Q value of 27500, a good sensitivity (Q / γ) of 21.2, and a secondary temperature coefficient of −0.020 (ppm / ° C. ² ). In contrast, the conventional ST-cut quartz SAW resonator had a Q value of 15000, a good sensitivity (Q / γ) of 10.7, and a secondary temperature coefficient of −0.034 (ppm / ° C. ² ). Comparing these, the SAW resonator of the present invention has a Q value slightly higher than 1.8 times and a good sensitivity (Q / γ) approximately twice as large as those of the conventional ST-cut quartz crystal SAW resonator. You can see that it is obtained.

  Further, FIG. 3 shows the relationship between the electrode film thickness H / λ and the Q value in the SAW resonator of the present invention. From the figure, it can be seen that the SAW resonator of the present invention can obtain a higher Q value than the ST cut quartz SAW resonator in the range of 0.04 <H / λ <0.12. Furthermore, a higher Q value of 20000 or more can be obtained by setting the electrode film thickness in the SAW resonator of the present invention in the range of 0.05 <H / λ <0.10.

  As described above, in the present invention, by setting the electrode film thickness H / λ to be large, the SAW can be concentrated on the surface of the piezoelectric substrate to improve the SAW reflection efficiency and enhance the confinement effect of the SAW energy. Therefore, it is possible to reduce the size of the piezoelectric substrate while realizing a higher Q value than before.

Furthermore, in order to realize excellent frequency stability in a practical use temperature range (−50 ° C. to + 125 ° C.), not only the secondary temperature coefficient but also the apex temperature Tp was examined in detail. As a result, in the SAW resonator of the present invention, when the cut angle θ is −50.5 °, the relationship between the electrode film thickness H / λ and the apex temperature Tp is expressed by the following approximate expression.
Tp (H / λ) = − 41825 × (H / λ) ² + 2855.4 × (H / λ) −26.42 (1)
From this, it can be seen that the vertex temperature Tp decreases as the electrode film thickness H / λ is increased.

In the SAW resonator of the present invention, when the electrode film thickness H / λ is 0.06, the relationship between the cut angle θ and the vertex temperature Tp is expressed by the following approximate expression.
Tp (θ) = − 43.5372 × θ−2197.14 (2)
From this, it can be seen that the vertex temperature Tp decreases as the absolute value of the cut angle θ decreases.

  From the above formulas (1) and (2), when the electrode film thickness H / λ is 0.04 <H / λ <0.12, the apex temperature Tp is set to a practical operating temperature range (−50 to + 125 ° C. It can be seen that the cut angle θ should be set in the range of −59.9 ° ≦ θ ≦ −48.9 °.

Further, when considering both the electrode film thickness H / λ and the cut angle θ, the apex temperature Tp is expressed by the following approximate expression from the above expressions (1) and (2).
Tp (H / λ, θ) = Tp (H / λ) + Tp (θ) = − 41825 × (H / λ) ² + 2855.4 × (H / λ) −43.5372 × θ−2223.56 (3)
From this equation (3), in order to set the apex temperature Tp within the operating temperature range (−50 to + 125 ° C.), the electrode film thickness H / λ and the cut angle θ are set within the range represented by the following equation (4). You can see that it should be set.
0.9613 ≦ −18.498 × (H / λ) ² + 1.2629 × (H / λ) −0.019255 × θ ≦ 1.0387 (4)

  Thus, by setting the cut angle θ in the range of −59.9 ° ≦ θ ≦ −48.9 ° and the electrode film thickness H / λ of the IDT to 0.04 <H / λ <0.12, In a practical operating temperature range (−50 ° C. to + 125 ° C.), it is possible to realize a SAW sensor that is smaller than the conventional one, and has a high Q value and excellent frequency stability.

Further, considering more optimal design conditions, it is preferable that the electrode film thickness H / λ is set in the range of 0.05 <H / λ <0.10 in which a Q value of 20000 or more can be obtained from FIG. Further, in order to set the vertex temperature Tp to a more practical use temperature range (0 ° to 70 ° C.), the cut angle θ is set to a range of −55.7 ° ≦ θ ≦ −50.2 °. Further, it is preferable to set the cut angle θ and the electrode film thickness H / λ within the range of the following equation (5) obtained from the equation (3).
0.9845 ≦ −18.518 × (H / λ) ² + 1.2643 × (H / λ) −0.019277 × θ ≦ 1.0155 (5)

Furthermore, when an experiment was conducted for a wide range of cut angles θ, more detailed conditions could be found as will be described below. In the above-described SAW resonator of the present invention, when the apex temperature Tp is −50 ° C., 0 ° C., 70 ° C., 125 ° C., the relationship between the cut angle θ of the quartz substrate and the electrode film thickness H / λ is the Tp characteristic. Is expressed by the following approximate expression.
When Tp = −50 (° C.):
H / λ≈−1.02586 × 10 ⁻⁴ × θ ³ −1.73238 × 10 ⁻² × θ ² −0.977607 × θ−18.3420
When Tp = 0 (° C.):
H / λ≈−9.875991 × 10 ⁻⁵ × θ ³ −1.70304 × 10 ⁻² × θ ² −0.981173 × θ−18.7946
When Tp = + 70 (° C.):
H / λ≈−1.44605 × 10 ⁻⁴ × θ ³ −2.50690 × 10 ⁻² × θ ² −1.45086 × θ−27.9464
When Tp = + 125 (° C.):
H / λ ≒ −1.34082 × 10 ⁻⁴ × θ ³ −2.34969 × 10 ⁻² × θ ² −1.37506 × θ−26.7895

In order to set the apex temperature Tp to the practical use temperature range −50 ≦ Tp ≦ 125 from the approximate expression showing these Tp characteristics, it is surrounded by the curve of the approximate expression at Tp = −50 ° C. and Tp = 125 ° C. Area, ie
−1.34082 × 10 ⁻⁴ × θ ³ −2.34969 × 10 ⁻² × θ ² −1.37506 × θ−26.7895 <H / λ <−1.02586 × 10 ⁻⁴ × θ ³ −1.73238 × 10 ⁻² × θ ² −0.977607 × θ-18.3420
It can be seen that the cut angle θ and the electrode film thickness H / λ may be set so that In addition, the range of the electrode film thickness H / λ at this time is set to 0.04 <H / λ <0.12 in which characteristics superior to those of the prior art can be obtained as described above, and the cut angle corresponding to the range is obtained. The range of θ is preferably −64.0 <θ <−49.3.

Further, considering more optimal conditions, it is desirable that the vertex temperature Tp (° C.) is set to a more practical use temperature range 0 ≦ Tp ≦ 70. For that purpose, from the above approximate expression showing the Tp characteristics, a region surrounded by the curve of the approximate expression at Tp = 0 ° C. and Tp = 70 ° C., that is,
−1.44605 × 10 ⁻⁴ × θ ³ −2.50690 × 10 ⁻² × θ ² −1.45086 × θ−27.9464 <H / λ <−9.87591 × 10 ⁻⁵ × θ ³ −1.70304 × 10 ⁻² × θ ² −0.981173 × θ-18.7946
The cut angle θ and the electrode film thickness H / λ may be set so that At this time, the electrode film thickness H / λ is desirably in the range of 0.05 <H / λ <0.10, where a Q value of 20000 or more can be obtained as described above, and corresponds to the range of the electrode film thickness. Thus, the cut angle θ is preferably set to −61.4 <θ <−51.1.

  From the above detailed examination results, the SAW resonator of the present invention has a cut angle θ of −64.0 ° <θ <−49.3 °, preferably −61.4 ° <θ <−51.1 °. Using a rotating Y-cut quartz substrate in the range as a piezoelectric substrate, and using SH waves excited in a SAW propagation direction substantially perpendicular to the X axis, IDT is made of an electrode material of Al or an alloy mainly composed of Al. The electrode film thickness H / λ is 0.04 <H / λ <0.12, preferably 0.05 <H / λ <0.10. As a result, a higher Q value and superior temperature characteristics than the conventional ST-cut quartz SAW resonator can be obtained, and the apex temperature Tp can be set within the practical operating temperature range described above.

  Further, the Tp characteristic when the IDT line occupancy mr was changed without being fixed to the above-described value 0.60 was examined. As a result, it was found that the product H / λ × mr of the electrode film thickness and the line occupancy rate increases the vertex temperature Tp as the value is increased.

Next, when the apex temperature Tp is −50 ° C., 0 ° C., 70 ° C., 125 ° C., the relationship between the product H / λ × mr of the electrode film thickness and the line occupation rate and the cut angle θ of the quartz substrate is It is represented by the following approximate expression indicating the Tp characteristic.
When Tp = −50 (° C.):
H / λ × mr≈−6.115517 × 10 ⁻⁵ × θ ³ −1.03943 × 10 ⁻² × θ ² −0.586564 × θ−11.0052
When Tp = 0 (° C.):
H / λ × mr≈−5.92554 × 10 ⁻⁵ × θ ³ −1.02183 × 10 ⁻² × θ ² −0.588704 × θ−11.2768
When Tp = 70 (° C.):
H / λ × mr≈−8.67632 × 10 ⁻⁵ × θ ³ −1.50414 × 10 ⁻² × θ ² −0.870514 × θ−16.7678
When Tp = 125 (° C.):
H / λ × mr≈−8.04489 × 10 ⁻⁵ × θ ³ −1.40981 × 10 ⁻² × θ ² −0.825038 × θ−16.0737

In order to set the apex temperature Tp to the practical use temperature range −50 ≦ Tp ≦ 125 from the approximate expression showing these Tp characteristics, it is surrounded by the curve of the approximate expression at Tp = −50 ° C. and Tp = 125 ° C. Area, ie
−8.04489 × 10 ⁻⁵ × θ ³ −1.40981 × 10 ⁻² × θ ² −0.825038 × θ−16.0737 <H / λ × mr <−6.15517 × 10 ⁻⁵ × θ ³ −1.03943 × 10 ⁻² × θ ² − 0.586564 × θ-11.0052
It can be seen that the cut angle θ and the product H / λ × mr of the electrode film thickness and the line occupancy should be set so that In addition, the range of the electrode film thickness H / λ at this time is set to 0.04 <H / λ <0.12 in which characteristics superior to those of the prior art can be obtained as described above, and the cut angle corresponding to the range is obtained. The range of θ is preferably −64.0 <θ <−49.3.

Further, considering more optimal conditions, it is desirable that the vertex temperature Tp (° C.) is set to a more practical use temperature range 0 ≦ Tp ≦ 70. For that purpose, from the above approximate expression showing the Tp characteristics, a region surrounded by the curve of the approximate expression at Tp = 0 ° C. and Tp = 70 ° C., that is,
−8.67632 × 10 ⁻⁵ × θ ³ −1.50414 × 10 ⁻² × θ ² −0.870514 × θ−16.7678 <H / λ × mr <−5.92554 × 10 ⁻⁵ × θ ³ −1.02183 × 10 ⁻² × θ ² − 0.588704 × θ−11.2768
The product H / λ × mr of the cut angle θ and the electrode film thickness and the line occupation ratio may be set so that At this time, it is desirable that the electrode film thickness H / λ is 0.05 <H / λ <0.10, which can obtain a Q value of 20000 or more as described above, and corresponds to the range of the electrode film thickness. The cut angle θ is preferably set to −61.4 <θ <−51.1.

  FIG. 4 shows a first embodiment of a SAW sensor according to the present invention. This SAW sensor has a so-called transversal structure, and has an excitation IDT 2, a reception IDT 3, and a receptor 4 such as a detection substance reaction film disposed on a SAW propagation surface therebetween on the surface of the piezoelectric substrate 1. . As the receptor 4, various conventionally known substances such as a gas adsorbent, an enzyme, a microorganism, an antibody, and DNA can be used in accordance with the properties and characteristics of the chemical substance to be detected. It is used in various conventionally known forms such as a membrane and a cell. When the target chemical substance is chemically bound to the receptor and its weight changes, the propagation speed of the SAW 5 excited by the excitation IDT 2 changes, and this is measured by the reception IDT 3 as a change in oscillation frequency. Thus, the target substance and / or its physical properties can be detected with high accuracy.

  The piezoelectric substrate 1 sets the cut angle θ of the rotated Y-cut quartz substrate in the vicinity of the rotation of −64 to −49.3 ° counterclockwise from the crystal Z axis, and the SAW propagation direction with respect to the crystal X axis. It is a quartz plate in a substantially vertical direction (90 ± 5 °). This rotated Y-cut quartz substrate can display the cut surface and the SAW propagation direction with an Euler angle of (0 °, 26-40.7 °, 90 ± 5 °). Each IDT 2 and 3 is an electrode material made of Al or an alloy containing Al as a main component, and is formed using a conventional method such as photolithography, vapor deposition, or sputtering. The electrode film thickness H of each IDT 2 and 3 is set to 0.04 <H / λ <0.12 where λ is the wavelength of the SAW excited by the IDT.

  The SAW sensor of this embodiment excites the SH wave by using the rotary Y-cut quartz substrate set in this way as the piezoelectric substrate 1 and forming IDTs 2 and 3. Therefore, an excellent confinement effect of surface wave energy can be obtained, thereby reducing the propagation loss, increasing the Q value, and decreasing the CI value, thereby obtaining excellent resonance characteristics as shown in FIG. . Further, since the SH wave is excited, the SAW sensor of this embodiment can also be used for a liquid phase sensor. Furthermore, since a good temperature characteristic and a high Q value can be obtained, the CI value can be suppressed low, and a sensor with high sensitivity and high measurement accuracy can be realized.

  FIG. 6 shows a second embodiment of the SAW sensor according to the present invention. Similarly, the SAW sensor 10 is a piezoelectric substrate made of a quartz plate having a cut surface of a rotating Y-cut quartz plate and a SAW propagation direction represented by Euler angles (0 °, 26 to 40.7 °, 90 ± 5 °). An IDT 13 composed of a pair of crossed finger electrodes 12a and 12b is formed at approximately the center of the surface of the electrode 11. In the approximate center of the IDT 13, a receptor 14 is disposed on the SAW propagation surface between the electrode fingers constituting the cross finger electrode. The IDT 13 is made of electrode material of Al or an alloy containing Al as a main component, and the electrode film thickness H is set to 0.04 <H / λ <0.12 where λ is the wavelength of the excited SAW. Has been.

  On the left and right sides of the IDT 13 and the receiver 14, reflectors 15 and 15 having a lattice structure are arranged, respectively. The reflector can be formed of Al or an alloy containing Al as a main component at the same time as IDT13. In this one-port resonator type SAW sensor 10, when a predetermined high-frequency signal voltage is applied between the input-side cross finger electrode 12a and the output-side cross finger electrode 12b, a SAW having the same frequency as the input signal is generated on the surface of the piezoelectric substrate 11. Excited. The SAW propagates to the left and right sides of the IDT 13 and is reflected by the left and right reflectors 15, 15 and returns toward the center of the IDT 13. As a result, a SAW standing wave is generated between the two reflectors. By confining the surface wave energy between the reflectors 15 and 15 in this way, the influence of the reflected wave due to the end face of the SAW piezoelectric substrate 11 can be effectively eliminated.

  When the weight of the receptor 14 increases, for example, by adsorbing a chemical substance to be detected, the propagation speed of the SAW changes and the frequency changes. By measuring this frequency change, the target chemical substance can be detected and / or its physical properties such as its concentration and pH can be measured. Due to the confinement effect of the surface wave energy by the reflector, not only the influence of the SAW reflected wave by the end face of the piezoelectric substrate 11 can be eliminated, but also the propagation loss is reduced, the Q value is increased, the CI value is decreased, and more excellent. Since the resonance characteristic is obtained, the sensitivity of the SAW sensor is improved, and highly accurate detection / measurement is possible.

  FIG. 7 shows a modification of the SAW sensor of the second embodiment shown in FIG. The SAW sensor 20 of this modification has the same 1-port resonator type configuration as that of the second embodiment, but the IDT 23 and the receptor 24 formed on the surface of the piezoelectric substrate 21 are composed of input side and output side cross finger electrodes 22a and 22b. Are different from the first embodiment in that the reflectors 25 and 25 are arranged in parallel along the SAW propagation direction.

  Also in this modified example, when a predetermined high-frequency signal voltage is applied between the two crossed finger electrodes of the IDT 23, SAW of the same frequency is excited on the surface of the piezoelectric substrate 21, propagates to the left and right sides of the IDT 23, and the left and right reflectors. The SAW standing wave is generated between the two reflectors. Due to the confinement effect of the surface wave energy, the influence of the reflected wave from the end face of the piezoelectric substrate 21 of SAW can be effectively eliminated.

  When the receptor 24 arranged on the SAW propagation surface between the IDT 23 and the one reflector 25 adsorbs the chemical substance to be detected, a change in weight due to this changes into a change in SAW propagation speed, which is detected as a change in frequency. Thereby, the detection of the target chemical substance and / or the measurement of physical properties can be performed with high accuracy.

  FIG. 8 shows a third embodiment of the SAW sensor according to the present invention. This SAW sensor 30 is a two-port resonator type. Similarly, the cut surface of the rotating Y-cut quartz plate and the SAW propagation direction are set to Euler angles (0 °, 26 to 40.7 °, 90 ± 5 °). It has a piezoelectric substrate 31 made of a quartz plate. The surface of the piezoelectric substrate 31 is provided with the excitation IDT 32 and the reception IDT 33 as in the first embodiment, and the receptor 34 disposed on the SAW propagation surface between the two IDTs, and both left and right sides so as to sandwich them. Are provided with reflectors 35 and 35 having a lattice structure. Each of the excitation IDT 32 and the reception IDT 33 is formed of an electrode material of Al or an alloy containing Al as a main component, and the electrode film thickness H is 0.04 <H / λ <0.12 is set.

  When a predetermined high-frequency signal voltage is applied to the excitation IDT 32, a SAW having the same frequency is excited on the surface of the piezoelectric substrate 31 and propagates to both the left and right sides of the IDT 32 and the left and right reflectors 35, as in the second embodiment. Therefore, a SAW standing wave is generated between the two reflectors. Similarly, due to the confinement effect of the surface wave energy, the influence of the reflected wave from the end face of the SAW piezoelectric substrate 31 can be effectively eliminated.

  The SAW excited by the excitation IDT 32 is received by the reception IDT 33 and its frequency is measured. At this time, if the weight of the receptor 34 is changed by adsorbing the chemical substance to be detected, a change in the SAW propagation speed is detected as a frequency change. Alternatively, physical properties can be measured with high accuracy.

FIG. 9 shows an embodiment of a multi-channel SAW sensor system according to the present invention. In this SAW sensor system 40, a large number of SAW sensors 42 are arranged in series and in parallel in the SAW propagation direction on the surface of a single and common piezoelectric substrate 41, in this embodiment, in a 4 × 4 matrix. Each SAW sensor 42 of the present embodiment has the same configuration as the SAW sensor of the second embodiment shown in FIG. 6, the IDT 43 consisting of a pair of cross finger electrodes on the surface of the piezoelectric substrate 41, and the cross at the approximate center thereof. It includes a receptor 44 disposed on the SAW propagation surface between the finger electrodes, and reflectors 45 and 45 having a lattice structure respectively disposed on the left and right sides thereof.

  Similarly, the piezoelectric substrate 41 is a crystal flat plate in which the cut surface of the rotating Y-cut quartz plate and the SAW propagation direction are expressed by Euler angles (0 °, 26 to 40.7 °, 90 ± 5 °). The IDT 43 of each SAW sensor 42 is formed of an electrode material of Al or an alloy containing Al as a main component, and the electrode film thickness H is 0.04 <H, where the wavelength of the excited SAW is λ. /Λ<0.12.

  In each SAW sensor 42, when a predetermined high-frequency signal voltage is applied to the IDT 43, a SAW having the same frequency is excited on the surface of the piezoelectric substrate 41, propagates to the left and right sides of the IDT, and is reflected by the left and right reflectors 45 and 45. The As a result, a SAW standing wave is generated between the left and right reflectors for each channel. As a result of the surface wave energy being confined between the reflectors 45 and 45 in each SAW sensor 42 in this way, in addition to improving the sensitivity of each channel, even when the SAW sensors of each channel are simultaneously oscillated, It is possible to effectively prevent the SAW from propagating to the SAW sensor of another channel adjacent in the propagation direction. Further, similarly to the SAW sensors of the first and second embodiments described above, the influence of the reflected wave from the end face of the piezoelectric substrate 41 can be effectively eliminated.

As described above, the present invention has been described with reference to the preferred embodiments. However, the present invention can be variously modified and changed within the technical scope thereof. For example, in the SAW sensor system of FIG. 9, each SAW sensor 42 can be replaced with the SAW sensor of FIGS. 6 to 8, and a plurality of SAW sensors 42 are arranged in a line in series or in parallel in the SAW propagation direction. Or can be arranged in various forms. Further, a plurality of SAW sensors shown in FIG. 4 are arranged in parallel with respect to the SAW propagation direction, whereby a multi-channel SAW sensor system can be obtained.

Explanatory drawing which shows the rotation Y cut 90 degree X propagation quartz plate used for this invention. The diagram which shows the frequency temperature characteristic of the SAW resonator which comprises the SAW sensor of this invention compared with the case where the conventional ST cut quartz plate is used. The relationship between the electrode film thickness H / λ and the Q value of the SAW sensor according to the present invention is shown. The top view which shows 1st Example of the SAW sensor by this invention. FIG. 5 is a waveform diagram showing transmission characteristics of the SAW sensor shown in FIG. 4. The top view which shows 2nd Example of the SAW sensor by this invention. The top view which shows the modification of 1st Example of FIG. The top view which shows 3rd Example of the SAW sensor by this invention. The top view which shows the Example of the multichannel type SAW sensor system by this invention. Diagram showing a frequency-temperature characteristic of the LiTaO ₃ and quartz. Graph showing the transmission characteristics of LiTaO _3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11,21,31,41 ... Piezoelectric substrate, 2,32 ... Excitation IDT, 3,33 ... Reception IDT, 4,14,24,34,44 ... Receptor, 5 ... SAW 10,20, 30, 42 ... SAW sensor, 12a, 12b, 22a, 22b ... cross finger electrode, 13, 23, 43 ... IDT, 15, 25, 35, 45 ... reflector, 40 ... SAW sensor system.

Claims (6)

  A piezoelectric substrate, an IDT formed on the surface of the piezoelectric substrate, and a receptor for recognizing a target substance fixed to a propagation surface of a surface acoustic wave excited by the IDT, the piezoelectric substrate rotating A Y-cut quartz plate, comprising a quartz plate whose cut surface and propagation direction of the surface acoustic wave are expressed in Euler angles (0 °, 26 to 40.7 °, 90 ± 5 °), and the IDT is The electrode film is made of Al or an alloy containing Al as a main component, and the thickness H of the electrode film is 0.04 <H / λ <0.12 where λ is the wavelength of the surface acoustic wave. There is provided a surface acoustic wave sensor.   The surface acoustic wave sensor according to claim 1, further comprising a pair of reflectors disposed on both sides of the IDT and the receptor so as to sandwich the IDT and the receptor along a propagation direction of the surface acoustic wave. .   The elastic surface according to claim 1 or 2, wherein the IDT includes an excitation IDT and a reception IDT, and the receptor is disposed between the excitation IDT and the reception IDT. Wave sensor.   The IDT is composed of one IDT having a pair of cross finger electrodes, and the receptor is disposed between the electrode fingers of the cross finger electrodes. Surface acoustic wave sensor.   3. The surface acoustic wave sensor according to claim 2, wherein the IDT includes one IDT, and the receptor is disposed between the IDT and one of the reflectors.   A plurality of surface acoustic wave sensors according to any one of claims 1 to 5, wherein the plurality of surface acoustic wave sensors are arranged in series and / or in parallel with respect to the propagation direction of the surface acoustic wave, The surface acoustic wave sensor system, wherein each surface acoustic wave sensor is provided on a single common piezoelectric substrate.

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