CN101526501A - Unidirectional low-loss love wave sensor - Google Patents

Abstract

The invention relates to a unidirectional low-loss Love wave sensor, comprising a piezoelectric substrate and input interdigital transducers and output interdigital transducers respectively deposited on both ends of the piezoelectric substrate, the piezoelectric substrate is covered with a waveguide layer, the waveguide layer adopts a low-acoustic film whose shear wave velocity is lower than that of the piezoelectric substrate, and the middle part of the waveguide layer is covered with a sensitive film, and the sensitive film is placed between the input IDT and the output IDT In the middle of the device, it is characterized in that: the input interdigital transducer and the output interdigital transducer are all single-phase unidirectional transducers; the waveguide layer is made of gold, silicon dioxide, polymethyl methacrylate or epoxy resin; the sensitive film can be a biosensitive film according to the needs of the detection substance; the input IDT and output IDT parts can be covered in the waveguide layer or completely exposed outside the waveguide layer. The invention can reduce the bidirectional loss of the transducer, thereby reducing the insertion loss of the whole device.

Description

A One-way Low Loss Love Wave Sensor

technical field

The invention relates to a Love-type acoustic wave (abbreviated as Love-wave) sensor, in particular to a unidirectional low-loss Love-wave sensor using a single-phase unidirectional structure interdigitator (SPUDT).

Background technique

Love wave is a kind of acoustic wave, which is a surface shear shear wave propagating in a thin-layer acoustic waveguide on the surface of a piezoelectric substrate. The particle vibration direction of the Love wave is parallel to the basic surface, so when the substrate surface is in contact with the liquid load, its propagation is less affected by the load. And because the thin-layer acoustic waveguide binds the Love wave energy on the surface, the Love wave is very sensitive to surface disturbance. Coupled with the uncomplicated manufacturing process of the device, the Love wave sensor is suitable for liquid phase measurement.

The conventional Love wave sensor structure is shown in Fig.1. As described in the three documents of Sensors and Actuators A 123-124 (2005) 267-273, U.S. Patent 5216312, 5283037 and 5321331, a bidirectional interdigital transducer 1 is made on a piezoelectric substrate 5, and then, the covering low The sound velocity membrane 4, finally, places the object to be measured between the two transducers 1. Since the interdigital transducer uses a bidirectional transducer, the sound waves propagate toward both sides of the transducer, but actually only the sound waves propagating in opposite directions of the two transducers are effectively used, and the energy of the sound wave propagating in the back direction is lost, so the loss of the sensor Usually relatively large (greater than 15dB).

The conventional single-phase unidirectional interdigital transducer (SPUDT), as shown in Figure 2, as a structure that can effectively reduce the bidirectional loss of the transducer (as shown in Figure 2), is obtained in the surface acoustic wave filter Wide range of applications. Such as literature IEEE Ultrasonics Symp., 1986, p.59-64 (Ddistributed Acoustic Reflection TransducerDART distributed acoustic reflection single-phase unidirectional transducer), IEEE 1989 Ultrasonics Symposium Proceedingpp79-89 (Electrode Width Controlled SPUDT EWC/SPUDT electrode width control Single-phase unidirectional transducer), 1995 Ultrasonics Symposium Proceeding pp39-50 (Resonant SPUDT RSPUDT resonant single-phase unidirectional transducer), 2000 IEEE Ultrasonics Symposium pp105-108, (Different-WidthSplit-Finger SPUDT, DWSF SPUDT not Uniform width split refers to single-phase unidirectional transducer) four documents, when the reflection center of the interdigital transducer deviates from the transduction center by 3/8λ and 5/8λ (λ: transducer cycle length), the sound wave Propagation is strengthened in one direction and weakened in the other direction, forming a unidirectional structure.

In the prior art, the insertion loss of the transducer, which is one of the key factors determining the detection lower limit of the Love wave sensor, has always been a key problem to be solved. The conventional Love wave sensor adopts a bidirectional structure, and the lower detection limit of the sensor is limited due to the bidirectional loss of the transducer.

Contents of the invention

The purpose of the present invention is to overcome the defects of the prior art, improve the performance of the sensor from the structure of the sensor, reduce the bidirectional loss of the existing Love wave sensor of the device, thereby providing a unidirectional low loss Love wave sensor.

The purpose of the present invention is achieved like this:

The unidirectional low-loss Love wave sensor provided by the present invention comprises a piezoelectric substrate 5 and an input interdigital transducer 1 and an output interdigital transducer 2 respectively deposited on its two ends, the piezoelectric substrate 5 is covered with a waveguide layer 4, the waveguide layer 4 adopts a low-acoustic film whose shear wave velocity is lower than that of the piezoelectric substrate 5, the middle part of the waveguide layer 4 is covered with a sensitive film 3, and the sensitive film 3 is placed on the input Between the IDT 1 and the output IDT 2, the feature is that both the input IDT 1 and the output IDT 2 are single-phase unidirectional transducers (SPUDT).

As an option of the present invention, the waveguide layer adopts silicon dioxide (SiO2), polymethyl methacrylate (PMMA), zinc oxide (ZnO), gold (Au) or epoxy resin (Epoxy); The above-mentioned sensitive membrane 3 can be a biologically sensitive membrane according to the needs of detection substances.

As an improvement of the present invention, the input IDT 1 and the output IDT 2 can be partly covered in the waveguide layer 4 or completely exposed outside the waveguide layer, as shown in Fig. 2 and Figure 3 shows.

As another option of the present invention, the input IDT 1 and the output IDT 2 adopt electrode width control single-phase unidirectional IDT (EWC/SPUDT), distributed single-phase A unidirectional IDT (DART), a resonant single-phase unidirectional IDT (RSPUDT), or a dual-electrode single-phase unidirectional IDT (DWSF). There is no restriction on whether the input and output use a certain type of single-item and one-way at the same time, but the conventional design generally uses the same type.

As another option of the present invention, the input IDT 1 and the output IDT 2 adopt Al film, Au film or Cu film.

As another option of the present invention, the piezoelectric substrate 5 is made of various tangential materials, such as lithium niobate LiNbO3, lithium tantalate LiTaO3, quartz or piezoelectric ceramics.

As shown in Figure 1, the technical solution of the present invention includes a piezoelectric substrate 5, an input IDT 1, an output IDT 2, a waveguide layer 4 and a sensitive film 3, and is characterized in that: the input IDT The transducer 1 excites the sound wave propagation in the piezoelectric substrate 5 and the waveguide layer 4, the output transducer 2 receives the sound wave, and the loaded measured object reacts with the sensitive film 3 to cause the change of the characteristics of the sound wave (such as frequency, speed, etc.), These changes allow conclusions to be drawn about the analyte. Both the input IDT 1 and the output IDT 2 adopt a single-phase unidirectional IDT structure, and the sound wave excited by the transducer mainly propagates in the direction of another transducer, reducing the Bidirectional loss of the transducer.

The Love wave sensor adopts the Love wave mode, and the waveguide layer 4 is covered on the piezoelectric substrate 5, and the shear wave velocity of the material of the waveguide layer must be lower than that of the substrate (referred to as the low sound velocity film). The low-sonic film usually adopts Au, SiO2, PMMA, Epoxy, etc. The bulk shear wave velocities are shown in Table 1. The low-sonic film makes the Love wave propagate along the waveguide layer and the surface of the substrate.

Table 1:

Low sound velocity membrane material Au SiO2 PMMA Epoxy Bulk shear wave velocity [m/s] 1215 2800 1180 1210

The advantage of the present invention is that the input and output transducers of the Love wave sensor of the present invention all adopt single-phase unidirectional interdigital transducers (SPUDT). Due to the adoption of the SPUDT structure, the bidirectional loss of the transducer can be reduced, thereby reducing the insertion loss of the entire device. Compared with the prior art, the single-phase and one-way Love wave sensor of the present invention has low loss and can realize a lower detection limit.

Description of drawings

Fig. 1 is the three-dimensional schematic diagram of the Love wave sensor structure of unidirectional low loss of the present invention;

Fig. 2 is the plan view of the Love wave sensor structure of unidirectional low loss of the present invention;

Fig. 3 is a schematic sectional view of a structure of the Love wave sensor of the present invention;

Fig. 4 is the sectional schematic diagram of another kind of structure of Love wave sensor of the present invention;

Fig. 5 is a structural diagram of the electrode width control single-phase unidirectional interdigital transducer in Embodiment 1 of the present invention;

Fig. 6 is a structural diagram of a distributed single-phase unidirectional interdigital transducer in Embodiment 2 of the present invention;

7 is a structural diagram of a resonant single-phase unidirectional IDT in Embodiment 3 of the present invention;

Fig. 8 is a structure diagram of a split-finger single-phase unidirectional transducer with uneven width in Embodiment 4 of the present invention.

Detailed ways

Embodiment 1: According to Fig. 1, a low-loss Love wave sensor with a single-phase and unidirectional structure is fabricated.

The piezoelectric substrate 1 is made of St-cut 90-degree quartz, and the input IDT 3 and the output IDT 4 are deposited on the surface of the substrate, and then covered with polymethyl methacrylate (PMMA, commonly known as: plexiglass) as a musical instrument. Just waveguide layer 2. The input IDT 3 and the output IDT 4 adopt the electrode width control single-phase unidirectional interdigital transducer (EWC/SPUDT) structure, as shown in Figure 2, the period λ is 16 microns, and the gold film The thickness is 1200 angstroms, the index logarithm is 50, the aperture is 1.5 mm, the distance between the centers of the two transducers is 2 mm, the center frequency f ₀ of the device is about 300 MHz; the electrode width of each cycle of the transducer is one-eighth of the wavelength, and the reflection The electrode width is a quarter wavelength. The silica waveguide layer is 1 micron thick. Comparing the two-way loss, the present invention reduces the 6dB loss of the transducer.

Embodiment 2: make a low-loss Love wave sensor with single-phase unidirectional structure according to Fig. 1, its basic structure is identical with embodiment 1.

The difference is: the piezoelectric substrate 1 uses 36-degree YX lithium tantalate LiTaO3; the input IDT 3 and the output IDT 4 adopt a distributed single-phase unidirectional interdigital transducer (DART) structure, As shown in Figure 3, the period λ is 40 microns, the thickness of the gold film is 1000 angstroms, the logarithm is 60, the aperture is 4 mm, the distance between the centers of the two transducers is 4 mm, and the center frequency _f0 is about 104 MHz; Polymethyl methacrylate is used as the waveguide layer with a thickness of 0.2 microns. The electrode width of each period is one-eighth of the wavelength, the width of the reflective electrode is three-eighth of the wavelength, and there are distributed blank areas on the reflective electrode.

Embodiment 3: make a low-loss Love wave sensor with single-phase unidirectional structure according to Fig. 1, its basic structure is identical with embodiment 1.

The difference is: the input IDT 3 and the output IDT 4 adopt a resonant single-phase unidirectional IDT (RSPUDT) structure, as shown in Figure 4, the period λ is 50 microns, aluminum The film thickness is 2000 angstroms, the logarithms are 16 and 64 respectively, the aperture is 2 mm, the distance between the centers of the two transducers is 4.5 mm, and the center frequency f ₀ =90 MHz; each acoustic cavity contains a forward excitation unit , a negative excitation unit, and a transition unit whose length is a quarter wavelength. The Love wave waveguide layer is made of zinc oxide with a thickness of 2.8 microns.

Embodiment 4: Make a low-loss Love wave sensor with single-phase unidirectional structure according to Fig. 1, its basic structure is identical with embodiment 1.

The difference is: the piezoelectric substrate 1 adopts 31-degree XY cut quartz; the input IDT 3 and the output IDT 4 adopt the structure of the non-uniform width split-finger single-phase unidirectional transducer (DWSF RSPUDT), As shown in Figure 4, the cycle λ is 52 microns, the copper film thickness is 4500 angstroms, the index logarithm is 50, the aperture is 3 mm, and the center frequency _f0 is about 86 MHz; A pair of interdigitated electrodes. The Love wave waveguide layer is made of silicon dioxide with a thickness of 5 microns.

Claims (7)

1, a kind of unidirectional low-loss love wave sensor, comprise piezoelectric substrate (5) and be deposited on the input interdigital transducer (1) and the output interdigital transducer (2) at its two ends respectively, be coated with ducting layer (4) on the described piezoelectric substrate (5), described ducting layer (4) adopts the shear wave velocity low velocity of sound film lower than piezoelectric substrate (5), the middle part of this ducting layer (4) is coated with sensitive membrane (3), described sensitive membrane (3) is placed in the middle of input interdigital transducer (1) and the output interdigital transducer (2), and it is characterized in that: described input interdigital transducer (1) and output interdigital transducer (2) all adopt single phase unidirectional transducer.

2, love wave sensor according to claim 1 is characterized in that: described ducting layer adopts silicon dioxide, polymethyl methacrylate, zinc paste, gold or epoxy resin.

3, love wave sensor according to claim 1 is characterized in that: described sensitive membrane (3) is a bio-sensitive film.

4, love wave sensor according to claim 1 is characterized in that: described input interdigital transducer (1) and output interdigital transducer (2) part can be coated within the ducting layer (4) or be exposed to outside the ducting layer (4).

5, love wave sensor according to claim 1 is characterized in that: described input interdigital transducer (1) and output interdigital transducer (2) adopt electrode width control single phase single direction interdigital transducer, distributed single phase single direction interdigital transducer, resonant mode single phase single direction interdigital transducer or bipolar electrode single phase single direction interdigital transducer.

6, love wave sensor according to claim 1 is characterized in that: described input interdigital transducer (1) and output interdigital transducer (2) adopt Al film, Au film or Cu film.

7, love wave sensor according to claim 1 is characterized in that: described piezoelectric substrate (5) adopts various tangential materials, can adopt lithium niobate LiNbO3, lithium tantalate LiTaO3, quartz or piezoelectric ceramics.

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