JP4483323B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device, and more particularly, to a structure of a surface acoustic wave device including surface acoustic wave excitation means or surface acoustic wave detection means formed on the surface of a piezoelectric thin film, and surface acoustic wave reflection means. About.

  In general, surface acoustic wave devices that form resonators, filters, and the like are used for communication equipment and various signal processing. This surface acoustic wave device uses the piezoelectricity of a piezoelectric material such as ZnO. In a conventional surface acoustic wave device, a surface acoustic wave excitation means or surface acoustic wave detection means composed of an IDT (interdigital transducer, for example, comb-like electrode) on the surface of a piezoelectric body, and a reflector, etc. The surface acoustic wave reflecting means is formed, and a bus bar for connecting these IDTs and reflectors to each other and wiring for connecting the bus bar to the bonding pad are provided. In a normal surface acoustic wave device, a device chip is disposed in a sealed state inside a casing, and a bonding pad formed on the device chip and an external terminal provided on the casing are conductively connected by a conductive wire. It has become.

In particular, there is known a surface acoustic wave device having a laminated structure in which a piezoelectric thin film is formed on a substrate such as a silicon substrate, and the IDT and the reflector are formed on the surface of the piezoelectric thin film (for example, the following) Non-Patent Documents 1 and 2). In a device having such a laminated structure, various semiconductor elements and wirings are formed by monolithically forming various semiconductor elements on the surface region of the substrate or by forming a thin film structure on a silicon substrate. Thus, a semiconductor integrated circuit can be configured. Usually, in communication circuits and various signal processing circuits, many parts are configured as a semiconductor integrated circuit.For example, it is possible to configure the surface acoustic wave device on a silicon substrate on which a semiconductor integrated circuit is configured. This is considered to be an important point in miniaturizing communication circuits and signal processing circuits. For this reason, conventionally, surface acoustic wave devices formed on a silicon substrate constituting a semiconductor integrated circuit have been proposed (for example, see Patent Documents 1 and 2 below).
Tsutsuo Sanro and 4 others “Thin Film Surface Acoustic Wave Devices” Matsushita Technical Report Vol.22 No.6 Dec 1976 P.905-923 S. J. et al. Martin et al. “HIGH Q, TEMPERATURE STABLE ZnO-on-SILICON SAW RESONATORS” 1980 ULTRASONICS SYMPOSIUM P. 113-P. 117 JP-A-6-125226 JP 2000-151451 A

  By the way, in the surface acoustic wave device having the above-described laminated structure, the surface acoustic wave excited or detected by the surface acoustic wave excitation means such as IDT or the surface acoustic wave detection means is the piezoelectricity, elastic coefficient or thickness of the piezoelectric body. When the wavelength of the excited surface acoustic wave is changed, the propagation speed is changed, and the electromechanical coupling coefficient and the reflection coefficient of the reflector are changed during excitation or detection. In this case, in the surface acoustic wave device provided with surface acoustic wave excitation means or surface acoustic wave detection means such as IDT and surface acoustic wave reflection means such as a reflector, the thickness of the piezoelectric thin film is elastic. The influence on the excitation efficiency of the surface wave excitation means or the detection efficiency of the surface acoustic wave detection means is different from the influence on the reflection efficiency of the surface acoustic wave reflection means. However, in the conventional surface acoustic wave device, no structure proposal has been made from the viewpoint of improving both the excitation efficiency or the detection efficiency (electromechanical coupling coefficient) and the reflection efficiency at the same time. That is, in the conventional structure, consideration is not given to separately improving the excitation efficiency or detection efficiency of each means and the reflection efficiency, and the device performance resulting from these efficiencies can be sufficiently improved. could not.

  Therefore, the present invention solves the above problems, and separately forms the formation area of surface acoustic wave excitation means or surface acoustic wave detection means such as IDT and the formation area of surface acoustic wave reflection means such as a reflector. It is an object of the present invention to provide a surface acoustic wave device capable of easily improving device performance by optimization.

In view of such circumstances, the surface acoustic wave device of the present invention includes a piezoelectric thin film formed on a substrate and a surface acoustic wave excitation means or a detection electrode including an excitation electrode formed on the surface of the piezoelectric thin film. In a surface acoustic wave device comprising a surface acoustic wave detection means and a surface acoustic wave reflection means including a reflective electrode formed on the surface, the surface acoustic wave excitation means or the surface acoustic wave detection means in the formation region The thickness of the piezoelectric thin film is different from the thickness of the piezoelectric thin film in the region where the surface acoustic wave reflecting means is formed.
In one embodiment, the conductive layer formed on the substrate, the piezoelectric thin film formed on the conductive layer, the interdigital transducer formed on the piezoelectric thin film, and the piezoelectric thin film In the surface acoustic wave device including the grating reflector, two of the grating reflectors are formed, and the interdigital transducer is formed between the two grating reflectors. When the wavelength is λ, the thickness of the piezoelectric thin film is tp, and the thickness of the piezoelectric thin film normalized by the wavelength λ of the surface acoustic wave is 2πtp / λ, the interdigital transducer is formed. 2πtp / λ in the region is in the range of 0.04 to 0.06, and 2πtp / λ in the formation region of the grating reflector is in the range of 0.01 to 0.04, The thickness of the piezoelectric thin film in the region where the interdigital transducer is formed is different from the thickness of the piezoelectric thin film in the region where the grating reflector is formed.

  In the conventional surface acoustic wave device, a surface acoustic wave excitation means such as IDT or surface acoustic wave detection means and a surface acoustic wave reflection means such as a reflector are formed on the flat surface of the piezoelectric thin film. The thickness of the piezoelectric thin film in the electrode or detection electrode formation region and the thickness of the piezoelectric thin film in the reflection electrode formation region were the same. However, the thickness of the piezoelectric thin film greatly affects the excitation efficiency and the detection efficiency, or the reflection efficiency, and values suitable for increasing these efficiency are different from each other. Furthermore, the degree of the influence of the thickness of the piezoelectric thin film on the efficiency varies depending on other parameters such as the piezoelectricity and elasticity of the material constituting the piezoelectric thin film, and this variation mode is also excited. The electrode or detection electrode is different from the reflective electrode. Therefore, the identity between the thickness of the piezoelectric thin film in the excitation electrode or detection electrode formation region in the conventional structure and the thickness of the piezoelectric thin film in the reflection electrode formation region is actually the excitation efficiency or detection efficiency and reflection efficiency. It was a major limitation in raising both.

  However, in the present invention, the thickness of the piezoelectric thin film in the formation area of the surface acoustic wave excitation means or the surface acoustic wave detection means differs from the thickness of the piezoelectric thin film in the formation area of the surface acoustic wave reflection means. Improvement of efficiency or detection efficiency and improvement of reflection efficiency can be achieved without being restricted by the same thickness of the piezoelectric thin film, making it easier to improve device performance than conventional structures There is an advantage of becoming. For example, it is possible to improve both the electromechanical coupling coefficient by improving the excitation efficiency or the detection efficiency and reducing the attenuation amount of the surface acoustic wave by improving the reflection efficiency. In addition, the improvement of the electromechanical coupling coefficient and the reflection coefficient contributes to the reduction of the number of electrodes as well as the improvement of the device performance, leading to the miniaturization of the device.

  By the way, the conventional non-patent document 2 discloses a surface acoustic wave device in which a piezoelectric thin film is periodically etched to form a groove / lift type reflector. However, this device is not intended to reduce the thickness of the piezoelectric thin film in the area where the reflector is formed, with the primary aim of periodically forming grooves or ridges to form the reflector. There is no mention of the relationship between the thickness of the piezoelectric thin film and the reflection efficiency. Furthermore, in the structure of Non-Patent Document 2, since the thickness of the piezoelectric thin film in the reflector formation region periodically fluctuates greatly, the reflection efficiency is affected by both the groove depth and the original thickness of the piezoelectric thin film. Changes complicatedly.

In the present invention, the thickness of the piezoelectric thin film in the formation region of the surface acoustic wave excitation means or the surface acoustic wave detection means is larger than the thickness of the piezoelectric thin film in the formation region of the surface acoustic wave reflection means. Is preferred. Electromechanical coupling coefficient K ² will vary greatly depending on the thickness of the piezoelectric thin film, the reflection coefficient of the reflector is usually increased gradually as the thickness of the piezoelectric thin film is reduced. Therefore, the thickness of the piezoelectric thin film in the formation area of the surface acoustic wave excitation means or the surface acoustic wave detection means is appropriately set, and the thickness of the piezoelectric thin film in the formation area of the surface acoustic wave reflection means is further reduced. By doing so, the reflection efficiency can be increased without lowering the electromechanical coupling coefficient, so that the device performance can be improved.

  In the present invention, the piezoelectric thin film preferably has a film thickness normalized by the wavelength of the surface acoustic wave in a range of 0.005 to 0.1 in any region. In this thickness range, the electromechanical coupling coefficient is large and the reflection coefficient is large, so that the device performance can be further improved. In this case, the film thickness of the piezoelectric thin film in the region where the surface acoustic wave excitation means or the surface acoustic wave detection means is formed may be in the range of 0.02 to 0.1 in order to obtain a high electromechanical coupling coefficient. In particular, it is desirable that it is in the range of 0.04 to 0.06. Further, the film thickness of the piezoelectric thin film in the region where the surface acoustic wave reflecting means is formed is preferably in the range of 0.005 to 0.06, particularly 0.01 to 0 in order to obtain a high reflection coefficient. Desirably within the range of .04. In the above-mentioned film thickness range, the thickness of the piezoelectric thin film is less than 1 μm at the normal surface acoustic wave wavelength, so the film formation time of the piezoelectric thin film is short, and the manufacturing cost is reduced and the manufacturing efficiency is reduced. Can be improved.

  In the present invention, an insulating layer is preferably provided between the substrate and the piezoelectric thin film. By interposing an insulating layer between the substrate and the piezoelectric thin film, a substrate made of a conductive material, a substrate in which a conductor such as a conductive pattern is formed on the substrate, or a semiconductor substrate Even if it uses, the influence which the electroconductivity of the board | substrate or the conductor on a board | substrate has on the characteristic of a surface acoustic wave device can be reduced.

In the present invention, the piezoelectric body may be composed of any one material selected from ZnO, AlN, PZT, LiNbO ₃ , TaNbO ₃ , KNbO ₃ , PMN-PT, and PNN-PT relaxor systems. preferable. Since these materials exhibit higher piezoelectricity than quartz, which is the most typical piezoelectric body, a high-performance surface acoustic wave device can be formed.

  A surface acoustic wave device according to the present invention includes a piezoelectric thin film formed on a substrate and a surface acoustic wave excitation means or a detection electrode including an excitation electrode formed on the surface of the piezoelectric thin film. And a surface acoustic wave device comprising the surface acoustic wave reflecting means formed on the surface, the thickness of the piezoelectric thin film in the formation region of the surface acoustic wave exciting means or the surface acoustic wave detecting means is A case where the thickness is smaller than the thickness of the piezoelectric thin film in the region where the surface acoustic wave reflecting means is formed is included. In this case, although the reflection coefficient is small, the thickness of the piezoelectric thin film in the formation area of the surface acoustic wave excitation means or the surface acoustic wave detection means is set to a suitable area (area having a high electromechanical coupling coefficient). Can do. For example, in the region where the electromechanical coupling coefficient changes greatly with respect to the change in thickness of the piezoelectric thin film, the device performance changes greatly only when the thickness of the piezoelectric thin film is slightly different from the set value. A thin film is formed thickly, and then the formation area of the surface acoustic wave excitation means or the surface acoustic wave detection means is subjected to etching or the like, so that the piezoelectric thin film has an appropriate thickness (electromechanical coupling coefficient) in the formation area. High thickness). In this case, by limiting the etching region to the formation region of the surface acoustic wave excitation means or the surface acoustic wave detection means, the effects of reducing the etching solution damage and increasing the etching accuracy can be obtained.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view schematically showing a cross-sectional structure of a surface acoustic wave device 100 according to an embodiment of the present invention, and FIG. 2 is a schematic plan view showing a planar shape of the surface acoustic wave device 100.

In this embodiment, an insulating layer made of SiO ₂ , TiO ₂ , Ta ₂ O ₅ or the like on the surface of a substrate 101 made of various materials such as a semiconductor substrate such as a silicon substrate, a glass substrate, or a ceramic substrate. 102 is formed, and a piezoelectric thin film 103 is formed on the insulating layer 102. As a material constituting the piezoelectric thin film 103, any material having piezoelectricity can be used, and in particular, ZnO, AlN, PZT (Pb—Zn—Ti), LiNbO ₃ , TaNbO ₃ , KNbO. _3. It is desirable to use a material having high piezoelectricity such as PMN-PT or PNN-PT relaxor. The thickness of the piezoelectric thin film 103 is not particularly limited. For example, the thickness khp = 2πtp / λ (tp is the thickness of the piezoelectric body) normalized by the wavelength λ of the surface acoustic wave is 0.005 to 3 About 0.0. When the film thickness of the piezoelectric thin film is less than this range, the electromechanical coupling coefficient rapidly decreases and it becomes difficult to obtain a sufficient film quality as the piezoelectric thin film. In particular, it is preferable that the film thickness khp is either 0.005 to 0.1 or 0.3 to 3.0 in that an electromechanical coupling coefficient can be secured to some extent.

  On the surface of the piezoelectric thin film 103, surface acoustic wave excitation detection means provided with excitation detection electrodes 104a and 104b (corresponding to the excitation electrodes or detection electrodes described above) for exciting and detecting surface acoustic waves. 104 (corresponding to the above-mentioned surface acoustic wave excitation means or surface acoustic wave detection means) is formed. In the case of the illustrated example, the surface acoustic wave excitation detection means 104 has excitation detection electrodes 104a and 104b arranged alternately. The plurality of excitation detection electrodes 104a are conductively connected to the connection terminal 104A and given the same potential, and the plurality of excitation detection electrodes 104b are conductively connected to the connection terminal 104B and given the same potential. The surface acoustic wave excitation detecting means 104 is constituted by an interdigital transducer (IDT) in this embodiment. Specifically, in the illustrated example, a pair of comb-like electrodes are arranged to face each other so as to mesh with each other. In the following description, the surface acoustic wave excitation detecting means 104 is simply referred to as “IDT 104”.

  Further, on both sides of the surface acoustic wave propagation direction (left-right direction in the illustrated example) generated by the surface acoustic wave excitation detecting means 104, surface acoustic wave reflecting means 105 each having a reflective electrode 105a is provided. The surface acoustic wave reflecting means 105 is a grating reflector in which a plurality of reflecting electrodes 105a are arranged in the propagation direction. In the surface acoustic wave reflecting means 105, the reflecting electrodes 105a are conductively connected to each other. In practice, a high reflectance can be obtained by providing several tens or more of the reflective electrodes 105a. In the following description, the surface acoustic wave reflecting means 105 is simply referred to as a “reflector 105”.

  In the present embodiment, the thickness t1 of the piezoelectric thin film 103 in the IDT 104 formation region (the region where the excitation detection electrodes 104a and 104b are formed) and the reflector 105 formation region (the reflection electrode 105a are formed). The thickness t2 of the piezoelectric thin film 103 in the region) is different from each other. More specifically, in the present embodiment, the thickness t1 is configured to be greater than the thickness t2, and a surface step corresponding to the difference between the thicknesses t1 and t2 is formed between the two regions.

  3A to 3C are schematic process cross-sectional views (a) to (c) illustrating the manufacturing method of the embodiment. In the present embodiment, first, as shown in FIG. 3A, the insulating layer 102 is formed on the substrate 101. For example, if the substrate 101 is a silicon substrate, the insulating layer 102 can be formed by thermally oxidizing the substrate 101. Further, an insulating material may be formed over the substrate 101 by a sputtering method, a CVD method, or the like. An uncured resin or water glass may be applied and dried and fired.

  The piezoelectric thin film 103 formed on the insulating layer 102 is formed by sputtering or CVD. In particular, in order to form a high-quality thin film, the film is preferably formed by an RF magnetron sputtering method, an MOCVD (organometallic CVD) method, or the like.

  Next, as shown in FIG. 3B, a second region 103B thinner than the first region 103A is formed in the piezoelectric thin film 103. In this step, a mask such as a resist is formed on the first region 103A, and an etching process is performed to thin the piezoelectric thin film in the second region 103B by etching. When the piezoelectric thin film is ZnO, the etching process can be performed with an aqueous nitric acid solution. The mask is then removed.

  Thereafter, as shown in FIG. 3C, a conductor such as aluminum is formed on the surface of the piezoelectric thin film 103 by vapor deposition or sputtering, and patterned by using a resist as a mask by photolithography. An IDT 104 and a reflector 105 are formed. Here, the IDT 104 is formed in the first region 103A, and the reflector 105 is formed in the second region 103B. For patterning at this time, for example, an alkaline solution such as KOH is used. Thereafter, necessary wiring connections are made.

  In the above embodiment, the second region 103B of the piezoelectric thin film 103 is etched, so that the IDT 104 formation region (first region 103A) and the reflector 105 formation region (second region 103B) have different thicknesses. However, it may be formed thicker by stacking the piezoelectric thin films a plurality of times (twice) in the first region 103A. That is, the piezoelectric thin film in the first region 103A is formed thick by forming an extra piezoelectric thin film while masking the second region 103B.

  In this embodiment, the IDT 104 is a one-port type resonator that serves as both an input port and an output port, but has surface acoustic wave excitation means having an excitation electrode as an input port and a detection electrode as an output port. A two-port resonator having a surface acoustic wave detection means can also be configured. In this case, the surface acoustic wave reflecting means is configured on both sides in the arrangement direction of the surface acoustic wave exciting means and the surface acoustic wave detecting means.

  In the above embodiment, the piezoelectric thin film 103 is formed on the substrate 101 via the insulating layer 102. However, the piezoelectric thin film 103 may be formed directly on the substrate 101. Further, a conductive layer formed over the entire surface acoustic wave propagation region may be provided between the insulating layer 102 and the piezoelectric thin film 103 or between the substrate 101 and the piezoelectric thin film 103. This conductive layer reduces the potential gradient on the surface of the piezoelectric thin film 103 opposite to the surface on which each electrode is formed, so that an electromechanical coupling coefficient can be obtained even in a thin piezoelectric film that is easy to form. Shows a high value, the propagation characteristics of the surface acoustic wave device can be improved.

FIG. 4 shows the electromechanical coupling coefficient K ² and the surface acoustic wave propagation velocity v of the above embodiment and the normalized film thickness khp (IDT 104) of the piezoelectric thin film 103 when ZnO is used as the piezoelectric thin film 103. It is a graph which shows the relationship with the film thickness khp1) in the formation area of. Here, the solid line in the figure indicates the electromechanical coupling coefficient, and the dotted line in the figure indicates the propagation speed. As shown in this graph, the electromechanical coupling factor K ₂ is relatively large in the range of thickness of the piezoelectric thin film khp is 0.02 to 0.10, in the front and rear is rapidly decreased. In particular, the electromechanical coupling coefficient is highest when khp is in the range of 0.04 to 0.06. In the region shown in this graph, the film thickness khp is small and the film formation time of the piezoelectric thin film 103 is shortened, which is advantageous for mass production, but the film thickness dependence of the electromechanical coupling coefficient is large, and the film thickness Device performance tends to vary if accuracy is poor. Further, the propagation speed of the surface acoustic wave gradually increases as the film thickness khp decreases.

  FIG. 5 shows a reflection coefficient τ per reflection electrode 105a of the reflector 105 of the above embodiment when ZnO is used as the piezoelectric thin film 103, and a normalized film thickness khp (reflection) of the piezoelectric thin film 103. 6 is a graph showing the relationship with the film thickness khp2) in the formation region of the vessel 105. As shown in this graph, the reflection coefficient τ decreases as the film thickness khp increases. In particular, when the film thickness is 0.06 or less, the reflection coefficient τ increases rapidly.

As shown in FIGS. 4 and 5 above, in the region where the film thickness of the piezoelectric thin film is as small as 0.005 to 0.1, the film thickness khp1 of the piezoelectric thin film in the IDT 104 formation region is set to 0.02. can increase the electromechanical coupling coefficient K ₂ by the range of 0.1, also increases τ reflection coefficient by increasing the thickness khp2 of the piezoelectric thin film in the forming region of the reflector 105 Can be made. Therefore, by making the film thickness khp1 larger than the film thickness khp2, it is possible to increase both the electromechanical coupling coefficient and the reflection coefficient to improve device performance. For example, by setting the film thickness khp1 in the range of 0.02 to 0.10, setting the film thickness khp2 in the range of 0.005 to 0.06, and setting khp1> khp2, the electromechanical coupling coefficient And the reflection coefficient can be made high. In particular, it is more desirable to set the film thickness khp1 in the range of 0.04 to 0.06 and the film thickness khp2 in the range of 0.01 to 0.04.

  6 shows a range where the electromechanical coupling coefficient and the surface acoustic wave propagation speed of the surface acoustic wave device of the above embodiment are wider than the range shown in FIG. 4, that is, the film thickness khp of the piezoelectric thin film is close to 3.0. It is a graph shown in the range. The electromechanical coupling coefficient decreases greatly when the film thickness khp is in the range of 0.1 to 0.3, but when the film thickness khp exceeds 0.3, the film thickness khp increases rapidly to near 1.0, and then The film thickness khp is substantially constant up to about 3.0. Therefore, the electromechanical coupling coefficient is sufficiently large when the film thickness khp is in the range of 0.6 to 3.0, which is an area thicker than the film thickness shown in FIGS. In the region where the film thickness khp is 0.005 to 0.6, the electromechanical coupling coefficient is small, but the reflection coefficient τ is large. Therefore, by setting the film thickness khp1 in the range of 0.6 to 3.0 and the film thickness khp2 in the range of 0.005 to 0.6, both the electromechanical coupling coefficient and the reflection coefficient can be set large. In particular, it is more desirable to set the film thickness khp1 to 0.8 to 3.0 and set the film thickness khp2 to a range of 0.01 to 0.5.

  Next, a surface acoustic wave device 200 having a structure different from the above will be described with reference to FIG. In this embodiment, since the same substrate 201, insulating layer 202, IDT 204, and reflector 205 as those in the above embodiment are provided, description thereof will be omitted.

  The surface acoustic wave device 200 differs from the above embodiment in that the thickness t1 of the piezoelectric thin film 203 in the IDT 204 formation region is smaller than the thickness t2 of the piezoelectric thin film 203 in the reflector 205 formation region. The thickness is reversed. As described in the above embodiment, generally, the reflection efficiency of the reflector 205 can be increased by making the thickness t2 smaller than t1, but even when the thickness t2 is thicker than t1, Sufficient electromechanical coupling coefficient and reflection coefficient may be obtained.

  For example, if the above-described film thickness khp shown in FIGS. 4 and 5 is a small region of 0.005 to 0.1, a sufficiently high reflection coefficient can be obtained when khp is 0.06 or less. By setting the film thickness khp1 of the piezoelectric thin film 203 in the region to be in the range of 0.03 to 0.05, and setting the film thickness khp2 of the piezoelectric thin film 203 in the region in which the reflector 205 is formed to be 0.05 to 0.06. Both the electromechanical coupling coefficient and the reflection coefficient can be set high.

  Also, as shown in FIG. 6, a sufficiently high electromechanical coupling coefficient can be obtained if the thickness khp of the piezoelectric thin film 203 is 0.6 to 3.0. Since it is not so large, a device with sufficient performance can be obtained even if the film thickness khp1 is set smaller than the film thickness khp2.

  In the present embodiment, the piezoelectric thin film 203 can be formed so as to have a thickness t2, and thereafter, only the formation region of the IDT 204 can be etched to have the thickness t1. For example, the formation region of the reflector 205 is covered with a mask made of resist or the like, and the piezoelectric thin film 203 in the formation region of the IDT 204 is etched with an etching solution such as an aqueous nitric acid solution. In this way, the thickness t1 of the piezoelectric thin film 203 in the IDT 204 formation region can be accurately set to a set value. Therefore, it is particularly effective when the change in the electromechanical coupling coefficient is large with respect to the change in the thickness t1. In addition, by limiting the etching range to the IDT 204 formation region, it is possible to improve etching accuracy and uniformity. The device 200 can also be manufactured by a method in which an extra film is formed only in the formation region of the reflector 205 as in the above embodiment.

  Note that the surface acoustic wave device of the present invention is not limited to the illustrated examples described above, and it is needless to say that various modifications can be made without departing from the gist of the present invention. For example, in the above description, a case where a resonator is configured as a surface acoustic wave device has been described. However, the present invention is directed to at least one of surface acoustic wave excitation means or surface acoustic wave detection means, and surface acoustic wave reflection means. It is sufficient if it has. For example, a surface acoustic wave propagating from the outside is detected by a surface acoustic wave detecting means via a surface acoustic wave reflecting means, and a surface acoustic wave excited by a surface acoustic wave exciting means is used as a surface acoustic wave reflecting means. It can be sent out to the outside through this.

1 is a schematic cross-sectional view of an embodiment of a surface acoustic wave device. 1 is a schematic plan view of an embodiment. Schematic process sectional drawing (a)-(c) which shows the manufacturing method of embodiment. The graph which shows the relationship between the electromechanical coupling coefficient of embodiment, the propagation velocity of a surface acoustic wave, and the film thickness khp of a piezoelectric thin film. The graph which shows the relationship between the reflection coefficient (tau) of embodiment, and the film thickness kh2 of a piezoelectric material thin film. The graph which shows the relationship between the electromechanical coupling coefficient of embodiment, the propagation speed of a surface acoustic wave, and the film thickness khp of a piezoelectric thin film in a wider range. The schematic sectional drawing which shows the device structure of another embodiment different from embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Surface acoustic wave device, 101 ... Board | substrate, 102 ... Insulating layer, 103 ... Piezoelectric thin film, 104 ... Surface acoustic wave excitation detection means, 104a, 104b ... Excitation detection electrode, 105 ... Surface acoustic wave reflection means, 105a ... Reflection Electrode, t1 ... thickness of piezoelectric thin film in IDT formation region, t2 ... thickness of piezoelectric thin film in reflector formation region, khp ... normalized film thickness of piezoelectric thin film, khp1 ... IDT formation region The standardized film thickness of the piezoelectric thin film in, khp2 ... The standardized film thickness of the piezoelectric thin film in the reflector formation region

Claims (2)

A conductive layer formed on a substrate;
A piezoelectric thin film formed on the conductive layer;
An interdigital transducer formed on the piezoelectric thin film;
In a surface acoustic wave device comprising a grating reflector formed on the piezoelectric thin film,
Two grating reflectors are formed, and the interdigital transducer is formed between the two grating reflectors;
When the wavelength of the surface acoustic wave is λ, the thickness of the piezoelectric thin film is tp, and the thickness of the piezoelectric thin film normalized by the wavelength λ of the surface acoustic wave is 2πtp / λ,
2πtp / λ in the formation region of the interdigital transducer is in the range of 0.04 to 0.06,
The grating 2πtp / λ in reflector forming region Ri near the range of 0.01 to 0.04,
A surface acoustic wave device , wherein a thickness of the piezoelectric thin film in a region where the interdigital transducer is formed differs from a thickness of the piezoelectric thin film in a region where the grating reflector is formed . The piezoelectric body is made of any one material selected from ZnO, AlN, PZT, LiNbO ₃ , TaNbO ₃ , KNbO ₃ , PMN-PT, and PNN-PT relaxor system. Item 2. The surface acoustic wave device according to Item 1.

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