JP4345328B2 - Surface acoustic wave device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device and a method for manufacturing the same, and more particularly to a surface acoustic wave device having a laminated structure having a plurality of layers on a dielectric substrate.
[0002]
[Prior art]
A surface acoustic wave (SAW) is a wave in which energy concentrates and propagates on the surface of an elastic body in the same manner as a wave traveling on the surface of water. As a device that uses this surface acoustic wave, a thin film electrode transducer (hereinafter simply referred to as “IDT”) is formed on the surface of a piezoelectric substrate, and an electrical signal and SAW are converted through the transducer. There is something that performs inverse transformation. This device can be formed only by the process technology for the substrate surface as in the case of the semiconductor IC. Elastic vibration in the crystal is very short as about one wavelength 10 ⁵ minutes compared to the electromagnetic wave of the same frequency, it is suitable as waves responsible for the operation of the high frequency device. SAW is suitable for microwave devices in the band of several tens of MHz to several GHz, and has an advantage of drastically reducing the size of devices such as filters and resonators that are difficult to be integrated into an IC.
[0003]
In some cases, a piezoelectric film or a magnetic film is formed on the surface of the substrate, and these thin films are used as a surface acoustic wave propagation medium. Here, if an IDT is provided on the surface of the thin film, a thin film converter that directly excites and detects a surface acoustic wave in a high frequency band can be configured. In this case, since it is not necessary to use a piezoelectric material for the substrate, the degree of freedom of selection of the substrate material is increased, so that it is possible to achieve multi-functions, and an inexpensive surface acoustic wave device for communication with good characteristics. Realization is expected.
[0004]
Conventionally, a surface acoustic wave device using a piezoelectric thin film is known in which a zinc oxide thin film is formed on a silicon substrate. This type of device has a high electromechanical coupling coefficient to achieve high performance. In addition, a structure in which a piezoelectric thin film is sandwiched between an IDT and a short-circuit electrode is known (for example, see Non-Patent Document 1 below). In this device structure, a large electromechanical coupling coefficient is obtained when the thickness of the piezoelectric thin film is several percent of the wavelength. In FIG. 23 of Non-Patent Document 1, a structure (a) in which an IDT, a piezoelectric thin film, and a short-circuit electrode are stacked in this order on a dielectric substrate, and a short-circuit electrode, a piezoelectric thin film, and an IDT are stacked in this order on the dielectric substrate. Structure (b) is illustrated.
[0005]
[Non-Patent Document 1]
National Technical Report Vol.22 No.6 Dec. 1976, P.905: "Thin film surface acoustic wave device" Tsutsuo Sanro et al. (Especially, refer to 4.3 on page 918 and Fig. 23)
[0006]
[Problems to be solved by the invention]
However, in the conventional surface acoustic wave device, in the structure shown in FIG. 23 (a) of Non-Patent Document 1, a piezoelectric thin film must be formed on the surface having a step where the IDT is formed. It is difficult to form a thin body film, and the film quality may be affected. On the other hand, in the structure shown in FIG. 23 (b), since the piezoelectric thin film must be formed on the short-circuit electrode made of metal, the film quality of the piezoelectric thin film deteriorates and good performance cannot be obtained. There is a problem that there is.
[0007]
Therefore, the present invention solves the above-mentioned problems, and the problem is that the influence on the film quality of the piezoelectric thin film in a surface acoustic wave device in which a piezoelectric thin film is formed on a dielectric substrate via a short-circuit electrode. Is to realize a high-quality device configuration.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a surface acoustic wave device according to the present invention includes a laminated structure of a base electrode layer and a piezoelectric thin film on a dielectric substrate, and includes an electrode for inducing surface acoustic waves in the piezoelectric thin film. In the surface acoustic wave device, the base electrode layer has a function of reducing potential fluctuation on an interface of the piezoelectric thin film, and the base electrode layer is made of a semiconductor.
[0009]
In the surface acoustic wave device in which the base electrode layer and the piezoelectric thin film are provided on the dielectric substrate, the inventor of the present application has an electromechanical coupling coefficient under a predetermined condition even when the base electrode layer is made of a semiconductor. I found it to improve. In this case, by configuring the base electrode layer with a semiconductor, it becomes possible to improve the film quality of the piezoelectric thin film laminated on the base electrode layer, compared with the case where the base electrode layer is configured with a metal, As a result, it has been found that a high-performance surface acoustic wave device can be constructed. In particular, when the base electrode layer and the piezoelectric thin film are made of the same material, manufacturing is facilitated and the film quality of the piezoelectric thin film is further improved.
[0010]
In the present invention, the base electrode layer preferably has a resistivity of 1 to 1000 Ω · cm. In general, the term “semiconductor” broadly includes a material located between a conductor having a resistivity of 10 ⁻³ Ω · cm or less and an insulator having a resistivity of 10 ⁸ Ω · cm or more. It preferably has a resistivity of ˜1000 Ω · cm. It is difficult to lower the resistivity below the above range unless it is doped with a general material, and when the resistivity is higher than the above range, it is difficult to sufficiently function as a short-circuit electrode. become. The resistivity of the piezoelectric thin film is 1 MΩ or more, and particularly preferably 100 MΩ or more (100 MΩ to 1 GΩ).
[0011]
In the present invention, the base electrode layer is preferably made of zinc oxide having semiconductor characteristics. When the base electrode layer is made of zinc oxide having semiconductor characteristics, it becomes easy to form the upper piezoelectric thin film with good film quality. When zinc oxide is used as a material, a thin film having semiconductor characteristics can be easily formed.
[0012]
In the present invention, the piezoelectric thin film is preferably composed of zinc oxide having piezoelectric characteristics. When zinc oxide is used as a material, a thin film having piezoelectric characteristics can be easily formed. In addition, when both the base electrode layer and the piezoelectric thin film are made of zinc oxide, the manufacturing becomes easy. For example, it can be formed in a continuous process by changing only the manufacturing conditions, and the film quality (crystallinity) of the piezoelectric thin film can be increased. And orientation) can be further improved.
[0013]
In the present invention, when the wavelength of the surface acoustic wave is λ and the thickness of the piezoelectric thin film is Tp, the normalized film thickness khp = 2πTp / λ is about 0.1 to 0.8. Is preferred. When the film thickness khp is about 0.1 to 0.8, the electromechanical coupling coefficient is significantly increased as compared with the case where the base electrode layer is not provided.
[0014]
In the present invention, the piezoelectric thin film is made of LiNbO _3, where the wavelength of the surface acoustic wave is λ and the thickness of the piezoelectric thin film is Tp, the normalized film thickness khp = 2πTp / λ is It is preferably about 2.0 to 3.0. When LiNbO ₃ is used as the piezoelectric thin film, the electromechanical coupling coefficient is significantly higher when the film thickness khp is about 2.0 to 3.0 than when the base electrode layer is not provided. .
[0015]
In the present invention, it is preferable that a hard dielectric layer is provided between the dielectric substrate and the base electrode layer. According to this means, by providing a hard dielectric layer harder than the dielectric substrate, even if a relatively inexpensive material such as a silicon substrate or a glass substrate is used as the dielectric substrate, the surface acoustic wave The propagation speed can be increased, the device can be increased in speed and frequency, and the device can be reduced in size.
[0016]
Next, the surface acoustic wave device manufacturing method of the present invention includes a step of forming a base electrode layer made of a semiconductor on a dielectric substrate, and forming a piezoelectric thin film on the base electrode by forming a piezoelectric body. And a step of forming.
[0017]
In the present invention, it is preferable that the step of forming the base electrode layer is performed in a film forming apparatus, and the step of forming the piezoelectric thin film is performed by subsequently changing the film forming conditions in the film forming apparatus. . According to this, it is possible to improve the cleanliness of the interface between the base electrode layer and the piezoelectric thin film and reduce the manufacturing time and cost.
[0018]
In the present invention, the base electrode layer is preferably composed of zinc oxide having semiconductor characteristics, and the piezoelectric thin film is preferably composed of zinc oxide having piezoelectric characteristics.
[0019]
In the present invention, in the step of forming the base electrode layer, sputtering using zinc oxide or zinc as a target is performed in an atmosphere having a low oxygen partial pressure, and in the step of forming the piezoelectric thin film, zinc oxide or zinc is used. Sputtering as a target is preferably performed in an atmosphere having a high oxygen partial pressure. According to this, zinc oxide having n-type semiconductor characteristics can be formed as a base electrode layer by forming a film in an atmosphere having a low oxygen partial pressure, and forming a film in an atmosphere having a high oxygen partial pressure. Accordingly, zinc oxide having piezoelectric characteristics can be formed as a piezoelectric thin film.
[0020]
In each of the above inventions, a silicon semiconductor or another compound semiconductor can be used as the base electrode layer in addition to the zinc oxide. Further, it may be a low resistance layer formed by lowering the resistivity by introducing carriers on the surface of the dielectric substrate.
[0021]
In each of the above inventions, examples of the piezoelectric thin film include LiNbO ₃ , LiTaO ₃ , KNbO ₃ , and PZT in addition to the above zinc oxide. Other piezoelectric thin films can be used.
[0022]
Examples of the dielectric substrate include silicon, glass, quartz, and quartz. The dielectric substrate is preferably made of a material that does not easily deteriorate the quality of the upper layer or a relatively inexpensive material. Other dielectrics and dielectric thin films can be used.
[0023]
Furthermore, examples of the material for the hard dielectric layer include silicon nitride, diamond, sapphire, aluminum nitride, silicon carbide, and titanium oxide. The hard dielectric layer contributes to speeding up the surface acoustic wave by being a dielectric or piezoelectric material of a material having hardness higher than that of the dielectric substrate. Other hard dielectric thin films can be used.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a surface acoustic wave device according to the present invention will be described in detail with reference to the accompanying drawings.
[0025]
[First Embodiment]
FIG. 1 is a schematic perspective view schematically showing a configuration of a first embodiment which is an example of a surface acoustic wave device according to the present invention. In the surface acoustic wave device 100, a base electrode layer 102 made of a semiconductor such as a silicon semiconductor or a compound semiconductor is formed on the surface of a dielectric substrate 101 made of a silicon substrate, a glass substrate, a quartz substrate, or the like. A piezoelectric thin film 103 made of a piezoelectric material such as zinc oxide (ZnO), LiNbO ₃ , LiTaO ₃ , KNbO ₃ , or PZT is formed on the base electrode layer 102. An IDT 110 having a comb-like electrode 104 is formed on the surface of the piezoelectric thin film 103. In the illustrated example, the grating reflectors 120 are disposed on both sides of the IDT 110. The surface acoustic wave device 100 in the illustrated example constitutes a resonator in which the surface acoustic wave formed in the IDT 110 by the interdigital electrode 104 resonates between the grating reflectors 120. Note that the surface acoustic wave device according to the present invention is not limited to the above-described resonator, and may include a filter, a delay line, a convolver (correlator), and the like. In these cases, two or more IDTs may be provided, unlike the illustrated example.
[0026]
The wavelength λ of the surface acoustic wave excited by the IDT 110 is determined by the formation interval of the interdigital electrodes 104 provided in the IDT 110. The wavelength λ of the surface acoustic wave to be excited is provided with a pair of electrode bodies 110S and 110T as shown in FIG. 1, and the interdigital electrode 104S connected to the electrode body 110S and the electrode body 110T as shown in FIG. When the interdigital transducers 104T connected to each other are alternately formed, the interdigital transducers are formed at the same period as each interdigital transducer. In general, the interdigital electrode 104 of the IDT 110 has an array structure corresponding to a surface acoustic wave having a wavelength λ of about 0.5 to 10 μm. For example, in the case of a single electrode structure as in the illustrated example, the interdigital electrodes 104 are arranged at an interval of ½ of the wavelength λ. In the double (split) electrode structure, the electrodes are arranged at intervals of 1/4 of the wavelength λ.
[0027]
Underlying electrode layer 102 composed of a semiconductor as described above is formed by the piezoelectric thin film 103 is formed on the underlying electrode layer 102, the electromechanical coefficient K ² of the device in a predetermined thickness range As a result, the device performance can be improved and the size can be reduced.
[0028]
FIG. 2 is a schematic longitudinal sectional view schematically showing a sectional structure of the surface acoustic wave device 100 of the present invention. The dielectric substrate 101 has a thickness that can be handled. For example, a dielectric substrate having a thickness of about several hundred μm to several mm is used. The base electrode layer 102 can be composed of a compound semiconductor such as a silicon semiconductor, an n-type semiconductor such as zinc oxide, or InP. It can also be composed of zinc oxide. The thickness of the base electrode layer 102 is usually set to about 0.001 to 1.0 μm. If the thickness of the base electrode layer is too thin, it becomes difficult to exhibit the function as a short-circuit electrode (equipotential layer), and if the thickness of the base electrode layer is too thick, the manufacturing efficiency is deteriorated. The resistivity of the base electrode layer 102 is preferably in the range of about 1 to 1000 Ω · cm. Semiconductors with resistivity below this range are usually limited to some extent, so the selection range of materials is limited. Further, if the resistivity exceeds the above range, the equipotential effect for reducing the potential fluctuation at the interface of the piezoelectric thin film may be insufficient. The resistivity of the base electrode layer 102 can be adjusted by introducing carriers such as doping and ion implantation, changing film forming conditions (gas partial pressure ratio, pressure, power, etc.) in addition to a method of selecting a constituent material. it can.
[0029]
Furthermore, the piezoelectric thin film 103 has a basic configuration of, for example, zinc oxide (ZnO). Usually, the piezoelectric thin film 103 is formed to have piezoelectric characteristics by a method described later. The thickness Tp of the piezoelectric thin film 103 is usually formed to about 0.5 to 50 μm. Here, in the following description, as the standardized film thickness of the piezoelectric thin film 103, khp = 2πTp / λ (that is, the product of the thickness and the wave number k) based on the wavelength λ of the surface acoustic wave. Use. In this case, the thickness Tp uses [μm] as a unit.
[0030]
FIG. 3 shows the dependence of the surface acoustic wave propagation velocity V [m / s] of the surface acoustic wave device 100 of this embodiment on the film thickness khp of the piezoelectric thin film 103. In the surface acoustic wave device 100 used here, the dielectric substrate 101 is a silicon substrate having a plane orientation (100), and the base electrode layer 102 is zinc oxide that is an n-type semiconductor (formed by a manufacturing method described later). Resistivity: 10 ⁻⁸ to 10 ⁴ Ω · cm, carrier concentration: 10 ¹⁵ to 10 ²⁰ cm ⁻³ ), and the piezoelectric thin film 103 is made of zinc oxide (resistivity of 100 MΩ or more). . In this graph, the line on the low speed side (the lower side of the graph) shows Rayleigh wave data, and the line on the high speed side (the upper side of the graph) shows secondary wave (Sezawa wave) data. In any case, the propagation speed increases as the film thickness khp of the piezoelectric thin film 103 decreases.
[0031]
FIG. 4 shows the dependence of the electromechanical coupling coefficient K ² [%] of the device on the film thickness khp. The line on the lower side of the graph indicates the Rayleigh wave data, and the line on the upper side of the graph indicates the secondary wave (Sezawa wave) data. The electromechanical coupling coefficient of Rayleigh waves shows a significant increase in the region where khp is about 0.1 or more and 1.0 or less.
[0032]
FIG. 5 is different from FIG. 5 only in that the base electrode layer 102 is not formed, and the other is a graph showing the dependence on the film thickness khp in the propagation velocity V [m / s] of the first comparative example configured in the same manner as the above embodiment. FIG. 6 is a graph showing the dependence of the electromechanical coupling coefficient K ² [%] on the film thickness khp in the first comparative example. In each graph, the line on the lower side of the graph indicates the Rayleigh wave data, and the line on the upper side of the graph indicates the secondary wave (Sezawa wave) data. This comparative example basically shows a tendency similar to that of the above embodiment.
[0033]
FIG. 7 is a graph comparing the present embodiment and the first comparative example with surface acoustic wave propagation velocity data. FIG. 8 is a graph showing the electromechanical coupling coefficient of the present embodiment and the first comparative example. It is a graph compared with data. As can be seen from these graphs, the surface acoustic wave propagation velocity is almost the same between the first embodiment and the first comparative example, but the electromechanical coupling coefficient related to the Rayleigh wave is approximately equal to the film thickness khp of the piezoelectric thin film. In the range of 0.1 to 0.8, the present embodiment surpasses the first comparative example. In particular, when the film thickness khp is in the range of about 0.1 to 0.5, the electromechanical coupling coefficient of the present embodiment shows a value two to three times that of the first comparative example.
[0034]
[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. The surface acoustic wave device according to the second embodiment has substantially the same structure as the device 100 according to the first embodiment, and the dielectric substrate 101, the base electrode 102, and the interdigital electrode 104 are exactly the same as those in the first embodiment. Therefore, the description about the same part is abbreviate | omitted. The only difference between the second embodiment and the first embodiment is that LiNbO ₃ is used instead of zinc oxide as the piezoelectric thin film 103.
[0035]
FIG. 9 shows the dependence of the surface acoustic wave propagation velocity V [m / s] of the surface acoustic wave device 100 of this embodiment on the film thickness khp of the piezoelectric thin film 103. In this graph, the line on the low speed side (the lower side of the graph) shows Rayleigh wave data, and the line on the high speed side (the upper side of the graph) shows secondary wave (Sezawa wave) data. In any case, the propagation speed increases as the film thickness khp of the piezoelectric thin film 103 decreases.
[0036]
FIG. 10 shows the dependency of the electromechanical coupling coefficient K ² [%] of the device on the film thickness khp. The line on the lower side of the graph indicates the Rayleigh wave data, and the line on the upper side of the graph indicates the secondary wave (Sezawa wave) data. The electromechanical coupling coefficient of Rayleigh waves shows a significant increase in the region where khp is about 0.5 or more and 3.0 or less.
[0037]
FIG. 11 is different from FIG. 11 only in that the base electrode layer 102 is not formed, and the other is the dependence on the film thickness khp in the propagation velocity V [m / s] of the second comparative example configured in the same manner as the second embodiment. FIG. 12 is a graph showing the dependence of the electromechanical coupling coefficient K ² [%] on the film thickness khp in the second comparative example. In each graph, the line on the lower side of the graph indicates the Rayleigh wave data, and the line on the upper side of the graph indicates the secondary wave (Sezawa wave) data. This comparative example basically shows a tendency similar to that of the above embodiment.
[0038]
FIG. 13 is a graph comparing the present embodiment and the second comparative example with surface acoustic wave propagation velocity data, and FIG. 14 shows the electromechanical coupling coefficient of the device between the present embodiment and the second comparative example. It is a graph compared with data. As can be seen from these graphs, the surface acoustic wave propagation velocity is almost the same between the second embodiment and the second comparative example, but the electromechanical coupling coefficient related to the Rayleigh wave is approximately equal to the film thickness khp of the piezoelectric thin film. This embodiment surpasses the second comparative example in the range of 2.0 to 3.0.
[0039]
[Other Embodiments]
The structure of the modification of the said embodiment is shown in FIG. The surface acoustic wave device 200 according to this modification is formed of silicon nitride (Si ₃ N ₄ ), diamond, sapphire, aluminum nitride, silicon carbide, titanium oxide, or the like on the surface of a dielectric substrate 201 such as a silicon substrate. A hard dielectric layer 202 is formed, and a base electrode layer 205, a piezoelectric thin film 203, and an interdigital electrode 204 similar to those of the above embodiments are sequentially formed on the hard dielectric layer 202. By forming the hard dielectric layer 202 between the dielectric substrate 201 and the base electrode layer 205 in this way, even if a relatively inexpensive substrate such as a silicon substrate or a glass substrate is used as the dielectric substrate 201, an elastic surface is obtained. Wave speed can be increased.
[0040]
[Production method]
Next, a method for manufacturing the surface acoustic wave device according to the embodiment will be described with reference to FIG. Here, in this manufacturing method, a case where the surface acoustic wave device 100 according to the above-described embodiment is manufactured will be described, but also in the surface acoustic wave device 200 according to the above-described modification, the number of steps for forming the hard dielectric layer 202 increases. Other than that, the same applies. The hard dielectric layer 202 such as silicon nitride (Si ₃ N ₄ ) can be formed by atmospheric pressure CVD, plasma CVD, or the like. In the case of silicon nitride, SiH ₄ , NH ₃ , and H ₂ are usually used as the film forming gas.
[0041]
First, the surface of the dielectric substrate 101 is cleaned. A dielectric substrate such as a silicon substrate can be cleaned by cleaning with pure water or a solvent. For example, it is neutralized after being treated with sulfuric acid, further washed with pure water and then dried.
[0042]
Next, as illustrated in FIG. 15A, a zinc oxide that is an n-type semiconductor is formed on the surface to form a base electrode layer 102. This film forming step can be performed by a sputtering method, a vapor deposition method, a laser ablation method, a CVD method, or the like. For example, the sputtering method includes high frequency magnetron sputtering. When the sputtering method is used, the target material may be metal Zn or zinc oxide when the piezoelectric thin film is composed of zinc oxide. However, it is preferable to use a zinc oxide target in order to improve the film quality. As a specific example of the target material, for example, there is ZnO—Li ₂ O (1.5 mol% lithium oxide added to zinc oxide). In the following description, this target is used for experiments.
[0043]
As an atmosphere, when a zinc oxide target is used, an inert gas such as Ar is used. Here, a small amount of oxygen gas may be introduced. When using a zinc target, a certain amount of oxygen gas is introduced. However, the oxygen partial pressure in the atmosphere is set to a value lower than that in the step of forming a piezoelectric thin film described later. As an example of other conditions, when an RF magnetron sputtering apparatus is used, the power is 200 to 600 W, the substrate temperature is 270 to 330 ° C., the degree of vacuum (chamber pressure) is 5 Pa or less, and the Ar flow rate is 100 SCCM. Under such conditions, a zinc oxide thin film having n-type semiconductor characteristics can be formed.
[0044]
Next, as shown in FIG. 15B, a piezoelectric thin film 103 is formed on the base electrode layer 102 with zinc oxide. The film forming process of the piezoelectric thin film 103 can be performed by sputtering, vapor deposition, laser ablation, CVD, or the like. For example, the sputtering method includes high frequency magnetron sputtering. When the sputtering method is used, the target material may be metal Zn or zinc oxide when the piezoelectric thin film is composed of zinc oxide. However, it is preferable to use a zinc oxide target in order to improve the film quality. As a specific example of the target material, for example, there is ZnO—Li ₂ O (1.5 mol% lithium oxide added to zinc oxide). In the following description, this target is used for experiments.
[0045]
As the atmosphere, an inert gas such as Ar mixed with oxygen (for example, a mixing ratio of 50:50 by volume) is used. As an example of other conditions, when using an RF magnetron sputtering apparatus, the power is 200 to 600 W, the substrate temperature is 270 to 330 ° C., the degree of vacuum (chamber pressure) is 5 Pa or less, the Ar flow rate is 50 SCCM, and the oxygen flow rate is 50 SCCM. Moreover, the power of sputtering affects the film quality. In the above range, generally, the higher the power, the higher the film forming speed, but the film quality decreases. Under such conditions, a zinc oxide thin film having piezoelectric characteristics can be formed.
[0046]
By forming a zinc oxide thin film having piezoelectric characteristics on a zinc oxide thin film having semiconductor characteristics as described above, the film quality of the upper piezoelectric thin film 103 can be improved, and a high-performance device can be manufactured. . In particular, in the case of this embodiment, since the base electrode layer 102 and the piezoelectric thin film 103 are formed of the same zinc oxide, the interface consistency is improved, and the crystallinity of the piezoelectric thin film is also greatly improved. .
[0047]
Note that the base electrode layer 102 and the piezoelectric thin film 103 can be successively formed by the same film forming apparatus. In the above example, the base electrode layer 102 is formed by initially reducing the oxygen partial pressure in the film formation atmosphere (or cutting off the oxygen supply). Thereafter, the oxygen partial pressure in the film formation atmosphere is increased (oxygen supply is started), and the piezoelectric thin film 103 is formed. As a result, it is not necessary to perform the film forming process of each layer with a separate apparatus, so that the manufacturing efficiency can be dramatically increased. Also, the interface between the base electrode layer 102 and the piezoelectric thin film 103 can be formed cleanly.
[0048]
FIG. 16 shows a schematic configuration of a sputtering apparatus used in the film forming process. The apparatus 10 supplies power to the apparatus main body 12 such as a high-frequency sputtering apparatus that receives a predetermined gas supplied from the gas supply means 11, a gas supply means 11 that supplies a mixture of source gases, and the like. An electric power supply means 13 and an exhaust device 14 for exhausting the inside of the chamber of the apparatus main body 12 are provided. In the chamber of the apparatus main body 12, a target (not shown) and a substrate holder on which the dielectric substrate 101 is disposed are disposed to face each other.
[0049]
Next, as illustrated in FIG. 15C, an electrode material layer 104 </ b> A is formed on the piezoelectric thin film 103. As the electrode material layer 104A, for example, a metal such as Al can be used. As a film forming method, a sputtering method, a vapor deposition method, a laser ablation method, or the like can be used. Thereafter, a resist layer 105A is formed over the electrode material layer 104A. The resist layer 105A can be formed, for example, by applying a photosensitive resist by a spin coating method or the like, and drying or heat curing. Thereafter, the resist layer is patterned. For this patterning, for example, a normal photolithography method or the like is used. More specifically, the resist layer 105A is subjected to pattern exposure using a predetermined exposure mask, and then the resist layer 105A is developed to form the resist mask 105 shown in FIG.
[0050]
Next, using the resist mask 105, the electrode material layer 104A is patterned by etching or the like to form the interdigital electrode 104 shown in FIG. Thereafter, by removing the resist mask 105, a structure of a surface acoustic wave device having interdigital electrodes 104 on the surface is formed as shown in FIG.
[0051]
In addition, it is preferable to coat the surface of the interdigital electrode 104 with a resin mold material such as silicone resin (not shown) or an inorganic insulating film such as SiO ₂ . This can reduce the corrosion and damage of the interdigital electrode.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing the appearance of a surface acoustic wave device according to the present invention.
FIG. 2 is a schematic cross-sectional view of the surface acoustic wave device according to the first embodiment.
FIG. 3 is a graph showing the relationship between the propagation speed of surface acoustic waves and the film thickness khp according to the first embodiment.
FIG. 4 is a graph showing the relationship between the electromechanical coupling coefficient and the film thickness khp of the first embodiment.
FIG. 5 is a graph showing the relationship between the propagation speed of surface acoustic waves and the film thickness khp of the first comparative example.
FIG. 6 is a graph showing the relationship between the electromechanical coupling coefficient of the surface acoustic wave and the film thickness khp of the first comparative example.
FIG. 7 is a graph showing the relationship between the propagation speed of surface acoustic waves and the film thickness khp in comparison between the first embodiment and the first comparative example.
FIG. 8 is a graph showing a comparison between the first embodiment and the first comparative example regarding the relationship between the electromechanical coupling coefficient and the film thickness khp.
FIG. 9 is a graph showing the relationship between the propagation speed of surface acoustic waves and the film thickness khp according to the second embodiment.
FIG. 10 is a graph showing the relationship between the electromechanical coupling coefficient and the film thickness khp of the second embodiment.
FIG. 11 is a graph showing the relationship between the propagation speed of surface acoustic waves and the film thickness khp of the second comparative example.
FIG. 12 is a graph showing the relationship between the electromechanical coupling coefficient of the surface acoustic wave and the film thickness khp of the second comparative example.
FIG. 13 is a graph showing a comparison between the second embodiment and the second comparative example regarding the relationship between the propagation speed of the surface acoustic wave and the film thickness khp.
FIG. 14 is a graph showing a comparison between the second embodiment and a second comparative example regarding the relationship between the electromechanical coupling coefficient and the film thickness khp.
FIG. 15 is a process cross-sectional view (a) to (f) showing a manufacturing process of a surface acoustic wave device.
FIG. 16 is a schematic configuration diagram of an apparatus for manufacturing a piezoelectric thin film.
FIG. 17 is a schematic cross-sectional view of a modification of the surface acoustic wave device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Surface acoustic wave device, 101 ... Dielectric substrate, 102 ... Base electrode layer, 103 ... Piezoelectric thin film, 104 ... Interdigital electrode, 110 ... IDT, 120 ... Grating reflector, khp ... Standardization of piezoelectric thin film Film thickness, Tp: thickness of piezoelectric thin film, λ: wavelength of surface acoustic wave

Claims (2)

A surface acoustic wave device provided with a laminated structure of a base electrode layer and a piezoelectric thin film on a dielectric substrate, and comprising an electrode for inducing surface acoustic waves in the piezoelectric thin film,
The base electrode layer is made of zinc oxide having semiconductor characteristics,
The piezoelectric thin film is made of LiNbO 3, and the normalized film thickness khp = 2πTp / λ is 2.0 to 3 when the wavelength of the surface acoustic wave is λ and the thickness of the piezoelectric thin film is Tp. 0. A surface acoustic wave device characterized by being 0.0 . The surface acoustic wave device according to claim 1, wherein the base electrode layer has a resistivity of 1 to 1000 Ω · cm.

Images