JP3770035B2 - Surface acoustic wave device and electronic apparatus, method for manufacturing surface acoustic wave device, and method for manufacturing piezoelectric material for surface acoustic wave device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device and electronic equipment having excellent high-frequency characteristics, a method for manufacturing a surface acoustic wave device, and a method for manufacturing a piezoelectric material for a surface acoustic wave device.
[0002]
[Prior art]
Due to demands for large information capacity, overcrowding, miniaturization of terminal devices, etc., high frequency communication is inevitable. Accordingly, a surface acoustic wave device (SAW device), which is a key device used for communication, is also required to have a higher frequency. In particular, a SAW device suitable for a microwave band important for next-generation communication is desired.
[0003]
The frequency f of the SAW device is expressed by a relational expression of f = V / λ using the surface acoustic wave velocity V of the substrate formed of a piezoelectric material and the period λ of the comb-shaped electrode. In order to increase the frequency, the frequency f may be increased. Therefore, an approach method using a material having a large surface acoustic wave velocity V or a period λ may be considered for increasing the frequency. However, in order to reduce the period λ, the method of reducing the width of the comb-shaped electrode by the microfabrication technique has problems such as power durability and withstand voltage because the electrode width and the electrode interval are reduced in addition to the equipment and process margin. Occurs. Since these problems greatly affect the reliability and life of the SAW device, there are various problems to be solved in the method of narrowing the electrode width.
[0004]
On the other hand, in order to increase the surface acoustic wave velocity V, 1) a high-speed piezoelectric material is used, 2) a high-speed wave such as a leaky wave is used, and 3) a piezoelectric thin film on a high-speed substrate such as diamond. There are three known methods of forming Conventionally, among these methods, the above-mentioned 2, 3) have been actively researched.
[0005]
[Problems to be solved by the invention]
However, the above method 2) using a leaky wave or the like has a problem in that waves of various modes are simultaneously excited in addition to the leaky wave, and spurious (sub-resonance) that becomes noise occurs. Further, in the method 3) using the high-speed substrate, the substrate price is high, there is a wave reflection at the boundary between the high-speed substrate and the piezoelectric thin film, the thickness of the piezoelectric thin film is difficult to control, and the characteristics vary. Many problems will occur. As for the high-speed piezoelectric material of 1), AlN (aluminum nitride) has the maximum surface acoustic wave velocity among the conventionally known piezoelectric crystals. It was not found.
[0006]
The present invention has been made in view of the above-described problems, and a surface acoustic wave device and an electronic apparatus capable of obtaining good surface acoustic wave characteristics at a high frequency, a method for manufacturing a surface acoustic wave device, and a surface acoustic wave device. It is an object to provide a method for manufacturing a piezoelectric material for use.
[0007]
[Means for Solving the Problems]
As a result of searching for new high-speed piezoelectric materials for use in surface acoustic wave devices, the present inventors have found that a single crystal of SrB ₄ O ₇ , which has been conventionally known as a nonlinear optical crystal, has a high-speed piezoelectricity. In addition to being a material, it was found that the electromechanical coupling coefficient (coefficient indicating the interconversion efficiency between electric energy and mechanical energy) was of the order of quartz. Therefore, the present invention is a technique based on this finding, and the following configuration is adopted in order to solve the above problems.
[0008]
The surface acoustic wave device of the present invention is a surface acoustic wave device in which an electrode for transmitting and receiving surface acoustic waves is formed on the surface of a piezoelectric material, and the piezoelectric material is formed of a SrB ₄ O ₇ single crystal. It is characterized by being.
In this surface acoustic wave device, the piezoelectric material is formed by SrB ₄ O ₇ single crystal, the electromechanical coupling coefficient of the crystal parallel with faster than material SrB ₄ O ₇ single crystal is conventionally known Therefore, it is possible to obtain excellent surface acoustic wave characteristics in a high frequency region.
Further, an electronic apparatus according to the present invention includes the surface acoustic wave device according to the present invention.
In this electronic apparatus, since the surface acoustic wave device of the present invention is mounted, for example, when a surface acoustic wave device is mounted as a surface acoustic wave filter in a mobile phone or the like, excellent communication in a high frequency region such as a microwave band. Can have properties.
[0009]
The method for producing a piezoelectric material for a surface acoustic wave device according to the present invention is a method for producing a piezoelectric material used for a surface acoustic wave device, and a raw material of SrB ₄ O ₇ is placed in a crucible and heated to form a molten liquid. It is characterized by melting and pulling up a single crystal of SrB ₄ O ₇ as the piezoelectric material from the melt in the crucible by the Czochralski method.
In this method of manufacturing a surface acoustic wave device for piezoelectric material, since the piezoelectric material by pulling a single crystal is grown in SrB ₄ O ₇ by the CZ method (Czochralski method), SrB ₄ defects is less high quality A piezoelectric material formed of O ₇ single crystal can be obtained.
[0010]
In the method for producing a piezoelectric material for a surface acoustic wave device according to the present invention, the raw material is preferably produced from SrCO ₃ and B ₂ O ₃ .
Furthermore, in the method for producing a piezoelectric material for a surface acoustic wave device according to the present invention, the raw material is mixed with SrCO ₃ (strontium carbonate) and B ₂ O ₃ (boric acid), formed into a pellet, and sintered. It is preferable. That is, since SrCO ₃ and B ₂ O ₃ are mixed, formed into a pellet and sintered, a stable melt having a composition of SrB ₄ O ₇ can be obtained quickly at the time of melting the raw material.
[0011]
In the method for producing a piezoelectric material for a surface acoustic wave device according to the present invention, a platinum wire is immersed in a melt in the platinum crucible to produce a SrB ₄ O ₇ seed crystal, and the seed crystal is further added to the crucible. It is preferable to pull up the SrB ₄ O ₇ single crystal by immersing it in the melt.
In this method of manufacturing a surface acoustic wave device for piezoelectric materials, so to prepare a seed crystal of the SrB ₄ O ₇ soak the platinum wire into the melt of a platinum crucible, the seed crystal of SrB ₄ O ₇ single crystal Even if not, a small crystal (polycrystal or single crystal) of SrB ₄ O ₇ prepared using platinum as a seed can be used as a seed crystal for pulling and growing.
[0012]
The surface acoustic wave device manufacturing method of the present invention is a surface acoustic wave device manufacturing method in which an electrode for transmitting and receiving surface acoustic waves is formed on the surface of a piezoelectric material, and includes the above-described surface acoustic wave device piezoelectric device of the present invention. An SrB ₄ O ₇ single crystal manufactured by a method for manufacturing a conductive material is used as the piezoelectric material.
In this surface acoustic wave device manufacturing method, the SrB ₄ O ₇ single crystal manufactured by the piezoelectric material manufacturing method for a surface acoustic wave device of the present invention is used as the piezoelectric material. A surface acoustic wave device having excellent surface acoustic wave characteristics even in a high frequency region can be manufactured by using a piezoelectric material having an ordinary electromechanical coupling coefficient.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of a surface acoustic wave device and an electronic apparatus according to the invention, a method for producing a surface acoustic wave device, and a method for producing a piezoelectric material for a surface acoustic wave device will be described with reference to FIGS. To do.
[0014]
The SAW device (surface acoustic wave device) of the present embodiment is a SAW filter (bandpass filter), and as shown in FIG. 1, the surface of the substrate 1 made of a piezoelectric material made of SrB ₄ O ₇ single crystal. Input and output comb-shaped electrodes 2 and 3 are formed to face each other on the (polished surface).
[0015]
A method for manufacturing the SAW device will be described with reference to FIG.
First, SrCO ₃ and B ₂ O ₃ which are raw materials of SrB ₄ O ₇ are mixed, formed into pellets and sintered, charged into a platinum crucible 4, and a heater ( (Not shown) is heated and melted to obtain a melt L. Then, with the melt L heated to a predetermined temperature, the tip is immersed in the melt L using the platinum wire 5 as a seed and grown by the CZ method to produce a small crystal (polycrystal or single crystal) of SrB ₄ O _7. The seed crystal S is used. Next, the seed crystal S is used as a seed and the single crystal C of SrB ₄ O ₇ is pulled up from the melt L by the CZ method, and the growth is repeated.
[0016]
A Laue photograph of the SrB ₄ O ₇ single crystal C pulled up in this way is shown in FIG. As can be seen from this photograph, Laue spots indicating that the pulled crystal is a single crystal can be confirmed.
Next, the SAW device is manufactured by cutting the single crystal C of SrB ₄ O ₇ into a plate shape to form the substrate 1 and forming the comb electrodes 2 and 3 on the polished surface of the surface. The
[0017]
The SAW device manufactured in this way may have excellent communication characteristics in a high frequency region such as a microwave band by being mounted as a SAW filter connected to an antenna in a mobile phone (electronic device), for example. it can.
[0018]
【Example】
Next, the surface acoustic wave device according to the present invention will be specifically described with reference to examples.
[0019]
In a SAW device in which comb electrodes 2 and 3 having a period λ (distance between electrodes λ / 2) of 4 μm are formed on the surface of a substrate 1 of SrB ₄ O ₇ single crystal, the surface acoustic wave characteristics (filter FIG. 4 shows the results of actual measurement of the transmission characteristics. As can be seen from this figure, in the SAW device of this example, the resonance frequency f is 1.55 GHz, and a high-speed surface acoustic wave velocity V of 6200 m / s can be obtained. This value is 20% higher than the conventional AlN having the maximum surface acoustic wave velocity (V = about 5000 m / s). Moreover, the electromechanical coupling coefficient at that time was 0.1 to 0.2%, which was equivalent to quartz.
[0020]
【The invention's effect】
As described above in detail, according to the present invention, the piezoelectric material is formed by SrB ₄ O ₇ single crystal, the electromechanical coupling coefficient of quartz parallel with SrB ₄ O ₇ single crystal is faster Therefore, excellent surface acoustic wave characteristics can be obtained even in a high frequency region. Therefore, if the surface acoustic wave device of the present invention is used, it is possible to reduce the size and the frequency of various communication means. For example, a duplexer dielectric resonator such as a cellular phone can be replaced with the surface acoustic wave device of the present invention, and the surface acoustic wave device of the present invention can be used as a filter for a high frequency region. It can be used for a communication filter (2.5 to 10 GHz), a high frequency RF filter (3 to 6 GHz), a first IF filter for millimeter waves (1 to 2 GHz), and the like.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a surface acoustic wave device according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing pulling growth by a CZ method in a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention.
FIG. 3 is a Laue photograph of SrB ₄ O ₇ single crystal grown in the method for manufacturing a surface acoustic wave device according to one embodiment of the present invention.
FIG. 4 is a graph showing surface acoustic wave characteristics (passage characteristics of SAW filter (insertion loss with respect to frequency)) of a surface acoustic wave device according to an embodiment of the present invention.
[Explanation of symbols]
1 Substrate (piezoelectric material)
2, 3 Comb electrode 4 Platinum crucible 5 Platinum wire C SrB ₄ O ₇ single crystal L Melt S Seed crystal

Claims (7)

A surface acoustic wave device in which an electrode for transmitting and receiving surface acoustic waves is formed on the surface of a piezoelectric material,
2. The surface acoustic wave device according to claim 1, wherein the piezoelectric material is made of SrB ₄ O ₇ single crystal. An electronic apparatus comprising the surface acoustic wave device according to claim 1. A method of manufacturing a piezoelectric material used in a surface acoustic wave device,
A raw material of SrB ₄ O ₇ is put in a crucible and heated to melt into a melt, and a single crystal of SrB ₄ O ₇ is pulled up from the melt in the crucible as the piezoelectric material by the Czochralski method. A method for producing a piezoelectric material for a surface acoustic wave device. The raw material, SrCO ₃ and B ₂ O ₃ Metropolitan method of manufacturing a surface acoustic wave device for piezoelectric material according to claim 3, characterized in that it is made from. 5. The method for producing a piezoelectric material for a surface acoustic wave device according to claim 4, wherein the raw material is a mixture of SrCO ₃ and B ₂ O ₃ , formed into a pellet and sintered. A platinum wire is immersed in the melt in the platinum crucible to produce a seed crystal of SrB ₄ O ₇ , and the seed crystal is immersed in the melt in the crucible to pull up the single crystal of SrB ₄ O _7. 6. The method for manufacturing a piezoelectric material for a surface acoustic wave device according to claim 3, wherein the piezoelectric material is a piezoelectric material. A method of manufacturing a surface acoustic wave device in which an electrode for transmitting and receiving surface acoustic waves is formed on the surface of a piezoelectric material,
A surface acoustic wave device manufactured by using the SrB ₄ O ₇ single crystal manufactured by the method for manufacturing a piezoelectric material for surface acoustic wave device according to claim 3 as the piezoelectric material. Method.

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