JPH0583068A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To provide the surface acoustic wave element operated at a higher frequency band with less loss. CONSTITUTION:Comb type electrodes 2a, 2b are subjected to ion injection by a focused ion beam in a diamond layer in the surface acoustic wave element provided with the diamond layer 1, a piezoelectric layer 3 provided on the diamond layer 1 and the comb type electrodes 2a, 2b provided between the diamond layer 1 and in close contact with both layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device used for high frequency filters and the like.

[0002]

2. Description of the Related Art Surface acoustic wave devices propagate on the surface of an elastic body.
Is an electro-mechanical conversion element using surface waves,
For example, it has a general structure as shown in FIG. Surface acoustic wave
In the element 20, the piezoelectric body 21 excites the surface wave.
The piezoelectric phenomenon is used. One provided on the piezoelectric body 21
When an electric signal is applied to the comb electrode 22, the piezoelectric body 21
Strain is generated, which becomes a surface acoustic wave and causes the piezoelectric body 21 to move.
Propagate, and the other comb-shaped electrode 23 collects it as an electric signal.
Will be issued. The frequency characteristic of this element is, as shown in the figure,
The electrode period of the comb electrode is λ₀, Surface acoustic wave speed
If the degree is ν, f ₀= Ν / λ₀Frequency f defined by
₀The band pass characteristic is centered around.

The surface acoustic wave device has a small number of parts, can be made compact, and can easily input and output signals on the propagation path of the surface wave. This element is a filter,
It can be applied to delay lines, oscillators, resonators, convolvers, correlators, and the like. In particular, the surface acoustic wave filter has been put to practical use as an intermediate frequency filter for television from early on, and further applied to a VTR and various communication device filters.

Regarding the surface acoustic wave element, for example, a surface acoustic wave filter used in the field of mobile communication is
A device that can be used in a higher frequency range is desired. As shown in the above equation, when the electrode period λ ₀ becomes smaller or the surface wave velocity ν becomes larger, the frequency characteristic of the device has a higher center frequency f ₀ . In this regard, for example, Japanese Patent Application Laid-Open No. 64-6291
No. 1 discloses a surface acoustic wave element in which a piezoelectric material is laminated on a diamond layer in order to increase the velocity ν of the surface acoustic wave. The speed of sound in diamond is the highest and yet diamond is physically and chemically stable. Therefore, diamond is a suitable material for increasing the element f ₀ .

[0005]

On the other hand, the comb-shaped electrode is
Conventionally, it has been formed using photolithography. When using photolithography, it was difficult to make the electrode width smaller than about 0.5 μm due to the restriction of the fine processing technology. As described above, it is possible to increase the center frequency f _{0 of the} element by using diamond, but in order to increase f ₀ further, it was necessary to change the electrode width.

In the element using diamond described above, a structure in which a comb-shaped electrode is sandwiched between the diamond and the piezoelectric body is preferable in order to increase the velocity of the elastic wave, but in order to form this structure, a comb is formed on the diamond layer. When a mold electrode was formed and a piezoelectric layer was laminated on it, the thickness of the piezoelectric layer was different between the portion on the diamond layer and the portion on the electrode. When the piezoelectric layers have different thicknesses in this manner, elastic waves are more scattered and loss increases.

An object of the present invention is to solve the above problems,
It is an object of the present invention to provide a surface acoustic wave device that can operate in a higher frequency range and has less loss.

[0008]

A surface acoustic wave device according to the present invention is provided with a diamond layer, a piezoelectric layer provided on the diamond layer, and between the diamond layer and the piezoelectric layer, and adheres to both layers. An element having a comb-shaped electrode is characterized in that the comb-shaped electrode is a region of the diamond layer that is ion-implanted by a focused ion beam.

The focused ion beam according to the present invention can be formed by using a liquid metal ion source. In the focused ion beam, for example, B-Pt, B
-Ni-Pt, B-Ni or B-Be-Si-Ni-
If Pd is the liquid metal ion source, B ⁺ ions are
As ²⁺ ions can be implanted by using Pt as the liquid metal ion source. Further, since the focused ion beam can have a minimum beam diameter of several tens nm, it is possible to implant ions in a fine region (a region of quarter micron level). Furthermore, if a focused ion beam is used, maskless ion implantation can be performed.

The diamond layer according to the present invention can be used as a substrate for forming a surface acoustic wave device,
It may be a diamond layer formed on a substrate made of a suitable material. The diamond layer may be either single crystal or polycrystal. Further, the diamond layer can be formed by vapor phase synthesis using hydrocarbon or the like as a source gas. This vapor phase synthesis method is a method of activating a raw material gas by heating an electron emitting material, a method of exciting the raw material gas by plasma, a method of decomposing and exciting the gas by light, and a method of ion-impacting polycrystalline diamond from the raw material gas. Including a method of growing. On the other hand, the diamond as the substrate can be prepared, for example, by processing a single crystal diamond synthesized under an ultrahigh pressure by a temperature difference method.

The piezoelectric layer according to the present invention is made of ZnO, Al.
N, Pb (Zr, Ti) O_Three, (Pb, La) (Zr,
Ti) O_Three, LiTaO_Three, LiNbO_Three, SiO_Two,
Ta _TwoO₅, Nb_TwoO₅, BeO, Li_TwoB_FourO₇, K
NbO_Three, ZnS, ZnSe and CdS?
Based on one or more compounds selected from
You can The piezoelectric layer is made of single crystal or polycrystal.
Can be offset, but use the device in a higher frequency range
For this reason, single crystals with less surface wave scattering are more preferable.
Yes. In addition, ZnO, AlN and Pb (Zr, Ti) O
_ThreeThe piezoelectric layer such as can be formed by the CVD method.
Wear.

[0012]

In the element of the present invention, a predetermined region on the surface portion of the diamond layer is electrically activated by ion implantation to form a comb-shaped electrode. Since the comb-shaped electrode is formed in the diamond layer in this way, the piezoelectric layer formed on top of it has a uniform thickness with no difference in thickness between the electrode and diamond layer. It Therefore, according to the present invention, it is possible to provide a low-loss element in which the scattering of elastic waves is suppressed as compared with the above-described conventional surface acoustic wave element.

Further, in the element of the present invention, since the comb-shaped electrode is formed by the focused ion beam, the electrode width λ ₀ can be set to the quarter micron level.
The accuracy of the electrode width is also high. Therefore, the device of the present invention can be operated in a higher frequency range than before, and has excellent reliability.

Further, the ion implantation by the focused ion beam can be carried out without a mask as described above. That is, since the comb-shaped electrode can be directly formed without the resist forming step, the manufacturing process can be greatly shortened. Furthermore, since the electrode formation by the focused ion beam can be automatically performed according to the information of the computer, it is possible to easily provide a custom-made surface acoustic wave element for the electrode. As described above, the device of the present invention is suitable for low-volume, high-mix production.

[0015]

EXAMPLE A high frequency filter according to the present invention was prepared as follows.

Referring to FIG. 1A, first, a single crystal diamond substrate was prepared. This substrate was placed in a focused ion beam apparatus, B-Ni was used as a liquid metal ion source, and a voltage of about 100 keV was applied between the extraction electrode and the emitter electrode to generate a B ⁺ ion beam. B ⁺ ions were implanted into the substrate 1 without a mask while scanning the ion beam. The ion-implanted region was formed into a comb-shaped electrode by scanning the beam. Next, by annealing, the ion-implanted region has a p-type low resistance layer of 0.3 μm.
The electrodes were made into m-line & space comb-shaped electrodes 2a and 2b (FIG. 1 (b)). Then, the substrate is transferred to a magnetron sputtering device, the sputtering output is 100 W, the substrate temperature is 380
The ZnO piezoelectric body 3 was deposited on the substrate 1 by magnetron sputtering in which the ZnO polycrystal was sputtered with a mixed gas of Ar: O ₂ = 1: 1 under the condition of ° C. (Fig. 1
(C)). The resonance frequency of the high frequency filter formed by the above method was about 8 GHz.

On the other hand, in the above-mentioned embodiment, B ⁺ implantation was carried out only by the formation of the comb-shaped electrode by using the ordinary photolithography and the ordinary ion implantation equipment, and the surface acoustic wave device was formed in the same manner as in the above-mentioned embodiment. .. As a result, about 0.
A 6 μm line & space comb-shaped electrode was formed, and the resonance frequency of the device was about 4 GHz.

From the above results, it became clear that the device according to the present invention can operate in a higher frequency range.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of an example of a surface acoustic wave device according to the present invention.

FIG. 2 is a perspective view showing a general structure of a surface acoustic wave device.

[Explanation of symbols]

 1 Substrate 2a, 2b Comb type electrode 3 ZnO piezoelectric body

Continued Front Page (72) Inventor Naoji Fujimori 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (1)

[Claims] 1. A surface acoustic wave device comprising a diamond layer, a piezoelectric layer provided on the diamond layer, and a comb-shaped electrode provided between the diamond layer and the piezoelectric layer and in close contact with both layers. 2. The surface acoustic wave device according to claim 1, wherein the comb-shaped electrode is a region of the diamond layer that is ion-implanted by a focused ion beam.