JPS60171822A - Piezoelectric thin film resonator - Google Patents

Abstract

PURPOSE:To prevent deterioration of a piezoelectric thin film resonator by providing a thick dielectric layer to a part between electrodes and an Si substrate to decrease the capacitance between the electrode part and the Si substrate. CONSTITUTION:After an Si 1 is specularly polished, an SiO2 film is formed on both faces of the wafer. A part of the SiO2 film on the surface of wafer is removed by etching. The Si layer is etched selectively by using the remaining SiO2 film as a protection film. The selective etching is stopped when it reaches the SiO2 on the upper part of the Si substrate. A lower electrode 4 for excitation is formed on an SiO2/Si diaphragm by vapordeposition of a metal, then a piezoelectric thin film 5 is formed and an upper electrode 6 for excitation is formed on the uppermost part with vapor deposition. In this case, the thickness of the dielectric layer 2 is increased at a part independently of the resonance system of the piezoelectric resonator.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention involves forming a piezoelectric thin film on a silicon substrate, and forming a recessed portion on the other surface of the silicon substrate facing the piezoelectric thin film by anisotropic etching or the like. The present invention relates to a formed high frequency diaphragm type piezoelectric resonator.

[Technical background of the invention and its problems]

Piezoelectric resonators that utilize the thickness vibration of a piezoelectric substrate have been put into practical use, but due to the structure of such devices that utilize thickness vibration, it is difficult to reduce the thickness of the piezoelectric substrate to several tens of micrometers or less. The basic operating frequency was 100 MHz or less. However, in recent years, diaphragm type piezoelectric resonators that can operate at high frequencies of 100 MHz or more have been reported. As an example, FIG. 1 shows ZnO/S i O,/S
An example of the basic structure of a piezoelectric resonator with an i-diaphragm structure is shown.

Such a diaphragm type piezoelectric resonator is generally manufactured by the following relatively simple process. First, after polishing 51(1) to a mirror surface, both sides of the woofer are heated by thermal oxidation, etc.
O, film +21, f3+ are formed. Next, a part of the SiO□ film (3) on the back surface of the woofer is removed by etching.

After that, using the remaining S i 02 film as a storage film, 81
Selective etching of the layer. This selective etching is
It stops when it reaches the SiO□ film (2) on the r substrate.

A lower excitation electrode (4) is formed on the 8+02/SI diaphragm thus formed by metal vapor deposition, and a piezoelectric thin film (5) of ZnO, AIN, etc. of about 10-odd μm is further deposited by magnetron sputtering. A diaphragm type piezoelectric resonator can be obtained by forming an excitation upper electrode (6) on the top by vapor deposition.

Such diaphragm-type piezoelectric resonators use vibrations with a relatively large electromechanical coupling coefficient, such as thickness longitudinal vibration or thickness transverse vibration, so resonators using surface acoustic waves that compete in this frequency band are It is possible to make the capacitance ratio smaller than that of a surface acoustic wave, and it is easy to achieve broadband characteristics when configuring a filter.Furthermore, the reflector structure is different from that of a surface acoustic wave, and a simple free surface can be used as a reflecting surface. Because it can do this, it has the advantage of being extremely compact. However, the conventional diamond slam type piezoelectric vibrator shown in FIG. 1 has the following drawbacks. In other words, due to its structure, a capacitance Op+f71 exists between the Si substrate (1) and the lower electrode (4), and a capacitance Op2 (81) exists between the upper electrode (6) and the Si substrate. .

Therefore, in addition to the admittance of the vibration system, there is a capacitance OpI + between the lower electrode and the upper electrode.
Opt and the 8i substrate resistor Rp (9) connected in series are added.

The equivalent circuit in this case is as shown in Figure 2, where O, R, and Oo are impedance elements representing a normal resonant system, and Op is the above two capacitances Op I
*Op = Op I・Opt is connected in series.
C1ot/(OpI+OI)! ). As can be easily seen from Figure 1, the larger 0p10o is, the more W
It can be seen that the smaller rOoRp (Wr is the resonance frequency), the lower the resonance frequency becomes, and the smaller the amount of dent in the admittance at the anti-resonance point. This phenomenon becomes a major problem when configuring a filter using a diaphragm type piezoelectric resonator, as it causes an increase in insertion loss, a decrease in guaranteed attenuation, and the like.

[Purpose of the invention]

This invention was made to solve the above-mentioned drawbacks.
It is an object of the present invention to provide a piezoelectric thin film resonator with a small parasitic capacitance ap, which does not cause deterioration in insertion loss, guaranteed attenuation, etc. when a filter is configured.

[Summary of the invention]

That is, the present invention is characterized in that a thick dielectric layer is provided in a portion between the electrode portion and the Si substrate in order to reduce the capacitances CpI and Cp2 between the lower electrode and the upper electrode and the Si substrate. .

〔Effect of the invention〕

According to the present invention, it is possible to reduce the capacitance between the electrode portion and the Si substrate, and when a filter is configured, it is possible to obtain a piezoelectric thin film resonator that does not cause deterioration in insertion loss, guaranteed attenuation, etc. .

[Embodiments of the invention]

The present invention will be explained below with reference to the drawings.

FIG. 3 shows an embodiment of a piezoelectric thin film resonator according to the present invention. In Fig. 3, the dielectric layer (2) is a part that is not related to the resonance system of the piezoelectric resonator, and its thickness is increased, thereby reducing the capacitance between the stain pole and the Si substrate. can. Such a thick dielectric layer can be easily formed by conventional methods such as sputtering, vapor deposition, ion blasting, and OVD. Further, it is desirable that the dielectric material has a dielectric constant as small as possible, for example, 5in2. Al, 0. , Si, N, etc. can be considered.

In the embodiment of FIG. 3, the lower electrode (4) and the upper electrode (6
) are both provided through a thick dielectric layer, but only one of the electrodes may be provided with a thick dielectric layer. Further, as shown in FIG. 4, the same effect can be obtained by providing the dielectric layer in two layers so as to sandwich the piezoelectric thin film.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the structure of a conventional piezoelectric thin film resonator, Fig. 2 is an equivalent circuit diagram thereof, Fig. 3 is a sectional view showing an embodiment of a piezoelectric thin film resonator according to the present invention, and Fig. 4 is a sectional view showing the structure of a conventional piezoelectric thin film resonator. FIG. 3 is a sectional view showing another embodiment of the present invention. 1... Semiconductor crystal substrate, 2, 3... Dielectric, 4...
- Lower electrode, 5... piezoelectric thin film, 6... upper electrode. Agent Patent Attorney Kensuke Chika (and 1 other person) No. 1
Figure 3

Claims (1)

[Claims] In a piezoelectric thin film resonator in which a semiconductor crystal substrate is used as a supporting member of a diaphragm, a single or multilayer dielectric film is provided on the semiconductor crystal substrate, and the effective thickness of the dielectric film varies depending on the location. Features a piezoelectric thin film resonator.