JPS6294010A - Manufacture of piezoelectric thin film resonator - Google Patents

Abstract

PURPOSE:To obtain a thin film piezoelectric resonator having a high Q by making a support substrate by zinc oxide so as to avoid a silicon oxide film from being etched in etching the substrate. CONSTITUTION:A silicon oxide film 10, a lower electrode 12, a ZnO piezoelectric thin film 14, an upper electrode 15 and a protection film 16 are formed sequentially on a major surface 11a of the ZnO sintered compact made support substrate 11. Then a mask is formed on a major surface 11b of the substrate 11, the substrate is etched in a hydrochloric acid solution to form a recess 18. Since the Si oxide film 10 is resistant to acid, the film is not etched and the oxide film with a uniform thickness is left under the vibration region 21 of the piezoelectric thin film. Then the reflecting characteristic at the lower electrode 12 of the piezoelectric thin film 14 is uniformed to improve the sharpness Q of the piezoelectric thin film resonator 19.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a piezoelectric thin film resonator that can be used in the V HF and U HF frequency bands.

(Prior art) In general, so-called bulk wave resonators, which utilize the basic thickness vibration of a piezoelectric support substrate such as ceramic or crystal, have been developed due to limitations in the processing technology of the piezoelectric support substrate and mechanical strength limitations.
The thickness of the piezoelectric support substrate is limited to several IO μm, and therefore the usable resonance frequency is also limited to several tens of MHz.

Therefore, in recent years, configurations such as those shown in FIGS. 3 and 4 have been developed, which can utilize semiconductor manufacturing technology as is and operate in the VHF and tJHF ultra-high frequency bands.
So-called diaphragm type piezoelectric thin film resonators have been studied (for example, Japanese Patent Laid-Open No. 1-68706, Japanese Patent Laid-Open No. 60-687IO, and Japanese Patent Laid-Open No. 68-687).
168711)).

The piezoelectric thin film resonator mentioned above has a silicon oxide thin film 2 formed on one main surface of a Noricon crystal support substrate 1, and a first electrode 3, a piezoelectric thin film 4 of zinc oxide, and While the second electrodes 5 are sequentially formed, the silicon single crystal support substrate 1 is anisotropically etched into a diaphragm shape from the other main surface of the silicon single crystal support substrate 1 toward the piezoelectric thin film 4, and the piezoelectric thin film A recess 6 is formed to enable thickness vibration of 4.

By the way, the formation of the recess 6 by the above-mentioned anisotropic etching of the silicon single crystal support substrate 1 utilizes the difference in etching speed between the (100) plane and the (111) plane of the silicon single crystal support substrate l. When the silicon oxide thin film 2 reaches the silicon oxide thin film 2 from the silicon single crystal support substrate 1, this silicon oxide thin film 2 is also etched. For this reason, the silicon oxide thin film 2 in the recess 6 of the silicon single crystal support substrate l
There was a problem in that the thickness of the piezoelectric thin film resonator became non-uniform and the sharpness Q of the piezoelectric thin film resonator during resonance decreased.

(Objective of the Invention) An object of the present invention is to provide a method for manufacturing a piezoelectric β1V film resonator having high sharpness.

(Group of the invention) For this reason, the present invention forms a silicon oxide film on one main surface of a support substrate made of a sintered body of zinc oxide, while masking the other main surface of the support substrate, and The method is characterized in that the supporting substrate is etched from the other main surface toward the silicon oxide film using an acidic etching solution until etching is stopped at the oxide film. That is, in the present invention, when a support substrate made of a sintered body of zinc oxide is etched from one main surface thereof with an acidic etching solution, the silicon oxide film formed on one main surface of the support substrate stops etching. [It is designed to function as an E layer.]

(Effects of the Invention) According to the present invention, etching is stopped at the silicon oxide film formed on one main surface of the support substrate, so that the thickness of the piezoelectric thin film and the thickness of the silicon oxide film located under the vibrating portion are reduced. Since the piezoelectric thin film resonator is uniform, it is possible to manufacture a piezoelectric thin film resonator with high sharpness. Further, according to the present invention, since a support substrate of zinc oxide is used, a piezoelectric thin film resonator can be obtained which is cheaper than one using a single crystal support substrate of silicon. Since they are made of the same material, both have the same coefficient of thermal expansion, making it possible to obtain a piezoelectric thin film resonator with stable temperature characteristics. Furthermore, according to the present invention, since the silicon oxide film and the zinc oxide piezoelectric thin film have temperature coefficients of opposite signs,
Changes in the electrical characteristics of the piezoelectric thin film resonator due to temperature can be reduced to zero in an ideal state.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, zinc oxide (ZnO) was mixed with MnCO5 and v, 0. are added and wet-mixed so that manganese (Mn) and vanadium (V) are contained at 5 atomic % and 0.1 atomic %, respectively. This was pulverized in a wet mill and then sintered at about 1200° C. for 2 hours under pressure. The resulting sintered body (not shown) with a thickness of 10 mm and a size of 50 x 50 mm was cut into slices of 0.5 mm in diameter and mirror-polished with #8000 SiC, as shown in Figure 1 (a).
A flat support substrate 1 with a thickness of 0.3 mm as shown in
Create 1. - The reason why manganese is added to zinc oxide is to increase the insulation resistance of the support substrate 11, and the support substrate 11 has an insulation resistance of io'' ohm or more. Also, vanadium is added to zinc oxide. This is to improve the sinterability of zinc oxide and obtain a sintered body with high density.

As shown in FIG. 1(b), a silicon oxide film 10 is deposited on one main surface 11a of the support substrate 11 created in the manner described above using an RF magnetron sputtering method, with a thickness of approximately 60 mm.
Formed to a polish of 0.00 angstroms.

Next, on this silicon oxide film IO, as shown in FIG. 1(C), a lower electrode 12 of constant modulus steel composition consisting of iron (Fe), nickel (Ni) and chromium (Cr) is deposited using a vapor deposition method. is formed by a sputtering method. When forming the lower electrode 12 by this sputtering method, the silicon oxide film 10 is an oxide, and the lower electrode 12 to be formed
Since it is easily oxidized, it is preferable to carry out the process in a mixed gas of Ar:Ht=80+20. Note that this silicon oxide film 10 functions as an etching stop layer for the support substrate 11, as will be described later.

Next, as shown in FIG. 1(d), the lower electrode 12
A piezoelectric film 14 made of C-axis oriented zinc oxide crystal is formed on the silicon oxide film 10 by RF magnetron sputtering.

On the piezoelectric thin film 14, as shown in FIG. 1(e), an upper electrode 1 having the same constant elastic steel composition as the lower electrode 12 is placed.
5 is formed by a sputtering method.

Thereafter, in order to prevent the piezoelectric film @ 14 made of zinc oxide from absorbing moisture and deteriorating its characteristics, a photosensitive polyimide film is coated over the piezoelectric thin film 14 and the upper electrode 15, as shown in FIG. 1(f). A protective film is formed by spin coating and exposure to ultraviolet light.
form 6. This protective film 16 preferably has a small mass and a small thickness so that the original vibration of the piezoelectric thin film 14 is not inhibited.

The thickness of the piezoelectric thin film 14 is determined by t=N/f, where f (Hz) is the desired resonance frequency and N (Hz, mm) is the frequency constant of the composite vibration membrane stiffening. Ru.

On the other hand, as shown in FIG. 1(g), photosensitive polyimide is spin-coated on the other main surface 11b of the support substrate II.
A mask (7) is formed by exposure to ultraviolet light.

Thereafter, the supporting substrate 11 is immersed in an aqueous solution (50° C.) of 50% hydrochloric acid (I(ci2)) for 30 minutes to etch the supporting substrate 11 as shown in FIG. 1(h). It stops when it reaches the acid-resistant silicon oxide film 10 formed on one main surface 11a of the support substrate 11. As a result, the piezoelectric thin film 14 sandwiched between the lower electrode 12 and the upper electrode 15 is attached to the support substrate 11. Four parts 18 are formed that allow for thickness vibration.

After forming the recesses 18 in the support substrate 11 by etching as described above, in order to prevent the support substrate 11 made of zinc oxide from absorbing moisture, the recesses 18 are etched as shown in FIG. 1(i). A protective film 20 is formed from the inner wall surface of the substrate 18 to the other main surface 11b of the support substrate It. This protective film 20 can be made of the same photosensitive polyimide as the protective film I6.

Through the above steps, a piezoelectric thin film resonator 19 as shown in a plan view in FIG. 2 can be obtained. In this pressure@thin film resonator 19, the recess 18 of the support substrate 11 is formed below the vibration region 21 sandwiched between the lower electrode I2 and the upper electrode 15 of the piezoelectric thin film 14. The thickness can be vibrated. The lower electrode 12 and the upper electrode 15 are drawn out to the peripheral edge of the support substrate 11 by lead electrodes 12a and 15a, respectively.

As described above, if the piezoelectric thin film resonator 19 is manufactured by the steps shown in FIGS. 1(a) to 1(i), the silicon oxide film 10 formed under the lower electrode 12 of the piezoelectric thin film 14 has acid resistance. Therefore, this lower electrode 12 functions as a stop layer for etching of the supporting substrate 11 with hydrochloric acid. As a result, the etching is stopped with the thickness of the lower electrode 12 being uniform, and the reflection characteristics of the thickness vibration generated in the piezoelectric thin film 14 on the lower electrode 12 are made uniform, and the sharpness Q of the piezoelectric thin film resonator 19 is reduced. can be increased.

In the above example, as shown in FIG. 1(c), the lower electrode 12 was formed on one main surface 11a of the support substrate 11, and the lower electrode 12 was formed in the same manner as explained in FIG. After etching the support substrate 11 to form the recess 18, a piezoelectric thin film 14 is formed on one main surface 11a side of the support substrate II.
, the upper electrode 15, the protective film 16, etc. may be formed.

[Brief explanation of drawings]

Figure 1(a), Figure 1(b), Figure 1(c), Figure 1(
d), FIG. 1(e), FIG. 1(f), FIG. 1(g), FIG. 1(h), and FIG. 1(i) respectively show the manufacturing process of the piezoelectric thin film resonator according to the present invention. FIG. 2 is a plan view showing the electrode structure of a single piezoelectric thin film resonator manufactured by the method of the present invention, FIG. 3 is a perspective view of a piezoelectric thin film resonator manufactured by the conventional method, and FIG. FIG. 4 is a sectional view taken along line A-, A in FIG. 3; 11... Support substrate, lla, llb... Main surface,
10... Noricon oxide film, 12... Lower electrode,
13...Metal layer, 14...Piezoelectric thin film, +5...
・Top electrode, 16...protective film, +7...mask,
18... Concavity, 20... Protective film. Patent applicant Murata Manufacturing Co., Ltd. Agent Patent attorney Aoyama Aoyama and 2 others 1a 1b ib 1b +5 16 14 1b Se1b = 23 G Hemp 4 diagram

Claims (1)

[Claims] (1) A step of preparing a support substrate made of a sintered body of zinc oxide and forming a silicon oxide film on one main surface of the support substrate, a step of forming a lower electrode on this silicon oxide film, and a step of forming a lower electrode on the silicon oxide film. forming a piezoelectric thin film of zinc oxide on the silicon oxide film, forming an upper electrode on the piezoelectric thin film, and forming an acid-resistant protective film over the piezoelectric thin film and the upper electrode. masking the other main surface of the support substrate, and applying an acidic etching solution to the support substrate from the other main surface toward the silicon oxide film until etching stops at the silicon oxide film; A method of manufacturing a piezoelectric thin film resonator, comprising the steps of etching.