JPH01231412A - Method for adjusting frequency characteristic of surface acoustic wave device - Google Patents

Abstract

PURPOSE:To eliminate the forming of a protection film onto a pattern electrode and to prevent the reduction in the propagation efficiency of a surface acoustic wave attended with the frequency adjustment by using a pattern electrode as a mask and applying sputter etching to the surface of a piezoelectric substrate so as to displace the frequency characteristic of a surface acoustic wave device toward a low frequency. CONSTITUTION:The frequency characteristic of the surface acoustic wave device 24 is shifted toward a low frequency by using a pattern electrode 27 as a mask so as to apply sputter etching to the surface of the piezoelectric substrate 25. Since the side etching of the pattern electrode 27 itself is not implemented substantially, the unarrangement of the electrode finger width of the pattern electrode and the ununiformity of the line width of each electrode finger are prevented. Moreover, the adjustment of the etching time and the minute adjustment of the etching speed are facilitated and water rinsing as the post-processing is not required, then the succeeding stabilizing processing is executed in a short time. Thus, the forming process of the protection film onto the pattern electrode is not required and the deterioration in the propagation efficiency of a surface acoustic wave attended with the frequency adjustment is prevented.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a method for adjusting the frequency characteristics of a surface acoustic wave device including a piezoelectric substrate and a patterned electrode formed on the surface thereof and having a shape corresponding to a desired frequency characteristic. Adjustment work and subsequent post-processing can be carried out easily in a short time, and moreover, it eliminates the problem of retaining adhesive on the pattern electrode, which is a disadvantage of the conventional dry etching method for pattern electrodes. The purpose of the present invention is to provide a method for adjusting the frequency characteristics of a SAW device that can eliminate the need for a film formation process and prevent a decrease in the propagation efficiency of surface acoustic waves due to frequency adjustment. By sputter etching the surface acoustic wave device, the frequency characteristics of the surface acoustic wave device are shifted to the lower frequency side.

[Industrial application field]

The present invention relates to a method for adjusting frequency characteristics of a surface acoustic wave device (hereinafter referred to as a SAW device), and more specifically, the present invention relates to a method for adjusting frequency characteristics of a surface acoustic wave device (hereinafter referred to as a SAW device), and more specifically, the present invention relates to a method of adjusting frequency characteristics of a surface acoustic wave device (hereinafter referred to as a SAW device), and more specifically, the present invention relates to a method of adjusting frequency characteristics of a surface acoustic wave device (hereinafter referred to as a SAW device). This invention relates to a method for adjusting frequency characteristics of surface acoustic wave devices.

-M, SAW devices used as filters and oscillators for V HF generation or U HF generation are made of a conductor film such as an aluminum (AI) film that serves as an electrode on a piezoelectric substrate made of silicon dioxide (SiO2), etc. After forming by vapor deposition,
It is made by etching a conductive film using photolithography or the like to form a patterned electrode according to desired frequency characteristics on a piezoelectric substrate. However, if multiple sets of pattern electrodes are formed on a common piezoelectric substrate and then the piezoelectric substrate is cut to create multiple SAW devices at the same time, variations in processing accuracy tend to occur in the pattern electrodes. , it is necessary to fine-tune the frequency characteristics of individual SAW devices.

[Prior Art and Problems to be Solved by the Invention] 'Conventionally, as a method for adjusting the frequency characteristics of a SAW device, a method has been used in which a pattern electrode on a piezoelectric substrate is etched by wet etching or dry etching.

In the case of wet etching, the piezoelectric substrate on which patterned electrodes are formed is immersed in a weakly alkaline solution such as a diluted sodium hydroxide (NaOH) solution or a weakly acidic solution such as a diluted phosphoric acid solution to etch the electrode pattern. The thickness of the electrode pattern is adjusted by adjusting the dipping time.

However, in this adjustment method using wet etching, it is difficult to adjust the immersion time because the etching rate varies greatly due to variations in the concentration and temperature of the etching solution and deterioration due to the use of the etching solution.

In particular, when a piezoelectric substrate having a two-layer pattern electrode is immersed in an etching solution, the etching rate is slow until the stable alumina (Aj'zO,l) film on the surface of the Al film is destroyed by the etching solution. , and Afiffi03
After the film is destroyed and the pure Al film is exposed, etching proceeds rapidly and the amount of etching is not proportional to the immersion time, making it difficult to adjust the immersion time.

Further, since cleaning such as water washing is required after the etching process, the number of work steps increases. Moreover, depending on the degree of cleaning, S
Since the adhesion state of impurities to the surface of the AW device is different, the stabilization treatment in the post-process takes time.

Furthermore, etching with an etching solution reduces not only the thickness of the patterned electrode but also the pattern width, which deteriorates the propagation characteristics of surface acoustic waves.

On the other hand, a method for adjusting the frequency characteristics of a SAW device by dry etching patterned electrodes is disclosed in Japanese Patent Application Laid-Open No. 154814/1983 by the present applicant. In this method, a protective film made of Sin, Altos, etc. is formed on a patterned electrode formed on a piezoelectric substrate,
By dry etching (side etching) the pattern electrode using this protective film as a mask, the width of the pattern electrode is adjusted.

Although this dry etching method can overcome the drawbacks of the wet etching method described above, it requires a step of forming a protective film on the patterned electrodes, resulting in an increase in the number of work steps. In addition, due to variations in etching, the width of the electrode fingers becomes uneven, or the width of each electrode finger becomes uneven, which causes diffuse reflection of surface acoustic waves and reduces the propagation efficiency of surface acoustic waves. arise.

Therefore, the present invention allows frequency characteristic adjustment work and subsequent post-processing to be easily performed in a short time, and also eliminates the disadvantage of forming a protective film on the pattern electrode, which is a disadvantage of the conventional dry etching method for pattern electrodes. It is an object of the present invention to provide a method for adjusting the frequency characteristics of a SAW device that can eliminate the need for a process and prevent a decrease in the propagation efficiency of surface acoustic waves due to frequency adjustment.

[Means to solve the problem]

A method for adjusting the frequency characteristics of a SAW device according to the present invention includes using a piezoelectric substrate as a mask using a pattern electrode of a surface acoustic wave device comprising a piezoelectric substrate and a pattern electrode formed on the surface thereof and having a shape corresponding to a desired frequency characteristic. By sputter etching the surface of the surface acoustic wave device, the frequency behavior of the surface acoustic wave device is shifted to the lower frequency side.

[For production]

According to the method for adjusting the frequency characteristics of a SAW device having the above configuration, there is no need to form a protective film as a mask on the pattern electrode in the previous process, so it requires less work than the conventional dry etching method in which the pattern electrode is side-etched. Man-hours can be reduced. Furthermore, since side etching of the pattern electrode itself is not substantially performed, it is possible to prevent a decrease in surface acoustic wave propagation efficiency due to uneven electrode finger widths of the pattern electrode or non-uniform line width of each electrode finger.

Of course, compared to the conventional wet etching method, it is easier to adjust the etching time and finely adjust the etching speed, and since rinsing with water is not required as a post-treatment, the subsequent stabilization treatment can be carried out in a short time. There are advantages such as being able to

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

Fig. 1 shows the frequency characteristics of a SAW device adjusted by the method of the present invention, and Fig. 2 shows the configuration of a frequency characteristic adjusting device and a frequency measuring device for carrying out the method of the present invention. be. First, the configurations of the frequency characteristic adjustment device and frequency measurement device will be explained with reference to FIG.

In Fig. 2, 11 is a vacuum chamber, 12, 13 is a vacuum pump, 14 is a vacuum adjustment valve, and 15.16.
are gas introduction valves, 17 is a grounded lower electrode, 18 is an upper electrode connected to an RF power supply 20 via a radio frequency (RF) matching box 19, and 21 is connected to the upper electrode 18 via a seal ring 22. The held product holder 24 is connected to the product holder 2 through the seal ring 23.
This is a SAW device held at 1.

As shown in FIG. 1, the SΔW device 24 is, for example, S
iO□Piezoelectricity made of single crystal)! i, a plate 25, a metal base 26 supporting this piezoelectric substrate 25, and a comb-shaped electrode (for example, made of an A1 film) formed on the piezoelectric substrate 24;
A pattern electrode 27 such as an IDT electrode) is provided. This pattern electrode 27 is formed by a well-known method so as to obtain desired frequency characteristics.

Referring again to FIG. 2, reference numerals 28 and 29 indicate one plane pressure contact type contact connected to the pattern electrode 27 of the SAW device 24, and both contacts 28 and 29 are fixed to the housing 30.

The other flat pressure contact 32, 33 connected to the frequency measuring device 31 can be connected and disconnected to the contact 28, 29 by a contact drive device 34.

Next, a method for adjusting the frequency characteristics of a SAW device using the frequency characteristic adjusting device and frequency measuring device described above will be described.

As shown in FIG. 2, the SAW device 24 is attached to the opening of the upper electrode 18 while being held in the product holder 20. Next, after evacuating the inside of the vacuum chamber 12 using the vacuum pump 12.13, the gas introduction valve 15.1
A suitable amount of gas is supplied to the vacuum chamber 1 through one or both of the
The inside of the vacuum chamber 12 is maintained at a desired degree of vacuum by adjusting the vacuum degree adjusting valve 14.

Next, the RF power supply device 20 is activated to apply an RF lightning voltage between the upper electrode 18 and the lower electrode 17.

At this time, set the power of the RF power supply device 20 appropriately,
By synchronizing with the RF matching box 19, sputtering can be performed efficiently. During this time, contacts 32, 33 are separated from contacts 28, 29 by drive device 34, so that the RF
This prevents damage to the measuring device 31 due to power.

Sputter etching of the piezoelectric substrate 25 is performed within the vacuum chamber 12 by applying an RF lightning voltage.

FIG. 1 shows a state in which the surface of the piezoelectric substrate 25 has been scraped off by sputter etching. Piezoelectric substrate 26
As a result of this sputter etching, the film thickness of the pattern electrode 25 of the SAW device 24 is artificially increased, so that the frequency characteristics of the SAW device 24 are shifted to the lower frequency side.

In the present invention, since the surface of the piezoelectric substrate 25 is sputter etched using the pattern electrode 27 as a mask,
The gases introduced into the vacuum chamber 12 are argon (Ar) and nitrogen (N2).

It is necessary to use an inert gas such as helium (He).

Only inert gas may be introduced into the vacuum chamber 12, but especially when Ar gas is used, the pattern electrode (AI film) 27 as a mask is also subject to some sputtering action, so this should be suppressed. Therefore, it is preferable to introduce oxygen into the vacuum chamber 12 together with an inert gas.

0, stable Altos is added to the surface of the AI film.
A film is formed to protect Al1p14.

Furthermore, since the surface of the A1 film is protected by the stable Altos film, when the SAW device 24 is exposed to the air after adjusting the frequency characteristics, it is possible to prevent fluctuations in the frequency characteristics due to oxidation of the Altos film.

After applying the RF lightning voltage for a given period of time, the RF power supply 20 is de-energized and the contact 32.3 is then activated by the driver 34.
3 are connected to the contacts 28 and 29, and the frequency characteristics of the SAW device 24 after the sputter etching process are measured by the measuring device 31. During this time, the gas atmosphere within the vacuum chamber 12 can be kept the same as during the sputtering process.

When the frequency characteristic of the W device 24 is higher than the target value, the RF lightning voltage is applied again to perform sputter etching of the piezoelectric substrate 25.

According to the adjustment method described above, RF power, gas pressure, RF
The etching speed can be finely adjusted by adjusting the voltage application time, etc., and the adjustment work and measurement work can be easily automated.

FIG. 3 shows a modification of the frequency characteristic adjustment device. In this figure, the same components as those of the adjusting device of FIG. 2 described above are given the same reference numerals. In the adjustment device shown in FIG. 3, the lower electrode 17 is connected to the RF power supply device 20 via the RF matching box 19, and the upper electrode 18 is grounded. Also, SA
Since the product holder 21 supporting the W device 24 is provided on the lower electrode 17, there is no need for a sealing structure between the product holder 21 and the lower electrode 17, and the structure is simplified. In the case of this adjustment device, by fixing the container having the upper electrode 18 and moving the lower electrode 17 up and down using the lifting device, it is possible to easily take out the SAW device 24 and mount it on the product holder 21. can.

Even when the adjustment device shown in FIG. 3 is used, the frequency characteristics of the SAW device can be adjusted and measured using the same adjustment method and frequency measurement method described above.

FIGS. 4 and 5 show the RF power application time (min.
) and the amount of change Δfo in the frequency characteristics of the SAW device
(MH2). SA used
The W device uses SiO□ single crystal as the piezoelectric substrate, and I' D T T1. An AN film (film thickness of approximately 300 mm) was used as the polar film. In addition, the gas atmosphere during sputter etching is set to have the flow rates of A and OX at the same ratio.
The degree of vacuum in the vacuum container is set to 0. I Torr.

From Figure 4, the applied RF power is 30W.

It can be seen that when the power is kept constant at 60 W, 90 W, etc., the excitation frequency of the SAW device changes (decreases) approximately proportionally to the application time of the RF power. In FIG. 4, two characteristic curves are shown when the RF power is 60 W, but this is because there were variations in the patterned electrodes formed in the SAW device.

In FIG. 5, the symbol Pl of the three characteristic curves.

P,,P! At the time indicated by , the RF power changes from 60W to 30W.
has been switched to. As can be seen from Figure 5, by switching the RF power midway, it is possible to slow down the rate of change (decrease) in the frequency of the SAW device (i.e., the etching rate), making it easier to fine-tune the frequency characteristics. .

According to the above-described frequency characteristic adjustment method according to the present invention, the adjustment that required approximately 45 minutes using the conventional wet etching method can now be performed in approximately 10 minutes. In addition, with the conventional wet etching method, it took about 48 hours to perform the stabilization process after adjusting the frequency characteristics, but with the SAW device whose frequency characteristics were adjusted by the method of the present invention, the subsequent stabilization process took about 48 hours. It can be completed in 20 hours.

〔Effect of the invention〕

As is clear from the above explanation, according to the method of the present invention,
By sputter etching the surface of the piezoelectric substrate using the patterned electrode formed on the piezoelectric substrate of the SAW device as a mask, the frequency characteristics of the SAW device are shifted to the lower frequency side, making it easier to perform etching than the conventional wet etching method. In comparison, frequency characteristic adjustment work and subsequent post-processing can be significantly shortened and facilitated. Moreover, since sputtering is performed using the pattern electrode as a mask, it is possible to eliminate the step of forming a protective film on the pattern electrode, which is a disadvantage of the conventional dry etching method for pattern electrodes, and to improve the propagation efficiency of surface acoustic waves due to frequency adjustment. This has the effect of preventing a decrease in .

[Brief explanation of the drawing]

Figure 1 shows a SAW whose frequency characteristics have been adjusted using the method of the present invention.
A cross-sectional view of the main parts of the device; FIG. 2 is a partial cross-sectional side view of a frequency characteristic adjusting device and a frequency measuring device for carrying out the method of the present invention; and FIG. 3 is a side view of a frequency characteristic adjusting device for carrying out the method of the present invention. FIGS. 4 and 5 are graphs showing the relationship between the RF power application time and the frequency change amount of the SAW device according to the method of the present invention, respectively. In the figure, 24 represents a SAW device, 25 represents a piezoelectric substrate, and 27 represents a pattern electrode.

Claims (1)

[Claims] 1. A method for adjusting frequency characteristics of a surface acoustic wave device (24) comprising a piezoelectric substrate (25) and a patterned electrode (27) formed on the surface thereof and having a shape according to desired frequency characteristics, the method comprising: Using the piezoelectric substrate (27) as a mask,
1. A method for adjusting frequency characteristics of a surface acoustic wave device, comprising displacing the frequency characteristics of the surface acoustic wave device (24) to a lower frequency side by sputter etching the surface of the surface acoustic wave device (24).