JPS5832528B2 - surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device having regular multi-peak frequency characteristics with high frequency accuracy and deep peak-to-peak attenuation.

Conventionally, a surface acoustic wave device having a structure as shown in FIG. 1 has been used as a surface acoustic wave device having regular multi-peak frequency characteristics.

As shown in FIG. 1, in a conventional surface acoustic wave device, an input electrode 2 consisting of an interdigital transducer is disposed on a piezoelectric substrate 1, and is placed at a position a predetermined distance from the input electrode 2. Output electrodes 3 and 4 made of interdigital transducers are arranged at a distance of xK from each other, and are electrically connected in parallel.

In the structure shown in FIG. 1, the mutual distance X causes a delay time of -X/VS between the output electrodes 3 and 4, where the surface acoustic wave velocity of the piezoelectric substrate 1 is v8.

Further, the phase difference φ between the output electrodes 3 and 4 becomes φ-2πf, where the frequency of the high frequency signal h applied to the input electrode 2 via the input bonding pads 5 and 5' is 1.

Therefore, the frequency f- at which the phase difference φ is a natural number n times 2π
At fn-n/τ, an output is generated between the output bonding pads 6 and 6', and at frequency 1=(n++)/τ, the electric signals generated between the output electrodes 3 and 4 have equal absolute values and opposite phases. Therefore, no output is generated between the output bonding pads 6 and 6'.

This passband frequency characteristic has a multi-peak characteristic with a frequency interval of 1f-1/τ and has a comb-shaped shape as shown in FIG.

In this way, in the conventionally used surface acoustic wave device shown in FIG. 1, the electrical signal generated at the output electrode 3 arrives with a delay of the distance Since the effective delay time τl is shorter than the delay time τ, a deviation from the set value occurs in the peak frequency ff1='n/τ' and the frequency interval Af=17τ'.

Conventionally, this deviation was not taken into consideration because the ratio of the speed of light in a vacuum to the speed of sound in a piezoelectric material is as large as 105.

However, as a practical matter, the electrical signal from the output electrode 3 propagates through the piezoelectric material and reaches the output electrode 4, and since the dielectric constant of this piezoelectric material is large, the electromagnetic wave velocity in the piezoelectric material v-
The value of 1//71 becomes smaller.

Therefore, the ratio between the electromagnetic wave velocity and the sound velocity becomes small, and the contribution of the delay time of the electric signal cannot be ignored.

For example, LiNbO3 has a dielectric constant of 5148, PZ
At T, εr is -1,00 to 1.000, the ratio of electromagnetic wave velocity to sound velocity is about 104, and the frequency accuracy is 4
The digits will change.

This degree of variation in frequency accuracy poses a problem when the surface acoustic wave device is applied to a frequency analyzer or the like.

Furthermore, even if the dielectric constant of the piezoelectric material is small, a similar problem will occur if strict frequency accuracy is required.

Furthermore, in the conventionally used surface acoustic wave device shown in FIG. 1, the attenuation caused by the high frequency line during the propagation of the electrical signal through the wiring electrode cannot be ignored.

For this reason, the output signal from the output electrode 3 reaches the attenuated state, and when combined with the output signal from the output electrode 4,
The amount of attenuation between the peaks shown in Figure 2 cannot be obtained sufficiently,
This causes a problem in the application of the conventionally used surface acoustic wave device shown in FIG.

On the other hand, in conventional surface acoustic wave devices, when the output electrodes 3 and 4 are separately connected to the terminals of the external mounting package by means of wire bonding, ding, etc., the wire length is completely Problems such as an increase in the number of filters (which cannot be set equal due to wire bonding) and mutual interference of signals due to the formation of a large number of filters on the same chip are unavoidable.

The surface acoustic wave device according to the present invention solves the problems of these conventional devices and has regular multi-peak frequency characteristics with high frequency accuracy and deep peak-to-peak attenuation.

Hereinafter, the surface acoustic wave device according to the present invention will be described in detail based on examples thereof.

FIG. 3 is a diagram showing the configuration of the first embodiment of the surface acoustic wave device according to the present invention.

As shown, in this first embodiment, a manual interdigital transducer 14 is disposed near one end of a piezoelectric substrate 13, and a manual bonding pad 21.
An input terminal 11°11' is installed via 21'.

On the other hand, output interdigital transducers 15 and 16 are disposed near the other end of the piezoelectric substrate 13, and the output terminals 12 and 16 are connected to the output terminals 15 and 16 through output bonding pads 22 and 22'.
, 12' are installed.

Further, 17 and 18 are wiring electrodes, and 19 is a shield electrode disposed between the human-powered interdigital transducer 14 and the output interdigital transducer 15.

In this case, in order to realize a predetermined frequency interval if, the output interdigital transformer users 15 and 16
The distance X between them is set to x=v8/If, where the surface acoustic wave velocity of the piezoelectric substrate is V8.

Further, the output bonding pads 22, 22' are arranged at an intermediate position x/2 from the output interdigital transducers 15 and 16.

With this configuration, the electrical signals propagated from the output interdigital transducers 15 and 16 reach the output bonding pad 22 with equal delay time and equal attenuation.

Therefore, in the surface wave device according to the present invention, it is easy to ignore the influence of the electrical delay time on the frequency interval IJf, and the peak-to-peak attenuation based on the difference from the electrical attenuation is shallow. There is no possibility that it will happen.

FIG. 4 is a diagram showing the configuration of a second embodiment of the surface acoustic wave device according to the present invention.

In this second embodiment, the position setting conditions of the present invention are given only to the output bonding pad 22 on the non-grounded side of the output electrode.

Therefore, the position of the output bonding pad 22' is
As shown in the figure, it is arranged below the output interdigital transducer 16.

Moreover, FIG. 5 shows the third surface acoustic wave device according to the present invention.
It is a figure showing the composition of an example.

In this third embodiment, as shown in the figure, the output bonding pad 22 on the non-grounded side of the output electrode is connected to the terminal end of the wiring electrode 20 drawn out from the midpoint of the output interdigital transducers 15 and 16. It is arranged.

These surface acoustic wave devices having the structures shown in the second and third embodiments are suitable for mounting a plurality of devices on one piezoelectric substrate; This structure has the advantage that the wire bonding wires do not come into contact with each other or that signals do not interfere with each other, and that the wire bonding process can be easily performed and the manufacturing yield is improved.

As explained in detail above, according to the present invention, it is possible to provide a surface acoustic wave device with high frequency accuracy of 5 digits or more, deep and regular multi-peak frequency characteristics with deep peak-to-peak attenuation, and with strict control over connection external circuits. This eliminates the need for specific specification conditions, making it easier to use, expanding the range of applications, and simplifying manufacturing technology.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventionally used surface acoustic wave device, FIG. 2 is a diagram showing the characteristics of a conventionally used surface acoustic wave device, and FIG. 3 is a surface acoustic wave device according to the present invention. Figures 4 and 5 showing the configuration of the first embodiment of
The figure is a diagram showing the configuration of second and third embodiments of the surface acoustic wave device according to the present invention. Explanation of symbols: 1...Piezoelectric substrate, 2...
・Input electrodes, 3, 4... Output electrodes, 5, 5'
...Input bonding pad, 6,6'...
・・Output bonding pad, 11, 11'・・・・
...Input terminal, 12, 12'...Output terminal,
13... Piezoelectric substrate, 14... Input interdigital transducer, 15, 16...
...Output interdigital transducer, 17
．． 18, 20... Wiring electrode, 19...
Shield electrode, 21, 21'... Input bonding pad, 22, 22'... Output bonding pad.

Claims (1)

[Claims] 1 a piezoelectric substrate, a first transducer disposed on the piezoelectric substrate, second and third transducers disposed on the piezoelectric substrate at different distances from the first transducer, and a second transducer disposed on the piezoelectric substrate; and third
A surface acoustic wave device comprising wiring electrodes connecting transducers in parallel on a piezoelectric substrate, characterized in that the bonding pad of each wiring electrode is provided at a position equidistant from the second and third transducers. surface acoustic wave device.