JPH0583084A - Surface acoustic wave filter - Google Patents

Abstract

(57) [Abstract] [Purpose] To form a monolithic filter by forming two surface acoustic wave resonators on one piezoelectric substrate. [Structure] Two surface acoustic wave resonators, each of which is composed of a interdigital transducer 3 and grating reflectors 4 on both sides thereof, are provided on the surface of a piezoelectric substrate 7 so that the propagation directions of surface waves are parallel to each other, and are electrically connected in series. Connect the intermediate connection point 10 and the terminal 8 ',
It is characterized in that a comb-shaped electrode 5 is provided between 9'and 9'as a coupling capacitor in a direction perpendicular to the propagation direction of the surface wave.

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 filter used in communication equipment.

[0002]

2. Description of the Related Art FIG. 2 is a diagram of a conventional filter configuration using a bulk wave oscillator such as a crystal oscillator. Figure 2 (A)
Is a discrete type configuration in which two oscillators 1 such as independent crystal oscillators are connected in cascade, and a coupling capacitor 2 is provided at an intermediate connection point 10 to form a filter. Further, FIG. 2B shows a monolithic type configuration, in which a single piezoelectric material such as a piezoelectric ceramic is provided with electrodes for forming two bulk wave oscillators in close proximity to each other and a monolithic filter 11 utilizing acoustic coupling is provided. is there.

[0003]

However, the discrete filter shown in FIG. 2 (A) is assembled by sealing each transducer in an independent package or by fixing the two transducers separately. However, it is generally configured to seal the whole. Therefore, it becomes a big obstacle in downsizing the filter. Further, the frequency depends on the thickness of the vibrator, and as the frequency becomes higher, the thickness becomes thinner, and the processing accuracy becomes a problem.

Further, the monolithic filter shown in FIG. 2B can cope with miniaturization to some extent because two oscillators are formed in one chip. However, as with the discrete type filter, there is a limit in increasing the frequency. Furthermore, since the discrete type and monolithic type filters use both front and back surfaces of the piezoelectric plate,
At the time of packaging, there is a drawback that a fixing method is limited because it is necessary to provide a gap between the front and back sides and the case. It is an object of the present invention to provide a surface acoustic wave filter that solves the problems of the conventional technology for miniaturization and high frequency, and eliminates restrictions on the mounting surface.

[0005]

According to the surface acoustic wave filter of the present invention, the surface of the piezoelectric substrate 1 is propagated through the surface of the piezoelectric substrate 1 through the interdigital transducers of the two one-terminal surface acoustic wave resonators and the electrodes of the grating reflector. Are arranged in parallel along the direction, the two resonators are electrically connected in cascade, and the interdigital transducer (IDT) of the two resonators is further connected to the connection point.
It is characterized in that a comb-shaped capacitor comb-shaped electrode, which is arranged so as to be at a right angle to the nsducer), is connected to form a filter. Hereinafter, the present invention will be described in detail with reference to the drawings.

[0006]

1 is a block diagram showing an embodiment of a surface acoustic wave filter according to the present invention. In the figure, there are two energy trapping surface acoustic wave resonators in which the interdigital transducer 3 and the grating reflectors 4 are arranged on both sides of the interdigital transducer 3 on the surface of the piezoelectric substrate 7 in the propagation direction of the surface wave. Are arranged in parallel along each other, and the I of the two one-terminal pair resonators are arranged.
The DTs 3 are electrically connected in series to form an input terminal 8, an output terminal 9 and a connection point 10. Further, the interdigital transducer 5 for the coupling capacitor is connected to the connection point 10 and the terminals 8'and 9 '.
And the interdigital transducers 3 of the two surface acoustic wave resonators at right angles to each other. And the terminals 8 and 8'become an input terminal pair,
The terminals 9 and 9'form an output terminal pair.

Comparing the structure of the present invention of FIG. 1 with the conventional structure of FIG. 2A, the vibrator 1 and the capacitor 2 in the circuit structure of FIG. Since the surface acoustic wave resonator including the grating reflector 4 and the interdigital transducer 5 for capacitors respectively correspond to the filter theory of the configuration of the present invention, the theory of the conventional configuration can be applied as it is.

However, the feature of the present invention is that it has a merit that two resonators and a coupling capacitor can be formed as one chip only on one surface of the piezoelectric substrate 7, so that the size of the chip can be greatly reduced. Since only one side is used, there is flexibility in packaging. The two surface acoustic wave resonators and the interdigital transducer-shaped electrode 5 for capacitors can be formed in the same step at the same time by a photolithography technique, and since their dimensions can correspond to the submicron region, they can be put to practical use up to the high frequency region. You can

The interdigital transducer 5 in FIG. 1 is used as a capacitor, but the interdigital transducer 5 also excites surface waves due to its nature. However, in the electrode arrangement of FIG. 1, the surface wave propagation direction (opening direction) of the interdigital transducer 5 is the surface wave propagation direction of the surface acoustic wave resonator, that is, the direction in which the surface wave is excited most efficiently in the piezoelectric substrate 7. Almost no surface wave is excited because it is perpendicular to the surface wave. Also,
Even if a weak surface wave is excited, since it is arranged outside the grating reflector 4 of the surface acoustic wave resonator, it is not electrically coupled to the resonator. When the interdigital transducer electrode 5 for a capacitor may excite a surface wave, a sound absorbing material 6 such as an insulating epoxy resin is formed on the surface thereof.
Can be treated completely as a capacitor only by applying. Further, since the interdigital electrodes 5 are used as capacitors, it goes without saying that the electrode pitch can be set arbitrarily.

[0010]

As described above in detail, by implementing the present invention, the size can be greatly reduced and the degree of freedom in packaging can be increased. Further, it is possible to significantly increase the frequency.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention.

FIG. 2 is a diagram of a conventional filter configuration example.

[Explanation of symbols]

 1 Piezoelectric vibrator 2 Capacitor 3 Interdigital transducer (IDT) 4 Grating reflector 5 Interdigital electrode for capacitor 6 Insulating resin 7 Piezoelectric substrate 8,8 'Input terminal pair 9,9' Output terminal pair 10 Connection point 11 Monolithic Piezoelectric filter

Claims (1)

[Claims] 1. A piezoelectric substrate, a interdigital transducer on the piezoelectric substrate, and grating reflectors on both sides of the interdigital transducer, which are arranged so that the surface acoustic wave propagation directions are parallel to each other. Two surface acoustic wave resonators connected in series, and one terminal is connected to an intermediate connection point of the two surface acoustic wave resonators, and the surface is provided outside the one grating reflector of the two surface acoustic wave resonators. A comb-shaped interdigital transducer electrode arranged so that the wave propagation direction is perpendicular to the surface acoustic wave propagation directions of the two surface acoustic wave resonators, and the other of the comb-shaped interdigital transducer electrodes. Terminal and the above 2
A surface acoustic wave filter configured to form an input terminal pair and an output terminal pair with the input side terminal and the output side terminal of one surface acoustic wave resonator.