JPS58145213A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To realize broad band characteristics, by forming a unidirectional transducer from a 3-phase electrode and a lead electrode provided on a piezoelectric substrate. CONSTITUTION:Electrodes 14A, 14B, 14C having three phases of 0 deg., 120 deg. and 240 deg. are formed on the surface of an elastic substance substrate 13. Lead electrodes 15B, 15C provided on the surface of the substrate 13 are connected respectively to the electrodes 14B, 14C. A dielectric film 16 is formed on the surface of the substrate 13 so as to cover the electrodes 14B, 14C, and the lead electrode 15A provided along the surface of the film 16 is connected to the electrode 14A. Power feeding terminals 17A-17C to supply each phase signal are connected to the lead electrodes. Thus, the unidirectional transducer is formed and the broad band characteristics are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device equipped with a unidirectional transducer that makes it possible to achieve broadband characteristics.

A so-called surface acoustic wave, which propagates with concentrated energy along the flat surface of an elastic body, is superior in various respects to the conventionally used bulk waves, so it is possible to utilize this property. Surface acoustic wave devices are being applied to various electronic components including filters. 1st
The figure shows a filter as an example. 1 is a piezoelectric substrate, 2 is an input transducer consisting of a pair of interdigital electrodes 3A and 3B, and 4 is a pair of interdigital electrodes 5A.

Output transducer consisting of 5B, input terminal IN
The input signal is converted into a surface acoustic wave by the input transducer 2, propagates on the surface of the elastic substrate 1 as shown by the arrow, and reaches the output transducer 4, where it is converted into an electrical signal and output. The device is configured with a terminal OUT.

By the way, in a filter having two transducers 2.4 each including a pair of interdigital electrodes 3A, 3B and 5A, 5B'i, such as the surface wave device having the structure shown in FIG. 4 act to propagate surface waves in both left and right directions, so electro-mechanical conversion loss is unavoidable, and there is a drawback that the loss increases as a filter.

In order to eliminate this drawback, a so-called unidirectional transducer has been proposed, which is designed to propagate surface waves only in one direction on the surface of a piezoelectric substrate. Specific configurations of this unidirectional transducer include a method using a 12δ phase shifter as shown in FIG. 2, a method using a 90 phase shifter,
Furthermore, a method using a reflector as shown in FIG. 3 is known.

In FIG. 2, 6, 6A, and 6B are electrodes having a phase difference of 120 degrees, and 6 is constructed so that a gap 7 or an insulating film is interposed between it and another electrode 6A to generate surface waves. It works to propagate only in one direction (.

However, this method of using a phase shifter has the disadvantage that the manufacturing process is complicated because it is necessary to provide the crossing portions in the electrodes as described above.

, On the other hand, in FIG. 3, 8A and 8B are a power supply part and a reflection part provided to constitute a part of the interdigital electrode, both of which are regular electrodes, and 9 is the electrode 8.
A, common electrode for 8 BICs, ]0 is a signal source, 1] is a matching circuit, and 12 is a reactance circuit. In the above, the signal applied from the signal source 10 via the matching circuit 11 is converted into a surface acoustic wave from the power feeding section 8A and propagated in both left and right directions. At this time, the surface wave propagated to the left is reflected by the reflecting section 8B connected to the reactance circuit 12 and returned to the right, and the surface wave propagating to the right and the reflected surface wave are combined at the power feeding section 8A. will be held. As a result, when the center frequencies of surface waves are the same, the two waves overlap, but when the center frequencies deviate from each other, the waves act to cancel each other out, so the surface waves move in the opposite direction to the desired direction. It will spread. Therefore, there is a drawback that the propagation characteristics of the surface waves are limited to narrow band characteristics.

The present invention has been made in response to the above problems, and includes three leads to be connected to each of three electrodes having phases of 0'', 120' and 24δ formed on a piezoelectric substrate. To provide a surface acoustic wave device including a transducer in which one of the electrodes is provided along a surface of a dielectric film formed on the piezoelectric substrate.
This is the purpose.

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 4 and 5 are a schematic top view and a schematic sectional view showing a surface acoustic wave device according to an embodiment of the present invention.
, 12σ and 24δ.
A, 14B, and 14C are formed.

For electrodes 14B and 14C among the above three-phase electrodes,
In response to these, lead-out electrodes 15B and 15C provided on the surface of the elastic substrate 13 are connected, respectively.

In addition, an elastic substrate 1 is provided so as to cover the electrodes 14B and 14C.
A dielectric film 16 made of silicon dioxide or the like is formed on the third surface, and an extraction electrode 15A provided along the surface of the dielectric film 16 is connected to the upper ve electrode 14A.

Furthermore, for each of the above extraction electrodes 15A, 15B, +5c, a power supply terminal 1 for supplying each phase signal is connected.
7A, 17B, and 17C are wired by wire bonding or the like.

One method for manufacturing the above structure is to first attach a suitable metal to the entire surface of the elastic substrate 13 by vacuum evaporation or the like, and then remove unnecessary metal by photoetching to form the three-phase electrode. Of these, only the patterns of 1.4B, 14C and extraction electrodes 15B, 15C are left. Then each of these electrodes 1.413, 14C and 35B
, 15 C' includes a dielectric film 1 on the surface of the elastic substrate 13.
6 is uniformly attached. Thereafter, windows are formed in the necessary portions of the dielectric film 16 in order to configure the electrodes 14A on the elastic substrate 13 and the electrodes 14C and 14B with the same electrode width. Further, the surface of the dielectric film 16 and the dielectric 11
By forming a metal film on the surface of the elastic substrate 13 where 1[16 is not present, an electrode 14A is formed on the elastic substrate 13 and an extraction electrode 15A is formed along the surface of the dielectric film 16.

Next, appropriate metal wires are connected to the respective extraction electrodes 15A, 15B, and 15C by wire bonding to form power supply terminals 17'A, 17B, and 17C, thereby completing the structure shown in FIG. 4.

The three-phase electrode 14A of the transducer having the above configuration.

Power supply terminal 17 A for each of 1.1B and 14C,
By applying three-phase electrical signals via 17B, 17C, it can be operated as a unidirectional transducer over a wide operating frequency range.

Here, as the elastic substrate 13, lithium niobate (LiN
If silicon dioxide (5i02)'(1' is used as the dielectric film 16, the disadvantage is that the temperature coefficient becomes large in the case of a single lithium niobate substrate. The key point is that the temperature coefficient can be kept small by the combination of

Furthermore, this combination increases the electro-mechanical coupling coefficient compared to the case of the above-mentioned substrate alone, making it possible to reduce the number of electrode pairs that make up the transducer, increasing operating efficiency and achieving higher band characteristics. be able to.

As is clear from the above description, according to the present invention, three extraction electrodes to be connected to each of three electrodes having phases of 0, 120° and 240° formed on a piezoelectric substrate are One is to configure a unidirectional transducer so as to be provided along the surface of the dielectric film formed on the piezoelectric substrate, so that broadband characteristics can be achieved. Moreover, the three-phase signal electrode system can be easily formed by applying conventional techniques to the manufacturing method, which also reduces manufacturing costs.

Furthermore, the combination of lithium niobate and silicon dioxide allows for highly efficient operation, making it possible to achieve higher band characteristics.

The manufacturing method shown in the examples is just an example.
Any additions or changes to the manufacturing process can be made as necessary.

[Brief explanation of the drawing]

Figures 1 to 3 are all schematic diagrams showing conventional examples;
Both the figure and FIG. 5 are a schematic top view and a schematic cross-sectional view showing an embodiment of the present invention. 13... Elastic substrate, 14 A, 14 B,
14 C...3-phase electrode, +5 A, 15 B,
15 C... Extraction electrode, 16... Dielectric film,
+7 A, 17 B, 17 C...Power supply terminals. A

Claims (1)

[Claims] 1. Electrodes with phases of 0°, 12δ and 240 are formed on a piezoelectric substrate, and one of the three extraction electrodes to be connected to each of these three electrodes is A surface acoustic wave device characterized by comprising a transducer configured to be provided along a surface of a dielectric film formed on the piezoelectric substrate. 2. The surface acoustic wave device according to claim 1, wherein extraction electrodes for the remaining two electrodes are provided along the surface of the piezoelectric substrate. 3. The surface acoustic wave device according to claim 1 or 2, characterized in that a dielectric film is formed to cover the remaining two electrodes. 4. The surface acoustic wave device according to any one of claims 1 to 3, wherein the piezoelectric substrate is made of lithium niobate, and the dielectric film is made of silicon dioxide.