GB2247776A

GB2247776A - Piezo electric resonator

Info

Publication number: GB2247776A
Application number: GB9019564A
Authority: GB
Inventors: Osamu Ishii
Original assignee: Toyo Communication Equipment Co Ltd
Current assignee: Toyo Communication Equipment Co Ltd
Priority date: 1990-09-07
Filing date: 1990-09-07
Publication date: 1992-03-11
Also published as: DE4028546A1; FR2666705A1; GB9019564D0

Abstract

A piezo-electric resonator comprises a piezo-electric plate (11) on one surface of which a recess (12) is formed by an etching process in order to obtain a thick ring portion (15) surrounding a thin vibrating portion (18). On the entire surface of the side having the recess, an overall electrode (14) is formed by a maskless evaporation process, while a partial electrode (16a) is formed on the part of the opposite surface corresponding to the vibrating portion with a lead pattern (16b) extending from the partial electrode onto the ring portion. With this construction, a good electrical connection of the overall electrode at a step portion (8) at the periphery of the recess is ensured. <IMAGE>

Description

1 PIEZO-ELECTRIC RESONATOR The present invention relates to a

piezo-electric resonator which resonates at a fundamental vibration mode preferably of more than 50 MHz.

As a piezo-electric resonator for outputting a stable and high fundamental resonant frequency, there is known a quartz resonator of a thickness shear mode in which an AT cut plate is formed thinly. With the prior art process, it is not possible to make the AT cut plate thinner than about 40 M, and therefore the highest resonant frequency of the quartz resonator reaches only about 40 MHz. A quartz resonator of a SAW (surface acoustic wave) resonator is able to obtain a high frequency of about 1 GHz. However, the SAW resonator has a temperature characteristic which is inferior to that of the AT cut quartz resonator.

In order to obtain a high frequency resonator with the temperature characteristic of the AT cut quartz resonator, resonators such as those shown in Figures la, lb and Figures 2a, 2b have been studied. In the prior art resonator shown in Figures la and lb, recesses 2 are excavated at centre portions of both surfaces of a quartz crystal plate 1 by dry etching or wet etching in order to obtain a thin vibrating portion 3. on both sides of the crystal plate 1, electrode patterns 5, 6 having shapes as shown in Figure la are formed by metal evaporation processes or the like.

In the other prior art resonator shown in Figure 2a and 2b, a recess 2 is formed at a centre portion of only one surface of a quartz crystal plate 1, with the rest of the construction being the same as for the resonator shown in Figures la and lb.

In those prior arts, the electrode patterns 5, 6 include exciting electrodes 5a, 6a on the centre portion of the vibrating portion 3 and lead patterns 5b, 6b extending from the exciting electrodes 5a. 6a to connection pads on a thick ring portion 7 surrounding the vibrating portion 3.

4 1 2 However,, since the lead patterns 5b and/or 6b, which extend f rom the exciting electrodes 5a, 6a to the pads on the thick ring portion 7 through step portion(s) 8 between the thin vibrating portion 3 and the thick ring portion 7, have. thin widths, the forming of the lead patterns 5b, 6b at the step portions 8 is not carried out smoothly during the metal evaporation process. Thus, a poor connection of the lead patterns 5b, 6b occurs sometimes at the step portion (s) 8. As a result, the ef f iciency of the prior art resonators was not very high.

In accordance with the invention, a piezo-electric resonator comprises a plate of piezo-electric material having first and second surfaces, with a thick ring portion surrounding a thin vibrating portion which has been formed by means of excavating a recess on the first surface of the plate; an overall electrode formed on substantially all of the first surface; and a partial electrode pattern formed on the second surface, the partial electrode pattern including an exciting electrode on the thin vibrating portion and a lead pattern extending from the exciting electrode onto the edge portion.

An AT cut quartz resonator in accordance with the invention may provide a fundamental frequency higher than 50 MHz while guaranteeing a good electrical connection of the electrode at the step portion between the recess and thicker ring portion surrounding the recess.

The invention also includes a piezo-electric f ilter element comprising a plate of piezo-electric material having first and second surfaces with a thick ring portion surrounding a thin vibrating portion which has been formed by means of excavating a recess on the first surface of the plate; an overall electrode formed on substantially all of the first surface; and a plurality of electrodes arranged adjacent to each other on the thin vibrating portion on the second surface with a pair of lead patterns extending from the electrodes onto the ring portion.

A 1 1 3 In the accompanying drawings:

Figure la is a plan view of a prior art quartz resonator;

Figure 1b is a sectional view taken on a line C-C in 5 Figure la; Figure 2a is a plan view of another prior art quartz resonator;

Figure 2b is a sectional view taken on a line D-D in Figure 2a; Figure 3a is a plan view of an embodiment of a piezoelectric resonator according to the present invention; Figure 3b is a sectional view taken on a line A-A in Figure 3a; Figures 4a and 4b are vibration energy distribution charts of the prior 'art resonator and the resonator according to the present invention, respectively; Figure 5a is a plan view of another embodiment of a piezo-electric resonator according to the present invention; and, 20 Figure 5b is a sectional view taken on a line B-B in Figure 5a. As shown in Figures 3a and 3b, the quartz resonator includes a quartz crystal plate 11 on one surface of which a recess 12 is excavated by dry etching or wet etching in order to obtain a thin vibrating portion 18. on all of the surface having the recess 12, an electrode 14 is formed by an evaporation process. On the opposite plane surface an electrode pattern 16 substantially the same as the prior art electrode pattern 5 shown in Figure 2a, and consisting of a partial exciting electrode 16a, and a lead pattern 16b leading to a connection pad 16c on the ring 15 near to the periphery thereof, is formed by a photo-lithographic process or the like. With this construction in which the overall electrode 14 is formed on the entire surface of the side having the recess 12, an electrical connection over a step 8 between an exciting electrode 14a on the thin vibrating portion 18 and an electrical connection pad 14b 1 4 on a thick ring portion 15 surrounding the recess 12 is guaranteed.

Figures 4a and 4b are vibration energy distribution charts of the prior art resonator shown in Figures la, 1b,

2a and 2b and the resonator according to the present invention shown in Figures 3a and 3b, respectively.

As shown in Figure 4a, the prior art resonator has on both surfaces of the thin vibrating portion 3 the exciting electrodes Sa, 6a having essentially the same shape and the same thickness t. This gives rise to the vibration energy distribution shown in Figure 4a.

on the other hand, as shown in Figure 4b, the thin vibrating portion 18 of the resonator according to the present invention has the overall electrode 14a formed on the entire surface of one side thereof, with the exciting electrode 16a being formed on the other side. Then, since it is possible to consider the overall exciting electrode 14a as an integral part of the thin vibrating portion 18, the vibration energy distribution depends to a certain extent on the area and thickness of the exciting electrode 16a. Therefore, if the exciting electrode 16a of this embodiment is formed to have a thickness 2t, a vibration energy distribution substantially the same as that of the above-mentioned prior art resonator (Figure 4a) is achieved, as shown in Figure 4b.

Moreover, the resonant frequency of the thin vibrating portion 18 can be defined by the sum of the thickness of the vibrating portion 18 and the equivalent thickness t. of the overall exciting electrode 14a. (t. = to x p.1p; where to is the electrode thickness; p. is the material density of the electrode; and p is the density of the quartz crystal). Thus, it is possible slightly to adjust the resonant frequency of the thin vibrating portion 18 by adjusting the thickness of the overall electrode 14a without changing the overall characteristics of the resonator.

1 4 1 A further embodiment of the present invention is shown in Figures 5a and 5b. This embodiment is a monolithic crystal filter element which has at least two electrodes 19a, 20a formed closely to each other on a plane surface of a quartz crystal plate 11.

Furthermore, in the manufacturing process of the embodiments, since the overall electrode 14 can be formed without a mask or the like on the surface having the recess 12, the evaporation process becomes simpler than that of 10 the prior art resonator.

The descriptions of the above embodiments of the present invention relate to quartz resonators. However, it should be noted that this invention may also be applied to resonators utilizing many kinds of piezo-electric materials and the like.

In summary, a piezo-electric resonator according to the present invention includes a thin vibrating portion and a thick ring portion surrounding the vibrating portion to provide support therefor. Further, an overall electrode is 20 formed on the entire surface of the side having the recess. Therefore, a good electrical connection of the overall electrode at a step between the vibrating and ring portions can be obtained. Furthermore, the resonator can be manufactured using a simple electrode evaporation process.

1 6

Claims

CLAIMS, is 1. A piezo-electric resonator comprising piezo-electric

material having first and second surfaces with a thick ring portion surrounding a thin vibrating portion which has been formed by means of excavating a recess on the first surface of the plate; an overall electrode formed on substantially all of the first surface; and a partial electrode pattern formed on the second surface, the partial electrode pattern including an excit ing electrode on the thin vibrating portion and a lead pattern extending from the exciting electrode onto the ring portion.
2. A resonator according to claim 1, in which the piezoelectric plate is a cut quartz crystal plate.
3. A resonator according to claim 1 or claim 2, in which the recess has been formed by an etching process.
4. A resonator according to any one of the preceding claims, in which the overall electrode has been formed by a maskless evaporation process.
5. A resonator according to any one of the preceding claims, in which the exciting electrode and lead pattern therefrom has been formed by a photolithographic process.
6. A piezo-electric filter element comprising a plate of piezo-electric material having f irst and second surfaces with a thick ring portion surrounding a thin vibrating portion which has been f ormed by means of excavating a recess on the f irst surface of the plate; an overall electrode formed on substantially all of the first surface; and a plurality of electrodes arranged adjacent to each other on the thin vibrating portion on the second surface j 7 with a pair of lead patterns extending from the electrodes onto the ring portion.
7. A piezo-electric resonator, substantially as described with reference to 3a, 3b and 4b of the accompanying drawings.
8. A piezo-electric f ilter element, substantially as described with reference to Figures Sa and 5b of the 10 accompanying drawings.

Published 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch, Unit 6. Nine Mile Point, Cwn-delinfach. Cross Keys, Newport. NP1 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent.