GB2040560A

GB2040560A - Piezoelectric tuning fork resonator

Info

Publication number: GB2040560A
Application number: GB7939629A
Authority: GB
Original assignee: SSIH Management Services SA
Current assignee: SSIH Management Services SA
Priority date: 1978-11-16
Filing date: 1979-11-15
Publication date: 1980-08-28
Also published as: DE2946222A1; JPS5568717A; GB2040560B; CH633921A5; FR2441959B1; FR2441959A1

Abstract

A piezoelectric tuning fork resonator of small dimensions and comprising a minimum of distinct or separate elements. A resonating element 1 and its support 2 are blanked from a thin slab of piezoelectric material so as to form a single planar element of which the central portion comprises a tuning fork and the periphery constitutes a framework support. The portions are united at the foot of the tuning fork. Cover members 8 in flattened cap or planar form are fastened to the framework support. The cover members, if metal, or metallized layers 7, may have connection tabs 10. <IMAGE>

Description

SPECIFICATION Piezoelectric tuning fork resonator This invention concerns piezoelectric tuning for resonators of small dimensions. In such resonators the resonant element comprises a tuning fork of piezoelectric material of which the foot which exhibits minimum vibrations is fastened to a support by means of a brazing or gluing. The entire unit is then mounted in a casing or glass bulb provided with metallic traverses or within a metallic capsule likewise provided with metallic traverses, the latter being however, insulated from the remainder of the encapsulation by glass beads or ceramic-to-metal fastenings.

To be sure of good performance, resonators of top quaiity are hermetically enclosed within their encapsulation and generally under vacuum, in order to shelter them from all contamination and to avoid losses of energy due to the presence of air.

In such case the electrical traverses must necessarily be tightly sealed and this gives rise to numerous problems.

When for certain applications it becomes of the greatest importance to reduce as far as possible the overall dimensions of the resonator, the problems posed by the fastening of the tuning fork to its support and by the sealed traverses become overbearing and certain obstacles appear insurmountable in view of the limits of known technology. In particular, for resonators having to operate under vacuum, the very small interior volume imposes not only a requirement for an almost absolute sealing in order to maintain the performance during several years but requires a heat treatment of the components before closing in order to eliminate the emission of gas from surfaces on the interior of the evacuated enclosure. Such heat treatment must be carried out under vacuum, at a high temperature and during a period of time progressively reduced as the temperature rises.Thus one is evidently soon limited by the maximum temperature which may be applied without damaging the selders or glues used for assembling the component.

The present invention has as its principal object the overcoming of these several difficulties and proposes a piezoelectric tuning fork resonator having only a minimum of separate components therein, capabie of being realised in very small dimensions and for which the machining as well as the assembly are ciearly more simple than that of the known technology.

The invention is further illustrated within the following description for greater understanding of which, reference is made to the attached drawings in which: figure 1 shows a tuning fork and its support in accordance with this invention figure 2 shows a further stage in the termination of the -same elements figure 3 shows a section of the resonant element enclosed according to one example of the invention figure 4 shows the resonator as a finished product figure 5 is an exploded view showing a second example of the invention In figure 1 will be seen a resonant element according to the invention.It may be obtained by simple blanking in a plate of piezoelectrical material of generally rectangular form and it is fashioned into distinct portions the totality of which form a single planar piece: a central portion having the form of a tuning fork 1 which is the resonating element and a peripheral portion 2 which forms a frame surrounding completely the tuning fork 1 and separated from this latter by a slot 3. The slot 3 is such that the tuning fork 1 remains united with no physical or mechanical discontinuity to the frame 2 by its foot or base 4 which serves as a support and is a neutral zone which will thus not be affected by the vibrations of the tuning fork 1.

At a later stage as shown in figure 2, a bipolar electrode system 5 is metallized in a thin layer on the arms of tuning fork 1, the connections being arranged in a fashion such that each electrode or pole ends up on a contact track 6 deposited respectively on each of the two opposed faces of the piezoelectric plate at the level of the base 4 of tuning fork 1. The frame support 2 is then coated on both opposed faces with a metallized layer 7 which should adhere perfectly thereto and which is thereby coupled electrically to the contact track 6 of the corresponding pole.

Cover members 8 comprising for example metallic sheets, pressformed as flattened caps as shown in the example of figure 3 so as to provide peripheral lip 9, are applied to each metallized layer 7 of the frame support 2 and along the entire periphery thereof without entering into contact with tuning fork 1. A fastening of cover members 8 on to the framework support 2 in the case where these are of metal, as in present example, may be effected by brazing or by means of a conductive glue or cement. When the fastening is effected by brazing or soldering the metallic layer 7 may initially be coated with an appropriate alloy by a galvanic or silkscreening process.The heat treatment of the assembly may then be carried out under vacuum at a temperature which may exceed the melting point of the alloy and assembly of cover members 8 to the frame 2 will be carried out under vacuum or in a neutral atmosphere by fusion of the alloy and this in a perfectly hermetic manner.

Cover members 8 so lony as they are metallic may advantageously serve as hermetic connections or terminals for electric connections to the resonator, thus as shown in figure 4, which represents a finished product, covers 8 may be provided with connection tabs 10 according to any suitable arrangement as for example that represented by the solid or dotted lines. The remainder of the encapsulation may be protected and insulated by means of a lacquer or varnish.

A further example of the realisation of this invention is shown by figure 5. In this case the metallic layer 7 carried on the framework support 2 is given a greater thickness in a manner such that it is possible to use cover members 8 perfectly planar in form without risk that they come in contact with the tuning fork 1. Such cover members 8 may then be either metallic or of a insulating material such as glass, ceramic or quartz. In this latter hypothesis each cover member 8 is coated on one of its faces with a metallic layer 11 which forms a frame. The thick layer 7 will as in the preceding case be provided with connection tabs 10 and the assembly will be effected as in the case of the metallic cover members.

Claims

1. Piezoelectric tuning fork resonator in which a resonant element and a support therefor are blanked from a thin slab of piezoelectric material to form a single planar element of which the central portion comprises a tuning fork resonator and the peripheral portion forms a framework support, the two portions remaining attached to one another at the foot of the tuning fork, the upper and lower surfaces of the framework support serving as attaching zones for first and second cover members of flattened cap or planar form.

2. Piezoelectric tuning fork resonator as in claim 1 wherein the cover members are metallic and are brazed or welded to a metallic layer applied to the upper and lower surfaces of the framework support thus being adapted to serve as electrical connecting terminals to the resonator.

3. Piezoelectric tuning fork resonator as in claim 2 wherein the metallic layer is thin, the cover members being in the form of flattened caps.

4. Piezolectric tuning fork resonator as in claim 2 wherein the metallic layer is thick, the cover members being in planar form.

5. Piezoelectric tuning fork resonator as in claim 1 wherein the cover members are of electrically insulating material, the framework support having on its upper and lower surfaces a thick metallic layer on which the cover members are supported, the metallic layers having externally projecting tabs serving as electrical connecting terminals to the resonator.

6. Piezoelectric tuning fork resonator as in claim 5 wherein the cover members are in planar form executed in material such as glass ceramic or quartz and coated on one surface with an adhering metallic layer forming a frame.

7. A piezoelectric tuning fork resonator substantially as herein described with reference to Figures 1 to 4 or 5 of the accompanying drawings.