CH633921A5 - PIEZOELECTRIC DIAPASON RESONATOR. - Google Patents

Description

The invention relates to piezoelectric resonators with tuning fork of small dimensions. In these resonators, the resonant element is a tuning fork made of piezoelectric material and the base of which, which is a zone of minimum vibration, is fixed to a support by means of a solder or an adhesive. The whole is then mounted in a box which is most often in the form of a glass capsule or bulb fitted with metal bushings or a metal capsule also fitted with metal bushings but these being isolated from the rest of the capsule by glass beads or ceramic-metal bonds.

To guarantee good performance, good quality resonators are hermetically sealed in their capsule and generally under vacuum, to protect them from any contamination and eliminate energy losses due to the presence of air. . In this case, the electrical bushings must necessarily be sealed, which is the source of many problems.

When, for certain applications, it becomes of the utmost importance to reduce the total overall dimensions of the resonator as much as possible, the problems posed by the fixing of the tuning fork to its support and by the tight crossings become preponderant and insurmountable obstacles quickly appear due to the limits. of the known technique. In particular for resonators having to operate under vacuum, the very small internal volume not only imposes an almost absolute tightness to maintain performance for several years, but also makes it necessary to steam the components before closing to avoid any subsequent degassing of the surfaces inside the evacuated enclosure. This steaming must be carried out under vacuum and at a fairly high temperature, and this for a time that is shorter the higher the temperature. Now we are obviously very quickly limited by the maximum temperature that can withstand without damage the solder and the adhesives used for assembly.

The object of the present invention is to overcome all of these drawbacks by proposing a piezoelectric tuning fork resonator comprising only a minimum of distinct components, which can be produced in very small dimensions and whose machining and mounting are clearly simpler than those offered by known methods.

The invention is set out in the description which follows and for the intelligence of which reference will be made to the drawings among which:

FIG. 1 shows a tuning fork and its support produced in accordance with the invention,

FIG. 2 represents a later stage in the production of the same elements,

FIG. 3 represents in section the encapsulated resonant element 15 according to an exemplary embodiment of the invention,

Figure 4 shows the resonator as a finished product, Figure 5 is an exploded view illustrating a second embodiment of the invention.

FIG. 1 shows a resonant element according to the invention. It is produced by simple cutting from a plate of piezoelectric material. Generally rectangular in shape, it is formed of two distinct parts while constituting only a single and flat part: a central part in tuning fork configuration 1 and which is the resonant element proper 25 and a peripheral part 2 forming a frame completely surrounding the tuning fork 1 and separated from the latter by a cutout 3. The cutout 3 is such that the tuning fork 1 remains connected without any physical or mechanical discontinuity to the frame 2 serving as support by its foot or base 4 which is a neutral zone and which will therefore not be affected by the vibrations of tuning fork 1.

At a later stage shown in FIG. 2, a system of bipolar electrodes 5 is metallized in a thin layer on the branches of the tuning fork 1, the connections being organized in such a way that each electrode or pole ends in a contact track 6 deposited respectively on each of the two opposite faces of the piezoelectric plate at the level of the base 4 of the tuning fork 1. The support frame 2 is then coated on its two opposite faces with a metallized layer 7 perfectly adhered-40 and which is electrically connected to contact track 6 of the corresponding pole.

Lids 8, consisting for example of stamped metal sheets in the form of very flat covers, as in the example of FIG. 3, so as to have a peripheral lip 9, are applied to each metallized layer 7 of the frame. support 2 and on the entire periphery thereof without being able to come into contact with the tuning fork 1. The fixing of the covers 8 on the support frame 2 in the case where these are metallic, as in the present example, can be done by soldering or by means of a conductive adhesive or a conductive cement. When the fixing is done by brazing, the metallized layer 7 can first be coated with the appropriate alloy by galvanic or screen printing process. The steaming of the ensem-55 ble can then be done under vacuum at a temperature which may exceed the melting point of the alloy and the assembly of the covers 8 to the frame 2 will be done under vacuum or neutral atmosphere by recasting the alloy and perfectly sealed.

The covers 8, still in the case where they are metallic, 60 advantageously serve as hermetic connections or electrical connection terminals to the resonator. Thus, as shown in FIG. 4 which represents the finished product which constitutes the resonator, the covers 8 can be provided with connection tabs 10 according to any suitable arrangement, such as for example that shown in dotted lines. The rest of the encapsulation can be protected and isolated with a lacquer or varnish.

Another embodiment of the invention is illustrated in FIG. 5. In this case, the metal layer 7 is given

633,921

carried by the support frame 2 a much greater thickness so that it is possible to use covers 8 perfectly flat without that they can come into contact with the tuning fork 1. These covers 8 can then be either metallic either in insulating material such as glass, ceramic or even quartz. In this case, each cover 8 is coated on one of its faces with an adherent metal layer 11 forming a frame. This “thick” layer 11 will, as before, carry connection lugs 10 and the assembly will be done as in the case of metal covers.

VS

1 sheet of drawings

Claims (6)

633,921 2 1. Piezoelectric tuning fork resonator, characterized in that the resonant element and its support are cut to form a single flat part in a plate, the central part of which forms the tuning fork and the peripheral part forms a support frame, these two parts remaining connected to each other by the base of the tuning fork and that the upper and lower faces of the support frame serve as fixing zones for two flat or bowl-shaped lids. 2. Piezoelectric tuning fork resonator according to claim 1, characterized in that the covers are metallic and are welded on a metallized layer deposited on the upper and lower faces of the support frame and serve as terminals for electrical connection to the resonator. 3. Piezoelectric tuning fork resonator according to claim 2, characterized in that the metal layer is thin and that the covers are in the form of very flat bowls. 4. Piezoelectric tuning fork resonator according to claim 2, characterized in that the metal layer is thick and that the covers are planar. 5. Piezoelectric tuning fork resonator according to claim 1, characterized in that the covers are insulating and that the support frame carries on its upper and lower faces a thick metallic coating on which the covers are supported, the coating having towards the outside of the ears serving as terminals for electrical connection to the resonator. 6. Piezoelectric tuning fork resonator according to claim 5, characterized in that the covers are flat and made of material such as glass, ceramic or quartz and coated on one side with an adherent metallic layer forming a frame.