GB1571965A

GB1571965A - Quartz crystal tuning fork vibrator

Info

Publication number: GB1571965A
Application number: GB45784/77A
Authority: GB
Original assignee: Suwa Seikosha KK
Current assignee: Suwa Seikosha KK
Priority date: 1976-11-04
Filing date: 1977-11-03
Publication date: 1980-07-23
Also published as: JPS5832524B2; CH625100GA3; CH625100B; JPS5357788A

Abstract

The vibrating element (6) consists of an X-cut crystal plate with a rotation of 0 DEG to 10 DEG about the X axis and a rotation of 70 DEG to 90 DEG about the Y' axis. The electrodes are produced by means of photochemical etching techniques. The peripheral outer electrodes (3 and 4) are galvanically connected to side electrodes (7 and 8) over the greatest proportion of their longitudinal dimension. The peripheral electrodes (3, 4) are arranged in parallel with the plane of vibration of the crystal plate and have a width dimension which is equal to or less than the width dimension of the fork tine carrying them; the side electrodes (7, 8) are arranged perpendicular to the plane of vibration of the crystal plate and partially overlap the peripheral electrodes at their common joint. <IMAGE>

Description

(54) "QUARTZ CRYSTAL TUNING FORK VIBRATOR" (71) We, KABUSHIKIKAISHASUWA SEIKOSHA, a Japanese Company of 3-4-, 4-chome, Ginza, Chuo-ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention concerns a quartz crystal tuning fork vibrator, e.g. for use in an electronic wrist-watch.

According to the present invention, there is provided a quartz crystal tuning fork vibrator formed by photo-etching an X cut quartz crystal plate which has been turned through an angle of 0 to 10 with respect to its X axis and through an angle of 70" to 900 with respect to its Y' axis, each tine of the vibrator being provided, in at least one plane parallel to the plane of vibration thereof, with peripherally disposed electrodes which are electrically connected to each other and between which there is a centrally disposed electrode, the centrally disposed electrode of each tine being electrically connected to the peripherally disposed electrodes of the other or another tine, and each tine being provided, in planes perpendicular to the said plane of vibration, with side electrodes which are respectively electrically connected to the adjacent peripherally disposed electrodes.

Such a vibrator has been found to have a lower crystal impedance (hereinafter referred to as CI) than that of known vibrators.

Preferably each peripherally disposed electrode has a combined width with its respective side electrode which is at least 10y and which is not greater than one-sixth of the combined width of the respective tine and its side electrodes.

The vibrator preferably has two tines only.

The vibrator preferably has a thickness not greater than 150,u and, desirably, not greater than l00Cl.

The said combined width of each tine preferably does not exceed 500cm and may be no greater than 380cm.

Preferably the side electrodes have been formed on the vibrator after the formation thereon of the peripherally and centrally disposed electrodes. Thus the side electrodes may have been formed on the vibrator by means of deposition through a mask of a vacuum evaporated film.

Each side electrode preferably overlaps the respective peripherally disposed electrodes by at least 10cm.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is a perspective view of known quartz crystal tuning fork vibrator, Figure 2 is a cross-sectional view of the known vibrator of Figure 1, Figure 3 is a perspective view of a quartzcrystal tuning fork vibrator according to the present invention, Figure 4 is a cross-sectional view of the vibrator of Figure 3, Figure 5 is a cross-sectional view on a larger scale of one of the tines of the vibrator of Figures 3 and 4, Figure 6 is a graph showing the relationship between the width of a side electrode of the vibrator of Figures 3 - 5 and the crystal impedance of the vibrator, Figure 7 is a perspective view illustrating the manufacture of vibrators as shown in Figures 3-5, and Figure 8 is a diagrammatic broken-away cross-sectional view of part of the structure shown in Figure 7.

In Figures 1 and 2 there is shown a known quartz crystal tuning fork vibrator formed by photo-etching an X-cut quartz crystal plate of the 5"X group, the plate having an electrical axis X, a mechanical axis Y, and an optical axis Z. The plate has been turned through an angle a of 0 to 10 with respect to its X axis and through an angle ss of 70" to 90" with respect to its Y' axis.

The vibrator 1 of Figures 1 and 2 has two tines la, lb. On each of the obverse and reverse surfaces of the tine la there are provided peripherally disposed electrodes 3 which are electrically connected to each other and between which there is a centrally disposed electrode 5. Similarly, on each of the obverse and reverse surfaces of the tine 1b there are provided peripherally disposed electrodes 4 which are electrically connected to each other and between which there is a centrally disposed electrode 2. As will be appreciated, the peripherally disposed electrodes 2, 5 are thus arranged in planes parallel to the plane of vibration of the vibrator.Each centrally disposed electrode 2 of the tine 1b is electrically connected to the respective peripherally disposed electrodes 3 of the tine la while each centrally disposed electrode 5 of the tine la is electrically connected to the respective peripherally disposed electrodes 4 of the tine lb.

The directions of the electric fields in the tines la, ib are indicated by arrows in Figure 2 which is a sectional view taken on the vibrator 1 in the plane X-Z. In this sectional view, the angle ss has been set at 90" for simplicity of illustration.

The vibrator shown in Figures 1 and 2 enables one to obtain a lower CI than can be obtained in a conventional NT-cut vibrator.

However, it is very desirable to reduce the CI to a greater extent than that possible with the construction shown in Figures 1 and 2.

In Figures 3 and 4, therefore, there is shown a quartz-crystal tuning fork vibrator 6 which is generally similar to that of Figures 1 and 2 and which for this reason will not be described in detail, like reference numerals indicating like parts. Thus the vibrator 6 of Figures 3 and 4, whose thickness does not exceed 150y, is of the same 5"X group as that of the vibrator 1 of Figures 1 and 2.In the vibrator of Figures 3 and 4, however, the vibrator, in addition to being provided with the centrally disposed electrodes 2, 5 and the peripherally disposed electrodes 3, 4 is also provided on each of the opposite sides of each of its tines la, ib, and thus in planes perpendicular to the plane of vibration of the vibrator, with side electrodes 7, 8 respectively which are respectively connected to the adjacent peripherally disposed electrodes 3, 4.

In the sectional view shown in Figure 4, the angle ss has been set at 900 for simplicity of illustration. At the same time, the thickness of the electrode films has been exaggerated so that they can be more easily seen. As will be seen from Figure 4, the side electrodes 7 of the tine la have flange portions 7a which overlie the peripherally disposed electrodes 3 to ensure a good electrical connection thereto, while the side electrodes 8 of the tine ib are provided with flange portions 8a which overlie the peripherally disposed electrodes 4 to ensure a good electrical connection thereto.

The construction illustrated in Figure 4, in comparison with that illustrated in Figure 2, has an electric field with a larger component in the X-axis direction, the effect of the side electrodes being to lower the value of the CI. The value of CI can in fact be reduced by virtue of the provision of the side electrodes 7, 8 to one half of the value which it would otherwise have.

Figure 5 is a cross-sectional view showing the left-hand half of Figure 4 on a larger scale. It should be noted that the thickness of the electrodes has been very much exaggerated in Figure 5 so that they can be more easily seen.

The distortion of any part of each tine of the vibrator arising from the flexural movement of the latter is in proportion to the distance of said part from the centre-line A - A ' of the tine. Consequently it is desirable that the electric fields in the tines extend as far as possible from the centreline A - A', and thus extend to the sides of the tine, in order to lower the impedance.

In Figure 5 the combined width of the tine la and of its side electrodes 7 is indicated by W, whose value preferably does not exceed 500, while the combined width of each peripherally disposed electrode 3 and its respective side electrode 7 is indicated by d.

Figure 6 is a graph showing the relationship of the ratio d/W to CI in the case of a vibrator whose thickness is 1 00it and whose combined width W is 380y. As will be seen from Figure 6, in order to maintain CI at a maximum, it is desirable to ensure that the ratio d/W does not exceed l/6, i.e. it is desirable to ensure that the combined width d of a peripherally disposed electrode 3 together with its respective side electrode 7 should not be greater than l/6 of the combined width W of the respective tine la and its side electrodes 7. We have also found that in order to simplify manufacture and to provide a construction in which the electric fields can be applied most efficiently, it is desirable that the peripherally disposed electrodes have a width which is not less than 10,u.

Figures 7 and 8 illustrate diagrammatically the production of quartz crystal tuning fork vibrators as shown in Figures 3 to 5, the side electrodes 7, 8 being formed on the vibrator after the formation thereon of the peripherally and centrally disposed elec trodes 2-5. Thus in the process illustrated in Figure 7, a plurality of vibrators 6, each of which is provided with peripherally disposed electrodes 3, 4 and with centrally disposed electrodes 2, 5, is shown as having been formed from a common sheet of quartz crystal material by photo etching, the vibrators 6 being connected to each other by a strip 9 of the quartz crystal material. The vibrators 6 and strip 9 are then put in a vacuum evaporation system after having been covered on their obverse and reverse surfaces with deposition masks 10, 11 having openings 12 therein.The side electrodes 7, 8 are then formed on the vibrators 6 by means of deposition of a vacuum evaporated film through the masks 11, 12, in the directions indicated by the arrows in Figure 8.

The side electrodes will thus be restricted to the areas delimited by the openings 12 and, in order to deal with any error in alignment between the masks 10, 11 and the assembly of vibrators 6, the openings 12 of the masks 10, 11 need to be at least 10,u wider than is theoretically necessary to ensure electrical connection between the side electrodes 7, 8 and the peripherally disposed electrodes 3, 4. In other words, the flange portions 7a, 8a of the side electrodes 7, 8 overlap the peripherally disposed electrodes 3, 4 and have a width of about lOji.

This ensures good electrical connection between the side and peripherally disposed electrodes.

As indicated above, a vibrator according to the present invention can be made so that its CI is almost half that of a conventional vibrator, while at the same time ensuring that there is only a small increase in the number of manufacturing processes in volved. The invention thus enables a superior vibrator to be obtained which is especially useful as a miniature vibrator for an electronic wrist watch.

WHAT WE CLAIM IS: 1. A quartz crystal tuning fork vibrator formed by photo-etching an X cut quartz crystal plate which has been turned through an angle of O" to 10 with respect to its X axis and through an angle of 70" to 900 with respect to its Y' axis, each tine of the vibrator being provided, in at least one plane parallel to the plane of vibration thereof, with peripherally disposed elec trodes which are electrically connected to each other and between which there is a centrally disposed electrode, the centrally disposed electrode of each tine being electrically connected to the peripherally disposed electrodes of the other, or another tine, and each tine being provided, in planes perpendicular to the said plane of vibration, with side electrodes which are respectively electrically connected to the adjacent peripherally disposed electrodes.

2. A vibrator as claimed in claim 1 in which each peripherally disposed electrode has a combined width with its respective side electrode which is at least 10y and which is not greater than one-sixth of the combined width of the respective tine and its side electrodes.

3. A vibrator as claimed in claim 1 or 2 in which the vibrator has two tines only.

4. A vibrator as claimed in any preceding claim in which the vibrator has a thickness not greater than 150cm.

5. A vibrator as claimed in any preceding claim in which the combined width of each tine and its side electrodes does not exceed 500cm.

6. A vibrator as claimed in any preceding claim in which the side electrodes have been formed on the vibrator after the formation thereon of the peripherally and centrally disposed electrodes.

7. A vibrator as claimed in claim 6 in which the side electrodes have been formed on the vibrator by means of deposition through a mask of a vacuum evaporated film.

8. A vibrator as claimed in any preceding claim in which each side electrode overlaps the respective peripherally disposed electrodes by at least 10Cl.

9. A vibrator as claimed in any preceding claim in which each of the obverse and reverse surfaces of each tine is provided with the said peripherally and centrally disposed electrodes.

10. A quartz crystal tuning fork vibrato substantially as hereinbefore described with reference to and as shown in Figures 3 to 5 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. trodes 2-5. Thus in the process illustrated in Figure 7, a plurality of vibrators 6, each of which is provided with peripherally disposed electrodes 3, 4 and with centrally disposed electrodes 2, 5, is shown as having been formed from a common sheet of quartz crystal material by photo etching, the vibrators 6 being connected to each other by a strip 9 of the quartz crystal material. The vibrators 6 and strip 9 are then put in a vacuum evaporation system after having been covered on their obverse and reverse surfaces with deposition masks 10, 11 having openings 12 therein. The side electrodes 7, 8 are then formed on the vibrators 6 by means of deposition of a vacuum evaporated film through the masks 11, 12, in the directions indicated by the arrows in Figure 8. The side electrodes will thus be restricted to the areas delimited by the openings 12 and, in order to deal with any error in alignment between the masks 10, 11 and the assembly of vibrators 6, the openings 12 of the masks 10, 11 need to be at least 10,u wider than is theoretically necessary to ensure electrical connection between the side electrodes 7, 8 and the peripherally disposed electrodes 3, 4. In other words, the flange portions 7a, 8a of the side electrodes 7, 8 overlap the peripherally disposed electrodes 3, 4 and have a width of about lOji. This ensures good electrical connection between the side and peripherally disposed electrodes. As indicated above, a vibrator according to the present invention can be made so that its CI is almost half that of a conventional vibrator, while at the same time ensuring that there is only a small increase in the number of manufacturing processes in volved. The invention thus enables a superior vibrator to be obtained which is especially useful as a miniature vibrator for an electronic wrist watch. WHAT WE CLAIM IS:

1. A quartz crystal tuning fork vibrator formed by photo-etching an X cut quartz crystal plate which has been turned through an angle of O" to 10 with respect to its X axis and through an angle of 70" to 900 with respect to its Y' axis, each tine of the vibrator being provided, in at least one plane parallel to the plane of vibration thereof, with peripherally disposed elec trodes which are electrically connected to each other and between which there is a centrally disposed electrode, the centrally disposed electrode of each tine being electrically connected to the peripherally disposed electrodes of the other, or another tine, and each tine being provided, in planes perpendicular to the said plane of vibration, with side electrodes which are respectively electrically connected to the adjacent peripherally disposed electrodes.