Patent GB-888169-A (GB)
Title: Improvements in or relating to piezoelectric devices
IPC: H03H9/09
Filed: 1957-08-30
Abstract: 888,169. Piezo-electric devices. GENERAL ELECTRIC CO. Ltd., and WILSON, F. J. Oct. 30, 1958 [Aug. 30, 1957], No. 27414/57. Class 40(8). A piezo-electric device comprises a crystal I supported by two electrically conductive strips 8a, 9a, by which electrical connection is made to the two electrodes 12, 13 of the crystal, each of the strips having a longitudinal slot 10 therein and the crystal having two portions 1a, 1b lying within the two slots respectively. The crystal 1 is contained within a hermetically sealed casing constituted by a metal cover 2 and a metal base member 3. Metal pins 4, 5 project through glass seals 6, 7 and are soldered or welded to the metallic strips 8, 9. Each slot 10 has longitudinal sides 10a and concave ends 10b, the length of the slot 10 being approximately half the diameter of the crystal 1 and the width of the slot 10 being substantially greater than the thickness of the crystal so that the crystal 1 bears upon the concave ends 10b only. The crystal has gold electrodes 12, 13 which lie on opposite faces thereof and extend from the centre thereof in diagramatically opposite directions towards the edge of the crystal. The strips 8, 9 are connected to the crystal by electrically conductive hardened cement 14 on both faces of the crystal. In an alternative arrangement two strips of silver paste are fired on the crystal 1 before it is mounted between the strips 8, 9 and before the electrodes 12, 13 are deposited. The strips are fired at 530‹C., burnished and tinned with solder. The strips lie diametrically opposite one another on the peripheral portions 1a, 1b so that when the electrodes 12, 13 are deposited they make contact with the strips. The tinned strips are then soldered to the supporting strips 8 and 9. The crystal 1 can be an AT-cut quartz element with a resonant frequency in a thickness shear mode of 10 megacycles per sec. The mounting described can also be used for AT- and BT-cut quartz crystals having a resonant frequency in the thickness shear mode above 750 kilocycles per sec. For AT- and BT-cut quartz crystals having a resonant frequency in the thickness shear mode of less than 750 kilocycles, e.g. 500-750 kilocycles per sec., the construction shown in Figs. 4 and- 5. can be used in which the cement arrangement 14, which can cause too much damping, is modified Here the crystal 15 is supported by the nickel strips 16, 17 with peripheral portions 15a projecting through a slot 18, 19 in the strips 16, 17. A cover for the device is provided as in Figs. 1-3. The free ends of the strips 16, 17 are formed as inwardly directed V-shaped portions 16a, 17a and a ring 23 of insulating cement connects the V-shaped portions. The crystal 15 is a double convex AT-cut quartz element with electrodes 24, 25 on opposite faces thereof and extending in diametrically opposite directions to the edges of the peripheral portions 15a whereat each of the electrodes 24, 25 lies over, in electrical contact with, one of two strips of electrically conductive cement 26. The electrodes 24, 25 are deposited on the crystal 15 after the strips 26 of cement have been adhered to the edge of the crystal. The slot 18 has longitudinal sides 18a and V-shaped ends 18b, the width of the slot being large enough to ensure that the crystal 15 does not touch the sides 18a and the ends 18b being urged, by the ring 23, to bite into the strip of cement 26 upon the edge of the peripheral portion 15a. The cement 14 or 26 can be silver paste or can be made up from a phenolic resin such as "Bakelite" (Registered Trade Mark) and finely divided silver particles in equal proportions by weight.