GB2125211A

GB2125211A - Mechanical support of piezoelectric devices

Info

Publication number: GB2125211A
Application number: GB08222375A
Authority: GB
Inventors: Douglas Frank George Dwyer; Edward George Tuckett; Ann Muriel Harrison
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-08-03
Filing date: 1982-08-03
Publication date: 1984-02-29
Also published as: FR2532118A1; JPS5944117A

Abstract

A method of mounting a piezoelectric device, such as a surface acoustic wave filter or a crystal resonator, in which the piezoelectric device 1 is mounted on an intermediate support structure 4 of material having the same or similar temperature dependent characteristics as the piezoelectric device and having the same crystallographic orientation, the intermediate support structure being mounted in turn on a mechanical support 5, whereby stress due to differential expansion may be reduced. <IMAGE>

Description

SPECIFICATION Mechanical support of piezoelectric devices This invention relates to a method for mechanically supporting piezoelectric devices such as surface acoustic wave (SAW) filters, crystal resonators and the like.

The performance of piezoelectric devices can suffer modification due to stress from the support structure. Though this stress may be minimised at a given temperature, differential expansion between the support structure and the device over an operating temperature range can modify the device characteristics.

Various attempts have been made in the past to negate or eliminate the effects of differential expansion. For example it is known to mount a piezoelectric device such as a resonator in specially designed spring strips (British patent 1,459,609). Yet another proposed solution is to mount a piezoelectric device on a semiconductor device having a voltage or current dependent heat balance, whereby the temperature of the piezoelectric device is kept constant (British patent 1,435,655).

According to the present invention there is provided a method of mounting a piezoelectric device comprising inserting between the device and its mechanical support structure an intermediate support structure of material having the same or similar temperature dependent characteristics and crystal orientation as the piezoelectric device whereby differential expansion effects on the device are minimised and stress from the mechanical support structure is reduced.

Embodiments of the invention are now described with reference to the accompanying drawings, in which: Fig. 1 illustrates a mounting arrangement for a SAW resonator device, and Fig. 2 illustrates a mounting arrangement for a crystal resonator device.

In the arrangement shown in Fig. 1 a surface acoustic wave filter device comprises a rectangular body of quartz 11 provided on its upper surface at each end with an interdigitated electro-acoustic transducer 1 2, 1 3. The body 1 is adhesively bonded, e.g. by a layer of epoxy or polyimide resin to an intermediate, larger supporting body 14 of similar material, e.g. quartz, having the same crystal orientation as the filter body 1 The intermediate body 14 is in turn affixed to a mechanical support structure, e.g. a conventional header 1 5, which is provided with lead-through terminals 1 6. The transducers 1 2, 13 are connected to the terminals 16 by bonded wires 1 7.

In the arrangement shown in Fig. 2 a quartz crystal resonator slice 21 is provided on opposite faces with metallic electrodes patterns 22, 23.

The slice 21 is supported on two pellets of conductive paste 24, 25. Pellet 24 makes direct contact with electrode pattern 22, whilst pellet 25 is formed around and over the edge of the slice to make contact with the electrode pattern 23. The pellets are supported on metallic conductors 26, 27 deposited on a rectangular body 28 of quartz having the same crystallographic orientation as the slice 21. The quartz body is then affixed to a suitable mechanical support (not shown). The pellets of conductive paste allow a clearance gap between the main resonating portion of the crystal and the intermediate support.

Although only two specific examples have been given it is apparent that the invention is applicable to any piezoelectric structure including bulk crystal resonators, multipole filters, SAW transversal filters, SAW delay lines etc. The invention is also applicable to any piezoelectric material, of which quartz and lithium niobate are the most commonly used examples. In some cases it may be that the centre of the device is supported on a compressed pellet of paste and electrical connections are made by bonded wires. Because of reduced mounting strain, the use of a supporting substrate of the same material as the electronics device provides improved long term drift, temperature stability, acceleration and vibration performance, and very often simplifies the mounting of complex devices.

1. A method of mounting a piezoelectric device comprising inserting between the device and its mechanical support structure and intermediate support structure of material having the same or similar temperature dependent characteristics and crystal orientation as the piezoelectric device whereby differential expansion effects on the device are minimised and stress from the mechanical support structure is reduced.

2. A method according to claim 1 wherein the device is adhesively bonded to the intermediate support structure.

3. A method according to claim 1 wherein the device is affixed to the intermediate support structure by pellets of conductive paste making electrical connections between electrodes on the device and conductors on the intermediate support.

4. A method according to any preceding claim wherein the device and the intermediate support are both made of quartz or lithium niobate.

5. A method of mounting a piezoelectric device substantially as described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

6. A piezoelectric device mounted on an intermediate support structure which is in turn mounted on a mechanical support structure, said intermediate support structure being made of the same or similar material I' as the piezoelectric device and having the same crystaliographic orientation as the piezoelectric device.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Mechanical support of piezoelectric devices This invention relates to a method for mechanically supporting piezoelectric devices such as surface acoustic wave (SAW) filters, crystal resonators and the like. The performance of piezoelectric devices can suffer modification due to stress from the support structure. Though this stress may be minimised at a given temperature, differential expansion between the support structure and the device over an operating temperature range can modify the device characteristics. Various attempts have been made in the past to negate or eliminate the effects of differential expansion. For example it is known to mount a piezoelectric device such as a resonator in specially designed spring strips (British patent 1,459,609). Yet another proposed solution is to mount a piezoelectric device on a semiconductor device having a voltage or current dependent heat balance, whereby the temperature of the piezoelectric device is kept constant (British patent 1,435,655). According to the present invention there is provided a method of mounting a piezoelectric device comprising inserting between the device and its mechanical support structure an intermediate support structure of material having the same or similar temperature dependent characteristics and crystal orientation as the piezoelectric device whereby differential expansion effects on the device are minimised and stress from the mechanical support structure is reduced. Embodiments of the invention are now described with reference to the accompanying drawings, in which: Fig. 1 illustrates a mounting arrangement for a SAW resonator device, and Fig. 2 illustrates a mounting arrangement for a crystal resonator device. In the arrangement shown in Fig. 1 a surface acoustic wave filter device comprises a rectangular body of quartz 11 provided on its upper surface at each end with an interdigitated electro-acoustic transducer 1 2, 1 3. The body 1 is adhesively bonded, e.g. by a layer of epoxy or polyimide resin to an intermediate, larger supporting body 14 of similar material, e.g. quartz, having the same crystal orientation as the filter body 1 The intermediate body 14 is in turn affixed to a mechanical support structure, e.g. a conventional header 1 5, which is provided with lead-through terminals 1 6. The transducers 1 2, 13 are connected to the terminals 16 by bonded wires 1 7. In the arrangement shown in Fig. 2 a quartz crystal resonator slice 21 is provided on opposite faces with metallic electrodes patterns 22, 23. The slice 21 is supported on two pellets of conductive paste 24, 25. Pellet 24 makes direct contact with electrode pattern 22, whilst pellet 25 is formed around and over the edge of the slice to make contact with the electrode pattern 23. The pellets are supported on metallic conductors 26, 27 deposited on a rectangular body 28 of quartz having the same crystallographic orientation as the slice 21. The quartz body is then affixed to a suitable mechanical support (not shown). The pellets of conductive paste allow a clearance gap between the main resonating portion of the crystal and the intermediate support. Although only two specific examples have been given it is apparent that the invention is applicable to any piezoelectric structure including bulk crystal resonators, multipole filters, SAW transversal filters, SAW delay lines etc. The invention is also applicable to any piezoelectric material, of which quartz and lithium niobate are the most commonly used examples. In some cases it may be that the centre of the device is supported on a compressed pellet of paste and electrical connections are made by bonded wires. Because of reduced mounting strain, the use of a supporting substrate of the same material as the electronics device provides improved long term drift, temperature stability, acceleration and vibration performance, and very often simplifies the mounting of complex devices. CLAIMS

7. A piezoelectric device mounted by the method claimed in any one of claims 1-5.

8. A piezoelectric device mounted substantially as described with reference to Fig. 1 or Fig. 2 of the drawings.