WO2002073644A1

WO2002073644A1 - A millimetre wave switch

Info

Publication number: WO2002073644A1
Application number: PCT/GB2002/001092
Authority: WO
Inventors: Anthony Needham; Anthony Lane; Giles Humpston; Crofton Brierley
Original assignee: Bookham Technology Plc
Priority date: 2001-03-12
Filing date: 2002-03-11
Publication date: 2002-09-19
Also published as: GB0105930D0; GB2373373A

Abstract

A micromachined electrical switch comprising: a plurality of electrical paths (25) each of which has a break (A; B; C) therein; a plurality of moveable electrical contacts (19) each of which includes piezoelectric material (32) which changes dimensionally in response to an electrical signal; and a plurality of actuators for applying electrical signals to the respective contacts (19), each of the contacts (19) being arranged such that when moved to a closed position in response to an electrical signal from the respective actuator, it bridges the break (A; B; C) in a respective one of said electrical paths (25).

Description

A MILLIMETRE WAVE SWITCH

TECHNICAL FIELD

This invention relates to electrical switches which are capable of broadband operation, high isolation and low loss, and which are typically, but not exclusively, used in communication systems.

BACKGROUND ART

A micromachined microwave switch is described in WOOl/13457 in which there is described an electrical switch comprising a pair of electrical contacts which are movable relative to each other between an open and closed state by means of an actuator which imparts relative movement to the contacts and which includes piezoelectrical material which changes dimensionally in response to an electrical field applied across the material. Such a switch will hereinafter be called a switch of the type referred.

In such switches, a contact on the actuator is preferably moved to bridge the break in an electrical path when the switch is in a closed state

These switches are capable of broad band operation (DC-50GHz), high isolation (25dB at 40GHz) and low loss (0.1 dB) and the piezo actuation enables the switches to be actuated at low voltages (3V).

The present invention provides a switch of the kind referred which is suitable for use in RF cross connect circuits having a plurality of inputs each of which may be individually connected to plurality of outputs.

SUMMARY OF THE INVENTION

According to the present invention there is provided an electrical switch of the kind referred, wherein the switch includes a plurality of pairs of contacts, the contacts of each pair being relatively moveable by a respective actuator, and a base which comprises at least two separate layers each being provided with at least one electrical path which is completed when a respective one of said pairs of contacts is in a closed state. Electrostatic versions of actuator may be used with multilayer bases but would require the use of 30-lOOv to actuate.

Each electrical path may have a break therein and the break is bridged by a contact on the respective actuator when in the closed state.

Preferably, the base comprises two layers of a suitable dielectric material, in particular low temperature co-fired ceramic (LTCC) which enables signal lines and ground planes to be buried and excellent isolation between lines to be achieved.

The electrical paths in any layers of said base remote from the actuators are connected to their respective contacts by respective interlayer paths and vias.

The switch may include three different electrical paths, at least one being on the layer remote from the actuators, and three pairs of different contacts arranged so that respective contacts moved by each of the three actuators bridges between two selected contacts as is desired, there are two inputs and two outputs through the switch, one input being connectable to the two outputs and the other input being connectable only to one of said outputs. The three actuators may be operated individually as is desired. The actuators preferably move cantilevers which extend substantially parallel to each other and each has a contact on the end thereof.

The invention also relates to a switching arrangement having N inputs and N outputs, each input being connectable to any one of the outputs, the arrangement including N x N switches as described above, wherein said one output of each switch is connected to said other input of a first adjacent switch in the array, and the second output of each switch being connected to said one input of a second adjacent switch in the array.

In another embodiment, the switch includes four different electrical paths, with four pairs of different contacts arranged so that the contact on each respective actuator bridges between two selected contacts as is desired, there being one central contact and four satellite contacts, the central contact being connectable to any of the four satellite contacts. A switching arrangement having N inputs and N outputs in which each input which is directly connectable to each output the array including 2N switches according the alternative embodiment, wherein the input for a first array of N switches comprises the respective central contacts and the output for a second array of N switches also comprises the respective central contacts, and each switch of the first array has each satellite contact connectable to a corresponding satellite contact of the second array of switches.

In both switching arrangements described above, the arrangements are operated by an external control so that only one cantilever of each switch is operable at any one time.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described by way of example and with reference to the accompanying drawings in which :

Fig. 1 is a drawing showing a part section through a switch according to the present invention,

Fig. 2 is a schematic drawing of the switch node used in the switch in Fig.1 ,

Fig. 3 is a drawing showing the arrangement of the cantilevers and contacts in the switch shown in Fig 1,

Fig. 4 shows a switching arrangement having 8 X 8 switches as shown in Figs. 2 & 3 configured in a cross-connect,

Fig. 5 shows a schematic drawing of a second switch according to the present invention,

Fig. 6 is a section through the switch shown in Fig.5, and

Fig. 7 shows a switching arrangement of switches as shown in Figs. 5 & 6 configured in a cross connect .

BEST MODE OF CARRYING OUT THE INVENTION

With reference to Figs 1 to 3, there shown a micromachined switch 10 for microwave apphcations and which is similar to a switch described in apphcation 0003186 and although sufficient information is given herein for an understanding of the present invention more detailed information is disclosed in that application the contents of which are hereby imported into the present application.

The switch 10, shown in Fig.l, comprises a base 12 of a suitable low loss microwave substrate, preferably a laminate of multiple layers of dielectric material 13,14,15 & 16 which insulate signals having frequencies from DC up to 50 GHz, and conductive material forming electrical paths and ground planes. Any number of layers of dielectric material may be used as is required by the particular application. The insulating material may be selected from: organic materials such as PTFE ( polytetrafluoroethylene) polycarbonates, polyamides and polyimides; glasses such as Borosilicates and LTCC's; ceramics for example Aluminium Silicates, Aluminium Nitride, sapphire, & quartz, semi-conductors such as Gallium Arsenide, Gallium Nitride, Silicon, Germanium, Silicon Nitride, & Indium Phosphide. The preferred dielectric is an LTCC.

Three parallel extending cantilevers 19 are mounted in a body 41 in fixed relationship to the base 12. The body 41 is formed from silicon and is flip-chip bonded to the base 12 using solder bumps 40 . The cantilevers 19 are micromachined from the silicon body 41.

Within the base 12 there are provided conducting paths 21, 22,23 & 24 & ground planes 18. The paths 21-24 have respective contacts 26,27,28,29 on the upper surface 17 of the base 12 to which they are each connected by a respective substantially vertical path 25 commonly known as a via. The paths 21 & 22, 22 & 23 and 23 & 24 are switchable signal lines and have switchable gaps A,B & C which are electrically insulating. Each gap A,B and C is located under a cantilever 19 and each cantilever 19 has a complementary and opposing electrically conducting contact 31 which overlays the respective gap A,B or C. The contact 31 can bridge the respective gap A,B,or C between the pairs of contacts 26,27 and 27,28 and 28,29, to complete the electrical path. This is best seen in Fig.3.

An actuator 32 is provided on the lower surface of each cantilever 19 and comprises a thin layer piezo electric material, preferably lead zirconate titanate. Each actuator 32 is coupled to the respective cantilever 19 so that a deformation of the actuator causes a corresponding deformation of the respective cantilever. In operation when a potential difference, preferably a DC voltage of between 3 - 10 volts is apphed across the piezo electric material of each actuator 32 via respective drive signal paths 30, it causes the respective cantilever 19 to bend bringing its contact 31 into contact with a respective pair of contacts 26,27, or 27,28, or 28,29 bridging the respective gap A,B or C, and completing the paths 21,22 or 22,23 or 23,24 through vias 25 passing through the dielectric layers. Removal of the electric field allows the cantilever 19 to straighten and the contacts open.

The gaps A, B , & C are about 100- 200 microns in width, and there is a switchable gap, typically, of 5-11 microns between the contacts 31 and the contacts 26-29 on the base 12 to provide an electrical isolation of at least 25 dB at 40GHz.

Referring now to Figs. 2 & 3 there is shown in schematic form the "node" switching arrangement within the switch 10 which enables the switch to be used in a DC-millimeterwave cross connect in which any one signal input can be connected to any one signal output. This cross connect array is shown in Fig 4 and will be described below.

The switch includes three different electrical paths 21 & 22, 22 & 23 and 23, 24. The paths are isolated on their different layers 13,14 & 15. The switch has a signal first input path 22, and a second signal input (path) 24. The switch also has a first signal output 21 and a second signal output 23. The input 22 is connectable to the two outputs 21 and 23 by bridging the gaps A & B, and the other input 24 is connectable only to the output 23 by bridging the gap C.

With reference to Fig. 4 there is shown as an example, an 8 X 8 cross connect. The switch 10 allows for a switching arrangement or matrix which uses a minimal number of switches, that is 8 x 8 (i.e. a total of 64) switches, to minimise losses and complexity. It can be seen how by closing pairs of contacts (A,B or C) in each switch 10, each input 22S-Z can be selectively connected to a particular output 23S-Z. The individual switches are controlled by an external controller which may be programmable. In the preferred arrangement only one cantilever 19 is operable at any "node". This simplifies the control of the switching matrix. The arrangement allows different input signals of differing frequencies to be simultaneously sent to different outputs without generating intermodulation products. The different routes around the cross-net allow the simultaneous connection of each input to a respective selected output. Although the arrangement has been shown for an 8 x 8 cross-net other arrangements are possible e.g 4 X 4, 16 x 16, 32 x 32 etc..

With reference to Figs 5 & 6 there is shown a second micromachined switch 50 which in operation is similar to the switch 10, the main differences being in relation to the number of pairs of contacts , the arrangement of the cantilevers and the "node" switching arrangement. The switch 50 has a silicon body 61 having an open centre into which four cantilevers 59 project, h this case the body 61 is rectangular and one cantilever 59 projects inwardly from each side of the body. As before the cantilevers 59 each carry a contact and are each operated by piezo electric actuators.

The base 52 comprises a multilayer LTCC conductive/dielectric laminate carrying electrical various paths 55,56,57,58,62,63, & 64 on the layers of substrate, as previously described. There are, for example; paths 55 & 63 for drive signals for the actuators, signal input/output path 64 which is linked to a central contact 84 on the upper surface of the base, and signal output/input paths 56,57,58,62 which are each linked to a respective contact 86,87,88, and 92 equiangularly spaced around the central contact 84. The contacts on the cantilevers 59 can bridge the gap between the central contact 84 and a selected one of the surrounding contacts 86,87,88 or 92.

h use the signal path 64 may act as an input path and the paths 56,57,58, & 62 act as signal output paths, or their functions may be reversed.

A second example of a cross connect is shown in Fig 7, which connects any one of four input 64A,64B,64C & 64D with any one of four outputs 164A, 164B,164C, and 164 D. The array comprises eight switches 50, there being one input connected to the central contact 84 of four switches 50A-50D , and one output connected to the central contact 84 of the other four switches 50E-50H. The four surrounding contacts 86,87,88 & 92 of each input switch 50A-D are connected to a contact on each output switch.

This means that any input signal can be directly connected to any output with minimum and substantially equal, and symmetrical losses.

Although a 4 x 4 cross connect is shown the switches are applicable to other cross-connects.

Claims

1. An electrical switch of the kind referred, wherein the switch includes a plurality of pairs of contacts, the contacts of each pair being relatively moveable by a respective actuator, and a base which comprises at least two separate layers each being provided with at least one electrical path which may be completed when a respective one of said pairs of contacts is in a closed state.

2. A switch as claimed in Claim 1, wherein each electrical path has a break therein and the break is bridged by a contact on the respective actuator when in the closed state.

3. A switch as claimed in Claim 1 or Claim 2 wherein the electrical paths in any layer of said base remote from the actuators are connected to their respective contacts by a respective interlayer path.

4. A switch as claimed in any one of claims 1 to 4 wherein the base is formed from layers of low temperature co-fired ceramic (LTCC).

5. A switch as claimed in any one of claims 1 to 4, wherein the switch includes three different electrical paths, at least one being on a layer remote from the actuators, and three pairs of different contacts arranged so that the contact moveable by each respective actuator bridges between two selected contacts as is desired, there being two inputs and two outputs into the switch, one input being connectable to the two outputs and the other input being connectable only to one of said outputs.

6. A switch as claimed in Claim 5 wherein each actuator may be individually operated to open or close the respective contacts as is desired.

7. A switch as claimed in Claim 5 or Claim 6 wherein the actuators each move a cantilever and the three cantilevers extend substantially parallel to each other, and the inputs and outputs each have a contact, the four contacts extending in a line transverse to the cantilevers.

8. A switching arrangement having N inputs and N outputs, each input being connectable to any one of the outputs, the arrangement including N x N switches as claimed in any one of Claims 5 to 7, wherein said one output of each switch is connected to said other input of a first adjacent switch in the arrangement, and the second output of each switch being connected to said one input of a second adjacent switch in the arrangement.

9. A switching arrangement as claimed in Claim 8 when used as a signal cross-connect utilising 8 x 8 switches.

10. A switch as claimed in any one of claims 1 to 4, wherein the switch includes four different electrical paths, four pairs of different contacts arranged so that the contact on each respective actuator bridges between two selected contacts as is desired, there being one central contact and four satellite contact, the central contact being connectable any of the four satellite contacts.

11. A switch as claimed in Claim 10 wherein the central contacts is individually connectable to each satellite contact by a respective actuator as is desired.

12. An electrical switch substantially as hereinbefore described with reference to or substantially as illustrated in any one of Figs. 1, 2, 3, 5 or 6 of the accompanying drawings.

13. A switching arrangement having N inputs and N outputs in which each input which is directly connectable to each output, the arrangement including 2N switches according to claim 10 or Claim 12, wherein the input for a first array of N switches comprises the respective central contacts and the output for a second array of N switches also comprises the respective central contacts, and each switch of the first array has each satellite contact connected to a corresponding satellite contact of the second array of switches.

14. A switching arrangement as claimed in Claim 13 when used as a signal cross connect.

15. A switching arrangement as claimed in any one of Claims 8, 9, 12 & 13 , wherein only one cantilever of each switch is operable at any one time.

16. A switching arrangement having N inputs and N outputs substantially as hereinbefore described with reference to or substantially as illustrated in Fig. 4 or Fig. 6 of the accompanying drawings.

17. A micromachined electrical switch comprising: a plurality of electrical paths each of which has a break therein; a plurality of moveable electrical contacts each of which includes piezoelectric material which changes dimensionally in response to an electrical signal; and a plurality of actuators for applying electrical signals to the respective contacts, each of the contacts being arranged such that when moved to a closed position in response to an electrical signal from the respective actuator, it bridges the break in a respective one of said electrical paths.