ROBUST MICROELECTROMECHANICAL SWITCH

Abstract

A microelectromechanical system switch includes a signal input line, a signal output line, a deformable conducting membrane electrically connected to the signal output line and including a contact dimple facing the signal input line, and an actuation electrode. The membrane has a planar round shape, with a radial opening in the direction of the signal input line, narrowing from the periphery towards the center of the membrane, the contact dimple being formed in the central region of the membrane, the actuation electrode has the same shape as the membrane, and the gap between the membrane, facing the actuation electrode, and the actuation electrode is an airgap only.

Claims

1. A microelectromechanical (MEMS) switch, comprising: a substrate, a signal input line formed on the substrate, a signal output line formed on the substrate, a deformable conducting membrane, electrically connected to the signal output line, said the deformable conducting membrane being suspended into a plane parallel to the plane of the substrate by anchors arranged on the substrate, the deformable conducting membrane comprising a contact dimple facing the signal input line such that, in a non-deformed state of the deformable conducting membrane, the contact dimple is not in contact with the signal input line and, in a deformed state of the deformable conducting membrane, said the contact dimple is in contact with the signal input line for transmitting a signal from the signal input line to the signal output line, an actuation electrode formed on the substrate below the deformable conducting membrane, paid the actuation electrode being intended to deform the deformable conducting membrane for making an electrical contact between the contact dimple of the deformable conducting membrane and the signal input line, wherein: the deformable conducting membrane comprises a planar round shape, the anchors being arranged at its periphery so as to concentrate a lower stiffness in the central region of the deformable conducting membrane, with a radial opening forming an acute angle in the direction of the signal input line narrowing from the periphery towards the center of the deformable conducting membrane, the contact dimple being formed in the central region of the deformable conducting membrane such that the end of the signal input line is opposite the contact dimple, the actuation electrode comprises the same shape as the deformable conducting membrane, surrounding on the substrate the end of the signal input line, and the gap between the lower surface of the deformable conducting membrane, facing the actuation electrode, and the actuation electrode is an airgap only.

2. The microelectromechanical switch according to claim 1, wherein an anchor is formed in the median axis of the radial opening.

3. The microelectromechanical switch according to claim 1, wherein two anchors are formed symmetrically with respect to the median axis of the radial opening, on a circle having the same center as the circumcircle of the deformable conducting membrane, the angle formed on the circle having the same center as the circumcircle of the deformable conducting membrane between each anchor and the median axis of the radial opening being not higher than 30°.

4. The microelectromechanical switch according to claim 1, wherein the other anchors are formed symmetrically with respect to the median axis of the radial opening.

5. The microelectromechanical switch according to claim 1, wherein at least one cutout is formed on the deformable conducting membrane between two diametrically-opposed anchors on a circle having the same center as the circumcircle of the deformable conducting membrane.

6. The microelectromechanical switch according to claim 1, wherein a cutout is formed on the deformable conducting membrane proximate to each anchor, the cutouts being formed on the perimeter of a circle having the same center as the circumcircle of the deformable conducting membrane.

7. The microelectromechanical switch according to claim 6, wherein the one or more cutouts pass through the thickness of the deformable conducting membrane.

8. The microelectromechanical switch according to claim 1, wherein through holes are formed on a circle having the same center as the circumcircle of the deformable conducting membrane.

9. The microelectromechanical switch according to claim 1, wherein one or more stoppers are formed on the lower surface of the deformable conducting membrane, each stopper facing a metal island electrically isolated from the actuation electrode.

10. The microelectromechanical switch according to claim 1, wherein the contact dimple is made of metal belonging to the platinum group or their oxides or both.

11. The microelectromechanical switch according to claim 1, wherein the deformable conducting membrane is made of gold, or is a metal alloy or a set of layers comprising at least one conductor.

12. The microelectromechanical switch according to claim 1, wherein the actuation electrode is made of gold or any other conducting or semi-conducting material.

13. The microelectromechanical switch according to claim 1, wherein the stoppers are made of metal belonging to the platinum group or their oxides or both.

Description

[0044] In these drawings:

[0045] FIG. 1 is a top view of a microelectromechanical switch according to a particular embodiment of the present invention, the actuation electrode being shown in dotted lines;

[0046] FIG. 2 is a view similar to FIG. 1, with the elements arranged below the deformable conducting membrane being shown in dotted lines;

[0047] FIG. 3 is a cross-sectional view of the switch of FIG. 1 along the line A-A′, in its open position;

[0048] FIG. 4 is a cross-sectional view of the switch of FIG. 1 along the line A-A′, in its actuated position;

[0049] FIG. 5 is a simulation of the deflection of the membrane of the switch of FIG. 1 for different temperatures, along the axis y indicated on the detailed view, the simulated membrane being made of gold;

[0050] FIG. 6 is the measurement of the evolution of the contact resistance of the switch of FIG. 1 as a function of the number of cycles, a cycle being defined as the succession of an actuation action (passing state or down-state) and an opening action (isolation state or up-state) of the switch, the switch being cycled at a frequency of 4 kHz; and

[0051] FIG. 7 is the measurement of the evolution of the actuation voltage of the switch of FIG. 1 as a function of the number of cycles, at a frequency of 4 kHz.

[0052] If referring to FIGS. 1 to 4, it can be noted that a microelectromechanical (MEMS) switch 1 according to the invention is shown.

[0053] The microelectromechanical switch 1 is formed on a substrate S and mainly comprises a deformable conducting membrane 2, an actuation electrode 3, a signal input line 4 and a signal output line 5.

[0054] The signal input line 4, the signal output line 5 and the actuation electrode are formed on the substrate S.

[0055] The deformable conducting membrane 2 is planar, generally round-shaped, with a radial opening 2a in the direction of the signal input line 4, narrowing from the periphery towards the center of the deformable conducting membrane 2. The deformable conducting membrane 2 is suspended above the actuation electrode 3, by means of anchors 6, distributed at its periphery, so as to concentrate the lowest stiffness area of the deformable conducting membrane 2 at the contact dimple with the signal input line 4 (described below) arranged at a distance from the top of the radial opening lower than 30% of the radius of the deformable conducting membrane 2.

[0056] One of the anchors 6 is arranged in the direction of the signal input line 4, and allows to provide an electrical connection between the deformable conducting membrane 2 and the signal output line 5.

[0057] The other anchors 6 are distributed by pairs, opposed with respect to the center of the circumcircle of the deformable conducting membrane 2. It can be noted that, although the embodiment shown comprises five anchors 6, the invention is not limited in this respect within the scope of the present invention.

[0058] According to a preferred embodiment, the number of anchors is odd, one of the anchors 6 thus being arranged on the median axis of the radial opening 2a, in the direction of the signal input line 4.

[0059] Each anchor 6 is constituted by a tether extending perpendicularly to the surface of the deformable conducting membrane 2, towards the substrate S, said tether extending along two tabs 6a, enclosing a block 6b integral with the substrate S, both tabs 6a being suspended into the same plane as the deformable conducting membrane 2, ensuring an optimum distribution of the stresses when the temperature raises.

[0060] Cutouts 7 are formed on the deformable conducting membrane 2, in front of each anchor 6, the cutouts 7 being aligned on a circle having the same center as the circumcircle of the deformable conducting membrane 2.

[0061] Finally, holes 8 are formed on a smaller circle, having the same center as the circumcircle of the deformable conducting membrane 2. These holes are optional within the scope of the invention.

[0062] If referring more particularly to FIG. 2, it can be noted that the lower surface of the deformable conducting membrane 2, facing the actuation electrode 3, carries a contact dimple 9, proximate to the top of the radial opening 2a, intended, under the deformation of the deformable conducting membrane 2 by the actuation electrode 3, to come into contact with the end of the signal input line 4.

[0063] Stoppers 10, substantially formed on the same circles as the holes 8 and the cutouts 7, are formed on the lower surface of the deformable conducting membrane 2, their function being described in more detail below.

[0064] The actuation electrode 3 has substantially the same shape as the deformable conducting membrane 2, and surrounds the end of the signal input line 4.

[0065] If referring to FIG. 2, it can be noted that islands 3a, electrically isolated from the rest of the actuation electrode, are formed opposite the stoppers 10.

[0066] The function of the stoppers 10 and islands 3a consists in allowing, during the deformation of the deformable conducting membrane 2 attracted by the actuation electrode, to limit the deformation of the deformable conducting membrane 2 by contact of the stoppers 10 on the islands 3a. Although the presence of the islands 3a and stoppers 10 is preferred, since it limits the deformation of the deformable conducting membrane 2 and allows the electrical isolation thereof, a switch which does not comprise them is also within the scope of the present invention, which is not limited in this respect.

[0067] The substantially identical shapes of the deformable conducting membrane 2 and the actuation electrode 3 allow to ensure an uniform and homogeneous deformation while ensuring the generation of a high electrostatic force.

[0068] The overall shape of the microelectromechanical switch 1 according to the invention, which is round with an opening 2a on the signal input line 4, allows to ensure a high contact force, localized at the center of the circle due to the position of the anchors and the shape of the membrane, thereby ensuring an electrically stable contact with the end of the signal input line 4.

[0069] The opening 2a also allows to limit the surface of the deformable conducting membrane 2 facing the current input line 4, reducing the electrical couplings therebetween.

[0070] FIGS. 3 and 4 illustrate the two open and closed positions, respectively, of the microelectromechanical switch 1 according to the invention.

[0071] In FIG. 3, it can be noted that an airgap between the deformable conducting membrane 2 and the actuation electrode 3 is provided. The microelectromechanical switch 1 is open, and the signal does not pass between the signal input line 4 and the signal output line 5.

[0072] In FIG. 4, it can be noted that the contact dimple 9 is in contact with the end of the signal input line 4, the stoppers 10 being in contact with the islands 3a. The microelectromechanical switch 1 is closed, and the signal passes between the signal input line 4 and the signal output line 5.

[0073] In FIG. 5, it can be noted that the deflection of the membrane according to the invention is low (<0.15 μm) when subjected to high temperature stresses (500° C.)

[0074] In FIG. 6, one can note the stability of the contact resistance due to the high localized contact force generated by the present invention, during more than one billion of actuations.

[0075] In FIG. 7, one can note the stability of the actuation voltage due to the homogeneous deformation and the airgap allowed by the invention.

[0076] The substrate is advantageously silicon. The actuation electrode is advantageously made of gold, but can also be made of any other conducting or semi-conducting material.

[0077] The deformable conducting membrane 2 is advantageously made of gold, but can also be a metal alloy or a set of layers comprising at least one conductor.

[0078] The contact dimple 9 and the stoppers 10 are integrally formed with the deformable conducting membrane 2. They can advantageously be covered with a harder material so as to increase their resistance.

[0079] As a non-limiting example, a switch according to the invention is contained in a circle having a radius of 140 μm.

[0080] In an embodiment, the thickness of the switch is 7 μm, its lowering voltage is 55V, its return force is 1.8 mN and its contact force is between 2 and 4 mN at 70V.