Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/0036—Switches making use of microelectromechanical systems [MEMS]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/0036—Switches making use of microelectromechanical systems [MEMS]
  • H01H2001/0042—Bistable switches, i.e. having two stable positions requiring only actuating energy for switching between them, e.g. with snap membrane or by permanent magnet
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H61/00—Electrothermal relays
  • H01H2061/006—Micromechanical thermal relay
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H59/00—Electrostatic relays; Electro-adhesion relays
  • H01H59/0009—Electrostatic relays; Electro-adhesion relays making use of micromechanics

Definitions

• the present invention relates to a bistable microswitch, with low consumption and with horizontal displacement.
• a micro-switch finds particular utility in the field of mobile telephony and in the space field.
• the RF components intended for these areas are subject to the following specifications: supply voltage lower than 5 volts, - insulation higher than 30 dB, - insertion losses lower than 0.3dB, - reliability corresponding to a number of cycles greater than 10 9 , - * surface less than 0.05 mm 2 , - lowest possible consumption.
• certain switches are used only once, to switch from one state to another state in the event of equipment failure for example.
• bistable switches which do not require a supply voltage once they have switched from one state to another.
• double switches which considerably simplify the matrixes of switches of the redundant circuits used in the case of critical functions. This type of application is found in particular in the space field (satellite antennas). These dual switches allow an input signal to be switched from one electronic circuit to another in the event of a fault. These are therefore switches which have the possibility of switching either a first set of two electrical tracks between them, or a second set of two electrical tracks.
• Double switches have the advantage of obtaining circuits comprising fewer components (for example 10 redundancy functions require 10 double switches instead of 20 single switches), which means among other things less reliability tests, less mounting, space saving and overall lower cost.
• micro-switches that is to say those relating to microelectronics
• they are used in signal routing, impedance tuning networks, gain adjustment of amplifiers, etc.
• the frequency bands of the signals to be switched can range from a few MHz to several tens of GHz.
• switches from microelectronics are used, which allow integration with the electronics of the circuits and which have a low manufacturing cost. In terms of performance, these components are however quite limited.
• silicon FET switches can switch high power signals at low frequencies, but not at high frequencies.
• MEMS Metal Semiconductor Field Effect Transistor
• MEMS switches have the following characteristics: - low insertion losses (typically less than 0.3dB), significant isolation from MHz to millimeter (typically greater than -30dB), - no response non-linearity (IP3).
• ohmic contact the two RF tracks are contacted by a short circuit (metal-metal contact). This type of contact is suitable for both continuous signals and for high frequency signals (above 10 GHz).
• capacitive contact switch an air space is electromechanically adjusted to obtain a variation in capacity between the closed state and the open state.
• thermally actuated microswitches that can be described as conventional are not bistable. They offer the advantage of a low actuation voltage. They have several drawbacks: excessive consumption (especially in the case of mobile phone applications), low switching speed (due to thermal inertia) and the need for a supply voltage to maintain contact in closed position.
• Electrostatic actuated microswitches that can be described as conventional are non-bistable. They offer the advantages of fast switching speed and generally simple technology. They present reliability problems, this point being particularly sensitive in the case of electrostatic switches with low actuation voltage (bonding of structures).
• Electromagnetic actuation microswitches that can be described as conventional are not bistable. They generally operate on the principle of the electromagnet and essentially use magnetic circuits based on iron and an excitation coil. They have several drawbacks. Their technology is complex (coil, magnetic material, permanent magnet in some cases, etc.). Their consumption is important. They also require a supply voltage to maintain the contact in the closed position. There are two configurations of contact displacement: vertical displacement and horizontal displacement. In the case of a vertical displacement, the displacement is made outside the plane of the RF tracks. The contact is made on the top or on the bottom of the tracks. This configuration has the advantage that the metallization of the contact pad is easy to perform
• This stiffness is conditioned by the final shape of the beam which depends on the topology of a sacrificial layer and which itself depends on the shape and the thickness of the tracks located below.
• This configuration is well suited to a double contact, by means of a symmetrical actuator.
• Metallization "gold" can be done in the very last technological stage. All the preceding steps can be compatible with the production of integrated circuits.
• the shape of the contact is determined during the photolithography step.
• the shape of the beam is determined during the photolithography step. Its stiffness is therefore well controlled.
• the metallization on the side is delicate. The contact resistance can therefore be poorly controlled. This configuration is unsuitable for electrostatic actuation because of the very small facing actuation surfaces.
• Another characteristic of the movement of the switches is the number of equilibrium states. The standard case is that where the actuator has only one state balance. This implies that one of the two switch states (switched or non-switched) requires a DC voltage supply to maintain the position. Stopping the excitation returns the switch to its equilibrium position.
• the bistable case is the case where the actuator has two distinct states of equilibrium. The advantage of this operating mode is that the two positions "closed” and "open” of the switch are stable and do not require power until one switches from one state to another.
• a bistable micro-switch with low consumption and with horizontal displacement.
• This microswitch is particularly well suited to the field of mobile telephony and to the space field.
• the subject of the invention is therefore a bistable MEMS microswitch made on a substrate and capable of electrically connecting the ends of at least two conductive tracks, comprising a beam suspended above the surface of the substrate, the beam being embedded in its two ends and being constrained in compression when it is in the non-deformed position, the beam having means forming electrical contact arranged to make a lateral connection with the ends of the two conductive tracks during a deformation of the beam in a horizontal direction by relative to the surface of the substrate, the microswitch having means actuating the beam to place it either in a first deformed position, corresponding to a first stable state, or in a second deformed position, corresponding to a second stable state and opposite to the first deformed position relative to the undeformed position , the means forming
• the microswitch can be a double microswitch.
• the first deformed position corresponds to the connection of the ends of two first conductive tracks
• the second deformed position corresponds to the connection of the ends of two second conductive tracks.
• It can be a simple micro switch.
• the first deformed position corresponds to the connection of the ends of two conductive tracks
• the second deformed position corresponds to an absence of connection.
• the beam is made of dielectric or semiconductor material and the means forming electrical contact are formed of an electrically conductive pad and integral with the beam.
• the means for actuating the beam may include thermal actuators using a bimetal effect. Each thermal actuator can then comprise a block of thermal conductive material in intimate contact with an electrical resistance.
• the means for actuating the beam may include means for applying forces electrostatic. They can include thermal actuators using a bimetallic strip effect and means for implementing electrostatic forces.
• the beam is made of electrically conductive material.
• the beam actuation means can then include means for implementing electrostatic forces.
• the means forming an electrical contact may have a shape allowing it to be embedded between the ends of the conductive tracks to be connected. In this case, the ends of the conductive tracks can have a flexibility allowing to follow the shape of the means forming electrical contact during a connection.
• the microswitch can also include means forming a relaxation spring for at least one of the embedded ends of the beam.
• the means forming electrical contact can be means ensuring ohmic contact or means ensuring capacitive contact.
• FIG. 1 is a top view of a first variant of double microswitch according to the present invention
• - Figure 2 shows the microswitch of Figure 1 in a first stable operating state
• - Figure 3 shows the microswitch of Figure 1 in a second stable operating state
• - Figure 4 is a view of above of a second variant of double microswitch according to the present invention
• - Figure 5 is a top view of a third variant of double microswitch according to the present invention
• - Figure 6 is a top view of a simple micro-switch according to the present invention
• - Figure 7 is a top view of a fourth variant of a double micro-switch according to the present invention
• - Figure 8 is a top view of a fifth variant of double micro-switch according to the present invention
• FIG. 1 is a top view of a first variant of a double micro-switch according to the first invention.
• the microswitch is produced on a substrate 1 of which only a part is represented for the sake of simplification.
• This microswitch is a double switch. It is intended to make a connection either between the ends 12 and 13 of the conductive tracks 2 and 3, or between the ends 14 and 15 of the conductive tracks 4 and 5.
• the micro-switch of FIG. 1 comprises a beam 6 of dielectric material or semiconductor. It is located in the plane of the conductive tracks. The beam is embedded at its two ends in raised parts of the substrate 1.
• the beam shown is of rectangular section. It supports on its face directed towards tracks 2 and 3 (that is to say on one of its sides) actuators 20 and 30 and, on its face directed towards tracks 4 and 5 (that is to say on its other side), actuators 40 and 50.
• the actuators are located near the embedding zones of the beam.
• Each actuator consists of a block that is a good thermal conductor and an electrical resistance.
• the actuator 20 comprises a block 21 with which a resistor 22 is associated. The same applies to the other actuators.
• the beam is preferably made of dielectric or semiconductor material with a low coefficient of thermal expansion.
• the blocks of the thermal actuators are preferably made of metallic material with a high coefficient of thermal expansion to obtain a bimetallic strip effect at high efficiency.
• the displacement of the beam being done in the horizontal direction (the plane of the figure), the actuators are placed on the sides of the beam and in the vicinity of the embedments, always with a view to thermomechanical efficiency.
• the beam 6 also supports, in the central part and on its flanks, an electrical contact pad 7, intended to ensure an electrical connection of the ohmic type between the ends 12 and 13 of the tracks 2 and 3, and an electrical contact pad 8 between the ends 14 and 15 of tracks 4 and 5.
• a first set of actuators makes it possible to tilt the beam 6 in a position corresponding to one of its two stable states.
• FIG. 2 represents.
• the actuators 40 and 50 which induce a bimetallic strip effect in the beam 6, the latter deforms to place itself in a first stable state shown in the figure.
• the electrical contact pad 7 provides a connection between the ends 12 and 13 of the conductive tracks 2 and 3.
• the supplies of the electrical resistances of the actuators 40 and 50 are interrupted and the beam remains in this first stable state.
• the electrical contact pad 8 provides a connection between the ends 14 and 15 of the conductive tracks 4 and 5.
• the power supplies of the electrical resistors actuators 20 and 30 are interrupted and the beam remains in this second stable state.
• the electrical resistances of the actuators are preferably made of a conductive material having a high resistivity.
• the conductive tracks and the contact pads are preferably made of gold for its good electrical properties and its reliability over time, in particular with regard to oxidation.
• the recesses of the beam can be either rigid (simple recessing), or more or less flexible by varying the configuration of the recesses, for example by adding relaxation springs. Being able to play on flexibility of the beam makes it possible to control the stresses in the beam both initially (intrinsic stresses) that to pass from a stable state to the other (passage by a state of buckling). This has the advantage of limiting the risks of rupture of the beam but also of allowing a limitation of the consumption of the micro-switch (lowering of the switching temperature of the micro-switch).
• the beam may exhibit stress relaxation only at one of its embedded ends or at both of its ends.
• FIG. 4 is a top view of a second variant of a double microswitch according to the present invention, the two ends of the beam of which have a stress relieving recess.
• the variant embodiment of FIG. 4 comprises the same elements as the variant embodiment of FIG. 2 with the exception of the embedding of the ends of the beam.
• the substrate 1 has stress release slots 111 perpendicular to the axis of the beam.
• the slots 111 provide a certain flexibility to the part of the substrate located between them and the beam.
• the microswitch is shown in its initial position, before it is put into service.
• FIG. 5 is a top view of a third variant of a double micro-switch according to the present invention.
• This microswitch uses bimetal effect actuators and has electrostatic assistance. It is shown in its initial position, before it is put into service. We recognize the substrate 201, tracks
• the microswitch of FIG. 5 further comprises electrodes allowing the application of electrostatic forces. These electrodes are distributed on the beam and on the substrate.
• the beam 206 supports on a first side electrodes 261 and 262 and, on a second side, electrodes 263 and 264. These electrodes are located between the thermal actuators and the electrical contact pads.
• the substrate 201 supports electrodes 271 to 274 opposite each electrode supported by the beam 206.
• the electrode 271 has a part opposite the electrode 261, this part not being visible in the figure, and a part intended at its electrical connection, this part being visible in the figure. The same goes for electrodes 272, 273 and 274 relative to the electrodes
• the electrodes 271 to 274 have a shape which corresponds to the shape of the deformed beam. This makes it possible to limit the actuation or holding voltages (variable gap electrodes).
• the microswitch can be put in a first stable state, for example that corresponding to the connection of the conductive tracks 202 and 203 by the contact pad 207, by means of the thermal actuators 240 and 250 which are only put into service to obtain the first stable state.
• the application of a voltage between the electrodes 261 and 271 on the one hand and between the electrodes 262 and 272 on the other hand ensures a reduction in the contact resistance between the pad 207 and the tracks 202 and 203.
• the micro- switch can be put in the second stable state by means of actuators 220 and 230 which are put into service only to obtain the switching from the first stable state to the second stable state.
• the application of a voltage between the electrodes 263 and 273 on the one hand and between the electrodes 264 and 274 on the other hand ensures a reduction in the contact resistance between the pad
• FIG. 6 is a top view of a simple micro-switch according to the present invention.
• This micro-switch uses bimetal effect actuators, without electrostatic assistance. It is shown in its initial position, before being put into service. We recognize the substrate 301, tracks 302 and 303 to be connected by the contact pad 307 during a tilting of the beam 306 in a first stable state, the second stable state corresponds to an absence of connection. Actuators 320, 330 and 340, 350 are also recognized.
• FIG. 7 is a top view of a fourth variant of double microswitch according to the present invention. This microswitch only uses actuators with an electrostatic effect. It is shown in its initial position, before it is put into service. We recognize the substrate 401, tracks
• the microswitch of FIG. 7 includes electrodes allowing the application of electrostatic forces. These electrodes are distributed on the beam and the substrate.
• the beam 406 supports on a first side electrodes 461 and 462 and, on a second side, electrodes 463 and 464. These electrodes are located on each side of the electrical contact pads 407 and 408.
• the substrate 401 supports electrodes 471 to 474 opposite each electrode supported by the beam 406.
• the electrode 471 has a part opposite the electrode 461, this part not being visible in the figure, and a part intended for its electrical connection, this part being visible in the figure. The same is true for electrodes 472, 473 and 474 with respect to electrodes 462, 463 and 464 respectively.
• the microswitch can be put in a first stable state, for example that corresponding to the connection of the conductive tracks 402 and 403 by the contact pad 407, by applying a voltage between the electrodes 461 and 471 on the one hand and between the electrodes 462 and 472 on the other hand. Once the beam has switched to its first stable state, the applied voltage can be removed or reduced so as to reduce the contact resistance between the pad 407 and the tracks 402 and 403.
• FIG. 8 is a top view of a fifth variant of a double micro-switch according to the present invention. This fifth variant is an optimized version of the previous variant. The same references as in the previous line have been kept to designate the same elements.
• FIG. 9 is a top view of a sixth variant of a double micro-switch according to the present invention. It is shown in its initial position before it is put into service.
• the beam 506 is in this variant a metal beam, for example aluminum, supporting on its flanks the contact pads 507 and 508.
• the tilting of the beam in a first stable state for example that corresponding to the connection of the conductive tracks 502 and 503 is obtained by applying a tilting voltage between the beam 506 serving as an electrode and the electrodes 571 and 572.
• the applied voltage can be eliminated or reduced so as to reduce the contact resistance between pad 507 and tracks 502 and 503.
• the microswitch can be put in the second stable state by applying a voltage between the beam 506 and the electrodes 573 and 574 (and suppression of the voltage of electrostatic assistance of maintenance in the first stable state if this assistance was used).
• the applied tension can be eliminated or reduced as before.
• the electrostatic actuation has been optimized by the shape given to the electrodes 571 to 574.
• FIG. 10 is a top view of a double microswitch corresponding to the first variant but provided with optimized contacts .
• the microswitch is shown in its initial position before it is put into service.
• the same references as in FIG. 1 have been kept to designate the same elements.
• the ends 12 ', 13', 14 ', and 15' of the conductive tracks 2, 3, 4 and 5 respectively have been optimized to ensure better electrical contact with the contact pads 7 'and 8' .
• the contact pads 7 'and 8' have a wider shape at their base (that is to say near the beam) than at their top. They can thus be more easily fitted between the ends 12 ', 13' and 14 ', 15' which are themselves provided with a mounting leave.
• the ends of the conductive tracks can also be slightly flexible to match the shape of the contact pad and thus ensure better electrical contact.
• the microswitch according to the present invention has the following advantages. Its operation requires low consumption due to the bi-stability.
• the thermal actuator variants have a high actuation efficiency. Their switching time is low since it is not necessary to go very high in temperature to tilt the beam. They also have low tilting voltage when electrostatic actuators are associated with thermal actuators. This is due to: - the use of the thermal bimetal effect; the use of heating resistors integrated on the beam and located on
• the bi-stability presented by the microswitch is perfectly controlled for two reasons.
• the first reason is that bi-stability is obtained by the fact that the beam must be under compressive stress. This constraint is brought about by the constituent materials of the switch (shape, thickness). If the beam is designed to be perfectly symmetrical, and if the realization of each of the two sets of actuators is made during the same deposit, the constraint can only be perfectly symmetrical (same shape, same thickness and symmetry of the actuators). We are therefore in the presence of a device capable of not favoring a stable state over another which would be less stable.
• the microswitch according to the invention can advantageously be produced on a silicon substrate.
• the embedding part and the beam can be made of Si 3 N, SiO 2 or polycrystalline silicon.
• the conductive tracks, the contact pads, the electrodes, the thermal actuators can be made of gold, aluminum or copper, nickel, materials which can be deposited under vacuum or electrochemically (electrolysis, autocatalytic deposition).
• the heating resistors can be made of TaN, TiN or Ti.
• a method for producing an ohmic microswitch with thermal actuation on a silicon substrate may comprise the following steps: - deposition of an oxide layer 1 ⁇ m thick by PECVD on the substrate, - lithography and etching of a cavity in order to obtain embedding, - deposit of a polyide layer 1 ⁇ m thick, serving as a sacrificial layer, - dry planarization or chemical-mechanical polishing (CMP) of the sacrificial layer, deposition of a layer of SiO 2 3 ⁇ m thick, - etching of this layer of Si0 to obtain openings for the actuators, the contact pads and the conductive tracks, - deposition of an aluminum layer 3 ⁇ m thick, - planarization by CMP of the aluminum layer until the layer of Si0 2 is revealed, - deposition of a layer of Si0 2 0.15 ⁇ m thick, deposit of a layer of TiN 0.2 ⁇ m thick, - litho-etching of the heating resist
• a method for producing a thermally actuated micro-switch on a silicon substrate can comprise the following steps: - deposition of an oxide layer 1 ⁇ m thick by PECVD on the substrate, - lithography by etching of a cavity in order to obtain embedding, - deposition of a layer of polyimide 1 ⁇ m thick, serving as a sacrificial layer, - dry planarization or chemical mechanical polishing (CMP) of the sacrificial layer, deposition of a layer of Si0 2 3 ⁇ m thick, - etching of this layer of SiO 2 to obtain openings for the actuators, - deposition of a layer of aluminum 3 ⁇ m thick , - planarization by CMP of the actuators, - deposition of a TiN layer 0.2 ⁇ m thick, - litho-etching of the heating resistors in the TiN layer, - deposition of a Si0 2 layer of 0, 2 ⁇ m thick, -

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• 2003
  • 2003-07-01 FR FR0350278A patent/FR2857153B1/fr not_active Expired - Fee Related
• 2004
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  • 2004-06-30 EP EP04767860A patent/EP1639613B1/de active Active
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  • 2004-06-30 US US10/561,948 patent/US7489228B2/en active Active
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