Patent Application
20080060919
An electromechanical switch according to the invention is placed under reduced pressure or in helium gas atmosphere serving as environment in which the damping effect of the viscosity of air or the like is weakened. The electromechanical switch according to the invention is constituted by including a first electromechanical switch, in which a movable electrode having a weak spring force is pulled in toward a fixed electrode at high speed, and a second electromechanical switch in which a movable electrode having a strong spring force is pulled away from a fixed electrode. In a stationary state, signals can be switched only by turning on and off the first electromechanical switch.
Additionally, to allow a first electromechanical switch to obtain sufficient isolation in a transient state caused when a signal is shielded, the first electromechanical switch ensures isolation established within a time taken to make an electrode to be pulled away by a sufficient distance. The isolation in the transient state is ensured by bringing the second electromechanical switch into an off-state at high speed.
Also, the second electromechanical switch is adapted so that although a movable electrode is pulled away only for a moment, the movable electrode performs natural vibrations due to a strong spring force and to a weak damping effect, and that thus, the movable electrode returns to the neighborhood of an initial position. Consequently, the second electromechanical switch having a strong spring can be latched at a minute voltage.
Thus, the electromechanical switch according to the invention, which is a switch using a microelectromechanical elements, can achieve the on/off of a signal at high speed at a low driving voltage by combining the first electromechanical switch, which uses an electrode having a weak spring force and is pulled in at high speed and is restored at low speed, with the second electromechanical switch that uses an electrode having a strong spring force and is released from a latch and is immediately latched.
Hereinafter, a preferred embodiment of the electromechanical switch according to the invention is described below in detail. In the drawings, a same reference numeral is used to designate substantially the same or corresponding member.
As shown in
As shown in
In the first embodiment, each of the first movable electrode 14 and the second movable electrode 16 is constructed as an inboard beam. The first movable electrode 14 and the second movable electrode 16 are configured so that the first movable electrode 14 has a relatively weak spring force, and that the second movable electrode 16 has a relatively strong spring force.
A first electromechanical switch 22 is configured to include the first movable electrode 14 and the fixed electrode 18. A second electromechanical switch 24 is configured to include the second movable electrode 16 and the fixed electrode 18. These electromechanical switches are series-connected to each other.
The first movable electrode 14 and the second movable electrode 16 perform natural vibrations using an electrostatic force generated according to the applied voltage and the spring forces of these movable electrodes themselves. An air gap having a size equal to or larger than the maximum amplitude of the natural vibrations is ensured.
To reduce the damping effect, this air gap is filled with dry helium. Alternatively, the air gap is maintained at vacuum.
Incidentally, the input/output terminals of the first movable electrode 14 are a first electrode terminal 4 and a fifth electrode terminal 8. The input/output terminals of the second movable electrode 16 are a second electrode terminal 5 and a fourth electrode terminal 7. The input/output terminals of the fixed electrode 18 are a third electrode terminal 6 and a sixth electrode terminal 9.
For example, in a case where the fifth electrode terminal 8 is used as a signal input terminal, the second electrode terminal 5 and the fourth electrode terminal 7 are signal output terminals.
Further, a control voltage supply used to apply an electrostatic force between the fixed electrode 18 and each of the first movable electrode 14 and the second movable electrode 16 can be connected to each of the electrode terminals.
As shown in
As shown in
That is, in the initial condition, a drive control voltage is applied to the second movable electrode 16. The second movable electrode 16 is electrically connected to the fixed electrode 18 by an electrostatic force. However, no drive control voltage is applied to the first movable electrode 14.
Next, an operation of the electromechanical switch according to the first embodiment is described below.
Referring to
When the drive control voltage applied to the first movable electrode 14 and the second movable electrode 16 is canceled, the first movable electrode 14 and the second movable electrode 16 are pulled away from the fixed electrode 18 by a spring restoring force of each of the movable electrodes. First, the second electromechanical switch 24 is put into an off-state, so that the electromechanical switch 40 is turned off.
At that time, the second movable electrode 16 having a strong spring restoring force operates at a speed higher than a speed, at which the first movable electrode 14 having a weak spring restoring force, and is detached from the fixed electrode 18 to start performing natural vibrations.
In a case where when this vibrating second movable electrode 16 returns to the vicinity of the fixed electrode 16, a drive control voltage is applied thereto, the second movable electrode 16 is latched by the electrostatic force toward the fixed electrode 18. During that, the first movable electrode 15 is sufficiently away from the fixed electrode 18, so that the first electromechanical switch 22 is in an off-state. The electromechanical switch 40 remains turned off even when the second movable electrode 16 is latched, so that the second electromechanical switch 24 is put into an on-state.
Thus, the electromechanical switch according to the first embodiment can perform an on-response and an off-response at high speed according to the combination of the first electromechanical switch, which is put into an on-state at high speed, and the second electromechanical switch that is put into an off-state at high speed.
Next, an operation of the electromechanical switch in the case of employing inboard beams as the movable electrodes described in the description of the first embodiment is described in detail below by way of example.
In the case where the movable electrodes are constituted by inboard beams, as in the first embodiment, a constant k of spring of the movable electrode is expressed by an equation (1).
k=Ew(D/L)3+8σ(1−ν)w(D/L) (1)
Incidentally, “E” represents Young's modulus, and “w” represents a line width of the movable electrode. “D” represents a thickness of the movable electrode. “L” represents a length of the movable electrode, and “σ” represents an internal stress, and “ν” represents a Poisson's ratio.
As is apparent from the equation (1), the spring constant k can be changed by changing the shape, the material, and the physical property of the movable electrode.
Next, a motion equation in the case of applying an external force F to the movable electrode is given by the following equation (2).
md2Z(t)/dt2+b(1.2−Z(t)/g)−3/2Z(t)+kZ(t)=F (2)
Incidentally, “Z(t)” represents the position of the movable electrode with respect to the fixed electrode at a moment t, and “m” represents the mass of the movable electrode, and “b” represents a damping coefficient, and “g” represents an initial value of the distance between the electrodes, and “k” represents a spring constant of the movable electrode.
In the first electromechanical switch 22, the spring force of the first movable electrode 14 is extremely weak. The first movable electrode 14 is designed to respond to a minute driving force. Thus, when the first movable electrode 14 is pulled in, the first movable electrode 14 can be pulled in by responding to the driving force at high speed even when the driving force is minute.
For example, in a case where aluminum (the internal stress is 50 MPa, the Young's modulus is 70 GPa, the Poisson's ratio is 0.25, and the density is 2.69 kg/m3) is used as the material of the first movable electrode 14, where data representing the shape thereof, that is, the width w1 is 2.5 μm, the thickness D is 0.4 μm, and the length L is 500 μm, and where the gap between the electrodes g1 is 0.2 μm, the first movable electrode is pulled in toward the fixed electrode 18 in 0.2 μs when a voltage of 8V is applied thereto.
As is seen from
At that time, in a case where the first movable electrode 14 serving as a thin structure is caused to perform an operation at high speed, the operation becomes complex by being affected by fluids, such as ambient air. Thus, the influence of the fluid is non-negligible.
Accordingly, to alleviate such a damping effect, an enclosed space is formed in the inside of the switch, in which the beams and so on are formed, so that the magnitude of the damping effect in the switch is ( 1/25) the magnitude of the damping effect in the atmospheric air.
Next, an off-operation of the first electromechanical switch is described below.
As is apparent from the equation (2), when the control voltage is turned off to cancel the driving force, the first movable electrode returns to an initial position by employing the spring force thereof as a driving force. However, because the spring force is weak, a response time is longer than that in the case of turning on the switch.
As shown in
Consequently, although a high-speed on-operation is enabled only by using the first electromechanical switch 22, it is difficult to enable a high-speed off-operation.
Next, the structure of the second electromechanical switch 24 and an operation thereof are described below.
The second movable electrode 16 of the second electromechanical switch is configured so that the spring force thereof is extremely strong. In a case where the second electromechanical switch 24 is formed in the same shape as that of the first electromechanical switch 22, it is advisable to increase the gap g2 between the electrodes. Alternatively, it is advisable to configure the movable electrode according to the equation (1) so that the spring constant is increased.
For example, aluminum (the internal stress is 50 MPa, the Young's modulus is 70 GPa, the Poisson's ratio is 0.25, and the density is 2.69 kg/m3) may be used as the material of the second movable electrode. Also, the second movable electrode may be configured to have a shape so that the width w2 is 2.5 μm, that the thickness D is 0.4 μm, that the length L is 500 μm, and that the gap between the electrodes g2 is 1.5 μm.
With such a configuration of the second electromechanical switch, the spring force of the second movable electrode is stronger than that of the first movable electrode of the first electromechanical switch. Also, the damping force of the second movable electrode is weaker than that of the first movable electrode of the first electromechanical switch. Thus, as shown in
As shown in
Thus, the environment is established so that the damping of the second movable electrode is suppressed. Consequently, the position of the electrode gradually converges to the position corresponding to 1.5 μm.
Next, a switching operation of the electromechanical switch according to the invention, which is the combination of the first electromechanical switch and the second electromechanical switch, is described below in detail.
First, an operation of changing an off-state to an on-state of the electromechanical switch according to the invention is described below.
As shown in
When the drive control voltage is applied to the first electromechanical switch 22 in this state, the first movable electrode is pulled in toward the fixed electrode. Then, the first movable electrode and the fixed electrode are put into contact with each other and are electrically connected to each other. Thus, as shown in
As shown in (a) and (b) of
Next, an operation of changing an on-state to an off-state of the electromechanical switch according to the invention is described below.
The states of the first electromechanical switch and the second electromechanical switch at each moment are shown with an equivalent circuit in (a) to (d) of
In the on-state of the electromechanical switch according to the invention, both of the first electromechanical switch and the second electromechanical switch are in an on-state, that is, the movable electrodes are in contact with the fixed electrode, so that values of the positions of the movable electrodes are 0. The drive control voltage is applied to both of the first electromechanical switch and the second electromechanical switch.
When the drive control voltage applied to the first electromechanical switch 22 and the second electromechanical switch 24 at a moment 0 is set to be 0, as shown in
At a moment t2 (about 2 μs), the position of the second movable electrode of the second electromechanical switch 24 is near to the initial position, that is, 1.5 μm or so, while the first movable electrode of the first electromechanical switch 22 reaches the position of 0.2 μm. Thus, sufficient isolation can be ensured singly by the first electromechanical switch 22.
At a moment t3 (about 2.5 μs), the second movable electrode of the second electromechanical switch 24 returns to the latching position, that is, the vicinity to the position corresponding to a displacement of 0.
At this moment t3, the first electromechanical switch 22 singly has already ensured isolation. Thus, even in a case where a drive control voltage is applied to the second electromechanical switch 24 in this state to thereby latch the second movable electrode, the entire electromechanical switch according to the invention sufficiently ensures isolation of high-frequency signals.
The control voltage required to perform this latch can be a minute voltage, because the gap between the returned second movable electrode and the fixed electrode is small.
Thus, according to the invention, an electromechanical switch having a high-speed response characteristic can be realized by combining the first electromechanical switch with the second electromechanical switch.
According to the first embodiment, as shown in
The electromechanical switch may be configured as a capacity type switch by forming dielectric substances on one or both of surfaces that the movable electrodes and the fixed electrode face.
Also, although aluminum has been cited as the material of the movable electrodes, other metallic materials, for example, Mo, Ti, Au, and Cu may be used, instead of Al. Alternatively, electrically conductive materials may be used.
Also, a beam structure configured by depositing metal portions, whose sizes are of the order of nanometers, on a surface of a plate-like silicon material may be employed as the movable electrode. Also, a piezoelectric element, a shape-memory alloy, an electromagnetic distortion element, and a bimorph element utilizing a bimorph effect may be utilized as the movable electrode.
Although the movable electrode is pulled in toward the fixed electrode formed on the substrate in a case where the electrodes of the parallel plate type and the pectinate type are employed, the movable electrodes may be configured to operate horizontally with respect to the substrate.
Next, a modification of the first embodiment of the invention is described below.
As shown in
The gap between the first movable electrode 74 and the fixed electrode 78 has a width that is equal to the maximum amplitude of the first movable electrode 74 that performs natural vibrations. The gap between the second movable electrode 76 and the fixed electrode 78 has a width that is equal to the maximum amplitude of the first movable electrode 76 that performs natural vibrations. These gaps differ from each other.
The first electromechanical switch is configured by including the first movable electrode 74 and the fixed electrode 78. The second electromechanical switch is configured by including the second movable electrode 76 and the fixed electrode 78.
For example, the first movable electrode 74 is shaped so that the thickness is 2.5 μm, that the width is 0.4 μm, that the length is 500 μm, and that the gap between the first movable electrode 74 and the fixed electrode is 0.2 μm. The second movable electrode 76 is shaped so that the thickness is 5 μm, that the width is 0.4 μm, that the length is 500 μm, and that the gap between the second movable electrode 74 and the fixed electrode is 1.5 μm. The movable electrodes are shaped in this manner, so that the modification has advantages similar to those of the first embodiment.
Incidentally, the same members as those shown in
In the electromechanical switch 70 of this configuration, the first movable electrode 74 and the second movable electrode 76 horizontally operate with respect to the substrate.
In a case where the movable electrodes horizontally operate with respect to the substrate, the gap between the first electromechanical switch and the fixed electrode and the gap between the second electromechanical switch and the fixed electrode can easily be formed so that these gaps differ from each other. The remaining operations are similar to those of the first embodiment.
The above electromechanical switch is not necessarily driven by the electrostatic force. For example, an electromagnetic force, heat obtained using a heat source, and a piezoelectric element may be used to drive the electromechanical switch.
The above electromechanical switch can be used as an antenna diversity DPDT (Dual Pole Double Throw) switch for a wireless LAN or the like required to perform high-speed switching.
Next, a method of manufacturing the electromechanical switch according to the first embodiment is described below.
The silicon substrate 2 shown in
In the silicon substrate 2, a pair of first concave portions 82 used to fix and lay the first movable electrode, a pair of second concave portions 84 used to fix and lay the second movable electrode 16, a pair of third concave portions 86 used to take out the fixed electrode terminal therefrom, and a pair of fourth concave portions 88 used to form the fixed electrode 18.
The sealed cover glass 3 is shaped like a plate and has pairs of projection portions 92, 94, and 96, which respectively correspond to the first concave portions 82, the second concave portions 84, and the third concave portions 86 provided in the silicon substrate 2.
First, an Al-layer is deposited on the silicon substrate 2 by vacuum-evaporation or sputtering. Then, a resist film having a predetermined pattern is applied thereonto. Subsequently, the Al-layer is wet-etched or dry-etched by using this resist film as a mask. Thus, the fixed electrode 18, the third electrode terminal 6, and the sixth electrode terminal 9 are formed (see
Subsequently, a sacrifice layer 102 is formed by resist (see
Then, the resist film 104 and the sacrifice layer 102 are removed by plasma-ashing. Thus, the beam structure of each of the first movable electrode 14 and the second movable electrode 16 is formed. In a pressure reducing apparatus or a helium filling apparatus, the alignment of the silicon substrate 2 with the sealed cover glass 3 is performed using the projection portions of the sealed cover glass 3. Subsequently, the sealed cover glass 3 and the silicon substrate 2 are anode-connected to each other (see
Thus, thin-film-like beam structures, such as the first movable electrode 14 and the second movable electrode 16, can be formed. Also, an electromechanical switch, in which an air gap located around each movable electrode adapted to perform an operation at high speed is depressurized or is filled with dry helium, can be manufactured.
Next, a second embodiment is described below.
There is no limitation to the structure and the material of an electromechanical switch. As long as a response time, which is equal to or less than a desired value, of the electromechanical switch is obtained corresponding to the natural vibrations of a movable electrode by setting the shape and the material of the movable electrode, the set shape and material can be employed. In the second embodiment, the relative change of spring forces is performed.
As shown in
In the case of an example shown in
Additionally, a first electrode terminal 211 and the sixth electrode terminal 216 are formed at an end of the first movable electrode 202. A second electrode terminal 212 and a fifth electrode terminal 215 are formed at an end of the second movable electrode 204. A third electrode terminal 213 and the fourth electrode terminal 214 are formed at an end of the third movable electrode 206. Each of the electrode terminals can be connected to a control voltage supply adapted to apply an electrostatic force between the movable electrodes facing each other.
In the electromechanical switch 200 shown in
Incidentally, although not shown, the electromechanical switch 200 is covered with the sealed cover glass. The inside of the electromechanical switch 200 is maintained by being filled with dry helium or under reduced pressure.
Also, the electromechanical switch is configured so that a response time corresponding to the natural frequency of the second movable electrode 204 electrically connectable to the first movable electrode 202 and the third movable electrode 206 is equal to or less than a desired response time. Thus, the movable electrode can be displaced in a predetermined response time.
For example, in a case where the desired response times is 0.2 μs, the natural frequency should be equal or less than 5 MHz.
More specifically, to set the natural frequency at a value that is equal to or less than 5 MHz using the equations (1) and (2), for example, in a case where aluminum (the internal stress is 50 MPa, the Young's modulus is 70 GPa, the Poisson's ratio is 0.25, and the density is 2.69 kg/m3) is used as the material of the movable electrode, and where data representing the shape thereof, that is, the width w is 1 μm, the thickness D is 10 μm, and the length L is 50 μm, the natural frequency is 5 MHz. Additionally, the air gap among the movable electrodes is set to be 2.4 μm.
Basically, the second movable electrode 204 maintains a state in which the second movable electrode 204 is electrically connected to one of the first movable electrode 202 and the third movable electrode 206 always in the initial condition. That is, in the electromechanical switch 200, one of the first electromechanical switch and the second electromechanical switch is in an on-state, while the other electromechanical switch maintains an off-state.
In the example shown in
In a case where the drive control voltage applied to the third movable electrode 206 is set to be 0 in the initial condition shown in
Next, a switching operation of the second embodiment is described below.
Meanwhile, in a state in which the drive control voltage is applied to the third movable electrode 214 and in which the second movable electrode 204 and the third movable electrode 214 are in contact with each other, the drive control voltage is applied to the first movable electrode 202 at a moment 0 by simultaneously setting the drive control voltage applied to the third movable electrode 214 to be 0.
At that time, the second movable electrode 204 is displaced toward the first movable electrode 202 at high speed by a strong spring force. Moreover, the first movable electrode 202 having a relatively weak spring force responds to this due to an electrostatic force acting between the first movable electrode 202 and the second movable electrode 204. Then, the first movable electrode 202 goes closer to and latches the second movable electrode 204. At that time, a drive control voltage of 3V is sufficient to cause the first movable electrode 202 to latch the second movable electrode 204.
According to the electromechanical switch of this configuration, even at a low drive voltage, a switching operation can be performed at high speed.
Meanwhile, when no drive control voltage is applied thereto due to some reason, the second movable electrode 204 is not latched by the first movable electrode 202 or by the third movable electrode 206. Thus, the second movable electrode 204 can be put into a state in which the displacement thereof is 0.
A considerable drive control voltage is needed to pull in the second movable electrode 204 toward the first movable electrode 202 or the third movable electrode 206 by applying an electrostatic force thereto in this state of the second movable electrode 204 in which the displacement thereof is 0. In the case of the above movable electrode, it is necessary to apply 44V thereto.
Thus, to put one of the first electromechanical switch and the second electromechanical switch into an on-state, the second movable electrode is adapted to be pulled in by using another drive unit, instead of using an electrostatic force to be generated by applying a voltage between the movable electrodes.
For example, a structure element itself, which is deformed by applying a voltage thereto, for instance, a piezoelectric element, a shape-memory alloy, a bimorph element, and an electromagnetic distortion element may be used as the drive unit.
For example, instead of the second movable electrode 204, a second movable element adapted to be deformed by applying an initial voltage thereto may be provided. When this second movable element goes closer to the third movable electrode 206, a drive control voltage may be applied to the third movable electrode 206 to thereby latch the second movable element with an electrostatic force. Thereafter, the voltage applied to the second movable element may be canceled.
Alternatively, the second movable electrode 204 may be pulled in toward the first movable electrode 202 or the third movable electrode 206 through the use of a mechanical probe. A drive control voltage is applied to the first movable electrode 202 or the third movable electrode 206 when this second movable electrode 204 is pulled in.
With this configuration, a driving voltage to be applied to the first movable electrode 202 and the third movable electrode 206 can be reduced to be a low voltage. An electromechanical switch having a high speed switching characteristic can be provided.
Next, a third embodiment of the invention is described below.
That is, in a case where a voltage needed for latching the first movable electrode to the fixed electrode due to some failure is not externally supplied thereto, each of the first movable electrode and the second movable electrode goes to an intermediate position through a free vibration, so that both of the first movable electrode and the second movable electrode are put into an off-state.
At that time, because the second movable electrode has a strong spring force, a high pull-in voltage is needed for pulling in the electrode in an off-state and latching the electrode.
The third embodiment provides the following structure to prevent occurrences of the above problem.
This switch includes an input terminal 303 and two output terminals 301 and 302, as shown in
The input terminal 303 is connected to a higher spring movable electrode 306. The output terminals 301 and 302 are connected to a first lower spring movable electrode 304 and a second lower movable electrode 305, respectively. The relative magnitudes of the spring forces of the higher spring movable electrode, and the first and second lower movable differ from one another. The spring constant can be controlled according to the shape, the characteristic of the material, and the gap of the spring, similarly to the first embodiment. The movable electrodes 304 to 306 are fixed to the substrate by post portion 310. Also, the fist lower spring movable electrode 304 and the higher spring movable electrode 306 are mechanically connected to each other through a connecting portion 307. Similarly, the higher spring movable electrode 306 and the second lower spring movable electrode are mechanically connected to each other by a connecting portion 307. Additionally, a first fixed electrode 308 is formed at a region, with which the first lower spring movable electrode is in contact when displaced in a direction of the substrate, and at another region with which the higher spring movable electrode 306 is partly in contact when displaced in the direction of the substrate,
The connecting portion 307 has a spring force smaller than the spring forces of the first and second lower spring movable electrodes and is constituted by an insulating member. The first fixed electrode 308 and a second fixed electrode 309 are spatially separated from each other. Both of the fixed electrode 308 and the second fixed electrode 309 are sufficiently electrically separated from each other. Unless the higher spring movable electrode 306 is in contact with the first or second electrode 308 or 309, the isolation between the first fixed electrode 308 and the second fixed electrode 309 is sufficiently established.
Next, a basic operation of the switch is described below. The present embodiment is applied as an SPDT switch. However, the present embodiment can be applied as an SPST switch. A method of outputting a signal, which is inputted from the input terminal 303, to the output terminal 301 is described below. A control signal is externally applied between the higher spring movable electrode 306 and the first lower spring movable electrode 304. A difference in potential is provided between the movable electrode and the fixed electrode to thereby generate an electrostatic force. Then, the first lower spring movable electrode 304 and the higher spring movable electrode 306 are pulled in toward the fixed electrode. Then, the higher spring movable electrode 306 and the first lower spring movable electrode 304 are in contact with and are electrically connected to the first fixed electrode 308. A signal inputted from the input terminal 303 is outputted from the output terminal 301 through the higher spring movable electrode 306, the first fixed electrode 308, and the first lower spring movable electrode 305. Similarly, in a case where the signal is outputted to an output terminal 302, it is advisable to pull in the second lower spring movable electrode 305 and the higher spring movable electrode 306 toward the substrate, and to electrically connect the second lower spring movable electrode 305 and the higher spring movable electrode 306 to the second fixed electrode 309.
Next, a transient operation of the switch is described by referring to
At that time, control signals are applied to the first and second lower movable electrodes. Thus, a difference in potential is provided therebetween to thereby generate an electrostatic force. The first lower spring movable electrode 304 and the second lower spring movable electrode 305 are pulled in toward the substrate. The first lower spring movable electrode 304 is in contact with and is electrically connected to the first fixed electrode 308. The second lower spring movable electrode 305 is in contact with and is electrically connected to the second fixed electrode 309. An insulating film is formed on at least one of contact surfaces between electrodes corresponding to each other, which are respectively selected from a set of the first lower spring movable electrode 304 and the second lower spring movable electrode 305 and a set of the first fixed electrode 308 and the second fixed electrode 309, respectively, to thereby prevent a DC current from flowing.
The first and second lower spring movable electrodes 304 and 305 have small spring forces. Thus, the first and second lower spring movable electrodes 304 and 305 are pulled in at high speed by a minute difference in potential. Thus, the switch is put into an on-state at a moment (b).
Next, an operation of turning off the switch, which is in this on-state, is described below. At a moment (b) at which the switch is in an on-state, the difference in potential, according to which the first and second lower spring movable electrodes 304 and 305 and the higher spring movable electrode 306 are latched, is canceled. Then, the first and second lower spring movable electrodes 304 and 305 and the higher spring movable electrode 306 are released and start performing free oscillations.
At that time, the higher spring movable electrode 306 having a strong spring force is released at high speed. However, the higher spring movable electrode 306 is connected to the first and second lower spring movable electrodes 304 and 305. Thus, a force of upwardly lifting the first and second lower spring movable electrodes 304 and 305 is generated at a moment (c) to assist the high-speed release of the first and second lower spring movable electrodes 304 and 305.
At a moment (d), the higher spring movable electrode 306 largely overshoots. However, at that time, this prevents the first and second lower spring movable electrodes 304 and 305, which are connected by the connecting portion 307, from largely overshooting.
Further, it is advisable to latch the higher spring movable electrode 306, which has returned to the side of the fixed electrode (that is, the first and second fixed electrodes 308 and 309) at a moment (f).
Thus, the higher spring movable electrode 306 is connected to the first and second lower spring movable electrodes 304 and 305 by the connecting portion 307. Consequently, the overshooting can be alleviated. Moreover, the high speed release of the first and second lower spring movable electrodes 304 and 305 can be assisted.
It is assumed that no voltage is applied to the electrode, which is adapted to latch the high spring movable electrode 306, due to some failure to thereby release the higher spring movable electrode 306, so that the switch is brought into a state shown in
Thus, first, as shown in
Also, in a case where a desired pull-in voltage is not obtained in this operation, the pull-in and the release of the first and second lower spring movable electrodes is repeated during the higher spring movable electrode performs natural vibrations. Then, the first and second lower spring movable electrodes are excited. The amplitude of the vibrations is increased. At a desired pull-in voltage, the movable electrode can be latched.
The connection state of the higher spring movable electrode and the first and second lower spring movable electrodes, which are connected by the connecting portion 307, can be controlled according to the mounting position of the connecting portion 307.
The movable electrode, both of the ends of which are fixed, does not perform oscillation with uniform amplitude in all regions. The movable electrode vibrates with a maximum amplitude in the vicinity of the center of the beam serving as a movable electrode. Conversely, the movable electrode hardly vibrates in the vicinity of the post portion 310. Thus, the connecting state of the movable electrode changes according to the position in the beam, at which the movable electrodes are connected to each other. In a case where the movable electrodes are connected to each other in the vicinity of a position at which the amplitude has a maximum value, the influence of the electrodes is maximized, so that the connection therebetween is very strong. That is, when the higher spring movable electrode 306 is released at a moment (c) shown in
Conversely, in a case where the movable electrodes are connected to one another in the vicinity of the post portion 310, the state of the movable electrodes becomes close to a state in which no connecting portions 307 is provided. Thus, the release of the first and second lower spring movable electrodes is not assisted. Therefore, it is necessary to control the position of the connecting portion 307 to satisfy requested specifications.
Incidentally, in the description of the present embodiment, an example of employing two lower spring movable electrodes has been described. However, similar advantages are obtained by constituting the switch employing only one lower spring movable electrode.
The electromechanical switch according to the invention is enabled to operate at a low driving voltage and to turn on and off at high speed. The electromechanical switch according to the invention is usefully utilized as an RFMEMS switch, especially, an antenna diversity DPDT (Dual Pole Double Throw) switch for a wireless LAN required to perform high-speed switching.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-014019 | Jan 2005 | JP | national |
| 2006-012529 | Jan 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP06/00889 | 1/20/2006 | WO | 00 | 9/15/2006 |
