Abstract: A digitally tunable acoustic wave resonator includes, in part, a first electrode positioned above a substrate, a composite stack positioned above the first electrode, and a second electrode positioned above the composite stack. The composite stack may include one or more alternate layers of a ferroelectric layer and a transition-metal nitride layer. The transition-metal nitride layer can be positioned above the ferroelectric layer, except the ferroelectric layer at the top of the composite stack. The ferroelectric layer comprises an aluminum scandium nitride layer Al1-xScxN, where 0<x<1.

Abstract: A piezoelectric device includes a piezoelectric body, a vibration plate that vibrates when the piezoelectric body is driven, a first electrode positioned between the piezoelectric body and the vibration plate, and a second electrode positioned to be separated from the first electrode by the piezoelectric body. The piezoelectric body has an active portion that is a part sandwiched between the first electrode and the second electrode in a first direction along a thickness direction of the piezoelectric body, and a change width of a dC/dV value, which represents a change in capacitance with respect to a change in a voltage applied along a second direction orthogonal to the first direction, from one end of the active portion on a side of the first electrode to the other end of the active portion on a side of the second electrode in the first direction is 10% or less.

Abstract: Provided is a dielectric thin film. The dielectric thin film includes: a plurality of ferroelectric domains including phonons having displacement in a direction of a first axis; and a plurality of spacers configured to block elastic interaction between the phonons, wherein the ferroelectric domains and the spacers are alternately and repeatedly arranged along a second axis which is perpendicular to the first axis.

Abstract: An apparatus is provided. The apparatus includes a bidirectional comb drive actuator. The apparatus may also include a cantilever. The cantilever includes a first end connected to the bidirectional comb drive actuator and a second end connected to an inner frame. In addition, the cantilever may include first and second conductive layers for routing electrical signals. Embodiments of the disclosed apparatuses, which may include multi-dimensional actuators, allow for an increased number of electrical signals to be routed to the actuators. Moreover, the disclosed apparatuses allow for actuation multiple directions, which may provide for increased control, precision, and flexibility of movement. Accordingly, the disclosed embodiments provide significant benefits with regard to optical image stabilization and auto-focus capabilities, for example in size- and power-constrained environments.

Abstract: A pressure sensor may be provided that includes: an electrode; a drive unit which applies a drive signal to the electrode; a sensing unit which receives, through the electrode, a reception signal including information on a capacitance which is between the electrode and a reference potential layer and is changed according to a relative distance between the electrode and the reference potential layer spaced from the electrode; and a first impedance between the drive unit and the electrode, and a second impedance between the sensing unit and the electrode.

Abstract: A tunable capacitor that incorporates teachings of the subject disclosure may include: a substrate; a first dielectric layer over the substrate; a plurality of bias lines encapsulated between the substrate and the tunable dielectric layer; a first metal layer over the tunable dielectric layer (wherein the first metal layer has a plurality of first gaps); an upper bias layer over the first metal layer (herein each of a plurality of portions of the upper bias layer extend through a respective one of the plurality of first gaps to come into contact with the first dielectric layer, and wherein at least a second gap is disposed in the upper bias layer); and a second metal layer (wherein a portion of the second metal layer extends through the second gap to come into contact with the first metal layer). Other embodiments are disclosed.

Abstract: In one embodiment, a MEMS sensor includes a first fixed electrode in a first layer, a cavity defined above the first fixed electrode, a membrane extending over the cavity, a first movable electrode defined in the membrane and located substantially directly above the first fixed electrode, and a second movable electrode defined at least partially within the membrane and located at least partially directly above the cavity.

Abstract: A MOS varactor structure comprising a semiconductor body having a well region and a plurality of gate electrodes and a plurality of cathode electrodes arranged over the well region, wherein the gate electrodes comprise elongate pads, and the plurality of cathode contacts are connected by a cathode connection pattern, the cathode connection pattern comprising a plurality of arms, each of the plurality of arms arranged to extend over a part of a respective gate electrode pad.

Abstract: Utilizing a variable capacitor for RF and microwave applications provides for multiple levels of intra-cavity routing that advantageously reduce capacitive coupling. The variable capacitor includes a bond pad that has a plurality of cells electrically coupled thereto. Each of the plurality of cells has a plurality of MEMS devices therein. The MEMS devices share a common RF electrode, one or more ground electrodes and one or more control electrodes. The RF electrode, ground electrodes and control electrodes are all arranged parallel to each other within the cells. The RF electrode is electrically connected to the one or more bond pads using a different level of electrical routing metal.

Abstract: An electronic element includes a fixed portion, and a movable portion which is movable with respect to the fixed portion and which is provided to generate a spring force to make restoration to a predetermined position. The fixed portion is provided with a first driving electrode and a first signal electrode. The movable portion is provided with a second driving electrode and a second signal electrode. An electrostatic force is generated between the first driving electrode and the second driving electrode by a voltage applied therebetween so that the electrostatic force resists against the spring force; and the first and second driving electrodes and the first and second signal electrodes are arranged so that the electrostatic force is generated in a direction in which a spacing distance between the first and second signal electrodes is widened.

Abstract: The present subject matter relates to the use of current splitting and routing techniques to distribute current uniformly among the various layers of a device to achieve a high Q-factor. Such current splitting can allow the use of relatively narrow interconnects and feeds while maintaining a high Q. Specifically, for example a micro-electromechanical systems (MEMS) device can comprise a metal layer comprising a first portion and a second portion that is electrically separated from the first portion. A first terminus can be independently connected to each of the first portion and the second portion of the metal layer, wherein the first portion defines a first path between the metal layer and the first terminus, and the second portion defines a second path between the metal layer and the first terminus.

Abstract: A highly linear, variable capacitor array constructed from multiple cells. Each cell includes a pair of passive, capacitor components connected in anti-parallel. The capacitor components may be Metal Oxide Semiconductor (MOS) capacitors. A control circuit applies bias voltages to bias voltage terminals associated with each capacitor component, to thereby control the overall capacitance of the array.

Abstract: A varactor includes a first PTC region, which comprises a ceramic material with a positive temperature coefficient with respect to the resistance. The varactor also includes a capacitor region that includes a first electrode, a second electrode, and a first dielectric layer arranged between the first electrode and the second electrode. The first PTC region and the capacitor region are connected thermally conductively to one another. The capacitance of the capacitor region can be changed by applying a bias to the first PTC region, the capacitor region or to the first PTC region and the capacitor region.

Abstract: Micro-Electro-Mechanical System (MEMS) structures, methods of manufacture and design structures are provided. The method of forming a MEMS structure includes forming a wiring layer on a substrate comprising actuator electrodes and a contact electrode. The method further includes forming a MEMS beam above the wiring layer. The method further includes forming at least one spring attached to at least one end of the MEMS beam. The method further includes forming an array of mini-bumps between the wiring layer and the MEMS beam.

Abstract: A variable capacitance semiconductor structure is disclosed. Embodiments include a capacitor having three plates, a top plate, a middle plate, and a bottom plate. The top plate serves as a positive plate. The middle and bottom plates serve as ground plates for the capacitor. A switching circuit selects between the middle plate and the bottom plate for use as the ground plate of the capacitor. The middle plate is slotted, allowing electric fields to penetrate through the middle plate to the bottom plate. The slots prevent the electric fields from terminating at the middle plate. A different capacitance value can be selected, depending on whether the middle plate or bottom plate is selected as the ground plate. Logic circuitry is configured to control the selection of plates to achieve a variety of capacitance values.

Abstract: Tunable MEMS resonators having adjustable resonance frequency and capable of handling large signals are described. In one exemplary design, a tunable MEMS resonator includes (i) a first part having a cavity and a post and (ii) a second part mated to the first part and including a movable layer located under the post. Each part may be covered with a metal layer on the surface facing the other part. The movable plate may be mechanically moved by a DC voltage to vary the resonance frequency of the MEMS resonator. The cavity may have a rectangular or circular shape and may be empty or filled with a dielectric material. The post may be positioned in the middle of the cavity. The movable plate may be attached to the second part (i) via an anchor and operated as a cantilever or (ii) via two anchors and operated as a bridge.

Abstract: A highly linear, variable capacitor array constructed from multiple cells. Each cell includes a pair of passive, capacitor components connected in anti-parallel. The capacitor components may be Metal Oxide Semiconductor (MOS) capacitors. A control circuit applies bias voltages to bias voltage terminals associated with each capacitor component, to thereby control the overall capacitance of the array.

Abstract: A MEMS tunable capacitor comprises first and second opposing capacitor electrodes, wherein the second capacitor electrode is movable by a MEMS switch to vary the capacitor dielectric spacing, and thereby tune the capacitance. A tunable dielectric material and a non-tunable dielectric material are in series between the first and second electrodes. The tunable dielectric material occupies a dimension gd of the electrode spacing, and the non-tunable dielectric material occupies a dimension g of the electrode spacing. A third electrode faces the movable second electrode for electrically controlling tunable dielectric material. A controller is adapted to vary the capacitor dielectric spacing for a first continuous range of adjustment of the capacitance of the MEMS capacitor, and to tune the dielectric material for a second continuous range of adjustment of the capacitance of the MEMS capacitor, thereby to provide a continuous analogue range of adjustment including the first and second ranges.

Abstract: An integrated circuit includes a substrate. A fixed main capacitor electrode is disposed in a metal layer overlying the substrate. A second main capacitor electrode is disposed in a metal layer and spaced from the fixed main capacitor electrode. A movable capacitor electrode is disposed adjacent the fixed main capacitor electrode. The movable capacitor electrode is switchable between a first configuration in which the movable capacitor electrode and fixed main capacitor electrode are mutually spaced out in such a manner as to form an auxiliary capacitor electrically connected to the main capacitor. In a second configuration, the movable capacitor electrode and the fixed main capacitor electrode are in electrical contact in such a manner as to give a second capacitive value.

Abstract: An electrical contactor for use in a high voltage bus utilizes two capacitor plates and a dielectric element movable in a gap between the plates under a charging voltage applied to the plates. The dielectric element is biased to a contactor off, or open, position by a biasing element, such as a spring. Once activated, the contactor remains closed under the influence of the charging voltage across the capacitor plates, yet does not draw a current during this state. The contactor may be released by a controllable discharge circuit placed across the capacitor plates.

Abstract: To suppress changes in capacitance due to displacement between electrodes opposing each other across a dielectric layer, thereby allowing stable manufacturing of a capacitance device having a desired capacitance. The capacitance device according to the present invention is of a configuration including a dielectric layer (10), a first electrode (11) formed on a predetermined surface (10a) of the dielectric layer (10), and a second electrode (12) formed on a surface (10b) on the opposite side of the dielectric layer (10) from the predetermined surface (10a). The forms of the first and second electrodes (11, 12) are set so that even in the event that the first electrode (11) is relatively displaced regarding position in a predetermined direction as to the second electrode (12), the area of the opposing-electrode region between the first electrode (11) and to the second electrode (12) is unchanged.

Abstract: In accordance with the present disclosure, one embodiment of a fractal variable capacitor comprises a capacitor body in a microelectromechanical system (MEMS) structure, wherein the capacitor body has an upper first metal plate with a fractal shape separated by a vertical distance from a lower first metal plate with a complementary fractal shape; and a substrate above which the capacitor body is suspended.

Abstract: A high-frequency device includes an antenna coil, a variable capacitance element, and an RFIC. The variable capacitance element is configured by capacitor units in each of which a ferroelectric film is sandwiched between capacitor electrodes, and a capacitance value changes according to a control voltage applied between the capacitor electrodes. A control voltage application circuit configured by a plurality of resistance elements of different resistance values, and a resistance element of the variable capacitance element unit configured to apply a control voltage to the variable capacitance element are arranged in a layered manner above the capacitor unit. Thus, a variable capacitance element and a high-frequency device that includes a control voltage application circuit eliminating problems such as distortion due to active elements and growing IC size along with complication of circuit architecture, and ensuring reliability on impact due to falling or the like, are provided.

Abstract: The present invention generally relates to a variable capacitor for RF and microwave applications. The variable capacitor includes a bond pad that has a plurality of cells electrically coupled thereto. Each of the plurality of cells has a plurality of MEMS devices therein. The MEMS devices share a common RF electrode, one or more ground electrodes and one or more control electrodes. The RF electrode, ground electrodes and control electrodes are all arranged parallel to each other within the cells. The RF electrode is electrically connected to the one or more bond pads using a different level of electrical routing metal.

Abstract: A tunable capacitor includes a substrate, a movable member, a first capacitive plate, a second capacitive plate, a third capacitive plate and a set of electrode plates. The movable member is disposed on the substrate. The movable member is adapted for moving away or toward the substrate to have a first position and a second position, respectively. The first capacitive plate is disposed on the movable member and faces the substrate. The second capacitive plate and the third capacitive plate are disposed on the substrate and face the first capacitive plate. The set of electrode plates, disposed on the substrate, faces the at least one movable member. The set of electrode plates, driven by an electrical voltage, generates electrostatic force causing the movable member to be drawn from the first position to the second position thereof to correspondingly adjust capacitance between the capacitive plates.

Abstract: The invention relates to electronic device having an operation temperature range, wherein the electronic device comprises a tunable capacitor (CST) comprising a first electrode (BE), a second electrode (TE), and a dielectric (FEL) arranged between the first electrode (BE) and the second electrode (TE). The dielectric (FEL) comprises dielectric material (FEL) having a value of a relative dielectric constant (?r) varying at least within the operation temperature range. The electronic device further comprises a temperature varying means (RES) being thermally coupled to the tunable capacitor for providing a temperature of the dielectric (FEL) causing a predetermined capacitance of the tunable capacitor (CST). The invention, which relies on the idea of varying temperature to vary a capacitance of a capacitor stack, provides an alternative tunable capacitor type for the known types.

Abstract: A variable capacity composite component has structures connecting four variable capacitors, for example, to signal terminals in series with bias application terminals of opposite polarities facing each other, connecting a power supply terminal to the bias+ sides of the first and second variable capacitors via a first bias resistance, and also to the bias+ sides of the third and fourth variable capacitors via a second bias resistance, connecting a grounding terminal to the bias? side of the first variable capacitor via a third bias resistance, also to the bias? sides of the second and third variable capacitors via a fourth bias resistance, and also to the bias? sides of the fourth variable capacitor via a fifth bias resistance, and setting the value of the first, second, and fourth bias resistances to one-half the value of the third and fifth bias resistances.

Abstract: The disclosure concerns a method for etching a PVD deposited barium strontium titanate layer, wherein a non-ionic surfactant at a concentration between 0.1 and 1 percent is added to an acid etching solution.

Abstract: A varactor comprises a substrate having sets of gate units each having parallel gate strips. The gate units are located such that the gate strips of neighbouring gate units are oriented transverse to each other. An electrically conducting gate connection layer comprises gate connection units comprising parallel gate connection strips located over the gate strips, and a cathode connection frame around each of the gate connection units. A first electrically conductive anode layer comprises first layer anode strips located parallel to the gate connection strips and connected to alternate gate connection strips, and a first anode connection frame connected to the anode strips. A second electrically conductive anode layer comprises anode strips located parallel to the gate connection strips and connected to opposite alternate gate connection strips, and a second anode connection frame connected to the second layer anode strips.

Abstract: A ceramic header configured to form a portion of an electronic device package includes a mounting portion configured to provide a mounting surface for an electronic device. In addition, the ceramic header includes one or more conductive input-output connectors operable to provide electrical connections from a first surface of the ceramic header to a second surface of the ceramic header. The ceramic header also includes one or more thermally polished surfaces.

Abstract: Tunable MEMS resonators having adjustable resonance frequency and capable of handling large signals are described. In one exemplary design, a tunable MEMS resonator includes (i) a first part having a cavity and a post and (ii) a second part mated to the first part and including a movable layer located under the post. Each part may be covered with a metal layer on the surface facing the other part. The movable plate may be mechanically moved by a DC voltage to vary the resonance frequency of the MEMS resonator. The cavity may have a rectangular or circular shape and may be empty or filled with a dielectric material. The post may be positioned in the middle of the cavity. The movable plate may be attached to the second part (i) via an anchor and operated as a cantilever or (ii) via two anchors and operated as a bridge.

Abstract: Disclosed is a MEMS variable capacitor including: a first electrode; a second electrode spaced apart from the first electrode; a third electrode floating above the first electrode; and an actuator including a fourth electrode facing the second electrode, a connector connecting the third electrode and the fourth electrode, and a support supporting a portion of the connector, wherein the third electrode and the connector are integrally formed with each other, and wherein a capacitance is changed by applying a voltage to the second electrode and by adjusting a gap between the first electrode and the third electrode.

Abstract: A variable capacitance element includes a piezoelectric substrate, a buffer layer located on the piezoelectric substrate with an orientation, a dielectric layer located on the buffer layer and having a relative dielectric constant that varies in accordance with an applied voltage, and a first electrode and a second electrode arranged to apply an electric field to the dielectric layer.

Abstract: According to one embodiment, a variable-capacitor device includes a first MEMS variable-capacitor element, and a second MEMS variable-capacitor element including one end series-connected to one end of the first MEMS variable-capacitor element. In a down-state, a first capacitance value of the first MEMS variable-capacitor element differs from a second capacitance value of the second MEMS variable-capacitor element.

Abstract: The present subject matter relates to MEMS tunable capacitors and methods for operating such capacitors. The tunable capacitor can feature a primary stationary actuator electrode on a substrate, a secondary stationary actuator electrode on the substrate, a stationary RF signal capacitor plate electrode on the substrate, a sprung cantilever disposed over the substrate, a beam anchor connecting a first end of the sprung cantilever to the substrate, and one or more elastic springs or other biasing members connecting a second end of the sprung cantilever to the substrate, the second end being located distally from the first end. The spring cantilever can be movable between an OFF state defined by the potential difference between the stationary and moveable actuator electrodes being zero, and an ON state defined by a non-zero potential difference between the stationary and moveable actuator electrodes.

Abstract: Provided is a MEMS device that includes first and second lower electrodes on a substrate. The MEMS device also includes a first driving electrode forming a capacitance element having a first capacitance between the first lower electrode and the first driving electrode, a second driving electrode forming a capacitance element having a second capacitance between the second lower electrode and the second driving electrode, and an upper electrode supported in midair above the driving electrodes. The upper electrode moves toward the driving electrodes and has a variable third capacitance between the first driving electrode and the upper electrode and a variable fourth capacitance between the second driving electrode and the upper electrode.

Abstract: A variable capacitance device includes a substrate, a beam portion, lower drive electrodes and upper drive electrodes. The beam portion is made of an insulating material and is connected to the substrate via an anchor portion. In the lower drive electrode and the upper drive electrode, electrostatic attraction generated by the application of a DC voltage continuously changes. In the lower drive electrodes and the upper drive electrode, electrostatic capacitance generated by the application of an RF signal between the electrodes on both sides continuously changes in accordance with the deformation of the beam portion due to the electrostatic attraction. The beam portion includes an inner circumferential portion including the upper drive electrode, an outer circumferential portion including the upper drive electrode, and ladder portions sandwiched by the inner circumferential portion and the outer circumferential portion. The beam portion has a cross-sectional area that is reduced by the ladder portions.

Abstract: An embodiment of the present disclosure provides a method to reduce acoustic vibration in a multilayered capacitor stimulated by a radio frequency signal by placing a first capacitor layer adjacent to second capacitor layer sharing a common electrode such that the acoustic vibration is reduced by applying one or more anti-acoustic vibration bias voltages to the multilayered capacitor. Other embodiments are disclosed.

Abstract: Driving is made possible in a moving range equivalent to or wider than the conventional range, with a driving voltage having a range smaller than a pull-in voltage. An electronic element includes a fixed portion provided with a first driving electrode and a first signal electrode, and a movable portion provided with a second driving electrode and a second signal electrode, movable with respect to the fixed portion and provided to generate a spring force to make restoration to a predetermined position. An electrostatic force is generated between the first and second driving electrodes by a voltage applied therebetween so that the electrostatic force resists against the spring force; and the first and second driving electrodes and the first and second signal electrodes are arranged so that the electrostatic force is generated in a direction in which a spacing distance between the first and second signal electrodes is widened.

Abstract: Embodiments of a method include forming a metal-insulator-metal (MIM) capacitor including a first electrode and a second electrode and an insulator layer between the first and second electrodes, the MIM capacitor also including a reactive layer; and altering the reactive layer to change a capacitive value of the MIM capacitor.

Abstract: A method for manufacturing a mirror device is presented. The method includes forming a mirror from a first substrate and forming a hinge/support structure from a second substrate. The hinge/support structure is formed with a recessed region and a torsional hinge region. The mirror is attached to the hinge/support structure at the recessed region. Further, a driver system is employed to cause the mirror to pivot about the torsional hinge region.

Abstract: This disclosure provides systems, methods and apparatus for electromechanical systems variable capacitance devices. In one aspect, an electromechanical systems variable capacitance device includes a substrate with a bottom bias electrode on the substrate. A first radio frequency electrode above the bottom bias electrode defines a first air gap. A non-planarized first dielectric layer is between the bottom bias electrode and the first radio frequency electrode. A metal layer above the first radio frequency electrode defines a second air gap. The metal layer includes a top bias electrode and a second radio frequency electrode.

Abstract: Disclosed herein is an MEMS variable capacitor and its driving method, the MEMS variable capacitor including, a first electrode, a second electrode floating over the first electrode upper part, a fixed electrode separated at the second electrode side surface, and a drifting electrode placed between the second electrode and the fixed electrode, connected to the second electrode, and physically contacting the fixed electrode by a voltage applied to the fixed electrode.

Abstract: A variable capacitor and a control method thereof capable of responding to applications of electronic apparatuses including various electronic devices and communication mobile devices. The variable capacitor includes a pair of electrodes formed so as to sandwich a ferroelectric material layer, in which polarization processing higher than a coercive field in hysteresis characteristics of polarization has been performed to the ferroelectric material layer, and the capacitance can be varied in accordance with a control voltage applied to the electrodes.

Abstract: A construction system for a capacitive sensor comprises a source electrode (210), a screening element (220) with partition (221) which forms a first and a second screened chamber (220.a, 220.b), a field sensor (230), a circuit (250), a spacing member (260) with a through-duct, and a screw (270). The partition (221) is provided with a hole (224) and said spacing member (260) is positioned inside the first chamber (220.a) with the axis (260.y) of the duct arranged coaxial with the axis (224-y) of said hole (224). The same spacing member (260) is positioned between the proximal face (223) of the partition (221) and the distal face (232) of the field sensor (230) and said field sensor (230) is provided with a threaded hole (233). The head (271) of the screw (270) is arranged inside the second chamber (220.

Abstract: Systems including varactor devices are provided. A varactor device (400) includes a gap closing actuator (GCA) varactor (200), includes a drive comb structure (201), an output varactor structure (514) defining an output capacitance, a reference varactor structure (214) defining a reference capacitance, and a movable truss comb structure (204) interdigitating the drive comb, the output varactor, and the reference varactor structures. The truss comb structure moves along a motion axis (205) between interdigitating positions based on a bias voltage. The device also includes a feedback circuit (404) configured for modifying an input bias voltage based on the reference capacitance to produce the output bias voltage that provides a target capacitance associated with the input bias voltage at the output varactor structure.

Abstract: MEMS varactors capable of handling large signals and/or achieving a high capacitance tuning range are described. In an exemplary design, a MEMS varactor includes (i) a first bottom plate electrically coupled to a first terminal receiving an input signal, (ii) a second bottom plate electrically coupled to a second terminal receiving a DC voltage, and (iii) a top plate formed over the first and second bottom plates and electrically coupled to a third terminal. The DC voltage causes the top plate to mechanically move and vary the capacitance observed by the input signal. In another exemplary design, a MEMS varactor includes first, second and third plates formed on over one another and electrically coupled to first, second and third terminals, respectively. First and second DC voltages may be applied to the first and third terminals, respectively. An input signal may be passed between the first and second terminals.

Abstract: A crystalline perovskite crystalline composite paraelectric material includes nano-regions containing rich N3? anions dispersed in a nano-grain sized matrix of crystalline oxide perovskite material, wherein (ABO3-?)?-(ABO3-?-?N?)1-?. A represents a divalent element, B represents a tetravalent element, ? satisfies 0.005???1.0, 1-? satisfies 0.05?1-??0.9, and 1-? is an area ratio between the regions containing rich N3? anions and the matrix of remaining oxide perovskite material.

Abstract: A varactor includes a first PTC region, which comprises a ceramic material with a positive temperature coefficient with respect to the resistance. The varactor also includes a capacitor region that includes a first electrode, a second electrode, and a first dielectric layer arranged between the first electrode and the second electrode. The first PTC region and the capacitor region are connected thermally conductively to one another. The capacitance of the capacitor region can be changed by applying a bias to the first PTC region, the capacitor region or to the first PTC region and the capacitor region.

Abstract: A MEMS device comprises first and second opposing electrodes (42,46), wherein the second electrode (46) is electrically movable to vary the electrode spacing between facing first sides of the first and second electrodes. A first gas chamber (50) is provided between the electrodes, at a first pressure, and a second gas chamber (52) is provided on the second, opposite, side of the second electrode at a second pressure which is higher than the first pressure. This arrangement provides rapid switching and with damping of oscillations so that settling times are reduced.