Abstract: An electronic device comprises a “waterproof” package including a substrate of an organic material permeable to humidity and/or moisture as well as one or more electronic components arranged on the substrate. The substrate comprises a barrier layer capable of countering penetration of humidity and/or moisture into the package through the organic material substrate.

Abstract: A GNSS RHCP stacked patch antenna with wide dual band, high efficiency and small size is made of a molded high-permittivity material, such as ceramics, with a patterned cavity in the dielectric substrate. The perforated cavities in the substrate reduce the effective dielectric constant, increase the bandwidth and efficiency. The high-order modes can be manipulated through the design of cavities.

Abstract: The present disclosure discloses a MEMS microphone including a printed circuit board, a shell assembled with the printed circuit board for forming a receiving space and provided with a sound hole communicating with the receiving space, a MEMS Die with a cavity accommodated in the receiving space and mounted on the shell for covering the sound hole, and an ASIC chip accommodated in the receiving space and mounted on the shell through a substrate. The cavity of the MEMS Die communicates with the sound hole. The MEMS Die electrically connects with the ASIC chip. The ASIC chip electrically connects with the substrate. The substrate electrically connects with the printed circuit board.

Abstract: A microphone assembly comprises a substrate. An acoustic transducer is disposed on the substrate and configured to generate an electrical signal responsive to an acoustic signal. An integrated circuit is disposed on the substrate and electrically coupled to the acoustic transducer. An enclosure is disposed on the substrate, and comprises a main body, and a sidewall projecting axially from outer edges of the main body towards the substrate and contacting the substrate such that an internal volume is defined between the enclosure and the substrate. An insulating layer is insert molded on an inner surface of the enclosure, or over molded on an outer surface of the enclosure such that the insulating layer is not disposed on a portion of the sidewall proximate to the substrate.

Abstract: A sound-producing balanced armature receiver, as disclosed, includes a receiver housing with a first internal volume, a second internal volume, and a sound outlet. The receiver includes a first diaphragm separating the first internal volume into a first front volume and a first back volume and a second diaphragm separating the second internal volume into a second front volume and a second back volume.

Abstract: A multi-function acoustic sensor may include a plate structure having a plurality of open spaces that are spaced apart from each other; a plurality of sensors provided on the plate structure, the plurality of sensors including a plurality of sensor elements respectively provided to overlap the plurality of open spaces; and a case having an inner space in which the plurality of sensors are provided, the case including: a first case surface on which the plurality of sensors are provided, the first case surface having at least one first hole, and a second case surface opposite to the first case surface, the second case surface having at least one second hole, wherein the at least one first hole and the at least one second hole form at least one path along which sound is transmitted and sensed through at least one of the plurality of open spaces of the plate structure.

Abstract: The invention provides a MEMS microphone. The MEMS microphone includes a substrate, having a first opening. A dielectric layer is disposed on the substrate, wherein the dielectric layer has a second opening aligned to the first opening. A diaphragm is disposed within the second opening of the dielectric layer, wherein a peripheral region of the diaphragm is embedded into the dielectric layer at sidewall of the second opening. A backplate layer is disposed on the dielectric layer and covering over the second opening. The backplate layer includes a plurality of acoustic holes arranged into a regular array pattern. The regular array pattern comprises a pattern unit, the pattern unit comprises one of the acoustic holes as a center hole, and peripheral holes of the acoustic holes surrounding the center hole with a same pitch to the center hole.

Abstract: A MEMS transducer system has a transducer configured to convert a received signal into an output signal for forwarding by a transducer output port, and an integrated circuit having an IC input in communication with the transducer output port. The IC input is configured to receive an IC input signal produced as a function of the output signal. The system also has a dividing element coupled between the IC input and the transducer output port. The dividing element is configured to selectively attenuate one or more signals into the IC input to at least in part produce the IC input signal. Other implementations may couple a feedback loop to the ground of the transducer (similar to bootstrapping), or pick off voltages at specific portions of the transducer.

Abstract: In some embodiments, a manufacturing process includes injection molding a palladium-catalyzed material into a substrate, forming a thin copper film over exterior and exposed surfaces of the substrate; ablating or removing copper film from the substrate to provide first, second and optional third portions of the copper film and ablated sections; electrolytically plating each portion to form metallic-plated portions; and ablating or removing the second portion in order to isolate the first portion. The metallic-plated first portion comprises a circuit portion of a molded interconnect device (MID), and where the metallic-plated third portion comprises a Faraday cage portion of a MID. A soft etching step may be included. A solder resist application step can be added, along with an associated solder resist removal step.

Abstract: A method of manufacturing a semiconductor structure includes providing a first substrate, disposing and patterning a plate over the first substrate, disposing a first sacrificial oxide layer over the plate, forming a plurality of recesses over a surface of the first sacrificial oxide layer, disposing and patterning a membrane over the first sacrificial oxide layer, disposing a second sacrificial oxide layer to surround the membrane and cover the first sacrificial oxide layer; and forming a plurality of conductive plugs passing through the plate or the membrane, wherein the plate includes a semiconductive member and a tensile member, and the semiconductive member is disposed within the tensile member.

Abstract: A package structure includes a housing and a sound producing chip. The sound producing chip is disposed within the housing. The sound producing chip includes a membrane and an actuator. The membrane includes a coupling plate and a spring structure connected to the coupling plate. The actuator is configured to receive a driving signal to actuate the membrane. The spring structure is situated between the coupling plate and the actuator. The coupling plate is actuated to move by the actuator via the spring structure.

Abstract: Systems and apparatuses for a microelectromechanical system (MEMS) device. The MEMS device includes a housing, a transducer, and a sensor. The housing includes a substrate defining a port and a cover. The substrate and the cover cooperatively form an internal cavity. The port fluidly couples the internal cavity to an external environment. The transducer is disposed within the internal cavity and positioned to receive acoustic energy through the port. The transducer is configured to convert the acoustic energy into an electrical signal. The sensor is disposed within the internal cavity and positioned to receive a gas through the port. The sensor is configured to facilitate detecting at least one of an offensive odor, smoke, a volatile organic compound, carbon monoxide, carbon dioxide, a nitrogen oxide, methane, and ozone.

Abstract: A MEMS microphone includes a substrate, a lower membrane supported on the substrate, an upper membrane suspended above the lower membrane, a first electrode supported on the lower membrane, and a second electrode supported on the upper membrane. The lower membrane and the upper membrane enclose a cavity in which the first electrode and the second electrode are located. The lower membrane and the upper membrane are each formed of silicon carbonitride (SiCN). The first electrode and the second electrode are each formed of polysilicon.

Abstract: A production method for a MEMS component includes providing a layer arrangement on a carrier substrate, where the layer arrangement includes a first and second layer structure. A sacrificial material is arranged in an intermediate region between the first and second layer structures, an etch stop structure extending between the first and second layer structures subdivides the intermediate region into an exposure region and an edge region laterally adjoining the exposure region, and at least one of the first layer structure or the second layer structure has access openings to the exposure region. The method further includes removing the sacrificial material from the exposure region through the access openings using an etching process to expose the exposure region. The etch stop structure provides a lateral delimitation for the etching process, and the sacrificial material present in the edge region provides a mechanical connection between the first and second layer structures.

Abstract: The application describes MEMS transducers having a patterned membrane electrode which incorporates a plurality of openings or voids. At least a portion of the peripheral edge of the opening is provided with a plurality of discontinuities e.g. projections and recesses which extend within the plane of the membrane electrode.

Abstract: A transducer includes: a substrate having a hole; a backplate facing an opening of the hole; and a diaphragm facing the backplate with an air gap therebetween. The backplate includes a backplate body, a backplate support secured to the substrate, and through-holes perforating the backplate body; the backplate body includes a center region and three or more peripheral regions partially or completely surrounding the center region; the through-holes defines a percentage open area in each of the center region and the three or more peripheral regions, and the percentage open areas are mutually different; the percentage open area in the center region is larger than the percentage open area in each of the three or more peripheral regions; and the percentage open area in the outermost peripheral region of the backplate body is smaller than the percentage open area in the peripheral region near the center region.

Abstract: The present invention relates to a sound transducer assembly with a MEMS sound transducer for generating and/or detecting sound waves in the audible wavelength spectrum. The MEMS sound transducer includes a first cavity, and the sound transducer assembly includes an ASIC electrically connected to the MEMS sound transducer. The ASIC is embedded in a first substrate, and the first MEMS sound transducer is arranged on a second substrate. The first substrate and the second substrate are electrically connected to one another, and the first cavity is at least partially formed in one of the first substrate and the second substrate.

Abstract: Disclosed are various embodiments of systems, devices, components and methods for reducing feedback between a transducer and one or more microphones in a magnetic bone conduction hearing device. Such systems, devices, components and methods include acoustically sealing or welding first and second compartments of the hearing device from one another, where the first compart contains the one or more microphones, and the second compart contains the transducer.

Abstract: A silicon microphone with a suspended diaphragm and a system with the same are provided, the microphone comprises: a silicon substrate provided with a back hole therein; a compliant diaphragm disposed above the back hole of the silicon substrate and separated from the silicon substrate; a perforated backplate disposed above the diaphragm with an air gap sandwiched in between; and a precisely defined support mechanism, disposed between the diaphragm and the backplate with one end thereof fixed to the edge of the diaphragm and the other end thereof fixed to the backplate, wherein the diaphragm and the backplate are used to form electrode plates of a variable condenser. The microphone with a suspended diaphragm can improve the repeatability and reproducibility in performance and can reduce the diaphragm stress induced by the substrate.

Abstract: Provided are an element applicable to a high-precision, high-sensitivity pressure detecting sensor and switch, a manufacturing method for the element; and a sensor, an electronic circuit, and an input device that include the element. The electret element of the present invention has a semiconductor sandwiched between a pair of electrodes, and an electret film disposed at a location opposite to the semiconductor via a gap. The electret element of the present invention may be structured so that the semiconductor contacts with the electret film, or so as to have micro-sized gaps therebetween. The electret film is semi-permanently kept in a positively or negatively charged state. By having a structure in which the electret film can contact with or approach the semiconductor, an amount of electric currents flowing between the pair of electrodes can be controlled.

Abstract: A method for forming a microelectromechanical device may provide forming a first layer at least one of in or over a semiconductor carrier; forming a second layer at least one of in or over at least a central region of the first layer, such that a peripheral region of the first layer is at least partially free of the second layer; removing material under at least a central region of the second layer to release at least one of the central region of the second layer or a central region of the first layer; and/or removing material under at least the peripheral region of the first layer to such that the second layer is supported by the semiconductor carrier via the first layer.

Abstract: Provided is an acoustic transducer including: a semiconductor substrate; a vibrating membrane provided above the semiconductor substrate, including a vibrating electrode; and a fixed membrane provided above the semiconductor substrate, including a fixed electrode, the acoustic transducer detecting a sound wave according to changes in capacitances between the vibrating electrode and the fixed electrode, converting the sound wave into electrical signals, and outputting the electrical signals. At least one of the vibrating electrode and the fixed electrode is divided into a plurality of divided electrodes, and the plurality of divided electrodes outputting the electrical signals.

Abstract: A MEMS may include a backplate comprising first and second electrodes electrically isolated from one another and mechanically coupled to the backplate in a fixed relationship relative to the backplate, and a diaphragm configured to mechanically displace relative to the backplate as a function of sound pressure incident upon the diaphragm. The diaphragm may comprise third and fourth electrodes electrically isolated from one another and mechanically coupled to the diaphragm in a fixed relationship relative to the diaphragm such that the third and fourth electrodes mechanically displace relative to the backplate as the function of the sound pressure. The first and third electrodes may form a first capacitor, the second and fourth electrodes may form a second capacitor, and the first capacitor may be configured to sense a displacement of the diaphragm responsive to which the second capacitor may be configured to apply an electrostatic force to the diaphragm to return the diaphragm to an original position.

Abstract: A microphone includes a substrate including a penetration hole; a vibration membrane disposed over the substrate and covering the penetration hole; a fixed electrode disposed over the vibration membrane and spaced apart from the vibration membrane; a fixed plate disposed over the fixed electrode; and a plurality of air inlets disposed in the fixed electrode and the fixed plate. The vibration membrane includes a plurality of slots positioned over the penetration hole, and an entire area of the plurality of slots is approximately 8% to approximately 19% of an entire area of the vibration membrane.

Abstract: A microphone porting structure, comprises a substrate (312) having a bearing surface and a porting through-hole (344) formed therethough for aligning with a microphone port of a bottom ported microphone (334). The bearing surface provides an area against which to seal and the through-hole provides for acoustic path alignment for the audio ports of paired bottom ported microphones mounted to a printed circuit board.

Abstract: A microphone system includes a diaphragm suspended by springs and including a sealing layer that seals passageways which, if left open, would degrade the microphone's frequency response by allowing air to pass from one side of the diaphragm to the other when the diaphragm is responding to an incident acoustic signal. In some embodiments, the sealing layer may include an equalization aperture to allow pressure to equalize on both sides of the diaphragm.

Abstract: A structural concept for a vertically hybridly integrated assembly having at least one MEMS component is provided, whose MEMS structure is developed at least partially in the front side of the component and which is electrically contactable via at least one connection pad on the front side of the component. This structural concept is able to be realized in an uncomplicated and cost-effective manner and allows the largely stress-free mounting of the MEMS structure within the chip stack and also ensures a reliable electrical linkage of the MEMS component to further component parts of the assembly. For this purpose, the structural concept provides for mounting the MEMS assembly headfirst on a further component of the chip stack via an interposer and for electrically linking it to the further component via at least one plated contacting in the interposer.

Abstract: A microphone base includes a plurality of metal layers and a plurality of core layers. Each of the plurality of core layers is disposed between selected ones of the metal layers. A dielectric membrane is disposed between other selected ones of the plurality of metal layers. A port extends through the metal layers and the core layers but not through the dielectric membrane. The dielectric membrane has a compressed portion and an uncompressed portion. The uncompressed portion extends across the port and the compressed portion is in contact with the other selected ones of the metal layers. The compressed portion of the membrane is effective to operate as a passive electronic component and the uncompressed portion is effective to act as a barrier to prevent at least some external debris from traversing through the port.

Abstract: A plate, a transducer, a method for making a transducer, and a method for operating a transducer are disclosed. An embodiment comprises a plate comprising a first material layer comprising a first stress, a second material layer arranged beneath the first material layer, the second material layer comprising a second stress, an opening arranged in the first material layer and the second material layer, and an extension extending into opening, wherein the extension comprises a portion of the first material layer and a portion of the second material layer, and wherein the extension is curved away from a top surface of the plate based on a difference in the first stress and the second stress.

Abstract: An acoustic sensor includes a back plate; at least one back plate electrode coupled to the back plate; a proof of mass with the proof of mass elastically coupled to the back plate; and a proof of mass electrode coupled to the proof of mass. Movement of the sensor causes a capacitance between the proof of mass electrode and the at least one back plate electrode to vary and the capacitance represents a magnitude of the movement of the sensor.

Abstract: Provided is a microphone. The microphone includes a substrate including an acoustic chamber, a lower backplate disposed on the substrate, a diaphragm spaced apart from the lower backplate on the lower backplate, the diaphragm having a diaphragm hole passing therethrough, a connection unit disposed on the lower backplate to extend through the diaphragm hole, and an upper backplate disposed on the connection unit, the upper backplate being spaced apart from the diaphragm. Thus, the microphone may be improved in sensitivity and reliability.

Abstract: The present disclosure provides one embodiment of an integrated microphone structure. The integrated microphone structure includes a first silicon substrate patterned as a first plate; a silicon oxide layer formed on one side of the first silicon substrate; a second silicon substrate bonded to the first substrate through the silicon oxide layer such that the silicon oxide layer is sandwiched between the first and second silicon substrates; and a diaphragm secured on the silicon oxide layer and disposed between the first and second silicon substrates, wherein the first plate and the diaphragm are configured to form a capacitive microphone.

Abstract: A packaging concept for MEMS components having at least one diaphragm structure formed in the front side of the component is provided, according to which the MEMS component is mounted on a support which at least laterally delimits a cavity adjoining the diaphragm structure. In addition, at least one electrical feedthrough is formed in the support which allows electrical contacting of the MEMS component through the support. To achieve the largest possible rear volume for the diaphragm structure of the MEMS component for a given chip surface area, and also to simplify the processing of the support, according to the invention the electrical feedthroughs are integrated into the wall of the cavity adjoining the diaphragm structure, in that at least one section of such a feedthrough is implemented in the form of an electrically conductive coating of a side wall section of the cavity.

Abstract: A silicon condenser microphone is disclosed. The microphone includes a transducer, an IC chip, a first board, a second board spaced from the first board by a frame, and a third board located between the first board and the second board. A cavity is accordingly formed by the first board, the frame and the third board to accommodate the transducer and the IC chip. The IC chip is electrically connected to a surface of the third board facing the second board. The microphone provides an enlarged back volume to the transducer and provides the transducer with a shield against electro-magnetic interference. A manufacturing process is also disclosed.

Abstract: An electret microphone having reduced noise due to reduced leakage current is provided. The microphone includes a flexible diaphragm, and sensor member disposed in opposing, spaced relation to the diaphragm and comprising a semi-conductor channel. At least one electret surface, comprised of a dielectric material having a permanently-embedded static electric charge, is disposed on one of the diaphragm and the sensor member. In turn, the semi-conductor channel of the sensor member has an electrical conductivity dependent upon relative movement of the diaphragm and support member responsive to acoustic signals incident upon the diaphragm, wherein the channel provides an output signal indicative of the acoustic signals. The electret surface may be disposed on the diaphragm. Alternatively, the electret surface may be disposed on the sensor member in spaced, face-to-face relation to an electrically conductive surface located on the diaphragm.

Abstract: A semiconductor device includes a microphone module implemented on a first semiconductor die and a signal processing module implemented on a second semiconductor die. The microphone module includes a movable microphone element arranged at a main side of the first semiconductor die and the second semiconductor die is mounted to the main side of the first semiconductor die.

Abstract: Measures for improving the acoustic properties of a microphone component produced in sacrificial layer technology. The micromechanical microphone structure of such a component is implemented in a layered structure, and includes at least one diaphragm, which is deflectable by sound pressure and which is implemented in a diaphragm layer, and a stationary acoustically permeable counterelement for the diaphragm which is implemented in a thick functional layer above the diaphragm layer and which is provided with through openings for introducing sound. The through openings for introducing sound are situated above the middle region of the diaphragm, while perforation openings which are largely acoustically passive are provided in the counterelement, above the edge region of the diaphragm.

Abstract: A packaged microphone has a lid structure with an inner surface having a concavity, and a microphone die secured within the concavity. The packaged microphone also has a substrate coupled with the lid structure to form a package having an interior volume containing the microphone die. The substrate is electrically connected with the microphone die. In addition, the packaged microphone also has aperture formed through the package, and a seal proximate to the microphone die. The seal acoustically seals the microphone and the aperture to form a front volume and a back volume within the interior volume. The aperture is in acoustic communication with the front volume.

Abstract: Microelectromechanical systems (MEMS) microphone devices and methods for packaging the same include a package housing, an interior lid, and an integrated MEMS microphone die. The package housing includes a sound port therethrough for communicating sound from outside the package housing to an interior of the package housing. The interior lid is mounted to an interior surface of the package housing to define an interior lid cavity, and includes a back volume port therethrough. The MEMS microphone die is mounted on the interior lid over the back volume port, and includes a movable membrane. The back volume port is configured to allow the interior lid cavity and the MEMS movable membrane to communicate, thereby increasing the back volume of the MEMS microphone die and enhancing the sound performance of the packaged MEMS microphone device.

Abstract: A microphone package is described that includes a plastic lid, a substrate base, and two electrical components. The plastic lid includes a first conductive lid trace and the substrate base includes a first conductive substrate trace. The plastic lid is sealably coupled to the substrate base to form a sealed cavity. The substrate trace and the lid trace are arranged such that, when the cavity is sealed, an electrical connection is formed between the substrate trace and the lid trace. The first component is mounted on the substrate base and electrically coupled to the substrate trace. The second component is mounted on the lid and is electrically coupled to the lid trace. The electrical connection between the substrate trace and the lid trace provides electrical coupling between the first component and the second component. At least one of the first component and the second component includes a MEMS microphone die.

Abstract: A MEMS microphone has a base, a backplate, and a backplate spring suspending the backplate from the base. The microphone also has a diaphragm forming a variable capacitor with the backplate.

Abstract: A vacuum sealed directional microphone and methods for fabricating said vacuum sealed directional microphone. A vacuum sealed directional microphone includes a rocking structure coupled to two vacuum sealed diaphragms which are responsible for collecting incoming sound and deforming under sound pressure. The rocking structure's resistance to bending aids in reducing the deflection of each diaphragm under large atmospheric pressure. Furthermore, the rocking structure exhibits little resistance about its pivot thereby enabling it to freely rotate in response to small pressure gradients characteristic of sound. The backside cavities of such a device can be fabricated without the use of the deep reactive ion etch step thereby allowing such a microphone to be fabricated with a CMOS compatible process.

Abstract: A microphone unit (1) comprises a first vibrating part (14), a second vibrating part (15), and a housing (20) for accommodating the first vibrating part (14) and the second vibrating part (15), the housing being provided with a first sound hole (132), a second sound hole (101), and a third sound hole (133). The housing (20) is provided with a first sound path (41) for transmitting sound pressure inputted from the first sound hole (132) to one surface (142a) of a first diaphragm (142) and to one surface (152a) of a second diaphragm (152), a second sound path (42) for transmitting sound pressure inputted from the second sound hole (101) to the other surface (142b) of the first diaphragm (142), and a third sound path (43) for transmitting sound pressure inputted from the third sound hole (133) to the other surface (152b) of the second diaphragm (152).

Abstract: An electrostatic loudspeaker includes: a first electrode having acoustic transmission property; a second electrode having acoustic transmission property, and disposed so as to be opposed to the first electrode; a vibrating member having conductibility, and disposed between the first electrode and the second electrode; a first elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the first electrode; a second elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the second electrode; and a first separation member having insulation property and acoustic transmission property, and disposed on an opposite side of a face of the first electrode, which is opposed to the first elastic member.

Abstract: An electret material having excellent charge retentivity against heat is provided. The electret material 10 includes an electrode plate 1, a semiconducting layer 2 formed on the electrode plate 1, and an electret layer 3 formed on the semiconducting layer 2. The semiconducting layer 2 includes carbon and a fluororesin. This electret material 10 can be inhibited from decreasing in the surface potential of the electret layer 3 when heated to a high temperature.

Abstract: A packaged microphone has a lid structure with an inner surface having a concavity, and a microphone die secured within the concavity. The packaged microphone also has a substrate coupled with the lid structure to form a package having an interior volume containing the microphone die. The substrate is electrically connected with the microphone die. In addition, the packaged microphone also has aperture formed through the package, and a seal proximate to the microphone die. The seal acoustically seals the microphone and the aperture to form a front volume and a back volume within the interior volume. The aperture is in acoustic communication with the front volume.

Abstract: The invention is directed to echo cancellation for a microphone system. An exemplary microphone system comprises a first transistor, wherein a gate terminal of the first transistor is connected to a ground terminal via a microphone electret element, the microphone electret element being associated with a capacitance and a voltage, the microphone electret element reverse biasing the first transistor; and a second transistor in parallel with the first transistor, wherein a gate terminal of the second transistor is connected to the ground terminal via a capacitor, the capacitance of the capacitor being selected to suppress at least a portion of a common mode signal, and wherein the gate terminal of the second transistor is not connected to the microphone electret element. The common mode signal comprises the echo, which may be the output of a speaker system that is received as input to the microphone system.

Abstract: A microphone has a package, and an acoustic sensor, an under surface of which is fixed to an inner face of the package. The acoustic sensor has a substrate having a plurality of hollows penetrating the substrate from a top surface to an under surface, and a capacitor structure made by a movable electrode plate and a fixed electrode plate disposed above each of the hollows. A package sound hole is opened in the package in a position opposed to the under surface of the acoustic sensor. A dent which is communicated with each of the hollows and open below the under surface side of the substrate is formed below the under surface of the substrate. A height of the dent measured from the under surface of the substrate is equal to or less than half of a height of the hollow.

Abstract: A MEMS microphone. The MEMS microphone includes a substrate, a transducer support that includes or supports a transducer, a housing, and an acoustic channel. The transducer support resides on the substrate. The housing surrounds the transducer support and includes an acoustic aperture. The acoustic channel couples the acoustic aperture to the transducer, and isolates the transducer from an interior area of the MEMS microphone.

Abstract: A MEMS microphone has 1) a backplate with a backplate interior surface and a plurality of through-holes, and 2) a diaphragm spaced from the backplate. The diaphragm is movably coupled with the backplate to form a variable capacitor. At least two of the through-holes have an inner dimensional shape (on the backplate interior surface) with a plurality of convex portions and a plurality of concave portions.