Abstract: Microfabricated filters constructed with permeable polysilicon membranes and methods for fabricating such filters. The filters include a frame structure having a plurality of openings therethrough and a permeable polysilicon membrane disposed over the openings in the frame structure. The frame structure provides support for the permeable polysilicon membrane. The pores of the filter may be smaller than the resolution limit of photolithography. The width of the pores may be as small as about 0.01 .mu.m, while the length of the pores may be as small as about 0.05 .mu.m. The filters feature a relatively high throughput due to the extremely short pore length. The filters may be fabricated utilizing standard microfabrication processes. Also, microfabricated shells constructed with permeable membranes for encapsulating microfabricated devices such as microelectromechanical structures (MEMS) and methods for fabricating such shells.

Abstract: A method and apparatus for providing a sub-ground plane for a micromachined device. The sub-ground plane is formed in or on the substrate. Above the sub-ground plane is a dielectric and then a discontinuous conductive layer used for interconnects for parts of the micromachined device. A movable microstructure is suspended above the interconnect layer. A conductive layer can be suspended above the movable microstructure. In one embodiment, the sub-ground plane is diffused into the substrate or a well in the substrate, and is of an opposite type from the type of silicon into which it is diffused. Alternatively, the sub-ground plane is formed from a conductive layer, deposited over the substrate before the layer used for interconnects.

Abstract: A method and apparatus for providing a conductive plane beneath a suspended microstructure. A conductive region is diffused into a substrate. A dielectric layer is added, covering the substrate, and then removed from a portion of the conductive region. A spacer layer is deposited over the dielectric and exposed conductive region. A polysilicon layer is deposited over the spacer layer, and formed into the shape of the suspended microstructure. After removal of the spacer layer, the suspended microstructure is left free to move above an exposed conductive plane. The conductive plane is driven to the same potential as the microstructure.

Abstract: Mixing, modulation and demodulation using the nonlinear properties of microelectromechanical resonators and filters are described. Mixing followed by filtering is implemented using microelectromechanical filters with nonlinear input transducers. AM modulation is implemented by passing a carrier signal through the output transducer of a microelectromechanical filter. FM and FSK demodulation is accomplished using parallel banks of microelectromechanical filters. The invention can be implemented using integrated circuit technology.

Abstract: A method and apparatus for providing a sub-ground plane for a micromachined device. The sub-ground plane is formed in or on the substrate. Above the sub-ground plane is a dielectric and then a discontinuous conductive layer used for interconnects for parts of the micromachined device. A movable microstructure is suspended above the interconnect layer. A conductive layer can be suspended above the movable microstructure. In one embodiment, the sub-ground plane is diffused into the substrate or a well in the substrate, and is of an opposite type from the type of silicon into which it is diffused. Alternatively, the sub-ground plane is formed from a conductive layer, deposited over the substrate before the layer used for interconnects.

Abstract: A method and apparatus for providing a conductive plane beneath a suspended microstructure. A conductive region is diffused into a substrate. A dielectric layer is added, covering the substrate, and then removed from a portion of the conductive region. A spacer layer is deposited over the dielectric and exposed conductive region. A polysilicon layer is deposited over the spacer layer, and formed into the shape of the suspended microstructure. After removal of the spacer layer, the suspended microstructure is left free to move above an exposed conductive plane. The conductive plane is driven to the same potential as the microstructure.

Abstract: A micromechanical filter having planar components, and manufacturable using very large scale integrated circuit microfabrication techniques. The input and output transducers are interdigitated comb electrodes. The mechanical coupling between the input and output transducers includes planar flexures, displacement of the electrodes producing bending of the elements of the flexures. By sealing micromechanical filters in a vacuum and providing on-board circuitry, high signal-to-noise ratios and quality factors are achievable. Construction of a real-time spectrum analyzer using many micromechanical resonators, provides a device with high accuracy and a short sample time.

Abstract: A micromachined force sensor containing separate sensing and actuator structures. A member is suspended above the substrate so that it is movable along an axis in response to a force. The member includes a set of parallel sense fingers and a separate set of parallel force fingers. The sense fingers are positioned between fingers of two sense plates, to form a first differential capacitor, whose capacitance changes when the member moves in response to a force along the axis. The change in capacitance induces a sense signal on the member, which permits the measurement of the magnitude and duration of the force. The force fingers are positioned between fingers of two actuator plates, to form a second differential capacitor. The sense signal can be used to provide feedback to the second differential capacitor to generate different electrostatic forces between the force fingers and the two actuator plates, to offset the force applied along the preferred axis.

Abstract: An electro-mechanical micromachined structure uses bumpers to prevent contact between structures at different potentials. A beam is connected to one or more anchors by flexible suspensions, which permit the beam to move along a predetermined axis relative to one or more plates. The suspension includes at least one bumper positioned so that the bumper will contact another part of the suspension before the beam contacts the plates. The bumper is made from the same material as the suspension, during the same processing step. The bumper is positioned to take advantage of shrinkage or expansion of the beam during processing which forces the bumper closer to its contact point then would otherwise be possible.

Abstract: A micromechanical filter having planar components, and manufacturable using very large scale integrated circuit microfabrication techniques. The input and output transducers are interdigitated comb electrodes. The mechanical coupling between the input and output transducers includes planar flexures, displacement of the electrodes producing bending of the elements of the flexures. By sealing micromechanical filters in a vacuum and providing on-board circuitry, high signal-to-noise ratios and quality factors are achievable. Construction of a real-time spectrum analyzer using many micromechanical resonators, provides a device with high accuracy and a short sample time.

Abstract: Resonator systems with controlled quality factors including a resonator having a plurality of ports and a first quality factor greater than the system quality factor, and an amplifier providing negative feedback among the ports to render the system quality factor independent of the resonator quality factor.

Abstract: A micromechanical filter having planar components, and manufacturable using very large scale integrated circuit microfabrication techniques. The input and output transducers are interdigitated comb electrodes. The mechanical coupling between the input and output transducers includes planar flexures, displacement of the electrodes producing bending of the elements of the flexures. By sealing micromechanical filters in a vacuum and providing on-board circuitry, high signal-to-noise ratios and quality factors are achievable. Construction of a real-time spectrum analyzer using many micromechanical resonators, provides a device with high accuracy and a short sample time.

Abstract: A micromachine is lubricated in a fluid-based process. The known fluid-based process of releasing a sacrificial layer from a micromachine is followed by a fluid-based hydrophilic processing of the micromachine surfaces. A lubricating monolayer surface is then formed on the resultant hydrophilic micromachine surfaces. Afterwards, the surfaces are dried through conventional means.

Abstract: A suspended microstructure fabrication process. Photoresist pedestals are inserted in a sacrificial layer between the suspended microstructure and the substrate and photoresist spacers are inserted in the microstructure layer between non contacting portions of the suspended microstructure so that the photoresist pedestals and spacers support the microstructure bridge during the wet etching and drying process used to remove the sacrificial layer.

Abstract: An electrostatic micromotor employs a side drive design. The stator operates in a plane above a substract and a moveable member lies and moves in the plane of the stator. An electrostatic field of operational strength is generated and sustained without breakdown in the plane between the stator and edges of the moveable member. Three fabrication processes enable formation of a moveable member in the plane of operation of the stator and spaced apart from the stator by a micron amount. One fabrication process deposits and patterns a structural layer to form the stator and moveable member over a sacrificial layer. A second fabrication process etches channels in a first structural layer to outline a stator, moveable member, and if desired, a bearing. A substrate is connected to the side of the structural layer through which the channels are etched and the opposite side is ground down to the ends of the channels to form salient stator, rotor and, if desired, bearing structures.

Abstract: A microbridge device for use as a sensor or an actuator is driven parallel to a substrate as a resonant microstructure. The microstructure comprises a stationary thin-film electrode secured to the substrate and located in a plane above it. A movable plate overlaying the substrate is suspended above it. The movable plate and electrode are patterned to provide for each at least one comb with fingers interdigitated with those of the other.

Abstract: An electrostatically driven microactuator is micromachined in a monolithic process. Sacrificial layers are placed between a moving element and stator structural layers. Removal of the sacrificial layers leaves a free standing moving element and micron wide air gaps within a stator. An electric field of about 100 Mv/m and higher is supported across the micron wide gap without breakdown and enables high energy torque densities to be produced between the stator and the moving element. One electrostatic drive scheme involves a series of stator electrodes attached to the stator and a series of electrodes attached to the moving element charged in sequence to attract each other in a direction of movement and to oppose each other in a direction normal to movement. A bearing is aligned with the moving element within the stator during the layering of a sacrificial layer over an edge of the moving element structural layer. The bearing and stator laterally stabilize the moving element.

Abstract: An electrostatically driven microactuator is micromachined in a monolithic process. Sacrificial layers are placed between a moving element and stator structural layers. Removal of the sacrificial layers leaves a free standing moving element and micron wide air gaps within a stator. An electric field of about 100 Mv/m and higher is supported across the micron wide gap without breakdown and enables high energy torque densities to be produced between the stator and the moving element. One electrostatic drive scheme involves a series of stator electrodes attached to the stator and a series of electrodes attached to the moving element charged in sequence to attract each other in a direction of movement and to oppose each other in a direction normal to movement. A bearing is aligned with the moving element with the stator during the layering of a sacrificial layer over an edge of the moving element structural layer. The bearing and stator laterally stabilize the moving element.

Abstract: A microbridge is used for the accurate measuring of time varying shear forces in the presence of fluctuating pressure. A microdimensioned plate is suspended by arms to form a microbridge. The microdimensions enable the smallest turbulence scales of interest to be sensed uniformally throughout the entire surface of the plate. The cavity beneath the microbridge is so small that a viscous drag is created in the air within the cavity and dampens normal movement of the plate. The microdimensions in conjunction with the damping effect of the cavity enable the sensor to be substantially insensitive to pressure and thus sense lateral forces independent of normal forces. The microbridge sensor is fabricated by surface micromachining. A sacrificial layer is deposited over a substrate. A structural layer is deposited and patterned to form the plate and support arms over the sacrificial layer.

Abstract: The present invention comprises a circuit for measuring the capacitive differences of small capacitors. The circuit comprises a reference capacitor and a sensor capacitor. Connected to one of the plates of each capacitor is a switch which connects the capacitors to one of two reference voltages. The other plate of the capacitors are connected to an input terminal of a voltage comparator. The comparator compares the input voltage with a third reference voltage. Differences in voltages detected by the comparator are applied to a feedback loop for generating an offset voltage at the input terminal. The offset voltage applied at the input terminal is proportional to the capacitive difference between the reference capacitor and the sensor capacitor. The feedback loop comprises a successive approximation register for digitizing the offset voltages and a digital to analog converter for converting the digitized voltages into analog voltages which are applied at the input terminal.