Showing papers on "Surface micromachining published in 1992"

Capillary electrophoresis and sample injection systems integrated on a planar glass chip

Abstract: The feasibillity of miniaturizing a chemical analysis system on a planar substrate has been demonstrated for a system utilizing electrokinetic phenomena for sample separation and solvent pumping. Using micromachining techniques, a complex manifold of capillary channels has been fabricated in a planar glass substrate and the separation of a mixture of fluorescein and calcein within the channels was achieved using electrophoresis. The maximum number of theoretical piates abtained was about 35 000 for calcein, with 5000 V applied, corresponding to 2100 V between the injection and fluorescence detection points in the channels

Dependence of the quality factor of micromachined silicon beam resonators on pressure and geometry

Abstract: An experimental study of damping and frequency of vibrating small cantilever beams in their lowest eigenstate is presented. The cantilever beams are fabricated from monocrystalline silicon by means of micromachining methods. Their size is a few millimeters in length, a few 100 µm in width, and a few 10 µm in thickness. Damping and resonance frequency are studied as a function of the ambient pressure p (1–105 Pa) and the geometry of the beam. The purpose of this research was to obtain design rules for sensors employing vibrating beams. The analysis of the experimental results in terms of a semiqualitative model reveals that one can distinguish three mechanisms for the pressure dependence of the damping: viscous, molecular, and intrinsic. For viscous damping a turbulent boundary layer dominates the damping at high pressures (105 Pa), while at smaller pressure laminar flow dominates. In the latter region, this leads to a plateau for the quality factor Q and in the former to Q p. The pressure pc at which the transition from laminar flow dominated damping to turbulent flow dominated damping occurs depends on the geometry of the beams. pc is independent on the length and decreases with both, the width and the thickness of the beams.

A glass/silicon composite intracortical electrode array.

Abstract: A new manufacturing technique has been developed for creating silicon-based, penetrating electrode arrays intended for implantation into cerebral cortex. The arrays consist of a 4.2 mm x 4.2 mm glass/silicon composite base, from which project 100 silicon needle-type electrodes in a 10 x 10 array. Each needle is approximately 1,500 microns long, 80 microns in diameter at the base, and tapers to a sharp point at the metalized tip. The technique used to manufacture these arrays differs from our previous method in that a glass dielectric, rather than a p-n-p junction, provides electrical isolation between the individual electrodes in the array. The new electrode arrays exhibit superior electrical properties to those described previously. We have measured interelectrode impedances of at least 10(13) omega, and interelectrode capacitances of approximately 50 fF for the new arrays. In this paper, we describe the manufacturing techniques used to create the arrays, focusing on the dielectric isolation technique, and discuss the electrical and mechanical characteristics of these arrays.

Microelectromechanical filters for signal processing

Abstract: Microelectromechanical filters based on coupled lateral microresonators are demonstrated. This new class of microelectromechanical systems (MEMS) has potential signal-processing applications for filters which require narrow bandwidth (high Q), good signal-to-noise ratio, and stable temperature and aging characteristics. Microfilters presented in this paper are made by surface-micromachining technologies and tested by using an off-chip modulation technique. The frequency range of these filters is from approximately 5 kHz to on the order of 1 MHz for polysilicon microstructures with suspension beams having a 2-/spl mu/m-square cross section. A series-coupled resonator pair, designed for operation at atmospheric pressure, has a measured center frequency of 18.7 kHz and a pass bandwidth of 1.2 kHz. A planar hermetic sealing process has been developed to enable high quality factors for these mechanical filters and make possible wafer-level vacuum encapsulations. This process uses a low-stress silicon nitride shell for vacuum sealing, and experimental results show that a measured quality factor of 2200 for comb-shape microresonators can be achieved.

Manipulation of the Wettability of Surfaces on the 0.1 to 1-Micrometer Scale Through Micromachining and Molecular Self-Assembly

Abstract: Micromachining allows the formation of micrometer-sized regions of bare gold on the surface of a gold film supporting a self-assembled monolayer (SAM) of alkanethiolate. A second SAM forms on the micromachined surfaces when the entire system-the remaining undisturbed gold-supported SAM and the micromachined features of bare gold-is exposed to a solution of dialkyl disulfide. By preparing an initial hydrophilic SAM from HS(CH(2))(15)COOH, micromachining features into this SAM, and covering these features with a hydrophobic SAM formed from [CH(3)(CH(2))(11)S](2), it is possible to construct micrometer-scale hydrophobic lines in a hydrophilic surface. These lines provide new structures with which to manipulate the shapes of liquid drops.

Surface micromachined, digitally force-balanced accelerometer with integrated CMOS detection circuitry

Abstract: The authors have described a surface micromachined accelerometer with digital electrostatic feedback using Sigma - Delta modulation technique, fabricated in a modular CMOS/microstructure process. Detection circuits have been tested successfully. The unity gain buffer with low input capacitance can also be used for other capacitive detection applications. The accelerometer has been characterized in the self-testing mode and has demonstrated the functionality of the device. >

A Fabry-Perot microinterferometer for visible wavelengths

Abstract: The authors report on their efforts to develop a silicon-based microinterferometer for optical applications in the visible spectral region using micromachining fabrication techniques. The interferometer is formed by two parallel dielectric mirrors supported on membranes which are electrostatically deflected for wavelength control. A simplified two-wafer fabrication process was designed and investigated. They obtained 250 nm membrane deflection for an applied voltage of 100 V. Hafnium dioxide-silicon dioxide dielectric mirrors with high reflectivity and low stress were fabricated on membrane supports and also free-standing. Anticipated applications include microinstrument spectroscopy systems for atomic absorption, ellipsometry, imaging, optical fiber communications, and general spectrophotometer uses as well as accelerometry. >

Minimum thickness of cut in micromachining

Abstract: The authors discuss the significance of the minimum thickness of cut (MTC) which is defined as the minimum undeformed thickness of chip removed from a work surface at a cutting edge under perfect performance of a metal cutting system. Following a brief look at the relation between MTC and the extreme machining accuracy attainable for a specific cutting condition, it is shown that a very fine chip with an undeformed thickness of the order of a nanometer can be obtained from experimental face turning of electroplated copper by a well-defined diamond tool. To understand the nanometric metal cutting process, a computer simulation using an atomistic model is proposed.

Vacuum microelectronics-1992

Abstract: Vacuum microelectronics is a new interdisciplinary field utilizing the mechanism of electron emission into a vacuum for devices requiring bulk and surface micromachining. By fabricating arrays of conductive or semiconductive structures that are either gated or ungated, a multitude of devices can be formed that utilize cold emission and ballistic transport of electrons from emitting cathodes to appropriate collector electrodes. Potential applications include flat panel vacuum fluorescent displays, ultrahigh-frequency power sources and amplifiers, high-speed logic and signal processing circuits, and sensors. The technology of vacuum microelectronics may be capable of operation within extremely harsh environments in terms of temperature and radiation, assuming the availability of compatible packaging materials. The author summarizes the state of the art for vacuum microelectronics, with special emphasis on operation, device fabrication, testing, experimental results, and potential applications.

Electrical and optical characteristics of vacuum-sealed polysilicon microlamps

Abstract: A silicon-filament vacuum-sealed incandescent light source has been fabricated using IC technology and subsurface micromachining. The incandescent source consists of a heavily doped p/sup +/ polysilicon filament coated with silicon nitride and enclosed in a vacuum-sealed ( approximately=80-mT) cavity in the silicon-chip surface. The filament is formed beneath the surface and later released using sacrificial etching to obtain a microstructure that is protected from the external environment. The filament is electrically heated to reach incandescence at a temperature near 1400 K. The power required to achieve this temperature (for a filament 510*5*1 mu m) is 5 mW. The emitted optical power is 250 mu W, and the peak in the spectrum distribution is near 2.5 mu m. The radiation approximately follows Lambert's cosine law. The subsurface micromachining technique used to produce the evacuated cavity has applications in other micromechanical devices. >

High aspect ratio electroplated microstructures using a photosensitive polyimide process

Abstract: A polymide-based process for the fabrication of high-aspect ratio microstructures is presented. The process exploits the sharp-sidewall characteristics of photosensitive polyimide to create the electroplating form through which the high-aspect-ratio structures are electroplated. Although the resolution of this process is inferior to the synchrotron-based process, this process has several advantages: it is simple and can be carried out using commercially available materials and common clean room equipment; the excellent chemical and thermal resistance of polyimide allows plating to take place in a variety of environments; and multiple coats of polyimide can be used to fabricate vertically integrated structures which have variation in the third dimension. The process is completely compatible with surface micromachining sacrificial layer techniques to create released electroplated microstructures. >

Thermoelectric AC power sensor by CMOS technology

Abstract: The authors report the development of a thermoelectric AC power sensor (thermoconverter) realized by industrial CMOS IC technology in combination with postprocessing micromachining. The sensor is based on a polysilicon heating resistor and a polysilicon/aluminum thermopile integrated on an oxide microbridge. The thermopile sensitivity is 9.9 mV/mW and the burn-out power of the sensor is 50 mW. The time constant is 1.85 ms and the SNR (signal-to-noise ratio) is 8*10/sup 9//W. The linearity error with respect to frequency is less than 0.1% below 400 MHz and less than 1% up to 1.2 GHz. >

Internal stress compensation and scaling in ultrasensitive silicon pressure sensors

Abstract: The pressure sensitivity of boron-doped silicon membranes has been characterized as a function of diaphragm dimensions and internal membrane stress. Using an electrostatic technique based on silicon microbridges, the internal stress for p/sup ++/ silicon (on glass), LPCVD silicon dioxide, and LPCVD silicon nitride was measured; typical values are 40, -300, and 950 MPa, respectively. Silicon membranes with several different edge lengths and deposited oxide and/or nitride coatings were characterized for sensitivity. While the pressure sensitivity can be reduced by more than a factor of twenty in the membranes due to boron-induced internal stress, the use of stress-compensating dielectrics can improve this sensitivity by a factor of six or more. Based on this theory and the measured material parameters, scaled experimental devices show typical sensitivities within 10-20% of the theoretical design targets. Pressure sensitivities as high as 2900 ppm/Pa have been achieved. >

Silicon cantilevers and tips for scanning force microscopy

Abstract: Monocrystalline silicon cantilevers with integrated silicon tips for scanning force microscopy are fabricated by means of micromachining techniques. Theoretical considerations including finite element modelling have been carried out in order to find a suitable shape and dimensions according to the mechanical requirements. Several different cantilever designs have been fabricated: a simple beam with various cross sections as well as a folded meander shape with square cross section. Special attention has been paid to the application of these silicon microprobes to measure friction. Moreover, high-aspect-ratio silicon tips with variable geometries are presented and their integration onto cantilevers is demonstrated. Finally, the fabrication of an array of such microprobes is described, which enables multiple parallel or serial surface profiling to be achieved. These integrated micromachined cantilevers have been successfully applied in standard atomic force microscope measurement systems.

Micro-hotplate devices and methods for their fabrication

Abstract: A design and fabrication methodology, for silicon micromachined micro-hotplates which are manufactured using commercial CMOS foundries techniques with additional post-fabrication processing. The micro-hotplates are adaptable for a host of applications. The methodology for the fabrication of the micro-hotplates is based on commercial CMOS compatible micromachining techniques. The novel aspects of the micro-hotplates are in the design, choice and layout of the materials layers, and the applications for the devices. The micro-hotplates have advantages over other similar devices in the manufacture by a standard CMOS process which include low-cost and easy integration of VLSI circuits for drive, communication, and control. The micro-hotplates can be easily incorporated into arrays of micro-hotplates each with individualized circuits for control and sensing for independent operation.

Integrated grating/detector array fabricated in silicon using micromachining techniques

Abstract: Silicon bulk micromachining techniques have been employed to fabricate an integrated grating and detector array in silicon for operation in the visible and near-infrared spectral range. Two wafers are machined in such a way that an optical path of about 4 mm in length is obtained in which dispersed light from a 32-slit diffraction grating is projected onto an array of photodiodes. The wafers are subjected to an electrochemically controlled etch. The interior of one of the wafers is subsequently coated with a reflective film. The grating and the array of photodetectors are integrated in the second wafer, which remains uncoated. The wafers can be bonded using the direct silicon-to-silicon fusion bonding technique. The functional division into a reflective wafer and a grating/readout wafer greatly simplifies the integration of the complete device in a smart silicon sensor.

Micromachined atomic force I microprobe with integrated I I capacitive read-out I

Abstract: . We developed a micromachining process for the fabrication of highly sensitive capacitor probes to be used for displacement measurement of an atomic force cantilever. The capacitive structure consists of two adjacent single-crystal silicon beams, one carrying a sharp tip for the force interaction, the other being the counter-electrode. The air gap of 1.5 pm separating the two electrodes is obtained by removal of the oxide in between by selective etching. The capacitance has a typical value of -0.2 pF. Forces acting on the tip induce a bending of the cantilever and change the caDacitance which can be detected bv electronic circuits. 1. Introduction Using capacitive variation to sense physical displace- ments represents an interesting alternative to optical, tunneling or piezoresistive methods. Sensors that use single-crystal silicon as highly elastic material and capacitance change as the readout principle are known to be reliable and accurate [I]. Additionally, thermal silicon dioxide provides good electrical insulation and allows, in combination with highly doped silicon, the

Micromotor fabrication

Abstract: Micromotor fabrication and related issues are discussed. The micromotors under study are of the variable-capacitance side-drive type with salient-pole and wobble (harmonic) designs. Polysilicon surface micromachining forms the basis of the micromotor fabrication process. In this process, LPCVD heavily phosphorus-doped polysilicon is used for the structural parts, LPCVD silicon nitride is used for electrical isolation, and CVD low-temperature oxide is used to as the sacrificial material. The fabrication process affects the performance characteristics of the micromotor through the reproduction accuracy of the design geometry and through the modification of the characteristics of contacting surfaces. Pattern definition and delineation are among the most critical steps of the micromotor fabrication process because of the increasing surface topography during fabrication and the large film thicknesses utilized. The release and testing process can affect the frictional characteristics of the micromotor significantly, determining success or failure of operation by dielectric excitation. >

A smart accelerometer with on-chip electronics fabricated by a commercial CMOS process

Abstract: Piezoresistive accelerometers with a monolithically integrated operational amplifier were produced, the fabrication process based on a commercial 3 μm CMOS process. The mechanical structures were realized using wet anisotropic etching of silicon with KOH and the electrochemical etch-stop at p—n junctions. Measurements show that the integration of these necessary micromachining process steps into the IC process do not influence the parameters of the electronic devices. Also, the parameters of the mechanical structures are comparable to discrete devices. The realization of application-specific smart mechanical sensors and actuators using a standard CMOS process is now possible.

Micromachined subminiature condenser microphones in silicon

Abstract: Silicon subminiature microphones can be manufactured with the methods of micromachining technology. Several condenser-type microphones have been designed and fabricated at our institute. Capacitive microphones are described, which have a structured back electrode and a membrane of silicon nitride. A smooth frequency response up to 30 kHz with a maximum open-circuit sensitivity of 10 mV/Pa is obtained. A special design of a capacitive sensor has been realized with the FET microphone. The drain current of a field-effect transistor with a suspended gate is modulated by the vibrations of the membrane. This design represents the first suspended-gate sensor, the drain current of which is deflection controlled. Design, construction and experimental results of sensitivity and frequency response are given.

Micromachined atomic force microprobe with integrated capacitive read-out

Abstract: The authors developed a micromachining process for the fabrication of highly sensitive capacitor probes to be used for displacement measurement of an atomic force cantilever. The capacitive structure consists of two adjacent single-crystal silicon beams, one carrying a sharp tip for the force interaction, the other being the counter-electrode. The air gap of 1.5 mu m separating the two electrodes is obtained by removal of the oxide in between by selective etching. The capacitance has a typical value of approximately=0.2 pF. Forces acting on the tip induce a bending of the cantilever and change the capacitance which can be detected by electronic circuits.

Investigation of attractive forces between PECVD silicon nitride microstructures and an oxidized silicon substrate

Abstract: A troublesome phenomenon encountered during the realization of free-standing microstructures, for example, beams, diaphragms and micromotors, is that initially released structures afterwards stick to the substrate. This effect may occur during wafer drying after the etching process has been completed, as well as during normal operation as soon as released structures come into contact with the substrate. In this paper the most important types of attractive forces are discussed with respect to their possible influence on the performance of micromachined structures. It is concluded that the main reason for sticking of PECVD silicon nitride micromachined structures is adsorption of water molecules. The water molecules, adsorbed on both surfaces, attract each other as soon as the surfaces come into contact. It is shown that a chemical surface modification, in order to achieve hydrophobic surfaces, is an effective method for avoiding adsorption of water, and therefore reduces sticking. Sticking of micromachined structures during drying is reduced by rinsing with a non-polar liquid before wafer drying.

Surface micromachined polysilicon accelerometer

Abstract: A surfaced micromachined polysilicon accelerometer is designed and manufactured. The sensing element represents a differential capacitor comprised of three polysilicon layers. The structure is made such that the seismic mass (polysilicon layer 2) is movable while the other polysilicon layers (layers 1 and 3) are nonmovable (fixed). The seismic mass is centered between the two fixed layers, thereby creating a differential capacitance: the bottom capacitance being formed between polysilicon layers 1 and 2, and the top capacitance being formed between polysilicon layers 2 and 3. The sensitive axis of the structure is in the direction perpendicular to the surface of the substrate. The device can be used with a signal processing circuit configured as an open loop system to achieve a sensitivity of 0.35 mV/g/V. >

Micromachined microaccelerometer for measuring acceleration along three axes

Abstract: The present invention relates to a microaccelerometer employing a single free-mass and capable of measuring acceleration along three coordinate axes, and a process for fabricating through micromachining and microelectronic techniques a microaccelerometer employing a free-mass. A microaccelerometer preform is constructed by chemically coating and etching a silicon wafer to form a support member and a free-mass surrounded by the member. The free-mass is movable with respect to, but constrained by the silicon support member. Acceleration measurements are obtained by circuits which sense changes in the position of the free-mass with respect to an equilibrium position, induced by a change in the rate of acceleration of the accelerometer, and the electromagnetic force required to restore the free-mass to its equilibrium position.

An integrated lateral tunneling unit

Abstract: A micromachined device developed to perform displacement-controlled tunneling is described. Its performance was experimentally confirmed. The lateral tunneling unit (LTU), composed of a comb-drive actuator, a tunneling tip, and an opposing wall integrated on the same wafer was fabricated using surface micromachining with only one photomask. Integration of the tip and its opposing wall eliminated coarse positioning of the specimen, and realized a fully micromachined tunneling unit. The lateral configuration is easy to fabricate and suitable for integrating other structures such as an atomic force microscope (AFM) tip. The LTU can be used as an extremely sensitive position detector. Possible applications, such as an accelerometer and an integrated AFM/LTU chip, are discussed. >

Optical micromachined pressure sensor for aerospace applications

Abstract: An optical pressure sensor has been designed using silicon micromachining technology. A resonant silicon beam is mounted above a diaphragm and its resonant frequency changes with applied pressure. The sensor is temperature compensated by way of a second pressure-insensitive resonator. Both resonators are optically addressed via the same optical fiber. The sensor is designed to give an overall accuracy of 0.05% full-scale pressure, which is currently between 130 kPa or 3 MPa. Optical technology allows the optical pressure sensor to operate in a harsh aerospace environment where electronic pressure sensors cannot survive.

Method of manufacturing a multiple microelectrode assembly

Abstract: A method of manufacturing a multiple microelectrode assembly is disclosed. Micromachining technology (such as micro-electrical-discharge machining technology, laser-beam micromachining, electron-beam micromachining) is used to manufacture an electrode/base assembly. The electrode/base assembly is placed within a container; a liquid material is placed into the container; the liquid material surrounds the electrodes of the electrode/base assembly and is allowed to solidify; and the solidified liquid material in combination with the electrode/base assembly is separated from the container. The bottom (or base) portion of the electrode/base assembly is then removed. The electrodes of the electrode/base assembly comprise a plurality of rod-like members of very small (on the order of 1 micron) metallic members of preselected dimension, shape and spacing, by which they are adapted in combination with the surrounding insulating material as a multiple microelectrode assembly.

Model of thermoelectric radiation sensors made by CMOS and micromachining

Abstract: The feasibility of thermopile infrared detectors on CMOS silicon oxide cantilever beams isolated by post-processing anisotropic etching is assessed by an analytical model. The sensitivity and detectivity are calculated for a variety of device geometries. An optimal design with a predicted sensitivity of 20 V/W for a receiving area of 0.5 mm2 is proposed.

Stereo laser micromachining of silicon

Abstract: A technique has been developed for 1‐μm resolution, high speed micromachining of three‐dimensional (3D) silicon parts. The method, based on acousto‐optic deflection of laser microchemical chlorine etching reactions, creates parts directly from a file generated with computer‐aided design/computer‐aided manufacturing (CAD/CAM) software. In this demonstration, 1‐μm3 pixels are removed at a rate of 2×104 pixels/s. The laser‐driven process relies on one of the fastest‐known sustained gas/solid interface reactions, and the size‐ and pressure‐scaling laws permit micromachining at ≳2×105 μm3/s at 10‐μm resolution. This is ∼3000 times the rate of current electrodischarge matching methods. Exchange of the etchant gas for organometallic vapor precursors has permitted laser deposition of 3D platinum and cobalt metallization on the laser‐etched structures. It is proposed that this approach can satisfy the need for primary patterning of 3D parts and molds for micromechanics, in analogy with two‐dimensional (2D) electro...