Charles F. McConaghy

Vertical-actuated electrostatic comb drive with in situ capacitive position correction for application in phase shifting diffraction interferometry

This research utilizes the levitation effect of electrostatic comb fingers to design vertical-to-the-substrate actuation for optical phase shifting interferometry applications. For typical polysilicon comb drives with 2 /spl mu/m gaps between the stationary and moving fingers, as well as between the microstructures and the substrate, the equilibrium position is nominally 1-2 /spl mu/m above the stationary comb fingers. This distance is ideal for most phase shifting interferometric applications. A parallel plate capacitor between the suspended mass and the substrate provides in situ position sensing to control the vertical movement, providing a total feedback-controlled system. The travel range of the designed vertical microactuator is 1.2 /spl mu/m. Since the levitation force is not linear to the input voltage, a lock-in amplifier capacitive sensing circuit combined with a digital signal processor enables a linearized travel trajectory with 1.5 nm position control accuracy. A completely packaged micro phase shifter is described in this paper. One application for this microactuator is to provide linear phase shifting in the phase shifting diffraction interferometer (PSDI) developed at LLNL which can perform optical metrology down to 2 /spl Aring/ accuracy.

A One Gigasample per Second Transient Recorder

A DC-to-200MHz, CCD-based transient data recorder is currently under development. Multiple recorders will be operated via a conventional computer interface. Each recorder is designed to acquire 512 samples of data at intervals as small as one nanosecond (±25ps) and to an amplitude accuracy of eight bits (±0.2%). Developmental data is presented.

Low-power direct-sequence spread-spectrum modem architecture for distributed wireless sensor networks

Emerging CMOS and MEMS technologies enable the implementation of a large number of wireless distributed microsensors that can be easily and rapidly deployed to form highly redundant, self-configuring, and ad hoc sensor networks. To facilitate ease of deployment, these sensors should operate on battery for extended periods of time. A particular challenge in maintaining extended battery lifetime lies in achieving communications with low power. This paper presents a direct-sequence spread-spectrum modem architecture that provides robust communications for wireless sensor networks while dissipating very low power. The modem architecture has been verified in an FPGA implementation that dissipates only 33 mW for both transmission and reception. The implementation can be easily mapped to an ASIC technology with an estimated power performance of less than 1 row.

Hydrogel-Actuated Capacitive Transducer for Wireless Biosensors

This article introduces a new type of transducer that combines capacitive pressure sensing techniques with biosensitive hydrogels, using an adaptable MEMS fabrication platform. Hydrogel swelling in response to analyte concentration exerts contact pressure on a deformable conducting diaphragm, producing a capacitance change. Initial results are reported for testing device feasibility. Uncrosslinked PHEMA hydrogel was tested for swelling pressure in response to calcium nitrate tetrahydrate. Diaphragm deflection due to applied air pressure was measured on NiTi-based diaphragms and compared with hydrogel-actuated deflections of the same diaphragms to determine the pressure generating characteristics of the hydrogel. The PHEMA sample exhibited greatest sensitivity in the concentration range 0–0.5 M, generating an average of 110 mN/M/μl. The device was incorporated into a passive LC resonant circuit. Resonance frequency was measured as a function of applied air pressure, in the range of pressures generated by hydrogel swelling. Resonance frequency shifted from 66 MHz to 33 MHz over the pressure range 0–32 kPa, corresponding to an estimated average sensitivity of 66 Hz per μmol of calcium nitrate tetrahydrate over the range 0–0.5 M.

Electrostatic comb drive for vertical actuation

The electrostatic comb finger drive has become an integral design for microsensor and microactuator applications. This paper reports on utilizing the levitation effect of comb fingers to design vertical-to-the-substrate actuation for interferometric applications. For typical polysilicon comb drives with 2 micrometers gaps between the stationary and moving fingers, as well as between the microstructures and the substrate, the equilibrium position is nominally 1-2 micrometers above the stationary comb fingers. This distance is ideal for many phase shifting interferometric applications. Theoretical calculations of the vertical actuation characteristics are compared with the experimental result, and a general design guideline is derived from these result. The suspension flexure stiffness, gravity forces, squeeze film damping, and comb finger thicknesses are parameters investigated which affect the displacement curve of the vertical microactuator. By designing a parallel plate capacitor between the suspended mass and the substrate, in situ position sensing can be used to control the vertical movement, providing a total feedback-controlled system. Fundamentals of various capacitive position sensing techniques are discussed. Experimental verification is carried out by a Zygo distance measurement interferometer.

Miniature Accelerometer and Multichannel Signal Processor for Fiberoptic Fabry–Pérot Sensing

A miniature accelerometer based on silicon microelectromechanical systems (MEMS) fabrication technology has been developed. Using a beam-suspended proof mass and a Fabry-Peacuterot sensing gap, this accelerometer is fiber coupled to a miniature, multichannel, optical readout system which was developed for application in compact optical sensor systems. The approximately 4 mmtimes7 mmtimes2 mm accelerometer can be tailored to cover milli-g to kilo-g acceleration ranges. The miniature readout system is enclosed in approximately a 2 cmtimes8 cmtimes1 cm package, one of the smallest ever reported, and implements the complete optical path for a three-channel embodiment of a multichannel, highly sensitive and accurate, in-phase and quadrature (IQ) optical measurement system for Fabry-Peacuterot sensors. A variety of fiber-based sensors (temperature, strain, pressure, etc.) are commercially available using this Fabry-Peacuterot technique. The complete measurement system with the accelerometer was tested using a shaker table. Sample results are presented for 100 Hz, 10-g peak-peak acceleration

A high-voltage CMOS VLSI programmable fluidic processor chip

A high-voltage (HV) SOI CMOS VLSI chip has been demonstrated to transport droplets on programmable paths across its coated surface. This HV exciter for a fluidic lab-on-a-chip system creates dielectrophoretic forces that move and help inject droplets. Electrode excitation voltage and frequency are variable: at 100V, f/sub ELECmax/ = 200Hz. Data communication rate is variable up to 250kHz. This 10,377/spl mu/m-by-8210/spl mu/m demonstration chip has a 32/spl times/32 array of nominally 100V electrode drivers dissipating 1.87W max.

A high-voltage integrated circuit engine for a dielectrophoresis-based programmable micro-fluidic processor

A high-voltage (HV) integrated circuit has been demonstrated to transport droplets on programmable paths across its coated surface. This chip is the engine for a dielectrophoresis (DEP)-based micro-fluidic lab-on-a-chip system. This chip creates DEP forces that move and help inject droplets. Electrode excitation voltage and frequency are variable. With the electrodes driven with a 100V peak-to-peak periodic waveform, the maximum high-voltage electrode waveform frequency is about 200Hz. Data communication rate is variable up to 250kHz. This demonstration chip has a 32/spl times/32 array of nominally 100V electrode drivers. It is fabricated in a 130V SOI CMOS fabrication technology, dissipates a maximum of 1.87W, and is about 10.4 mm /spl times/ 8.2 mm.

Characterization of Lithium Niobate Electro-Optic Modulators at Cryogenic Temperatures

This paper reports on the operation of lithium niobate electro-optic waveguide modulators at temperatures down to 15 degree(s)K. Commercial and laboratory fiber pigtailed devices have successfully been cooled without any increases in insertion loss from temperature induced stresses in device packaging. Three x-cut devices exhibited a linear increase in Vpi voltage of 8% +/- 1% when cooled from room temperature to approximately 20 degree(s)K. The broadband frequency response improved at lower temperatures. A velocity-matched experimental modulator has shown increased bandwidth when cooled to liquid nitrogen temperature.

A High-Voltage SOI CMOS Exciter Chip for a Programmable Fluidic Processor System

A high-voltage (HV) integrated circuit has been demonstrated to transport fluidic droplet samples on programmable paths across the array of driving electrodes on its hydrophobically coated surface. This exciter chip is the engine for dielectrophoresis (DEP)-based micro-fluidic lab-on-a-chip systems, creating field excitations that inject and move fluidic droplets onto and about the manipulation surface. The architecture of this chip is expandable to arrays of N X N identical HV electrode driver circuits and electrodes. The exciter chip is programmable in several senses. The routes of multiple droplets may be set arbitrarily within the bounds of the electrode array. The electrode excitation waveform voltage amplitude, phase, and frequency may be adjusted based on the system configuration and the signal required to manipulate a particular fluid droplet composition. The voltage amplitude of the electrode excitation waveform can be set from the minimum logic level up to the maximum limit of the breakdown voltage of the fabrication technology. The frequency of the electrode excitation waveform can also be set independently of its voltage, up to a maximum depending upon the type of droplets that must be driven. The exciter chip can be coated and its oxide surface used as the droplet manipulation surface or it can be used with a top-mounted, enclosed fluidic chamber consisting of a variety of materials. The HV capability of the exciter chip allows the generated DEP forces to penetrate into the enclosed chamber region and an adjustable voltage amplitude can accommodate a variety of chamber floor thicknesses. This demonstration exciter chip has a 32 x 32 array of nominally 100 V electrode drivers that are individually programmable at each time point in the procedure to either of two phases: 0deg and 180deg with respect to the reference clock. For this demonstration chip, while operating the electrodes with a 100-V peak-to-peak periodic waveform, the maximum HV electrode waveform frequency is about 200 Hz; and standard 5-V CMOS logic data communication rate is variable up to 250 kHz. This HV demonstration chip is fabricated in a 130-V 1.0-mum SOI CMOS fabrication technology, dissipates a maximum of 1.87 W, and is about 10.4 mm x 8.2 mm.