Robert B. Darling

Effects of low work function metals on the barrier height of sulfide‐treated n‐type GaAs(100)

A comparative study of the Schottky barrier height variation on sulfide‐treated GaAs(100) surfaces with low work function metal contacts was made using current‐voltage and capacitance‐voltage measurements. Five different wet chemical sulfide treatments were found to cause little variation in the Sm (0.72 eV) and Mg (0.59 eV) Schottky barrier heights, but caused significant variation in the Al (0.58–0.75 eV) barrier heights when compared to the untreated control diodes. A low temperature (160 °C) anneal was found to cause variation in all of these, uniformly raising the barrier heights of the Sm (+0.07 eV) and Al (+0.04 eV) contacts, and degrading the Mg contacts. These results demonstrate the critical importance of both the reaction specifics and the stability of the interface on the Schottky barrier height.

A multiparameter wearable physiologic monitoring system for space and terrestrial applications

A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described.

Compact analytical modeling of squeeze film damping with arbitrary venting conditions using a Green's function approach

An analytical method based upon a Greens function solution to the linearized Reynolds equation is presented which allows the resulting forces from compressible squeeze film damping to be rapidly calculated for arbitrary acoustic venting conditions along the edges of a moveable structure. The resulting models are computationally compact, and thus applicable for dynamic system simulation purposes. Arbitrary deflection profiles can also be treated, enabling the calculation of damping effects for cantilevers, diaphragms, tilting plates, and drum-head modes. The method is theoretically described and a catalog of several useful cases is then presented to illustrate its use.

CMOS integrated ciliary actuator array as a general-purpose micromanipulation tool for small objects

The first micromachined bimorph organic ciliary array with on-chip CMOS circuitry is presented. This ciliary array is composed of an 8/spl times/8 array of cells each having four orthogonally oriented actuators in an overall die size of 9.4/spl times/9.4 mm. The polyimide-based actuators were fabricated directly above the selection and drive circuitry, Selection and activation of actuators in this array shows that integration was successful. The array was programmed to do simple linear and diagonal translations and squeeze-, centering-, and rotating-field manipulations. All three tasks were demonstrated using silicon pieces of various shapes and either 0.55 mm or 0.10 mm thick.

Organic thermal and electrostatic ciliary microactuator array for object manipulation

Abstract An organic thin-film ciliary microactuator array using independent thermal and electrostatic actuation is described. A polyimide thermal bimorph structure provides for large angle deflection with high load capacity. Electrostatic electrodes provide low-power hold-down, capacitive sensing, and feedback control capabilities. Integrating four orthogonally oriented actuators into a unit cell and replicating this cell into an array allows for precise movement of small objects in arbitrary directions. The ciliary microactuator array has immediate applications for positioning, alignment, inspection, and assembly of small parts, such as IC dice, with micron-scale resolution.

Integration of Microelectrodes with Etched Microchannels for In-Stream Electrochemical Analysis

Microelectrodes integrated with etched microfluidic flow channels allow traditional electroanalytical techniques to be performed on microliter and smaller volumes and also enable new detection techniques which are based upon the interaction between the microelectrodes and the diffusional mixing that occurs between flow lamina at low Reynolds numbers. Conductivity versus mixing measurements, anodic stripping voltammetry, and isolation of microelectrodes by sheath flow are demonstrated for an experimental device.

Thermopower and electrical conductivity of sodium-doped V2O5 thin films

Thermopower and electrical conductivity of sodium-doped vanadium pentoxide (V2O5) thin films synthesized by a solution technique were investigated. An aqueous solution based V2O5 thin film is a good candidate for thin film devices using ink-jet deposition and screen printing techniques. To improve its thermoelectric properties for practical applications, Na was systematically introduced into V2O5 as a dopant to study how it influences the thermoelectric properties. A melt-quench technique was implemented to dope various concentrations of sodium ions into sol-gel solutions, and thin films were fabricated from these. X-ray diffraction showed that the Na doped V2O5 samples dominantly form the crystalline phase β-NaxV2O5. It was shown that by increasing the Na concentration, the electrical conductivity could be increased by a factor of up to ∼104, whereas the Seebeck coefficient decreased only by a half. Direct measurement of the thermoelectric power output verified that the power factor was improved up to 35...

Micromachined Faraday cup array using deep reactive ion etching

A micromachined Faraday cup array (MFCA) for position sensitive ion detection has been developed using a deep reactive ion etching (DRIE) process. Linear, closely spaced arrays of 64, 128, and 256 cups have been produced with pitches of 250 /spl mu/m and 150 /spl mu/m. Low leakage MOS capacitors formed into DRIE trenches form effective ion collection traps with stable and electrostatically isolated capacitances. These closely spaced arrays of Faraday cups enable a new generation of compact mass spectrometers with true multi-channel detection capability. Since all of the incident ion flux is continuously intercepted by the array, no ion flux is lost as in scanning systems, and the overall sensitivity of the mass spectrometer is drastically improved by a factor approximately equal to the number of cups in the array. The MFCA is thus an ideal component for miniaturized mass spectrometers, ion beam profiling, and chemical analyzers which must work with very small sample volumes or high throughputs.

Chemical electrode surface plasmon resonance sensor

The first experimental results are presented for a device that combines a surface plasmon resonance sensor with the technique of anodic stripping voltammetry. Concentrations of 10 ppm Cu and 13.76 ppm Pb are selectively detected by the surface plasmon resonance sensor in a 0.05 M acetate buffer solution. Standard current versus voltage electrochemical measurements are presented for comparison with the surface plasmon resonance data. The potential advantages and limitations of using surface plasmon resonance electrochemical sensors are discussed.

Thermally Actuated Omnidirectional Walking Microrobot

We describe a walking microrobot that is propelled by cilialike thermal bimorph actuator arrays. The robot consists of two actuator array chips, each having an 8 × 8 array of “motion pixels,” which are composed of four orthogonally oriented cilia. Each group of unidirectional cilia is controlled independently for each chip, which provides planar motion with three degrees of freedom (x, y, θ). The robot is approximately 3 cm in length, 1 cm in width, and 0.9 mm in height and has a mass of 0.5 g. By varying the actuation frequency and motion gait strategy, the direction and velocity of the motion can be controlled. In this paper, we present the system architecture, control mechanism, and modeling of the robot, as well as experimental results, during linear and rotary motion. The robot can carry loads up to seven times its own mass, and it can operate at speeds up to 250 μm/s with step sizes from 1 to 4 μm.