James G. Boyd

Design, fabrication, and testing of a bistable electromagnetically actuated microvalve

A bistable electromagnetically actuated microvalve was designed, processed, and tested. The valve was designed to control a water flow of 0.05-0.5 /spl mu/s from a reservoir at a pressure of 1-2000 Pa. The two valve components were fabricated in silicon, the upper piece comprises an electroplated gold coil, and the lower piece is an Ni/Fe alloy beam. The bistable capability was achieved by balancing the elastic forces on the beam with the magnetic forces due to a 46-/spl mu/m-thick rolled magnetic foil. The design includes the flow through the orifice, squeeze film damping due to beam motion, beam elasticity, and electromagnetics. The microvalve was tested for power consumption, flow rate, time response, Ni/Fe alloy composition, and magnetic foil properties. The valve operates at 1-2 V in both air and water.

A microfabricated electrochemical actuator for large displacements

A large-displacement electrochemical actuator was designed, fabricated, and tested. The large displacement is obtained by using a corrugated membrane made by physical vapor deposition of Parylene sandwiched with an intermediate layer of sputtered platinum. The layered structure is approximately 8-/spl mu/m thick, with 26 grooves approximately 120-/spl mu/m deep, and with a radial period of 350 /spl mu/m. The electrochemical cell consists of platinum electrodes with a 1 M H/sub 2/SO/sub 4/ solution. Hydrogen and oxygen gas is generated to displace the membrane. Although the actuator can operate at a voltage as low as 1.23 V, the experimentally determined efficiency of converting electrical energy to mechanical work is only 0.37%. The governing equations for the conservation of mass, momentum (equilibrium), energy, and the entropy generation rate were formulated assuming that the gas bubbles either nucleate without growth or grow without nucleation. For the nucleation case, simulations were performed for constant pressure isothermal actuation, and the average experimental efficiency was bounded by simulations with gas bubble radii between 1/spl times/10/sup -6/ m and 1/spl times/10/sup -6/ m. The predicted ratio of the power dissipated to the electrical power supplied is 1.37 for isothermal actuation.

A positive displacement micropump for microdialysis

Abstract Miniature fluid pumps, measuring 15×4×1 mm, have been microfabricated with silicon, glass, and polyimide. Pumps have been tested with deionized water and 10% glycerol solutions as the working solutions. The pumps have been operated with a pneumatic drive or a piezoelectric drive. Flow rates from 0.1 to 110 μl min−1 have been achieved. The maximum pressure generated by the pumps was 56 cm of water. Pumps have been operated with a dialysis probe and with a microchannel load. The pump lifetime is limited by the degradation in the performance of the polyimide components in the pump. The power consumption was less than 1 mW at a drive frequency of 10 Hz.

Electroplated electro-fluidic interconnects for chemical sensors

Abstract A wet chip electro-fluidic packaging technology based on electroplating is described. An electroplated gold seal provides the sensors fluid connection to a silicon multi-chip module. A hermetic seal is obtained using the gold–silicon eutectic bond. The sensors electrical connections to the multi-chip module are made by eutectic bonding electroplated gold–tin solder bumps on the sensor to gold pads on the substrate. The fluid and electrical connections are made simultaneously, and the process is compatible with the flip-chip bonding technique.

A thermodynamic field theory for anodic bonding of micro electro-mechanical systems (MEMS)

An anodic bond is modeled as a moving nonmaterial line forming the intersection of three material surfaces representing the unbonded conductor, the unbonded insulator, and the bonded interface. Global integral equations are written for the conservation of mass, momentum, and energy, Maxwells equations, and the second law of thermodynamics. The global equations are then localized in the volume, the material surfaces, and the nonmaterial bond line. The second law is used to determine the thermodynamic conjugates in the thermodynamic potential and the dissipation inequality. It is demonstrated that the jump in the Poynting vector across a surface is equal to the surface Joule heating due to surface electric conduction currents.

Biosensors and Microfluidic Systems

Tribological issues have received little attention in microfabricated system. Although work on miniature mechanical devices was initiated in the early 1970’s with the suspended beam and rotating electrostatic motor, issues of surface interactions in these structures has prevented their reliable operation. The application of the technology for the miniaturization of integrated circuits has also found utility in the miniaturization of chemical analysis systems (Manz et al., 1995). Semi-automated chemical analysis systems have been commercialized (Ruzicka and Hansen, 1988) and the key advantages of further reduction in size is the higher through-put of analyses can be achieved resulting in lower cost per analysis. Therefore application of microfabrication technologies facilitates the fabrication of miniature analysis systems. Furthermore, the economic benefits from batch fabrication processes will make miniature, light weight, portable, low cost analysis systems possible. In fluidic devices, the range of scaling does not offer the benefits as the volume of analyte becomes too small. Two issues arise, that of increased surface tension and pressure drop in miniature channels, and the fact that statistically there needs to be enough of the analyte molecule for the sensor to function. Many assays in biomedical analysis are at low concentration and hence volumes of at least 10 nL are required. The issues of control of sample volume without loss due to evaporation and sample reproducibility are important to solve in designing these systems. Miniature fluid handling systems can be applied to a variety of applications. Those in which the fluid is the primary component in microdialysis and drug delivery, for miniature hydraulics for the transmission of power, and in precision manufacturing for dispensing fluids in a controlled manner. The range of chemical analysis systems that can be miniaturized is likewise very broad.

Finite element analysis of electric field assisted bonding

An anodic bond is modeled as a moving nonmaterial line forming the intersection of three material surfaces representing the unbonded conductor, the unbonded insulator, and the bonded interface. The component mass balance equations, Gauss law, and the linear momentum equations are placed in a finite element formulation, which is used to predict the evolution of the sodium ion concentration, electric potential, and stress during anodic bonding of Pyrex glass and silicon.

Magnetically actuated metallic microgripper

The design and the fabrication of a magnetically actuated microgripper are described. The device is designed to have an out-of-plane motion; a novel concept among the microfabricated grippers. The gripper consists of three metallic fingers, radially directed and equally spaced on a circle; each finger composed by two beams, whose motion is driven by a magnetic field. The microgripper is modeled as an elastic system of two rectilinear beams, using Euler- Bernoulli theory for small deflections. The boundary value problem is solved and the deflection of the structure is calculated as a function of the magnetic force. The microgripper is fabricated using a UV-lithography based 3D electroforming technique. Each layer of the structure is made by metal electrodeposition into a polyimide mold. Several layers are stacked by repeated deposition and the final structure is obtained by dissolving the mold. Details about the fabrication techniques are presented and discussed. Properties and problems related to the photosensitive polyimide used (such as moisture absorption, loss of adhesion, etc.) are addressed. Electroforming of nickel, copper and permalloy are performed and optimized. In particular, a nickel activating solution is applied successfully for electroforming of microstructures. A shadow mask technique for seed-layer patterning is presented and discussed. A planar electromagnetic coil is fabricated by micromolding of thick photoresist and copper electroforming into the mold. The magnetic circuit is made by electrodeposition of permalloy.

Shape memory alloy heat pipe

Shape memory alloy (SMA) actuators can be heated quickly using electrical resistance heating. However, the slow cooling of the SMA actuator limits the actuation frequency. Therefore, the current research was undertaken to increase the actuation frequency by making a SMA heat pipe. The heat pipe is a hollow NiTi SMA cylinder partially filled with a wick and water. The condenser end of the pipe is maintained at 5C. The evaporator was cycled between a temperature below Ms and above As by adding electrical current when necessary. A pipe partially filled with water cycled faster than both a dry pipe and a fully filled pipe. Thus, the heat pipe allows for faster cycling of SMA actuators with no need for complicated or moving parts. However, the heat pipe works best with a constant temperature difference between the evaporator and the condenser, whereas the SMA must cycle. Therefore, the heat pipe is best suited to SMA materials with a small difference between the Mf and the Af temperatures.

A finite-element formulation for anodic bonding

An anodic bond is modeled as a moving non-material line forming the intersection of three material surfaces representing the unbonded conductor, the unbonded insulator, and the bonded interface. The component mass balance equations, Gauss law, and the linear momentum equations are cast in a finite-element formulation, which is used to predict the evolution of the sodium ion concentration, electric potential, and stress during the anodic bonding of Pyrex glass and silicon. The method is applicable to the viscoplasticity of solid electrolytes, and the volume and interface free energies can be modified to model electromechanical interface phenomena such as debonding, space charge accumulation and sliding at grain boundaries in ionic crystals, and a cohesive zone theory of piezoelectric fracture.