E.G. Lovell

Thermo-magnetic metal flexure actuators

Deep X-ray lithography and metal plating when coupled with a sacrificial layer, SLIGA, lends itself to the fabrication of very high aspect ratio metal structures which are mechanically stiff in the substrate direction and can be very flexible in the direction parallel to the substrate. These properties can be exploited by producing a family of new flexure actuators which can produce very significant motion via thermal expansion and magnetic forces. The magnitude of thermal effects and magnetic forces are dependent on actuator geometry. An understanding of each effect allows the design of an actuator which is dominated by one or both effects. The end result is devices intended for large motion actuators in microswitch and positioning applications. They are also useful for material constant measurements of electroplated metals.<<ETX>>

Diagnostic microstructures for the measurement of intrinsic strain in thin films

Freestanding flexible microstructures fabricated from deposited thin films become mechanically unstable when internal stresses exceed critical values. A series of structures with varying geometries is used to determine the critical geometry at which buckling occurs. Observation with an optical microscope quickly reveals qualitative and quantitative information about the internal strain in the film. Strain values between +or-1.5% can be measured for a 2.0 mu m thick film using doubly-supported beams for compressive strain fields, and ring and beam structures for tensile strain fields. Parametric formulae are developed for diagnostic structure response with selected verification by finite element computations.

Fabrication and testing of the planar magnetic micromotor

Planar micromotors have the potential for high-speed control applications. These systems require closed loop control and therefore involve not only the motor but also associated high-speed control circuitry. Electrostatic devices with submicron gaps and CMOS controllers offer one possible construction technique. Magnetic motors with bipolar microelectronics are an attractive alternative. Magnetic micromotors have been constructed by using deep X-ray lithography and metal plating with a modified LIGA process. The devices are designed as reluctance motors and consist of a stator that is rigidly attached to the substrate and a rotor that is fabricated as a fully released, free part. Both pieces are formed from nickel and are typically 100 mu m in thickness. The rotor is assembled onto the stator shaft with submicron tolerances. The structure is driven by an external rotating magnet or a fixed electromagnet. Rotational speeds of up to 8000 rpm have been obtained and maintained for several days.

Fabrication of assembled micromechanical components via deep X-ray lithography

A variant of deep X-ray lithography, the LIGA process, is described. The fundamental processing sequence has been augmented with a locally defined sacrificial polyimide layer. This requires alignment of the X-ray mask to the optically defined sacrificial pattern via specially developed align-and-clamping jigs. The end results of this process are either fully unsupported metal structures or components which are locally attached to the substrate. Attempts to use this type of processing to produce assembled devices have been successful. Thus, free gears and fully attached shafts have been connected to form a nickel gear box. More complex assembly experiments have been completed successfully and are encouraging enough to pursue this approach further.<<ETX>>

Improved analysis of microbeams under mechanical and electrostatic loads

Stretching effects in axially constrained doubly clamped microbeams have been analysed for mechanical and electrostatic loads. A computer code based on the shooting method, a numerical integration procedure, has been developed for calculating the induced tension, deflections and stresses. Analytic solutions for concentrated force, distributed pressure and electrostatic loading were derived and verified by numerical simulation. Typical dimensions for microbeams considered are . Various cases have been evaluated, with and without induced tension and/or residual strain. Displacements and stresses are reduced when induced tension is included and are considerably smaller with intrinsic tension.

Deep X-ray and UV lithographies for micromechanics

A bilevel photoresist system which uses optical processing only is presented. The photoresist for this work is poly(methyl methacrylate) or PMMA. It is sensitive to X-ray photons and deep ultraviolet radiation. It can be used for spin coating or can be applied by casting and in situ polymerization. This implies that there are at least four possible versions of the deep lithography process. All of them hinge on the availability of a developer with very high selectivity and low stress formation during liquid processing. Deep X-ray and UV lithography (DUVL) results in PMMA definitions with excellent resolution for photoresist thicknesses of up to 10 mu m. It can be extended to 30 mu m or so by a simple process change. The progress reported indicates that DUVL is a viable tool for micromechanics which is accessible without synchrotron access. This process can be used with many metals which can be plated and therefore extends the micromechanics material base considerably.<<ETX>>

Development of pressure transducers utilizing deep X-ray lithography

Mechanical analysis and design of an improved class of differential pressure transducers is presented. Double-sided overload protection for a planar transducer is achieved with three-dimensional stops, produced with a process involving X-ray lithography and precision electroplating. Such metallic stops limit motion, suppress diaphragm stress, and facilitate the option of a second signal to verify performance. Computations indicate that the proposed device can generally sustain pressures substantially greater than those producing initial contact between the diaphragm and the metallic stops.<<ETX>>

SIRIUS-T, an Advanced Tritium Production Facility Utilizing Symmetrically Illuminated Inertial Confinement Fusion

SIRIUS-T is a study of an advanced tritium production facility which utilizes direct drive symmetric illumination inertial confinement fusion provided by a KrF laser. Symmetrically illuminated reactor systems have some very unique problems which have to do with a large number of beams. In SIRIUS-T, a single shell ICF target is illuminated by 92 symmetrically distributed beams around a spherical cavity of 4 m radius. The driver energy is 2 MJ and the target gain 50. The first wall consists of graphite tiles bonded to an actively cooled vanadium structure. There is a 1.0 torr xenon buffer gas in the cavity. The structural material is the vanadium alloy V-3Ti-1Si, the breeding/cooling material is lithium 90% enriched in Li-6 and the neutron multiplier is Be, giving a tritium breeding ratio of 1.903. The total tritium inventory in the reactor is 184 g. A routine release of 29 Ci/d is estimated and the maximum accidental release is 19.9 g. At 100 MJ yield, a repetition rate of 10 Hz and an availability of 70%, a tritium surplus of 33.3 kg per calendar year is achieved. Using 100% debt financing, and a 30 full power year (FPY) reactor lifetime, the cost of tritium production is

A near symmetrically illuminated direct drive laser fusion power reactor - SIRIUS-P

8,885/g at 5% interest on capital and

Mechanical analysis of pressure transducers with two-sided overload protection

14,611/g at 10% in 1990 dollars.