No abstract

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.

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.

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.

Immersion lithography has been proposed as a method for improving optical lithography resolution to 50 nm. The premise behind the concept is to increase the index of refraction in the space between the lens and wafer by insertion of a high refractive index liquid in place of the low refractive index air that currently fills the gap. Because the liquid will act as a lens component during the lithographic process, it must maintain high uniform optical quality. One source of optical degradation may be due to changes in the liquid’s index of refraction caused by a change in temperature. During the exposure process, energy is deposited onto the wafer, causing a rise in temperature. Consequently, any liquid in direct contact with elevated temperature portions of the wafer will also experience an increase in temperature. Two-dimensional computational fluid dynamics models were created to assess the thermal and fluid effects of the exposure process on the liquid temperature. This article presents the results of the numerical thermal and flow simulations. Both aligned and opposing flow directions were investigated for a range of inlet pressures that is consistent with what can be expected with active filling jets.