MESA+ University of Twente
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This thesis focused on the development of microactuators and micromachining methods for their fabrication. There are numerous possible applications of microactuators, including data storage, microassembly, microscopy, robotics and optical systems. The performance goals for our microactuators were motivated by their potential use in a magnetic memory based on scanning probe technology, the micro Scanning Probe Array Memory (µSPAM).

We have concentrated on electrostatic linear stepper micromotors with built-in mechanical leverage as potential candidates to satisfy demanding target specifications of the µSPAM. Due to its favorable scaling properties, electrostatic actuation allows large energy density, fast response and low power consumption at the micron scale. Deflection of an elastic plate (beam) by electrostatic force is employed to generate a longitudinal contraction of the motors. Since this deflection is much larger than the induced contraction there is a built-in mechanical leverage, resulting in a powerful, high-resolution step. A voltage controlled clamping mechanism is employed to add small steps in sequence, creating large displacements, limited only by the dimension of the guidance.

We devised, fabricated and operated three different electrostatic linear stepper micromotors for positioning of a recording medium in the µSPAM: a shuffle motor, a 2DOF shuffle motor and a contraction beams micromotor. The required specifications for small size (<1 mm2), high output force (mN range), large stroke (hundreds of mm), good positioning resolution (nm range) and speed (mm/s range) have successfully been fulfilled. The feasibility of stepping motion along two axes, required in the µSPAM, was demonstrated with success.

Successful operation of these motors and electrostatic microactuators in general requires proper electrical insulation between mechanically connected components. The widely accepted surface micromachining approach uses stacks of many dielectric and conductive layers connected by vertical conduction paths. We made a radical departure from this by employing vertical trench isolation. This technique utilizes trenches refilled with dielectric material to create electrical insulation between mechanically joined components in a single conductive layer. In this way, distinct electrical domains can be defined on both fixed and movable parts, allowing a large freedom of design. In this thesis we extensively explored the use of vertical trench isolation in both surface and bulk micromachining.