Microfabricated Torsional Actuators Using Self-Aligned Plastic Deformation of Silicon

Abstract

Abstract-In this paper, we describe angular vertical-combdrive torsional microactuators made in a new process that induces residual plastic deformation of single-crystal-silicon torsion bars. Critical dimensions of the vertically interdigitated moving-and fixed-comb actuators are self-aligned in the fabrication process and processed devices operate stably over a range of actuation voltages. We demonstrate MEMS scanning mirrors that resonate at 2.95 kHz and achieve optical scan angles up to 19.2 degrees with driving voltages of 40V dc plus 13V pp . After continuous testing of five billion cycles at the maximum scanning angle, we do not observe any signs of degradation in the plastically deformed silicon torsion bars.[1550]

A review of fabrication processes for vertical comb drives

“…The first process (Kim et al 2006a) also etches away the parts of the handle wafer that lie beneath the areas of the device layer that will be displaced. It also etches extra holes through the device layer along with the outlines of the combs so that another silicon wafer, that has been DRIEed to have matching pillars, can be positioned on top of the SOI wafer.…”

“…Often vertical comb drives have torsion springs, while their fixed and movable comb pairs are positioned on either side of a mirror so that they may apply a force to one edge of the mirror or the other as voltage differences are applied between the combs of one pair at a time. Besides their obvious functions as micromotors and micropositioners (Selvakumar and Najafi 2003), the motion of vertical comb drives is often used to position micromirrors (Yeh et al 1999;Krishnamoorthy et al 2003;Hah et al 2003Hah et al , 2004Sasaki et al 2004;Tsai et al 2004;Carlen et al 2005;Lin et al 2005;Zhang et al 2005;Fang 2006, 2005;Selvakumar and Najafi 2003;Iwase et al 2008;Kim et al 2006aKim et al , 2009Ko et al 2006;Kumar et al 2008;Kumar and Zhang 2009) by lifting and/or tilting them in one or two axes. Actuating optical switches or scanners (Yeh et al 1999;Krishnamoorthy et al 2003;Hah et al 2003Hah et al , 2004Sasaki et al 2004;Tsai et al 2004;Carlen et al 2005;Lin et al 2005;Zhang et al 2005;Fang 2006, 2005;Selvakumar and Najafi 2003;Chung and Hsu 2008;Kim et al 2006aKim et al , 2009Ko et al 2006;Kumar et al 2008;Kumar and Zhang 2009), vertical comb drives can be used to obstruct a beam of light coming from optical fibres, or to steer a beam of light in a one-or two-dimensional space.…”

Dynamic Properties of Angular Vertical Comb-Drive Scanning Micromirrors With Electrothermally Controlled Variable Offset

“…For AVC actuators various fabrication schemes have been demonstrated including the use of stiction pads [19], the reflow of photoresist [11], [12], [20], plastic deformation [21], mechanical pre-tilt of the torsion beams [22], or the use of non-actuated bimorph layers on the moving [23] or fixed comb structures [24]. In these cases the emphasis has been mainly on investigating the static behavior of the MEMS devices incorporating the AVC actuators and the influence of the comb-drive geometry and initial vertical offsets on the electro-mechanical characteristics (such as static rotation angles, pull-in stabilities or comb-drive capacitances) of the devices when operated at dc voltages.…”

Plastic deformation of microstructures using carbon nanotubes film as latching surface

“…Non-planar shaped microstructures which require high temperature fabrication processes such as plastic deformation of predefined microstructures [1][2][3] are occasionally adopted in microelectromechanical systems (MEMS). As for the silicon, this plastic deformation process generally involves high temperature process environment that heats up to 900°C while stressing the microstructure, simultaneously.…”