High-aspect ratio vertical comb-drive actuator with small self-aligned finger gaps

A review of fabrication processes for vertical comb drives

“…The Epipoly layer process (Carlen et al 2005), like the doubled SOI process, deposits another insulating layer and another silicon layer on top of a standard SOI wafer to create a double SOI wafer. It etches its lower comb teeth from the device layer of the original SOI wafer, and etches through the handle wafer and the original insulator layer beneath the movable structures to release them.…”

“…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.…”

“…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. These abilities can be useful in applications such as laser printing, barcode reading, laser machining, and laser projection displays-as well as in optical communications networks (Hah et al 2003(Hah et al , 2004Carlen et al 2005;Wu and Fang 2006;Ko et al 2006;Kim et al 2009;Kumar and Zhang 2009). They can also be useful in portable confocal microscopes that can be used in vivo for early detection of cancers (Kumar et al 2008;Kumar and Zhang 2009), and for guided precision surgery (Kumar and Zhang 2009).…”

“…If such mirrors are arranged into arrays they can act as wavelength-selective switches or crossconnects (Carlen et al 2005;Iwase et al 2008;Kouma et al 2005). Diffraction gratings and pinholes can also be actuated by vertical comb drives, and the focal planes of microlenses can be controlled .…”

Computation of capacitance and electrostatic forces for the electrostatically driving actuators considering fringe effects

“…In micro-electro-mechanical systems (MEMS) devices, such as switch (Naito et al 2010), variable capacitor (BakriKassem and Mansour 2004), resonator (Elshurafa et al 2011), micro mirror (Amaya et al 2011;Kim et al 2009), gyroscope (Guo et al 2010), microtweezer (Harouche and Shafai 2005) microscanner (Ataman and Urey 2006), interferometer (Lee et al 2011), attenuator (Yeh et al 2006), energy harvester , force sensor (Rajagopalan and Saif 2011), etc., electrostatic capacitors are mostly used components, which are contained of movable mechanical structures for electrostatic actuation or capacitive sensing (Amaya et al 2009;Elata and Leus 2005;Tilleman 2004;Carlen et al 2005;Sun et al 2002;Eswaran and Malarvizhi 2012;Zhang and Fang 2009). Accurate estimation of electrostatic forces or driven voltages on the MEMS structures is very important for efficient design and performance even subsequent use of the electrostatically driving devices (Jaecklin et al 1992;Chen and Miao 2007;Kang et al 2009;Harness and Syms 2000;Beyeler et al 2009).…”