A 2DOF SOI-MEMS Nanopositioner With Tilted Flexure Bulk Piezoresistive Displacement Sensors

We describe a novel high-bandwidth two degree of freedom microelectromechanical system nanopositioner. On-chip piezoresistive sensors and four electrostatic actuators are incorporated. The bulk piezoresistivity of tilted clamped-guided beams is used to facilitate the fabrication process by eliminating the need for implementing highly doped regions on flexures. To enhance the mechanical characteristics of the nanopositioners, folded springs are also proposed, analytically modeled, and implemented as a component of the device suspension system. The nanopositioner demonstrates a displacement range larger than 15
$\mu \text{m}$
and in-plane resonance modes above 3.6 kHz in both axes. A significant increase in the bandwidth of the piezoresistive sensors is achieved by improving their on-chip signal routing layout. Sensing bandwidths as wide as 55 kHz are experimentally demonstrated for the modified sensors. Characterization reveals a phase response with minimal delay over a large bandwidth, making the device a promising platform for implementation of high-performance feedback control systems. The nanopositioner is also used as the scanning stage of an atomic force microscope for imaging purposes.