ResearchFields

Implantable devices and low power biosensors used for identification, monitoring and treatment of patients, are critical to future healthcare industries. Supplying energy continuously to a biosensor microsystem is a key requirement for its continuous and reliable operation. MEMS devices can be tailored to act as implantable vibration scavengers to supply this energy.

High precision nanopositioners have been used extensively in many applications such as scanning probe microscopy (SPM), atomic force microscopy (AFM), and data storage. Closed-loop feedback control of the positioners is highly desirable for high degrees of displacement precision, and needs an accurate source of position information. However, the in-plane movements are mostly measured by laser reflectance microscope, making the footprint of the system fairly huge. In this research, a novel thermal position sensor is integrated with a thermal actuator in the same MEMS chip.

RF tunable capacitors are key building blocks in many wireless communication applications, such as voltage controlled oscillators (VCO), tunable filters and phase shifters. The devices typically require a wide tuning range and high quality factor. Compared to semiconductor varactors, MEMS tunable capacitors have the potential for an extended tuning range, higher linearity and low loss. However, traditional MEMS capacitor designs clearly exhibit a Q factor versus actuation voltage trade-off: the Q of micromechanical tunable capacitor is limited by resistive losses in the suspension beams, which are often made narrow and long to make it soft for low voltage actuation. A method of moving electrically floating plate has been proposed to provide much better Q by eliminating the inevitable spring resistance in the RF signal path. However, the tuning ratio is relatively low (41%) because of the pull-in effect. In this paper, we introduce a novel MEMS tunable capacitor with floating plate, which has high tuning ratio of 367% and a Q of 56 at 1GHz.

With the development of the MEMS technology, MEMS-based positioning stages have attracted more and more attention in numerous applications in micro-/nano-scale positioning and manipulation systems due to their small size, low cost, fast response, and flexibility for system integration. Compared with piezoelectric stages, MEMS-based positioning stages have many advantages such as small size, high resonance frequency, precise positioning control, and flexibility in system integration. Among MEMS actuators, electrostatic comb-drive actuator is popular due to its fabrication compatibility with micromachining process. Advantages of electrostatic actuation are summarized as simplicity, low power consumption and fast response, while the well recognized disadvantage is high actuation voltage requirement. Recent research related to electrostatic actuation mainly focused on the optimization of structure shape to maximize electrostatic force and elimination of side effects. In this project, a MEMS-based 2DOF nanopositioning stage is developed, which integrates comb-drive actuators and capacitive displacement sensors to allow for simultaneous actuation and position sensing.