BULK-PIEZOELECTRIC TRANSDUCTION OF MICROSYSTEMS WITH APPLICATIONS TO BATCH-ASSEMBLY OF MICROMIRRORS, CAPACITIVE SENSING, AND SOLAR ENERGY CONCENTRATION

摘要

Electromechanical modeling, actuation, sensing and fabrication aspects of bulkpiezoelectricceramic integration for microsystems are investigated in this thesis.A small-signal model that describes the energy exchange between surface micromachinedbeams and bulk-lead zirconium titanate (PZT) actuators attached tothe silicon substrate is presented. The model includes detection of acoustic waveslaunched from electrostatically actuated structures on the surface of the die, aswell as their actuation by bulk waves generated by piezoelectric ceramics. Theinteraction is modeled via an empirical equivalent circuit, which is substantiatedby experiments designed to extract the model parameters.As a die level application of bulk-PZT, an Ultrasound Enhanced ElectrostaticBatch Assembly (U2EBA) method for realization of 3-D microsystems is demonstrated.U2EBA involves placing the die in an external DC electric field perpendicularto the substrate and actuating the die with an off-chip, bulk-piezoelectricceramic. Yield rates reaching up to 100% are reported from 8×8 arrays of hingedmirrors with dimensions of 180 × 100 micrometre-squared.U2EBA is later improved to provide temporary latching at intermediate anglesbetween fully horizontal and vertical states, by using novel latching structures. Itis shown that the micromirrors can be trapped and freed from different rotationangles such that zero static power is needed to maintain an angular position.The zero-idle-power positioning of large arrays of small mirrors is later investigatedfor energy redirection and focusing. All-angle LAtchable Reflector (ALAR)concept is introduced, and its application to Concentrated Solar Power (CSP)systems is discussed. The main premise of ALAR technology is to replace bulkyand large arrays of mirrors conventionally used in CSP technologies with zeroidle-power, semi-permanently latched, low-profile, high-fill factor, micrometer tocentimeter scale mirror arrays. A wirelessly controlled prototype that can move a2-D array of mirrors, each having a side length of less than 5 cm, in two degreesof freedom to track the brightest spot in the ambient is demonstrated.Capacitive sensing using bulk-piezoelectric crystals is investigated, and a Time-Multiplexed Crystal based Capacitive Sensing (TM-XCS) method is proposed toprovide nonlinearity compensation and self-temperature sensing for oscillator basedcapacitive sensors. The analytical derivation of the algorithm and experimentalevidence regarding the validity of some of the relations used in the derivation arepresented.This thesis also presents results on microfluidic particle transport as anotherapplication of bulk-PZT in microsystems. Experiments and work regarding actuationof micro-scale, fluorescent beads on silicon nitride membranes are described.