Browse Theses

These days, sensor chips in very small form factors are ubiquitous. In this dissertation, I explain my efforts and achievements in proposing the first center-clamped 3C-SiC RF microdisk resonators with out-of-plane vibration as a candidate for future resonant sensing applications. First, nanomachining of 3C-SiC material using Focused Ion Beam (FIB) to find sputtering yield and lateral deformations for many different FIB conditions as well different patterns (and scales), is investigated accompanied by SRIM simulations.Then, I report theoretical analysis, fabrication and measurement of (center-clamped) RF multi-mode micromechanical resonators based upon vibrating circular disks made of a ~500nm thin SiC epilayer grown on single crystal Si. The fabrication method - composed of FIB sputtering and HNA etching - has been used for the first time and the vibration resonance peaks (in frequency spectrum) are detected through laser-interferometry measurements. A ~40µm-diameter SiC disk with a slender (~800nm) anchor exhibits more than a dozen flexural modes between ~2MHz¿20MHz with quality factors (Q's) of ~1000¿4000. Two other disks with diameters of ~40µm and ~30µm, and wide anchors (~20µm and ~10.3µm, respectively) have their set of major flexural peaks (associated with modes of zero-circular nodes) between 15¿19MHz with Q's of ~500¿2500.This dissertation then describes the efforts to achieve an improved self-sustained oscillator based on such resonators. First, a theory-inspired method is developed for design of electrostatically-transduced MEMS/NEMS referenced Pierce oscillators to improve phase noise (by increasing motional inductance and thus motional resistance) while also addressing oscillation start-up and other specifications e.g. frequency detuning and power consumption.Finally, the laser-based optical transduction scheme is used to make self-sustained oscillators from microdisk resonators. Laser actuation is very compatible with 3C-SiC material and the targeted application of sensing in harsh-environments and very immune to the undesired circuit loading effects and power handling inefficiencies of other transductions. The oscillator is analyzed by behavioral simulations and also measured with a home-built setup. The transduction with the microdisk resonator is via interferometry-based sensing and laser-based optical actuation. The measured phase noise of such oscillator shows a noticeable improvement of the effective Q (~2.3) over that of the open-loop microdisk resonators.