AbstractsEngineering

Silicon based micromechanical resonators have been successfully utilized as a replacement for Quartz in time keeping applications. Addition of silicon dioxide allows a reduction in the total temperature induced frequency shift for silicon based resonators from 3600 ppm to less than 100 ppm between -40 ??C to +85 ??C. While this makes their temperature stability comparable to Quartz, much improvement is needed to satisfy requirements for next generation wireless communication applications. This thesis describes a novel algorithm utilizing three AlN-on-silicon micromechanical oscillators with unique temperature dependence to eliminate the 100 ppm temperature-induced frequency shift of individual oscillators. The frequency outputs from the three oscillators undergo frequency multiplication and mixing in two stages to achieve the temperature-insensitive frequency reference, without the need for accurate temperature sensing on-chip. The output of the mixers generate a number of spurious frequency products that need to be filtered out. AlN-on-silicon acoustically coupled filters are implemented to achieve the filtering function with a potential for a system-on-chip implementation. Such temperature-insensitive precision clocks are potential candidates for use in small form factor systems, such as miniaturized inertial measurement units. The design, fabrication, and experimental investigation of two critical building blocks in the clock algorithm are discussed; namely temperature-compensated MEMS resonators and acoustically coupled bandpass filters. Finite element modeling has been rigorously used in the design process to eliminate unnecessary fabrication trials. A novel passive temperature compensation strategy is implemented using silicon dioxide refilled trenches within the resonator body. Through control of the position of the oxide within the resonator, a fine control over the frequency-temperature characteristics of the oscillators is obtained, thus allowing for their use in the clock system. Using these oscillators, the multi-resonator clock is shown to provide a total frequency shift of less than ??4 ppm across -20 ??C to +50 ??C in a proof of concept implementation, demonstrating a 10?? improvement over silicon oscillators compensated passively using silicon dioxide.