"Quartz crystal-based oscillators have been employed for timing and frequency references applications since the 1950s. However, the quartz fabrication process imposes limitations in terms of robustness, size, cost, and direct on-chip integration with Complementary Metal-Oxide Semiconductor (CMOS) circuits. An unmatched infrastructure investment in advanced semiconductor foundries has allowed for the introduction of a new silicon based timing references, the MicroElectroMechanical Systems (MEMS) resonator. These new devices are able to provide superior timing performance while at the same time setting new standards in terms of robustness, power consumption and miniaturization. This work describes the fabrication of wafer-level vacuum-encapsulated silicon resonators fabricated in MEMS Integrated Design for Inertial Sensors (MIDIS), a commercial pure-play MEMS process, provided by Teledyne DALSA Semiconductor Inc. (TDSI). MIDIS offers a 30 [mu]m thick silicon device layer that is wafer-level vacuum encapsulated at 10 mTorr. The total leak rate equivalent is noted to be as low as 6.5 x 10−17 atm cm3/s, which provides an ultra-clean environment for the operation of the devices. The Lamé mode resonators developed in this work achieved a quality factor of 3.24 million at a resonance frequency of 6.89 MHz, resulting in the highest recorded f-Q product of 2.23e13 Hz for wafer-level vacuum-encapsulated silicon resonators. The device was integrated in a PCB based oscillator in order to build a high performance frequency reference that meets most Global System for Mobile Communications (GSM) specifications.Furthermore, low polarization voltage breath-mode ring resonators are presented here. The ring resonators are designed to operate with a low DC polarization voltage, starting at 5V, while providing a high frequency-Quality factor (f-Q) product. The vacuum packaging quality is evaluated using an automated testing setup over an extended time period. The fabricated devices had a resonant frequency of 10 MHz with the quality factor exceeding 8.4e4. Finally, this works presents wafer-level vacuum-encapsulated silicon resonators with transduction gap of 200 nm. The devices are fabricated in MIDIS where the default minimum transduction gap in the MIDIS process is 1.5 [mu]m. A gap reduction technique that relies on arc-welding is introduced here. The prototype Lamé mode resonators are encapsulated in an ultra-clean 10 mTorr vacuum cavity that ensures long-term stability. The Quality factor was measured to be 1.37 million at a resonance frequency of 6.89 MHz. With the narrower gap, the motional resistance of the resonators is reduced by a factor of 10 times." --