Capacitively transduced polycrystalline GeSi MEM resonators

Abstract

Wireless communication technology has revolutionized our daily life through rapid development in the areas of broadcasting, wireless local area networks, wireless sensor networks, mobile communication, and satellite communication etc. Wireless communication systems rely on their ability to select or generate signals with a very precise frequency. Filters are used for the reception of a desired signal in an overly crowded frequency spectrum, in the presence of a substantial amount of interference. In the same systems, oscillators are required for a stable reference frequency. The common feature of filters and oscillators is their use of resonators. The contemporary wireless systems, now a days, utilize off–chip components that occupy large space at board level and consumes substantial amount of power. Bulk mode MEM resonators can be used as frequency selection and generation components due to their ability to resonate at GHz frequencies and their exceptionally high quality factors. They are envisioned to replace the existing off–chip components with on–chip micromachined counterparts. Therefore, the integration of micromechanical components on top of CMOS chip paves the way towards miniaturized, low–power, low cost, and high–performance wireless communication systems on a single chip. The objective of this research is to apply CMOS post–processing compatible material to fabricate bulk mode MEM resonators that can be used for filtering and oscillator functions in wireless front–end architectures. Therefore, these MEM resonators needs to conform to the requirements of low motional resistance (ideally 50 Ω for filtering), exceptionally high quality factor, about 100,000 (like quartz crystal) and low operational voltages. This research provides a proof of principle that MEM resonators can be fabricated on top of CMOS with exceptionally high quality factors using low stress and highly conductive poly Ge0.7Si0.3 structural layers. The motional resistance is still high for the fabricated devices that limits their use for filtering applications. However, they can potentially replace the quartz crystals used for local oscillators due to their high–Q exceeding 100,000, generally required for quartz crystals in wireless front-end architectures for local oscillators.