CMOS-MEMS resonators for mixer-filter applications

Complementary-Metal-Oxide-Silicon Micro-Electrical-Mechanical-Systems (CMOS-MEMS) technology is a potential platform to provide narrow-band filters and mixers (mixer-filters) for future single-chip transceivers. This work is an initial step to introduce the theories, to explore the design space of mixing and filtering functions with capacitively transduced CMOS-MEMS resonators, and to study the implementation challenges in aspects of resonant frequency, bandwidth, transmission gain, linearity, quality factor and termination resistance. Theories and models of the energy loss mechanisms in resonators are developed for use in design space selection. Finite element analysis results are compared with the analytical energy loss models and provide a more accurate estimation for CMOS-MEMS resonators with composite structures and multi-layer anchors. Anchor loss dominates the damping mechanism for high frequency resonators while thermoelastic damping becomes the dominant loss mechanism for beams with resonant frequency below 1 MHz. The effect of material energy loss due to grain-boundary damping in the CMOS-MEMS aluminum alloy layers is significant. Measured quality factor of CMOS-MEMS cantilever resonators covering a frequency span from 24 kHz to 5.4 MHz and over a 100°C temperature range is compared with the results of finite element analysis. Thermoelastic damping was the dominant loss mechanism and the material quality factor of the aluminum alloy layer was estimated as 1700.;A new linearity measurement technique is introduced to characterize highly linear CMOS-MEMS resonators. The linearity performance of a CMOS-MEMS resonator was measured for the first time, and compared to models that included the structural and capacitive transduction nonlinearities. The 1-dB desensitization point was 28.9 Vac (equivalent to the 1-dB compression point of 32 dBm) for a 5.8 MHz test resonator with 840 nm electrode gaps. This level of linearity is beyond the measurement range of existing techniques.;The design trade-offs between the requirements of high linearity, low transmission, high frequency stability, and low termination impedance are revealed. An analytic design is provided to fulfill these requirements simultaneously. By incorporating self-assembly actuators, experimental CMOS-MEMS test structures achieved 275 nm lateral narrow gaps without custom gap processing. This level of electrode gaps is essential to satisfy the proposed analytic mixer-filter design. A temperature stability test on self-assembly actuated electrodes demonstrates that self-assembly electrodes can operate up to 105° C, which fulfills the temperature requirements of commercial electronic standards.;Several prototype CMOS-MEMS resonators are introduced. Silicon-fin resonators incorporate silicon structures with a measured quality factor of 3589 and resonant frequency of 8.04 MHz. Flexural-mode free-free beam resonators have a tuning-fork type support structure design to reduce anchor loss. Square-frame resonators incorporated the self-assembly mechanisms for narrow gas. On-chip pre-amplifier circuitry was implemented with these resonators to demonstrate the capability of on-chip integration.