Design, Fabrication and Characterization of CMOS-MEMS Novel Resonator with Embedded Heater for Filter, and Temperature Sensor Applications Open Access
MEMS resonators cover a wide range of applications, such as oscillators, gyroscopes, biosensors, temperature sensors, and gas sensors. The novel MEMS resonators in this work were designed in both PZT and CMOS process and fabrication was conducted on both technologies; however, the final design was completed in CMOS process. The advantages of CMOS and MEMS process are combined, and the CMOS-MEMS resonator was designed, fabricated, and tested successfully. The performance of the novel CMOS-MEMS resonators in this work were tested as both temperature sensors and wide range tunable resonators. The results are compared with literature and promising results are achieved with very low power consumption. This thesis presents CMOS-MEMS fixed-fixed beam type resonators with high temperature sensitivity attributed to the large axial load occurring on fixed ends with the increase in the ambient temperature. An analytical model to address the reason for the high sensitivity and large axial load is presented, and closely matches with both simulation and measurement results. The 120um resonators consisting of multiple metal dielectric layers, and poly1 layers, were designed and measured with a center frequency around 640 kHz achieving a resolution of 0.00035 °C/Hz without sacrificing a low stiffness constant. The effect of CMOS packaging on temperature sensitivity is also investigated, and almost two times greater temperature sensitivity is achieved. The CMOS-MEMS fixed-fixed beam resonators with wide active frequency tuning range capability attributed to the axial stress modulation using embedded heaters are presented. This is in contrast to frequency tuning based on Elastic Modulus change, or material phase transition with respect to temperature given in previous literature. Two resonators, consisting of multiple metal, dielectric layers and poly1 layers, were designed; the first resonator at 303.4 kHz, while the second at 2053 kHz, achieve frequency tuning ranges of 35.7% & 42.6% respectively. Electrostatic transduction is achieved by embedded metal beams, and used to drive the device into resonance. The heaters, made of poly1, are embedded directly into the resonators during the CMOS process to achieve low power consumption and optimum heating efficiency. A power consumption of 900µW/beam is achieved for the first design -152µm length beam- while providing a frequency tuning of 35.7%. The high efficiency of the fixed-fixed beam type MEMS resonator over the traditional cantilever is well established for mass sensing applications. The total active area increased from 20% to 80% while the mass sensitivity increased around 4 times. In addition, the resonators were built as an in-plane resonator rather than an out-of-plane resonator. This enabled a compact area with more flexibility in designing high frequency resonators. Building resonators from two movable beams rather than one fixed one movable beam also provided 1.4 times smaller power consumption.
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