| PhD Viva

Name of the Speaker: Mr. Bhadri Narayanan K N (EE15D055)
Guide: Prof. Amitava Das Gupta
Co-Guide: Prof. Deleep R Nair
Online meeting link: https://meet.google.com/zxi-jtpp-bbw
Date/Time: 28th March 2024 (Thursday), 12:00 PM
Title: DESIGN, SIMULATION, FABRICATION AND MODELING OF TPoS MEMS RESONATORS FOR RF TIMING APPLICATIONS

Abstract :

Modern communication systems need high frequency acoustic resonators to realize filters and frequency reference oscillators. Micro-machined MEMS resonator is an ideal candidate to replace the bulky quartz crystal in low power multi-modal filters, oscillators and on-chip sensors. In this work, thin-film piezoelectric on Silicon (TPoS) MEMS resonators with resonance frequencies close to 1 GHz are designed, fabricated, characterized and modeled. TPoS technology enables high frequency resonators with low motional impedance, relatively high Q-factor and high linearity, which are required to improve the stability of oscillators. Anchor loss can be reduced by introducing phononic crystal (PnC) tethers instead of conventional tethering. However, at higher frequencies, the bandgap of the PnC tethers decreases, leading to unreliable performance. Hence, in this work, we have used conventional tethers. The width (W) of the resonator plays an essential role in deciding the Rm and Q-factor. We have designed and fabricated resonators of different widths and number of anchors, and excited them at different modes to study their effects on the Q-factor. The impact of geometrical dimensions, the mode of vibration and the number of anchors on the Q-factor is modeled considering different loss mechanisms and excellent agreement with experimental data is achieved. To study the effect of thickness of silicon, resonators were fabricated on Silicon-on-insulator (SOI) substrates with 2 µm and 5 µm thicknesses. A 92 µm x 225 µm resonator on 5 µm silicon excited in its 23rd order longitudinal mode provided Rm = 107 Ω, linear thermal coefficient of frequency (TCF) of -28.4 ppm/C. and unloaded Q of 9556, which exceeds the highest value (to the best of our knowledge) reported in literature for TPoS resonators.