Lowering Motional Impedance in Micromachined Frequency-Synthesizer Using Ultra-thin (SiO2 ~ 30 nm) Internal Dielectric

The unparalleled performance of micro resonators in terms of mechanical quality factor (Q) and transduction efficiency (ηe) made them a perfect fit for on-chip radio frequency (RF) signaling. Their large Q ⋅ ηe product directly translates into the low motional resistance (Rm), ensuring efficient frequency-synthesizing at the CMOS mixing stage. However, high coupling efficiency in gap-closing electrostatic transducers is not viable due to the unity dielectric constant. Herein, we report a micromachined MEMS resonator based on the internal dielectric transduction (IDT) principle. Using an ultra-thin ~ 30 nm dielectric layer between two electrodes, this IDT featuring resonators reports a superior Rm value near 50 Ω compared to tens of kΩ of conventional air-gap configuration. FEM analysis computes a Q-value of ~ 2282 and synthesizes a fin = 246 kHz signal at the output terminal. The simulated frequency response of an equivalent electrical circuit in Cadence virtuoso shows Conversion-Gain ~ 38 dB at resonance (for 2.5 V bias with Rm = 34 Ω). Notably, the device scalability is substantially better than the previous concepts since the forming 30 nm airgap is not direct in MEMS microfabrication. The thickness independent frequency tuning flexibility in the IDT device performances and high Qs . ηe product translates the optimal Rm value which could be applied as self-matching networks.