Contour Mode Acoustic Resonance in Silicon-on-insulator Mechanical Resonators using Internal Depletion Layer Transducers

Description

Semiconductor manufacturing represents one of the largest industries globally, estimated at $250 billion, mostly dominated by silicon-based electronics. As a material, silicon has been extensively studied for its electronic and optoelectronic properties. But silicon is also an excellent mechanical material. A case in point is integrated silicon-based clocks, which merges electronics with a high-performance mechanical component that vibrates at a precise frequency (called aresonator).While silicon mechanical resonators can be found in the market today, their full potential has only barely been tapped. Resonators are commonly activated via narrowly defined gaps. A narrower gap yields higher activation efficiency as the activation process involves coupling interchangeably between electrical and mechanical domains. Considering practical limits in fabricating narrow gaps on a large scale, this method of activation is inefficient. Alternative methods to efficiently activate silicon resonators, reliably replicable on a large scale, are needed. Another major challenge is to reduce the temperature sensitivity of these devices, which in silicon is intrinsically much higher than quartz.This proposal aims to address some of these bold challenges – all within the same platform. This project proposes to use depletion layers, commonly found in silicon semiconductors, as efficient force transducers that are embedded within the resonator. The transducers will not only be used to drive the vibration, but also convert it back into a detectable electrical output. Depletion layers are common place in semiconductors, and their electrical characteristics are documented in textbooks. By contrast, the understanding of how depletion layers function as force actuators and motion-to-current converters is still elementary. Depletion layers provide a dielectric layer much thinner than what is realistically achievable when fabricating air gaps. This approach is also intrinsic to semiconductor processes and holds potential for trimming the temperature sensitivity.The first objective is to create a fabrication process to embed depletion layer transducers in the resonator, designed in such a way for driving and detecting laterally propagating (contour) acoustic modes. Next, process enhancements will be studied to trim temperature sensitivity to 1/3 the intrinsic value. Validated models will be formulated to further our understanding on how depletion layers behave as electromechanical transducers. These achievements will culminate with an implementation of higher order contour modes to reach resonance at 1GHz.Based on our initial theoretical assessments and simulations, combined with our experience, we are confident that these research objectives are achievable. These outcomes will initiate breakthrough advancements of scientific and technological significance.