Nano-beam clamping revisited

TL;DR

This paper revisits nano-beam clamping, showing that fabrication undercuts naturally induce soft clamping, enhancing quality factors and affecting resonance frequencies, supported by analytic theory and experimental validation.

Contribution

It introduces an analytic model explaining how fabrication undercuts produce natural soft clamping in nano-beams, aiding design of high-Q resonators.

Findings

Undercuts produce natural soft clamping in nano-beams.

Analytic expressions fit experimental data and predict Q and frequency shifts.

Model validation through finite element simulations.

Abstract

Within recent years, the field of nano-mechanics has diversified in a variety of applications, ranging from quantum information processing to biological molecules recognition. Among the diversity of devices produced these days, the simplest (but versatile) element remains the doubly-clamped beam: it can store very large tensile stresses (producing high resonance frequencies $f_0$ and quality factors $Q$), is interfaceable with electric setups (by means of conductive layers), and can be produced easily in clean rooms (with scalable designs including multiplexing). Besides, its mechanical properties are the simplest to describe. Resonance frequencies and $Q$s are being modeled, with as specific achievement the ultra-high quality resonances based on ``soft clamping'' and ``phonon shields''. Here, we demonstrate that the fabrication undercut of the clamping regions of basic nano-beams produces a ``natural soft clamping'', given for free. We present the analytic theory that enables to fit experimental data, which can be used for $\{ Q , f_0 \}$ design: beyond Finite Element Modeling validation, the presented expressions provide a profound understanding of the phenomenon, with both a Q enhancement and a downwards frequency shift.