High-Performance Wafer-Scale Transfer-Free Graphene Microphones

A repeatable method to fabricate multi-layer graphene (ML-gr) membranes of 2r = 85 – 155 μm (t < 10 nm) with a 100% yield on 100 mm wafers is demonstrated. These membranes show higher sensitivity than a commercial MEMS-Mic combined with an area reduction of 10x. The process overcomes one of the main limitations when integrating graphene diaphragms in microphones due to the absence of automatic transfer methods on non-planarized target substrates. This method aims to overcome this limitation by combining a full-dry release of Chemical Vapor Deposition (CVD) graphene by Deep Reactive Ion Etching (DRIE) and vapor HF (VHF).

Introduction

Condenser MEMS-Mic lack a clear direction for miniaturization and high performance due to the Si-metal diaphragm’s physical properties, i.e., high-tension. The microphone sensitivity S (eq.1) is determined by the membrane displacement per pressure load (C_m) towards the counter electrode at distance x₀ and the constant bias voltage (V_b) that maintains a fixed charge on the electrodes [1].

$$\begin{equation*}S = \frac{{{V_b}{C_m}}}{{{x_0}}}\tag{1}\end{equation*}$$