RF Ring Oscillator Graphene-Based Strain Sensor

Graphene-based RF ring oscillator sensor was demonstrated as a high gauge factor (GF) strain sensor. CVD-grown graphene monolayer on a flexible Cu layer was integrated on a five-stage RF ring oscillator platform and utilized to measure elastic strain. The main features of the proposed technique are high sensitivity (i.e., high gauge factor), low power, and high signal-to-noise-ratio due to the digital operation, which leads to noise suppression. Strains in the range of
$8\times 10^{-4}$
to
$2.5\times 10^{-2}$
were measured with the detected change in surface resistance in the order of
$1.6-1.8\ \Omega/$
, and average gauge factor,
$\text{GF}\approx 64.36$
. The main advantage of the proposed approach with frequency change detection as compared to the widely investigated graphene on PDMS strain gauges are higher sensitivity due to higher conductivity of the graphene layer, and lower noise due to the overall low resistance of the circuit and better CMOS integration as compared to the conventional resistive change sensing platforms.