Giant gauge factor of Van der Waals material based strain sensors

Abstract

There is an emergent demand for high-flexibility, high-sensitivity and low-power strain gauges capable of sensing small deformations and vibrations in extreme conditions. Enhancing the gauge factor remains one of the greatest challenges for strain sensors. This is typically limited to below 300 and set when the sensor is fabricated. We report a strategy to tune and enhance the gauge factor of strain sensors based on Van der Waals materials by tuning the carrier mobility and concentration through an interplay of piezoelectric and photoelectric effects. For a SnS₂ sensor we report a gauge factor up to 3933, and the ability to tune it over a large range, from 23 to 3933. Results from SnS₂, GaSe, GeSe, monolayer WSe₂, and monolayer MoSe₂ sensors suggest that this is a universal phenomenon for Van der Waals semiconductors. We also provide proof of concept demonstrations by detecting vibrations caused by sound and capturing body movements.

Fig. 1. Giant gauge factor (GF) of SnS₂ based strain sensors.

a Schematic of the Van der Waals strain sensor devices. b I–V curves under various strain conditions measured in darkness. c The variation of $\mathrm{\Delta }R/R_0$ as a function of strain for the sensor measured in darkness. d I–V curves under various strain conditions measured with 365 nm light illumination. e The function of $\mathrm{\Delta }R/R_0$ versus strain of the sensor measured under 365 nm illumination. f GF value of the strain sensor as a function of the power density of 365 nm illumination.

Fig. 2. Origin of enhanced GF value by photo illumination.

a Calculated relative change of equivalent potential variation ($\mathrm{\Delta }\varphi$) of the SnS₂ based strain sensor with strain (s) with and without external illumination. b Calculated relative change of $\mathrm{\Delta }\varphi$ at zero strain (s) as a function of power density of illumination. c Calculated mobility as a function of strain in darkness (red line) and under 365 nm laser illumination (blue line). d Demonstration of the universality of GF enhancement phenomenon by photo illumination for Van der Waals semiconducting materials including SnS₂, GaSe, GeSe, monolayer WSe₂, and monolayer MoSe₂.

Fig. 3. Model of measured sensor currents.

Calculated currents (black lines) and measured currents (colored symbols) for a selection of strains for a dark and b 365 nm laser illuminating conditions.

Fig. 4. Demonstration of real world application of VdWLM strain sensor.

a The performance of a SnS₂ based strain sensor working under illumination when detecting vibrations induced by sound in comparison to signal when working in darkness. b Schematic of strain points produced by motion of a human body used for strain detection by SnS₂ based devices. c The measured response produced by smile motion for sensor mounted on cheek, as shown in insert. d Response to wrist bending following positions shown below. e Sensor response to motion of standing and sitting corresponding to the insert image for sensor fixed on knee. f Signals from sensor on knee showing comparative response for slow and rapid walking.

Fig. 5. Dynamic strain sensing of SnS₂ based strain sensors working under illumination.

a–c The top row shows dynamic strain applied to a sensor at three different frequencies: a 0.11 Hz, b 0.21 Hz and c 0.28 Hz. The second row shows the current response corresponding to each dynamic strain state. d–f The bottom row shows frequencies calculated by Fourier transforms of I–t curve in figure (a–c).