Microstructured graphene arrays for highly sensitive flexible tactile sensors

The development of artifi cial skin is drawing increasing attention due to potential applications in sensing a variety of physical quantities, such as tactility, vibration, and temperature. [1-6] Natural skin possesses excellent tactile sensitivity which contributes to describing the pressure distribution of surrounding environment. [7] In order for artifi cial skin emulate the exquisite sensation of natural skin, it is necessary to incorporate tactile sensors with both fl exibility and high sensitivity with respect to low-range pressure distribution (<1 kPa). Currently, great progress has been made in the design of such "skin-like" sensors, including resistive, [8-17] piezoelectric, [18-24] capacitive, [25-27] optical, [28] as well as triboelectric [29-31] sensing technologies. Among these, resistive sensors appear to be more predominantly used. [15-17] The performance of resistive sensors relies on the resistance change in sensitive elements, which could arise from the change in either resistivity of piezoresistive materials or contact resistance of strain gauges upon the modulation of external pressures. [8-14, 32] However, the intrinsic characteristics of piezoresistive materials restrict further development in the applications of state-of-the-art resistive tactile sensors. For example, the inherent stiffness and brittleness of piezoresistive semiconductors render them unsuitable for fl exible devices. [7] Not only that, for strain gauges without three-dimensional (3-D) deformable structures, the fl at crosssections limit their sensitivity towards low-range pressures. To counter this, winding structures are often introduced, but challenges remain in devising fl exible tactile sensors [6, 19, 27, 33, 34] with superior sensitivity towards low pressures.