Ultrahighly Sensitive\nFlexible Pressure Sensors with\nDual-Mode Response Based on Monolayer Films of Calcium Niobate Nanosheets

Flexible pressure sensors present enormous potential\nfor applications\nin health monitoring, human–machine interfacing, and electronic\nskins (e-skin). However, at the cost of flexibility, the design of\nflexible pressure sensors has been facing the trade off between high\nsensitivity and wide sensing range. Herein, we propose a sandwiched\nstructure composed of monolayer films of calcium niobate nanosheets\nto endow the device with both ultrahigh sensitivity and a wide sensing\nrange. Tunable contact between the two electrodes of the pressure\nsensor through the gaps in the insulative monolayer film and precise\nthickness modulation of the monolayer films at the nanoscale result\nin an ultrahigh sensitivity and wide sensing range of the sensors.\nBy virtue of these two traits, the pressure sensor distinguishes itself\nwith unprecedented performances of ultrahigh sensitivity (6.43 ×\n10<sup>4</sup> kPa<sup>–1</sup>), a wide sensing range (1.94–60.00\nkPa), a fast response time (<165 ms), and reliable repeatability.\nIn addition, the sensor has a sensing mechanism transition from capacitive\nmode to piezoresistive mode from low pressure to high pressure. The\nsensors demonstrates the ability for motion detection of the human\nbody. This work sheds light on the development of highly sensitive\nflexible pressure sensors.