Schottky Effect-Enabled High Unit-Area Capacitive Interface for Flexible Pressure Sensors

Flexible capacitive pressure sensors play a crucial role in wearable electronics and robotics. However, their susceptibility to environmental noise poses challenges to sensing precision. To mitigate the impact of environmental influences, a sensor capable of producing signals orders of magnitudes larger than the noise becomes essential. One straightforward method to enhance capacitance values involves reducing the thickness of the dielectric layer. Yet, when this reduction reaches nanometer scale, the dielectric layer may become mechanically vulnerable and more importantly, their charge storage capability is compromised due to electron tunneling. To address these challenges, here the naturally formed alumina (Al2O3) on aluminum (Al) surface is employed as a stable and ultra-thin dielectric layer. Simultaneously, the Schottky effect at the Al-Al2O3-carbon black (CB) interface is harnessed to prevent electron tunneling. These strategies collectively yielded a large unit-area capacitance (UAC) of 50 nF cm-2 and demonstrated high electrical and environmental stability. Furthermore, hollow hemispherical microstructures are incorporated at the interface, resulting in a flexible pressure sensor with high sensitivity (8.6 kPa-1) and a linear response up to 50 kPa. With its simple two-layer structure, this sensor can be seamlessly integrated in situ and offers commercial-grade resolution at mN-level for monitoring human biomechanical signals. The Schottky effect at the junction between a semiconductor and a conductor is harnessed to mitigate tunneling current across the nanometer-scale dielectric layer. This strategy facilitates the creation of a frequency-independent interface with ultrahigh unit-area capacitance. Further construction of microstructures at this interface yields a flexible pressure sensor with high sensitivity, wide linear range, and environmental stability. image