Monolithically\nIntegrated Flexible Black Phosphorus\nComplementary Inverter Circuits

Abstract

Two-dimensional\n(2D) inverters are a fundamental building block\nfor flexible logic circuits which have previously been realized by\nheterogeneously wiring transistors with two discrete channel materials.\nHere, we demonstrate a monolithically integrated complementary inverter\nmade using a homogeneous black phosphorus (BP) nanosheet on flexible\nsubstrates. The digital logic inverter circuit is demonstrated <i>via</i> effective threshold voltage tuning within a single BP\nmaterial, which offers both electron and hole dominated conducting\nchannels with nearly symmetric pinch-off and current saturation. Controllable\nelectron concentration is achieved by accurately modulating the aluminum\n(Al) donor doping, which realizes BP n-FET with a room-temperature\non/off ratio >10³. Simultaneously, work function engineering\nis employed to obtain a low Schottky barrier contact electrode that\nfacilities hole injection, thus enhancing the current density of the\nBP p-FET by 9.4 times. The flexible inverter circuit shows a clear\ndigital logic voltage inversion operation along with a larger-than-unity\ndirect current voltage gain, while exhibits alternating current dynamic\nsignal switching at a record high frequency up to 100 kHz and remarkable\nelectrical stability upon mechanical bending with a radii as small\nas 4 mm. Our study demonstrates a practical monolithic integration\nstrategy for achieving functional logic circuits on one material platform,\npaving the way for future high-density flexible electronic applications.