▎ 摘　　要

Ultra-thin polymeric dielectrics are of great interest for the ever-increasing development of high-performance novel electronics. Up to date, the fabrication of polymer layers as thin as few nanometers is still an extremely demanding process. Here, we report a facile method to fabricate molecularly thin (4 nm-5 nm) plasma-hardened photoresist (PHPR) layers by applying O-2 plasma to treat the surface of the photoresist (SPR 220) to cross-link the constituent novolac resin. It is found that such ultra-thin PHPR layers also possess molecular-scale smoothness, superior chemical resistance, and thermal endurance. Furthermore, we develop an in situ transfer technique that is compatible with the planar process to stabilize the patterning of the PHPR layers. By using PHPR layers as the gate dielectric and tunneling barrier (breakdown strength up to 500 kV/mm), a graphene-PHPR-graphene (G-PHPR-G) sandwich-like structure is demonstrated, exhibiting a high photo-responsivity (>13 A/W) under low operating voltages (<1 V), which enables the ultra-thin PHPR layers to be a very promising candidate for the dielectrics in low-power, flexible electronic applications.