Exploiting In Situ Redox and Diffusion of Molybdenum to Enable Thin‐Film Circuitry for Low‐Cost Wireless Energy Harvesting

Abstract

Direct additive fabrication of thin‐film electronics using a high‐mobility, wide‐bandgap amorphous oxide semiconductor (AOS) can pave the way for integration of efficient power circuits with digital electronics. For power rectifiers, vertical thin‐film diodes (V‐TFDs) offer superior efficiency and higher frequency operation compared to lateral thin‐film transistors (TFTs). However, the AOS V‐TFDs reported so far require additional fabrication steps and generally suffer from low voltage handling capability. Here, these challenges are overcome by exploiting in situ reactions of molybdenum (Mo) during the solution‐process deposition of amorphous zinc tin oxide film. The oxidation of Mo forms the rectifying contact of the V‐TFD, while the simultaneous diffusion of Mo increases the diode’s voltage range of operation. The resulting V‐TFDs are demonstrated in a full‐wave rectifier for wireless energy harvesting from a commercial radio‐frequency identification reader. Finally, by using the same Mo film for V‐TFD rectifying contacts and TFT gate electrodes, this process allows simultaneous fabrication of both devices without any additional steps. The integration of TFTs alongside V‐TFDs opens a new fabrication route for future low‐cost and large‐area thin‐film circuitry with embedded power management.A facile solution processing method is developed that can fabricate vertical thin‐film diodes and lateral thin‐film transistors in a single process. By exploiting in situ redox and diffusion of a bottom molybdenum electrode occurring during semiconductor deposition, the thin‐film diodes achieve high voltage and high‐frequency operation. Furthermore, their use in full‐wave rectifiers is demonstrated for wireless energy harvesting.