In Situ Rapid Fabrication of Graphene and Copper Heterojunctions using Fiber Laser Direct Writing

Despite challenges with complex architectural designs and manufacturing processes, multifunctional three-dimensional (3D) heterostructures have generated interest in research due to their unique structural formability, superior electronic, and optoelectronic properties. Furthermore, conventional fabrication methods are not transferable to flexible substrates. Herein, a straightforward, fiber laser direct writing (FLDW) process was demonstrated to fabricate [PN Junction] diodes and bipolar junction transistors (BJTs) simultaneously by depositing multifunctional P-or-N type conductive metal copper oxide films and porous graphene films on flexible polyimide substrates. The PN junctions exhibited good diode rectification and appropriate behaviour in light-dark, and high-temperature conditions. Due to the flexibility of the FLDW deposition process by varying the laser writing parameters, the controllability of the conductivity nature (P-or N-type) of the copper oxide films was observed through SEM, EDS, and RAMAN characterization. Likewise, the current gain of NPN (or PNP) BJTs can be configured effectively through tunable laser power density and various base gap widths of the BJTs. The maximum gain for NPN BJT and PNP BJT was 35.5 and 38.2, respectively. In addition, the FLDW process technique was utilized to form multifunctional NPN (or PNP) BJTs matrices composed of GO/Cu_xO heterostructure as a proof of concept. The proposed processing of 3D heterostructure devices with FLDW, with its facile operation, versatility, and low cost of production, displays promise for large-scale flexible electronics.