Wiring of Transistor Paper for On-Demand Flexible Microelectronics
Authors: Rebecca K. Banner,*I Hubert Elly,* Kaifan Yue,+ Siddharth Kurup,^ Kira Barton,+ Victor Breedveld,* Eric M. Vogel,I Michael A. Filler*I
School of Chemical & Biomolecular Engineering,* Georgia Institute of Technology School of Material Science & Engineering,I Georgia Institute of Technology Robotics Department,+ University of Michigan School of Electrical & Computer Engineering,^ Georgia Institute of Technology
We present a versatile and scalable manufacturing process for the mass customization of flexible microelectronics by wiring modular metal-oxide-semiconductor field effect transistors arrayed on paper substrates – transistor paper – using electrohydrodynamic jet (e-jet) printing. This work synergistically combines silicon-on-insulator transistor fabrication, thermal release tape device liftoff and transfer, cellulose nanofibril (CNF) coatings, and e-jet printing to produce plastic free, flexible, and high performing circuitry. Transistors transferred to and subsequently wired on paper exhibit effective mobilities as high as 315 cm2/V-s and subthreshold slopes near 100 mV/dec. We investigate the impact of interconnect annealing conditions, paper surface roughness, mechanical manipulation, and humidity on the performance of circuits created from transistor paper. While analogous processes are used for paper and plastic electronics, we make the following key advances: (i) A XeF2 isotropic etch suspends as-fabricated transistors prior to transfer to paper, avoiding degradation of the SiO2 dielectric commonly caused by HF. (ii) CNFs serve as an adhesive coating that binds devices to paper, reduce paper’s surface roughness, and act as an alternative to plastic adhesives for improved sustainability. The CNFs are evenly distributed on paper substrates using a doctor blade technique. As water is removed from the CNF coating, the drying fibrils attach onto the transistors, creating integrated transistors on paper with a fully cellulose substrate. (iii) Thermal release tape is used to transfer 99% of devices to paper substrates rather than the commonly used polydimethylsiloxane (PDMS) stamp, as the CNF coating must be damp for successful transistor adhesion. (iv) A desktop-sized e-jet printer is used to wire modular transistors on paper post-transfer. The footprint, print speed, and line resolution of e-jet wiring makes an excellent platform for on-demand customizable circuitry compared to common monolithic circuits with pre-designed interconnects. Importantly, post-fabrication wiring enables in situ error correction by identifying misaligned and misplaced devices, ensuring functional circuitry. E-jet’s standoff distance also means that it can print to substrates with nanometer and microscale topology, which is common when non-planar modular components are arrayed on a nominally rough surface. In summary, transferring modular transistors to a paper substrate provides a platform for the fabrication of on-demand, customizable, and flexible electronics.