Vacuum-thermal-evaporation: the route for roll-to-roll production of large-area organic electronic circuits

Abstract

Surprisingly little consideration is apparently being given to vacuum-evaporation as the route for the roll-to-roll (R2R) production of large-area organic electronic circuits. While considerable progress has been made by combining silicon lithographic approaches with solution processing, it is not obvious that these will be compatible with a low-cost, high-speed R2R process. Most efforts at achieving this ambition are directed at conventional solution printing approaches such as inkjet and gravure. This is surprising considering that vacuum-evaporation of organic semiconductors (OSCs) is already used commercially in the production of organic light emitting diode displays. Beginning from a discussion of the materials and geometrical parameters determining transistor performance and drawing on results from numerous publications, this review makes a case for vacuum-evaporation as an enabler of R2R organic circuit production. The potential of the vacuum route is benchmarked against solution approaches and found to be highly competitive. For example, evaporated small molecules tend to have higher mobility than printed OSCs. High resolution metal patterning on plastic films is already a low-cost commercial process for high-volume packaging applications. Similarly, solvent-free flash-evaporation and polymerization of thin films on plastic substrates is also a high-volume commercial process and has been shown capable of producing robust gate dielectrics. Reports of basic logic circuit elements produced in a vacuum R2R environment are reviewed and shown to be superior to allsolution printing approaches. Finally, the main issues that need to be resolved in order to fully develop the vacuum route to R2R circuit production are highlighted.

Graphene-Based Hole-Selective Layers for High-Efficiency, Solution-Processed, Large-Area, Flexible, Hydrogen-Evolving Organic Photocathodes

“…80,84,85 Moreover, the obtained results are approaching the current records measured for rr-P3HT:PCBM-based architecture produced through evaporation of protective metallic Ti-based layers 81 or pulsed laser deposition of TiO 2 . However, the fabrication techniques for these photocathodes require controlled high vacuum 81 and/or atmosphere conditions, 83 and large scale uniform deposition, 189,190 which are challenging if compared with solution-processed techniques. [90][91][92][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132] Beside the aforementioned improvements in PEC performances, a clear increase of stability is also observed for the two photocathodes, as reported in Figure 5b.…”

Organic Flexible Electronics

“…Currently, spin‐casting can only deposit uniform thin films suitable for small‐area devices (laboratory‐scale, typically ≈1 cm 2 ). Despite vacuum–thermal evaporation already used commercially in the fabrication of organic light‐emitting diode (OLED) displays, vacuum‐compatible roll‐to‐roll (R2R) approach to produce high‐speed, low‐cost, and large‐area organic electronic circuits is still open to challenge . To this end, two solution‐processing approaches, namely, coating and printing, have been employed, and both have good compatibility with low‐temperature, large‐volume, and high‐throughput R2R production of organic flexible electronics.…”

Stable organic static random access memory from a roll-to-roll compatible vacuum evaporation process

“…It has been suggested that a vacuum roll-to-roll (R2R) process, in which all layers are vacuum-evaporated [27], could provide the route to fewer production steps and better circuit performance than achieved to date using mass-printing methods. Clear benefits of vacuumevaporation include solvent-free production, high deposition rates and high yield.…”

“…Clear benefits of vacuumevaporation include solvent-free production, high deposition rates and high yield. Furthermore, deposition and patterning methods compatible with R2R production are already available for each layer [27] and allow significant reduction in the number of process steps. In the following, we show that R2R-compatible, vacuum-evaporation processes can be used to produce stable organic SRAM arrays with good response times.…”