Roll-to-roll printing for flexible silicon electronics
Researchers in Glasgow have developed a method for manufacturing circuits which prints high-performance silicon nanoribbon transistors onto flexible materials.
Engineers from the University of Glasgow’s Bendable Electronics and Sensing Technologies (BEST) group outline how they have streamlined and improved the conventional three-stage transfer printing process for creating flexible large area electronics. Instead of transferring nanoribbon FET transistors to a soft polymeric stamp before it is transferred to the final substrate, the direct roll transfer prints silicon straight onto a flexible surface.
The process begins with the fabrication of the thin silicon nanoribbon (NR) devices of less than 100 nanometres on a silicon wafer. A polyimide substrate is covered with a layer of chemicals to improve adhesion and wrapped around a metal tube, and a computer-controlled machine developed by the team then rolls the tube over the silicon wafer, transferring it to the flexible polyimide substrate.
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The team have managed to create highly-uniform prints over an area of about 10 square centimetres, with around 95 percent transfer yield. This is significantly higher than most conventional transfer printing processes at the nanometre scale.
The NR transistors printed using direct roll transfer consistently show high performance with a high on-state current (Ion) over 1 mA, high mobility (μeff) over 600 cm 2 /Vs and high on/off ratio ( Ion /off) of around 10 6 with a low hysteresis of 0.4V.
“Although we used a square silicon wafer sample of 3cm on each side in the process we discuss in this paper, the size of the flexible donor substrate is the only limit on the size of silicon wafers we can print. It’s very likely that we can scale up the process and create very complex high-performance flexible electronics, which opens the door to many potential applications,” said Professor Ravinder Dahiya, leader of the BEST group at the University of Glasgow’s James Watt School of Engineering.
“The performance we’ve seen from the transistors we’ve printed onto flexible surfaces in the lab has been similar to the performance of comparable CMOS devices – the workhorse chips which control many everyday electronics,” he said.
“That means that this type of flexible electronics could be sophisticated enough to integrate flexible controllers into LED arrays, for example, potentially allowing the creation of self-contained digital displays which could be rolled up when not in use. Layers of flexible material stretched over prosthetic limbs could provide amputees with better control over their prosthetics, or even integrate sensors to give users a sense of ‘touch’.
“It’s a simpler process capable of producing high-performance flexible electronics with results as good as, if not better, than conventional silicon based electronics. It’s also potentially cheaper and more resource-efficient, because it uses less material, and better for the environment, because it produces less waste in the form of unusable transfers.”
The team’s paper, titled ‘Direct Roll Transfer Printed Silicon Nanoribbon Arrays based High-Performance Flexible Electronics’, is published in NPJ Flexible Electronics.
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