Solution process has received many attentions in recent years because of low-cost manufacturability of flexible electronic devices owing to the additive process. Organic and metal-oxide semiconductors can be printed at low-temperature however carrier mobility and reliability of TFTs using those materials are still much inferior than those for silicon. Silicon as the base material, on the other hand, has advantages in terms of high-mobilities for the both of electron and holes, chemical and electrical stability, and low-power consumption by CMOS circuit configuration.

Silicon can be printed using liquid silicon ink, which is a mixture of polymerized cyclopentasilane (CPS) and a solvent [1]. However, low-temperature formation and fabrication of polycrystalline-Si (poly-Si) and transistors on top of low-cost flexible substrates, such as paper, were outstanding challenges.

In this paper, we review a novel method that forms poly-Si patterns directly on paper using the same liquid silicon with doctor-blade coating and local irradiation of excimer-laser with room temperature process [2]. We review also the process and electrical properties of poly-Si TFTs fabricated on the paper [3]. Both p- and n-channel poly-Si TFTs were fabricated directly on top of paper with field-effect mobilities of 6.2 cm²/Vs and 2.0 cm²/Vs, respectively. Owing to the low-cost, biodegradable nature of paper, and superior electrical performance and reliability and biocompatibility of silicon, this technique will break-though the printed electronics by enabling applications such as fast printed electronics that are inexpensive, fully-recyclable, biodegradable and even edible.

[1] T. Shimoda, et al., “Solution-processed silicon films and transistors” Nature 440, 783-786 (2006).

[2] M. Trifunovic, T. Shimoda and R. Ishihara, “Solution-processed polycrystalline silicon on paper”, Appl. Phys. Lett. 106, 163502 (2015)

[3] M Trifunovic, PM Sberna, T Shimoda, R Ishihara, “Solution-based polycrystalline silicon transistors produced on a paper substrate”, npj Flexible Electronics 1 (1), 12 (2017)