Miki Trifunovic

Single-grain Si thin-film transistors on flexible polyimide substrate fabricated from doctor-blade coated liquid-Si

Solution process of silicon will provide high-speed transistor fabrication with low-cost by, for example, roll-to-roll process. In this paper, a low-temperature process (350 °C) is reported for fabrication of high-quality Si devices on a polyimide substrate from doctor-blade coated liquid-Si. With this method, different semiconductor devices have been fabricated, reporting a carrier mobility of 460 cm2/V s and 121 cm2/V s for electrons and holes, respectively. The devices were peeled off and transferred onto a polyethylene naphthalate foil to achieve flexible devices. CMOS inverters were also fabricated and show full output swing.

Polycrystalline silicon TFTs on a paper substrate using solution-processed silicon

Solution-processing has gained widespread attention over the past years due to their potential low-cost advantage in terms of fabrication of electronics as well as application to flexible electronics. Cyclopentasilane is used for the solution-based processing of silicon. As a liquid, the material has the potential to be applied directly on low-cost flexible substrates that generally have a low thermal budget, by annealing the liquid using an excimer laser treatment. So far, electronics based on this material have only been demonstrated on rigid and high cost substrates. In this work, silicon has been applied as a solution on top of a paper substrate and processed into PMOS and NMOS thin-film transistors (TFTs). The maximum fabrication temperature was limited to approximately 100° C. By being able to fabricate devices on top of a paper substrate, a pathway opens towards new applications that combine the true low-cost and biodegradability with the high performance of silicon electronics.

Solution-based polycrystalline silicon transistors produced on a paper substrate

Printing of electronics is pursued as a low-cost alternative to conventional manufacturing processes. In addition, owing to relatively low process temperatures, flexible substrates can be used enabling novel applications. Among flexible substrates, paper was found to be a particularly interesting candidate, since it has an order of magnitude lower price than low-cost polymer alternatives, and is biodegradable. As ink materials, organic and metal-oxide semiconductors are thoroughly being investigated; however, they lack in electric performance compared to silicon in terms of device mobility, reliability, and energy efficiency. In recent years, liquid precursors for silicon were found and used to create polycrystalline silicon (poly-Si). However, fabrication of transistors on top of low-cost flexible substrates such as paper has remained an outstanding challenge. Here we demonstrate both p-channel and n-channel poly-Si thin-film transistors (TFTs) fabricated directly on top of paper with field-effect mobilities of 6.2 and 2.0 cm2/V s, respectively. Many fabrication challenges have been overcome by limiting the maximum process temperature to approximately 100 °C, and avoiding liquid chemicals commonly used for etching and cleaning. Patterning of poly-Si has been achieved by additive selective crystallization of the precursor film using an excimer laser. This work serves as a proof of concept, and has the potential to further improve device performance. Owing to the low-cost, biodegradable nature of paper, and the high performance, reliability, and energy efficiency of poly-Si TFTs, this work opens a pathway toward truly low-cost, low-power, recyclable applications including smart packages, biodegradable health monitoring units, flexible displays, and disposable sensor nodes.

Solution-Based Fabrication of Polycrystalline Si Thin-Film Transistors from Recycled Polysilanes

Currently, research has been focusing on printing and laser crystallization of cyclosilanes, bringing to life polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with outstanding properties. However, the synthesis of these Si-based inks is generally complex and expensive. Here, we prove that a polysilane ink, obtained as a byproduct of silicon gases and derivatives, can be used successfully for the synthesis of poly-Si by laser annealing, at room temperature, and for n- and p-channel TFTs. The devices, fabricated according to CMOS compatible processes at 350 °C, showed field effect mobilities up to 8 and 2 cm2/(V s) for n- and p-type TFTs, respectively. The presented method combines a low-cost coating technique with the usage of recycled material, opening a route to a convenient and sustainable production of large-area, flexible, and even disposable/single-use electronics.

Solution-processed poly-Si TFTs fabricated at a maximum temperature of 150°C

Printing liquid silicon devices using cyclopentasilane as the precursor have led to solution processed devices with high mobilities. The fabrication process, however, required a relatively high process temperature of 350°C, incompatible to inexpensive plastics. A novel processing method is presented that decreases the maximum processing temperature of poly-Si TFTs to 150°C, compatible to low-cost plastics and paper, by using a XeCl excimer laser treatment that would directly transform a solution with polysilane chains into solid polycrystalline silicon. Mobilities as high as 23.5 and 21.0cm2/Vs were obtained for the PMOS and NMOS devices respectively.