Low-temperature polysilicon thin film transistors on polyimide substrates for electronics on plastic

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Among the state-of-the-art flexible TFT technologies, metal oxide semiconductors are especially suitable, owing to their high optical transparency, 29 good electrical performance [electron carrier mobility of !10 cm 2 V À1 s À1 even if processed at room temperature (RT)], 29 as well as excellent mechanical properties (large bendability down to 25 lm radii and good insensitivity to strain). 23,30 Table I provides a summary and a comparison of the most important device properties for the established flexible TFT technologies: amorphous silicon (a-Si), 31,32 organic semiconductors, 14,33 low temperature poly-crystalline silicon (LTPS), 34,35 and metal oxide semiconductors. As evident from Table I, metal oxide semiconducting technology presents several advantages typical of a-Si and organic materials, such as low cost, low process complexity and temperature, and large-area scalability, but at the same time yields a larger carrier mobility.…”

Single-Grain Si Thin-Film Transistors for Monolithic 3D-ICs and Flexible Electronics

“…The mobilities are much higher than those of the organic (0.5 cm 2 /Vs, [6]) and metal oxide (10 cm 2 /Vs, [8]) TFTs on a plastic substrate. The values are higher than polySi TFTs (50 cm 2 /Vs, [11]) as well because of the absence of the random grain-boundaries inside the channel. The leakage current is below 0.1 pA/µm, which is lower than that of the poly-Si TFTs and suitable for display application.…”

“…To avoid Si eruption due to hydrogen effusion during the laser irradiation [11], the sample is dehydrogenated by laser annealing using the same laser with multiple shots at lower energies. During the laser, the energy density is gradually increased from 300 mJ/cm 2 to 900 mJ/cm 2 with steps of 50 mJ/cm 2 , while the number of shots for each energy density is decreased from 100 to 1 with a step of 10 shots.…”

“…However the former has cost and technical issues since the limited size of the wafer and pick and place process, and in the latter, the electrical performance is low, although the laser release technique requires lesser cost. On the other hand, poly-Si TFTs can be fabCopyright c 2014 The Institute of Electronics, Information and Communication Engineers ricated on a plastic substrate [11] because of the short diffusion length during the pulsed-laser crystallization process [12], [13]. The mobilities of the poly-Si TFTs are, however, still much lower than those of the crystalline-silicon devices, and the fabrication is still based on vacuum and non-printing process.…”

Polysilicon thin-film transistors on polymer substrates

“…The use of polymer substrates with 250 1CoT M o350 1C appears more attractive for several reasons: (i) it is possible to use many of the conventional processes adopted for LTPS TFT fabrication with minor modifications; (ii) key materials, such as dielectrics, which are fundamentally poorer at low temperatures ( o250 1C), show adequate performance in the T-range 250-350 1C; (iii) ULTPS TFT performance are generally inferior to those fabricated at T4250 1C, as key fabrication steps, such as device hydrogenation, are problematic at very low temperatures [8]. Therefore, more recent activities have focused on the use of PAR [8,17] and PI [8,[26][27][28][29][30][31][32][33] and devices with performance comparable to those fabricated on glass have been demonstrated, with field effect mobility for n-channel devices up to 370 cm 2 /Vs [33] and for p-channel devices up to 124 cm 2 /Vs [31]. In the next sections we will describe in some detail the main steps for the direct fabrication of polysilicon TFTs on polymer substrates, including the process we developed on ultra-thin PI, the electrical characteristics of the devices fabricated on polymer substrates and some of the issues and, finally, the applications.…”