Low-Voltage-Driven Flexible InGaZnO Thin-Film Transistor With Small Subthreshold Swing

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Finally, mechanically active multilayer substrates using a highly cross-linked hydrogel swelling layer and a stiff PI have been shown. Typical adhesion or buffer layers are made of silicon nitride (SiN x ), 92,106,113,114,140,[143][144][145][146]150,151,173,182,183 silicon oxide (SiO x ), 78,82,135,148,154,157,168,170,181,205 and photoresist sandwiched between SiN x and SiO x . 158 Organic materials, 78,82,136,148,154,157,168,170,181,205 in particular, SU8, 153 or PVP is especially well-suited as smoothing layers.…”

“…158 The advantages of aluminum oxide are comparably high R around 9.5, low pinhole density if deposited by atomic layer deposition (ALD), and, especially in combination with IGZO, a good interface quality. Employed materials with a higher R include hafnium oxide (HfO 2 ), 177,180,181 hafnium lanthanum oxide (HfLaO), 170 titanium oxide (TiO 2 ), 154 and yttrium oxide (Y 2 O 3 ). 29,69 The drawback of these dielectrics is a scarcer availability, a worst interface quality, as well as a reduced compatibility with the TFT fabrication process.…”

“…84 Consequently, a variety of different metals: silver (Ag), 189 Al, 59,132,149,153,174,178,202,204 Au, 38,136,167 Cr, 155 and tantalum nitride (TaN) metal alloys have been used as gate contacts. 154,157,170 Especially for BG TFTs, the adhesion of the gate contact to the flexible substrate appears to be the main concern. To this aim, Cr and Ti show good results, whereas Cr often suffers from a high built-in strain.…”

“…Moreover, also other properties like adhesion or transparency need to be considered. These requirements resulted in the use of different metals: Al, 77,149,152,154,157,165,170,172,179,208 Au, 38,167 Cu, 147 Mo, 41,82,137,138,148,164,168 palladium (Pd), 145 and Ti, 90,93,144,169 whereas Mo and Ti seem to exhibit the lowest specific contact resistance R C . At the same time, a big variety of multi-layer contacts have been developed to combine the advantageous properties of different materials; recent examples are: Ti/ Au, 59,69,81,84,113,140,141,143,146,150,151,[181][182][183] Ni/Au, 79 Mo/ Al, 166,173 Cr/Au, 114 Mo/AlNd, 156 Cr/Au/Cr, 92 Mo/Al/Mo, 153 Ti/Au/Ti, …”

“…40,41,132,136,139,153,[158][159][160]163,[166][167][168][169][170]173,174,202,204 This can either be done using native adhesion forces or utilizing an additional adhesive. Alternatively, a flexible foil can also be mechanically fixed on particularly designed holders using metallic clamps.…”