Invited Paper TF-FrM3
Amorphous and Crystalline Metaloxide Semiconductors for Transistor Applications

Friday, November 13, 2009, 9:00 am, Room B4

In this presentation I will discuss our latest results in developing semiconductor metal oxide (SMO) formulations for solution-processed thin-film transistors based on crystalline and amorphous metal metaloxide films. Solution-processed amorphous semiconductor film fabrication by spin-coating and eventually printing is advantageous because of process simplicity, low cost, high reproducibility, chemical composition/stechiometry control, and possible high throughput enabling inexpensive electronics. Regarding crystalline SMO films, In₂O₃ thin-film transistors (TFTs) were fabricated on various dielectrics [SiO₂ and self-assembled nanodielectrics (SANDs)] by spin-coating In₂O₃ film precursor solutions consisting of methoxyethanol (solvent), ethanolamine (EAA, base), and InCl₃ as the In³⁺ source. Importantly, an optimized film microstructure characterized by the high-mobility In₂O₃ 004 phase, is obtained only within a well-defined base: In³⁺ molar ratio after annealing at 400 C. The greatest electron mobilities of ~ 44 cm², for EAA :In³⁺ molar r atio = 10, V⁻¹s⁻¹, is measured for n⁺-Si/SAND/In₂O₃/Au devices. This result combined with the high I_on:I_off ratios of ~ 10⁶ and very low operating voltages (< 5 V) is encouraging for high-speed applications. We have also developed amorphous Sn-In-O and Zn-Ga-In-O formulations in which the corresponding films can be annealed at far lower temperatures (< 250 ºC). For instance, solution-processed amorphous tin-doped indium oxide (ITO) films for TFT fabrication at temperatures <250 °C can be achieved by controlling film precursor solution In ⁺³ vs. Sn ⁺⁴ molar ratio resulting in electron mobilities > 2 cm² V⁻¹s⁻¹ and I _on:I _off > 10 ⁴ for TFTs using SiO ₂ as the gate dielectric. Furthermore, w e demonstrate that hybrid integration of solution-processed ITO semiconductor films SAND enables m ~ 20 cm² V⁻¹s⁻¹.