• Adamopoulos, George

Abstract

Thin-film transistors (TFTs) using oxide semiconductor channels have intensively been investigated as oxide semiconductors such as In–Ga–Zn–O (IGZO) show field effect electron mobilities in excess of 10 cm2 V−1 s−1, higher than that of hydrogenated amorphous silicon. Despite however the tremendous potential, further advancements have been hampered by a lack of hole-transporting oxides with similar or comparable transport characteristics to their n-type counterparts, limiting the applications of oxide-semiconductor-based TFTs to monotype devices and circuits. Although there are a reports on p-type doping of traditional n-type oxides, the subject still remains controversial as doping of metal oxides is typically one-sided due to self-compensation so alternative metal oxides that show intrinsic p-type characteristics are required. To date, only a few compounds such as SnOx and Cu2O have been realised and incorporated into p-type TFTs. Both compounds however show relatively low hole field-effect mobilities in the range between 0.001 and 4 cm2 /Vs, high operational voltages and most importantly the TFTs show very high off currents. Collectively, however, these results reaffirm that field-effect mobility of > 1 cm2 /Vs is generally achievable with Cu2O-based TFTs. In the case of Cu2O this is further supported by the fact that Hall Effect measurements showed mobilities exceeding 100 cm2 /Vs reaching values as high as 250 cm2 /Vs. This presentation reports on the deposition of both p-type Cu2O-based as well as n-type In2O3:W-based thin films by spray coating in air at substrates temperatures of about 320 oC from Copper(II) hexafluoroacetylacetonate and Indium(III) isopropoxide. Furthermore, TFT’s employing spray coated cubic MgO gate dielectrics and Cu2O and In2O3:W semiconducting channels showed excellent operating characteristics, in particular low operation voltage (5V), high charge carrier mobility on the order of 10 cm2 Vs, low off currents (<1 nA) and high current modulation ratio >105.Finally, this work reports on the fabrication of a CMOS inverter based on the above TFTs of optimised structures. Results obtained from optimised structures demonstrate CMOS operation with switching at around Vdd/2 and highr gain in excess of 15. The deposition methodology as well as the results that are presented here, demonstrate a route for the manufacturing of large-area compatible oxide electronics and represent a significant step towards the development of low-cost, large-area CMOS technologies at moderate temperatures.

Topics

• Deposition
• impedance spectroscopy
• compound
• amorphous
• mobility
• thin film
• semiconductor
• copper
• Silicon
• spray coating
• Indium