A novel AZO capping approach on SnO thin-film transistors for efficient threshold voltage modulation and electrical performance enhancement

초록

A p-type oxide semiconductor, SnO, is promising candidate for the channel material of monolithic 3D integration due to its low-temperature process compatibility and high hole mobility. In this study, we demonstrate the novel capping approach enabling passivation and doping, based on Al-doped ZnO (AZO), to the SnO channel. This AZO capping technique successfully enhanced the overall electrical performance of SnO thin-film transistors (TFTs) through oxygen diffusion driven by the oxygen areal density difference, compared to SnO TFTs without a capping layer. The field effect mobility increased from 1.6 to 2.4 cm2/V center dot s, achieving one of the best values reported. ION/ IOFF was increased from 3.5 x 102 to 2.6 x 103, subthreshold swing reduced from 15.2 to 9.3 V/dec. Moreover, the AZO capping also enables wide-range threshold voltage (VTH)control via Al-induced modulation of hole concentration in the SnO through AZO thickness control. The VTH shift per gate voltage sweep range was tunable up to 13 %, reaching one of the highest values reported and enhancing design flexibility. This VTH controllability significantly improved the noise margin of SnO-IGZO inverters. Therefore, the proposed AZO capping technique addresses fundamental limitations in SnO TFTs, enabling overall performance enhancement and improved design flexibility for oxide semiconductor circuits.

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