SnO Nanosheet Transistor with Remarkably High Hole Effective Mobility and More than Six Orders of Magnitude On-Current/Off-Current

Abstract

Using novel SiO2 surface passivation and ultraviolet (UV) light anneal, a 12 nm thick SnO p-type FET (pFET) shows hole effective mobilities (µeff) of more than 100 cm2/V·s and 31.1 cm2/V·s at hole densities (Qh) of 1 × 1011 and 5 × 1012 cm−2, respectively. To further improve the on-current/off-current (ION/IOFF), an ultra-thin 7 nm thick SnO nanosheet pFET shows a record-breaking ION/IOFF of 6.9 × 106 and remarkable µeff values of ~70 cm2/V·s and 20.7 cm2/V·s at Qh of 1 × 1011 cm−2 and 5 × 1012 cm−2, respectively. This is the first report of an oxide semiconductor transistor achieving a hole effective mobility µeff that reaches 20% of that in single-crystal Si pFETs at an ultra-thin body thickness of 7 nm. In sharp contrast, the control SnO nanosheet pFET without surface passivation or UV anneal exhibits a small ION/IOFF of 1.8 × 104 and a µeff of only 6.1 cm2/V·s at 5 × 1012 cm−2 Qh. The enhanced SnO pFET performance is attributed to reduced defects and improved quality in the SnO channel, as confirmed by decreased charges related to sub-threshold swing (SS) and threshold voltage (Vth) shift. Such a large improvement is further supported by the increased Sn2+ after passivation and UV anneal, as evidenced by X-ray photoelectron spectroscopy (XPS) analysis. The ION/IOFF ratio exceeding six orders of magnitude, remarkably high hole µeff, and excellent two-month stability demonstrate that this pFET is a strong candidate for integration with SnON nFETs in next-generation ultra-high-definition displays and monolithic three-dimensional integrated circuits (3D ICs).

Keywords

• effective mobility
• transistor
• SnO
• passivation
• UV anneal