Tin Oxide Field-Effect Transistors Deposited by Thermal Atomic Layer Deposition with H2O Reactant

In this work, SnO2-based field-effect transistors were fabricated and characterized. SnO2 channel (Thickness = 6.5 or 9.0 nm) was deposited by thermal atomic layer deposition (T-ALD) with H2O as reactant. The conductivity of the channel layer was tuned by a post-annealing process, with annealing temperature limited to 400 circle C. When the channel thickness was 9 nm, the channel could not be properly modulated due to high intrinsic carrier concentration. On the other hand, a 6.5-nm thick SnO2 channel exhibited excellent device characteristics in general, including clear channel pinch-off and current on/off ratio higher than 104. Increasing the annealing duration from 1 to 2 hours led to higher channel conductivity and transconductance, such that the drain current increased by a factor of 2.5 at the given gate and drain biases. On average, the field-effect mobility increased from 110 to 125 cm2/Vs, and the subthreshold swing decreased from 4 to 2 V/dec. This work demonstrates that SnO2 deposited by T-ALD can be an attractive channel material for back-end-of-line compatible transistors, which are crucial for hyper-scaling of current Si technology.