Comparative studies on vertical-channel charge-trap memory thin-film transistors using In-Ga-Zn-O active channels...

Vertical-channel charge-trap memory thin film-transistors (V-CTM TFTs) using oxide semiconductors were fabricated and characterized, in which In-Ga-Zn-O (IGZO) channels were prepared by sputtering and atomic-layer deposition (ALD) methods to elucidate the effects of deposition process. The vertical-channel gate stack of the fabricated device was verified to be well implemented on the vertical sidewall of the spacer patterns due to excellent step-coverage and self-limiting mechanisms of ALD process. The V-CTM TFTs using ALD-IGZO channel exhibited a wide memory window (MW) of 15.0 V at a V_GS sweep of ±20 V and a large memory margin of 1.6 × 10² at a program pulse duration as short as 5 ms. The programmed memory margin higher than 10⁵ did not experience any degradation with time evolution for 10⁴ s. The mechanical durability was also evaluated after the delamination process of polyimide (PI) film. There were no marked variations in charge-trap-assisted MW even at a curvature radius of 1 mm and programmed memory margin even after repeated program operations of 10⁴ cycles. The introduction of ALD process for the formation of IGZO active channel was suggested as a main process parameter to ensure the excellent memory device characteristics of the V-CTM TFTs.