Quantum Mechanical Analysis of Dual-Gate InGaZnO TFTs Employing a Gated-Multiprobe

The channel potential distribution of the dual-gate a-IGZO thin-film transistors (TFTs) was analyzed in the active layer using a gated-multiprobe method (GMP method) combining theory of quantum mechanics for the analysis of TFTs having very thin active layer. From the GMP method, the channel potential distribution follows the conventional gradual channel approximation rule from the source to the drain electrodes in case of linear region operation. In the saturation region, pinch-off with the formation of a space-charge-limited region was observed. To compare the result with the theory of quantum mechanics, ATLAS from Silvaco Inc. (ATLAS) device simulation was performed using both classical and quantum mechanical approach. The resulting parasitic resistance values of the dual-gate biasing (DGB) mode differed from the classical approach, owing to the same current spreading path of the top- and bottom-gate channel electrons, when the quantum mechanical density gradient method was applied. The accuracy of the quantum theory was confirmed using the prolonged stress results, which indicated defect creation near the middle of the channel region was the dominant mechanism for the bias stress instability, considering quantum mechanical channel electron distribution.