Vertical Electric Field-Induced Abnormal Capacitance–Voltage Electrical Characteristics in a-InGaZnO TFTs

This study investigates an abnormal degradation induced in a moist environment. Although devices maintain optimal performance under bias stress operation in a vacuum, an abnormal hump is observed in capacitance–voltage (
${C}$
–
${V}$
) electrical characteristics under negative bias stress (NBS) operation in a moist environment. Electrolysis of the H
₂
O model is proposed to explain the degradation. An asymmetric stress condition, with
${V} _{\text {GD}} = {0}$
V, is designed to confirm that a vertical electric field causes the electrolysis of H
₂
O, which is the reason for the hump phenomenon in the
${C}$
–
${V}$
curve. Moreover, COMSOL simulation and
${C}$
–
${V}$
measurement of the source and drain parasitic capacitances are utilized to clarify the precise degradation position and support the mechanism. The results from electrical measurement suggest that a vertical electric field can cause instability in a moist environment.