Extraction of sub-gap density of states via capacitance–voltage measurement for the erasing process in a TFT charge-trapping memory

Abstract

Charge-trapping memories (CTMs) based on zinc tin oxide (ZTO) semiconductor thin-film transistors (TFTs) can be programmed by a positive gate voltage and erased by a negative gate voltage in conjunction with light illumination. To understand the mechanism involved, the sub-gap density of states associated with ionized oxygen vacancies in the ZTO active layer is extracted from optical response capacitance–voltage (C–V) measurements. The corresponding energy states of ionized oxygen vacancies are observed below the conduction band minimum at approximately 0.5–1.0 eV. From a comparison of the fitted oxygen vacancy concentration in the CTM-TFT after the light-bias erasing operation, it is found that the pristine-erased device contains more oxygen vacancies than the program-erased device because the trapped electrons in the programmed device are pulled into the active layer and neutralized by the oxygen vacancies that are present there.

(Invited) Ultrabroadband Photoconduction Response of Sub-gap Defects in Amorphous In-Ga-Zn-O Thin Film Transistors

“…Finally, the characteristic shape of N Tot becomes clear: when there is a peak in the DoS there is a sharp increase in the number of states accessible by each E ph , which leads to the series of steps observed. The values recovered for the density of states shown in Figure 3b are in agreement with DoS orders of magnitude reported previously (7,14,17,18).…”