The understanding of the memory nature and mechanism of the Ta2O5-gate-dielectric-based organic phototransistor memory

Abstract The memory nature and mechanism of the Ta2O5-gate-dielectric-based organic phototransistor memory (OPTM) have been studied. The UV–Vis absorption spectra and the X-ray photoelectron spectroscopy indicate that Ta2O5 owns positive interfacial charge because of the existence of Ta–OH. The hydroxide results in oxygen deficiency in Ta2O5 which is proposed to trap electrons. The characteristics of Ta2O5-based capacitor and the energy level alignment at Ta2O5–pentacene interface reveal that the electron-injection process is favorable which stimulates the electron-trapping process in Ta2O5. The Kelvin probe force microscopy of the Ta2O5-pentacene interface certificates the electron-injection and electron-trapping processes as well. It is the positive charges in Ta2O5 and energy level alignment that lead to the memory effect of Ta2O5-gate-dielectric-based OPTM. Compared to Ta2O5, polymethyl methacrylate (PMMA) does not have so strong a positive interface. Accordingly, PMMA films of different thickness are adopted on Ta2O5 to tune the Ta2O5-pentacene interface, offering control of the memory properties including the memory window and retention time. The understanding of the mechanism is at the forefront of devising high-performance OPTM devices.