Photo-Stable Transparent Nonvolatile Memory Thin-Film Transistors Using In–Ga–Zn–O Channel and ZnO Charge-Trap Layers

We propose fully transparent charge-trap-type memory thin-film transistors (TFTs) with a top-gate structure composed of ZnO charge-trap and In-Ga-Zn-O active channel layers on glass substrates. Nonvolatile memory characteristics, such as a wide memory window, high-speed programming, and stable retention characteristics, were confirmed even under the illumination of red, green, blue, and white lights. The photo-stable characteristics of the proposed memory TFTs originate from the robust bias illumination stress stabilities of the employed gate-stack structure. The turn-ON voltages (V_ON) did not fluctuate with the variations of the bias polarity and wavelength of the illumination stresses. The maximum shift of V_ON observed was as small as -0.4 V at a negative bias stress of -20 V under a blue wavelength after 600 s.