Abstract
Multi-valued charge trapping memory is demonstrated based on an amorphous-indium-gallium-zinc oxide thin-film transistor (a-IGZO-TFT) with a Ga2O3/Al2O3 stack gate insulator. The memory device shows a positive shift of threshold voltage as large as 12.6 V after +20 V/1 s programming. The erasing process can be divided into two stages. Vertical electrical field erases the trapped electrons partially, resulting in negative threshold voltage shift with hump current in sub-threshold region. It is defined as a first erasing stage. Furthermore, the memory can be erased by UV-light effectively due to the generated electron-hole pairs in a-IGZO channel. It is defined as second erasing stage. The good retention characteristics are confirmed for various storage states. The storage mechanism is analyzed according to the energy band alignment obtained by XPS narrow scans and valence band spectra.
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