Fabrication and Characterization of Twin Poly-Si Thin Film Transistors EEPROM with a Nitride Charge Trapping Layer

This study investigates the characteristics of the planar twin poly-Si thin film transistor (TFT) EEPROM that utilizes a nitride (Si₃N₄) charge trapping layer. A comparison is made of two devices with different gate dielectrics, one a 16 nm-thick oxide (SiO₂) layer for O-structure and the other 5 nm/10 nm-thick oxide/nitride layers for O/N-structure. Incorporating a nitride charge trapping layer and reducing the tunneling oxide thickness enable the O/N-structure EEPROM to enhance the program/erase (P/E) efficiency. Additionally, EEPROM formed with the tri-gate nanowires (NWs) structure can further enhance P/E efficiency and a large memory window because of its high electric field across the tunneling oxide. Reliability results indicated that, since the nitride layer contains discrete traps, the memory window can be maintained 2.2 V after 10⁴ P/E cycles. For retention, the memory window can be maintained 1.9 V, and 30% charge loss for ten years of data storage. This investigation indicates that its possibility in future system-on-panel (SOP) of thin-film transistor liquid crystal display (TFTLCD) and 3-D stacked high-density Flash memory applications.