Low-Temperature Polycrystalline Silicon Thin-Film Flash Memory With Hafnium Silicate

In this paper, we have successfully fabricated poly-Si-oxide-nitride-oxide-silicon (SONOS)-type poly-Si-thin-film transistor (TFT) memories employing hafnium silicate as the trapping layer with low-thermal budget processing (les600degC). It was demonstrated that the fabricated memories exhibited good performance in terms of relatively large memory window, high program/erase speed (1 ms/10 ms), long retention time (>10⁶ s for 20% charge loss), and 2-bit operation. Interestingly, we found that these memories depicted very unique disturbance behaviors, which are obviously distinct from those observed in the conventional SONOS-type Flash memories. We thought these specific characteristics are closely related to the presence of the inherent defects along the grain boundaries. Therefore, the elimination of the traps along the grain boundaries in the channel is an important factor for achieving high performance of the SONOS-type poly-Si-TFT Flash memory