Skip to Main Content
We demonstrated SONOS flash memory with a SiO/sub 2//High-k/SiO/sub 2/ structure based on a 2-bit/cell scheme. We evaluated three kinds of high-k dielectric films which were Si/sub 3/N/sub 4/, Al/sub 2/O/sub 3/ and HfO/sub 2/. Among these films, Al/sub 2/O/sub 3/ showed superior retention characteristics. The charge loss amount of Al/sub 2/O/sub 3/ at 150/spl deg/C is almost the same as that of Si/sub 3/N/sub 4/ at 25/spl deg/C. HfO/sub 2/ showed poor retention characteristics. In addition, we have found that each film has a different charge loss mechanism. We speculate that Si/sub 3/N/sub 4/ causes vertical charge migration, Al/sub 2/O/sub 3/ causes scarcely any leakage, and HfO/sub 2/ causes lateral charge migration. As a consequence, Al/sub 2/O/sub 3/ is very suitable for a charge trapping layer in multi-bit SONOS memory.