Yoshihisa Sugiura

A 130-mm/sup 2/, 256-Mbit NAND flash with shallow trench isolation technology

Higher density flash memories for mass storage are attractive for application in the audio-video field, for example, in digital cameras and for voice recording. A 100 MB Flash records one hour CD-quality music. Improvements in video compression techniques are expected to realize gigabyte flash, enabling movies on silicon in the near future; a development that is expected to lead to rapidly rising demand for high-density flash. Both the low bit cost due to the small cell size and the high program and read performance are important factors for the high density flash. A NAND flash has potential advantages in those respects. Shallow trench isolation (STI) shrinks bit line pitch to 73% of that in the case of conventional LOCOS isolation, enabling 0.29 um/sup 2/ cell 0.25 /spl mu/m design rules. The 129.76 mm/sup 2/ chip is made possible by using NAND type memory cell and STI.

A 35 ns cycle time 3.3 V only 32 Mb NAND flash EEPROM

A 32 Mb NAND type flash EEPROM in 0.425 /spl mu/m CMOS achieves 35 ns cycle time for data read-out and programming data load by adopting a pipeline scheme. Metal-strapped select gates and boosted word line reduce read-out access time. Tight-programmed cell Vth distribution can be realized by program verify, using a simplified data register circuit. Multiple blocks can be erased at the same time by adopting erase block registers for each block. Simultaneous-erase verify for one block reduces total erase time. All funtions require only 3.3 V power supply.