Chapter 3: Flash

In many applications, the data stored in non-volatile memory are changed. A logic circuit manufacturing process compatible non-volatile memory is necessary to allow these data changes. NeoFlash, a type of Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) device, invented by Hsu, Shen, Chen and Lee [1], is a true logic based, single-poly, two-transistor (2T) p-channel (pMOST) embedded SONOS flash technology. Owing to its simple cell structure, NeoFlash has lower process integration complexity and requires less device tuning. Program disturb and read disturb are no longer problems. Furthermore, because electrons are stored in the Oxide-Nitride-Oxide (ONO) film instead of the conventional floating gate, no tail bit is observed during endurance test, even if a defect is generated in the tunneling oxide. Compared with other embedded Flash technologies that have complicated structures, expensive process and long development cycles, NeoFlash responds promisingly to the demands of SoC applications of embedded flash technology due to its simple process, low operating voltage, and low cost. This chapter provides an overview of NeoFlash technology, including cell structure, operation scheme, process integration, design, test methodology, and reliability.