VOLTAGE VARIANT SOURCE SIDE INJECTION FOR MULTILEVEL CHARGE STORAGE IN FLASH EEPROM

The growing demand for high-density Flash memories in portable computi ng, smart cards, and telecommunications applications has boosted the e fforts on Flash memory cell size scaling and cost reduction [1], In or der to further increase the storage capability and, consequently, redu ce the cost per bit of Flash memories, multilevel charge storage (MLCS ) techniques have recently gained a lot of interest [1], [2], Furtherm ore, MLCS is considered a viable route for increasing embedded Flash d ensity as well, The devices investigated so far, rely either on conven tional channel hot electron (CHE) injection or on Fowler-Nordheim tunn eling (FNT) for programming [3]. For the first time, this paper shows that source side injection (SSI) is also an excellent candidate for ML CS. The main advantages of SSI for MLCS are the very narrow threshold- voltage distributions after SSI programming, the symmetrical threshold -voltage window and the overerase immunity, which allows an overall wi der threshold-voltage window, and hence more separated distributions.