Flash Memory/EEPROM
Comparison of Cell Structure
Typical Stacked-gate Structure
EEPROM generally employ a stacked-gate cell structure. Data is retained by controlling an electric charge stored in the floating gate (FG) in the memory cell.
"Susceptible to Over-Erasure Problems"
Over-erasure may occur if the FG becomes unstable.
Thus, the charge in the FG must always be kept under a specific level, and weakening of the charge during long-term data retention is a concern. There are also concerns from the complexity of the control circuit structure and the larger scale of peripheral circuits.
Split-gate Cell Structure from SANYO
SANYO EEPROM employ a split-gate cell structure. In a split-gate cell, the drain side is under the gate, and this suspended portion fulfills the role of a select gate.
"Advantage: No Over-Erasure"
Regardless of the FG potential, the structure prevents cell current (Ir) from flowing when the gate is not selected.
1 cell (split-gate cell) = 1 Tr + stacked-gate cell structure
Comparison of Reliability
Typical Cell Structure
Because over-erasure problems may occur, there is an upper limit to potential on the data erasure side.
SANYO Cell Structure
Because no over-erasure problems can occur, there is no upper limit to potential on the data erasure side.For this reason, an ample difference between the potentials for erasure data and for program data can be ensured,offering a wider data retention margin than in the memory devices of other manufacturers.
SANYO Cell Advantages
- No over-erasure, for superior data retention
- Extremely fast erasure
- Efficient programs are possible at low current.
- Highly reliable, from the use of thick tunnel oxide film
| WL | SL | BL | WL | SL | BL | |
|---|---|---|---|---|---|---|
| Erase | 0V | Vee | Open | Vee | 0V | 0V |
| Erase Time | A few seconds | 25ms | ||||
| Program | Vpp | 0V | Vcc | 2V | Vpp | 1V |
| Program Time | 10µs | 10µs | ||||
| Program Current | On the order of mA | 2 to 3µA | ||||
Flash products are licensed from Silicon Storage Technology, Inc., (USA), and manufactured and sold by SANYO Semiconductor Co., Ltd.