i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

7.1.1 Erase Operation
Figure 7-3: IV Characteristics of a virgin FLOTOX transistor
An ERASE operation is said to be performed when a positive pulse is applied to the CG terminal
while the S,B and D are grounded. The positive pulse causes a large electric filed across the
tunneling oxide region. Fowler-Nordheim (FN) tunneling causes electrons to flow from the drain
to the floating gate where they are stored. The negative charge on the floating gate attracts holes
in the channel between the drain and the source. This effectively increases the threshold voltage
of the device. Under this condition, conduction will not occur between the drain and source
terminals for normal voltages that are applied to the gate terminal. The device is then said to be
in an erased state. Figure 7-4 shows the physical operation using FN tunneling when the
EEPROM cell is erased [19] and Figure 7-5 shows the charge on the floating gate after an erase
operation [19].
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