i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

7.1.2 Write Operation
Figure 7-6: IV Characteristics of an erased FLOTOX transistor
A write operation is said to be performed when a positive pulse is applied to the drain while the
source, bulk and control gate are grounded. Under such a condition, electrons flow from the
floating gate to the drain because of Fowler-Nordheim tunneling. Thus the floating gate
accumulates more positive charge and thus induces electrons to be attracted to the oxide -
substrate interface. This causes a decrease in the threshold voltage of the transistor. Under such a
state, the device allows conduction between the drain and the source for normal voltages applied
to the gate terminal of the device. Figure 7-7 shows the physical operation using FN tunneling
when the EEPROM cell is written [19] and Figure 7-8 shows the charge on the floating gate after
the write operation [19].
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