ELECTRICALLY ERASABLE/ELECTRICALLY PROGRAMMABLE READ ONLY MEMORY HAVING SELECTABLE THRESHOLD VOLTAGE VALUE AND UTILIZING METHOD THEREOF

摘要

PURPOSE: To vary a threshold voltage in an EEPROM. CONSTITUTION: An N channel memory cell 12 is operated so as to charge and discharge a floating gate 24 by Fowler-Nordheim tunneling when a voltage is applied to a control gate 26 and a drain 16. A P channel field effect transistor 30 is provided with a source 34 and the drain 36 separated by a channel 38 and the conductance of the channel 38 is controlled by the floating gate 24. A threshold value control circuit 76 is provided so as to bias the channel 38 of the P channel field effect transistor 30 to the control gate 26. A monitoring circuit 90 controls the supply of the voltage to the control gate 26 in response to a conducting state between the source 34 and the drain 36 of the P channel field effect transistor 30.