Method for erasing a flash memory cell or an array of such cells having improved erase coupling ratio

Abstract

A flash memory cell is of the type having a substrate of a first conductivity type having a first region of a second conductivity type at a first end, and a second region of the second conductivity type at a second end, spaced apart from the first end, with a channel region between the first end and the second end. The flash memory cell has a plurality of stacked pairs of floating gates and control gates with the floating gates positioned over portions of the channel region and are insulated therefrom, and each control gate over a floating gate and insulated therefrom. The flash memory cell further has a plurality of erase gates over the channel region which are insulated therefrom, with an erase gate between each pair of stacked pair of floating gate and control gate. In a method of erasing the flash memory cell, a pulse of a first positive voltage is applied to alternating erase gates ('first alternating gates'). In addition, a ground voltage is applied to erase gates other than the first alternating gates ('second alternating gates'). In a second method to erase the flash memory cell, a pulse of a first positive voltage is applied to the first alternating gates and a negative voltage is applied to the second alternating gates and to all control gates.