Patent ID: 7339835

Claim:
A method of erasing a non-volatile memory (NVM) cell, the NVM cell including a first NMOS transistor and a second NMOS transistor formed in p-type semiconductor material, the first NMOS transistor having a first n-type diffusion region, a second n-type diffusion region spaced apart from the first n-type diffusion region to define a first p-type channel region therebetween and a conductive floating gate having a first portion thereof formed over the first p-type channel region and separated therefrom by intervening dielectric material, the second NMOS transistor having a third n-type diffusion region that is spaced apart from the second n-type diffusion region to define a second p-type channel region therebetween and a conductive select gate formed over the second p-type channel region and separated therefrom by intervening dielectric material, the NVM cell further including a conductive control gate that includes an n-type control gate diffusion region formed in the p-type semiconductor material in proximity to a second portion of the conductive floating gate and separated therefrom by intervening dielectric material, the method comprising: discharging the second n-type diffusion region, maintaining the conductive floating gate at low voltage, maintaining the conductive select gate at zero volts, and maintaining the first and second NMOS transistors in an off state; raising the conductive select gate from zero voltage to a high voltage for an erase time such that, during the erase time, the first NMOS transistor is off and the second NMOS transistor is on, whereby tunneling current flows from the conductive floating gate to the second n-type diffusion region, the erase time being such that the floating gate voltage comes close to but remains below the threshold voltage of the first NMOS transistor; after the erase time has elapsed, returning the conductive select gate to zero voltage, such that the second NMOS transistor is off, but current flow continues from the conductive floating gate to the second n-type region until the floating gate voltage comes to the threshold voltage of the first NMOS transistor, whereby the first NMOS transistor turns on, the second N-type region discharges and current flow from the conductive floating gate to the second n-type region stops.