Method of programming a split gate non-volatile floating gate memory cell having a separate erase gate
View Patent ↗A non-volatile memory cell includes first and second regions and a channel region therebetween, a word line gate over a first portion of the channel region, a floating gate over another portion of the channel region and adjacent to the word line gate, a coupling gate over the floating gate, and an erase gate adjacent to the floating gate on an opposite side to the word line gate and over the second region. Programming the memory cell includes applying a first positive voltage to the word line gate, applying a voltage differential between the first and second regions, applying a second positive voltage to the coupling gate (where the voltages and the voltage differential are applied substantially at the same time), and applying a third positive voltage to the erase gate after a period of delay from the application of the first and second positive voltages and the voltage differential.
1. A method of programming a non-volatile memory cell having a single crystalline substrate of a first conductivity type and having a top surface, with a first region of a second conductivity type in said substrate along the top surface, and a second region of the second conductivity type, in said substrate along the top surface, spaced apart from the first region, with a channel region between the first region and the second region; a word line gate is positioned over a first portion of the channel region, spaced apart from the channel region by a first insulating layer; a floating gate is positioned over another portion of the channel region, adjacent to and separated from the word line gate, wherein the floating gate is separated from the channel region by a second insulating layer; a coupling gate is positioned over the floating gate and insulated therefrom by a third insulating layer; and an erase gate is positioned adjacent to the floating gate and on a side opposite to the word line gate; said erase gate positioned over the second region and is insulated therefrom; said method comprising:
applying a first positive voltage to the word line gate to turn on the portion of the channel region beneath the word line gate;
applying a voltage differential between the first region and the second region;
applying a second positive voltage to the coupling gate, substantially at the same time as the first positive voltage, to cause hot electrons to be injected to the floating gate from the channel region;
applying a third positive voltage to the erase gate after a period of delay after the start of the first and second positive voltages and a voltage differential between the first region and the second region, to cause electrons to be injected to the floating gate.
2. The method of claim 1 wherein said first, second and third positive voltages terminate at substantially the same time.
3. The method of claim 1 wherein said voltage differential between the first region and the second region is applied at substantially the same time as the first and second positive voltages.
4. The method of claim 1 wherein each of said first, second and third voltages is a pulse shaped signal, and wherein said third voltage is a delayed pulse signal.
5. The method of claim 4 wherein said first, second and third positive voltages terminate at substantially the same time.
6. The method of claim 1 whereby the period of delay is long enough to reduce the maximum potential on the floating gate during the programming operation.
7. The method of claim 1 wherein said erase gate has an overhang over the floating gate.