Non-volatile memory device and a method of operating same
View Patent ↗An array of non-volatile memory cells in a semiconductor substrate of a first conductivity type. Each memory cell comprises first and second regions of a second conductivity type on a surface of the substrate, with a channel region therebetween. A word line overlies one portion of the channel region, is adjacent to the first region, and has little or no overlap with the first region. A floating gate overlies another portion of the channel region, and is adjacent to the first portion and the second region. A coupling gate overlies the floating gate. An erase gate overlies the second region. A bit line is connected to the first region. A negative charge pump circuit generates a negative voltage. A control circuit generates a plurality of control signals in response to receiving a command signal, and applies the negative voltage to the word line of unselected memory cells.
1. A non-volatile memory device comprising:
a semiconductor substrate of a first conductivity type;
an array of non-volatile memory cells in the semiconductor substrate arranged in a plurality of rows and columns, each memory cell comprising:
a first region on a surface of the semiconductor substrate of a second conductivity type;
a second region on the surface of the semiconductor substrate of the second conductivity type;
a channel region between the first region and the second region;
a word line overlying a first portion of the channel region and insulated therefrom, and adjacent to the first region and having little or no overlap with the first region;
a floating gate overlying a second portion of the channel region, adjacent to the first portion, and insulated therefrom and adjacent to the second region;
a coupling gate overlying the floating gate;
an erase gate overlying the second region and insulated therefrom;
a bit line connected to the first region;
a negative charge pump circuit for generating a first negative voltage; and
a control circuit for receiving a command signal and for generating a plurality of control signals to control the application of the first negative voltage to the word line of the unselected memory cells, in response thereto.
2. The non-volatile memory device of claim 1 wherein said plurality of control signals are generated in response to an erase command.
3. The non-volatile memory device of claim 2 wherein said negative charge pump for generating a second negative voltage, and wherein said control circuit for applying the second negative voltage to the coupling gate of the selected memory cell.
4. The non-volatile memory device of claim 1 wherein said plurality of control signals are generated in response to a read command.
5. The non-volatile memory device of claim 1 wherein said plurality of control signals are generated in response to a program command.
6. The non-volatile memory device of claim 1 wherein said negative charge pump is in a triple well in said semiconductor substrate.
7. The non-volatile memory device of claim 1 wherein said memory cells, negative charge pump, control circuit are formed in a semiconductor P substrate provided in a twin wells P-sub CMOS process.
8. The non-volatile memory device of claim 1 wherein said control circuit comprises a negative voltage diode-decoding circuit.
9. The non-volatile memory device of claim 1 wherein said control circuit comprises a negative level shifter circuit and a clocked negative bootstrapping circuit.
10. The non-volatile memory device of claim 1 further comprises a negative test pad circuit that includes a high voltage PMOS transistor and a high voltage NMOS transistor.
11. The non-volatile memory device of claim 1 further comprising a negative regulation circuit having a capacitor-divider-based comparator.
12. The non-volatile memory device of claim 1 wherein said control circuit comprises a current limiter in the high voltage decoder for supplying positive or negative high voltages to said memory cells.
13. A method of operating a non-volatile memory device of the type having a semiconductor substrate of a first conductivity type; an array of non-volatile memory cells in the semiconductor substrate arranged in a plurality of rows and columns; with each memory cell having a first region on a surface of the semiconductor substrate of a second conductivity type; a second region on the surface of the semiconductor substrate of the second conductivity type; a channel region between the first region and the second region, a word line overlying a first portion of the channel region and insulated therefrom, and adjacent to the first region and having little or no overlap with the first region; a floating gate overlying a second portion of the channel region, adjacent to the first portion, and insulated therefrom, and adjacent to the second region; a coupling gate overlying the floating gate; an erase gate overlying the second region and insulated therefrom; a bit line connected to the first region; wherein said method comprising:
applying a first negative voltage to the word line of the unselected memory cells; and
applying a non-negative voltage to the word line, bit line, coupling gate, erase gate and second region of the selected memory cell.
14. The method of claim 13 wherein said method is for erasing the selected memory cell.
15. The method of claim 14 wherein a zero voltage is applied to the word line, bit line, coupling gate and second region of the selected memory cell, and a positive voltage is applied to the erase gate of the selected memory cell.
16. The method of claim 15 wherein the negative voltage is applied to the wordline before other voltages are applied to the erase gate and second region of the selected memory cells.
17. The method of claim 13 wherein in said voltage applied to the coupling gate of the selected memory cells is negative.
18. The method of claim 13 wherein said method is for reading the selected memory cell.
19. The method of claim 13 wherein said method is for programming the selected memory cell.
20. The method of claim 13 wherein said method of applying a non-negative voltage to the word line, bit line, coupling gate, erase gate and second region of the selected memory cell is for only the operations of read and program.
21. The method of claim 20 , wherein said method further comprising:
applying a second negative voltage to the coupling gate of the selected memory cell during an erase operation.
22. The method of claim 19 , wherein said method further comprising:
applying a second negative voltage to the second region of the selected memory cell during a programming operation.
23. The method of claim 21 wherein said second negative voltage is different from the first negative voltage.
24. The method of claim 20 wherein during said programming, the voltage is applied to the coupling gate after the voltage is applied to the erase gate and second region of the selected memory cells.
25. The method of claim 14 wherein during said erase, the voltage is applied to the coupling gate before the voltage is applied to the erase gate of the selected memory cells.
26. The method of claim 14 wherein during said read, the voltage applied to the coupling gate is applied before the voltage is applied to the wordline and bitline of the selected memory cells.
27. The method of claim 14 wherein during said read, the voltage is applied to the coupling gate before the voltage is applied to the erase gate.