Non-volatile memory embedded in a conventional logic process and methods for operating same
View Patent ↗A non-volatile memory system including an array of cells, each having an access transistor and a capacitor sharing a floating gate. The access transistors in each row are fabricated in separate well regions, which are independently biased. Within each row, the source of each access transistor is coupled to a corresponding virtual ground line, and each capacitor structure is coupled to a corresponding word line. Alternately, the source of each access transistor in a column is coupled to a corresponding virtual ground line. Within each column, the drain of each access transistor is coupled to a corresponding bit line. Select memory cells in each row are programmed by band-to-band tunneling. Bit line biasing prevents programming of non-selected cells of the row. Programming is prevented in non-selected rows by controlling the well region voltages of these rows. Sector erase operations are implemented by Fowler-Nordheim tunneling.
1. A non-volatile memory system comprising:
a non-volatile memory cell consisting of an NMOS transistor and a PMOS capacitor sharing a floating gate;
means for injecting electrons into the floating gate using a Fowler-Nordheim tunneling mechanism; and
means for injecting holes into the floating gate using a band-to-band tunneling mechanism.
2. The non-volatile memory system of claim 1 , wherein the means for injecting electrons into the floating gate are configured to induce electrons to tunnel from a channel of the NMOS transistor into the floating gate.
3. The non-volatile memory system of claim 1 , wherein the means for injecting holes into the floating gate are configured to induce holes to tunnel from a drain junction of the NMOS transistor into the floating gate.
4. The non-volatile memory system of claim 1 , further comprising one or more input/output transistors, each having a gate oxide layer, wherein the NMOS transistor and PMOS capacitor further include a gate oxide layer having a thickness substantially the same as a thickness of the gate oxide layer of the input/output transistors.
5. The non-volatile memory system of claim 4 , wherein the non-volatile memory system is fabricated with a conventional logic process having one and only one polysilicon layer, wherein the floating gate is fabricated from the polysilicon layer.
6. The non-volatile memory system of claim 1 , wherein the NMOS transistor and PMOS capacitor further include a gate oxide layer having a thickness of 70Angstroms or greater.
7. The non-volatile memory system of claim 1 , wherein the NMOS transistor has a gate capacitance and the PMOS capacitor has a coupling capacitance, wherein the coupling capacitance is larger than the gate capacitance.
8. The non-volatile memory system of claim 7 , wherein the coupling capacitance is about four times larger than the gate capacitance.
9. The non-volatile memory system of claim 1 , wherein the NMOS transistor includes a source region and a drain region located in a p-well region, and wherein the means for injecting holes comprises:
means for applying a positive voltage to the drain region of the NMOS transistor;
means for applying a negative voltage to the floating gate through the PMOS capacitor; and
means for applying a ground voltage to the p-well region and the source region of the NMOS transistor.
10. The non-volatile memory system of claim 9 , wherein the p-well region is located in a deep n-well region, wherein the means for injecting holes comprises means for applying a positive voltage to the deep n-well region.
11. The non-volatile memory system of claim 1 , wherein the NMOS transistor includes a source region and a drain region located in a p-well region, and wherein the means for injecting electrons comprises:
means for applying a negative voltage to the source and drain regions of the NMOS transistor and the p-well region; and
means for applying a positive voltage to the floating gate through the PMOS capacitor.
12. The non-volatile memory system of claim 11 , wherein the p-well region is located in a deep n-well region, wherein the means for injecting electrons comprises means for applying the positive voltage to the deep n-well region.
13. A method of operating a non-volatile memory cell consisting of an NMOS transistor and a PMOS capacitor sharing a floating gate, the method comprising:
injecting electrons into the floating gate using a Fowler-Nordheim tunneling mechanism; and
injecting holes into the floating gate using a band-to-band tunneling mechanism.
14. The method of claim 13 , wherein the step of injecting electrons into the floating gate comprises inducing electrons to tunnel from a channel of the NMOS transistor into the floating gate.
15. The method of claim 13 , wherein the step of injecting holes into the floating gate comprises inducing holes to tunnel from a drain junction of the NMOS transistor into the floating gate.
16. The method of claim 13 , wherein the NMOS transistor includes a source region and a drain region located in a p-well region, and wherein the step of injecting holes comprises:
applying a positive voltage to the drain region of the NMOS transistor;
applying a negative voltage to the floating gate through the PMOS capacitor; and
applying a ground voltage to the p-well region and the source region of the NMOS transistor.
17. The method of claim 16 , wherein the p-well region is located in a deep n-well region, wherein the step of injecting holes further comprises applying a positive voltage to the deep n-well region.
18. The method of claim 13 , wherein the NMOS transistor includes a source region and a drain region located in a p-well region, and wherein the step of injecting electrons comprises:
applying a negative voltage to the source and drain regions of the NMOS transistor and the p-well region; and
applying a positive voltage to the floating gate through the PMOS capacitor.
19. The method of claim 18 , wherein the p-well region is located in a deep n-well region, wherein the step of injecting electrons further comprises applying the positive voltage to the deep n-well region.