Erase of a memory having a non-conductive storage medium
View Patent ↗A non volatile memory includes a plurality of transistors having a non conductive storage medium. The transistors are erased by injecting holes into the storage medium from both the source edge region and drain edge region of the transistor. In one example, the storage medium is made from silicon nitride isolated from the underlying substrate and overlying gate by silicon dioxide. The injection of holes in the storage medium generates two hole distributions having overlapping portions. The combined distribution of the overlapping portions is above at least a level of the highest concentration of program charge in the overlap region of the storage medium. In one example, the transistors are programmed by hot carrier injection. In some examples, the sources of groups of transistors of the memory are decoded.
1. A method for erasing a single bit nonvolatile memory transistor having a non conductive storage medium, the method of erasing comprising:
injecting holes into a drain side region of the storage medium from a drain edge region of the transistor;
injecting holes into a source side region of the storage medium from a source edge region of the transistor.
2. The method of claim 1 wherein:
the injecting holes into the drain side region further includes injecting holes to generate a first hole distribution in the storage medium; the injecting holes into the source side region further includes injecting holes to generate a second hole distribution in the storage medium;
the first hole distribution has a portion that overlaps a portion of the second hole distribution in an overlap region of the storage medium;
wherein a combination of the portion of the first hole distribution and the portion of the second hole distribution in the overlap region of the storage medium is at least above a level of a highest concentration of program charge in the overlap region of the storage medium.
3. The method of claim 1 wherein the injecting holes into the drain side region is performed concurrently with the injecting holes into the source side region.
4. The method of claim 1 wherein the injecting holes into the drain side region is performed at a different time from the injecting holes into the source side region.
5. The method of claim 1 wherein the injecting holes into the source side region further includes:
applying an erase gate voltage to a gate of the transistor;
applying an erase source voltage to a source of the transistor;
applying an erase substrate voltage to a substrate of the transistor;
wherein the erase source voltage is at a higher voltage level than the erase substrate voltage;
wherein the erase substrate voltage is at a higher voltage level than the erase gate voltage.
6. The method of claim 1 wherein the injecting holes into the drain side region further includes:
applying an erase gate voltage to a gate of the transistor;
applying an erase drain voltage to a drain of the transistor;
applying an erase substrate voltage to a substrate of the transistor;
wherein the erase drain voltage is at a higher voltage level than the erase substrate voltage;
wherein the erase substrate voltage is at a higher voltage level than the erase gate voltage.
7. The method of claim 1 further comprising:
introducing a programming charge in the storage medium to program a first value in the storage medium.
8. The method of claim 1 wherein the transistor has a channel length of 0.2 microns or less.
9. A method for erasing a non volatile memory transistor having a non conductive storage medium, the method of erasing comprising:
injecting holes into a drain side region of the storage medium from a drain edge region of the transistor to generate a first hole distribution in the storage medium;
injecting holes into a source side region of the storage medium from a source edge region of the transistor to generate a second hole distribution in the storage medium;
wherein the first hole distribution has a portion that overlaps a portion of the second hole distribution in an overlap region of the storage medium;
wherein a combination of the portion of the first hole distribution and the portion of the second hole distribution in the overlap region of the storage medium is at least above a level of a highest concentration of program charge in the overlap region of the storage medium.
10. The method of claim 9 wherein the injecting holes into the drain side region is performed concurrently with the injecting holes into the source side region.
11. The method of claim 10 wherein the injecting holes into the drain side region is performed at a different time from the injecting holes into the source side region.
12. The method of claim 10 wherein the injecting holes into the source side region further includes:
applying an erase gate voltage to a gate of the transistor;
applying an erase source voltage to a source of the transistor;
applying an erase substrate voltage to a substrate of the transistor;
wherein the erase source voltage is at a higher voltage level than the erase substrate voltage;
wherein the erase substrate voltage is at a higher voltage level than the erase gate voltage.
13. The method of claim 10 wherein the injecting holes into the drain side region further includes:
applying an erase gate voltage to a gate of the transistor;
applying an erase drain voltage to a drain of the transistor;
applying an erase substrate voltage to a substrate of the transistor;
wherein the erase drain voltage is at a higher voltage level than the erase substrate voltage;
wherein the erase substrate voltage is at a higher voltage level than the erase gate voltage.
14. The method of claim 10 further comprising:
introducing a programming charge in the storage medium to program a first value in the storage medium.
15. A method for programming a non volatile memory transistor having a non conductive storage medium, the method comprising:
erasing a value stored in the storage medium, the erasing including:
injecting holes into a drain side region of the storage medium from a drain edge region of the transistor to generate a first hole distribution in the storage medium;
injecting holes into a source side region of the storage medium from a source edge region of the transistor to generate a second hole distribution in the storage medium;
wherein the first hole distribution has a portion that overlaps a portion of the second hole distribution in an overlap region of the storage medium;
wherein a combination of the portion of the first hole distribution and the portion of the second hole distribution in the overlap region of the storage medium is at least above a level of a highest concentration of program charge in the overlap region of the storage medium;
programming a first value in the storage medium by introducing a program charge in the storage medium by hot carrier injection.
16. The method of claim 15 wherein the programming the first value further includes:
injecting electrons into the storage medium from a drain edge region of the transistor.
17. The method of claim 16 wherein the injecting electrons further includes:
injecting electrons to generate an electron distribution, the electron distribution having a width greater than the first hole distribution.
18. The method of claim 15 wherein the programming a first value in the storage medium by introducing a program charge in the storage medium by hot carrier injection further includes:
injecting electrons into the storage medium by:
applying a programming source voltage to a source of the transistor;
applying a programming substrate voltage to a substrate of the transistor;
applying a programming drain voltage to a drain of the transistor;
wherein the programming drain voltage is at a higher voltage level than the programming source voltage;
wherein the programming source voltage is at a higher voltage level than the programming substrate voltage.
19. A method for erasing a plurality of single bit transistor memory cells having a non conductive storage medium, the method of erasing comprising:
injecting holes into a drain side region of the storage medium from a
drain edge region of the transistor for each transistor of the plurality;
injecting holes into a source side region of the storage medium from a source edge region of the transistor for each transistor of the plurality;
wherein each transistor of the plurality includes a source;
wherein the sources of at least a subset of the plurality are tied together.
20. The method of claim 19 wherein the plurality of transistors is arranged in a plurality of rows and a plurality of columns, wherein the sources of each of the transistors of the plurality of transistors are tied together.
21. The method of claim 19 wherein the plurality of transistors is arranged in a plurality of rows and a plurality of columns, wherein the sources of the transistors of each row of the plurality of rows are tied together and wherein a gate of the transistors of each row of the plurality of rows are tied together. Sources of each row tied together.
22. The method of claim 19 wherein the plurality of transistors is arranged in a plurality of rows and a plurality of columns, wherein the sources of the transistors of each row of each of two rows of the plurality of rows are tied together and wherein a gate of the transistors of each row of the plurality of rows are tied together.
23. The method of claim 19 wherein the plurality of transistors is arranged in a plurality of rows and a plurality of columns, wherein for each transistor of plurality the memory includes an select transistor located between a drain of the transistor and a bit line and wherein the select transistor is made conductive during the erasing of the transistor.