Resistive random access memory cell having three or more resistive states
View Patent ↗Provided are resistive random access memory (ReRAM) cells, each having three or more resistive states and being capable of storing multiple bits of data, as well as methods of fabricating and operating such ReRAM cells. Such ReRAM cells or, more specifically, their resistive switching layer have wide range of resistive states and are capable of being very conductive (e.g., about 1 kOhm) in one state and very resistive (e.g., about 1 MOhm) in another state. In some embodiments, a resistance ratio between resistive states may be between 10 and 1,000 even up to 10,000. The resistive switching layers also allow establishing stable and distinct intermediate resistive states that may be assigned different data values. These layers may be configured to switching between their resistive states using fewer programming pulses than conventional systems by using specific materials, switching pluses, and resistive state threshold.
1. A semiconductor device comprising:
a first layer operable as a first electrode;
a second layer operable as a second electrode; and
a third layer disposed between the first layer and the second layer,
wherein the third layer is operable to switch between a first resistive state corresponding to a first resistance and a second resistive state corresponding to a second resistance different from the first resistance,
wherein the third layer comprises a first sub-layer, a second sub-layer, and a third sub-layer,
wherein the second sub-layer is disposed between the first sub-layer and the third sub-layer,
wherein the first sub-layer comprises titanium oxide and has a thickness of about 8 Angstroms,
wherein the second sub-layer comprises hafnium oxide and has a thickness of about 50 Angstroms, and
wherein the third sub-layer comprises silicon oxide and has a thickness of about 20 Angstroms.
2. The semiconductor device of claim 1 , wherein the first sub-layer directly interfaces the first layer comprising titanium nitride.
3. The semiconductor device of claim 2 , wherein the third sub-layer directly interfaces the second layer comprising polysilicon.
4. The semiconductor device of claim 1 , wherein the third layer is further operable to switch to a third resistive state corresponding to a third resistance different from the first resistance and the second resistance.
5. The semiconductor device of claim 4 , wherein the third resistance is less than the second resistance, wherein the second resistance is less than the first resistance, and wherein a ratio of the first resistance to the third resistance is between 10 and 1000.
6. The semiconductor device of claim 5 , wherein the ratio of the first resistance to the second resistance is between 5 and 1000.
7. The semiconductor device of claim 1 , wherein each of the first sub-layer, the second sub-layer, and the third sub-layer is operable to switch between two different resistive states.
8. The semiconductor device of claim 1 , wherein hafnium oxide of the second sub-layer is doped with titanium.
9. The semiconductor device of claim 1 , wherein the first layer comprising titanium nitride.
10. The semiconductor device of claim 1 , wherein the second layer comprising doped silicon.
11. The semiconductor device of claim 1 , wherein at least one of the first layer or the second layer is a part of a signal line.
12. The semiconductor device of claim 1 , further comprising a current steering element.
13. The semiconductor device of claim 12 , wherein the current steering element is a diode.
14. The semiconductor device of claim 1 , further comprising a diffusion barrier layer disposed between the first layer and the third layer.