Multi-level memory arrays with memory cells that employ bipolar storage elements and methods of forming the same
In some embodiments, a memory array is provided that includes (1) a first memory cell having (a) a first conductive line; (b) a first bipolar storage element formed above the first conductive line; and (c) a second conductive line formed above the first bipolar storage element; and (2) a second memory cell formed above the first memory cell and having (a) a second bipolar storage element formed above the second conductive line; and (b) a third conductive line formed above the second bipolar storage element. The first and second memory cells share the second conductive line; the first bipolar storage element has a first storage element polarity orientation within the first memory cell; the second bipolar storage element has a second storage element polarity orientation within the second memory cell; and the second storage element polarity orientation is opposite the first storage element polarity orientation. Numerous other aspects are provided.
1. A memory array comprising:
a first memory cell having:
a first conductive line;
a first bipolar storage element formed above the first conductive line;
a second conductive line formed above the first bipolar storage element; and
a first steering element disposed above or below the first bipolar storage element; and
a second memory cell formed above the first memory cell and having:
a second bipolar storage element formed above the second conductive line;
a third conductive line formed above the second bipolar storage element; and
a second steering element disposed above or below the second bipolar storage element;
wherein the first and second memory cells share the second conductive line;
wherein the first bipolar storage element has a first storage element polarity orientation within the first memory cell;
wherein the second bipolar storage element has a second storage element polarity orientation within the second memory cell;
wherein the second storage element polarity orientation is opposite the first storage element polarity orientation;
wherein the first bipolar storage element comprises a first semiconductor material layer, and the first steering element comprises the first semiconductor material layer; and
wherein the second bipolar storage element comprises a second semiconductor material layer, and the second steering element comprises the second semiconductor material layer.
2. The memory array of claim 1 wherein the first and third conductive lines are bit lines and wherein the second conductive line is a word line.
3. The memory array of claim 1 wherein the first steering element is formed between the first and second conductive lines and the second steering element is formed between the second and third conductive lines.
4. The memory array of claim 3 wherein the first steering element is bipolar and has a first steering element polarity orientation within the first memory cell and the second steering element is bipolar and has a second steering element polarity orientation within the second memory cell that is opposite the first steering element polarity orientation.
5. The memory array of claim 4 wherein the first and second steering elements comprise vertical polycrystalline semiconductor diodes.
6. The memory array of claim 3 wherein the first and second steering elements are unipolar.
7. The memory array of claim 6 wherein the first and second steering elements comprise punch through diodes.
8. The memory array of claim 1 wherein the first bipolar storage element comprises a bipolar metal-insulator-metal stack.
9. The memory array of claim 8 wherein the first bipolar storage element comprises:
a first conductive layer;
a reversible resistivity switching (RRS) material formed above the first conductive layer; and
a second conductive layer formed above the RRS material.
10. The memory array of claim 9 wherein the RRS material comprises HfO x , ZrO x , NiO x , TiO x , TaO x , NbO x or Al x O y .
11. The memory array of claim 9 wherein the first conductive layer comprises heavily doped semiconductor and the second conductive layer comprises metal nitride.
12. The memory array of claim 11 wherein the heavily doped semiconductor comprises n+ silicon.
13. The memory array of claim 11 further comprising a metal/metal-oxide layer stack formed between the RRS material and the metal nitride.
14. The memory array of claim 13 wherein the metal/metal-oxide layer stack comprises Ti/TiO x , Zr/ZrO x , Ni/NiO x , Al/Al x O y , Ta/TaO x , Nb/NbO x , or Hf/HfO x .
15. The memory array of claim 14 wherein the metal nitride comprises titanium nitride, tungsten nitride, or tantalum nitride.
16. The memory array of claim 9 wherein the first conductive layer comprises metal nitride and the second conductive layer comprises heavily doped semiconductor.
17. The memory array of claim 16 wherein the heavily doped semiconductor comprises n+silicon.
18. The memory array of claim 16 further comprising a metal/metal-oxide layer stack formed between the RRS material and the metal nitride.
19. The memory array of claim 18 wherein the metal/metal-oxide layer stack comprises Ti/TiO x , Zr/ZrO x , Ni/NiO x , Al/Al x O y , Ta/TaO x , Nb/NbO x , or Hf/HfO x .
20. The memory array of claim 19 wherein the metal nitride comprises titanium nitride, tungsten nitride or tantalum nitride.