Phase change memory cell with junction selector and manufacturing method thereof
View Patent ↗A memory cell includes a memory element and a selection element coupled to the memory element. The selection element includes a first junction portion, having a first type of conductivity, and a second junction portion, having a second type of conductivity and forming a rectifying junction with the first junction portion. The first junction portion and the second junction portion are made of materials selected in the group consisting of: chalcogenides and conducting polymers.
1. A memory cell comprising:
a memory element; and
a selection element coupled to said memory element, said selection element including a first junction portion having a first type of conductivity, and a second junction portion having a second type of conductivity and forming a rectifying junction with said first junction portion, said first junction portion and said second junction portion being made of materials selected in the group consisting of: chalcogenides and conducting polymers.
2. A memory cell according to claim 1 , wherein said first junction portion is made of a first material selected in the group consisting of: Pb X Ge 42-X Se 58 with X comprised between 0 and 20%, Pb 20 Ge Y Se 80-Y with Y comprised between 17% and 24%, and Ge 25 Se 75-Z Bi Z with Z comprised between 9% and 11%;
and wherein said second junction portion is made of a second material selected in the group consisting of: As 2 Se 3 , Ge 20 Se 80 and Ge 25 Se 75-Z Bi Z with Z comprised between 0 and 9%.
3. A memory cell according to claim 1 , wherein said selection element is stacked on said memory element.
4. A memory cell according to claim 3 , wherein said first junction portion is arranged between said memory element and said second junction portion.
5. A memory cell according to claim 4 , wherein said first junction portion is of N-type and said second junction portion is of P-type.
6. A memory cell according to claim 4 , further comprising a first conductive barrier region, arranged between said memory element and said first junction portion, and a second conductive barrier region on said second junction portion.
7. A memory cell according to claim 1 , wherein said memory element comprises an electric dipole including a storage element, said storage element having a low impedance state and a high impedance state.
8. A memory cell according to claim 7 , wherein said storage element is a phase change storage element.
9. A memory cell according to claim 8 , wherein said memory cell includes a resistive heater element in contact with said storage element and having at least one sublithographic dimension at a contact area with said storage element.
10. A memory cell according to claim 9 , wherein said resistive heater element includes a vertical elongated wall.
11. A memory cell according to claim 9 , wherein said resistive heater element is in the form of a rod.
12. A memory cell according to claim 9 , wherein phase change storage element is positioned between said resistive heater element and said selection element.
13. A process for manufacturing a memory cell, comprising the steps of:
forming a memory element; and
forming a selection element coupled to said memory element, forming said selection element including:
forming a first junction portion, having a first type of conductivity;
forming a second junction portion, having a second type of conductivity, so that said first junction portion and said second junction portion form a rectifying junction;
wherein said first junction portion and said second junction portion are made of materials selected in the group consisting of: chalcogenides and conducting polymers.
14. A process according to claim 13 , wherein said first junction portion is made of a first material selected in the group consisting of: Pb X Ge 42-X Se 58 with X comprised between 0 and 20%, Pb 20 Ge Y Se 80-Y with Y comprised between 17% and 24%, and Ge 25 Se 75-Z Bi Z with Z comprised between 9% and 11%;
and wherein said second junction portion is made of a second material selected in the group consisting of: As 2 Se 3 , Ge 20 Se 80 and Ge 25 Se 75-Z Bi Z with Z comprised between 0 and 9%.
15. A process according to claim 13 , wherein said selection element is formed on said memory element.
16. A process according to claim 13 , wherein said step of forming said selection element comprises forming a first junction layer on said memory element.
17. A process according to claim 16 , wherein said first junction layer has said first type of conductivity and includes said first junction portion and wherein said step of forming said selection element comprises forming said second junction portion on said first junction portion.
18. A process according to claim 17 , wherein said step of forming said second junction portion comprises depositing a second junction layer on said first junction layer, said second junction layer having said second type of conductivity.
19. A process according to claim 17 , wherein said step of forming said second junction portion comprises introducing at least a substance into said first junction layer to form a junction region with said second type of conductivity within said first junction layer.
20. A process according to claim 16 , wherein said first junction layer has said second type of conductivity and said step of forming said selection element comprises deep implanting a substance in said first junction layer, to change said second type of conductivity to said first type of conductivity in a junction region within said first junction layer, at a distance from a top surface thereof, said junction region including said first junction portion.
21. A process according to claim 13 , wherein said step of forming said first junction layer comprises vapor deposition of a mixture of substances and separately controlling vaporization rates of said substances for controlling a composition of said mixture.
22. A process according to claim 21 , wherein said step of forming said first junction layer comprises multiple sputtering.
23. A system comprising:
a processing unit;
an interface coupled to said processing unit; and
a nonvolatile phase change memory device coupled to said processing unit and including:
first and second memory elements;
first and second selection elements coupled to the first and second memory elements, respectively, each selection element including a first junction portion having a first type of conductivity, and a second junction portion having a second type of conductivity and forming a rectifying junction with said first junction portion, said first junction portion and said second junction portion being made of materials selected in the group consisting of:
chalcogenides and conducting polymers; and
a resistive heater element in contact with the first and second memory elements at first and second contact areas, respectively, the resistive heater element having a sublithographic dimension at the first and second contact areas.
24. A system according to claim 23 , wherein said interface is a wireless interface.
25. A memory device, comprising:
first and second memory elements;
first and second selection elements coupled to the first and second memory elements, respectively, each selection element including a first junction portion having a first type of conductivity, and a second junction portion having a second type of conductivity and forming a rectifying junction with the first junction portion, the first junction portion and the second junction portion being made of materials selected in the group consisting of:
chalcogenides and conducting polymers; and
a resistive heater element in contact with the first and second memory elements at first and second contact areas, respectively, the resistive heater element having a sublithographic dimension at the first and second contact areas.
26. The memory device of claim 25 , wherein the first junction portion is made of a first material selected in the group consisting of: Pb X Ge 42-X Se 58 with X comprised between 0 and 20%, Pb 20 Ge Y Se 80-Y with Y comprised between 17% and 24%, and Ge 25 Se 75-Z Bi Z with Z comprised between 9% and 11%;
and wherein the second junction portion is made of a second material selected in the group consisting of: As 2 Se 3 , Ge 20 Se 80 and Ge 25 Se 75-Z Bi Z with Z comprised between 0 and 9%.
27. The memory device of claim 25 , wherein the selection elements are stacked on the memory elements, respectively.
28. The memory device of claim 25 , wherein for each selection element the first junction portion is arranged between the respective memory element and the second junction portion.
29. The memory device of claim 25 , wherein the first junction portion is of N-type and the second junction portion is of P-type.
30. The memory device of claim 25 , further comprising:
a first conductive barrier region, arranged between each memory element and the first junction portion of the selection element coupled to the memory element; and
a second conductive barrier region on each second junction portion.
31. The memory device of claim 25 , wherein each memory element comprises an electric dipole including a storage element having a low impedance state and a high impedance state.
32. The memory device of claim 31 , wherein the storage element is a phase change storage element.
33. The memory device of claim 32 , wherein each phase change storage element is positioned between the resistive heater element and the respective selection element.