Ferroelectric memory devices
Embodiments of ferroelectric memory devices and methods for forming the ferroelectric memory devices are disclosed. In an example, a ferroelectric memory cell includes a first electrode, a second electrode, a doped ferroelectric layer disposed between the first electrode and the second electrode. The doped ferroelectric layer includes oxygen and one or more ferroelectric metals. The doped ferroelectric layer further includes a plurality of dopants including at least one dopant from one of Group II elements, Group III elements, or Lanthanide elements. The plurality of dopants are different from the one or more ferroelectric metals.
1. A ferroelectric memory cell, comprising
a first electrode;
a second electrode; and
a doped ferroelectric layer disposed between the first electrode and the second electrode and comprising:
oxygen and one or more ferroelectric metals; and
a plurality of dopants comprising at least one dopant from one of Group II elements, Group III elements, or Lanthanide elements, the plurality of dopants being different from the one or more ferroelectric metals.
2. The ferroelectric memory cell of claim 1 , wherein the plurality of dopants are distributed along a concentration gradient from a first level of the doped ferroelectric layer to a second level of the ferroelectric layer.
3. The ferroelectric memory cell of claim 2 , wherein the first level and the second level are each a respective one of surfaces in contact with the first electrode and the second electrode.
4. The ferroelectric memory cell of claim 3 , wherein
the plurality of dopants comprise a first group of dopants and a second group of dopants;
the first group of dopants comprise at least one dopant from Group IV elements; and
the second group of dopants comprise at least one dopant from one or more of Group V elements, Group II elements, Group III elements, or Lanthanide elements.
5. The ferroelectric memory cell of claim 4 , wherein
the first group of dopants comprise at least one of zirconium (Zr), hafnium (Hf), titanium (Ti), or silicon (Si); and
the second group of dopants comprise at least one of tantalum (Ta), niobium (Nb), dubnium (Db), vanadium (V), scandium (Sc), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), lanthanides, calcium (Ca), strontium (Sr), or barium (Ba).
6. The ferroelectric memory cell of claim 5 , wherein a molar ratio between the first group of dopants and the second group of dopants is between about 100:1 and about 1:100.
7. The ferroelectric memory cell of claim 3 , wherein
the plurality of dopants comprise a first group of dopants and a second group of dopants;
the first group of dopants comprise at least one dopant from Group V elements; and
the second group of dopants comprise at least one dopant from one or more of Group II elements, Group III elements, or Lanthanide elements.
8. The ferroelectric memory cell of claim 7 , wherein
the first group of dopants comprise at least one of Ta, Nb, Db, or V; and
the second group of dopants comprise at least one of Sc, Y, Al, Ga, In, lanthanides, Ca, Sr, or Ba.
9. The ferroelectric memory cell of claim 8 , wherein a molar ratio between the first group of dopants and the second group of dopants is between about 100:1 and about 1:100.
10. The ferroelectric memory cell of claim 3 , wherein
the plurality of dopants comprise a first group of dopants and a second group of dopants;
the first group of dopants comprise at least one dopant from Group III elements or Lanthanide elements; and
the second group of dopants comprise at least one dopant from one or more of Group II elements.
11. The ferroelectric memory cell of claim 10 , wherein
the first group of dopants comprise at least one of Sc, Y, Al, Ga, In, or lanthanides; and
the second group of dopants comprise at least one of Ca, Sr, or Ba.
12. The ferroelectric memory cell of claim 11 , wherein a molar ratio between the first group of dopants and the second group of dopants is between about 100:1 and about 1:100.
13. The ferroelectric memory cell of claim 2 , wherein the first level and the second level are each a respective one of a middle level of the doped ferroelectric layer and a surface in contact with one of the first electrode and the second electrode.
14. The ferroelectric memory cell of claim 2 , wherein
the first level comprises a surface in contact with one of the first electrode and the second electrode and a middle level of the doped ferroelectric layer, a dopant concentration at the surface being the same as or different from a dopant concentration at the middle level; and
the second level comprises another middle level of the doped ferroelectric layer between the surface and the middle level, a dopant concentration at the other middle level being the same as or different from the dopant concentration at surface and being the same as or different from the dopant concentration at the middle level.
15. The ferroelectric memory cell of claim 2 , wherein
the first level comprises another middle level of the doped ferroelectric layer between a surface in contact with one of the first electrode and the second electrode and a middle level of the doped ferroelectric layer, a dopant concentration at the other middle level being the same as or different from a dopant concentration at surface and being the same as or different from a dopant concentration at the middle level; and
the second level comprises the surface and the middle level of the doped ferroelectric layer, the dopant concentration at the surface being the same as or different from the dopant concentration at the middle level.
16. The ferroelectric memory cell of claim 1 , wherein the plurality of dopants are distributed along a plurality of concentration gradients along a direction perpendicular to a surface of the doped ferroelectric layer, the plurality of concentration gradients each extending from a first level of the doped ferroelectric layer to a second level of the doped ferroelectric layer, the first level of each of the plurality of concentration gradients being the same as or different from one another, the second level of each of the plurality of concentration gradients being the same as or different from one another.
17. The ferroelectric memory cell of claim 1 , wherein one or more of the first electrode and the second electrode comprises at least one of titanium nitride (TiN), titanium silicon nitride (TiSiN x ), titanium aluminum nitride (TiAlN x ), titanium carbon nitride (TiCN x ), tantalum nitride (TaN x ), tantalum silicon nitride (TaSiN x ), tantalum aluminum nitride (TaAlN x ), tungsten nitride (WN x ), tungsten silicide (WSi x ), tungsten carbon nitride (WCN x ), ruthenium (Ru), ruthenium oxide (RuO x ), iridium (Ir), doped polysilicon, transparent conductive oxides (TCO), or iridium oxide (IrO x ).
18. The ferroelectric memory cell of claim 17 , wherein the one or more of the first and the second electrode includes TCO, which includes at least one of doped ZnO based TCOs, doped TiO 2 based TCOs, doped SnO 2 based TCOs, or perovskite TCOs.
19. The ferroelectric memory cell of claim 18 , wherein the one or more of the first and the second electrode includes La 1-x Sr x CrO 3 (LSCO).
20. A ferroelectric memory device, comprising:
a substrate; and
a plurality of ferroelectric memory strings extending vertically above the substrate, each of the ferroelectric memory strings comprising a conductor layer, a first electrode, a doped ferroelectric layer, and a second electrode layer disposed radially from a center of the ferroelectric memory string in this order,
wherein the doped ferroelectric layer comprises:
oxygen and one or more ferroelectric metals; and
a plurality of dopants comprising at least one dopant from one of Group II elements, Group III elements, or Lanthanide elements, the plurality of dopants being different from the one or more ferroelectric metals.
21. The ferroelectric memory cell of claim 20 , wherein
the plurality of dopants comprise a first group of dopants and a second group of dopants, distributed along a concentration gradient from one of the first electrode and the second electrode to the other one of the first electrode and the second electrode;
the first group of dopants comprise at least one of zirconium (Zr), hafnium (Hf), titanium (Ti), or silicon (Si); and
the second group of dopants comprise at least one of tantalum (Ta), niobium (Nb), dubnium (Db), vanadium (V), scandium (Sc), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), lanthanides, calcium (Ca), strontium (Sr), or barium (Ba).
22. The ferroelectric memory cell of claim 21 , wherein a molar ratio between the first group of dopants and the second group of dopants is between about 100:1 and about 1:100.
23. The ferroelectric memory cell of claim 20 , wherein
the plurality of dopants comprises a first group of dopants and a second group of dopants, distributed along a concentration gradient from one of the first electrode and the second electrode to the other one of the first electrode and the second electrode;
the first group of dopants comprise at least one of Ta, Nb, Db, or V; and
the second group of dopants comprise at least one of Sc, Y, Al, Ga, In, lanthanides, Ca, Sr, or Ba.
24. The ferroelectric memory cell of claim 23 , wherein a molar ratio between the first group of dopants and the second group of dopants is between about 100:1 and about 1:100.
25. The ferroelectric memory cell of claim 20 , wherein
the plurality of dopants comprises a first group of dopants and a second group of dopants, distributed along a concentration gradient from one of the first electrode and the second electrode to the other one of the first electrode and the second electrode;
the first group of dopants comprise at least one of Sc, Y, Al, Ga, In, or lanthanides; and
the second group of dopants comprise at least one of Ca, Sr, or Ba.
26. The ferroelectric memory cell of claim 25 , wherein a molar ratio between the first group of dopants and the second group of dopants is between about 100:1 and about 1:100.