Stacked ferroelectric structure
The present disclosure relates to an integrated circuit (IC) in which a memory structure comprises a ferroelectric structure without critical-thickness limitations. The memory structure comprises a first electrode and the ferroelectric structure. The ferroelectric structure is vertically stacked with the first electrode and comprises a first ferroelectric layer, a second ferroelectric layer, and a first restoration layer. The second ferroelectric layer overlies the first ferroelectric layer, and the first restoration layer is between and borders the first and second ferroelectric layers. The first restoration layer is a different material type than that of the first and second ferroelectric layers and is configured to decouple crystalline lattices of the first and second ferroelectric layers so the first and second ferroelectric layers do not reach critical thicknesses. A critical thickness corresponds to a thickness at and above which the orthorhombic phase becomes thermodynamically unstable, such that remanent polarization is lost.
1. An integrated circuit (IC) comprising a memory structure, wherein the memory structure comprises:
a first electrode; and
a ferroelectric structure vertically stacked with the first electrode, wherein the ferroelectric structure comprises:
a first ferroelectric layer;
a second ferroelectric layer overlying the first ferroelectric layer; and
a first restoration layer between and directly contacting the first and second ferroelectric layers, wherein the first restoration layer is a different material type than that of the first and second ferroelectric layers, and wherein the first and second ferroelectric layers have a same material composition.
2. The IC of claim 1 , further comprising:
a semiconductor channel layer vertically stacked with the first electrode and the ferroelectric structure, wherein the ferroelectric structure is entirely between the semiconductor channel layer and the first electrode, and wherein the first restoration layer is completely spaced from the semiconductor channel layer by the first or second ferroelectric layer; and
a pair of source/drain electrodes on the semiconductor channel layer, respectively on opposite sides of the ferroelectric structure.
3. The IC of claim 2 , further comprising:
a blocking layer vertically stacked with and between the ferroelectric structure and the semiconductor channel layer, wherein the blocking layer directly contacts the semiconductor channel layer and is configured to inhibit oxygen vacancies at an interface between the blocking layer and the semiconductor channel layer.
4. The IC of claim 2 , wherein the ferroelectric structure comprises:
a second restoration layer at a bottom of the ferroelectric structure, wherein the second restoration layer is crystalized in an orthorhombic phase and is configured to seed epitaxial growth of the first ferroelectric layer.
5. The IC of claim 4 , wherein the ferroelectric structure comprises:
a third restoration layer at a top of the ferroelectric structure, wherein the third restoration layer is configured to stabilize a crystalline lattice of the second ferroelectric layer to prevent thermodynamic instability of the orthorhombic phase.
6. The IC of claim 4 , wherein the first restoration layer is amorphous, and wherein the second restoration layer is crystalline.
7. The IC of claim 1 , wherein the ferroelectric structure comprises:
a second restoration layer at a top of the ferroelectric structure, wherein the second restoration layer is configured to stabilize a crystalline lattice of the second ferroelectric layer to prevent thermodynamic instability of an orthorhombic phase.
8. The IC of claim 1 , further comprising:
a buffer layer disposed vertically between the first electrode and the ferroelectric structure, wherein the buffer layer is configured to buffer thermal expansion of the first electrode.
9. An integrated circuit (IC) comprising a memory structure, wherein the memory structure comprises:
a first electrode;
a second electrode overlying the first electrode;
one or more restoration layers; and
a plurality of ferroelectric layers alternatingly stacked with the one or more restoration layers, wherein the ferroelectric layers have a plurality of crystalline phases and a critical thickness, which is a thickness at which a majority phase amongst the plurality of crystalline phases changes from an orthorhombic phase to a tetragonal and/or monoclinic phase, wherein the ferroelectric layers have individual thicknesses that are less than the critical thickness, and wherein the ferroelectric layers have a combined thickness greater than the critical thickness;
wherein the plurality of ferroelectric layers and the one or more restoration layers share a width with the first electrode and the second electrode and are all between the first electrode and the second electrode.
10. The IC according to claim 9 , wherein the one or more restoration layers comprises a plurality of restoration layers having a same material composition.
11. The IC of claim 9 , wherein the one or more restoration layers comprise zirconium oxide, and wherein the ferroelectric layers comprises hafnium zirconium oxide.
12. An integrated circuit (IC) comprising a memory structure, wherein the memory structure comprises:
a source and a drain;
a semiconductor channel extending from the source to the drain;
a gate electrode laterally between the source and the drain; and
a ferroelectric structure entirely under the semiconductor channel and entirely over the gate electrode, wherein the ferroelectric structure comprises a plurality of ferroelectric layers vertically stacked, wherein each of the ferroelectric layers comprises a plurality of crystalline phases in which an orthorhombic phase is a majority phase, and wherein the plurality of ferroelectric layers are spaced from each other and each has a material composition different than a material composition of the semiconductor channel.
13. The IC of claim 12 , wherein the ferroelectric structure further comprises one or more metal oxide layers spacing the ferroelectric layers from each other, and wherein each of the one or metal oxide layers is between and directly contacts two ferroelectric layers amongst the plurality of ferroelectric layers.
14. The IC of claim 13 , wherein the one or more metal oxide layers each has a thickness less than individual thicknesses of the ferroelectric layers and closer to zero than to the individual thicknesses.
15. The IC according to claim 1 , wherein the first and second ferroelectric layers are both in a ferroelectric state and have a ferroelectric phase.
16. The IC of claim 2 , wherein the pair of source/drain electrodes are separated from the ferroelectric structure by the semiconductor channel layer, which directly contacts the pair of source/drain electrodes and the second ferroelectric layer, and wherein the first electrode corresponds to a gate electrode and directly contacts the first ferroelectric layer.
17. The IC of claim 9 , further comprising:
a transistor overlying and inset into a top of a semiconductor substrate, wherein the transistor comprises a source/drain region, and wherein the memory structure is directly over the source/drain region; and
a wire and a plurality of vias that are alternatingly stacked to form a columnar structure, which separates the memory structure from the source/drain region and which extends from the source/drain region to a bottom of the first electrode.
18. The IC of claim 9 , wherein the plurality of ferroelectric layers comprise a first ferroelectric layer and a second ferroelectric layer sharing a same material composition, wherein the first and second ferroelectric layers are between and respectively directly contact the first and second electrodes, and wherein the one or more restoration layers comprise a first restoration layer, which is between and directly contacts the first and second ferroelectric layers.
19. The IC of claim 12 , further comprising:
an additional ferroelectric structure over and directly contacting a topmost surface of the semiconductor channel, wherein the additional ferroelectric structure comprises a first ferroelectric layer, a second ferroelectric layer overlying the first ferroelectric layer, and a metal oxide layer between and directly contacting the first and second ferroelectric layers, and wherein the first and second ferroelectric layers have a same material composition; and
an additional gate electrode over and directly contacting a topmost surface of the additional ferroelectric structure;
wherein the source and the drain are contacts extending from an elevation elevated relative to the topmost surface of the additional ferroelectric structure to direct contact with the topmost surface of the semiconductor channel.
20. The IC of claim 13 , wherein the plurality of ferroelectric layers have a same material composition, and wherein the one or more metal oxide layers are ferroelectric.