OXIDE FERROELECTRIC MATERIALS

Abstract

A meta-stable ferroelectric structure including one of the following oxides: an isovalent combination of the formula M.sub.xM.sub.1-xO.sub.2-, wherein M, M={Zr, Hf, Pb, W, Mo, Nb, Te, Ti}, 0x1, 00.5 excluding {Hf.sub.xZr.sub.1-xO.sub.2 all x in Pca2.sub.1 phase}; an aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2-, wherein MI, MII={Bi, Y, Ta, In, Mo, Nb, Sc, Tl, Pd, Sb, W, Cr, Ge, Rh, Ti, Ag, Sn, Au, Ir, Pd, Ni, Ru, Hg}, 0x1, 00.5, excluding certain aliovalent combinations; or an isovalent-aliovalent combination of the formula M.sub.xMI.sub.yMII.sub.1-x-yO.sub.2-, wherein M, MI, and MII are as set forth above, 0x1, 0y1, 00.5; wherein the ferroelectric structure is in a Pca2.sub.1 or Pmn2.sub.1 space group or a subgroup thereof.

Claims

1. A meta-stable ferroelectric structure comprising one of the following oxides: an isovalent combination of the formula M.sub.xM.sub.1-xO.sub.2-, wherein M and M are independently selected from the group consisting of Zr, Hf, Pb, W, Mo, Nb, Te, and Ti, wherein 0x1 and 00.5, excluding Hf.sub.xZr.sub.1-xO.sub.2 for all x in Pca2.sub.1 phase; an aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2-, wherein MI and MII are independently selected from the group consisting of Bi, Y, Ta, In, Mo, Nb, Sc, Tl, Pd, Sb, W, Cr, Ge, Rh, Ti, Ag, Sn, Au, Ir, Ni, Ru, and Hg, wherein 0x1 and 00.5, excluding aliovalent combinations in which MI is Ta, Nb or W where MII is Y or Sc or in which MI is Y or Sc where MII is Ta, Nb or W; or an isovalent-aliovalent combination of the formula M.sub.xMI.sub.yMII.sub.1-x-yO.sub.2-, wherein M, MI, and MII are as set forth above and 0x1, 0y1, and 00.5; wherein the ferroelectric structure is in a Pca2.sub.1 or Pmn2.sub.1 space group or a subgroup thereof.

2. The meta-stable ferroelectric structure of claim 1, wherein the oxide is the isovalent combination.

3. The meta-stable ferroelectric structure of claim 1, wherein the oxide is the aliovalent combination.

4. The meta-stable ferroelectric structure of claim 1, wherein the oxide is the isovalent-aliovalent combination.

5. The meta-stable ferroelectric structure of claim 2, wherein the oxide is selected from the group consisting of PbO.sub.2, WO.sub.2, NbO.sub.2, and MoO.sub.2, and wherein the ferroelectric structure is in the Pca2.sub.1 space group or a subgroup thereof.

6. The meta-stable ferroelectric structure of claim 2, wherein the oxide is selected from the group consisting of NbO.sub.2, TeO.sub.2, TiO.sub.2, and PbO.sub.2, and wherein the ferroelectric structure is in the Pmn2.sub.1 space group or a subgroup thereof.

7. The meta-stable ferroelectric structure of claim 3, wherein the oxide is aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2, wherein MI and MII are independently selected from the group consisting of Bi, In, Ag, Rh, Y, Mo, Ti, W, Ni, Au, Sn, Sc, Sb, Tl, Cr, Ru, Hg, Pd, Ge, Ir, Ta, and Nb, excluding aliovalent combinations in which MI is Ta, Nb or W where MII is Y or Sc or in which MI is Y or Sc where MII is Ta, Nb or W, and wherein the ferroelectric structure is in the Pca2.sub.1 space group of a subgroup thereof.

8. The meta-stable ferroelectric structure of claim 7, wherein MI and MII are selected from one of the following MI and MII combinations: TaMo, NbIn, BiNb, BiIn, BiSc, NbMo, BiPd, TaIn, BiTa, BiY, and NbTl.

9. The meta-stable ferroelectric structure of claim 3, wherein the oxide is aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2, wherein MI and MII are independently selected from the group consisting of Bi, Nb, In, Rh, Ti, Y, Ta, W, Cr, Sc, Tl, Au, Ir, Mo, and Ge, excluding aliovalent combinations in which MI is Ta, Nb or W where MII is Y or Sc or in which MI is Y or Sc where MII is Ta, Nb or W, and wherein the ferroelectric structure is in the Pmn2.sub.1 space group or a subgroup thereof.

10. A vertical channel transistor comprising a meta-stable ferroelectric structure of claim 1.

11. A FE-RAM comprising a meta-stable ferroelectric structure of claim 1.

12. A FTJ comprising a meta-stable ferroelectric structure of claim 1.

13. A FE-FET comprising a meta-stable ferroelectric structure of claim 1.

14. A capacitor comprising a meta-stable ferroelectric structure of claim 1.

15. A sensor comprising a meta-stable ferroelectric structure of claim 1.

16. A switch comprising a meta-stable ferroelectric structure of claim 1.

17. A meta-stable ferroelectric structure comprising one of the following oxides: an isovalent combination of the formula M.sub.xM.sub.1-xO.sub.2-, wherein M and M are independently selected from the group consisting of Zr, Hf, Pb, Mo, Nb, Te, and Ti, wherein 0x1 and 00.5, excluding Hf.sub.xZr.sub.1-xO.sub.2 for all x in Pca2.sub.1 phase; an aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2-, wherein MI and MII are independently selected from the group consisting of Bi, In, Mo, Tl, Pd, Sb, Cr, Ge, Rh, Ti, Ag, Sn, Au, Ir, Ni, Ru, and Hg, wherein 0x1 and 00.5; or an isovalent-aliovalent combination of the formula M.sub.xMI.sub.yMII.sub.1-x-yO.sub.2-, wherein M, MI, and MII are as set forth above and 0x1, 0y1, and 00.5; wherein the ferroelectric structure is in a Pca2.sub.1 or Pmn2.sub.1 space group or a subgroup thereof.

18. The meta-stable ferroelectric structure of claim 17, wherein the oxide is the aliovalent combination.

19. The meta-stable ferroelectric structure of claim 1, comprising one of the following oxides: an isovalent combination of the formula M.sub.xM.sub.1-xO.sub.2, wherein M and M are independently selected from the group consisting of Zr, Hf, Pb, W, Mo, Nb, and Te, wherein 0x1, excluding Hf.sub.xZr.sub.1-xO.sub.2 for all x; an aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2, wherein MI and MII are independently selected from the group consisting of Bi, Y, Ta, In, Nb, Sc, Tl, Rh, Ti, Au, and Ir, wherein 0x1, excluding aliovalent combinations in which MI is Ta or Nb where MII is Y or Sc or in which MI is Y or Sc where MII is Ta or Nb; or an isovalent-aliovalent combination of the formula M.sub.xMI.sub.yMII.sub.1-x-yO.sub.2, wherein M, MI, and MII are as set forth above and 0x1 and 0y1; wherein the ferroelectric structure is in a Pca2.sub.1 or Pmn2.sub.1 space group or a subgroup thereof.

20. The meta-stable ferroelectric structure of claim 17, comprising one of the following oxides: an isovalent combination of the formula M.sub.xM.sub.1-xO.sub.2, wherein M and M are independently selected from the group consisting of Zr, Hf, Pb, Mo, Nb, and Te, wherein 0x1, excluding Hf.sub.xZr.sub.1-xO.sub.2 for all x; an aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2, wherein MI and MII are independently selected from the group consisting of Bi, In, Tl, Rh, Ti, Au, and Ir, wherein 0x1; or an isovalent-aliovalent combination of the formula M.sub.xMI.sub.yMII.sub.1-x-yO.sub.2, wherein M, MI, and MII are as set forth above and 0x1 and 0y1; wherein the ferroelectric structure is in a Pca2.sub.1 or Pmn2.sub.1 space group or a subgroup thereof.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0059] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0060] Example embodiments of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing in which:

[0061] FIG. 1 shows ferroelectric HfO.sub.2 in its two distinct states.

[0062] FIG. 2 shows the FE-HfO.sub.2 structure with space group Pca2.sub.1.

[0063] FIG. 3 shows the NEB barrier computed for HfO.sub.2 and its comparison with previous reporting.

[0064] FIG. 4 shows NEB on an isovalent candidate, using Mo as an example.

[0065] FIG. 5 shows structures of the present disclosure for FE candidates from aliovalent 100% Hf substitution.

[0066] FIG. 6 shows an embodiment of the present disclosure based on an aliovalent combination.

[0067] FIG. 7 shows aliovalent combinations of the present disclosure (Ehull<50 meV/atom).

[0068] FIG. 8 shows aliovalent combinations of the present disclosure (50 meV/atom<Ehull<100 meV/atom).

[0069] FIG. 9 shows aliovalent combinations of the present disclosure (100 meV/atom<Ehull<150 meV/atom).

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0070] FIG. 2 shows the FE-HfO.sub.2 structure with space group Pca2.sub.1. A second phase with Pmn2.sub.1 is theorized to also be FE. FIG. 3 shows that the NEB barrier computed for HfO.sub.2 compares well with previous reporting, so P4.sub.2/nmc energies can be used to estimate switching barriers (a proxy for E-field).

[0071] Based on a systematic study of all possible isovalent oxides and aliovalent oxides that are meta-stable in the FE phases of HfO.sub.2, the present disclosure provides meta-stable ferroelectric structures including oxides of the following chemistries: [0072] an isovalent combination of the formula M.sub.xM.sub.1-xO.sub.2-, wherein M and M are independently selected from the group consisting of Zr, Hf, Pb, W, Mo, Nb, Te, and Ti, wherein 0x1 and 00.5, excluding Hf.sub.xZr.sub.1-xO.sub.2 for all x in Pca2.sub.1 phase; [0073] an aliovalent combination of the formula MI.sub.xMII.sub.1-xO.sub.2-, wherein MI and MII are independently selected from the group consisting of Bi, Y, Ta, In, Mo, Nb, Sc, Tl, Pd, Sb, W, Cr, Ge, Rh, Ti, Ag, Sn, Au, Ir, Ni, Ru, and Hg, wherein 0x1 and 00.5, excluding aliovalent combinations in which MI is Ta, Nb or W where MII is Y or Sc or in which MI is Y or Sc where MII is Ta, Nb or W; or [0074] an isovalent-aliovalent combination of the formula M.sub.xMI.sub.yMII.sub.1-x-yO.sub.2-, wherein M, MI, and MII are as set forth above and 0x1, 0y1, and 00.5; [0075] wherein the ferroelectric structure is in a Pca2.sub.1 or Pmn2.sub.1 space group or a subgroup thereof for applications including FE-RAM, vertical channel transistors, FE-FET, FTJ, capacitors, sensors and switches.

[0076] The identified oxides are nonmetallic with relatively low Ehull making them experimentally synthesizable under appropriate conditions (including choosing the right substrate). The appropriate substrate choice to stabilize these FE materials is also listed. Thus, the ferroelectrics can be grown on an appropriate substrate of choice (e.g., SiO.sub.2) using typical growth methods like thermal oxidation, atomic layer deposition, pulsed laser deposition, chemical vapor deposition, plasma oxidation, wet anodization or other chemical treatments. For example, atomic layer deposition growth of HfO.sub.2 can be done using CpHf(NMe.sub.2).sub.3 and (CpMe)Hf(NMez).sub.3 (Cp, cyclopentadienyl=C.sub.5H.sub.5) as precursors using O.sub.3 as the oxygen source between 250 C. and 400 C. (see Niinist et al., Growth and phase stabilization of HfO.sub.2 thin films by ALD using novel precursors, Journal of Crystal Growth, Vol. 312, Issue 2, Jan. 1, 2010, pp. 245-249), and embodiments of the present disclosure can be made in a similar manner using precursors appropriate for making those embodiments.

[0077] Thus, FE candidates from isovalent 100% Hf substitution include the following candidates shown in Table 1 below:

TABLE-US-00001 TABLE 1 Meta phase band e_hull P4_2/nmc gap lattice Composition (eV) (eV) (eV) spacegroup a () b () c () Substrate Spacegroup: Ref. HfO2 0.028 0.056 Pca2_1 5.046 5.078 5.27 Si_T/O/M Pca2_1 Ref. ZrO2 0.022 0.037 Pca2_1 5.123 5.154 5.342 Hf_M/ PbO2 0.002 0.042 0.15 Pca2_1 5.131 5.580 Hf_M WO2 0 2.758 Pca2_1 5.088 5.091 5.196 Si_H/M/O MoO2 0 1.500 Pca2_1 5.051 5.051 5.181 Si_T/Si_O NbO2 0.106 0.184 0.508 Pca2_1 5.017 5.050 5.215 Si_T Spacegroup: Ref. HfO2 0.049 0.056 Pmn2_1 3.407 5.149 3.845 /LTO-ac Pmn2_1 Ref. ZrO2 0.037 3.188 Pmn2_1 3.479 5.244 LTO-ac NbO2 0.045 0.077 Pmn2_1 3.168 5.094 3.994 PbO2 0.066 0.055 0.023 Pmn2_1 3.630 5.551 4.019 /NSO-ac TeO2 0.122 1.627 Pmn2_1 3.367 TiO2 0.140 0.144 1.795 Pmn2_1 3.163 3.679 AO-ac/LuAO-ac indicates data missing or illegible when filed

[0078] In Table 1, the meta phase value is indicative of a barrier to polarization switching.

[0079] Additionally, in Table 1, the substrate is a substrate stabilizing the meta-stable phase.

[0080] FIG. 4 shows NEB on an isovalent candidate, using Mo as an example.

[0081] With respect to the aliovalent embodiments, FE candidates from aliovalent 100% Hf substitution include the following candidates: [0082] Space group: Pca2.sub.1 [0083] Ehull<150 meV/atom with finite band gap [0084] MI.sub.xMII.sub.1-xO.sub.2 (MI, MII={Bi, Nb, In, Ag, Rh, Y, Ta, Ti, W, Ni, Au, Sn, Sc, Sb, Tl, Cr, Mo, Ru, Hg, Pd, Ge, Ir}) [0085] Examples of MI and MII combinations (under 30 meV/atom): TaMo, NbIn, BiNb, BiIn, NbY, TaY, BiSc, NbMo, BiPd, TaIn, BiTa, BiY, NbTl, etc. Particular embodiments of the present disclosure include TaMo, NbIn, BiNb, BiIn, BiSc, NbMo, BiPd, TaIn, BiTa, BiY, and NbTl. [0086] Space group: Pmn2.sub.1 [0087] Ehull<150 meV/atom with finite band gap [0088] MI.sub.xMII.sub.1-xO.sub.2 (MI, MII={Bi, Nb, In, Rh, Ti, Y, Ta, W, Cr, Sc, Tl, Au, Ir, Mo, Ge})

[0089] Structures of the present disclosure for FE candidates from aliovalent 100% Hf substitution are shown in FIG. 5, and an embodiment of the present disclosure based on an aliovalent combination is shown in FIG. 6. FIG. 7 shows aliovalent combinations of the present disclosure with Ehull<50 meV/atom, FIG. 8 shows aliovalent combinations of the present disclosure with 50 meV/atom<Ehull<100 meV/atom, and FIG. 9 shows aliovalent combinations of the present disclosure with 100 meV/atom<Ehull<150 meV/atom).

[0090] A list of substrates which can be used in connection with the present disclosure is shown in Table 2 below.

TABLE-US-00002 TABLE 2 Substrate list index mp-id Composition Spacegroup a b c band gap SiO2 Tetragonal SiO2_O1 SiO2 Orthorhombic SiO2_T2 SiO2 Tetragonal SiO2_M SiO2 SiO2_O2 SiO2 Orthorhombic SiO2_H SiO2 Hexagonal HfO2_M HfO2 HfO2_O HfO2 Orthorhombic Orthorhombic Orthorhombic Orthorhombic Tetragonal Cubic Orthorhombic Orthorhombic LAO Cubic YAO Orthorhombic Cubic Hexagonal Orthorhombic Orthorhombic index mp-id element 100 111 Cu Cu Ni Ni Si Si Fe Fe Materialsprojects Progress in Surface Science, Volume , Issue 2 (2017) Pages 117-141 indicates data missing or illegible when filed

[0091] The foregoing is illustrative of exemplary embodiments and is not to be construed as limiting the disclosure. Although a few exemplary embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the above embodiments without materially departing from the disclosure.