OxRAM oxide based resistive random access memory cell and associated manufacturing method

Abstract

An OxRAM oxide based resistive random access memory cell includes a first electrode; a layer M1Oss of a sub-stoichiometric oxide of a first metal; a layer M2N of a nitride of a second metal M2; a layer M3M4O of a ternary alloy of a third metal M3, a fourth metal M4 and oxygen O, or M3M4NO of a quaternary alloy of the third metal M3, the fourth metal M4, nitrogen N and oxygen O and a second electrode. The standard free enthalpy of formation of the ternary alloy M3M4O, noted ΔG.sub.f,T.sup.0 (M3M4O), or of the quaternary alloy M3M4NO, noted ΔG.sub.f,T.sup.0 (M3M4NO), is strictly less than the standard free enthalpy of formation of the sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔG.sub.f,T.sup.0 (M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔG.sub.f,T.sup.0 (M2NO):
ΔG.sub.f,T.sup.0(M3M4O)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO)
or ΔG.sub.f,T.sup.0(M3M4NO)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO).

Claims

1. An OxRAM oxide based resistive random access memory cell comprising an insulator layer arranged between a first metal layer and a second metal layer, wherein: the first metal layer is a first electrode; the insulator layer is a layer M1Oss of a sub-stoichiometric oxide of a first metal M1; the second metal layer comprises, in this order from the insulator layer: a first sub-layer M2N of a nitride of a second metal M2; a second sub-layer M3M4O of a ternary alloy of a third metal M3, a fourth metal M4 and oxygen O, or M3M4NO of a quaternary alloy of the third metal M3, the fourth metal M4, nitrogen N and oxygen O; a second electrode; and wherein the first, second, third and fourth metals M1, M2, M3 and M4 are such that the standard free enthalpy of formation of the ternary alloy M3M4O, noted ΔG.sub.f,T.sup.0 (M3M4O), or of the quaternary alloy M3M4NO, noted ΔG.sub.f,T.sup.0 (M3M4NO), is strictly less than the standard free enthalpy of formation of the sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔG.sub.f,T.sup.0 (M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔG.sub.f,T.sup.0 (M2NO):
ΔG.sub.f,T.sup.0(M3M4O)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO)
or ΔG.sub.f,T.sup.0(M3M4NO)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO).

2. The OxRAM oxide based resistive random access memory cell according to claim 1, further comprising a titanium reservoir layer Ti, intercalated between the insulator layer and the first sub-layer M2N of the nitride of the second metal M2 of the second metal layer.

3. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the fourth metal M4 has an oxygen solubility less than the oxygen solubility of the third metal M3.

4. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the first, second, third and fourth metals M1, M2, M3 and M4 are selected from transition elements of groups 4, 5 and 6 of the periodic table and the elements silicon Si and aluminium Al; the first and second metals M1 and M2 being identical or distinct and the second and third metals M2 and M3 being identical or distinct but the first, second and third metals M1, M2 and M3 being not all identical; and the third and fourth metals M3 and M4 being distinct.

5. The OxRAM oxide based resistive random access memory cell according to claim 4, wherein the first, second, third and fourth metals M1, M2, M3 and M4 are selected from the elements hafnium Hf, zirconium Zr, titanium Ti, tantalum Ta, niobium Nb, vanadium V, tungsten W, molybdenum Mo, silicon Si and aluminium Al.

6. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the sub-stoichiometric oxide of the first metal M1 is hafnium dioxide HfO.sub.z<2 or zirconium dioxide ZrO.sub.z<2 or titanium dioxide TiO.sub.z<2 or tantalum pentoxide Ta2O.sub.z<5 or vanadium dioxide VO.sub.z<2 or vanadium pentoxide V2O.sub.z<5 or tungsten oxide WO.sub.z<1 or tungsten dioxide WO.sub.z<2 or tungsten trioxide WO.sub.z<3 or aluminium oxide Al.sub.2O.sub.z<3 or silicon dioxide SiO.sub.z<2.

7. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the nitride of the second metal M2 is titanium nitride TiN or tantalum nitride TaN or zirconium nitride ZrN or hafnium nitride HfN or tungsten nitride WN or vanadium nitride VN or titanium carbonitride TiCN or tantalum carbonitride TaCN or molybdenum carbonitride MoCN or tungsten carbonitride WCN.

8. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the ternary alloy M3M4O is a ternary alloy of: titanium Ti, aluminium Al and oxygen O, or titanium Ti, silicon Si and oxygen O, or zirconium Zr, aluminium Al and oxygen O, or zirconium Zr, silicon Si and oxygen O, or hafnium Hf, aluminium Al and oxygen O, or hafnium Hf, silicon Si and oxygen O; and wherein the quaternary alloy M3M4NO is a quaternary alloy of: titanium Ti, aluminium Al, nitrogen N and oxygen O, or titanium Ti, silicon Si, nitrogen N and oxygen O, or zirconium Zr, aluminium Al, nitrogen N and oxygen O, or zirconium Zr, silicon Si, nitrogen N and oxygen O, or hafnium Hf, aluminium Al, nitrogen N and oxygen O, or hafnium Hf, silicon Si, nitrogen N, oxygen O.

9. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the second sub-layer of ternary alloy M3M4O or quaternary alloy M3M4NO comprises a proportion of the third metal M3 of (1-x) and a proportion of the fourth metal M4 of x, where x is from 1% to 60%.

10. The OxRAM oxide based resistive random access memory cell according to claim 9, wherein x is from 5% to 50%.

11. The OxRAM oxide based resistive random access memory cell according to claim 10, wherein x is from 10% to 40%.

12. The OxRAM oxide based resistive random access memory cell according to claim 11, wherein x is equal to 30%.

13. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the layer M1Oss of sub-stoichiometric oxide of the first metal has a thickness from 1 nm to 15 nm.

14. The OxRAM oxide based resistive random access memory cell according to claim 13, wherein the layer M1Oss of sub-stoichiometric oxide of the first metal has a thickness of 10 nm.

15. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the first sub-layer M2N of nitride of the second metal has a thickness from 2 nm to 20 nm.

16. The OxRAM oxide based resistive random access memory cell according to claim 15, wherein the first sub-layer M2N of nitride of the second metal has a thickness of 5 nm.

17. The OxRAM oxide based resistive random access memory cell according to claim 1, wherein the second sub-layer of ternary alloy M3M4O or quaternary alloy M3M4NO has a thickness from 1 nm to 50 nm.

18. The OxRAM oxide based resistive random access memory cell according to claim 17, wherein the second sub-layer of ternary alloy M3M4O or quaternary alloy M3M4NO has a thickness of 20 nm.

19. A method for manufacturing an OxRAM oxide based resistive random access memory cell according to claim 1, comprising, in this order: a) depositing a first electrode; b) depositing a layer M1O of a stoichiometric oxide of a first metal M1; c) depositing a layer M2N of a nitride of a second metal M2; d) depositing a layer M3M4 of a binary alloy of a third metal M3 and a fourth metal M4, or M3M4N of a ternary alloy of the third metal M3, the fourth metal M4 and nitrogen N; e) depositing a second electrode; the first, second, third and fourth metals M1, M2, M3 and M4 being selected in such a way that the standard free enthalpy of formation of any ternary alloy M3M4O of the third and fourth metals M3, M4 and oxygen O, noted ΔG.sub.f,T.sup.0 (M3M4O), or of any quaternary alloy M3M4NO of the third and fourth metals M3, M4, nitrogen N and oxygen O, noted ΔG.sub.f,T.sup.0 (M3M4NO), is strictly less than the standard free enthalpy of formation of any sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔG.sub.f,T.sup.0 (M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔG.sub.f,T.sup.0 (M2NO):
ΔG.sub.f,T.sup.0(M3M4O)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO)
or ΔG.sub.f,T.sup.0(M3M4NO)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other characteristics and benefits of the invention will become clear from the description that is given thereof below, for indicative purposes and in no way limiting, with reference to the appended figures, among which:

(2) FIG. 1a schematically shows a diagram of the steps of a first method for manufacturing an OxRAM oxide based resistive random access memory cell according to an aspect of the invention.

(3) FIG. 1b schematically shows the OxRAM oxide based resistive random access memory cell out of thermodynamic equilibrium, obtained in a transitory manner immediately after the different deposition steps of the method of FIG. 1a.

(4) FIG. 1c schematically shows the OxRAM oxide based resistive random access memory cell of FIG. 1b having reached its thermodynamic equilibrium.

(5) FIG. 2a schematically shows a diagram of the steps of a second method for manufacturing an OxRAM oxide based resistive random access memory cell according to an aspect of the invention.

(6) FIG. 2b schematically shows the OxRAM oxide based resistive random access memory cell out of thermodynamic equilibrium, obtained in a transitory manner immediately after the different deposition steps of the method of FIG. 2a.

(7) FIG. 2c schematically shows the OxRAM oxide based resistive random access memory cell of FIG. 2b having reached its thermodynamic equilibrium.

(8) FIG. 3a schematically shows a diagram of the steps of a third method for manufacturing an OxRAM oxide based resistive random access memory cell according to an aspect of the invention.

(9) FIG. 3b schematically shows the OxRAM oxide based resistive random access memory cell out of thermodynamic equilibrium, obtained in a transitory manner immediately after the different deposition steps of the method of FIG. 3a.

(10) FIG. 3c schematically shows the OxRAM oxide based resistive random access memory cell of FIG. 3b having reached its thermodynamic equilibrium.

(11) For greater clarity, identical or similar elements are marked by identical reference signs in all of the figures.

DETAILED DESCRIPTION

(12) FIG. 1a schematically shows a diagram of the steps of a first method for manufacturing 100 an OxRAM oxide based resistive random access memory cell 10 according to a first embodiment of the invention. FIG. 1b schematically shows the OxRAM oxide based resistive random access memory cell 1 out of thermodynamic equilibrium, obtained in a transitory manner immediately after the different deposition steps of the method 100 of FIG. 1a. FIG. 1c schematically shows the OxRAM oxide based resistive random access memory cell 10 having reached its thermodynamic equilibrium. FIGS. 1a, 1b and 1c are described jointly.

(13) The first manufacturing method 100 comprises a first step a) according to which a first electrode or lower electrode BE, for example made of titanium nitride TiN or any other metal neutral vis-à-vis oxygen, is typically deposited on a substrate (not represented); then a second step b) according to which a layer M1O of a stoichiometric oxide of a first metal M1 is deposited on the first electrode BE; then a third step c) according to which a layer M2N of a nitride of a second metal M2 is deposited on the layer M1O; then a fourth step d) according to which a layer M3M4 of a binary alloy of a third metal M3 and a fourth metal M4 is deposited on the layer M2N; then a fifth step e) according to which a second electrode or upper electrode TE, for example made of titanium nitride TiN or any other metal neutral vis-à-vis oxygen, is deposited on the layer M3M4.

(14) The first electrode BE forms a first metal layer Mel; the layer M1O of stoichiometric oxide of the first metal M1 forms an insulator layer I; and the layer M2N of nitride of the second metal M2, the layer M3M4 of binary alloy of the third and fourth metals M3, M4 and the second electrode TE form a second metal layer Me2.

(15) The first, second, third and fourth metals M1, M2, M3 and M4 are such that the standard free enthalpy of formation of any ternary alloy M3M4O of the third and fourth metals M3, M4 and oxygen O, noted ΔG.sub.f,T.sup.0 (M3M4O), is strictly less than the standard free enthalpy of formation of any sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔG.sub.f,T.sup.0(M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔG.sub.f,T.sup.0(M2NO):
ΔG.sub.f,T.sup.0(M3M4O)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO)

(16) Thus, the stack 1 represented in FIG. 1b evolves spontaneously, at ambient temperature or with thermal assistance, to the stack 10 represented in FIG. 1c: the layer M1O of stoichiometric oxide of the first metal M1 becomes a layer M1Oss of sub-stoichiometric oxide of the first metal M1, and the layer M3M4 of binary alloy of the third and fourth metals M3, M4 becomes a layer M3M4O of ternary alloy of the third and fourth metals M3, M4 and oxygen O. FIGS. 1b and 1c show respectively the schematic oxygen profile of the stacks 1 and 10: in the stack 1, oxygen is found essentially in the layer M1O. In the stack 10, an oxygen gradient has formed in the layer M1Oss, with a localised oxygen depletion on the side of the first electrode BE. At the limit, the oxygen gradient is such that the layer M1Oss is broken down into a first sub-layer M1 of the first metal M1 on the side of the first electrode, and a second sub-layer M1O of stoichiometric oxide of the first metal M1. Furthermore, the oxygen having migrated from the layer M1O is henceforth found localised in the layer M3M4O.

(17) FIG. 2a schematically shows a diagram of the steps of a second method for manufacturing 200 an OxRAM oxide based resistive random access memory cell 20 according to a second embodiment of the invention. FIG. 2b schematically shows the OxRAM oxide based resistive random access memory cell 2 out of thermodynamic equilibrium, obtained in a transitory manner immediately after the different deposition steps of the method of FIG. 2a. FIG. 2c schematically shows the OxRAM oxide based resistive random access memory cell 20 having reached its thermodynamic equilibrium. FIGS. 2a, 2b and 2c are described jointly.

(18) The second manufacturing method 200 is identical to the first manufacturing method 100, with the exception of its fourth step d′), according to which a layer M3M4N of a ternary alloy of the third and fourth metals M3, M4 and nitrogen N, is deposited on the layer M2N. The first, second, third and fourth metals M1, M2, M3, M4 are such that the standard free enthalpy of formation of any quaternary alloy M3M4NO of the third and fourth metals M3, M4, nitrogen N and oxygen O, noted ΔG.sub.f,T.sup.0(M3M4NO), is strictly less than the standard free enthalpy of formation of any sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔG.sub.f,T.sup.0(M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔG.sub.f,T.sup.0(M2NO):
ΔG.sub.f,T.sup.0(M3M4NO)<ΔG.sub.f,T.sup.0(M1Oss)≤ΔG.sub.f,T.sup.0(M2NO)

(19) The stack 2 represented in FIG. 2b evolves spontaneously, at ambient temperature or with thermal assistance, to the stack 20 represented in FIG. 2c, in a manner analogous to the evolution described previously from the stack 1 of FIG. 1 b to the stack 10 of FIG. 1c, the layer M3M4N of ternary alloy of the third and fourth metals M3, M4 and nitrogen N becoming a layer M3M4NO of quaternary alloy of the third and fourth metals M3, M4, nitrogen N and oxygen O. FIGS. 2b and 2c show respectively the schematic oxygen profile of the stacks 2 and 20, which is analogous to that of the stacks 1 and 10 of FIGS. 1b and 1c.

(20) FIG. 3a schematically shows a diagram of the steps of a third method for manufacturing 300 an OxRAM oxide based resistive random access memory cell 30 according to a third embodiment of the invention. FIG. 3b schematically shows the OxRAM oxide based resistive random access memory cell 3 out of thermodynamic equilibrium, obtained in a transitory manner immediately after the different deposition steps of the method 300 of FIG. 3a. FIG. 3c schematically shows the OxRAM oxide based resistive random access memory cell 30 having reached its thermodynamic equilibrium. FIGS. 3a, 3b and 3c are described jointly.

(21) The third manufacturing method 300 is identical to the first manufacturing method 100, with the exception of an additional step b′) intercalated between steps b) and c), and according to which a titanium reservoir layer Ti is deposited on the insulator layer M1O of stoichiometric oxide of the first metal M1. The layer M2N of the nitride of the second metal is then no longer deposited on the layer M1O but on the titanium reservoir layer Ti. In the same way as for the first manufacturing method, the first, second, third and fourth metals M1, M2, M3, M4 are such that the standard free enthalpy of formation of any ternary alloy M3M4O of the third and fourth metals M3, M4 and oxygen O, noted ΔG.sub.f,T.sup.0(M3M4O), is strictly less than the standard free enthalpy of formation of any sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔG.sub.f,T.sup.0(M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔG.sub.f,T.sup.0(M2NO):
ΔG.sub.f,T.sup.0(M3M4O)<ΔG.sub.f,T.sup.0(M1Oss)<ΔG.sub.f,T.sup.0(M2NO)

(22) The stack 3 represented in FIG. 3b evolves spontaneously, at ambient temperature or with thermal assistance, to the stack 30 represented in FIG. 3c, in an analogous manner to the evolution described previously from the stack 1 of FIG. 1b to the stack 10 of FIG. 1c. FIGS. 3b and 3c show respectively the schematic oxygen profile of the stacks 3 and 30, which is analogous to that of the stacks 1 and 10 of FIGS. 1b and 1c.

(23) The second and third manufacturing methods 200, 300 each represent an alternative of the first manufacturing method 100: layer M3M4N instead of M3M4 for the second method 200; additional titanium Ti reservoir layer for the third method 300. These two alternatives are compatible with each other: a manufacturing method comprising both step b′) of deposition of a titanium reservoir layer Ti on the insulator layer M1O, and step d′) of deposition of a layer M3M4N on the layer M2N does not go beyond the scope of the invention. The stack obtained immediately at the end of this manufacturing method comprises the second electrode TE, on the layer M3M4N, on the layer M2N, on the Ti reservoir layer, on the layer M1O, on the first electrode BE. This stack evolves spontaneously, at ambient temperature or with thermal assistance, to a stack in which the layer M3M4N becomes the layer M3M4NO and the layer M1O becomes the layer M1Oss, in an analogous manner to the evolutions described previously.

(24) Several particular exemplary embodiments will now be described. According to a first example, the first metal M1 is hafnium Hf, the second and third metals M2, M3 are titanium Ti and the fourth metal M4 is aluminium Al. The layer M1O is a layer of stoichiometric hafnium dioxide HfO.sub.2; the layer M1Oss is a layer of sub-stoichiometric hafnium dioxide HfO.sub.z<2. The layer M2N is a layer of titanium nitride TiN. The layer M3M4 is a layer of titanium-aluminium TiAl; the layer M3M4O is a layer TiAlO of alloy of titanium, aluminium and oxygen.

(25) According to a second example, the first and second metals M1, M2 are hafnium Hf, the third metal is titanium Ti and the fourth metal is aluminium Al. The layer M1O is a layer of stoichiometric hafnium dioxide HfO.sub.2; the layer M1Oss is a layer of sub-stoichiometric hafnium dioxide HfO.sub.z<2. The layer M2N is a layer of hafnium nitride HfN. The layer M3M4 is a layer of titanium-aluminium TiAl; the layer M3M4O is a layer TiAlO of alloy of titanium, aluminium and oxygen.

(26) According to a third example, the first and second metals M1, M2 are vanadium V, the third metal is hafnium Hf and the fourth metal is silicon Si. The layer M1O is a layer of stoichiometric vanadium pentoxide V.sub.2O.sub.5; the layer M1Oss is a layer of sub-stoichiometric vanadium pentoxide V.sub.2O.sub.z<5. The layer M2N is a layer of vanadium nitride VN. The layer M3M4 is a layer of hafnium-silicon HfSi; the layer M3M4O is a layer HfSiO of alloy of hafnium, silicon and oxygen.

(27) According to a fourth example, the first metal M1 is hafnium Hf, the second metal M2 is zirconium Zr, the third metal is titanium Ti and the fourth metal is aluminium Al. The layer M1O is a layer of stoichiometric hafnium dioxide HfO.sub.2; the layer M1Oss is a layer of sub-stoichiometric hafnium dioxide HfO.sub.z<2. The layer M2N is a layer of zirconium nitride ZrN. The layer M3M4 is a layer of titanium-aluminium TiAl; the layer M3M4O is a layer TiAlO of alloy of titanium, aluminium and oxygen.

(28) More generally, the fourth metal M4 is selected to have an oxygen solubility less than the oxygen solubility of the third metal M3. The layer of binary alloy M3M4 or ternary alloy M3M4N comprises a proportion of the third metal M3 of (1-x) and a proportion of the fourth metal M4 of x, where x belongs to the interval [1%; 60%], in an embodiment [5%; 50%], and in another embodiment [10%; 40%]. For example, x is equal to 30%.

(29) The first, second, third and fourth metals M1, M2, M3 and M4 are selected from transition elements of groups 4, 5 and 6 of the periodic table and the elements silicon Si and aluminium Al; the first and second metals M1 and M2 being identical or distinct and the second and third metals M2 and M3 being identical or distinct but the first, second and third metals M1 M2 and M3 not all being identical; and the third and fourth metals M3 and M4 being distinct. The first, second, third and fourth metals M1, M2, M3 and M4 are for example selected from the elements hafnium Hf, zirconium Zr, titanium Ti, tantalum Ta, niobium Nb, vanadium V, tungsten W, molybdenum Mo, silicon Si and aluminium Al.

(30) The stoichiometric oxide of the first metal M1 is for example hafnium dioxide HfO.sub.2 or zirconium dioxide ZrO.sub.2 or titanium dioxide TiO.sub.2 or tantalum pentoxide Ta.sub.2O.sub.5 or vanadium dioxide VO.sub.2 or vanadium pentoxide V.sub.2O.sub.5 or tungsten oxide WO.sub.1 or tungsten dioxide WO.sub.2 or tungsten trioxide WO.sub.3 or aluminium oxide Al.sub.2O.sub.3 or silicon dioxide SiO.sub.2. The sub-stoichiometric oxide of the first metal M1 is thus for example hafnium dioxide HfO.sub.z<2 or zirconium dioxide ZrO.sub.z<2 or titanium dioxide TiO.sub.z<2 or tantalum pentoxide Ta.sub.2O.sub.z<5 or vanadium dioxide VO.sub.z<2 or vanadium pentoxide V.sub.2O.sub.z<5 or tungsten oxide WO.sub.z<1 or tungsten dioxide WO.sub.z<2 or tungsten trioxide WO.sub.z<3 or aluminium oxide Al.sub.2O.sub.z<3 or silicon dioxide SiO.sub.z<2.

(31) The nitride of the second metal M2 is titanium nitride TiN or tantalum nitride TaN or zirconium nitride ZrN or hafnium nitride HfN or tungsten nitride WN or vanadium nitride VN or titanium carbonitride TiCN or tantalum carbonitride TaCN or molybdenum carbonitride MoCN or tungsten carbonitride WCN.

(32) According to the first embodiment, the binary alloy M3M4 is for example a binary alloy of: titanium Ti and aluminium Al, or titanium Ti and silicon Si, or zirconium Zr and aluminium Al, or zirconium Zr and silicon Si. hafnium Hf and aluminium Al, or hafnium Hf and silicon Si.

(33) The ternary alloy M3M4O is thus for example a ternary alloy of: titanium Ti, aluminium Al and oxygen O, or titanium Ti, silicon Si and oxygen O, or zirconium Zr, aluminium Al and oxygen O, or zirconium Zr, silicon Si and oxygen O, or hafnium Hf, aluminium Al and oxygen O, or hafnium Hf, silicon Si and oxygen O.

(34) According to the second embodiment, the ternary alloy M3M4N is for example a ternary alloy of: titanium Ti, aluminium Al, and nitrogen N, or titanium Ti, silicon Si, and nitrogen N, or zirconium Zr, aluminium Al, and nitrogen N, or zirconium Zr, silicon Si, and nitrogen N, or hafnium Hf, aluminium Al, and nitrogen N, or hafnium Hf, silicon Si, and nitrogen N.

(35) The quaternary alloy M3M4NO is thus for example a quaternary alloy of: titanium Ti, aluminium Al, nitrogen N and oxygen O, or titanium Ti, silicon Si, nitrogen N and oxygen O, or zirconium Zr, aluminium Al, nitrogen N and oxygen O, or zirconium Zr, silicon Si, nitrogen N and oxygen O, or hafnium Hf, aluminium Al, nitrogen N and oxygen O, or hafnium Hf, silicon Si, nitrogen N oxygen O.

(36) According to any of the embodiments: the layer M1O of stoichiometric oxide of the first metal and the layer M1Oss of sub-stoichiometric oxide of the first metal are of thickness comprised in the interval [1 nm; 15 nm] and in an embodiment 10 nm; and the layer M2N of nitride of the second metal has a thickness comprised in the interval [2 nm; 20 nm] and in an embodiment 5 nm; the layer of binary alloy M3M4 or ternary alloy M3M4N, and the layer of ternary alloy M3M4O or quaternary alloy M3M4NO, are of thickness comprised in the interval [1 nm; 50 nm] and in an embodiment 20 nm.

(37) Naturally, the invention is not limited to the embodiments described with reference to the figures and alternatives could be envisaged without going beyond the scope of the invention.