Process for manufacturing a phase change material with a crystallographic structure of layers separated by van der Waals pseudo-gaps

1 . A method for manufacturing a phase change stack, the method comprising:

forming an orientation layer, configured to orient the phase change stack about a crystallographic axis c; and, thereafter

forming a phase change stack on a surface of a substrate, comprising (i) forming a first layer comprising a first material A, and (ii) forming a second layer, comprising a second material B, different from the first material A, on the first layer; and

after the forming of the phase change stack, first curing annealing such that the phase change stack has, after the curing annealing, a once-annealed nominal-defect rate less than 50% of an initial defect rate of the phase change stack, taken before the curing annealing,

wherein the phase change stack has a crystallographic structure made of layers separated by van der Waals pseudo-gaps and comprises:

the first layer of the first material A, and

the second layer of the second material B, and

wherein the forming of the phase change stack is done on a surface of the orientation layer.

2 . The method of claim 1 , further comprising, after the first curing annealing:

determining a defect rate in the phase change stack based on an X-ray diffraction (XRD) measurement.

3 . The method of claim 2 , further comprising:

second curing annealing if the defect rate in the determining is greater than the once-annealed defect rate.

4 . The method of claim 1 , further comprising, after the first curing annealing:

carrying out a plurality of stack integrations, to form a phase change device with a basis of the phase change stack.

5 . The method of claim 1 , wherein parameters of the first curing annealing are chosen such that the phase change stack has, after the first curing annealing, a once-annealed defect rate less than 60% of an initial defect rate of the phase change stack, taken before the first curing annealing.

6 . The method of claim 1 , further comprising, after the forming of the phase change stack and before the first curing annealing:

forming an upper electrode layer on the phase change stack.

7 . The method of claim 1 , wherein the material A is a two-dimensional material comprises a transition metal dichalcogenide of formula MX 2 , with M being Mo or W and X being S, Se, or Te, graphene, benzene, phosphorene, germanene, silicene, stanene, borophene, h-BN, or a two-dimensional chalcogenide alloy.

8 . The method of claim 1 , wherein the first layer comprising the material A and/or the second layer comprising the material B are deposited by van der Waals epitaxy.

9 . The method of claim 1 , wherein the first curing annealing is carried out at a temperature less than or equal to 500° C.

10 . The method of claim 9 , wherein the temperature of the first curing annealing is greater than a maximum stack formation temperature.

11 . The method of claim 9 , wherein the temperature of the first curing annealing is greater than 300° C.

12 . The method of claim 1 , wherein the orientation layer comprises Sb 2 Te 3 or Bi 2 Te 3 -based, and has a thickness less than or equal to 10 nm.

13 . The method of claim 1 , wherein the forming of the first and second layers comprises depositing the materials A and B and in amorphous form,

wherein the forming of the phase change stack further comprises, after the depositing of the materials A and B in amorphous form:

crystallization annealing carried out at a temperature less than or equal to 300° C.

14 . The method of claim 1 , wherein the forming of the phase change stack comprises a plurality of formations of first alternate layers with a plurality of formations of second layers ( 22 ), such that the phase change stack is a multilayer structure comprising a plurality of first and second alternate layers.

15 . The method of claim 14 , wherein at least one of the first layers have different thicknesses, and/or at least one of the second layers have different thicknesses, such that the multilayer structure of the phase change stack is aperiodic.

16 . The method of claim 1 , wherein the substrate comprises a lower electrode configured to make a phase change of the phase change stack.

17 . The method of claim 1 , wherein each van der Waals pseudo-gap separating two layers of the crystallographic structure is formed as a spacing between two pure planes of one same atom type, and

wherein the spacing has a dimension normal to the planes less than or equal to twice a van der Waals radius of the atom type.

18 . The method of claim 4 , wherein the phase change device is a phase change memory or a thermoelectric converter.

19 . The method of claim 1 , wherein parameters of the first curing annealing are chosen such that the phase change stack has, after the first curing annealing, a once-annealed defect rate less than 20% of an initial defect rate of the phase change stack, taken before the first curing annealing.

20 . A method for manufacturing a phase change stack, the method comprising:

forming a phase change stack on a surface of a substrate, comprising (i) forming a first layer comprising a first material A, and (ii) forming a second layer, comprising a second material B, different from the first material A, on the first layer; and

after the forming of the phase change stack, first curing annealing such that the phase change stack has, after the curing annealing, a once-annealed defect rate less than 50% of an initial defect rate of the phase change stack, taken before the curing annealing,

wherein the phase change stack has a crystallographic structure made of layers separated by van der Waals pseudo-gaps and comprises:

the first layer of the first material A, and

the second layer of the second material B,

wherein each van der Waals pseudo-gap separating two layers of the crystallographic structure is formed as a spacing between two pure planes of one same atom type, and

wherein the spacing has a dimension normal to the planes less than or equal to twice a van der Waals radius of the atom type.