Method for preparing a thin layer of ferroelectric material
A method for preparing a monodomain thin layer of ferroelectric material comprises: implanting light species in a ferroelectric donor substrate in order to form an embrittlement plane and to define a first layer therein; assembling the donor substrate with a support substrate by means of a dielectric assembly layer; and fracturing the donor substrate at the embrittlement plane. The dielectric assembly layer comprises an oxide having a hydrogen concentration lower than that of the first layer or preventing the diffusion of hydrogen to the first layer, or the dielectric assembly layer comprises a barrier preventing the diffusion of hydrogen to the first layer. A heat treatment of a free face of the first layer is used to diffuse the hydrogen contained therein and cause the multidomain transformation of a surface portion of this first layer, followed by a thinning of the first layer in order to remove the surface portion.
1. A method for preparing a thin monodomain layer of ferroelectric material, comprising:
implanting light species in a first face of a ferroelectric donor substrate to form an embrittlement plane and define a first layer between the embrittlement plane and the first face of the ferroelectric donor substrate;
assembling the first face of the ferroelectric donor substrate to a support substrate using a dielectric assembly layer;
fracturing the ferroelectric donor substrate at the embrittlement plane to transfer the first layer onto the support substrate and expose a free face of the first layer; and
finishing the first layer, the finishing comprising a heat treatment of the free face of the first layer, followed by thinning of the first layer to form the thin monodomain layer;
wherein the dielectric assembly layer comprises an oxide preventing diffusion of hydrogen toward the first layer, or the dielectric assembly layer comprises a barrier preventing diffusion of hydrogen toward the first layer.
2. The method of claim 1 , wherein the thinning of the first layer comprises a chemical-mechanical polishing applied to the free face of the first layer.
3. The method of claim 1 , wherein the heat treatment is carried out at a temperature between 300° C. and the Curie temperature of the ferroelectric material making up the first layer, and for a period of between 30 minutes and 10 hours.
4. The method of claim 1 , wherein the heat treatment is carried out under an oxidizing or neutral gaseous atmosphere.
5. The method of claim 1 , wherein the donor substrate comprises a ferroelectric material chosen from LiTaO 3 or LiNbO 3 .
6. The method of claim 1 , wherein the ferroelectric material has a crystal direction of between 30° and 60° RY.
7. The method of claim 1 , wherein the support substrate comprises silicon.
8. The method of claim 1 , wherein the donor substrate is a block of solid material.
9. The method of claim 1 , wherein the donor substrate comprises a thick layer of ferroelectric material positioned on a manipulator substrate.
10. The method of claim 9 , wherein the manipulator substrate has a thermal expansion coefficient identical or close to a thermal expansion coefficient of the support substrate.
11. The method of claim 1 , wherein a material of the first layer and a material of the support substrate have different thermal expansion coefficients.
12. The method of claim 1 , wherein the dielectric assembly layer comprises an oxide having nitrogen in a nitrogen/oxygen ratio greater than or equal to 0.01 or 0.05.
13. The method of claim 1 , wherein the dielectric assembly layer comprises a silicon oxide having nitrogen in a nitrogen/oxygen ratio of between 0.01 and 0.25.
14. The method of claim 1 , wherein the dielectric assembly layer comprises a stack of layers including a first oxide layer disposed on a side of the stack of layers adjacent the support substrate and a layer of silicon nitride disposed on a side of the stack of layers adjacent the first layer.
15. A device, comprising:
a thin fully monodomain layer of a ferroelectric material layer;
a dielectric assembly layer in contact with the thin layer and comprising an oxide preventing the diffusion of hydrogen toward the thin layer, or comprising a barrier preventing the diffusion of hydrogen toward the thin layer; and
a support substrate in contact with the dielectric layer.
16. The device of claim 15 , wherein the support substrate includes a charge trapping layer between a solid part of the support substrate and the dielectric assembly layer.
17. The device of claim 15 , wherein the dielectric assembly layer comprises an oxide having nitrogen in a nitrogen/oxygen ratio greater than or equal to 0.01 or 0.05.
18. The device of claim 15 , wherein the dielectric assembly layer comprises a silicon oxide having nitrogen in a nitrogen/oxygen ratio of between 0.01 and 0.25.
19. The device of claim 15 , wherein the dielectric assembly layer comprises a stack of layers including a first oxide layer on the side of the support substrate and a layer of silicon nitride on the side of the first layer.