Methods for forming memory devices with reduced operational energy in phase change material
Methods of forming and operating phase change memory devices include adjusting an activation energy barrier between a metastable phase and a stable phase of a phase change material in a memory cell. In some embodiments, the activation energy barrier is adjusted by applying stress to the phase change material in the memory cell. Memory devices include a phase change memory cell and a material, structure, or device for applying stress to the phase change material in the memory cell. In some embodiments, a piezoelectric device may be used to apply stress to the phase change material. In additional embodiments, a material having a thermal expansion coefficient greater than that of the phase change material may be positioned to apply stress to the phase change material.
1. A method of fabricating a memory device, comprising:
selectively stressing a phase change material in at least one memory cell of a partially fabricated semiconductor device to reduce a magnitude of an activation energy barrier between different phases of the phase change material, comprising:
inducing strain in a piezoelectric material using an electric field to expand or contract the piezoelectric material in a direction; and
using the induced strain in the piezoelectric material to stress the phase change material;
completing fabrication of the memory device; and
retaining the stress in the phase change material at least until fabrication of the memory device is complete.
2. The method of claim 1 , wherein selectively stressing the phase change material comprises stressing the phase change material to a stress of about 100 MPa or more.
3. The method of claim 1 , wherein selectively stressing the phase change material comprises reducing the magnitude of the activation energy barrier by about 0.05 eV or more.
4. The method of claim 1 , further comprising selecting the phase change material to comprise GeSbTe.
5. The method of claim 1 , wherein selectively stressing the phase change material comprises reducing the magnitude of the activation energy barrier.
6. The method of claim 1 , further comprising selecting the piezoelectric material from the group consisting of quartz, gallium orthophosphate (GaPO 4 ), barium titanate (BaTiO 3 ), lead titanate (PbTiO 3 ), lead zirconate titanate (PZT) (Pb[Zr x Ti 1-x ]O 3 , wherein 0<x<1), and lithium tantalate (LiTaO 3 ).
7. The method of claim 1 , further comprising disposing the piezoelectric material laterally beside the phase change material.
8. The method of claim 7 , wherein the piezoelectric material has a crystal structure oriented such that, when an electrical field is provided within the piezoelectric material, the piezoelectric material expands or contracts in the lateral direction.
9. The method of claim 1 , further comprising providing a dielectric material between the piezoelectric material and the phase change material, the dielectric material physically isolating the piezoelectric material from the phase change material.
10. A method of fabricating a memory device, comprising:
selectively stressing a phase change material in at least one memory cell of a partially fabricated semiconductor device to reduce a magnitude of an activation energy barrier between different phases of the phase change material, the selectively stressing comprising:
selecting a thermal expansion material comprising benzocyclobutene;
inducing strain in the thermal expansion material by at least one of heating and cooling the thermal expansion material; and
using the induced strain in the thermal expansion material to stress the phase change material;
completing fabrication of the memory device; and
retaining the stress in the phase change material at least until fabrication of the memory device is complete.
11. The method of claim 10 , further comprising selecting the thermal expansion material to exhibit a coefficient of thermal expansion that is at least about one and one-half (1.5) times a maximum coefficient of thermal expansion exhibited by the phase change material.
12. The method of claim 10 , further comprising disposing the thermal expansion material laterally adjacent the phase change material.