Multilevel phase change memory
View Patent ↗A multilevel phase change memory may be formed of a chalcogenide material formed between a pair of spaced electrodes. The cross-sectional area of the chalcogenide material may decrease as the material extends from one electrode to another. As a result, the current density decreases from one electrode to the other. This means that a higher current is necessary to convert the material that has the largest cross-sectional area. As a result, different current levels may be utilized to convert different amounts of the chalcogenide material to the amorphous or reset state. A distinguishable resistance may be associated with each of those different amounts of amorphous material, providing the opportunity to engineer a number of different current selectable programmable states.
1. A phase change memory comprising:
a bottom electrode;
a top electrode;
a dielectric material having a pore, tapering inwardly in at least three distinct steps as the dielectric material extends from said bottom electrode; and
a chalcogenide material between said electrodes.
2. The phase change memory of claim 1 wherein said material tapers inwardly in at least two discrete steps.
3. The phase change memory of claim 1 including at least two cylinders of chalcogenide material having a common axis, said cylinders having different cross-sectional areas.
4. The phase change memory of claim 3 including having three cylinders of different cross-sectional areas but having a common axis.
5. The phase change memory of claim 1 including a first material surrounding a first chalcogenide region and a second material surrounding a second chalcogenide region.
6. The phase change memory of claim 5 wherein said first and second chalcogenide regions have different cross-sectional areas.
7. The phase change memory of claim 6 including a first chalcogenide region of smaller cross-sectional area and a second chalcogenide region of larger cross-sectional area, a first material with a first heat transfer coefficient surrounding said first chalcogenide region and a second material having a coefficient of heat transfer lower than said first heat transfer coefficient surrounding said second chalcogenide region.
8. The phase change memory of claim 1 including cells having four programmable states including three amorphous states and one crystalline state.
9. The phase change memory of claim 8 including a chalcogenide material surrounded by three layers having different thermal transfer coefficients.
10. The phase change memory of claim 1 wherein said chalcogenide material includes three regions having distinctly different resistance values.
11. A phase change memory comprising:
a pair of spaced electrodes;
a dielectric material having a pore, said pore tapering inwardly as the material extends from one of said electrode to the other of said electrodes;and
a chalcogenide material between said electrodes, said material including:
a first chalcogenide region of smaller cross-sectional area and a second chalcogenide region of larger cross-sectional area, a first material with a first heat transfer coefficient surrounding said first chalcogenide region and a second material having a coefficient of heat transfer lower than said first heat transfer coefficient surrounding said second chalcogenide region.
12. The memory of claim 11 wherein said pore tapers from a top to a bottom electrode.
13. The memory of claim 11 including at least three different current densities along the length of said chalcogenide material.
14. The memory of claim 11 including a third chalcogenide region larger in cross-sectional area that said second chalcogenide region.