Nonvolatile memory cell operating by increasing order in polycrystalline semiconductor material
View Patent ↗A nonvolatile memory cell is described, the memory cell comprising a semiconductor diode. The semiconductor material making up the diode is formed with significant defect density, and allows very low current flow at a typical read voltage. Application of a programming voltage permanently changes the nature of the semiconductor material, resulting in an improved diode. The programmed diode allows much higher current flow, in some embodiments one, two or three orders of magnitude higher, at the same read voltage. The difference in current allows a programmed memory cell to be distinguished from an unprogrammed memory cell. Fabrication techniques to generate an advantageous unprogrammed defect density are described. The memory cell of the present invention can be formed in a monolithic three dimensional memory array, having multiple stacked memory levels formed above a single substrate.
1. A method for programming a nonvolatile memory cell, the method comprising:
providing the nonvolatile memory cell by applying the following steps:
forming a first conductor;
forming a second conductor;
depositing and doping semiconductor material to form a semiconductor junction diode, the semiconductor junction diode disposed between the first and second conductors;
crystallizing the semiconductor material such that the semiconductor junction diode is polycrystalline,
wherein, during the crystallizing step, the semiconductor material is not in contact with a template material having a lattice mismatch of less than 12 percent with the semiconductor material; and
programming the memory cell by applying a programming voltage between the first and second conductors,
wherein no resistance-switching element having its resistance changed by application of the programming voltage by more than a factor of two is disposed between the semiconductor junction diode and the first conductor or between the semiconductor junction diode and the second conductor.
2. The method of claim 1 , wherein the semiconductor material is silicon, germanium, or a silicon-germanium alloy.
3. The method of claim 1 , wherein the memory cell does not comprise a dielectric antifuse layer.
4. The method of claim 1 , wherein the memory cell does not comprise a chalcogenide material.
5. The method of claim 1 , wherein, during the crystallization step, the semiconductor material is not in contact with a template material having a lattice mismatch of less than 4 percent with the semiconductor material.
6. The method of claim 1 , wherein, during the crystallizing step, the semiconductor material is in contact with titanium nitride, tungsten nitride, tantalum nitride, tantalum, tungsten, or titanium tungsten.
7. The method of claim 1 , wherein, during the crystallizing step, the semiconductor material is not in contact with titanium silicide, cobalt silicide, or nickel monosilicide.
8. The method of claim 1 , wherein, before the programming step, the diode has a first maximum barrier height, and after the programming step, the diode has a second maximum barrier height, the second maximum barrier height at least 1.5 times the first maximum barrier height.