Reading a phase change memory
View Patent ↗A phase change memory cell may be read by driving a current through the cell higher than its threshold current. A voltage derived from the selected column may be utilized to read a selected bit of a phase change memory. The read window or margin may be improved in some embodiments. A refresh cycle may be included at periodic intervals.
1. A method comprising:
reading a cell on a line by triggering the phase change memory cell;
providing a reference level from said line;
comparing said reference level to a level on said line after a time delay;
using a reference level derived from the voltage on the line; and
comparing the reference voltage generated before a read current to the selected line is reduced, to a reference voltage generated on the selected line after the read current is reduced and then increased.
2. The method of claim 1 including obtaining said reference level when said cell is in a dV/dI region.
3. The method of claim 2 including storing said reference level from the line for comparison to a level on said line at a later time.
4. The method of claim 3 including comparing said levels after turning off the current to said address line.
5. The method of claim 1 wherein reading a cell on a line includes driving a line current greater than the threshold current of said cell.
6. The method of claim 5 including using a cell with a phase change memory element and a threshold device and driving a column current greater than the threshold current of said element.
7. The method of claim 6 including using a chalcogenide threshold device that is not programmable.
8. The method of claim 1 including refreshing said cell after reading said cell.