Device and method for pulse width control in a phase change memory device

DETAILED DESCRIPTION The invention is directed to an approach to programming phase-change memory devices, such as chalcogenide memory (PRAM).
The invention is directed to an approach to programming PRAM elements from a reset state to a set state or from a set state to the set state.
The invention provides a novel and nonobvious PRAM device and method in which a set pulse duration time is controlled by monitoring the state of the memory element during programming such as by comparing the voltage of a bit line with a reference voltage or comparing the cell resistance with a set state cell resistance.
The duration of the set pulse is controlled in response to the detected state of the memory element.
The result of the approach of the invention is the significant reduction in PRAM programming errors, such as those caused by a constant-duration set pulse, as well as reduction in programming time duration and power consumption.
In one aspect, the invention is directed to a method of programming a semiconductor memory device.
According to the method of the invention, a set pulse is applied to the memory device.
While the set pulse is applied, a state of the memory device is detected.
When the memory device is determined to be in a desired set state, the set pulse is removed, such that duration of the set pulse is controlled based on the state of the memory device.
In one embodiment, when the memory device is in a reset state, a programmable material of the memory device is in an amorphous state.
Also, when the memory device is in the set state, a programmable material of the memory device is in a crystalline state.
When the memory device is in a reset state, a programmable material of the memory device is in an amorphous state.
Detecting a state of the memory device can include detecting a resistance in the device.
The detected resistance comprises resistance in a programmable material of the memory device.
In one embodiment, resistance of the programmable material in an amorphous state of the programmable material is higher than resistance of the programmable material in a crystalline state of the programmable material