Phase Change Memory Cycling Endurance via Reverse Repair Pulses
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Phase change memory devices experience a decrease in cycling endurance due to repetition of writing and erasure operations, leading to an unwritable state caused by changes in the composition of the phase change material resulting from heat and high current, which induces thermal atomic diffusion and electromigration.
Innovation Solution
A phase change memory apparatus and programming method that includes a pulse generator supplying writing, erasure, and reverse repair current pulses, where the reverse repair current pulse has a polarity opposite to the writing and erasure pulses, and is used to move elements of the phase change material back to their initial states, thereby repairing the cycling endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If writing and erasure operations are repeated, then data can be stored and retrieved multiple times, but cycling endurance decreases due to composition changes in phase change material
Solution Approach 1:
The patent applies reverse repair current pulses with polarity opposite to the writing and erasure pulses. These reverse pulses induce electromigration in the opposite direction to compensate for the compositional changes caused by normal operations, thereby restoring the phase change material's properties and extending cycling endurance
Solution Approach 2:
The patent implements a feedback mechanism where the control unit monitors the state of phase change memory devices and selectively applies reverse repair current pulses based on detected conditions. This feedback-based approach allows the system to compensate for degradation effects and maintain reliable operation over extended cycling periods
2Speed
If high current is applied for writing and erasure operations, then phase change can be achieved quickly, but electromigration causes atomic movement and composition changes
Solution Approach 1:
The patent converts the harmful electromigration effect into a beneficial process by using reverse repair current pulses. The same electromigration mechanism that causes compositional degradation during normal operations is harnessed to restore the phase change material composition, turning the harmful effect into a restorative mechanism
Solution Approach 2:
The patent changes the parameter of current polarity by introducing reverse repair current pulses with opposite polarity to the writing and erasure pulses. This parameter change allows the system to induce electromigration in the opposite direction, compensating for the compositional changes caused by high-current normal operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The reverse repair current pulse significantly improves the cycling endurance of phase change memory devices by returning moved elements to their initial states, maintaining performance similar to the initial state even after repeated operations.
Implementation Method 1
The reverse repair current pulse may be of such a size that resultant Joule heat and electromigration may cause movement of elements of a phase change material in the phase change memory devices
Implementation Method 2
Heat and high current lead to thermal atomic diffusion or collision against electrons at high temperature, resulting in electromigration. The electromigration causes the movement of atoms of the phase change material
Implementation Method 3
During the writing operation, the phase change material is heated to a melting point or more using Joule heat produced by an electrical pulse
Implementation Method 4
Phase change memory devices use as nonvolatile data a difference in electrical resistivity due to a reversible phase change between amorphous and crystalline in a phase change material
Data Source
AI summary
A phase change memory apparatus includes a phase change memory array in which a plurality of phase change memory devices are arranged, and a pulse generator that supplies a writing current pulse, an erasure current pulse, and a reverse repair current pulse to the phase change memory devices in the phase change memory array. The reverse repair current pulse has opposite direction to the writing current pulse and the erasure current pulse of the phase change memory devices, and is of such a size that resultant Joule heat and electromigration move the elements of the reverse repair current pulse. The reverse repair current pulse has a width equal to or more than a smaller one of duration of a normal writing operation and duration of a normal erasure operation.