Variable Resistance Memory Writing Using Preliminary Voltage Pulse
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Solution Overview
Problem
Conventional variable resistance nonvolatile memory devices using bipolar ReRAM experience writing failures due to insufficient writing conditions, where the resistance value changes after verification, causing bits to fall below the threshold level, leading to reliability issues.
Innovation Solution
A variable resistance nonvolatile memory element writing method that applies a preliminary voltage pulse different in polarity and smaller in absolute value than the main voltage pulse to stabilize the resistance change, ensuring the memory element remains within the desired resistance state, even after multiple rewrite cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a verification operation and additional writing are performed in conventional bipolar ReRAM, then the resistance value changes, but the resistance value drops below the threshold level causing writing failure
Solution Approach 1:
The patent applies a preliminary voltage pulse before the main writing voltage pulse to prepare the memory element for stable resistance change. This preliminary action modifies the initial state of the variable resistance layer, ensuring that subsequent verification and additional writing operations maintain the resistance value above the threshold level, thereby preventing writing failures.
Solution Approach 2:
The patent changes the voltage pulse parameters by introducing a preliminary pulse with specific voltage magnitude and duration before the main writing pulse. This parameter modification allows precise control of the resistance change process, maintaining the resistance value within the desired operating window even after verification and additional writing operations.
2Productivity
If multiple rewrite cycles are performed, then the memory device operates faster, but the resistance value becomes unstable and falls below threshold
Solution Approach 1:
By applying a preliminary voltage pulse before each rewrite operation, the method prepares the memory element to maintain stable resistance changes even after multiple rewrite cycles. This preliminary action ensures that the resistance value remains above the threshold level throughout repeated operations, enabling fast rewriting without stability degradation.
Solution Approach 2:
The patent incorporates verification operations that monitor the resistance value after writing. When combined with the preliminary voltage pulse approach, this feedback mechanism allows the system to detect and correct potential resistance drift before it causes writing failures, thereby maintaining stability across multiple rewrite cycles.
3Reliability
If a high voltage pulse is applied to change resistance state, then the writing operation is effective, but the operating window becomes insufficient
Solution Approach 1:
The patent segments the writing operation into two distinct voltage pulse phases: a preliminary pulse with lower voltage to initiate the resistance change process, and a main writing pulse with higher voltage to complete the transition. This segmentation allows the memory element to maintain a sufficient operating window while ensuring effective writing, as each pulse phase serves a specific function in the resistance change process.
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
This method improves the reliability and stability of the writing operation by maintaining an appropriate operating window, preventing the resistance value from dropping below the threshold, thus enhancing the endurance and reliability of the nonvolatile memory device.
Implementation Method 1
the variable resistance layer includes an oxygen-deficient first transition metal oxide layer that is in contact with the first electrode, and a second transition metal oxide layer that is in contact with the second electrode and is lower in oxygen deficiency than the first transition metal oxide layer
Data Source
AI summary
A variable resistance nonvolatile memory element writing method of, by applying a voltage pulse to a memory cell including a variable resistance element, reversibly changing the variable resistance element between a first resistance state and a second resistance state according to a polarity of the applied voltage pulse is provided. The variable resistance nonvolatile memory element writing method includes applying a first preliminary voltage pulse and subsequently applying the first voltage pulse to the variable resistance element to change the variable resistance element from the second resistance state to the first resistance state, the first preliminary voltage pulse being smaller in voltage absolute value than the second threshold voltage and different in polarity from the first voltage pulse.