Variable Resistance Memory Writing via Intermediate State Segmentation
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Solution Overview
Problem
Conventional variable resistance nonvolatile memory devices face a trade-off between improving retention characteristics and enlarging the window of operation, as increasing the high resistance writing voltage pulse amplitude worsens low resistance state retention, while reducing it decreases the high resistance state resistance value, thereby reducing reliability.
Innovation Solution
A method involving weak writing and normal writing processes that change the variable resistance nonvolatile memory element from a first resistance state to a second state using specific voltage pulses with varying polarities and absolute values, allowing the element to transition through an intermediate resistance state, thereby improving retention characteristics and enlarging the operational window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the high resistance writing voltage pulse amplitude is increased to enlarge the window of operation, then the window of operation is enlarged, but the retention characteristics of the low resistance state worsen
Solution Approach 1:
The patent divides the writing process into two distinct stages: weak writing with a first voltage pulse of lower amplitude, and normal writing with a second voltage pulse of higher amplitude. This segmentation allows the system to first prepare the variable resistance element in a weak writing step, then complete the resistance change in a normal writing step, thereby achieving both enlarged window of operation and maintained retention characteristics
Solution Approach 2:
The patent applies a preliminary weak writing voltage pulse before the normal writing voltage pulse. This preliminary action partially changes the resistance state of the variable resistance element, preparing it for the subsequent normal writing step. By performing this preliminary action, the system can use a lower amplitude pulse first, then complete the transition with a higher amplitude pulse, achieving both goals
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 approach enhances the reliability of variable resistance nonvolatile memory devices by improving retention characteristics and enlarging the operational window, enabling high-speed and large-capacity storage capabilities.
Implementation Method 1
When a voltage that causes the potential of the electrode 1 to exceed the potential of the electrode 2 is applied to the variable resistance element 5, ions of the metal are pulled toward the electrode 2 and enter the insulative film 4. When the ions of the metal reach the electrode 2, the upper and lower electrode 1 and electrode 2 become conductive, resulting in a low resistance state (LR writing).
Implementation Method 2
a variable resistance element including ion conductive variable resistance elements, each of which comprises an insulating film (specifically amorphous Gd2O3) and a conductive film (specifically CuTe)
Data Source
AI summary
Provided is a method of writing to a variable resistance nonvolatile memory element which is capable of both improving retention characteristics and enlarging a window of operation. In the method of writing, to write “1” data (LR), first a weak HR writing process is performed in which a weak HR writing voltage pulse set for changing the variable resistance nonvolatile memory element to an intermediate resistance state is applied and, subsequently, a LR writing process is performed in which a LR writing voltage pulse set for changing the variable resistance nonvolatile memory element from the intermediate resistance state to a LR state is applied.