Variable Resistance Memory Device Current Steering Forming Control
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Solution Overview
Problem
In nonvolatile memory devices with variable resistance elements, the forming operation often results in an excessively large current flow, causing the resistance value to fall too low, making it difficult to perform subsequent normal writing operations due to the high initial breakdown voltage required.
Innovation Solution
A crosspoint nonvolatile memory device design that includes a write circuit generating bipolar voltage and incorporates a current steering element connected in series with the variable resistance element, limiting currents during the forming operation by controlling the voltage polarity and current values, thereby stabilizing the resistance state change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high initial breakdown voltage is applied to the variable resistance element during the forming operation, then the resistance value changes from an initial high state to a usable low state, but an excessively large current flows causing the resistance value to fall too low
Solution Approach 1:
A current steering element is introduced as an intermediary component between the variable resistance element and the external circuit. This current steering element actively controls and limits the current flowing through the variable resistance element during the forming operation, preventing excessive current while still allowing the necessary breakdown voltage to be applied for resistance state change.
Solution Approach 2:
The current steering element dynamically adjusts the current parameter during the forming operation. By changing the current limiting characteristic based on the operating conditions, it allows high voltage to be applied for forming while preventing the current from exceeding safe levels that would cause the resistance value to fall too low.
2Productivity
If the resistance value falls too low after the forming operation, then the forming operation completes, but subsequent normal writing operations cannot be performed due to insufficient voltage margin
Solution Approach 1:
The current steering element acts as a protective intermediary that prevents the resistance value from falling below a usable threshold. By limiting the current during forming, it ensures the resistance reaches a stable low state that maintains sufficient voltage margin for subsequent normal writing operations.
Solution Approach 2:
The current steering element provides beforehand cushioning by pre-establishing current limits before the forming operation completes. This prevents the resistance value from dropping too low in the first place, cushioning against the harmful effect of excessive current and ensuring the resistance remains in a usable range for future 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
This approach effectively limits current during the forming operation, preventing excessive resistance value drops and ensuring stable operation for subsequent writing processes.
Implementation Method 1
The resistance value of the variable resistance element is changed when the redox state of a variable resistance material is changed directly by electrical stimulation, i.e., through the gain or lose of electrons.
Implementation Method 2
a current steering element having a characteristic of limiting a current when a voltage is applied in a direction in which a resistance value is changed from a high resistance state to a low resistance state
Data Source
AI summary
Provided is a variable resistance element (Rij) the resistance state of which is reversibly changed by applying electrical signals of different polarities; and a current steering element (Dij) in which a first current is larger than a second current, the first current being a current which flows when a voltage of the first polarity having a first value is applied, the first value being less than a predetermined voltage value and having an absolute value greater than zero, the second current being a current which flows when a voltage of the second polarity having an absolute value which is the first value is applied, the second polarity being different from the first polarity, in which Rij and Dij are connected in series such that the polarity of a voltage to be applied to Dij is the second polarity when the resistance state of Rij is changed to high resistance state.