Resistance Change Memory Read Stability via Self-Reference Circuit
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Solution Overview
Problem
The existing memory devices face instability in read operations when the read current is less than the hold current, leading to oscillation of the voltage applied to the memory cell, making it difficult to determine the resistance state accurately.
Innovation Solution
The memory device employs a determination circuit that performs a first read operation to set a reference resistance state and a second read operation to determine the actual resistance state by comparing the voltage differences, ensuring stable read operations by eliminating parasitic resistances and using self-reference read methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If read current is used to read the resistance state, then read operation can be performed, but voltage oscillation occurs when read current is less than hold current, making accurate determination difficult
Solution Approach 1:
The patent applies preliminary action by performing a first read operation to set a reference resistance state before performing the second read operation to determine the actual resistance state. This preliminary setting of reference state eliminates the need for external reference circuits and prevents voltage oscillation during the determination phase, as the reference state is already established in the memory cell itself.
Solution Approach 2:
The patent implements self-service through the self-reference read method where the memory cell uses its own previously set reference resistance state as the reference for determination. The determination circuit compares the voltage from the actual resistance state with the voltage from the reference resistance state stored in the same memory cell, eliminating dependency on external reference circuits and achieving stable operation without voltage oscillation.
2Measurement precision
If conventional read method is used, then read operation can be performed, but parasitic resistances affect measurement accuracy
Solution Approach 1:
The patent extracts the reference resistance state from external reference circuits and stores it within the memory cell itself. By taking out the reference function from external circuits and embedding it in the memory cell, the patent eliminates the parasitic resistances associated with external reference circuits, achieving accurate voltage measurement without the harmful influence of parasitic resistance.
3Quantity of substance
If resistance change memory element is used, then high-density storage is achieved, but read operation becomes unstable when read current is low
Solution Approach 1:
The patent applies preliminary action by setting the reference resistance state in advance during the first read operation. This preliminary action ensures that when the second read operation is performed with low read current, the reference state is already established, preventing voltage oscillation and ensuring stable read operation while maintaining the high-density storage capability of the resistance change memory element.
Solution Approach 2:
The patent implements feedback by using the voltage difference between the actual resistance state and the reference resistance state to determine the stored data. The determination circuit receives feedback from the voltage comparison and uses it to accurately determine the resistance state, ensuring stable read operation even when read current is lower than the hold current, thus maintaining reliability while preserving high memory density.
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 prevents voltage oscillation and allows for accurate determination of the resistance state, ensuring stable read operations even when the read current is less than the hold current, and simplifies the read process by using self-reference voltages.
Implementation Method 1
a resistance change memory element to which a low-resistance state or a high-resistance state can be set
Implementation Method 2
the switching element possesses characteristics that when a voltage applied between two terminals thereof increases to reach a first voltage, the switching element makes a transition from an off-state to an on-state
Data Source
AI summary
According to one embodiment, a memory device includes first and second wiring lines, a memory cell connected between the first and second wiring lines and including a resistance change memory element and a switching element connected in series to the resistance change memory element, and a determination circuit determining a determination object resistance state set in advance to the resistance change memory element based on a determination object voltage applied to the second wiring line when the switching element makes a transition from an on-state to an off-state.