Nonvolatile Storage Self-Reference Reading Circuit
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Solution Overview
Problem
Existing nonvolatile storage devices do not perform read operations efficiently due to challenges in maintaining the two-terminal selector element in an ON state during reading and writing periods, leading to variations in resistance values and threshold voltage inconsistencies.
Innovation Solution
The implementation of a self-reference reading method with a constant current circuit that ensures current flows in the same direction during reading and writing periods, combined with an offset circuit for accurate voltage comparison, maintains the two-terminal selector element in an ON state and stabilizes resistance states, enabling efficient data reading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional reading method is used in nonvolatile storage devices, then the device structure is simple, but the reading operation is inefficient due to variations in resistance values and threshold voltage inconsistencies
Solution Approach 1:
The patent changes the reading method from conventional voltage-based reading to a current-based self-reference reading method. By applying a constant current through the memory cell and measuring the voltage drop, the system achieves more reliable reading operation. The parameter change involves using current as the controlled variable during reading operations to maintain consistency despite resistance variations.
Solution Approach 2:
The patent implements a self-reference reading method where the reading operation uses feedback from the memory cell's own state. By reading the memory cell twice (once before and once after writing) and comparing the results, the system compensates for resistance variations and threshold voltage inconsistencies. This feedback mechanism ensures reliable reading operation.
2Adaptability or versatility
If the two-terminal selector element transitions between ON and OFF states during reading and writing periods, then the device can perform both read and write operations, but resistance value variations occur leading to reading inaccuracies
Solution Approach 1:
The patent performs a preliminary reading operation before the writing operation to capture the initial state of the memory cell. This preliminary action allows the system to later compare the pre-write and post-write states, accurately determining whether data was successfully written. The preliminary reading compensates for any resistance variations that occur during state transitions.
Solution Approach 2:
The patent uses periodic reading operations (reading before write, then reading after write) to monitor the memory cell state. This periodic action ensures that even if the selector element transitions states during operations, the system can still accurately determine the memory cell's resistance state by comparing multiple readings taken at different periods.
3Adaptability or versatility
If current direction changes between reading and writing periods, then the device can support different operation modes, but the two-terminal selector element may enter OFF state causing operation failures
Solution Approach 1:
The patent dynamically adjusts the current direction based on the operation mode. During reading operations, current flows in one direction to maintain the selector element in ON state, while during writing operations, the current direction is adjusted to achieve the desired write effect. This dynamic adaptation ensures the selector element remains operational throughout different operation modes.
Solution Approach 2:
The patent changes the current direction parameter dynamically based on the operation being performed. By controlling the polarity and direction of the applied current, the system can switch between read and write modes while maintaining selector element conductivity. This parameter change ensures continuous reliable operation across different modes.
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 allows for reliable and efficient data reading by maintaining the two-terminal selector element in an ON state and stabilizing resistance states, improving reading accuracy and preventing OFF state issues during transitions between reading and writing periods.
Implementation Method 1
a variable resistance storage element capable of being set to a low resistance state or a high resistance according to a value of data stored in the memory cell
Implementation Method 2
a two-terminal switching element by which the variable resistance storage element is selected
Data Source
AI summary
A nonvolatile storage device includes a first wiring extending in a first direction, a second wiring extending in a second direction, a memory cell between the first and second wirings, a reading circuit configured to read data from the memory cell during a first and a second reading period, a writing circuit configured to write reference data into the memory cell during a writing period between the first and second reading periods, and a determination circuit configured to compare a first voltage which is based on the data read during the first reading period with a second voltage which is based on the data read during the second reading period, to determine the value of the data read during the first reading period. A current is caused to flow in the memory cell during the first reading period, the writing period, and the second reading period.