Auto-Referenced Memory Cell Reads Using Statistical Reference Voltage
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Solution Overview
Problem
Memory cells exhibit non-uniform, variable electrical characteristics due to factors like statistical process variations and cycling events, leading to unreliable read operations, especially in 3D XPoint memory cells, as separate read-reference memory cells often do not possess common electrical characteristics with user data memory cells.
Innovation Solution
An auto-referenced read technique that determines a reference voltage based on statistical properties of memory cells, such as standard deviation and median threshold voltages, to accurately identify logic states by encoding user data to ensure a specific weight pattern and applying a voltage that increases monotonically to trigger switching events, allowing for reliable identification of memory cells with logic state 1 or 0.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate read-reference memory cells are used, then read operations can be performed, but reliability is reduced because read-reference memory cells do not possess common electrical characteristics with user data memory cells
Solution Approach 1:
The patent merges the read-reference functionality with user data memory cells by storing both user data and reference data in the same memory cells. This eliminates the need for separate read-reference memory cells and ensures that both data types share common electrical characteristics, thereby improving read operation reliability while reducing device complexity.
Solution Approach 2:
The memory cells are designed to serve multiple functions: storing user data, storing reference data, and enabling read operations. By making the memory cells universal and capable of handling both user data and reference data, the patent eliminates the need for specialized read-reference memory cells and improves reliability through consistent electrical characteristics.
2Manufacturing precision
If memory cells exhibit variable electrical characteristics, then manufacturing variations occur, but read accuracy deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where reference data is read from the same memory cells along with user data, and the read reference voltage is adjusted based on the reference data values. This feedback loop compensates for manufacturing variations and electrical characteristic differences, thereby improving read accuracy despite variations in memory cell properties.
Solution Approach 2:
The patent dynamically adjusts the read reference voltage parameter based on the actual electrical characteristics of the memory cells and the reference data values. By changing the reference voltage parameter to match the actual cell characteristics, the system compensates for manufacturing variations and maintains high read accuracy.
3Measurement precision
If encoding is applied to ensure weight pattern, then read accuracy improves, but device complexity increases
Solution Approach 1:
The patent combines the encoding and decoding functions within the memory controller, utilizing the same hardware resources to perform both operations. The encoding process applies weight patterns to user data before storage, while the decoding process uses reference data to verify and correct read values. This integrated approach improves logic state identification accuracy while minimizing additional device complexity.
Data Source
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AI summary
Methods, systems, and devices related to auto-referenced memory cell read techniques are described. The auto-referenced read may encode user data to include a certain number bits having a first logic state prior to storing the user data in memory cells. Subsequently, reading the encoded user data may be carried out by applying a read voltage to the memory cells while monitoring a series of switching events by activating a subset of the memory cells having the first logic state. The auto-referenced read may identify a particular switching event that correlates to a median threshold voltage value of the subset of the memory cells. Then, the auto-referenced read may determine a reference voltage that takes into account a statistical property of threshold voltage distribution of the subset of the memory cells. The auto-referenced read may identify a time duration to maintain the read voltage based on determining the reference voltage.