Read Reference Voltage Control for Aging Non-Volatile Memory
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Solution Overview
Problem
Non-volatile memory (NVM) devices face finite lifespan and data retention issues, leading to changes in required read reference voltage over time, which existing solutions like moving read reference (MRR) voltage adjustments can't fully address due to iterative processes causing memory controller delays and unpredictable usage patterns.
Innovation Solution
Implementing a persistent moving read reference voltage system that uses error checking and correction feedback data to adjust voltages, combining temporary MRR adjustments with a persistent MRR algorithm to stabilize voltage levels for future reads, based on past usage patterns and device history, to minimize ECC errors and extend NVM device lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iterative moving read reference (MRR) voltage adjustment is used to compensate for device degradation, then data read reliability is improved, but memory controller delays increase due to the iterative feedback process
Solution Approach 1:
The patent pre-calculates and stores the optimal read reference voltage in a lookup table based on program count thresholds before actual read operations occur. When a read operation is needed, the controller simply queries the lookup table using the current program count, eliminating the need for iterative voltage adjustments during the read operation itself. This preliminary preparation resolves the contradiction by providing reliable voltage compensation without causing delays during critical read operations.
Solution Approach 2:
The patent anticipates future voltage drift by pre-establishing voltage compensation values in the lookup table corresponding to different program count thresholds. By preparing these compensation values in advance, the system cushions against the inevitable voltage degradation that will occur over time, ensuring that when reads are performed, the correct compensating voltage is already available without requiring iterative adjustments during the actual read operation.
2Reliability
If read reference voltage is adjusted to compensate for device aging and degradation, then data retention is improved, but device complexity increases due to additional voltage control logic
Solution Approach 1:
The patent creates a simplified copy of the voltage adjustment functionality by implementing a lookup table that stores pre-calculated voltage compensation values. Instead of implementing complex real-time voltage adjustment logic, the system copies the essential compensation data into a straightforward table structure that can be queried efficiently. This approach maintains data retention reliability while significantly reducing the complexity of the voltage control logic required to implement it.
Solution Approach 2:
The patent changes the control parameter from dynamic real-time voltage adjustment to discrete voltage levels selected from a lookup table based on program count thresholds. By transforming the continuous voltage control problem into a discrete parameter selection problem, the system achieves effective compensation for device aging while using simpler control logic that only needs to select from predefined voltage values rather than continuously adjust them.
3Productivity
If manufacturing reference voltages are configured based on expected usage models, then initial performance is optimized, but actual performance diverges due to unpredictable usage patterns and device variations
Solution Approach 1:
The patent implements a feedback mechanism where the program count is continuously tracked and used to query the lookup table for the appropriate read reference voltage. This feedback loop ensures that as the device ages and undergoes more program operations, the system automatically retrieves the pre-calculated voltage compensation values that correspond to the current state of the device. This maintains performance consistency despite unpredictable usage patterns because the voltage adjustment is always based on the actual program count rather than estimated usage models.
Data Source
AI summary
A device, method, machine-readable medium, and system are disclosed. In one embodiment the device is a memory controller capable of modifying a reference voltage to a persistent moving read reference (MRR) voltage level for use during one or more subsequent reads to a non-volatile memory array. This modification is in response to a change in a reference voltage supplying the non-volatile memory array from a previous reference voltage level to a temporary MRR voltage level.