Flash Storage Data Restoration via Iterative Voltage Adjustment
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Solution Overview
Problem
Flash storage devices with Multi-Bit per Cell (MBC) memory cells face data retention issues during the reflow soldering process, as excess heat causes memory cells to lose electric charge and transition to erroneous binary states, leading to data corruption.
Innovation Solution
A method involving a storage manager that applies initial reference voltages to read data from MBC cells, iteratively lowers these voltages to correct erroneous data bits, and rewrites the corrected data using conventional MBC storage scheme, ensuring data integrity post-reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If MBC cells are used to store user data, then storage capacity is increased and storage space is saved, but data retention durability is reduced and data corruption occurs during reflow soldering
Solution Approach 1:
The patent applies preliminary action by performing voltage compensation before the reflow soldering process. The storage manager detects threshold voltage shifts caused by reflow and compensates for them by adjusting read reference voltages, preventing data corruption before it occurs. This allows MBC cells to be used without suffering from reflow-induced data loss.
Solution Approach 2:
The patent changes the parameter of read reference voltage to compensate for reflow effects. By dynamically adjusting the read reference voltage based on detected threshold voltage shifts, the system maintains accurate data reading despite the thermal stress of reflow soldering, thereby preserving data integrity in MBC cells.
2Reliability
If SBC cells are used to store user data, then data retention durability is improved, but storage capacity is reduced and storage efficiency decreases
Solution Approach 1:
The patent changes the operational parameters of MBC cells to achieve SBC-level reliability. By adjusting read reference voltages to compensate for reflow-induced threshold voltage shifts, the patent enables MBC cells to maintain data integrity with the same reliability as SBC cells, while retaining the higher storage capacity of MBC.
3Productivity
If reflow soldering process is used to embed storage device, then manufacturing efficiency is improved, but data corruption occurs in MBC cells
Solution Approach 1:
The patent applies preliminary action by implementing a voltage compensation mechanism that activates before and during the reflow soldering process. The storage manager detects threshold voltage shifts and compensates for them, ensuring data integrity is maintained throughout the manufacturing process without requiring process changes.
Solution Approach 2:
The patent implements feedback by continuously monitoring threshold voltage shifts during reflow soldering and dynamically adjusting read reference voltages in response. This closed-loop control ensures that data integrity is maintained despite the thermal stress of the reflow process, allowing standard manufacturing procedures to be used.
4Ease of operation
If conventional read reference voltages are used after reflow, then reading operation is simple, but erroneous data bits increase due to threshold voltage shift
Solution Approach 1:
The patent changes the read reference voltage parameter dynamically based on detected threshold voltage shifts. By adjusting the reference voltage to match the shifted cell thresholds, the system maintains accurate data reading without complicating the read operation, as the adjustment is performed automatically by the storage manager.
Solution Approach 2:
The patent implements feedback by detecting threshold voltage shifts and automatically adjusting read reference voltages in response. This closed-loop mechanism maintains data reading accuracy without requiring manual intervention or complex external calibration, preserving ease of operation while improving reliability.
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 restores user data in MBC cells after the reflow process, maintaining data integrity and reducing the need for separate Single-Bit per Cell (SBC) storage devices, thereby optimizing storage efficiency and reducing manufacturing complexities.
Implementation Method 1
performing reading the data from the first group of memory cells by applying a first set of reference voltages and calculating a first number of erroneous data bits in the read data
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Programmer's data is initially stored in a memory device (120) of the storage device (100) by using an MBC storage scheme. After the storage device is embedded in a host device (170), the programmer's data is internally read from the memory device by using conventional read reference voltages, and the number of erroneous data bits in the programmer's data is calculated. If the programmer's data includes an uncorrectable number of erroneous data bits, the programmer' s data is iteratively reread by using unconventional read reference voltages with decreased levels. The iteration process, which includes decreasing the level of the read reference voltages and recalculating the number of erroneous data bits, is terminated when the number of erroneous data bits in the programmer' s is less than or equals a predetermined number of erroneous data bits, after which the storage device restores the programmer's data and conventionally rewrites it into the memory device.