Memory Device Readback Using Adjacent Word-Line Pass Voltages
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Solution Overview
Problem
Existing memory technologies suffer from threshold voltage shift due to long-term storage, leading to increased read error rates, which are exacerbated by error correction operations that occupy space, slow down memory read speed, and reduce lifespan.
Innovation Solution
A memory device and reading method that adjusts pass voltages on adjacent word lines during a re-read procedure to mitigate threshold voltage shift, using different pass voltages on second and third word lines to correct read errors in state marginal groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correction technology is used to reduce read error rate, then data accuracy is improved, but device area increases due to additional error correction operation circuit
Solution Approach 1:
The patent extracts the error correction function from a separate dedicated circuit and integrates it into the existing word line control mechanism. By reusing the word line infrastructure and introducing adjustable pass voltages on neighboring word lines, the solution eliminates the need for additional error correction operation circuits while maintaining the ability to correct threshold voltage shifts.
Solution Approach 2:
The word line structure is given multi-functionality: it serves both as a standard read operation conductor and as an error correction mechanism through adjustable pass voltages. The neighboring word lines (WL-1 and WL+1) are repurposed to provide threshold voltage adjustment for memory cells on the selected word line, eliminating the need for dedicated error correction hardware.
2Reliability
If error correction operation is performed to reduce read error rate, then data accuracy is improved, but memory read speed decreases due to increased latency
Solution Approach 1:
The patent applies preliminary action by adjusting the pass voltages on neighboring word lines before or during the read operation to pre-correct threshold voltage shifts. This prevents read errors from occurring in the first place, eliminating the need for subsequent error correction operations and associated latency.
Solution Approach 2:
The solution allows the read operation to proceed directly without pausing for separate error correction steps. By integrating the correction mechanism into the word line control itself, the system rushes through the read operation in a single pass, maintaining high speed while achieving error correction.
3Reliability
If error correction operations are frequently performed to reduce read error rate, then data accuracy is improved, but memory lifespan decreases
Solution Approach 1:
The patent provides beforehand cushioning by proactively adjusting threshold voltages using neighboring word lines before read errors can occur. This preventive approach reduces the frequency of corrective operations needed, thereby reducing wear on memory cells and extending overall device lifespan.
4Device complexity
If threshold voltage shift is not corrected to maintain read accuracy, then device complexity is reduced, but read error rate increases
Solution Approach 1:
The memory system provides self-service error correction by using its own existing word line infrastructure to correct threshold voltage shifts. The neighboring word lines serve the dual purpose of normal address selection and threshold voltage adjustment, allowing the system to correct its own errors without external intervention or additional complex circuitry.
Data Source
AI summary
A memory device and a reading method thereof are provided. A second word line and a third word line are adjacent to a first word line. The reading method includes the following steps. A read procedure is executed to read a plurality of memory cells of the first word line. When a read error occurs, a re-read procedure is executed for some of the memory cells belonging to a state marginal group. The read procedure includes: applying a read voltage to the first word line; applying a first pass voltage to the second word line and the third word line. The re-read procedure includes: applying the read voltage to the first word line; applying a second pass voltage and a third pass voltage different from the first pass voltage to the second word line and the third word line respectively.