Select Gate Maintenance in Memory Sub-Systems

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Solution Overview

Problem

Conventional memory devices using replacement gate transistors for select gate devices face signal leakage and threshold voltage shifts over time, leading to reliability issues and potential data integrity problems due to increased or decreased threshold voltage from its target value.

Innovation Solution

Periodic maintenance operations, such as touch up programs, are performed on select gate devices to adjust their threshold voltage back to the target value, ensuring proper functionality and preventing unrepairable shifts, thereby maintaining data integrity and extending the lifespan of memory devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If replacement gate transistors are used for select gate devices, then device versatility and programmability are improved, but signal leakage and threshold voltage shifts occur over time

Engineering Contradiction:

Improveprogrammability of select gate devicesVSAvoidsignal leakage and threshold voltage stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements periodic maintenance operations including threshold voltage scans and touch-up program operations at scheduled intervals (e.g., every 1000 P/E cycles or monthly). This periodic monitoring and adjustment prevents threshold voltage drift from causing reliability issues while maintaining the programmability benefits of replacement gate transistors.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs threshold voltage scans that measure actual threshold voltage values and compare them against target ranges. Based on this feedback, the controller determines whether touch-up operations are needed and adjusts programming parameters accordingly, creating a closed-loop control system that maintains reliability.

Inventive Principle:

Principle #23Feedback

2Reliability

If periodic maintenance operations are performed on select gate devices, then data integrity is improved, but additional time and operational complexity are required

Engineering Contradiction:

Improvedata integrityVSAvoidtime for maintenance operations

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs maintenance operations proactively before threshold voltage shifts cause data integrity issues. By scanning and adjusting threshold voltages periodically, the system prevents problems rather than reacting to them, reducing the need for time-consuming error correction later.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent adjusts programming parameters such as pulse voltage levels and durations based on measured threshold voltage values. This dynamic parameter adjustment optimizes maintenance operation efficiency, performing only the necessary corrections rather than blanket re-programming of all select gates.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If threshold voltage shifts are allowed to occur, then device operation simplicity is maintained, but unwanted effects on other sub-blocks and data integrity problems arise

Engineering Contradiction:

Improvesimplicity of device operationVSAvoidsignal leakage and interference with other sub-blocks

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The system applies counteracting programming operations to prevent threshold voltage shifts from causing harmful effects. When a select gate's threshold voltage begins to drift, the maintenance system applies corrective pulses that push the threshold back into the acceptable range, preventing signal leakage and interference with adjacent sub-blocks.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent applies maintenance operations selectively to individual select gates or groups of select gates based on their specific threshold voltage measurements. Rather than uniformly re-programming all select gates, the system targets only those needing adjustment, minimizing operational complexity while preventing harmful effects.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11456043B2Select gate maintenance in a memory sub-system

Publication Date: 2022.09.27 MICRON TECHNOLOGY INC

AI summary

A processing device in a memory system receives a request to erase a data block of a memory device, determines a number of program/erase cycles performed on the data block, and performs an erase operation to erase the data block. The processing device further determines that the number of program/erase cycles performed on the data block satisfies a scan threshold condition and performs a first threshold voltage integrity scan on the data block to determine a first error rate associated with a current threshold voltage of at least one select gate device of the data block. Responsive to the first error rate associated with the current threshold voltage of the at least one select gate device satisfying an error threshold criterion, the processing device performs a touch up operation on the at least one select gate device to adjust the current threshold voltage to the target threshold voltage.