Trimming Verify Level Offsets for Non-Volatile Memory
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Solution Overview
Problem
Non-volatile memory devices face challenges in maintaining memory cells in the second read condition due to variations in threshold voltage (Vth) across different data states, leading to data retention issues and performance bottlenecks.
Innovation Solution
A memory apparatus and method that apply verification pulses of program verify voltages to determine the threshold voltage of memory cells and trim these voltages based on the quantities of cells crossing over between data states, using a verify level trimming process to adjust the program verify voltages for each data state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If memory cells are operated in the second read condition with elevated word line voltages, then system performance is improved, but threshold voltage variations cause data retention issues and reliability degradation
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the verify voltages based on the detected threshold voltage distribution of memory cells. The system measures the actual Vth distribution and modifies the verify voltage levels to compensate for variations, thereby maintaining reliable data retention while operating in the second read condition with elevated word line voltages.
2Device complexity
If fixed program verify voltages are used for all memory cells, then device complexity is reduced, but manufacturing precision suffers due to Vth variations across different data states
Solution Approach 1:
The patent implements self-service by enabling the memory system to automatically characterize its own threshold voltage distribution and adjust verify voltages accordingly. The system performs self-diagnosis through read operations, detects Vth variations, and autonomously recalibrates the verify voltage levels without requiring external intervention or complex pre-programming.
3Reliability
If verify voltages are trimmed based on threshold voltage distribution, then data retention is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent employs feedback mechanisms where the system continuously monitors threshold voltage distributions through read operations and uses this information to adjust verify voltages. The feedback loop compares actual Vth measurements against target distributions and dynamically modifies verify voltage levels to maintain optimal data retention, balancing improved reliability with controlled complexity.
Data Source
AI summary
A memory apparatus and method of operation are provided. The apparatus includes memory cells each connected to word lines. The memory cells are disposed in strings and configured to retain a threshold voltage corresponding to data states. A control means is configured to apply verification pulses of program verify voltages each associated with one of the data states to selected ones of the word lines to determine whether the memory cells connected thereto have the threshold voltage above each of the program verify voltages targeted for each of the memory cells during a program-verify portion of a program operation. The control means is also configured to trim the program verify voltages for each of the data states for a grouping of the memory cells based on quantities of the memory cells having the threshold voltage crossing over between the data states in crossovers in a verify level trimming process.