Dynamic Memory Control Voltage Calibration via String Current Slope
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Solution Overview
Problem
Existing systems for dynamically calibrating memory control voltages, such as pass voltage and wordline read-verify voltage, are sensitive to temperature, pattern, and time of programming fluctuations, leading to inaccurate calibration and performance issues.
Innovation Solution
The calibration of memory control voltages is improved by measuring the change in slope of the string current over time, determining the final voltage based on the ratio of change in total string current, and comparing it against a threshold, reducing sensitivity to temperature, pattern, and time of programming variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dynamic calibration is performed as a function of average string current, then calibration adapts to operating conditions, but sensitivity to temperature changes and time of programming increases
Solution Approach 1:
The memory block is divided into multiple sub-blocks that can be independently controlled and calibrated. Each sub-block can be programmed and calibrated separately, allowing the system to isolate and compensate for temperature variations and timing differences in different regions, thereby maintaining calibration accuracy while adapting to operating conditions.
Solution Approach 2:
The calibration process is performed locally at the sub-block level rather than globally across the entire memory block. This allows each sub-block to have its own calibrated pass voltage and wordline read-verify voltage values that account for local temperature and timing conditions, improving measurement precision while maintaining adaptability.
2Productivity
If calibration is performed after comparator flip indicating completion, then calibration completes the memory operation, but unselected sub-blocks contribute high currents causing inaccurate calibration
Solution Approach 1:
The calibration process is initiated and performed before the comparator flip that indicates completion of the memory operation. By performing calibration in advance, the system can determine accurate pass voltage and wordline read-verify voltage values before unselected sub-blocks contribute high currents that would otherwise contaminate the calibration measurement.
Solution Approach 2:
The calibration function is extracted and performed as a separate preliminary step before the main memory operation completion signal. This allows the calibration process to be completed independently with accurate measurements, and then the results are used for the subsequent memory operations without interference from high currents in unselected sub-blocks.
3Device complexity
If temperature compensation is done only at sense current or sense Vt, then calibration is simple and fast, but temperature-induced variation of cell current causes inaccuracy
Solution Approach 1:
The calibration process measures and compensates for temperature effects across multiple current parameters, not just at the sense current or sense Vt point. By characterizing the cell current behavior at different current levels and temperatures, the system can accurately determine the temperature coefficient and apply appropriate compensation to maintain voltage calculation accuracy while keeping the process manageable.
Data Source
AI summary
Disclosed are systems and methods of dynamically calibrating a memory control voltage more accurately. According to disclosed implementations, a memory control voltage such as Vpass or Vwlrv may be calibrated during memory operation as a function of the change in slope of total string current, even during increase in the wordline voltage. In one exemplary method, the wordlines are increased in sequence from a start voltage to an end voltage in steps, slope change is measured at every step, the measured slope change is compared against a threshold, and an adjusted memory control voltage is determined as a function of a wordline voltage at which the change in slope reaches the threshold. As such, memory control voltage may be determined and dynamically calibrated with less sensitivity to operating parameters such as temperature, pattern, and/or time of programming.