Non-volatile Memory Continuous Scanning Time-Domain Sensing
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Solution Overview
Problem
Existing non-volatile memory technologies face challenges in achieving high capacity and performance, particularly in sensing operations, as the increase in storage density leads to longer sensing times due to the need for multiple read levels and corrections for perturbations from neighboring storage elements, resulting in inefficiencies and increased setup times.
Innovation Solution
The implementation of continuous scanning time-domain sensing, where a predetermined input sensing voltage is applied to the word line as an increasing function of time, allowing all thresholds of memory cells to be scanned in one sweep, and the conducting times of individual cells are used to derive their threshold voltages, reducing sensing time and improving performance regardless of the number of levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple read levels and corrections for perturbations from neighboring storage elements are used to increase storage density, then storage capacity is improved, but sensing time increases
Solution Approach 1:
The patent transforms the sensing operation from a voltage-domain multi-level comparison approach to a time-domain measurement approach. By applying a ramp voltage and measuring the time at which each cell transitions to conduction, the system encodes multiple threshold levels along the time dimension rather than requiring multiple sequential voltage comparisons. This dimensional transformation allows simultaneous sensing of multiple levels without increasing sensing time.
Solution Approach 2:
The patent replaces the conventional voltage-threshold comparison mechanism with a time-domain measurement mechanism. Instead of applying fixed voltages and comparing currents against reference levels, the system uses a time-varying ramp voltage and measures conduction transition times. This substitution eliminates the need for multiple read levels and perturbation corrections, resolving the trade-off between storage capacity and sensing time.
2Measurement precision
If multiple read levels are applied to sense multi-level memory cells, then measurement precision is improved, but duration of action increases
Solution Approach 1:
The patent moves the measurement from voltage domain to time domain. Instead of determining threshold levels by comparing currents at fixed voltages, the system applies a ramp voltage and measures the time at which each cell begins to conduct. This time-domain measurement provides precise threshold differentiation in a single operation, eliminating the need for multiple sequential read levels while maintaining measurement precision.
Solution Approach 2:
The patent employs a continuous ramp voltage applied to the word line that monotonically increases over time. This continuous voltage sweep allows all memory cells to be sensed simultaneously as they transition through their threshold voltages, rather than requiring discrete, sequential voltage steps. The continuous action maintains measurement precision while minimizing the total sensing duration.
3Reliability
If corrections for perturbations from neighboring storage elements are performed, then reliability is improved, but productivity decreases
Solution Approach 1:
The patent replaces the correction-based approach with a fundamental measurement paradigm change. Instead of measuring at fixed voltages and then correcting for neighboring cell perturbations, the system uses time-domain measurement with a ramp voltage. The conduction transition time directly indicates the threshold voltage, and the method inherently accounts for perturbations by measuring the actual transition point rather than relying on reference comparisons that require correction.
Solution Approach 2:
The time-domain sensing method is self-correcting in that it directly measures the threshold voltage through the conduction transition time without requiring separate correction steps. The measurement process itself captures the actual operating conditions including any perturbations, eliminating the need for additional correction operations that would reduce productivity.
Data Source
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AI summary
A page of non-volatile multi-level memory cells on a word line is sensed in parallel by sense amps via bit lines. A predetermined input sensing voltage as an increasing function of time applied to the word line allows scanning of the entire range of thresholds of the memory cell in one sweep. Sensing of the thresholds of individual cells is then reduced to a time-domain sensing by noting the times the individual cells become conducting. Each conducting time, adjusted for delays in the word line and the bit line, can be used to derive the sensing voltage level that developed at the word line local to the cell when the cell became conducting. The locally developed sensing voltage level yields the threshold of the cell. This time-domain sensing is relative insensitive to the number of levels of a multi-level memory and therefore resolve many levels rapidly in one sweep.