Auto-Referenced Read Voltage Adjustment for 3D Memory Arrays

Solution Overview

Problem

Existing memory devices face challenges in reliably accessing memory cells with variable electrical characteristics, particularly in 3D arrays, due to changes in resistance and voltage distributions over time, which affect read operations and data retention.

Innovation Solution

The proposed solution involves an auto-referenced read technique that uses encoded user data with modified bits to determine a proper read reference voltage, accounting for statistical properties of threshold voltage distributions, and storing additional data information representing the difference between first and second threshold voltages to adjust read voltages accordingly, ensuring accurate reading regardless of electrical characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional read operations are used in 3D memory arrays, then device complexity is reduced, but measurement precision deteriorates due to variable electrical characteristics affecting read accuracy

Engineering Contradiction:

Improveread accuracyVSAvoidread operation complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent performs preliminary characterization of threshold voltage distributions during manufacturing or initialization, storing statistical parameters (mean, standard deviation) that are later used to dynamically adjust read reference voltages. This preliminary action enables accurate reads without real-time complex measurements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent dynamically adjusts read reference voltages based on the stored statistical parameters of threshold voltage distributions. Instead of using fixed reference voltages, the system adapts the read voltage levels according to the actual electrical characteristics of memory cells, improving measurement precision while maintaining manageable complexity through algorithmic adjustment.

Inventive Principle:

Principle #15Dynamics

2Reliability

If fixed read reference voltages are used, then device complexity is reduced, but reliability deteriorates due to variable threshold voltage distributions over time

Engineering Contradiction:

Improvedata retentionVSAvoidread voltage adjustment

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent performs preliminary characterization of threshold voltage distributions during manufacturing or initialization, storing statistical parameters (mean, standard deviation) that are later used to dynamically adjust read reference voltages. This preliminary action enables accurate reads without real-time complex measurements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses stored statistical parameters from threshold voltage measurements to feedback-adjust the read reference voltages. This feedback mechanism ensures that read operations remain reliable even as threshold voltage distributions shift over time due to aging, wear, or manufacturing variations.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If statistical analysis of threshold voltage distributions is performed, then measurement precision is improved, but loss of time increases due to additional characterization steps

Engineering Contradiction:

Improvethreshold voltage measurementVSAvoidcharacterization time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent performs preliminary characterization of threshold voltage distributions during manufacturing or initialization, storing statistical parameters (mean, standard deviation) that are later used to dynamically adjust read reference voltages. This preliminary action enables accurate reads without real-time complex measurements.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11705211B2Methods and systems for improving access to memory cells

Publication Date: 2023.07.18 MICRON TECHNOLOGY INC

AI summary

The present disclosure relates to a method for accessing an array of memory cells, including storing a set of user data in a plurality of memory cells, storing, in a portion of the array, additional information representative of a voltage difference between a first threshold voltage and a second threshold voltage of the memory cells programmed to a first logic state, applying to the array a read voltage to activate a first group of memory cells corresponding to a preset number of memory cells, determining that the first group of memory cells has been activated based on applying the read voltage, wherein the read voltage is equal to the first threshold voltage when the first group of memory cells has been activated, and based on the additional data information, applying the voltage difference to the array to activate a second group of memory cells programmed to the first logic state.