Non-Volatile Memory Programming Order for Threshold Voltage Stability

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Solution Overview

Problem

In non-volatile memory systems, particularly in three-dimensional NAND flash memory structures, the scaling of memory cells for increased storage density leads to performance and durability risks due to electron interference and lateral shifting of threshold voltage distributions, which affects data retention and requires additional erase cycles, complicating programming and erase operations.

Innovation Solution

A method and system that initiates programming operations with an ascending order of program states, followed by programming an erase state as the final step, and ramps down the programming voltage bias after completing the highest program state, to tighten the threshold voltage distribution and mitigate disturbances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If memory cells are scaled down for increased storage density, then storage capacity is improved, but electron interference and lateral shifting of threshold voltage distributions occur, worsening data retention

Engineering Contradiction:

Improvestorage densityVSAvoiddata retention

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary action by programming the erase state as the first program state before programming other data states. This preliminary programming of the erase state establishes a reference threshold voltage distribution that compensates for anticipated electron interference and lateral shifting effects, thereby improving data retention in scaled memory cells without sacrificing storage density

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of programming order, specifically programming states in ascending order starting with the erase state rather than the conventional descending order. This parameter change in programming sequence allows the threshold voltage distribution to be established in a controlled manner, mitigating electron migration effects while maintaining high storage density in scaled memory structures

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If conventional programming order is used, then programming operation is simplified, but additional erase cycles are required, worsening programming efficiency

Engineering Contradiction:

Improveprogramming operation simplicityVSAvoidprogramming efficiency

Core Design Contradiction:

Ease of operationVSProductivity

Solution Approach 1:

The patent changes the programming parameter by implementing ascending programming order starting with the erase state, which eliminates the need for subsequent erase cycles. This parameter change in programming sequence improves programming efficiency by ensuring data is programmed in an order that prevents threshold voltage distribution shifts, while the programming operation remains straightforward and easy to implement

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If memory cells are scaled down, then storage capacity increases, but threshold voltage distribution shifts laterally, worsening programming precision

Engineering Contradiction:

Improvestorage capacityVSAvoidthreshold voltage distribution control

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by programming the erase state first to establish a stable reference threshold voltage distribution before programming other states. This preliminary step compensates for lateral shifting effects in scaled memory cells, improving threshold voltage distribution control and programming precision while maintaining high storage capacity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the programming parameter to ascending order starting with the erase state, which prevents threshold voltage distribution lateral shifting in scaled memory cells. This parameter change ensures precise control over threshold voltage distributions, enabling reliable programming in high-density memory structures with reduced cell dimensions

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enhances data retention and reduces the need for additional erase cycles, improving the efficiency and reliability of programming operations by stabilizing the threshold voltage distribution and minimizing electron migration.

Implementation Method 1

programming each of the multiple program states according to a programming order... programming an erase state as the final program state

Methodology Applied

Scientific EffectCharge distribution control: Electrical Accumulator

Implementation Method 2

electron interference and lateral shifting of threshold voltage distributions... tightening the threshold voltage distribution and mitigate disturbances

Methodology Applied

Scientific EffectElectron migration: Diffusion

Data Source

PatentUS20240290390A1Programming erase state as last program state during a programming cycle of a non-volatile memory structure

Publication Date: 2024.08.29 SANDISK TECHNOLOGIES LLC

AI summary

A method for performing a programming operation with respect to a memory structure. The method comprises: (1) initiating a programming operation with respect to multiple program states of a non-volatile memory structure; (2) programming each of the multiple program states according to a programming order; and (3) after completing the programming of each of the multiple program states, programming an erase state as the final program state of the programming order.