Adaptive Verify for Multi-State Flash Memory Programming

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Solution Overview

Problem

Existing programming techniques for non-volatile storage elements, particularly in multi-state flash memory devices, face inefficiencies due to unnecessary program verification steps, especially when programming a lower page to an intermediate state before an upper page, leading to increased programming time and power consumption.

Innovation Solution

Adaptive verification techniques are implemented to determine when to initiate verification processes by tracking the transition of non-volatile storage elements from one voltage threshold distribution to another, allowing for reduced unnecessary verification steps and optimizing the programming process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional sequential verify operations are performed for each programming step in multi-state flash memory, then programming verification reliability is improved, but programming time and power consumption increase significantly

Engineering Contradiction:

Improveprogramming verification reliabilityVSAvoidprogramming time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by pre-establishing verify levels and tracking storage element states before actual verification is needed. The controller maintains information about which storage elements have reached which verify levels, enabling it to skip unnecessary verification steps and initiate verification only when needed, thus reducing programming time while maintaining reliability

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The verification process is made dynamic by adapting the verification strategy based on real-time tracking of storage element transitions. The system dynamically determines which elements need verification and at what levels, rather than performing fixed sequential verification. This dynamic approach allows the system to optimize verification timing and scope, reducing both time and power consumption while ensuring reliable programming

Inventive Principle:

Principle #15Dynamics

2Reliability

If all storage elements are verified at all verify levels sequentially, then verification completeness is improved, but power consumption increases

Engineering Contradiction:

Improveverification completenessVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The system applies local quality by tailoring verification actions to individual storage elements based on their specific states and transitions. Rather than uniformly verifying all elements at all levels, the system identifies which elements need verification at which levels based on their individual programming progress. This localized verification approach reduces unnecessary verification operations and associated power consumption while maintaining complete verification where needed

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system performs partial verification actions only when and where necessary. By tracking which storage elements have reached which verify levels, the system can skip verification for elements that have already been verified or that do not need verification at certain levels. This partial action approach reduces overall verification operations and power consumption while ensuring complete verification for elements that require it

Inventive Principle:

Principle #16Partial or excessive action

3Device complexity

If fixed verification timing is used for all storage elements, then process simplicity is maintained, but programming efficiency decreases due to unnecessary verification steps

Engineering Contradiction:

Improveprocess simplicityVSAvoidprogramming efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The system implements feedback mechanisms where the controller continuously tracks the states of storage elements and uses this information to determine when verification should be performed. The feedback from monitoring storage element transitions enables the system to adjust verification timing dynamically, eliminating unnecessary verification steps and improving programming efficiency while maintaining manageable process complexity through automated state tracking

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7366022B2Apparatus for programming of multi-state non-volatile memory using smart verify

Publication Date: 2008.04.29 SANDISK TECHNOLOGIES LLC

AI summary

In a non-volatile memory, the initiation of program verification is adaptively set so that programming time is decreased. In one approach, non-volatile storage elements are programmed based on a lower page of data to have a voltage threshold (VTH) that falls within a first VTH distribution or a higher, intermediate VTH distribution. Subsequently, the non-volatile storage elements with the first VTH distribution either remain there, or are programmed to a second VTH distribution, based on an upper page of data. The non-volatile storage elements with the intermediate VTH distribution are programmed to third and fourth VTH distributions. The non-volatile storage elements being programmed to the third VTH distribution are specially identified and tracked. Verification of the non-volatile storage elements being programmed to the fourth VTH distribution is initiated after one of the identified non-volatile storage elements transitions to the third VTH distribution from the intermediate VTH distribution.