Flash Memory Programming Voltage Ramping to Reduce Program Disturb

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Solution Overview

Problem

Existing flash memory technologies face challenges in minimizing program disturb, particularly as memory devices scale, leading to unintended programming of unselected cells due to Gate Induced Drain Leakage (GIDL) and widening of threshold voltage distributions, especially near select gates.

Innovation Solution

A programming voltage signal is ramped to an intermediate voltage before applying the programming voltage, which is higher than the pass voltage but lower than the programming voltage, to reduce the risk of electron injection into unselected memory cells, thereby minimizing program disturb and maintaining tight threshold voltage distributions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If programming voltage is applied directly to selected memory cells, then programming speed is improved, but program disturb increases due to electron injection into unselected cells

Engineering Contradiction:

Improveprogramming speedVSAvoidprogram disturb

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary actions by first boosting the channel voltage of unselected memory cells to a high level before applying the programming voltage to selected cells. This preliminary boosting creates a protective voltage barrier that prevents electron injection into unselected cells during the subsequent programming operation, thereby eliminating program disturb while maintaining fast programming speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements preliminary anti-action by applying a counteracting voltage to unselected memory cells before the harmful programming process begins. The channel boosting voltage counteracts the potential electron injection by creating an opposing electric field that repels electrons away from unselected cells, thus preventing program disturb before it can occur.

Inventive Principle:

Principle #9Preliminary anti-action

2Quantity of substance

If memory devices are scaled down, then device density is improved, but program disturb worsens due to increased GIDL effects

Engineering Contradiction:

Improvememory densityVSAvoidprogram disturb

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The patent changes the voltage parameters dynamically during the programming process. By boosting the channel voltage of unselected cells to a high level before programming and then adjusting voltages during programming, the patent compensates for the increased GIDL effects in scaled devices. This parameter change strategy maintains tight threshold voltage distributions even as device density increases through scaling.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If high programming voltage is applied to unselected cells, then program disturb is reduced, but threshold voltage distribution widens

Engineering Contradiction:

Improveprogram disturb reductionVSAvoidthreshold voltage distribution

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent employs dynamic voltage adjustment where the channel boosting voltage is applied temporarily before programming and then adjusted or removed during the programming process. This dynamic approach allows the unselected cells to receive protective voltage initially, preventing program disturb, while subsequent voltage adjustments ensure that threshold voltage distributions remain tight and well-controlled.

Inventive Principle:

Principle #15Dynamics

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 effectively reduces program disturb by controlling the voltage levels applied to selected and unselected memory cells, minimizing unintended programming and maintaining precise threshold voltage distributions, even in multi-state flash memory devices.

Implementation Method 1

unintended programming of unselected cells due to Gate Induced Drain Leakage (GIDL)

Methodology Applied

Scientific EffectGate Induced Drain Leakage (GIDL):

Implementation Method 2

reduce the risk of electron injection into unselected memory cells

Methodology Applied

Scientific EffectElectron injection:

Data Source

PatentUS7706189B2Non-volatile storage system with transitional voltage during programming

Publication Date: 2010.04.27 SANDISK TECHNOLOGIES LLC

AI summary

To program one or more non-volatile storage elements, a set of programming pulses are applied to at least one selected non-volatile storage element and one or more particular unselected non-volatile storage elements, for example, via a common word line. A boosting voltage is applied to other unselected non-volatile storage elements during the programming process in order to boost the channels of the unselected non-volatile storage elements so that programming will be inhibited. Each of the programming pulses has a first intermediate magnitude, a second intermediate magnitude and a third magnitude. In one embodiment, the first intermediate magnitude is similar to or the same as the boosting voltage. The second intermediate magnitude is greater than the first intermediate magnitude, but less then the third magnitude. Such an arrangement can reduce the effects of program disturb.