Flash Memory Programming Voltage Ramping to Reduce Program Disturb

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Solution Overview

Problem

Existing non-volatile 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 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 minimize electron injection into unselected memory cells, thereby reducing 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 occurs in unselected memory cells due to GIDL

Engineering Contradiction:

Improveprogramming speedVSAvoidprogram disturb

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by ramping the programming voltage to an intermediate level before applying the full programming voltage. This preliminary voltage adjustment reduces GIDL current in unselected memory cells while still enabling effective programming of selected cells, thus preventing program disturb before it occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the voltage parameter dynamically by using multiple voltage levels (intermediate voltage followed by full programming voltage) instead of a single fixed voltage. This parameter change allows optimization of both programming efficiency and reduction of harmful GIDL effects in unselected cells.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If higher programming voltage is applied, then programming effectiveness is improved, but threshold voltage distribution widens due to electron injection

Engineering Contradiction:

Improveprogramming effectivenessVSAvoidthreshold voltage distribution

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent uses preliminary voltage ramping to an intermediate level before applying full programming voltage. This preliminary step ensures controlled electron injection, achieving effective programming while maintaining tight threshold voltage distributions by avoiding excessive voltage application.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs periodic voltage pulses with intermediate and full programming voltage levels. This periodic application of voltage allows controlled programming effectiveness while preventing excessive electron injection that would widen threshold voltage distributions.

Inventive Principle:

Principle #19Periodic action

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 differential across unselected memory cells, minimizing unintended programming and maintaining precise threshold voltage distributions, even in multi-state flash memory devices.

Implementation Method 1

Due to the voltage differential between the channel of the flash memory cell and the floating gate, electrons from the channel area under the floating gate are injected into the floating gate

Methodology Applied

Scientific EffectFowler-Nordheim tunneling:

Implementation Method 2

A problem arises when it's desired to program one cell on a word line without programming other cells connected to the same word line. Because the program voltage is applied to all memory cells connected to a word line, an unselected memory cell (a memory cell that is not to be programmed) on the same word line may become inadvertently programmed. The unintentional programming of the unselected memory cell on the selected word line is referred to as 'program disturb.'

Methodology Applied

Scientific EffectGate Induced Drain Leakage (GIDL):

Data Source

PatentUS7656703B2Method for using transitional voltage during programming of non-volatile storage

Publication Date: 2010.02.02 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.