Phase Change Memory Programming Using Segmented Crystallization Pulses

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The high RESET programming-current requirement in phase change memory (PCM) technologies hinders the downsizing of access transistors, making it challenging to achieve high density PCM arrays, and extending SET programming duration to address incomplete crystallization results in increased power consumption and degraded performance.

Innovation Solution

A programming method using a step waveform with two crystallization current or voltage pulses, where the first pulse has a high peak current/voltage for a short duration and a second pulse with a lower peak current/voltage for a longer duration, allowing for complete crystallization without unnecessary power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the pulse width of SET programming pulse is extended to achieve complete crystallization, then the sensing margin and resistance uniformity are improved, but the power consumption increases and speed performance degrades

Engineering Contradiction:

Improvesensing marginVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The programming pulse is segmented into two distinct phases: a first pulse with high amplitude and short duration to rapidly heat the PCM above melting point, followed by a second pulse with lower amplitude and longer duration to complete crystallization. This segmentation allows each pulse to be optimized for its specific function, avoiding the need for a single long high-power pulse.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The programming process uses periodic pulsed action instead of continuous power application. The first pulse melts the material, then the second pulse crystallizes it. This periodic approach with controlled intervals between pulses reduces overall power consumption while achieving complete crystallization and improving sensing margin.

Inventive Principle:

Principle #19Periodic action

2Manufacturing precision

If the pulse width of SET programming pulse is extended to achieve complete crystallization, then the resistance uniformity is improved, but the overheating increases

Engineering Contradiction:

Improveresistance uniformityVSAvoidoverheating

Core Design Contradiction:

Manufacturing precisionVSTemperature

Solution Approach 1:

The thermal process is segmented into two stages: rapid heating above melting point followed by controlled crystallization at lower temperature. This prevents excessive overheating while ensuring complete and uniform crystallization, improving resistance uniformity without causing thermal damage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first pulse performs the preliminary action of melting the PCM material, preparing it for subsequent crystallization. This preliminary melting action enables the second pulse to complete crystallization at lower temperature, preventing overheating while achieving uniform resistance characteristics.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the pulse width of SET programming pulse is extended to achieve complete crystallization, then the crystallization completeness is improved, but the programming speed degrades

Engineering Contradiction:

Improvecrystallization completenessVSAvoidprogramming speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The crystallization process is segmented into two phases: rapid melting followed by controlled crystallization. The first pulse quickly prepares the material by melting, and the second pulse completes crystallization. This segmentation achieves complete crystallization faster than a single extended pulse, improving programming speed while maintaining reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The programming uses periodic pulsed action with optimized timing: a short high-power pulse for melting, followed by a longer lower-power pulse for crystallization. This periodic approach achieves complete crystallization more efficiently than continuous power application, improving programming speed without sacrificing crystallization completeness.

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 method reduces SET resistance, enhances sensing margin and resistance uniformity, while minimizing power loss and overheating, and improves reliability and speed performance compared to conventional methods.

Implementation Method 1

phase change memory (PCM) based on the phase transformations between amorphous phase and crystalline phase

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

based on the phase transformations between amorphous phase and crystalline phase

Methodology Applied

Scientific EffectPhase change: Phase Change

Data Source

PatentUS7660147B2Programming method for phase change memory

Publication Date: 2010.02.09 NAN YA TECH

AI summary

A programming method for a phase change memory based on the phase transformations between amorphous and crystalline phases is disclosed. The programming method comprises a current pulse with step waveform providing a first crystallization current pulse to the phase change memory and providing a second crystallization current pulse to the phase change memory. The first crystallization current pulse has a first rising edge, a first falling edge and a first peak current held for a first hold time. The second crystallization current pulse has a second peak current. The second peak current follows the first falling edge and is held for a second hold time.