Phase Change Memory Electrode Sheath Reduces Programming Current

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Solution Overview

Problem

Existing phase change memory cells require high program currents to melt the phase change material, which limits memory cell density due to larger access transistors needed for higher currents.

Innovation Solution

A phase change memory cell design featuring a bottom electrode with a sleeve of high resistivity material surrounding a rod of lower resistivity material, reducing the effective cross-sectional area and programming current, and using a phase change layer between the electrodes to store data.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the cross sectional area of memory cell electrodes is reduced, then the program current is reduced, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveprogram currentVSAvoidelectrode cross sectional area precision

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The electrode is segmented into two distinct materials with different resistivities arranged in a composite structure. The first material (e.g., TaN) has higher resistivity and the second material (e.g., TiN) has lower resistivity, creating a composite electrode that reduces overall resistance while maintaining reduced cross-sectional area

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The electrode uses a composite structure combining two different electrically conductive materials with different specific electrical resistances. This composite approach allows optimization of both current reduction and manufacturing feasibility by selecting materials with appropriate resistivity ratios

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If the resistivity of the electrode material is increased, then the program current is reduced, but the electrical conductivity deteriorates

Engineering Contradiction:

Improveprogram currentVSAvoidelectrical conductivity

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

Different regions of the electrode have different resistivity properties. The first material region provides higher resistivity for current reduction, while the second material region provides lower resistivity for maintaining conductivity. This local differentiation allows simultaneous optimization of both program current and electrical conductivity

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The composite electrode structure combines materials with complementary electrical properties, where the higher resistivity material reduces program current and the lower resistivity material maintains adequate electrical conductivity for reliable operation

Inventive Principle:

Principle #40Composite materials

3Area of stationary object

If the program current is reduced, then the access transistor size is reduced, but the memory cell density increases

Engineering Contradiction:

Improveaccess transistor areaVSAvoidmemory cell density

Core Design Contradiction:

Area of stationary objectVSProductivity

Solution Approach 1:

The electrode resistivity parameters are changed by using a composite structure with materials of different resistivities. This parameter change enables reduction of program current, which in turn allows smaller access transistors and higher memory cell density

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

The design reduces the required reset current to melt the phase change material, allowing for higher memory cell density and faster read times while maintaining the structural integrity of the memory cell.

Implementation Method 1

Programming a phase change memory cell generally requires passing a program current through phase change material. The program current causes some or all of the phase change material to melt.

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

The first electrically conductive material and the second electrically conductive material have different specific electrical resistances

Methodology Applied

Scientific EffectElectrical resistance: Electrical Resistance

Data Source

PatentUS8648326B2Phase change memory electrode with sheath for reduced programming current

Publication Date: 2014.02.11 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

An example embodiment is a phase change memory cell that includes a bottom contact and an electrically insulating layer disposed over the bottom contact. The electrically insulating layer defines an elongated via. Furthermore, a bottom electrode is disposed at least partially in the via. The bottom electrode includes a sleeve of a first electrically conductive material surrounding a rod of a second electrically conductive material. The first electrically conductive material and the second electrically conductive material have different specific electrical resistances. The memory cell also includes a phase change layer electrically coupled to the first electrode.