Multiferroic Tunneling Barrier for STT Memory Cell Current Reduction

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Solution Overview

Problem

As semiconductor memory devices, such as STT RAM cells, shrink in size, they face increased cell disturb from current-carrying lines, leading to higher power consumption and thermal issues, necessitating reduced programming currents for improved reliability and energy efficiency.

Innovation Solution

Incorporating a multiferroic tunneling barrier material between ferromagnetic storage and pinned ferromagnetic materials, allowing magnetic switching via an applied electric field through exchange coupling, which reduces the programming current required for magnetization direction changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If the size of MRAM cells decreases, then integration density improves, but cell disturb from current-carrying lines increases

Engineering Contradiction:

Improvecell sizeVSAvoidcell disturb

Core Design Contradiction:

Area of moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the conventional write mechanism that uses external magnetic fields generated by current-carrying lines with a spin transfer torque mechanism. Spin-polarized electrons passing through the pinned layer exert a torque on the free layer magnetization, enabling switching without large external currents. This substitution eliminates the harmful electromagnetic fields that cause cell disturb while maintaining the ability to switch magnetization states for data storage.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Area of moving object

If the width of current carrying lines decreases, then cell density improves, but the current required to produce switching fields increases

Engineering Contradiction:

Improveline widthVSAvoidpower consumption

Core Design Contradiction:

Area of moving objectVSUse of energy by moving object

Solution Approach 1:

The invention replaces the external magnetic field generation method with spin transfer torque switching. Instead of requiring large currents (e.g., 10 mA) through word and bit lines to generate switching fields, the patent uses spin-polarized electrons that accumulate during a precharge phase and then switch the free layer magnetization when a threshold is reached. This internal switching mechanism dramatically reduces the current required in the word and bit lines, enabling smaller line widths and lower power consumption.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Use of energy by moving object

If programming current is reduced, then energy consumption decreases, but switching efficiency may be compromised

Engineering Contradiction:

Improveenergy consumptionVSAvoidswitching efficiency

Core Design Contradiction:

Use of energy by moving objectVSProductivity

Solution Approach 1:

The patent employs a precharge mechanism where spin-polarized electrons are accumulated in the free layer during a first time period before the actual switching occurs. This preliminary accumulation of spin polarization allows the system to reach the switching threshold with a smaller subsequent current pulse. The precharge phase prepares the magnetic moment for efficient switching, enabling low-energy operation without compromising switching reliability or speed.

Inventive Principle:

Principle #10Preliminary 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 decreases the programming current density, enhances data reliability by preventing thermal switching, and enables multi-bit capabilities with a reduced physical footprint, improving overall cell integrity and energy efficiency.

Implementation Method 1

allowing magnetic switching via an applied electric field through exchange coupling

Methodology Applied

Scientific EffectExchange coupling:

Implementation Method 2

unpolarized conduction electrons passing through a first magnetic material having its magnetic moment oriented in a given direction (e.g. a 'pinned' material) are preferentially polarized by their passage through that material by a quantum mechanical exchange interaction with the polarized bound electrons in the material

Methodology Applied

Scientific EffectSpin torque transfer:

Implementation Method 3

Methodology Applied

Scientific EffectSpin polarization:

Implementation Method 4

the polarized conduction electrons exert a torque on the bound electrons in the magnetic materials which, if sufficient, can reverse the polarization of the bound electrons and, thereby, reverse the magnetic moment of the magnetic material

Methodology Applied

Scientific EffectTorque: Torque

Data Source

PatentEP2617037B1Spin torque transfer memory cell structures and methods

Publication Date: 2017.08.09 MICRON TECHNOLOGY INC

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AI summary

Spin Torque Transfer (STT) memory cell structures and methods are described herein. One or more STT memory cell structures include a tunneling barrier material positioned between a ferromagnetic storage material and a pinned ferromagnetic material in contact with an antiferromagnetic material. The tunneling barrier material is a multiferroic material and the antiferromagnetic material, the ferromagnetic storage material, and the pinned ferromagnetic material are positioned between a first electrode and a second electrode.