Uni-directional STRAM Cell with Unpinned Reference Layer

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Solution Overview

Problem

Conventional non-volatile memory cells, such as STRAM, require bi-directional current flow and separate source and bit lines, leading to inefficiencies and signal margin degradation due to bit-to-bit resistance variations, which complicates data storage and retrieval.

Innovation Solution

A modified STRAM memory cell design utilizing a uni-directional write current and an unpinned ferromagnetic reference layer, where a magnetically permeable cladding layer induces a magnetic field to set the magnetic orientation of the storage layer, allowing for uni-directional current flow and reduced component complexity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bi-directional current flow is used in conventional STRAM memory cells, then data can be stored and retrieved, but component complexity increases and signal margin degrades due to bit-to-bit resistance variations

Engineering Contradiction:

Improvesignal marginVSAvoidcomponent complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and removes the reference layer from the memory cell structure, using an external reference instead. This eliminates the need for separate source and bit lines within the cell, reducing component complexity while maintaining reliable data storage and retrieval through uni-directional current flow

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional approach by using uni-directional current flow instead of bi-directional current flow. This inversion simplifies the cell structure and reduces bit-to-bit resistance variations, thereby improving signal margin while maintaining functionality

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of operation

If separate source and bit lines are used in conventional STRAM memory cells, then data storage and retrieval is enabled, but device complexity increases

Engineering Contradiction:

Improvedata storage and retrieval capabilityVSAvoidcomponent requirements

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent merges the functions of source and bit lines into a single line structure. The unpinned reference layer allows the same line to serve both as source and bit line, reducing component requirements while maintaining full data storage and retrieval capability through the external reference mechanism

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If bit-to-bit resistance variations occur in conventional memory cells, then data storage is possible, but measurement precision degrades

Engineering Contradiction:

Improvedata storage capabilityVSAvoidresistance measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent implements a self-reference mechanism where the memory cell compares its resistance against an external reference. This feedback approach compensates for bit-to-bit resistance variations, maintaining accurate measurement precision while preserving data storage capability

Inventive Principle:

Principle #23Feedback

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 simplifies the memory cell structure, reduces component requirements, and enhances data storage efficiency and accuracy by enabling precise resistance measurements and logical state differentiation using self-reference operations.

Implementation Method 1

a magnetically permeable cladding layer induces a magnetic field to set the magnetic orientation of the storage layer

Methodology Applied

Scientific EffectMagnetic field induction: Electromagnetic Induction

Implementation Method 2

A spin-torque current is passed from the reference layer to a storage layer of the memory cell to induce the selected magnetic orientation in the storage layer

Methodology Applied

Scientific EffectSpin torque transfer:

Implementation Method 3

Passage of a current along the cladded conductor induces a selected magnetic orientation in the reference layer, which is transferred through the tunneling barrier for storage by the storage layer

Methodology Applied

Scientific EffectMagnetic tunneling:

Data Source

PatentUS7940592B2Spin-torque bit cell with unpinned reference layer and unidirectional write current

Publication Date: 2011.05.10 SEAGATE TECH LLC

AI summary

Method and apparatus for using a uni-directional write current to store different logic states in a non-volatile memory cell, such as a modified STRAM cell. In some embodiments, the memory cell has an unpinned ferromagnetic reference layer adjacent a cladded conductor, a ferromagnetic storage layer and a tunneling barrier between the reference layer and the storage layer. Passage of a current along the cladded conductor induces a selected magnetic orientation in the reference layer, which is transferred through the tunneling barrier for storage by the storage layer. Further, the orientation of the applying step is provided by a cladding layer adjacent a conductor along which a current is passed and the current induces a magnetic field in the cladding layer of the selected magnetic orientation.