Spin-Torque MRAM Tunnel Junction Endurance via Polarity Reversal

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Solution Overview

Problem

Conventional programming methods for spin-torque magnetoresistive random access memory (MRAM) lead to dielectric breakdown of tunnel junctions due to repeated write voltage pulses, reducing the lifespan of memory cells.

Innovation Solution

A method and apparatus that provide a write pulse sequence for spin-torque MRAM, including a charging pulse with opposite polarity from the write pulse, either before or after the write pulse sequence, to enhance the endurance of tunnel barriers and minimize dielectric breakdown.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If repeated write voltage pulses are applied to program spin-torque MRAM, then data writing capability is achieved, but dielectric breakdown of tunnel junctions occurs reducing memory cell lifespan

Engineering Contradiction:

Improvedata writing capabilityVSAvoidmemory cell lifespan

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

A charging pulse is applied before the write pulse sequence to pre-charge the tunnel junction. This preliminary action prepares the junction by establishing an initial charge state that reduces the stress imposed by subsequent write pulses, thereby preventing dielectric breakdown while maintaining writing capability

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The write operation uses periodic pulsing with alternating polarity: a charging pulse followed by write pulses. This periodic action with opposite polarity pulses allows the tunnel junction to recover between write operations, reducing cumulative stress and extending memory cell lifespan

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

The proposed solution extends the lifetime of spin-torque MRAM memory cells by reducing the stress on tunnel junctions, thereby improving the durability and reducing the likelihood of dielectric breakdown, while maintaining efficient data storage and retrieval capabilities.

Implementation Method 1

The angular momentum carried by the spin-polarized tunneling current causes reversal of the free layer

Methodology Applied

Scientific EffectSpin-torque transfer: Angular Momentum

Implementation Method 2

exhibits an electrical resistance that depends on the magnetic state of the device

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS9589622B2Method of writing to a spin torque magnetic random access memory

Publication Date: 2017.03.07 EVERSPIN TECHNOLOGIES INC

AI summary

Circuitry and methods provide an increased tunnel barrier endurance (lifetime) previously shortened by dielectric breakdown by providing a charging pulses of opposite polarity in comparison with write pulses. The charging pulse of opposite polarity may comprise equal or different width and amplitude than that of the write pulse, may be applied with each write pulse or a series of write pulses, and may be applied prior to or subsequent to the write pulse. A register is also used to keep track of the read pulse polarity such that read pulses of alternating polarity can be used in reading operations.