MRAM Voltage Sensing Circuit for Write Operation Termination

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Solution Overview

Problem

Magneto-resistive random access memory (MRAM) devices, particularly spin-torque-transfer (STT)-MRAM, face significant dynamic energy consumption during write operations due to the higher current levels required to change the magnetic orientation of free layers in magnetic tunnel junctions (MTJs), which is inefficient for low power memory applications.

Innovation Solution

Implementing a voltage sensing circuit system that detects the completion of MTJ switching in MRAM bit cells by comparing reference and write operation voltages, allowing for the termination of write operations and reducing dynamic power consumption and average write times.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If higher current levels are applied to change the magnetic orientation of free layers in MTJs, then write operations can be performed, but dynamic energy consumption increases significantly

Engineering Contradiction:

Improvewrite operation capabilityVSAvoiddynamic energy consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent applies preliminary action by pre-charging sensing circuits and preparing voltage reference levels before the write operation begins. The sensing circuit is activated in a pre-charge phase to establish baseline voltage levels, enabling rapid detection of MTJ switching completion without extending the critical write operation duration, thus reducing energy consumption while maintaining write capability

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using voltage sensing circuits that continuously monitor the voltage across the MTJ during write operations. When the MTJ switches its magnetic orientation, the resistance change produces a detectable voltage signal that feeds back to the control logic, allowing the write operation to terminate immediately upon completion. This feedback mechanism eliminates the need for fixed-duration write cycles, reducing unnecessary energy consumption

Inventive Principle:

Principle #23Feedback

2Productivity

If higher current levels are applied to change the magnetic orientation of free layers in MTJs, then write operations can be performed, but write times increase due to energy dissipation

Engineering Contradiction:

Improvewrite operation capabilityVSAvoidwrite time

Core Design Contradiction:

ProductivityVSDuration of action of moving object

Solution Approach 1:

The voltage sensing circuit provides real-time feedback on MTJ switching status by detecting resistance changes through voltage measurements. This feedback allows the control logic to terminate the write operation immediately when switching is detected, preventing unnecessary extension of write time and reducing energy dissipation during the write process

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The sensing circuit is pre-charged and prepared in advance of the write operation to ensure it can immediately detect voltage changes when the MTJ switches. This preliminary preparation eliminates detection delays and ensures rapid response to switching events, minimizing the overall write operation duration

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 effectively reduces dynamic power consumption and write times by accurately detecting the completion of MTJ switching, optimizing energy usage in MRAM devices for low power applications.

Implementation Method 1

The resistance of the MTJ is a function of the magnetic orientation of a free layer in the MTJ

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Implementation Method 2

the spin polarization of carrier electrons, rather than a pulse of a magnetic field, is used to program the state stored in the MTJ

Methodology Applied

Scientific EffectSpin torque transfer:

Data Source

PatentUS10224087B1Sensing voltage based on a supply voltage applied to magneto-resistive random access memory (MRAM) bit cells in an MRAM for tracking write operations to the MRAM bit cells

Publication Date: 2019.03.05 QUALCOMM TECHNOLOGIES INC

AI summary

Sensing voltage based on a supplied to magneto-resistive random access memory (MRAM) bit cells in an MRAM for tracking write operations. Sensing voltage based on supply voltage applied to an MRAM bit cell in a write operation can be used to detect completion of magnetic tunnel junction (MTJ) switching in an MRAM bit cell to terminate the write operation to reduce power and write times. In exemplary aspects provided herein, reference and write operation voltages sensed from the MRAM bit cell in response to the write operation are compared to each other to detect completion of MTJ switching of voltage based on the supply voltage applied to the MRAM bit cell regardless of whether the write operation is logic `0` or logic `1` write operation. This provides a higher sensing margin, because the change in MTJ resistance after MTJ switching completion is larger at the supply voltage rail.