MTJ Breakdown Anti-Fuse Circuit for MRAM Data Retention
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Solution Overview
Problem
As semiconductor memory devices integrate more memory cells, downscaled MRAM cells lose their non-volatile data retention characteristics, making conventional MRAMs unsuitable for use as fuses or anti-fuses, necessitating new approaches for reliable operation.
Innovation Solution
An anti-fuse circuit utilizing the breakdown of a magnetic tunnel junction (MTJ) in downscaled MRAM cells, where TMR elements are series-connected with transistors, allowing for voltage-induced breakdown to store fuse information and provide distinct resistance states for sensing and amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If downscaled MRAM cells are used as anti-fuse circuits, then integration density is improved, but non-volatile data retention characteristic deteriorates
Solution Approach 1:
The patent changes the operational parameters of the MRAM cell by applying a high voltage pulse (first voltage higher than second voltage) to induce breakdown in the MTJ. This parameter change transforms the cell from a volatile memory state to a permanent anti-fuse state, enabling non-volatile data retention despite the downscaled size. The breakdown mechanism fundamentally alters the resistance state, creating a permanent change that maintains data retention.
Solution Approach 2:
The patent converts the harmful effect of voltage-induced breakdown (which would normally destroy the MTJ) into a beneficial permanent state change. By carefully controlling the breakdown process with appropriate voltage sequencing (first voltage for breakdown, second voltage for reading), the MTJ transition from high to low resistance state becomes the desired permanent storage mechanism, turning a destructive effect into a useful anti-fuse function.
2Adaptability or versatility
If conventional MRAM cells are used as fuses, then circuit functionality is achieved, but reliability deteriorates due to volatility
Solution Approach 1:
The patent utilizes the phase transition of the MTJ between high resistance and low resistance states to achieve permanent data storage. The breakdown process induces a permanent phase change in the MTJ material structure, transforming the volatile memory characteristic into a non-volatile anti-fuse state. This phase transition enables the cell to maintain its state without continuous power, solving the reliability issue.
3Reliability
If high voltage is applied to break down MTJ, then fuse information storage is achieved, but energy consumption increases
Solution Approach 1:
The patent employs periodic voltage application in two distinct phases: first applying a high breakdown voltage to induce MTJ breakdown and store fuse information, then applying a lower reading voltage to detect the stored information. This periodic action separates the high-energy writing operation from the low-energy reading operation, optimizing overall energy consumption while ensuring reliable information storage.
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
Enables the use of downscaled MRAM cells as effective anti-fuse circuits in semiconductor memory devices, allowing for reliable storage and retrieval of fuse information without requiring high voltages, thus addressing the volatility issue and reducing layout size.
Implementation Method 1
configured to breakdown a magnetic tunnel junction (MTJ) of the TMR element in response to an applied first voltage, such that alternately provided normal resistance and breakdown resistance for the TMR define an output signal
Data Source
AI summary
An anti-fuse circuit includes an array of anti-fuses. Each anti-fuse has a tunneling magneto-resistance (TMR) element series connected with a transistor, such that breakdown of a magnetic tunnel junction (MTJ) in response to an applied first voltage stores fuse information. A sensing circuit senses and amplifies respective output signals provided by the anti-fuses.