Double Tunnel Barrier MRAM for High Breakdown Voltage
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Solution Overview
Problem
Magnetoresistive random access memory (MRAM) devices face challenges in achieving reliable operation due to high write voltage requirements, which can lead to tunnel barrier breakdown, especially for devices with high retention temperatures, resulting in unreliable device performance.
Innovation Solution
A thermally assisted MRAM device is designed with a double tunnel barrier structure, where the voltage is split between an active tunnel barrier for reading and a heating-only tunnel barrier, reducing the load on each barrier and increasing the breakdown voltage, thereby enhancing the reliability of the MRAM device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single tunnel barrier structure is used in MRAM devices, then the device structure is simple, but the breakdown voltage is limited (0.9 V) and reliability is reduced
Solution Approach 1:
The single tunnel barrier is segmented into two separate tunnel barriers: a first tunnel barrier (MgO layer) and a second tunnel barrier (AlOx layer). This segmentation allows the voltage to be distributed across both barriers, increasing the overall breakdown voltage from 0.9V to 1.5V or more, while each barrier can be independently optimized for its specific function.
Solution Approach 2:
A non-magnetic spacer layer is introduced as an intermediary between the first and second tunnel barriers. This spacer layer acts as a mediator that electrically connects both barriers while maintaining their functional independence, allowing voltage distribution and heat management without direct contact between the two barrier layers.
2Ease of operation
If high write voltage is applied to switch magnetic layers, then the magnetic switching is effective, but the tunnel barrier breakdown occurs
Solution Approach 1:
The voltage applied during write operations is segmented across two tunnel barriers rather than concentrated across a single barrier. The first tunnel barrier handles a portion of the voltage while the second tunnel barrier handles the remainder, preventing any single barrier from experiencing excessive voltage that would cause breakdown.
Solution Approach 2:
The breakdown voltage parameter is changed from 0.9V (single barrier) to 1.5V or more (double barrier structure). This parameter change allows higher write voltages to be applied for effective magnetic switching while maintaining tunnel barrier integrity through the distributed voltage approach.
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 double tunnel barrier structure increases the breakdown voltage from 0.9 V to 1.5 V or more, ensuring reliable operation while maintaining sufficient tunneling magnetoresistance for practical circuit use, even with higher active barrier thicknesses.
Implementation Method 1
The non-magnetic tunnel barrier and the non-magnetic active tunnel barrier both generate resistive heating
Implementation Method 2
The electrical resistance of this stack depends on the relative magnetic orientation of the parts of the storage and sense layers that interface with the tunnel barrier; this effect is caused by the phenomenon of tunneling magnetoresistance (TMR)
Data Source
AI summary
A mechanism is provided for a thermally assisted magnetoresistive random access memory device (TAS-MRAM). A non-magnetic heating structure is formed of a barrier seed layer disposed on a buffer layer. A non-magnetic tunnel barrier is disposed on the barrier seed layer. A barrier cap layer is disposed on the non-magnetic tunnel barrier. A top buffer layer is disposed on the barrier cap layer. An antiferromagnetic layer is disposed on the top buffer layer of the non-magnetic heating structure. A magnetic tunnel junction is disposed on the antiferromagnetic layer. The magnetic tunnel junction includes a ferromagnetic storage layer disposed on the antiferromagnetic layer, a non-magnetic active tunnel barrier disposed on the ferromagnetic storage layer, and a ferromagnetic sense layer disposed on the non-magnetic active tunnel barrier.