Spin Hall Effect Magnetic RAM Three-Terminal Cell Design
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Solution Overview
Problem
Conventional spin-transfer torque magnetic random access memories (STT-MRAMs) face challenges with high switching energy barriers, leading to inefficient recording and potential tunnel barrier breakdown, resulting in readout errors and unreliable data storage due to the need for high voltages and currents.
Innovation Solution
A three-terminal magnetoresistive element with a functional magnetic coupling layer and a giant-Spin Hall effect (SHE) base metal layer is used to induce direct spin torque switching of the magnetization in the coupling layer and indirect switching of the recording layer, allowing for low-write current switching with a reduced energy barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage and current are applied to switch magnetization in conventional STT-MRAM, then magnetization switching can be achieved, but tunnel barrier breakdown occurs and reliability deteriorates
Solution Approach 1:
The patent introduces a spin Hall effect metal layer as an intermediary component between the current path and the magnetic tunnel junction. This mediator generates spin current through the spin Hall effect when charge current flows through it, and this spin current then acts on the recording layer to induce magnetization switching. This intermediary mechanism allows the use of lower charge currents compared to direct spin transfer torque methods, thereby preventing tunnel barrier breakdown while achieving reliable magnetization switching.
2Productivity
If high current is used for writing in STT-MRAM, then magnetization switching is achieved, but reading and writing voltage distinction becomes difficult causing readout errors
Solution Approach 1:
The patent exploits parameter changes in the spin Hall effect metal layer by utilizing the spin Hall angle as a key parameter. By selecting materials with high spin Hall angles (such as Pt, β-Ta, β-W), the system can achieve efficient spin current generation with lower charge currents. This parameter optimization enables the write current to be sufficiently low to distinguish from read currents, thereby preventing unintended magnetization switching during read operations and ensuring readout accuracy.
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 enables efficient and reliable magnetization switching with lower currents, reducing the risk of tunnel barrier breakdown and improving data retention by maintaining a high thermal energy barrier while allowing for low-write current operations.
Implementation Method 1
a spin current can, alternatively, be generated in non-magnetic transition metal material by a so-called Spin Hall Effect (SHE), in which spin-orbit coupling causes electrons with different spins to deflect in different directions yielding a pure spin current transverse to an applied charge current
Implementation Method 2
the angular momentum of the spin-polarized electrons is transmitted to the electrons in the magnetic material serving as the magnetic recording layer
Implementation Method 3
magnetic random access memories (hereinafter referred to as MRAMs) using the magnetoresistive effect of ferromagnetic tunnel junctions
Data Source
AI summary
A spin Hall effect magnetoresistive memory comprises apparatus of a three terminal magnetoresistive memory cell having an MTJ stack, a functional magnetic layer having a magnetization anti-parallel or parallel coupled with a recording layer magnetization in the MTJ stack, and a SHE-metal base layer. The control circuitry coupled through the bit line and the two select transistors to selected ones of the plurality of magnetoresistive memory elements to supply a reading current across the magnetoresistive element stack and two bottom electrodes and to supply a bi-directional spin Hall effect recording current, and accordingly to directly switch the magnetization of the functional magnetic coupling layer and indirectly switching the magnetization of the recording layer through the coupling between the functional magnetic coupling layer and the recording layer.