Magnetoresistive Memory Read Circuit With Dual Selectors
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Solution Overview
Problem
SOT-MRAM and OTT-MRAM memory technologies face challenges with unstable read margins and high risk of read disturbance due to heating-induced drift in read currents, limiting the dynamic range and reliability of memory cells.
Innovation Solution
A memory circuit design with two selectors and a read circuit that uses a read current instead of a read voltage, minimizing heating effects by detecting leakage currents and optimizing current flow through magnetic tunnel junctions, thereby stabilizing read margins and reducing read disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a read voltage is applied across the magnetic tunnel junction to measure current, then the read operation can be performed, but heating is induced causing drift in read currents and instability of read margin
Solution Approach 1:
The patent introduces a selector device as an intermediary element between the read circuit and the magnetic tunnel junction. The selector is configured to be in a high-resistance state during read operations, which blocks or limits the read current flow through the magnetic tunnel junction. This intermediary structure allows the read operation to be performed while minimizing the current that would otherwise cause heating and drift in the magnetic tunnel junction, thereby stabilizing the read margin over time.
2Measurement precision
If the difference between high and low resistive states is increased to improve dynamic range, then read differentiation capability improves, but the inherent small difference in SOT-MRAM limits this improvement
Solution Approach 1:
The patent employs the selector device as an intermediary that enhances the effective dynamic range. By configuring the selector in a high-resistance state during read operations, it creates a significant resistance contrast that amplifies the already small difference between high and low resistive states of the magnetic tunnel junction. This allows the read circuit to achieve better differentiation capability and larger effective dynamic range without modifying the intrinsic properties of the SOT-MRAM cell.
3Reliability
If repeated read operations are performed to maintain read margin, then reading reliability improves, but heating accumulates causing loss of spin stability and increased read disturbance
Solution Approach 1:
The selector device serves as an energy-dissipating intermediary that protects the magnetic tunnel junction from repeated heating cycles. During each read operation, the selector limits the current flow, reducing the thermal energy deposited into the magnetic tunnel junction. This allows multiple read operations to be performed while accumulating minimal heat, thereby maintaining spin stability and preventing read disturbance even after repeated access cycles.
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 solution enhances the reliability and stability of read operations by increasing the difference between low and high resistive states, minimizing heating, and improving the dynamic range of memory cells, thus reducing read disturbances.
Implementation Method 1
a write track made of a material exhibiting the spin Hall effect or a material exhibiting the orbital Hall effect
Implementation Method 2
based on a pillar-shaped magnetic tunnel junction the resistance of which varies as a function of the orientation of the magnetic layers
Data Source
AI summary
A memory circuit includes a read circuit and a memory array (M1, M2) including at least one magnetoresistive memory cell, the memory cell including: a pillar; a write track made of a material exhibiting the spin Hall effect or a material exhibiting the orbital Hall effect; a first selector and a second selector, each selector being configured to switch from an off state to an on state when the amplitude of the voltage across the terminals of the selector is higher than a predetermined threshold voltage Vth; the read circuit including: a current source configured to inject a read current (Iread) through the first selector; a detect circuit configured to detect when the second selector switches from an off state to an on state in response to injection of the read current (Iread) by detecting the resistive state of the magnetic tunnel junction.