Magnetic Shift Register Domain Wall Control
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Solution Overview
Problem
Current racetrack magnetic memory technologies face challenges in controlling domain wall movement, leading to data bit errors due to variability in pinning potential and stochasticity of domain wall motion, making it difficult to achieve precise control over single bit positions with low energy consumption.
Innovation Solution
A serial magnetic shift register design that applies multiple phases of current through strategically placed contacts along a magnetic track, allowing for precise control of domain wall movement without exceeding one bit position, reducing write energy and eliminating the need for track patterning, and enabling bidirectional data bit movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional spin transfer torque (STT) is used to shift domain walls with a single current pulse, then the domain wall shifting mechanism is simple, but precise control of single bit position is difficult due to variability in pinning potential and stochasticity of domain wall motion
Solution Approach 1:
The magnetic track is divided into multiple bitcells, each with its own set of contacts. This segmentation allows independent control of domain walls in different bitcells, enabling precise positioning of individual bits without affecting others, thus resolving the control precision issue while maintaining operational simplicity.
Solution Approach 2:
Multiple phases of current pulses are applied in a periodic sequence to the contacts. This periodic action allows margining of the current pulse, where larger currents can be applied to guarantee domain wall movement without causing excessive displacement, achieving both simplicity and precision in domain wall control.
2Reliability
If larger currents are applied to guarantee domain wall movement, then data bit errors are reduced, but domain walls may move beyond one bit position
Solution Approach 1:
By dividing the track into bitcells with dedicated contacts, the current path is segmented. This allows applying larger currents to specific bitcells without affecting adjacent bits, as each bitcell has its own contact set that isolates the current flow, thus achieving both reliability and position control.
Solution Approach 2:
Different contacts are activated in different phases to create local current fields. This local quality approach allows margining currents to be applied precisely where needed (in specific bitcells) without causing domain walls in other regions to move excessively, resolving the contradiction between reliability and precision.
3Manufacturing precision
If multiple phases of current are applied through strategically placed contacts, then precise control of domain wall movement is achieved, but device complexity increases
Solution Approach 1:
The contacts serve multiple functions: they act as current injection points for domain wall motion, provide addressing for specific bitcells, and enable margining of current pulses. This multi-functionality reduces the need for separate components for each function, offsetting the complexity of the contact arrangement with operational efficiency.
Solution Approach 2:
The patent combines the addressing mechanism, current injection, and domain wall control into a single contact structure. By merging these functions into the contact arrangement itself, the overall device complexity is reduced compared to having separate components for each function, thus achieving precise control without excessive complexity.
4Ease of operation
If write current is applied through magnetic tunnel junction, then data can be written, but write energy consumption is high
Solution Approach 1:
The patent replaces the magnetic tunnel junction-based write mechanism with a direct current-driven domain wall motion mechanism through contacts. This substitution eliminates the need for high-energy spin-polarized current through MTJ, using instead a more energy-efficient direct current path through the track, thus maintaining write capability while reducing energy consumption.
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 allows for high-density, low-energy, and low-latency data storage with improved control over domain wall shifting, achieving 1-2 ns shift time with 10 μA current pulses and reducing the need for stable power supplies, while maintaining non-volatility and high memory density.
Implementation Method 1
The domain wall shifting mechanism is current-driven, traditionally spin transfer torque (STT), where a spin-polarized input current imparts a torque on local magnetic moments causing them to align in the direction of the electron spin.
Implementation Method 2
Stored data bits of the racetrack are read out serially via a magnetic sensor (e.g., magnetic tunnel junction) in proximity to the track somewhere along the shift register.
Data Source
AI summary
This disclosure relates to a memory device that includes at least one magnetic track on a substrate, wherein the at least one magnetic track comprises one or more magnetic domains. Contacts can be disposed on the at least one magnetic track according to a predetermined arrangement to form a plurality of bitcells on the at least one magnetic track, wherein each one of the plurality of bitcells is configured to store at least one magnetic domain. The device can include a timing circuit connected to the contacts, with the timing circuit being configured to apply to the contacts multiple phases of electric currents according to a predetermined timing sequence to cause the at least one magnetic domain to shift from the each one of the plurality of bitcells to an adjacent one of the plurality of bitcells on the at least one magnetic track.