Three-Terminal Spin Accumulation Sensor for High Density Recording
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Solution Overview
Problem
Current read sensor technologies, such as TMR sensors, face challenges in achieving necessary signal and signal-to-noise performance at smaller sizes required for increased areal recording density in perpendicular magnetic data recording systems, and they are inadequate below a certain device size limit.
Innovation Solution
A three-terminal spin accumulation read head sensor design is introduced, where the reference layer is located away from the air bearing surface, and a non-magnetic conductive spin-transport layer extends to the free layer at the air bearing surface, allowing for improved signal detection without shunting spin current and simplifying fabrication, eliminating the need for a fourth contact that would interfere with hard bias stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If TMR sensors are reduced in size to increase areal recording density, then areal recording density is improved, but signal-to-noise performance deteriorates
Solution Approach 1:
The reference layer is moved from the air bearing surface to a position away from it, utilizing the vertical dimension to separate the reference layer from the sensing location. This dimensional repositioning allows the free layer at the air bearing surface to maintain small size for high areal density while the reference layer can be larger to provide stable spin polarization without the same size constraints
Solution Approach 2:
The sensor is divided into spatially separated components: the reference layer structure is positioned away from the air bearing surface while the free layer structure remains at the air bearing surface. This segmentation allows each layer to be optimized independently for its specific function without the conflicting size requirements that would apply if both layers were co-located
2Measurement precision
If a fourth contact is added to the sensor structure, then spin current measurement capability is improved, but fabrication complexity and hard bias stabilization deteriorate
Solution Approach 1:
The fourth contact is removed from the sensor structure. Instead of providing a direct electrical connection to the free layer at the air bearing surface, the design uses the three-terminal configuration where spin current is detected through the existing terminal connections, eliminating the fabrication complexity and hard bias stabilization problems that would arise from adding a fourth contact
3Measurement precision
If the reference layer is located at the air bearing surface, then sensing resolution is improved, but spin current shunting occurs
Solution Approach 1:
The reference layer is repositioned in the vertical dimension away from the air bearing surface, allowing the free layer to remain at the air bearing surface for high-resolution sensing while the reference layer is positioned where it can receive spin current without shunting losses
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 design enhances signal-to-noise performance and allows for increased areal recording density without compromising the narrow gap linear read-back resolution, making it practical for use in data recording systems by preventing spin current shunting and simplifying the fabrication process.
Implementation Method 1
an internal non-magnetic, conductive spin-transport conducting layer extending from said reference layer structure to said free layer structure
Implementation Method 2
The magnetization of the reference layer is fixed perpendicular to the air bearing surface (ABS) and the magnetization of the free layer is oriented parallel to the ABS, but free to rotate in response to external magnetic fields
Data Source
AI summary
A spin accumulation sensor having a three terminal design that allows the free layer to be located at the air bearing surface. A non-magnetic conductive spin transport layer extends from a free layer structure (located at the ABS) to a reference layer structure removed from the ABS. The sensor includes a current or voltage source for applying a current across a reference layer structure. The current or voltage source has a lead that is connected with the non-magnetic spin transport layer and also to electric ground. Circuitry for measuring a signal voltage measures a voltage between a shield that is electrically connected with the free layer structure and the ground. The free layer structure can include a spin diffusion layer that ensures that all spin current is completely dissipated before reaching the lead to the voltage source, thereby preventing shunting of the spin current to the voltage source.