CPP-GMR Sensor Spacer Layer Alloy Design
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Solution Overview
Problem
Current CPP-GMR sensors face challenges with high device resistance and susceptibility to corrosion during fabrication, leading to instability and reduced signal-to-noise ratios due to spin-torque effects and corrosion of metallic spacer layers.
Innovation Solution
A spacer layer comprising a silver alloy, such as Ag-Sn or Cu-Ge, is used to increase electrical resistivity and corrosion resistance, reducing spin-torque induced instability and maintaining signal quality during the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metallic spacer layer is used in CPP-GMR sensors, then the device resistance is reduced, but the spacer layer becomes susceptible to corrosion during fabrication
Solution Approach 1:
The patent applies composite materials by combining a metallic spacer layer with a protective capping layer to create a multi-layer structure. The metallic layer maintains low resistance while the capping layer provides corrosion protection during fabrication, resolving the contradiction between achieving low device resistance and preventing corrosion susceptibility.
2Power
If high current density is applied to CPP-GMR sensors, then the output signal increases, but spin-torque effects cause oscillatory instability
Solution Approach 1:
The patent changes material parameters by selecting specific metallic spacer materials and optimizing their thickness to alter the spin-torque characteristics. By adjusting these parameters, the sensor can operate at higher current densities for improved output signal while maintaining magnetization stability and avoiding oscillatory instability.
3Ease of manufacture
If lapping or CMP is performed during read head processing, then the air bearing surface is formed, but the metallic spacer layer oxidizes and hampers electrical current flow
Solution Approach 1:
The patent applies preliminary action by depositing a protective capping layer on the metallic spacer layer before the lapping or CMP process. This pre-protective measure prevents oxidation of the metallic layer during mechanical processing, ensuring that electrical current flow is not hampered while still enabling air bearing surface formation.
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 increased resistivity and corrosion resistance of the spacer layer allow for higher voltage across the sensor and improved signal-to-noise ratios, while minimizing the effects of corrosive materials during processing, thereby enhancing the stability and performance of CPP-GMR sensors.
Implementation Method 1
the spacer layer increases the electrical resistivity of the read head sensor relative to a spacer layer consisting entirely of the at least one metal
Implementation Method 2
a GMR read head has a resistance that varies according to the angle between the free and reference magnetic layers
Implementation Method 3
the CPP-GMR sensor uses spin-dependent scattering of the conduction electrons at both the interface between the magnetic and spacer layers as well as in the magnetic layers themselves
Implementation Method 4
the output signal and signal/noise ratio for a CPP-GMR sensor is limited by spin-torque effects, which originate from the torque induced on either the free or reference magnetic layers by the spin-polarized electron current density applied during operation
Data Source
AI summary
A method and apparatus for increasing the electrical resistivity and corrosion resistance of the material forming a spacer layer in current-perpendicular-to-the-plane (CPP) giant magnetoresistive (GMR) sensors. The increased resistivity of the spacer layer, and thus, the CPP-GMR sensor permits a larger voltage across the sensor and a higher signal-to-noise ratio. The increased corrosion resistance of the spacer layer minimizes the effects of exposing the spacer layer to corrosive materials during fabrication. For example, adding tin to silver to form a metallic alloy spacer layer increases the corrosion resistance of the spacer layer and the electrical resisitivity of the CPP-GMR sensor relative to a spacer layer consisting solely of silver. The Ag—Sn alloy permits a larger current to flow through the sensor, which increases the signal-to-noise ratio.