TDMR Disk Drive Sensor Pair Selection for Skew Compensation
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Solution Overview
Problem
In two-dimensional magnetic recording (TDMR) disk drives with multiple stacked sensors, the skew of sensors at the inside diameter (ID) and outside diameter (OD) regions causes misalignment with target tracks due to the radial actuator's arcuate path, leading to reduced readback accuracy, as the sensors are shielded by magnetic permeable materials that must maintain a minimum thickness to be effective.
Innovation Solution
The TDMR disk drive employs first and second sensors electrically coupled to a magnetic shield, with third and fourth sensors coupled to another shield, having different cross-track spacings, and switching circuitry selects the appropriate pair of amplifiers based on the radial location, ensuring alignment with data tracks despite high skew angles, and includes switchable impedance elements to maintain consistent transmission line resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple stacked sensors are used in TDMR to increase areal data bit density, then readback areal density is improved, but sensor skew at ID and OD regions causes misalignment with target tracks
Solution Approach 1:
The sensor array is segmented into multiple independently controllable sensor groups, where each group can be selectively activated based on the radial position on the disk. This allows the system to use only the sensors that are properly aligned with the target tracks at any given radial location, thereby maintaining measurement precision while avoiding the skew-induced misalignment problems.
Solution Approach 2:
The system dynamically selects which sensor group to activate based on the radial position of the read head. By switching between different sensor groups as the head moves across the disk surface, the system adapts to the changing skew conditions and maintains optimal alignment between sensors and target tracks throughout the entire disk surface.
2Object-affected harmful factors
If magnetic shields of minimum thickness are used to shield sensors from neighboring data bits, then shielding effectiveness is improved, but cross-track spacing between sensors is limited
Solution Approach 1:
The shield structure is segmented into multiple sections, with each sensor group having its own dedicated shield section. This segmentation allows for optimized spacing between sensors within each group while maintaining adequate shielding, as the shields can be positioned to protect specific sensor groups without constraining the overall sensor array layout.
Solution Approach 2:
Different regions of the sensor array have different shielding requirements and spacings optimized for their specific functions. Sensors that require closer spacing for TDMR operations are positioned in regions where shielding can be effectively provided, while maintaining the minimum shield thickness requirement for protecting against neighboring data bit interference.
3Manufacturing precision
If sensors are spaced closer along the track to reduce skew effect, then alignment accuracy is improved, but magnetic shield thickness requirements limit how close sensors can be spaced
Solution Approach 1:
The system uses dynamic sensor group selection to achieve high alignment accuracy without requiring minimal sensor spacing. By switching between sensor groups with different along-track positions, the system can maintain accurate alignment even when sensors are spaced farther apart, thereby reducing the constraints imposed by shield thickness requirements.
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 configuration allows for accurate reading of data tracks across the entire disk surface by compensating for skew angles, enhancing readback areal density and signal processing without altering the impedance characteristics, thus improving the overall performance of TDMR systems.
Implementation Method 1
Each of the individual CPP-MR sensors in a TDMR read head structure is required to be located between two shields of magnetically permeable material that shield the sensors from recorded data bits that are neighboring the data bit being read.
Implementation Method 2
A GMR spin-valve sensor has a stack of layers that includes two ferromagnetic layers separated by a nonmagnetic electrically conductive spacer layer... With a sense current applied to the sensor, the rotation of the free-layer magnetization relative to the pinned-layer magnetization due to the presence of an external magnetic field is detectable as a change in electrical resistance.
Implementation Method 3
In a CPP-TMR sensor the amount of tunneling current through the layers depends on the relative orientation of the magnetizations in the two ferromagnetic layers.
Data Source
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AI summary
A two-dimensional magnetic recording (TDMR) disk drive has a gas-bearing slider that includes first and second sensors with a first cross-track spacing electrically coupled to a first magnetic shield, and third and fourth sensors with a different cross-track spacing electrically coupled to a second magnetic shield. The different spacings results in the first and third sensors and the second and fourth sensors having a cross-track spacing to accommodate for the effect of head skew. Each sensor is connected to an associated amplifier by a suspension trace and a common trace connected to its associated shield. Switching circuitry selects either the first and third amplifiers or the second and fourth amplifiers as the active pair depending on the radial location where the data is to be read. Thus the appropriate pair of sensors are aligned with the data tracks despite the presence of high head skew.