STO Element Bias Voltage Stabilization in Magnetic Recording Heads
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Solution Overview
Problem
In magnetic disk devices using perpendicular magnetic recording, high frequency assist elements like STO elements face variability in dimensions and resistance values due to manufacturing difficulties, leading to unstable oscillations and potential damage from fluctuating voltage applications, especially with temperature changes.
Innovation Solution
A magnetic disk device with a controller that measures the resistance value of the STO element and adjusts the bias voltage applied, ensuring a constant voltage supply regardless of dimension variations and temperature fluctuations, using a system that calculates the optimal bias voltage based on measured resistance values and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant bias voltage is applied to the high frequency assist element to maintain constant current density, then oscillation stability is improved, but manufacturing variations in element dimensions cause resistance value variations leading to voltage fluctuations and potential element damage
Solution Approach 1:
The patent applies preliminary action by measuring the resistance value of each high frequency assist element before mounting it on the recording head, and storing this measured value in memory. This advance measurement and storage allows the system to later adjust the bias voltage based on the actual resistance value, compensating for manufacturing variations before they cause oscillation instability or element damage.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the bias voltage applied to each high frequency assist element based on its measured resistance value. The control unit calculates an appropriate bias voltage using the stored resistance value and temperature characteristics, ensuring that the current density remains constant despite variations in element dimensions. This parameter adjustment resolves the contradiction by adapting the voltage to match each element's actual characteristics.
2Reliability
If the bias voltage is increased to compensate for resistance variations, then current density stability is improved, but temperature fluctuations cause incidental resistance changes leading to voltage instability and element damage
Solution Approach 1:
The patent implements feedback by continuously monitoring temperature and using this information to adjust the bias voltage applied to the high frequency assist element. The control unit stores temperature characteristics (dR/dT values) for each element and uses this feedback to compensate for resistance changes caused by temperature fluctuations, maintaining stable current density and preventing element damage.
Solution Approach 2:
The patent applies preliminary action by pre-measuring and storing the temperature characteristics (dR/dT values) of each high frequency assist element before operation. This advance preparation allows the system to predict and compensate for resistance changes due to temperature variations, adjusting the bias voltage proactively rather than reactively to maintain stable operation across different temperatures.
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 stabilizes the oscillations of the STO element, improves recording density, and prevents damage from voltage fluctuations, ensuring reliable operation across varying conditions.
Implementation Method 1
The high frequency assist element generates magnetic resonance by generating specific a high frequency vibration at the time of recording and applying the high frequency vibration to a magnetic recording surface, thereby assisting a response of magnetization reversal. An example of the high frequency assist element includes a spin torque oscillating element (STO: Spin Torque Oscillator).
Implementation Method 2
a coil configured to excite a magnetic flux in the magnetic circuit formed by the main pole and the return pole to generate a recording magnetic field
Implementation Method 3
a narrowed portion made of a soft magnetic metal and configured to generate a magnetic field in the perpendicular direction
Data Source
AI summary
According to one embodiment, a magnetic disk device applies a bias voltage for measurement to a high frequency assist element according to a setting instruction of the bias voltage to measure a conduction current by in a recording head, calculates the resistance value in the supply path of the bias voltage from a relationship between the measured current and the bias voltage for measurement, and changes the bias voltage applied at the time of data recording based on the calculated resistance value.