A Dynamic Kink Test to Measure Sensor Instability In GMR Head
Original Publication Date: 2002-Nov-07
Included in the Prior Art Database: 2003-Jun-21
Introduction Disclosed is a Dynamic Magnetic Kink Sweep Test to capture GMR sensors with kink like features in their transfer curves. Kink like non-linearity in read sensor transfer functions are a low frequency signature of head instability, which is one of the major causes for a bit error event affecting hard drive performance. In the static magnetic test, quasi-static transfer curves have been used to catch this phenomenon. One of the key features in the transfer curve for an unstable head is the presence of kink. It is very important to detect this in the dynamic spin-stand magnetic test for design feedback. Previously published algorithms to test for head instabilities are frequency domain algorithms and focus on baseline popping phenomenon, which can be detected by monitoring the noise floor increase after a low frequency data pattern is written on the recording disk, as reported by Wallash and Li  . This dynamic kink sweep test focuses on the time domain amplitude/asymmetry changes induced by kinks in the transfer curve. Algorithm Disclosure The disclosed kink sweep test is a magnetoresistance version of an ac susceptibility test, where the dc field is provided by the bias current and the ac tickle field by data patterns of different frequencies. The test is based upon the Track Average Amplitude (TAA) and Track Average Amplitude Asymmetry (TAA Asymmetry) response of a sensor with a kink feature: 1) The amplitude response curve (Fig. 1) for a sensor with a kink in the transfer curve exhibits a plateau with a width which is the convolution of the kink width (in field) and the ac excitation field amplitude. Thus, if the exciting field is small, the amplitude response curve exhibits a plateau with a width similar to the kink width (for H 0.2, with kink size 3). If the exciting field is larger than the kink size, the amplitude response curve exhibits a plateau with a width proportional to the exciting field strength. 2) The idealized TAA Asymmetry response (Fig. 2) for a sensor with a kink in the transfer curve large asymmetry swing, as the exciting field scans across the transfer curve.