Effects of flying height deviations on glide height tests for manufacturing hard disks

In this study, theoretical analysis and experiments were carried out to investigate the effects of avalanche-point deviation and the deviation between the calibration and test-flying heights during the glide head calibration in the glide height tests for manufacturing hard disks. To obtain accurate glide height test results and improve the reproducibility of the test, flying height control should be carried out by limiting the acceptable deviation range of the flying heights of the glide heads. When the avalanche-point deviation is zero, the test results using different calibrated rails (or heads) are the same when they are used to detect the same defect. To avoid wrong test results due to avalanche-point deviation, the test-flying height should be the same as the calibration flying height because the difference of the output voltages of any two rails (or heads) is zero in this case. If these two deviations cannot be eliminated completely, the calibration and test-flying heights should be carefully selected because the error still can be minimised depending on the selection of the flying heights.