Flying Height Measurement Research Articles

Interferometric measurement of disk/slider spacing: the effect of phase shift on reflection

In an interferometric system for measurement of spacing between a transparent disk and a slider, the effect of phase shift on reflection off the slider surface must be considered to obtain an accurate measurement. Here, a theoretical treatment of the problem is described and typical measurements are provided of phase shift on reflection for several types of slider materials in use today. The technique used to measure phase shift utilizes an ellipsometric measurement of the slider's complex index of refraction from which the phase shift on reflection is calculated. Monochromatic interferometric theory is used to show that assuming the slider to behave as a dielectric with a phase shift on reflection of pi can result in flying height measurement errors on the order of 12 nm. The magnitude of the phase-shift effect is investigated for different slider materials. In addition, the variation in phase shift as a function of the wavelength of light is investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of slider roughness on asperity testing of thin-film media

Sliders used for glide (asperity) testing are typically composed of Al/sub 2/O/sub 3/-TiC composites, with average grain sizes from under 1 mu m to 1.5 mu m. The air bearing surfaces are polished to an average roughness of less than 25 nm. Atomic force micrographs measured on sliders of different grain sizes, but polished by the same manufacturer, showed a wide variety of surface morphology. However, all slider surfaces had asperities which were 25 nm or higher and on the order of the Al/sub 2/O/sub 3/-TiC grain size in diameter. These asperities will result in slider-disk spacing that is smaller than predicted from optical fly height measurement systems. consequently, avalanche curves measured using calibrated asperities show initial contact occurring a micro-inch or more above where optical fly height measurements had predicted. With slider-disk spacing, for asperity testing, falling below 50 nm, slider asperities represent a substantial portion of the slider-disk spacing and must therefore be factored into both testing and calibration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparison of flying height measurement between multi-channel laser interferometer and the capacitance probe slider

The authors studied the dynamics of a capacitance probe slider by measuring the head-disk spacing during CSS (contact-start-stop) cycles and during steady-state flying. They measured the head-disk spacing with both the MCLI and the capacitance probe slider simultaneously and then attempted to correlate the spacing fluctuation results. They first determined the calibration factor by measuring the flying height and the change in the capacitance during the CSS cycle. As expected, it was observed that the change in the capacitance is a nonlinear function of the change in the spacing. However, it was also discovered that the same calibration factor determined by a CSS cycle cannot be applied to calibrate the spacing fluctuation measurements made during steady-state flying conditions. The disagreement is due to spacing averaging caused by the finite size of the capacitance pad. >

Multi-channel interferometric measurements of slider flying height and pitch

A multichannel interferometer which measures relative displacements from the top of the slider and disk is used to make concurrent measurements of absolute slider flying height and pitch. This technique is applied to actual disks and sliders and is not subject to limitations of low spacing and surface textures which are problematic for white light interferometry and modeling. It is applicable to both constant speed operation and dynamic events including takeoff and landing. It has the bandwidth necessary for dynamic measurements of the interface, depending on the sampling rates used when acquiring data. These features combine to make this an excellent tool for various aspects of head-disk interface development including low flying heights, slider stability, and tribology. The results obtained with this technique are compared with those of white light interferometry and modeling for absolute flying height and pitch measurements. >

Flying height measurement of a head slider using color image processing technique.

A new method to measure the flying height of head sliders in magnetic disk devices was developed. The interference color fringe created in the clearance between the slider and the glass disk was characterized by using the color image processing technique. The relation between hue and the flying height was obtained within 0.0073μm accuracy. The presented method makes use of the phase difference among RGB signals, so it doesn't depend on the light intensity distribution in the TV field, which comes from the optical devices. In addition, the present method gives continuous flying height attitudes.

Comparison of optical and capacitive measurements of slider dynamics

A simultaneous slider air bearing thickness measurement is made using capacitive and optical techniques. The first technique measures the capacitance between a conducting disk and a probe attached to the slider, and the other measures the optical path length using interferometry. A quartz disk with a transparent conductive coating is used for this experiment. Measurements are made simultaneously at three corners of the slider from DC to 100 kHz. The DC flying height measurements agree to within 7 nm while the AC fluctuations agree to within the noise level of each technique (0.2 nm).

Unshielded capacitor probe technique for determining disk memory ceramic slider flying characteristics

Small (0.025-in diameter) capacitor probes mounted without shield rings in ceramic air-bearing sliders enable dynamic flying height measurements to be obtained in the 40- to 200-μin range for flying over aluminum disks protected with thin epoxy coatings. An absolute precision of 4 percent and a relative precision of better than 1 percent is realizable at a 60 μ,in height. Three probes per slider, monitored simultaneously, yield roll and pitch angle information in addition to height data. The measured height and pitch angle time-average values agree with those computed using Reynolds equation. Experimental calibration of the probes is in satisfactory agreement with a conformal-transform computed calibration. The probe technique has led to the development of a stable-flying slider of apertureless rectangular design.