An overview of glide testing

Abstract

Low flying air-bearings, "sliders," with contact sensors are used to "glide" test magnetic recording disks to be free of asperities above a predetermined height. A technical overview of the considerations necessary for accurate glide testing is illustrated by the example of an experimental flat plate PZT sensor, with electrodes divided into quadrants, to detect asperity contact. The flat plate PZT sensor detects the slider dynamic pitch, roll, and vertical vibrations of the air bearing by contact with asperities of sufficient mechanical stiffness. The sensor also detects contact by the extremely sensitive response of the resonant vibrations of the PZT/slider structure. Different linear combinations of the signal from the quadrants show mode selection based on mode symmetry. The signal response for increasing asperity interference is characterized for specific modes and a mode can be chosen by the appropriate linear combination of the signals from the quadrants. Calibration of the glide slider trailing edge flying height and roll using contact with artificial bumps of different heights is necessary for accurate glide testing. One can map the entire disk surface using the contact signal from both the air-bearing response and the bending mode response simultaneously to identify mechanically "stiff" asperities. Visualization of the mode shapes and characterization the PZT/slider structure using a laser heterodyne interferometer aid in the consistent fabrication of this class of PZT contact sensors. The considerations of sensor response, characterization of the contact signal, techniques to allow consistent PZT/slider fabrication, and calibration methods that allow the signal to be related to the test tolerances represent a technical overview of the requirements for any glide sensor technology.

Tribological issues in perpendicular recording media

“…The slider ABS itself is especially designed so that its flying height can also be adjusted by varying its velocity. To calibrate the slider flying height, a special piezoelectric (PZT) sensor is mounted on the slider, and flown on a specially made disk with bumps of known heights [13] By controlling the maximum interference with the bumps to be less than 2 nm during calibration of the flying height, we get repeatability to 0.1 nm indicating that bump wear or pad wear during calibration is small. The lowest bump is $5 nm tall and the maximum protrusion is $7 nm, so that flying heights below 5 nm can be spanned with thermal actuation until contact is made with the media.…”

“…The small size of the contact pad also reduces the effect of slider roll and slider roughness on the TDH measurement. The piezoelectric sensor is mounted over the entire back surface, and senses the second and third bending mode vibrations of the structure during asperity contact [13]. The high contact sensitivity of the sensor is shown by varying interference with a 10-nm-tall calibration bump (figure 13) by changing flying height or by changing heater power.…”

Ultra sensitive in-situ acoustic characterization system for HDD head disc interface defectoscopy

“…In-situ AE detection has been used in commercial CSS testers for decades where AE sensors are placed on the E-block or its spin-stand setup equivalents. A lead zirconium titanate (PZT) element integrated into the slider has been explored for several years in the device called piezo head/glider and used for contact detection in HDI development work (Ashar 1997;Ou-Yang et al 1999;Nayak et al 2003). A piezo glider senses HDI interactions via coupling with slider vibrational modes at 800 kHz-1.4 MHz frequency range.…”

Slider–bump contact and flying height calibration

“…One of the key issues of the bump disk method is how to detect the occurring of slider-bump contact. The glide slider with a piezoelectric transducer (PZT) plus bump disk is probably the most reliable and acceptable method to detect slider-bump/disk contact and calibrate FH [7][8][9][10]. It is also widely used in gliding tests [11] to control and assure the morphology quality of disk media surface.…”