Browse Prior Art Database

Latent Defect Detection in Thin-Film Magnetic Media

IP.com Disclosure Number: IPCOM000111739D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Farrow, RFC: AUTHOR [+3]

Abstract

Disclosed is a means for detecting latent, typically sub-surface defects in thin-film magnetic data storage media.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 87% of the total text.

Latent Defect Detection in Thin-Film Magnetic Media

      Disclosed is a means for detecting latent, typically
sub-surface defects in thin-film magnetic data storage media.

      Photothermal deflection employs an optical pump and a seperate
optical probe coincident on the surface under test to measure spatial
variations in the local heating caused by the pump beam.

      Photothermal deflection applied to thin-film magnetic recording
media employs an optical pump of selected wavelength which is focused
(from near normal incidence to the medium) at sufficient power to
cause a small local temperature rise.  The pump laser is pulsed or
modulated to facilitate detection suing a probe beam, coincident on
the medium, but oriented at an incident angle theta.    A
position-sensitive detector measures changes in probe reflected angle

(theta hyphen prime) caused by the time-dependent local heating.
Since the temperature rise is extremely sensitive to absorbed power
and thermal conductivity of the thin film, any contamination, voids,
or latent delamination causes a marked change in reflected angle
compared with defect-free regions.

      Using a rotary encoder and radial servo, defect location on a
spinning storage disk can be facilitated and correlated with magnetic
errors.  Spatial selectivity is limited by the numerical aperture of
the optics and by the trade-off between resolution and data rate.

      Pump wavelength is selected to optimize signal and...