The Use of Surface Segmentation Methods to Characterise Laser Zone Surface Structure on Hard Disc Drives

All surfaces, be they at the nano, micro or even macro scale are made up of a collection of fundamental features at many different scales which constitute the surface topography. The new generation of so called structured surfaces have features which are organised deterministic patterns these include MEMS/NEMS surfaces, micro-fluidic device surfaces, and surfaces with repeating features to improve their tribological properties. These types of surface are becoming both technologically and economically critical to high added value manufacturing. The deterministic features on these surfaces include tessellations, rotationally symmetric features and linear features. Surfaces possessing dominant deterministic features are considered to have a defined structure and are termed “structured surfaces” where the features are manufactured on the surface in order to give a specific functional response.
Surfaces with repeating features are of particular importance to tribological applications and have been designed to have specific contact, lubrication and bearing properties. Identification of the boundaries of such features presents particular problems in terms of measurement and characterisation and much recent research has focussed on “segmenting” measured surface data to allow for efficient characterisation of functional features. The characterisation methodology is based around extracting and characterising individual elements of the surface and secondly characterising their spatial relationships or pattern. The present paper uses the example of a laser zone textured surface used in the landing zones of hard disc drives to illustrate the latest developments in this type of surface metrology. These types of surface are used to “scrape out” the air bearings of read-write head and park the head effectively and without damage. The feature dimensions and spacing are therefore critical, and efficient measurement and characterisation is the critical element in assessing the disc functionality and life.