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As head-disk clearance has been reduced to nearly 1 nm, and a partial lube-contact head-disk interface (HDI) may even be necessary to meet future magnetic spacing needs, precise characterization of the slider-lube/disk contact state (or depth) becomes increasingly important. The currently used thermal fly-height control (TFC) sliders require a slight touchdown (or contact) to determine the reference position of the clearance, and accurate measurement and control of the penetration depth into the disk lubricant are essential to achieve a stable HDI for future lube-contact recording. In this paper, multiple techniques (e.g., acoustic emission technology, lubricant distribution mapping, slider wear detection, and slider dynamics measurement) are implemented to characterize the contact state/depth and HDI stability at different TFC actuation levels. Experimental results demonstrate the effectiveness of these methods and suggest that the clearance reference position determined through the acoustic emission technology is at the lubricant-air interface. Moreover, two dynamically stable contact states-light slider-lube contact and deep slider-disk contact-are found, but the latter causes slider wear and thereby is not practical for realizing a reliable lube-contact HDI.