Improvement of measurement sensitivity near contact in intensity-interferometry flying height testers

In the hard disk drive, the spacing between the read/write head and the magnetic disk or flying height has been greatly reduced to a few nanometers to achieve ultrahigh-density magnetic storage. At flying heights below 10 nm, intensity-interferometry flying height tester, the major technique for flying height measurement suffers from low measurement sensitivity. This paper reports a simple and inexpensive method to improve the sensitivity of intensity-interferometry method for measuring flying heights down to contact by using a glass disk coated with multiple layers of silicon and diamond-like carbon (DLC) films. The optimum film thicknesses were selected in order to improve the measurement sensitivity by theoretically analyzing the light interference at the head-disk interface. The improved sensitivity was confirmed in experiments performed in a flying height tester. It was found that the measurement sensitivity at very low flying heights (0–20 nm) was improved by 85 % using a glass disk coated with four layers: Si₁ of 1 nm, DLC₁ of 55 nm, Si₂ of 3 nm and DLC₂ of 25 nm. The proposed method not only significantly improves the sensitivity, but it also considerably increases the durability of glass disks promising the application of the intensity-interferometry flying height tester for measuring flying heights down to contact.