Electrochemical Impedance Characterization of Ultra-thin Carbon Overcoats

摘要

There is a strong drive in the magnetic hard disk industry to improve the sensitivity of the magnetic sensor, which will allow for a higher recording density. In order to protect the magnetic head from environmental degradation, a carbon overcoat, which consists of a diamond-like carbon (DLC) film on top of a seed layer, is deposited onto its surface. By decreasing the thickness of the carbon overcoat, a higher sensitivity of the sensor can be achieved. However, a reduction in carbon overcoat thickness increases the likelihood of electrical shorting across the sensor surface via the carbon overcoat. This results in a degradation of the sensor performance as it reduces the performance stability as well as causes the sensor to become more prone to noise pickup. These issues are key factors in determining whether a new sensor and/or protective film may be profitably manufactured. For this reason, it is crucial that the shorting effect, if any, is characterized using an appropriate technique. Electrochemical impedance spectroscopy (EIS) is one possibility as it measures the frequency-dependent response signal of the system of interest, which in theory will allow for the isolation of the interface and/or mechanism responsible for the response signal. This technique is also sensitive to small electrochemical signals, which is needed for this application as the current shorting effect, such as through pinholes in the film, is extremely subtle