Magnetic read sensors with improved thermal characteristics using high density amorphous carbon films as dielectric gaps
Original Publication Date: 2002-Jan-27
Included in the Prior Art Database: 2003-Jun-20
Disclosed is the use of dense amorphous carbon films with high thermal conductivities as a dielectric gap layer in magnetic recording heads. The maximum permissible amplitude of a bias current that can be applied to read sensors in magnetic recording heads is limited by their heat dissipation capability. This limitation, in turn, imposes a constraint on the read back signal amplitude and signal-to-noise ratio that can be attained for a given magnetic read sensor. As the recording areal density of the magnetic data storage continues to increase rapidly, engineering of magnetic materials alone is insufficient to achieve required improvement in sensor sensitivity. Heat conduction cooling of read sensors is strongly impeded by dielectric gap layers that physically separate the sensors from magnetic shield layers. The thermal resistance associated with these dielectric gap layers can be divided into two components. One component, henceforth called the bulk resistance, is related to the transport of microscopic energy carriers within the layers and scales with the layer thickness. The other component, commonly referred to as the thermal boundary or Kapitza resistance, arises from mismatch in physical properties across the layer interfaces. Because the thickness of these dielectric gap layers is expected to be less 20 nm in advanced magnetic heads, the thermal boundary resistance is comparable to or larger than the bulk resistance. Amorphous diamond-like carbon films for use as gap material in magnetoresistive heads are disclosed in U.S. patents 5,644,455 and 5,986,857. The thermal conductivity of amorphous carbon films of thickness smaller than 500A synthesized using the filtered cathodic arc method (Figure 1) is considerably higher 2.5x) than that of amorphous aluminum oxide (Figure 2), which is the most widely used material in the storage industry. Carbon films deposited using IBD method (Figure 2), in contrast, has rather poor thermal conductivity. A theory of heat conduction in amorphous materials suggests that the thermal conductivity of amorphous diamond films is intimately related to their density and sp3/sp2 bonding ratio. We expect that amorphous diamond films deposited using the pulsed laser deposition (PLD) technique, which also yields very high density films, are also suitable for the present applications. A previous study  indirectly measured the thermal conductivities of various carbon films of thickness 700A. The heat capacities of these films, which are needed to extract the thermal conductivity from these measurement were not measured independently, and rough theoretical estimates were used instead based on the elastic properties and densities of the films. Uncertainties in the thermal conductivity values introduced by this procedure can be very large but hard to estimate.