Ultrathin wear-resistant coatings for the tape bearing surface of thin-film magnetic heads for digital compact cassette

The introduction of the digital compact cassette system into the consumer market imposed some severe requirements on the durability of the thin-film heads used in this system. The reliability of the head´s record and playback functions has to be maintained under a wide variety of climatic conditions and tape types, as a consequence of the system´s backward compatibility with the analog compact cassette. This paper describes the results of several accelerated wear tests as well as of durability tests against tape, which were setup to find the best material and process conditions for a wear-resistant coating on the tape bearing surface of a DCC head. This ultrathin coating (<75 nm) appeared to be the best solution as a safeguard against severe pole-tip recession, which would cause an unacceptable distance loss in the recording system. The first material which showed a very high wear resistance was CrN. As CrN fulfils all requirements for wear and corrosion resistance in the home application, this material is presently used in all DCC home decks. However, under extremely abrasive conditions, such as may be encountered in a car environment (e.g. cold start at -20°C), CrN is surpassed by an even more wear-resistant material, called SPL (super protective layer). Therefore, SPL is preferred as a coating on thin-film heads for car stereo (as well as portable) DCC apparatus. Both materials are characterized by their specific wear performance, which has a superior impact on the electrical (record and playback) properties of the head during its life-time