Jaap Ruigrok

Rapid Thermal Magnetic Annealing: A Novel Technique in Thin-Film Recording Head Production?

A new emerging application area for Rapid Thermal Annealing (RTA) may be in the manufacturing of thin-film recording heads for high-density (hard disk drive, video, audio and data tape) recording. To that end we co-designed a new commercial reactor with an external electromagnet to anneal thin soft-magnetic films (nanocrystalline iron alloys) deposited on ceramic wafers of up to 150 mm diameter. The electromagnet generates a field controllable up to 660 Oe (52.8 kA/m). It is completely homogeneous in direction (i.e. fully parallel field lines) across the entire wafer area. Wafers can be annealed either statically, or while rotating (up to 120 rpm), or in two subsequent heating steps with a 90° wafer rotation in between. Nanocrystalline Fe-Nb-Si-N layers have better soft-magnetic properties after Rapid Thermal Magnetic Annealing (RTMA) in a static magnetic field than after conventional furnace annealing in a static field. Temperature-programmed resistance measurements and Transmission Electron Microscopy (TEM) show that the first nanocrystalline, body-centered cubic iron grains start growing already as of 350 °C from the amorphous as-deposited film, whereas the desired segregation of NbN starts only as of 530°C. RTA can be used to promote the kinetics of the segregation of NbN along the boundaries of nanocrystalline iron nuclei. This prevents the iron grains from further growth: with RTMA the iron alloys show smaller nanocrystalline iron particles (order: 10 nm) as observed by TEM.