Integration of Barium Ferrite on the 6H-SiC through Molecular Beam Epitaxy
The ferrite nonreciprocal microwave devices (i.e. circulators, isolators, filters, phase shifters, etc.) are critical components of the more than $1 trillion communications industry in United States including commercial cell phones, military radars, and satellites. Integration of nonreciprocal ferrite microwave devices with semiconductor platforms could allow for reduced volume and weight in phased array radar electronics, in addition to enhanced bandwidth and power management. Barium hexaferrite (BaFe12O19, BaM) has attracted much attention for microwave device applications because of its large (17 kOe) uniaxial magnetocrystalline anisotropy, and high resistivity and permeability at high frequencies (above 40 GHz). The performance of current ferrite devices would be enhanced and novel devices would be possible if ferrite films such as BaM were integrated with wide bandgap semiconductors (e.g. SiC), which can function in high-temperature, high-power, and high-frequency environments where Si or GaAs cannot. 

 

 

 

Fig.1. Three generations of interface engineering have produced decreased FMR linewidths below the 250 Oe goal, and high saturation magnetization above the 4000 Oe goal.

 

 

 

 

 

 

Fig.2. The films grown on MBE interface have maintained the c-axis perpendicular geometry and the surface smoothness has improved from 56 nm to 1 nm rms over a 2 micrometer area.
This research uses ultra-high vacuum (UHV) analytical techniques and molecular beam epitaxy (MBE) to investigate the nucleation and growth mechanisms of BaM thin films on 6H-SiC in order to produce BaM seed layers by MBE for subsequent pulsed laser deposition (PLD) or liquid phase epitaxy (LPE) growth of thick BaM films with desired stoichiometry, structure, and magnetic properties necessary for microwave device applications. X-ray photoelectron spectroscopy (XPS) surface analysis and depth profiling are used to verify film chemistry and detect diffusion across the interface. Atomic force microscopy (AFM), scanning electronic microscope (SEM), and X-ray diffraction (XRD) are used to characterize the surface morphology, and surface roughness, and crystal structure.

Improvement of PLD-grown Barium Ferrite on the 6H-SiC through the use of MBE-grown MgO interlayer
The ferromagnetic resonance (FMR) linewidth is a measure of the loss of signal due to the material, with a lower linewidth indicating a less “lossy” film. Device engineers would like an FMR linewidth of less than 250 Oe, but would optimally prefer less than 100 Oe. The highest possible saturation magnetization (Ms) is desired, and the goal value for devices is 4000 kOe. Following figures show the improvement in the FMR linewidth and Ms with the improved interfaces between BaM and SiC, and the improved film morphology. Integration of BaM with SiC is important for monolithic integrated microwave frequency devices .

References:
Chen, Z., Yang, A., Yoon, S.D., Ziemer, K.S., Vittoria, C., Harris, V.G. “Growth of Ba-hexaferrite films on single crystal 6-H SiC” Journal of Magnetism and Magnetic Materials, 301(1), pages 166-170, 2006


Z. Chen, A. Yang, Z. Cai, S.D. Yoon, K. Ziemer, C. Vittoria, and V.G. Harris, “Structure and magnetism of Ba-hexaferrite films grown on single crystal 6H-SiC with graduated interfacial MgO buffer layers”, IEEE Transactions on Magnetics, 42(10) pages 2855-2857, 2006.


Z. Cai, Z. Chen, T. L. Goodrich, V.G. Harris, K. S. Ziemer, “Chemical and structural characterization of barium hexaferrite films deposited on 6H-SiC with and without MgO/BaM interwoven layers”, Accepted to Journal of Crystal Growth, 2007


Z. Chen, Z. Cai, T. L. Goodrich, A. Yang, A. Gieler, V.G. Harris, C. Vittoria, P.R. Ohodnicki, K. Y. Goh, M. E. McHenry, and K. S. Ziemer, “Epitaxial growth of M-type Ba-hexaferrite films on MgO(111)//SiC (0001) with low ferromagnetic resonance linewidths”, Submitted to: Applied Physics Letters, 7/13/07