Polycrystalline ferrite films for microwave applications

Polycrystalline thick Mg-Mn ferrite and ferrochromite films were deposited on polycrystalline ceramic substrates and on platinum by using chemical transport in close-spaced configuration. The deposition process was mostly diffusion controlled. Epitaxial growth of ferrite on platinum and sapphire crystals was observed. Films in the 100 to 1000-μm thickness range were continuous only in the case of relatively small substrate-ferrite thermal expansion mismatch. Suitable substrate materials were forsterite and platinum. Ferrite grain size increased with film thickness. Thick deposits were coarse-grained and had rough surfaces requiring grinding. Magnetic and electric film properties at band, including reciprocal phase shift, were similar to those of bulk materials, with differences resulting from coarse-grain structure and from substrate effect. Promise for an -band microstrip phase shifter appeared.