Structural and dielectric properties of boron-doped and un-doped mullite thin films

A sol-gel technique being simple, low cost and application oriented has been used to synthesize doped and un-doped mullite sols. These films have been spin-coated onto copper substrates. Effect of boron doping on the transformation kinetics of mullite was studied by preparing two sols with ratio Al/Si/B = 3/1/0 and Al/Si/B = 3/1/0.5. Surface morphology of thermally stable films showed uniformity in doped and un-doped samples. X-ray diffractometer results revealed orthorhombic mullite formation from both sols at a temperature of 500 A degrees C for un-doped and at 350 A degrees C for doped mullite films. Small crystallite size similar to 11 nm and low dielectric value similar to 5.84 (at 3 MHz) were observed in boron-doped films. Un-doped mullite films also showed relatively low dielectric constant, similar to 6.36, as compared to the previously reported values. The stoichiometry of films was confirmed by EDX and spark source mass spectrometry.