Bandgap tuning of silicon micromachined 1-D photonic crystals by thermal oxidation

Fabrication and optical testing of high-aspect-ratio 1-D photonic crystals, obtained by electrochemical micromachining of silicon, are discussed in this paper. The devices consist of high-aspect-ratio periodic (P = 4 mu m) arrays of 1.22-mu m-thick silicon walls separated by 2.78-mu m-wide air gaps, with 100 mu m etching depth. They were-designed as hybrid quarter-wavelength reflectors with photonic bandgaps in the near-IR region, one in particular centered at lambda = 1.55 mu m. The fabrication process was improved to increase structure uniformity and strength. Thermal oxidation of the silicon structures was exploited to tune the wavelength position and width of the bandgaps. Fabricated devices, also with different silicon dioxide thicknesses, were optically tested by measuring their spectral reflectivity in the wavelength range of 1.0-1.7 mu m. Experimental results were found in good agreement with the calculated spectra.