CMOS-Compatible Integrated Spectrometer Based on Echelle Diffraction Grating and MSM Photodetector Array

Abstract

We demonstrate an integrated spectrometer-on-a-chip composed of an echelle diffraction grating (EDG) and metal-semiconductor-metal (MSM) waveguide photodetector array based on silicon-on-insulator (SOI). In the passive section, silicon oxynitride (SiON) is chosen as the material for the waveguide core and is deposited after selectively removing the top silicon layer of the SOI wafer. The buried silicon dioxide layer of the SOI wafer functions as the lower cladding for the SiON core waveguide. In the active section, the MSM photodetector array is fabricated on the top silicon layer of the SOI waveguide with a pitch width of 7.5 μm. With the butt-coupling structure, a responsivity of 0.41 A/W is obtained at 850 nm. Based on the CMOS-compatible fabrication process, we have fabricated a 60-channel spectrometer with a chip size of 9 mm × 6 mm operating around 850 nm. The measured channel spacing is 0.494 nm, with an adjacent channel crosstalk around 18 dB. The channel nonuniformity is less than 1.5 dB. The CMOS-compatible spectrometer with integrated silicon photodetector array can provide a low-cost solution for high-resolution on-chip spectral analysis for visible and near-infrared light with the wavelength below 1100 nm.