Fully CMOS-Compatible Room-Temperature Waveguide-Integrated Bolometer Based on Germanium-on-Insulator Platform at Mid-Infrared Operating Beyond 4 μm

We propose a novel concept of an uncooled waveguide-integrated bolometer on a Ge-on-insulator (Ge-OI) platform at mid-infrared (MIR) wavelength of 4.18 μm. To induce heat generation, we introduce a heavily-doped (p
⁺
) Ge that utilizes the mechanism of free-carrier absorption (FCA) in Ge. A bolometric material of H
2
plasma-treated TiO
2
film is integrated to facilitate highly efficient thermal-to-electrical conversion. The fabricated waveguide-integrated bolometer exhibits outstanding performance characteristics in the temperature coefficient of resistance (TCR) of - 1.911 %/K and a sensitivity of -22.25 %/mW at room temperature. Our proposed detector offers full complementary metal-oxide-semiconductor (CMOS) compatibility and features a remarkably simple device configuration. Moreover, due to its FCA-induced heating, we anticipate that our approach can cover the entire MIR regime without performance degradation. This work experimentally demonstrates a room-temperature waveguide-integrated bolometer operating beyond 4 μm, for the first time to our knowledge, paving the way towards the development of a fully integrated photonic platform capable of operating in the ultra-wide MIR spectral region.