Chip-scale chemical sensors were demonstrated using flexible mid-Infrared (mid-IR) photonic circuits consisting of aluminum nitride (AlN) waveguides on ultrathin substrates. The AlN waveguide structure was fabricated by the complementary metal–oxide–semiconductor (CMOS) process. The waveguide sensor is highly bendable because the thin device thickness, which effectively reduces the surface strain. Through spectrum scanning over the characteristic -OH absorption, the waveguide sensor can differentiate methanol, ethanol, and water, and accurately determine the chemical compositions of the water/ethanol mixtures. Real-time chemical monitoring was accomplished by measuring the waveguide mode attenuation at λ = 2.65 μm. Due to the high mechanical flexibility and mid-IR transparency, the AlN chemical sensor enables integrated photonics for biomedical wearables and remote environmental monitoring.
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