Bimaterial microcantilevers with black silicon nanocone arrays

•Bimaterial microcantilever sensors based on black silicon have improved infrared responsivity.•The black silicon consists of arrays of conic nanostructures, which are fabricated by plasma etching.•Optical and thermomechanical models predict the absorbance and responsivity of the bimaterial microcantilevers.•Modeled cantilever performance compares well with measurements.

The performance of infrared (IR) sensing bimaterial cantilevers depends upon the thermal, mechanical and optical properties of the cantilever materials. This paper presents bimaterial cantilevers that have a layer of black silicon nanocone arrays, which has larger optical absorbance and mechanical compliance than single crystal silicon. The black silicon consists of nanometer-scale silicon cones of height 104–336 nm, fabricated using a three-step O2–CHF3–Ar + Cl2 plasma process. The average cantilever absorbance was 0.16 over the 3–10 μm wavelength region, measured using a Fourier transform infrared (FTIR) microspectrometer. The measured cantilever responsivity to incident IR light compares well to a model of cantilever behavior that relate the spectral absorbance, heat transfer, and thermal expansion. The model also provides further insights into the influence of the nanocone height on the absorbance and responsivity of the cantilever. Compared to a cantilever with smooth single crystal silicon, the cantilever with black silicon has about 2× increased responsivity. The nanocone array fabrication technique for silicon bimaterial cantilevers presented here could be applied to other IR sensors.