Ultra-miniaturized monolithically integrated polymer coated Si optoelectronic cantilevers for gas sensing applications

The cantilever based devices relying on optical beam steering, even though sensitive as sensors, have rather limited penetration to the market. The obstacle that has prevented so far the wider spread of such devices is the inability to monolithically integrate the photonic components on the same die with the cantilever. In this work, a novel microsystem is presented comprising integrated Si light sources and detectors self aligned to suspended Si₃N₄ cantilevers, acting as waveguides, all monolithically integrated in the same Si chip through conventional microelectronics processing. The cantilever is coated with a polymeric film that selectively absorbs analyte molecules from the environment causing a change in the film stress and commensurate cantilever´s deflection which is monitored as change in the photocurrent. The PMMA coated device showed detection of VOCs, in a wide concentration range from few tens of ppm, limited only by the physicochemical properties and the chemical affinity of the polymer used.