3D flip-up structure of porous silicon with actuator and optical filter for microspectrometer applications

This paper reports a new fabrication method for a microactuated tunable optical filter based on porous silicon formation followed by electropolishing. This surface micromachining process generates in a single step a multilayered optical interference filter, releases it from the substrate and lifts it out of plane. The filter can be tilted by a thermal bimorph actuator in order to tune the wavelength it transmits or reflects. The fabrication process uses only two photolithography levels on ordinary silicon p⁺ substrates. Large, flat, actuatable flip-up Bragg mirrors of porous silicon have been realized with a typical thickness of 30 μm and areas ranging from 250 by 750 μm to 2400 by 4000 μm. Their capability to distinguish light sources with a wavelength separation of less than 20 nm in the visible is presented