Micromachined microbeams made from porous silicon for dynamic and static mode sensing

Abstract

Through a controlled variation of the applied current during porous silicon formation, newly developedprocesses enable previously unattainable structural integrity of all-mesoporous silicon microelectrome-chanical systems (MEMS) structures. Such structures are desirable for applications such as sensing wherethe large surface area and low Young’s modulus of the high porosity layer enable ultra-high sensitivitydetection of adsorbed species. In this work, micromachined all-mesoporous silicon microbeams werereleased, allowing both the dynamic and static sensing modes to be studied using such porous struc-tures. Resonant frequencies (50–250 kHz) of released doubly clamped porous silicon microbeams weremeasured, allowing mechanical properties to be extracted. Static mode sensing of vapour at the 1100 ppmlevel was also performed, with the released porous silicon cantilevers showing a significant 6.5 m (3.7%of a 175 m beam length) and repeatable deflection after exposure.