Finite element calculations and fabrication of cantilever sensors for nanoscale detection

Finite element analysis (FEA) is used to study the effect of geometric vari ations on the properties of rectangular cantilevers and U-shaped Joule-heat ed cantilevers. Simulations of locally thinned cantilevers as well as of ca ntilevers modified by the implementing of a hole or a side cut are compared with fabricated cantilevers, which are tuned by focused ion beam (FIB) mil ling. By locally thinning the cantilevers, the resonance frequency and the spring constant are reduced. For a hole, the internal stress is increased w hile for a side cut, the lateral spring constant is decreased. Good agreeme nt between the measured and the simulated resonance frequencies is observed . Simulations of the current density and the temperature distributions atta ined during the passage of current through a doped silicon layer are perfor med to optimize the design of Joule-heated cantilevers (U-shaped) for therm al gravimetric applications. A very uniform temperature distribution over a region near the apex can be realized by slitting the U-shaped cantilever. In such a way, the heating power can be minimized by effecting only a small variation in the geometry of a U-shaped cantilever. A simple fabrication p rocess for the fabrication of Joule-heated cantilevers is presented, which consists mainly of a uniform conductive p-doped layer. (C) 2000 Published b y Elsevier Science B.V. All rights reserved.