Fabrication of suspended microchannel resonators for biosensing application

Some diseases are characterized at the biomolecular level by a change in the mechanical properties of the cells in comparison to normal cells. Detecting this change could thus be useful for biomedical pplications. Micromechanical sensors are devices that are already used to study different phenomena at the micro-scale. The measurement of the eflection or the resonance frequency shift of a beam in response to an added mass for example enables to characterize samples obtaining information such as the size, the mass or the density of cells. The sensitivity of this sensors is degraded by the viscous losses due to the surrounding medium when they are used in liquids. This issue is overcome by embedding the fluid into the cantilever. In her thesis, A. De Pastina studied these devices, also called suspended microchannel resonators, she developed a fabrication method and characterized the sensors obtained. The purpose of this project is now to investigate a new process, aiming at improving the cost and time of the fabrication to enable efficient batch production of these sensors. The principle of the method, consisting in etching the channel directly into the silicon substrate through a low-stress silicon nitride membrane, is presented in this report. Test structures are made in cleanroom to determine the best process and design parameters. The reachable depth of the channel is studied. The preliminary results are then used to make cantilevers with embedded microchannels and to characterize them by measuring their resonance frequency shift in response to added fluids with different densities. Finally, the limitations of the current process at the end of this project are explained and some possible improvements are proposed. The results are promising and the fabrication method developed deserves to be further studied.