Piezoresistive scanning probe arrays for operation in liquids

Piezoresistive scanning probe arrays have been developed in view of operation in liquid environments. When the cantilevers are immersed in electrically conductive solutions like for instance physiological buffers, the piezoresistive sensing elements as well as the metal connections have to be passivated. For that purpose, the sensors and the metal wiring were covered with different protective coatings. Long term stability of these passivation layers was demonstrated by imaging in a buffer solution for several hours. Moreover, in view of reducing the damping and thus decreasing the hydrodynamic resistance in liquids, special truss cantilevers have been developed. It was found that this special design conferred no improvement in terms of Q-factor and resonant frequency when operated in water. In order to explain the behaviour of these probes, a theoretical model was established. The model predicted that truss structures could theoretically improve the cantilever performances in liquid, but the probes would need to be operated at high frequency, above 10MHz.