Large arrays of chemo-mechanical nanoswitches for ultralow-power hydrogen sensing

A hydrogen sensor based on large arrays of nanoswitches in palladium (Pd) is presented. An individual nanoswitch is realized by a suspended Pd/Ti/poly-Si trimorph electrode and a fixed Pd/Ti bottom electrode, which are separated by a vertical nanoscopic gap of approximately 10 nm in size. In hydrogen exposure, the volume expansion of Pd results in mechanical bending of the suspended electrode and the formation of an electric contact. A multitude of nanoswitches is arranged in interconnected arrays. These enable a dependence of the sensor signal on the H2 concentration by the occurrence of percolation effects. The combined use of thin film, etching and evaporation techniques allows for the large-scale fabrication of nanoswitch arrays in arbitrary topologies by design, such as parallel linear chains or square lattices. The results of hydrogen and temperature measurements are presented and discussed. In hydrogen exposure, reversible changes in the electrical resistance of up to three orders of magnitude are obtained for H2 concentrations below 4% and a power consumption down to a few picowatts.