Silicon nanowire pirani sensor fabricated using FIB lithography

As radio frequency microelectromechanical systems (RF-MEMS) mature as a manufacturable technology, packaging of the devices becomes increasingly important. Devices such as aluminum nitride (AlN) RF-filters require packaging which is either hermetic or under vacuum to protect the devices [1]. It then becomes critical to have a measurement of pressure inside the packaged chamber. Typically for this need, Pirani gauges are fabricated using poly silicon or metal patterned on suspended membranes [2]. These type of devices increase die area, add complexity to fabrication flows, and difficulty when attempting to suspend the membranes. In this work we fabricate and characterize a suspended silicon nanowire for use as Pirani gauge by utilizing Ga lithography and plasma reactive ion etching for defining the nanowire geometry and simultaneously releasing the wire. This method benefits from the high surface to volume ratio inherent in the nano regime, decreased thermal conductivity of amorphous silicon (from implantation) and increased electrical conductivity of Ga doping to reduce device area and fabrication complexity of a Pirani gauge.