Batteryless MEMS flow sensor within prosthetic vascular graft

This paper reviews our group's work on implantable MEMS flow sensor for detecting prosthetic vascular graft failure. The core sensing mechanism is by measuring the resistance change of a piezoresistor attached to the moving part of the flow sensor. Variations of blood flow rate causes pressure or flow change, which deflects the moving part, such as a cantilever beam or diaphragm, of the flow sensor. The mechanical deformation further causes stress change on the piezoresistor whose resistance value varies with its internal stress. By accurate measuring the resistance change on the piezoresistor one can deduce the blood flow variation. Two types of piezoresistor are studied: silicon nanowire (SiNW) and gate-all-around (GAA) nanowire FET. Two types of sensor architecture are discussed: cantilever beam and diaphragm membrane. Different materials (SiO₂, Si₃N₄, parylene) are tested for making diaphragm to achieve minimal residue stress and ensure good biocompatibility.