A*STAR develops robust MEMS pressure sensor
In principle, the design of a miniaturized pressure sensor is straightforward: create a pressure-deformable diaphragm and then embed a piezoresistor made from a material in which pressure causes a change in electrical resistance, such as a silicon nanowire. In practice, however, problems including difficulties with circuit design and fatally fragile components often plague development of a commercially useful sensor.
Since the diaphragm must transfer small pressure changes to the piezoresistor while maintaining resistance to deformation and breakage, material selection is crucial. Lou and his co-workers considered using silicon dioxide for its excellent pressure sensitivity. However, this useful property is countered by a strong tendency to buckle and twist even without pressure. Their solution was to use a double layer of silicon dioxide-with piezoresistive silicon nanowires embedded in between-topped by a stabilising layer of silicon nitride.
By etching down the silicon nitride and varying the thickness and treatment of the silicon nanowires, the team found an optimum combination. The final sensor resisted deformation and mechanical breakage while still providing the linear change in electrical output upon pressure that is desired for sensitive medical instrumentation.
The team's main target now is to realise an implantable miniaturized medical device. Despite this goal being reliant on advances in circuitry research and extensive testing prior to use in humans in robotic surgery, the sensor ushers further developments in silicon nanowire-based sensor design.