An integrated sensor for invasive blood velocity measurement

Invasive measurements of physical parameters in blood are very important for the intensive care. The integrated flow sensors presented here has been developed as a part of an "intelligent catheter" for measuring certain blood parameters. The sensor is based on the principles of hot-film anemometry. The temperature difference on a chip is measured by two diodes. One diode is heated by means of a polysilicon resistor in close proximity. This diode is (for thermal insulation) placed on a 5 mym x 260 mym x 260 mym silicon membrane. For the membrane formation the implanted oxide layer of SIMOX substrates (Separation by Implanted Oxygen) was used as a stop for backside etching. This technique allows batch processing and is compatible with a standard CMOS process. In addition, electronic CMOS devices can be mounted directly into the membrane. Switched capacitor circuits are used for sensor read-out electronics.