Thermoelectric Flow Sensors with Monolithically Integrated Channel Structures for Measurements of Very Small Flow Rates

A thermal flow sensor with monolithically integrated channel structures for measurements of flow rates down to 40 nlmin^-1 is presented. The sensor is based on a fabrication process using a high-temperature silicon nitride as protective coating. The channel is realised by means of surface micromachining and consists of SU-8. For chemical stability and to gain hydrophilic properties, the channel is coated on the inside by silicon-oxide and silicon-nitride as a moisture barrier. Sensor systems have been fabricated and characterised.