Micromachined flow sensor integrated with flow inception detection and make of the same

A micromachined silicon thermal mass flow sensor with flow inception detection comprising:

• a micromachined thermopile temperature sensor on a silicon substrate wherein the micromachined thermopile sensor are formed by an array of two serpentine-shaped dissimilar metals lines which are interlaced cross-joined;
• wherein the two dissimilar metals have high thermo-effects in two opposite polarity;
• wherein first set of junctions of the thermopile sensor is called active junctions and located on top of a first suspended membrane with a cavity underneath while second set of junctions of the thermopile sensor is called reference junctions and located on top of a non-membrane area where has no cavity underneath as to stay in ambient temperature by keeping good thermal conductivity to the silicon substrate;
• and wherein once a temperature variation is enduring between the first set and the second set of junctions, a differential voltage summed across the array will be generated;
• a heater thermistor which is located on a second suspended membrane with another cavity underneath and connected to a constant temperature control circuit;
• a reference thermistor which is located on the non-membrane area of the silicon substrate and connected with the heater thermistor as part of the constant temperature control circuit thus to provide a constant temperature control for the heater thermistor;
• a first temperature sensing thermistors which is disposed on the second suspending membrane and located on an upstream position beside the heater thermistor corresponding to gas flow direction;
• and
• a second temperature sensing thermistors which is disposed on the second suspending membrane and located on an downstream position beside the heater thermistor corresponding to gas flow direction;
• wherein the first and the second temperature sensing thermistors are connected to a second electronic circuit to measure temperature variation between the first and the second temperature sensing thermistors thus to measure flow speed.