This invention provides a miniaturized
silicon thermal flow sensor with improved characteristics, based on the use of two series of integrated thermocouples (6, 7) on each side of a heater (4), all integrated on a
porous silicon membrane (2) on top of a cavity (3).
Porous silicon (2) with the cavity (3) underneath provides very good
thermal isolation for the sensor elements, so as the power needed to maintain the heater (4) at a given temperature is very low. The formation process of the
porous silicon membrane (2) with the cavity (3) underneath is a two-step single electrochemical process. It is based on the fact that when the anodic current is relatively low, we are in a regime of
porous silicon formation, while if this current exceeds a certain value we turn into a regime of
electropolishing. The process starts at low current to form porous
silicon (2) and it is then turned into
electropolishing conditions to form the cavity (3) underneath. Various types of thermal sensor devices, such as flow sensors, gas sensors, IR detectors,
humidity sensors and thermoelectric power generators are described using the proposed methodology. Furthermore the present invention provides a method for the formation of microfluidic channels (16) using the same technique of porous
silicon (17) and cavity (16) formation.