A novel microfabrication technology on organic substrates - Application to a thermal flow sensor

A new technology that allows the formation of thermal sensors on organic substrates by combining the standard PCB technology with the well established microelectronic techniques, is proposed. The obtained structures consist of low thermal conductivity material, therefore the heat dissipation to the substrate is minimized, which result to the enhancement of the device sensitivity and the improvement of the corresponding response time. The proposed technology exhibits a series of advantageous characteristics such as significant cost reduction, elimination of both wire-die bonding and die cutting, direct integration with electronics and potential expansion on flexible substrates. Furthermore, the final structure provides a planar surface, which allows for further lithographic steps to take place, but is also a major advantage for specific type of applications such as non-invasive flow measurements. In the context of the proposed technology, a thermal gas flow sensor was fabricated and tested in a specially designed experimental set-up. The sensor consisted of three thin Pt strips directly connected to the copper tracks of the organic substrate. The middle Pt resistor act as a heater while the other two serve as temperature sensing elements.