Fabrication and characterisation of field-effect transistor-type pressure sensor with metal–oxide–semiconductor/microelectromechanical systems processes

A microfield-effect transistor pressure sensor has been fabricated using conventional complementary metal-oxide-semiconductor process and microelectromechanical systems technology. The sensor platform consisted of a field-effect transistor (FET) device, electrode and Si diaphragm. Six lithography masks were prepared to develop the sensor fabrication process for arsenic ion implantation and diffusion, gate insulation layer (SiO₂), gate metal, metal interconnection, passivation layer and bulk micromachining patterns. Pt/Ti thin films as the gate metal, interconnection and electrodes were deposited by DC/radio frequency magnetron sputtering, and patterned and etched using the reactive-ion etching process. The channel length and width between the source and the drain were approximately 10 and 5500 μm (W:L ratio = 550:1), respectively. The pressure sensor produced a change in current when pressure was applied to the sensing element and the electrical circuit was used to convert the current variation of the pressure sensor to a voltage output. The sensor response was measured using a voltage follower circuit to determine the change in drain current. The fabricated FET pressure sensor showed an almost perfect linear response for the applied pressure in the range 0-1200 kPa. The experimental results have shown that the pressure sensor had a sensitivity of 0.0096 μA/kPa.