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

Abstract

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.