In-plane-excited silicon nanowire arrays-patterned cantilever sensors for enhanced airborne particulate matter exposure detection

This paper presents the design, fabrication, and use of silicon nanowire (SiNW) arrays-patterned microcantilever sensors excited in the in-plane resonance mode to enhance the detection of airborne particulate matter (PM). Electrothermal excitation elements of p-diffused heating resistors were introduced in the current sensor system to replace the formerly used external piezoceramic stack actuator. The sensors exhibited high measured quality factors (Q-factors) of 4702 ± 102 during their in-plane mode operations in air, which are four times larger than those of the fundamental out-of-plane mode. To selectively define arrays of vertical SiNWs on the surface of the micromechanical cantilever, nanoimprint lithography (NIL) is combined with conventional photolithography. The diameter and position of the SiNWs can be adjusted depending on the nanoimprint stamp with the smallest cylindrical pattern possible down to 50 nm in diameter. By modifying the resonator surface, the PM sampling efficiency can be improved by a factor of 1.5 greater than that of a corresponding plain cantilever in a cigarette smoke exposure experiment because of the rise in collection surface area of the sensor given by the SiNWs.