Silicon-carbide MOS capacitors with laser-ablated Pt gate as combustible gas sensors

Sensing certain components present in the exhaust gas stream of internal combustion engines has become a very important application for chemical sensor technology. SiC-based metal-oxide-semiconductor (MOSiC) capacitors were prepared with platinum gates deposited by pulsed laser ablation. The response of their complex admittance, between 62.5 kHz and 1 MHz, to individual combustible species is presented. These devices with laser-ablated gates behaved similarly to their counterparts with sputtered gates exhibiting high sensitivity to propane, propylene, as well as to carbon monoxide. However, contrary to the sputtered Pt, the laser-ablated Pt showed no adhesion problems to the SiO2 even after prolonged operation at high temperature. The transient combustible response of these MOSiC devices revealed a fast and a slow component with the slow time constant being species-dependent. Furthermore, the clear response to CO strongly suggests that oxygen-related charged defects in the SiO2 may be playing a role in the sensing mechanism.