Charge Transfer Pathways in Thermalization Process of a Resistive Particulate Matter Sensor 2019-01-6501
Resistive particulate matter sensor (PMS) is a promising solution for the diagnosis of diesel/gasoline particulate filter (DPF/GPF) functionality. Frequently triggered regeneration of their sensing element, for cleaning the soot dendrites deposited on the surface, leads to experience high temperature and thermal stress and pose high risk of developing cracks in the electrodes or sensing substrate. A semiconductor with a dopant concentration of 100 ppm~10000 ppm is applied as a sensing element for PMS self-diagnosis. Upon cooling at air, the polarization doped-insulating layer in a resistive PMS starts to resume the electrical conductivity in the wake of experiencing high regeneration temperature, through the electron and hole directional mobility. At a temperature slightly lower than carbon equilibrium temperature of 600°C, the charge carriers’ migration rate reaches the maximum value and then steps down to near zero with cooling of the sensing element due to the carrier thermal movement and polarization. On the other hand, during percolation/quiescent process, the charged soot dendrites appear to be anchored between the gap of electrodes, not well interconnected but rather standing independent of each other. No conductive path forms between electrodes, but the mobility of charge carrier between carbonaceous particulate matter and sensing element suddenly increases and then is kept constant (saturation drift current occurrence) until the first soot conductive path is formed. This article tries to figure out electron transferring pathways from amorphous carbon to the insulating layer doped by a defined dopant and to shed some light on the mechanism of choking phenomenon.