Charge transport in SiO2/Si2N4 AND SiO2/Si-rich SiN electrets for high-temperature electrostatic energy micro-harvesters

This paper reports on the charge retention characteristics of SiO2/Si3N4 and SiO₂/Si-rich nitride (SiRN) electrets from the point of view of charge transport. A surface density of 8.7 mC/m² is achieved with SiO₂/Si₃N₄ electrets, which is twice as high as previously reported. This material combination can keep its charge for more than 100 days with a decay of less than 10%. In contrast, SiRN electrets exhibit 30% decay in about 10 days. To evaluate the mechanisms of charge decay, current density-electric field (J-E) analysis and partial charging experiments are conducted. As a result, vertical charge transport is well explained with a thermionic emission model at high temperature (> 350°C), while lateral charge transport, which occurs even at room temperature, can be explained with a hopping conduction model.