Effect of Aging under AC Superimposed Harmonic Voltage on Trap and Carrier Transport Properties of Silicone Rubber

The rapid growth of power grid capacity and the widespread use of a large number of power electronics and non-linear loads have led to harmonics in the power system. Harmonics in the power system will cause safety hazards to the normal operation of power equipment, exacerbate the aging of insulation materials, and reducing the overall operation reliability of the system. In the present work, we used power frequency ac voltage superimposed harmonics to carry out ageing experiments on power cable terminals. Then, we tested the infrared spectra, dielectric spectra, electrical conductivity, and surface potential decay characteristics of silicone rubber insulation materials on the cable terminals aged for different times. The experimental results show that the dielectric constant and dielectric loss of silicone rubber gradually increase with the aging time. In particular, the dielectric loss of silicone rubber changed greatly at low frequencies. The effect of dc conductance of aged silicone rubber on dielectric loss is significantly enhanced at low frequencies, which causes the dielectric loss to increase as the frequency decreases following an inverse power law. The surface potential decay rates of silicone rubber insulation after positive and negative corona charging accelerate with increasing the aging time, which is consistent with the experimental results of electrical conductivity. By analyzing the distribution characteristics of electron and hole traps in silicone rubbers, it is found that the trap energy levels of electron and hole traps become shallower as the operating time increases. The calculation of the carrier hopping conduction model shows that the shallow trap formed with increasing the aging time will lead to increases in both carrier mobility and conductivity. When the conductivity rises to a certain value, the silicone rubber will lose its insulation performance, resulting in insulation failure.

Study on NO Passivation on the Near Interface Electron and Hole Traps of n-Type 4H-SiC MOS Capacitors by Ultraviolet Light

The characteristics of near interface electron and hole traps in n-type 4H-SiC MOS capacitors with and without nitric oxide (NO) passivation have been systematically investigated. The hysteresis of the bidirectional capacitance-voltage (C-V) and the shift of flat band voltage (Vfb) caused by bias stress (BS) with and without ultraviolet light (UVL) irradiation are used for studying the influence of near interface electron traps (NIETs) and near interface hole traps (NIHTs). Compared with Ar annealed process, NO passivation can effectively reduce the density of NIETs, but induce excess NIHTs in the SiC MOS devices. What’s worse is that part of the trapped hole cannot be released easily from the NIHTs in the NO annealed sample, which may act as the positive fixed charge and induce the negative shift of threshold voltage.

Локальные колебания связей кремний-кремний в нитриде кремния

Raman spectra of films of nearly stoichiometric amorphous silicon nitride (a-Si_3N_4) reveal a contribution due to local oscillations of silicon–silicon (Si–Si) bonds. This observation directly confirms that the almost stoichiometric a-Si_3N_4 contains Si–Si bonds, which, according to theoretical predictions, act as electron and hole traps that are responsible for the memory effect in Si_3N_4.