"Multi-Scale Modeling of Dielectric Charging in RF-MEMS Devices"
October 5 @ 12:00 PM - 1:00 PM - BRK 2001
Abstract: We present a multi-scale modeling approach to rigorously calculate the electron trap energy levels and accurately model the dielectric charging phenomenon in a-Si3N4 dielectric, widely used for RF-MEMS devices. First principles charge state calculations are performed on an ensemble of a-Si3N4 structures to quantify the location of trap levels in the energy band gap. We find that the electron traps lie across a range of energy levels, which are in excellent agreement with recent Trap Spectroscopy by Charge Injection and Sensing experiments on a-Si3N4. The calculations also provide valuable information about the microscopic nature of defects and their corresponding relaxation mechanisms caused by charge trapping. In addition to the commonly postulated III-Si defects (K centers), new defect mechanisms responsible for electron trapping have been identified. A comprehensive dielectric charging model to compute charge accumulation and leakage currents in an amorphous dielectric like a-Si3N4 has been developed. We fit current transient measurements performed on MIM capacitors, and show that by using a distribution of trap levels from ab-initio calculations we are able to capture voltage and temperature dependences more accurately compared to using a single defect level, inspite of a reduction in empiricism. We observe an improvement of about 66% in relative error by using ab-initio informed dielectric charging simulations. From these calculations, we demonstrate that realistic modeling of the devices requires the incorporation of new multi-scale, multi-resolution approach spanning across various spatial and temporal scales.
- Bonnie Kauffman