Charge accumulation and their relaxation in SiO2 films containing silicon nanocrystals

For the first time, a metal-insulator-semiconductor (MIS) device that consists of silicon (Si) nanocrystals embedded in a silicon oxide film is proposed to investigate how the charge accumulation and relaxation can be manipulated by the nanocrystals for high reliable capacitive RF MEMS switch. A tri-layer structure, used as the insulator in our MIS device, comprises a thicker (about 100 nm) rapid thermal oxidation (RTO) silicon dioxide (SiO2) layer, a Si+SiO2 middle layer (about 100 nm) deposited by RF sputtering technique, and a RF-sputtered silicon dioxide capping layer. The electrical properties of the device have been characterized using capacitance versus voltage (C-V) measurements. The experiment results show a significant change of charge trapping and detrapping mechanisms in the composite insulator due to the presence of the Si nanocrystals in the middle layer. This result offers a possibility that the trapping or detrapping mechanisms in the dielectric can be manipulated by embedding nanocrystals in terms of materials (Ge, Si or other), density, size of nanocrystals and their distribution. It is anticipated that the charge trapping and their relaxation time in the dielectric of capacitive MEMS switch can be reduced.