Impact of nitrogen doping on the electrical resistivity and Q-factor of polycrystalline 3C-SiC MEMS resonators

Abstract

On the contemporary consumer market, a diverse range of MEMS resonators utilizing Si as structural material exists. This condition can be attributed to the desirable characteristics of Si such as durable mechanical robustness, resilience, cost-effectiveness and high reliability. However, given the growing interest in MEMS resonators designed for challenging conditions, it is suggested to select alternative mechanical materials for MEMS resonators. In this respect, SiC represents a promising structural material owing to its chemical inertness, wide band gap, excellent heat conduction and high melting point.Since doping can have an impact on the electrical and vibrational properties of MEMS resonators, the aim of the master’s thesis was to investigate the effect of nitrogen doping of polycrystalline 3C-SiC thin film on conductivity and quality factors (q-factors). Therefore, nitrogen doped SiC thin films were deposited on Si and SiO2 substrates using the Low Pressure Chemical Vapour Deposition system. In this regard, the thin film properties were analyzed by different analytical techniques, and to study the influence of doping on the vibrational properties, MEMS resonators were fabricated and quality factors were measured using a laser Doppler vibrometer.By nitrogen doping of SiC, different morphologies and microstructures were achieved. Further, XRD and XPS measurements indicate the formation of SiC but also Si-N compounds. Nevertheless, the injection of 2.5 sccm NH3 to the SiH4 and C3H8 gas flow contributed to a higher conductivity (4794 S/ m, compared to 100 S/ m of undoped polycrystalline 3C-SiC), but also to a reduction of the mean q-factor. In particular there was a 28% reduction of the mean q-factor for the 1st Euler Bernoulli mode while for the 2nd Euler Bernoulli mode, a 39% reduction was obtained.Consequently, in situ doping is an effective strategy to enhance the electrical conductivity of polycrystalline 3C-SiC, expanding its usability across diverse fields where adjustable levels of conductivity are needed and the use of Si as mechanical material is limited to its constraints.