AlN thin-film deposition for suppressing surface current losses in RF circuits on high-resistivity silicon

Thin aluminum nitride (AlN) films, deposited by means of Physical Vapor Deposition (PVD) to a thickness up to 200 nm, are studied as RF passivation layers for transmission lines High Resistivity Silicon (HRS) substrates. Excellent passivation properties are demonstrated by measuring RF losses on coplanar waveguides (CPWs) as well as the space-charge-layer sheet resistance (SCL-R_SH) on specially designed MISFET structures. Compared to oxide interfaces the losses go from a strongly bias-dependent ~ 10 dB/cm to a bias-independent 1.7 dB/cm for the AlN:Si interfacial layer, corresponding to an increase of SCL-R_SH from ~ 10⁴ Ω/□ to 10⁷ Ω/□. The results suggest that a high resistive AlN:Si layer is formed by interdiffusion of the AlN and underlying Si which then conducts the parasitic interface currents.