Electrothermal measurement techniques often require thin dielectric barriers to isolate active electrical test structures from samples of interest. The combined need for electrical passivation but thermal proximity necessitates the use of an electrically thick but thermally thin barrier layer. Here, we demonstrate a hybrid approach toward constructing sub-300 nm SiO2 multilayer barriers based upon low-temperature plasma-enhanced atomic layer deposition and high density plasma chemical vapor deposition. Using pairs of buried metal test structures, we quantify changes in device resistance and cross-talk after covering the dielectric barrier with thin evaporated gold films and thick electroplated copper films. We show that a hybrid approach to passivating electrothermal measurement devices outperforms individual homogenous barriers formed by either deposition technique.