The impact of surface passivation thickness on Kapitza resistance between quartz and liquid helium

In this paper, we describe an experimental investigation into the effect of nitride passivation layer thickness on heat dissipation between a fused quartz substrate and liquid helium. Using custom-fabricated quartz capacitors with embedded heaters and calibrated dielectric thermometry, we systematically vary SiN thickness and measure the resulting thermal boundary resistance under controlled cryogenic conditions. We have observed that by depositing SiN from 0 to 240 nm, the effective Kapitza resistance increases by ∼0.0365 m2 K/W per nanometer more than for an unpassivated substrate. We hypothesize that this increase in effective Kapitza resistance represents an additional barrier to the cooling of semiconductor devices in liquid helium and provides useful insight into phonon transmission across layered dielectric structures at cryogenic temperatures.