  We systematically study the performance of compact lumped element planar
microwave $\mathrm{Nb_{70}Ti_{30}N}$ (NbTiN) resonators operating at 5 GHz in
external in-plane magnetic fields up to 440 mT, a broad temperature regime from
2.2 K up to 13 K, as well as mK temperatures. For comparison, the resonators
have been fabricated on thermally oxidized and pristine, (001) oriented silicon
substrates. When operating the resonators in the multi-photon regime at $T=2.2$
K, we find internal quality factors $Q_{\mathrm{int}}\simeq$ $2\cdot10^5$ for
NbTiN resonators grown on pristine Si substrates, while resonators grown on
thermally oxidized substrates show a reduced value of $Q_{\mathrm{int}}\simeq$
$1\cdot10^4$, providing evidence for additional loss channels for the latter
substrate. In addition, we investigate the $Q$-factors of the resonators on
pristine Si substrates at millikelvin temperatures to asses their applicability
for quantum applications. We find $Q_{\mathrm{int}}\simeq$ $2\cdot10^5$ in the
single photon regime and $Q_{\mathrm{int}}\simeq$ $5\cdot10^5$ in the high
power regime at $T=7$ mK.
