The quality factor (Q) of inductors on silicon (Si) is limited by the series resisiance of the metal at low frequency and by the substrate resistivity at high frequency. Oxide is generally used to isolate the useful signal of the inductor from the lossy Si substrate. However, stoichiometric silica (SiO2) is processed at high temperature which restricts the possibility of post-complementary metal-oxide semiconductor integration, and due to the large thermal mismatch with Si, thick oxide films introduce considerable stress. In this work, we apply electrochemically formed porous Si (PS) and intrinsic amorphous Si (i-a-Si: H) deposited at low temperature (250 degrees C) in an approach as an isolation bilayer for planar inductors on Si for rf integrated circuits. An improvement of more than 45% in Q was measured at a frequency of 6.4 GHz for 1.6 nH inductor incorporating PS and i-a-Si: H films. The experimental results presented indicate that these low-temperature materials are promising for the isolation of rf devices on low-resistivity Si. (c) 2006 American Vacuum Society.