RF passive components on a low resistivity Si substrate with an ABF isolation layer

This paper presents an implementation of RF passive components on a low resistivity Si substrate with a thick ajinomoto build-up film (ABF) to reduce electromagnetic field interaction with the Si substrate. The comparison of three coplanar waveguides (CPWs) on different Si substrates has been performed to provide feasibility of ABF-layer approach. After that, a bandpass filter and baluns have been fabricated on the low resistivity Si substrate with a 40-μm and/or an 80-μm ABF as an isolation layer. A 3-μm SU-8 layer has been spun on the ABF layer to form insulator for Metal Insulator Metal (MIM) capacitors. The implemented bandpass filter and balun based on a 40-μm ABF isolation layer provide a relatively low in-band insertion loss. In order to further improve the overall performance, two 40-μm ABF layers on the low resistivity Si substrate have been used, resulting in more than 0.8-dB insertion loss improvement at the balun.