Horizontal Integration of Cavity Filters on High-Resistivity Silicon Thin-Film Technology

Miniature, light weight and low-loss filters are important components for wireless and mm-wave applications. Here, we present a novel implementation of integrated cavities on a thin-film technology with through-substrate vias on 100 $\mu{\hbox{m}}$ thick high-resistivity wafers. A 60 GHz horizontally integrated cavity bandpass filter is demonstrated. The filter has an insertion loss of 1.5 dB, a relative bandwidth of 6% and excellent agreement between simulations and measurements is obtained, even in terms of insertion loss. The measured unloaded quality factor is used to demonstrate that the losses in high-resistivity silicon are mainly due to dielectric damping rather than bulk conductivity at millimeter wave frequencies. A feeding point is presented for the excitation of rectangular cavities that greatly increases the attenuation of the filter at the higher frequency band by preventing the second order mode to be excited within the cavities. Finally, a size and performance comparison is made between this filter and a microstrip coupled lines filter in the same technology. The thin-film technology also integrates high- $Q$ inductors, high-density capacitors and resistors. Active circuits can also be included by means of flip chip and therefore, the technology allows the implementation of a novel architecture for millimeter wave transceivers.