Application of dielectric resonators to millimeter-wave on-chip filters and interconnects

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A growing number of applications in communications and sensing use frequencies in the millimeter-wave bands of the spectrum. This trend drives the need for and the development of innovative concepts for passive components such as new interconnects to monolithic integrated circuits and low-loss on-chip bandpass filters. Millimeter-wave integrated circuits are typically mounted on circuit board by flip-chip or wirebond technique. Many solutions then exist to connect all sorts of waveguiding structures to circuit boards. Solutions with less complexity were proposed with direct connections from chip to rectangular waveguide or to dielectric waveguide by means of suitably modified on-chip antennas. In the legacy project of the applicant, coupling from on-chip microstrip line to rectangular waveguide by means of a spherical dielectric resonator was realized. It was shown experimentally that this concept, with a measured transmission loss of 2.6 dB at 64 GHz, outperforms other solutions in terms of loss, while it also provides also provides advantages in chip area consumption, assembly complexity, and testability. Planar passive mm-wave bandpass filters, when integrated on-chip, are typically embedded in the top chip layers but still suffer from significant insertion loss and low selectivity. Alternatively, low-loss (high Q-factor) resonators are particularly important for oscillators, and on-chip dielectric resonator oscillators were proposed for frequencies up to 60 GHz. These oscillators use cylindrical dielectric resonators where accurate placement can be critical and chip-area consumption will be an issue. In the legacy project of the applicant, some investigations were done on low-loss (high-Q) on-chip spherical dielectric resonators. Radiation of these resonators in a specific higher-order resonance mode can indeed be very small and thus unloaded Q of these resonators can be very high, opening the possibility to realize highly selective on-chip resonators and filters. Measurements of on-chip spherical dielectric resonators made of alumina ceramic showed unloaded Q as large as 1400 at 64 GHz and 2200 at 103 GHz. The proposed continuation project aims to extend the basic idea of using on-chip spherical dielectric resonators for the realization of on-chip multi-resonator bandpass filters operating around 100 GHz. In consequence of some manufacturing issues with the previously designed test wafers, this project continuation will also give the opportunity to refine the manufacturing technology and to repeat and improve some of the previously designed coupling structures on a new test wafer.