High-Q Package Integrated Resonators

Modern trends in miniaturisation and demands for higher resolution have prompted radar technologies to explore and utilise W-band frequencies, i.e. 75-110 GHz, to exploit the higher available bandwidth. Moreover, due to low atmospheric losses W-band frequencies provide better Signal-to-Noise ratio (SNR) than the previously used frequency bands at around 24 GHz and 60 GHz. Consequently, current research activities are concentrated on the development of components for novel radar systems operating at the W-band.

A crucial part of radar systems is the frequency synthesis with low phase noise where voltage-controlled oscillators (VCOs) are required. A VCO can be implemented on chip-level in combination with a package-integrated resonator. Due to the advantageous packaging material properties, a high Q-factor can be achieved providing better phase noise performance in contrast to resonators realized on-chip. To overcome insufficient gain of active devices at high frequencies, the frequency synthesis can occur at lower frequencies and the output signal is then transferred to the actual carrier through frequency multipliers. The 77 GHz carrier can be generated at about 13 GHz, followed by a x8 frequency multiplication. Thus, the requirements on the VCO design become more cost-efficient and flexible as well as its external resonator is more robust towards fabrication tolerances providing wider tuning ranges.

At Fraunhofer IZM, a planar spiral resonator operating at 13 GHz was developed. The resonator was fabricated using fan-out wafer level packaging (FoWLP) technology. Laboratory measurements demonstrated a very good correlation in comparison with full-wave simulations.