High-Tunability and High- $Q$ -Factor Integrated Ferroelectric Circuits up to Millimeter Waves

Based on advanced industrial fabrication processes and on specialized design strategies, a new class of ferroelectric metal-insulator-metal (MIM) capacitors with high tunability and high quality factor ( Q-factor) is here presented. Modeled by means of lumped element equivalent circuits and experimentally validated up to 67 GHz, a maximum tunability of 81% (0-20-V bias), and a Q-factor improvement up to 30% (at 0 V) could be demonstrated at 1 GHz. These varactors have been exploited in the design of reconfigurable filters, with a center frequency at around 1 GHz that can be tuned up to 112%, and a figure of merit (FoM) per applied bias better than 31.5 dB^-1 /kV. Owing to their promising features, these materials have been exploited to design small-size capacitors suitable for millimeter-wave frequencies. The results demonstrate tunabilities and FoMs superior to the state-of-the-art. Based on this, two 60-GHz tunable phase shifters are proposed. They represent the first example of such devices based on MIM (Ba,Sr)TiO3 (BST) capacitors. In terms of insertion loss, size, FoM, and FoM per bias they show a remarkable improvement with respect to the state-of-the-art of ferroelectric-based devices, thus proving that the BST represents a promising candidate to operate into the millimeter frequency band.