Ferroelectric thin-film integrated capacitor and its application in radio-frequency phase shifter design

Tuning element is essential for the design of tunable and reconfigurable RF circuits. Ferroelectric thin-film integrated capacitor is proposed in this work as the tuning element for MCM-D SiP technology. The proposed ferroelectric capacitors are fabricated on a sapphire substrate. The fabrication process is described. Measurement results show that the capacitance density is about 19 fF/μm² at 0-V bias. The tunability of the ferroelectric capacitor reaches 2:1 as the bias voltage is increased from 0 V to 7 V. The quality factor at 2.4 GHz is 15.5 under 0-V bias and reaches 30 when the bias voltage is 8 V. The proposed ferroelectric capacitor is applied to a RF phase shifter design for the purpose of demonstrating the potential of using the proposed thin-film ferroelectric technology for realizing MCM-D SiP. All-pass network is adopted as the circuit topology for the phase shifter. The design of the phase shifter is explained. To implement the phase shifter, surface mount components are mounted on the substrate on which the ferroelectric capacitors are fabricated. Measurement results show that, for bias voltage ranging from 0 V to 10 V, the phase shifter exhibits an insertion loss less than 2.6 dB and a return loss greater than 9.5 dB from dc to 6 GHz. Maximum phase shift of 98.8° is achieved at 3.15 GHz.