Design, Integration and Characterization of CMOS-compatible RF Varactors Based on Ferroelectric HfO2 Thin Films

Wireless communication systems, including smartphones, Wi-Fi, GPS, and NFC, are vital to modern life. As data demands grow, higher bandwidths are needed, pushing technologies toward higher frequencies such as millimeter-wave and terahertz spectra, used in 5G/6G and the Internet of Things. These applications require devices with low energy consumption, minimal signal attenuation, and high miniaturization, crucial for integration into portable electronics. Ferroelectric materials offer great potential due to their low dielectric losses at microwave frequencies. However, conventional perovskite ferroelectrics are usually incompatible with CMOS fabrication due to contamination issues and high thermal processing requirements. Ferroelectric hafnium oxide, discovered in 2007, presents a CMOS-compatible solution. Its spontaneous polarization supports applications in memory devices, neuromorphic computing and energy harvesting. Its nonlinear dielectric properties enable its implementation as a varactor-an element with tunable capacitance, crucial for RF and mmWave systems. This book explores thin-film hafnium zirconium oxide varactors in metal-ferroelectric-metal configuration. The analysis is focused on the effects of doping, cycling, and temperature, and demonstrates their use in passive RF components such as phase shifters and filters through simulation and measurement.