Ferroelectric parallel-plate capacitors with copper electrodes for high-frequency applications

Tunable capacitors with a Cu∕PbxSr1−xTiO3∕Cu parallel-plate structure have been fabricated using a layer transfer method. The use of a Cu bottom electrode results in a giant electrode Q-factor×capacitor area product of QelecA=3.79×105μm2 at 1GHz. The dielectric constant at room temperature is 420 and the tunability amounts to 73% near a breakdown voltage of 35V. The major advantages of the layer transfer method include low electrode losses, the freedom to select an auxiliary substrate and seed layer for ferroelectric film growth irrespective of their high-frequency properties, and the possibility to utilize a large variety of device substrates as they no longer act as template for film growth.