Layout Optimization of Small-Size Ferroelectric Parallel-Plate Varactors

The extremely high permittivity of ferroelectric varactors (typically ϵ_r > 100) imposes specific design and fabrication constraints for microwave and millimeter-wave applications. In this paper, small-size parallel-plate ferroelectric varactors insensitive to fabrication misalignment tolerances are studied experimentally. It is shown that the total resistance of the varactors strongly depends on the shape factor of the plates. Moreover, due to the small sizes of the varactors, the interconnecting strips become narrow and their contribution to the total resistance dominates. A simple procedure for optimization of the shape factor to minimize the varactor resistance is proposed.