Fully printed varactors and phase shifters based on a BST/polymer ink for tunable microwave applications

A fully printed varactor and a phase shifter using direct ink writing methodologies will be described. A novel ferroelectric ink was developed to print high dielectric constant, low loss, and electrostatically-tunable dielectrics on plastic substrates. The dielectric is based on multiphase Barium Strontium Titanate (BST)/polymer composite made by suspending nano/submicron-sized particles of BST in a thermoplastic polymer, namely Cyclic Olefin Copolymer (COC). After printing with the ink, a low temperature curing process was performed at temperatures below 200°C. RF measurements and characterizations showed that the sinter-less dielectric had a very high relative permittivity of ε
_r
= 42 and a very low dielectric loss of tanδ = 0.0005 at f = 10GHz. As a result, all-printed, voltage-variable capacitors with up to 10% capacitance tunability at microwave frequencies were realized. Subsequently, the tunable BST/COC ink was used in a left handed transmission line design to realize a printed tunable phase shifter.