Low bias voltage tunable phase shifter based on inkjet-printed BST MIM varactors for C/X-band phased arrays

This paper presents a novel topology and method for the fabrication of tunable ferroelectric components based on inkjet printing for phased arrays applications at C/X-Band. This method enables low voltage biased tunable phase shifters by inkjet printing of tunable dielectric thick films. The loaded line tunable phase shifter is tuned by integrated metal-insulator-metal (MIM) varactors. The MIM varactors are fabricated by photo lithography and subsequently inkjet printing of barium-strontium-titanate striplines, enabling a simple and reliable process. In comparison to coplanar capacitors, such MIM varactors require significantly lower DC-voltage for tuning. A tunability of 32 % at 8.5 GHz is achieved by applying only 25 V across a 1.2 μm thick BST film and a tunability of 46 % by applying 50 V. The 11 unit cells loaded line tunable phase shifter achieves a figure of merit (FoM) above 40 °/dB across 7 to 8.5 GHz by applying maximum 50 V tuning voltage. The size of the phase shifter is 1×0.45 cm².