An investigation of dielectric tunable materials for microwave tunable devices

Today, many of the communication systems are operated in several different bandwidths. Till now, the common solution to get a multi bandwidth transmitter/receiver is to insert several fixed microwave devices with different bandwidth to the required standard. This increases the size and power consumption of trans/receiver. One solution is to develop electronically tunable microwave devices. By replacing several fixed microwave devices with a single electronically tunable device, the size and power consumptions of the transmitter/receiver can be significantly reduced. The tunable devices are usually implemented by high permittivity tunable materials that exhibit a change of dielectric constant with respect to a DC electric field. In this work, two different types of tunable materials: ferroelectric Barium Strontium Titanate (BST) Oxide and pyrochloe Bismuth Zinc Niobate Oxide (BZN) thin films are investigated. A simple and cost effective chemical solution deposition (CSD) method has been used to prepare the thin films. In addition, two different types of microwave devices (coplanar waveguide and metal insulated metal capacitors) were fabricated to measure the microwave dielectric properties of BST and BZN thin films. The maximum errors in the measured dielectric constants are 24% due to the calibration errors. To improve the dielectric properties of BST thin films, acceptor ions such as lithium (Li) and cobalt (Co) were doped into BST thin films. According to the measured results, the Li doped BST thin film exhibits an increase of dielectric constant and a decrease of dielectric loss, which makes it highly attractive for implementing microwave device. In contrast, the BZN thin films exhibit little dielectric tunability (3.0%) even when a large DC electric field (500kV/cm) is applied. These results demonstrate that ferroelectric BST thin films are still the only practical materials for implementing tunable microwave devices due to its high tunability.EThOS - Electronic Theses Online ServiceGBUnited Kingdo