Frequency-reconfigurable RF components are highly desired in the wireless industry to support the ever-increasing multi-band requirement for various communication systems and communication protocols at different frequency bands. In a wireless system, a single frequency-reconfigurable RF component can replace multiple RF components to reduce the size, cost, and weight. Typically, the reconfigurable RF components are realized using capacitive varactors, PIN diodes, or MEMS switches, which have two drawbacks. First, they are expensive as they are fabricated through expensive nanofabrication processes, and second they need tedious soldering steps for integration with the RF components. Both these issues become problematic, particularly, for higher frequencies. For example, the cost of an RF switch that can operate at 30 GHz can be as high as 38 USD. This brings the overall cost of the reconfigurable RF components very high. Finally, majority of these switches are rigid and not suitable for futuristic applications of flexible and wearable electronics. Therefore, there is a need to have a solution for low cost, flexible and easy to integrate RF switches.
All the above-mentioned issues can be alleviated if these switches can be simple printed at the place of interest. In this work, we have demonstrated vanadium dioxide (VO2) based RF switches that have been realized through additive manufacturing technologies (inkjet printing and screen printing), which dramatically brings the cost down to a few cents. Also, no soldering or additional attachment step is required as the switch can be simply printed on the RF component. The printed VO2 switches are configured in two types (shunt configuration and series configuration) where both types have been characterized with two activation mechanisms (thermal activation and electrical activation) up to 40 GHz. The measured insertion loss of 1-3 dB, isolation of 20-30 dB, and switching speed of 400 ns is comparable to other non-printed and expensive RF switches.
As an application for the printed VO2 switches, a fully printed frequency reconfigurable filter has also been designed in this work. An open-ended dual-mode resonator with meandered loadings has been co-designed with the VO2 switches, resulting in a compact filter with decent insertion loss of 2.6 dB at both switchable frequency bands (4 GHz and 3.75 GHz). Moreover, the filter is flexible and highly immune to the bending effect, which is essential for wearable applications.
Finally, a multi-parameter (switch thickness, width, length, temperature) model has been established using a customized artificial neural network (ANN) to achieve a faster simulation speed. The optimized model’s average error and correlation coefficient are only 0.0003 and 0.9905, respectively, which both indicate the model’s high accuracy.
Shuai Yang is a Ph.D. student supervised by Prof. Atif Shamim in Electrical Engineering program at King Abdullah University of Science and Technology. He received his Master degree in Electrical Engineering from Hong Kong University of Science and Technology in 2013. His research interests include printed electronics with vanadium dioxide, the application of vanadium dioxide in reconfigurable RF components, and the modeling of vanadium dioxide switches.