Polymer-based capacitor could improve electrical circuitry

Saudi Arabian researchers have used a blend of polymer materials to develop a novel type of component — one that could substantially improve the performance of electrical circuits.

Electronic circuitry is traditionally constructed from three primary elements: a resistor, a capacitor and an inductor. A sinusoidal electrical signal passing through these devices will change in signal strength, or amplitude, and the relative timing of the crest of the wave, known as its phase. A resistor will change amplitude only while a capacitor and an inductor can also change phase but only by exactly one-quarter of the length of the wave, or 90°.

Components that could alter the phase of the electrical signal by a different amount would enable electrical circuits with more varied functionality. One such device, known as a fractional-order capacitor, was realised by Agamyrat Agambayev, an electrical engineering doctoral student at King Abdullah University of Science and Technology (KAUST), under the supervision of Hakan Bagci and Khaled Salama.

“We use a solution-casting method to fabricate fractional-order capacitors,” explained Salama. “This method allows us to easily blend different polymers and provide a mechanism to tune the device’s properties.”

Numerous approaches to creating a fractional-order capacitor have been demonstrated in the past, but all have drawbacks. Using a liquid medium, for example, results in large devices that cannot be integrated with microelectronic circuits. Ideally, a fractional-order capacitor should be made from a dielectric material that is compatible with printed-circuit-board technology. It should also operate over a wide range of signal frequencies and have a controllable phase change, known as the constant phase angle or CPA.

The KAUST team created a fractional-order capacitor using a polymer based on poly (vinylidene fluoride). They deposited a thin film on a layer of gold on a silicon substrate. The film was patterned as required and bonded to the printed circuit board to create the final device. The electrical properties of the polymer were controlled using a simple solution-mixing approach to add different amounts of trifluoroethylene and/or cholorfluroethylene.

Writing in the journal ChemElectroChem, the researchers revealed they could tune the CPA of their devices from 66 to 88°, depending on the blend composition. What’s more, the devices acted over a wide range of frequencies from 0.1 to 10 MHz.

The team members believe the tunability offered by polymers represents a huge advance. Their next move, said Bagci, is to look into modelling these structures to better understand their behaviour.

“This will help design fractional capacitors with better performance,” he said.

Image caption: Blending polymer materials in the right combination can create fractional-order capacitors that are compatible with printed circuit boards. ©2017 KAUST