How we use and generate electricity has changed dramatically over the past century yet the basic components that control its flow remain remarkably similar. Researchers at KAUST have now developed a novel type of component that could 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 realized by electrical engineering doctoral student Agamyrat Agambayev, under the supervision of Hakan Bagci and Khaled Salama, and colleagues. "We use a solution-casting method to fabricate fractional-order capacitors," explains 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 have 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. They could tune the CPA of their devices from between 66 and 88 degrees depending on the blend composition. What's more, the devices acted over a wide range of frequencies from 0.1 to 10 megahertz.
The team has previously created graphene fractional-order capacitors, but they believe the tunablility offered by polymers represents a huge advance. "Next, we will look into modeling these structures to better understand their behavior," says Bagci. "This will help design fractional capacitors with better performance."
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Agamyrat Agambayev et al. Ferroelectric Fractional-Order Capacitors, ChemElectroChem (2017). DOI: 10.1002/celc.201700663