Despite the development of energy-efficient devices in various applications, microelectromechanical system (MEMS) electrostatic actuators yet require high voltages to generate large displacements. In this respect, electrets exhibiting quasi-permanent electrical charges allow large fixed voltages to be integrated directly within electrode structures to reduce or eliminate the need of DC bias electronics. For verification, a − 40   V biased electret layer was fabricated at the inner surface of a silicon on insulator (SOI) structure facing a 2 μm gap owing to the high compatibility of silicon micromachining and the potassium-ion-electret fabrication method. A − 10   V electret-augmented actuator with an out-of-plane motion membrane reached a sound pressure level (SPL) of 50 dB maximum with AC input voltage of V i n = 5   V pp alone, indicating a potential for acoustic transducer usage such as microspeakers. Such devices with electret biasing require only the input signal voltage, thus contributing to reducing the overall power consumption of the device system.

A novel triboelectric energy harvester has been developed using an ionic liquid polymer with cations fixed at the surface. In this report, the fabrication of the device and the characterization of its energy harvesting performance are detailed. An electrical double layer was induced in the ionic liquid polymer precursor to attract the cations to the surface where they are immobilized using a UV-based crosslinking reaction. The finalized polymer is capable of generating an electrical current when contacted by a metal electrode. Using this property, energy harvesting experiments were conducted by cyclically contacting a gold-surface electrode with the charge fixed surface of the polymer. Control experiments verified the effect of immobilizing the cations at the surface. By synthesizing a polymer with the optimal composition ratio of ionic liquid to macromonomer, an output of 77 nW/cm2 was obtained with a load resistance of 1 MΩ at 1 Hz. This tuneable power supply with a μA level current output may contribute to Internet of Things networks requiring numerous sensor nodes at remote places in the environment.

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Electrostatic microactuators require external DC biasing in order to achieve the widest possible range of displacements for a given AC input. This report proposes a novel microspeaker structure that utilizes a potassium-ion-electret to reduce the need for such DC voltage application. Electrets exhibiting quasi-permanent charges enable large fixed voltages to be integrated directly within the MEMS structure, acting as an ersatz DC bias. Prototype devices were fabricated and characterized to approximate the effects of electret incorporation on the device performance.