In vacuum-deposited film composed of organic polar molecules, polarization charges appear on the film surface owing to spontaneous orientation of the molecule. Because its density (σpol) determines an amount of accumulation charge (σacc) in organic light-emitting diodes and output power in polar molecular-based vibrational energy generators (VEGs), control of molecular orientation is highly required. Recently, several groups have reported that dipole-dipole interaction between polar molecules induces anti-parallel orientation which does not contribute to σpol. In other words, perturbation inducing the attenuation of the dipole interaction is needed to enhance σpol. In this study, to investigate an effect of light irradiation on σpol, we prepared 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) film under illumination during its deposition, and evaluated the σacc in TPBi-based bilayer device, which equals to σpol. We found that the σacc was increased by light irradiation, indicating that average orientation of TPBi is enhanced. These results suggest that light irradiation during device fabrication is promising process for organic electronic devices including polar molecule-based VEGs.

A demonstration of power enhancement by nonlinear oscillation in a millimeter-sized electrostatic vibrational energy harvester for the future Internet of Things is presented. To enable nonlinearity in microelectromechanical system (MEMS) devices, we selected a gold spring as a component of the MEMS structure for its lower Young's modulus than conventional materials, a ductile characteristic, and an electrical conductivity. The mechanical characteristics of the fabricated MEMS device related to the nonlinear phenomenon were examined. The charging characteristics of an ethylene tetrafluoroethylene copolymer (ETFE) electret film for electrostatic induction were also evaluated. Nonlinear oscillation for the millimeter-sized energy harvester with the ETFE electret was confirmed experimentally by applying external vibration. The oscillation resulted in a bandwidth two times broader than that by linear oscillation. The normalized harvester effectiveness of the nonlinear oscillation was 5.1 times higher than that of the linear one.

A 20 kHz audio-band ADC with a single pair of power and ground pads is implemented for a digital electret microphone. Under the limited power/ground pad condition, the switching noise effect on the signal quality is estimated via post simulations with parasitic models. Performance degradation is minimized by time-domain noise isolation with sufficient time-spacing between the sampling edge and the output transition. The prototype ADC was implemented in a 0.18 µm CMOS process. It operates under a minimum supply voltage of 1.6 V with total current of 420 µA. Operating at 2.56 MHz clock frequency, it achieves 84 dB dynamic range and a 64 dB peak signal-to-(noise+distortion) ratio. The measured power supply rejection at a 100 mVpp 217 Hz square wave is -72 dB.

An on-chip CMOS preamplifier for direct signal readout from an electret capacitor microphone has been designed with high immunity to common-mode and supply noise. The Gm-Opamp-RC based high impedance preamplifier helps to remove all disadvantages of the conventional JFET based amplifier and can drive a following switched-capacitor sigma-delta modulator in order to realize a compact digital electret microphone. The proposed chip is designed based on 0.18 µm CMOS technology, and the simulation results show 86 dB of dynamic range with 4.5 µVrms of input-referred noise for an audio bandwidth of 20 kHz and a total harmonic distortion (THD) of 1% at 90 mVrms input. Power supply rejection ratio (PSRR) and common-mode rejection ration (CMRR) are more than 95 dB at 1 kHz. The proposed design dissipates 125 µA and can operate over a wide supply voltage range of 1.6 V to 3.3 V.

We introduced a new electret condenser Microphone (ECM) water repellent coating structure for protection against common hazards, such as water or alcohol. This protection structure is composed of small acoustical holes with a water-repellent coating. The water-repellent coating has a contact angle of more than 150 degrees for water on a small acoustical hole having less than 0.2 mm aperture, which blocks water invasion but allows acoustical transmission. The reliability of the coating was confirmed by several tests, such as long-term immersion in water and alcohol, re-flow soldering test and surface scratching. These tests produced no damage to the coating. The fabricated ECM meets the requirements for the IEC 60526 class 7, which is 30 minutes under water at a depth of 1 meter. The diameter and number of holes is determined both by acoustic characteristics and water resistance.

Micromachined sensors and actuators applied with electrostatic fields are getting widely developed. At the same time, "electrets," which are dielectrics carrying non-equilibrium permanent space charges or polarization distribution, are in demand because they improve the transducer characteristics. In this paper, we have reported on our successful fabrication of silicon dioxide electrets with extremely superior long-term charge stability by plasma chemical vapor deposition (PCVD). We have also reported on the correlation between the deposition conditions, the long-term charge stability and thermally stimulated current (TSC). Finally, the characterization of the long-term stable electrets will be described and discussed.

In order to improve the sensitivity of micromachined sensors applied with electrostatic fields and increase their actuated force of electrostatic micromachined actuators, "electrets," which are dielectrics carrying non equilibrium permanent space charges of polarization distribution, are very important. In this paper, positively corona charged silicon dioxide electrets, which are deposited by Plasma Chemical Vapor Deposition (PCVD) and thermally oxidized, are investigated. Physical studies will be described, in which the charge stability is correlated to Thermally Stimulated Current (TSC) measurements and to Electron Spin Resonance (ESR) analysis. Some intrinsic differences have been observed between materials. The electrets with superior long-term charge stability contain 10,000 times as much E' center (Si3 as the ones with inferior long-term charge stability. Finally, some investigations on the long-term charge storage mechanism of the positively charged silicon dioxide electret will be described.

In this paper, an electrostatic actuator with electret is proposed. Electrets are the electrical equivalent of magnets. They are dielectric's carrying a non equilibrium permanent space charge or polarization distribution. This distribution can create either an external electric field or internal properties such as piezo or pyroelectricity. In the first case it is possible to make new types of electrostatic actuators by the external electric field. An electrostatic relay with electret is fabricated to demonstrate the possibility of an electrostatic actuator with electret. The size of relay is 5.2 mm11.5 mm. Its amature beam is 50 µm thick, 2.9 mm wide, 6.3 mm long, and acts as a moving electrode. Facing it, the stationary electrode is 20 µm away from the moving electrode. On the stationary electrode, new type of electret made from SiO2 is deposited. We have succeeded in making the armature operate at low applied voltage 20 V. On the same structure without electret, we need more than 120 V to make the same armature operation. We have also succeeded in making the armature latching.