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We evaluated the effective transverse piezoelectric coefficients (e 31,f ) of Pb(Zr,Ti)O 3 (PZT) thin films from both the direct and converse piezoelectric effects of unimorph cantilevers. (001) preferentially oriented polycrystalline PZT thin films and (001)/(100) epitaxial PZT thin films were deposited on (111)Pt/Ti/Si and (001)Pt/MgO substrates, respectively, by rf-magnetron sputtering, and their piezoelectric responses owing to intrinsic and extrinsic effects were examined. The direct and converse je 31,f j values of the polycrystalline PZT thin films were calculated as 6.4 and 11.5-15.0 C/m 2 , respectively, whereas those of the epitaxial PZT thin films were calculated as 3.4 and 4.6-4.8 C/m 2 , respectively. The large je 31,f j of the converse piezoelectric property of the polycrystalline PZT thin films is attributed to extrinsic piezoelectric effects. Furthermore, the polycrystalline PZT thin films show a clear nonlinear piezoelectric contribution, which is the same as the Rayleigh-like behavior reported in bulk PZT. In contrast, the epitaxial PZT thin films on the MgO substrate show a piezoelectric response owing to the intrinsic and linear extrinsic effects, and no nonlinear contribution was observed.

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We fabricated piezoelectric MEMS energy harvesters (EHs) of lead-free (K,Na)NbO3 (KNN) thin films on microfabricated stainless steel cantilevers. The use of metal substrates makes it possible to fabricate thin cantilevers owing to a large fracture toughness compared with Si substrates. KNN films were directly deposited onto Pt-coated stainless steel cantilevers by rf-magnetron sputtering, thereby simplifying the fabrication process of the EHs. From XRD measurement, we confirmed that the KNN films on Pt-coated stainless steel cantilevers had a perovskite structure with a preferential (001) orientation. The transverse piezoelectric coefficient e 31f and relative dielectric constant εr were measured to be -3.8 C/m2 and 409, respectively. From the evaluation of the power generation performance of a KNN thin-film EH (length: 7.5 mm, width: 5.0 mm, weight of tip mass: 25 mg), we obtained a large average output power of 1.6 µW under vibration at 393 Hz and 10 m/s2.

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-High efficiency power feeding systems are effective solutions for reducing ICT power consumption of ICT equipment, such as routers and servers, or high efficiency cooling systems. We developed a higher voltage direct current (HVDC) power feeding system prototype. This system is composed of a rectifier, power distribution cabinet, batteries, and ICT equipment. The configuration is similar to a -48 V DC power supply system. The output of the rectifier is 100 kW, and the output voltage is 401.4 V. We describe the advantage of an HVDC power feeding system and show that its basic characteristics are stable.

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The interleaved structure of LLC resonant converter with the phase shift modulation (PSM) is presented and then its optimum operating region is discussed. The LLC resonant converters can achieve zero voltage switching (ZVS) of the primary switches and zero current switching (ZCS) of the secondary switches. However, the secondary peak current is large due to the discontinuous conduction mode (DCM). The interleaved PFM LLC resonant converter has difficulty in synchronizing switching instants among phases owing to the parameter mismatch of resonant circuits. In the proposed method, the current unbalance caused by the parameter mismatch is compensated by PSM. It is confirmed that the proposed method achieves lower peak current even when there is parameter mismatch and that the operation of below resonant frequency is suitable, both of which are simulated and experimentally verified.Index Terms-LLC resonant converter, pulse frequency modulation, phase shift modulation, interleave.