Multimodal MEMS vibration energy harvester with cascaded flexible and silicon beams for ultralow frequency response

Scavenged energy from ambient vibrations has become a promising energy supply for autonomous microsystems.However,restricted by device size,most MEMS vibration energy harvesters have much higher resonant frequencies than environmental vibrations,which reduces scavenged power and limits practical applicability.Herein,we propose a MEMS multimodal vibration energy harvester with specifically cascaded flexible PDMS and"zigzag"silicon beams to simultaneously lower the resonant frequency to the ultralow-frequency level and broaden the bandwidth.A two-stage architecture is designed,in which the primary subsystem consists of suspended PDMS beams characterized by a low Young's modulus,and the secondary system consists of zigzag silicon beams.We also propose a PDMS lift-off process to fabricate the suspended flexible beams and the compatible microfabrication method shows high yield and good repeatability.The fabricated MEMS energy harvester can operate at ultralow resonant frequencies of 3 and 23 Hz,with an NPD index of 1.73μW/cm^(3)/g^(2)@3 Hz.The factors underlying output power degradation in the low-frequency range and potential enhancement strategies are discussed.This work offers new insights into achieving MEMS-scale energy harvesting with ultralow frequency response.

Thermoelectric effect and devices on IVA and VA Xenes

Emerging Xenes,mostly group IVA and VA elemental two-dimensional(2D)materials,have small and tunable band gaps between graphene and transition metal dichalcogenides,giving versatile electrical properties.While their microelectronic or optoelectronic properties are being extensively explored,there remains a lack of study on Xenes'uniquely advantageous thermoelectric performance.This review highlights state-of-the-art experimental and theoretical progress in the thermoelectric effect and devices of IVA and VA Xenes.Vertically displaced,a.k.a.“buckled”or“puckered,”atomic arrays result in exotic and tunable electrical or thermal transport behaviors.Different from chemical doping strategies usually employed in bulk thermoelectric materials,2D Xenes can be tuned by physical means,such as atomic layer control and quantum confinement effects.A precise and compatible platform for 2D thermoelectric effect and devices study is available via the engagement between micro/nanofabrication of 2D Xene transistors and thermal property measurement techniques.This review also reveals potential thermoelectric applications of Xenes and their compounds(Bi2Te3,Bi2Se3,etc.),such as accurate stretchable temperature sensors,fast terahertz photodetectors,and so on.