高效能微型能量擷取器之研製與工作模態最佳化研究

Abstract

隨著物聯網時代的來臨，越來越多的感測元件將連上網路，在人們的生活品質大幅的提升同時，也默默地造成了更多的電能量消耗，倘若能夠使得每一個感測元件皆有其發電系統，而此發電系統之能量來源完全取自於環境中，這未嘗不是件兩全其美之好事，然而從過去研究中知曉，環境中之振動能能量密度極高且取之不竭，也因此本研究將主軸鎖定於壓電能量擷取器之研製。過去幾年來，壓電能量擷取元件選用之材料近乎皆為鋯鈦酸鉛(PZT)，隨著時代的演進，各國研究團隊透過不同的製程方式，所得到之能量輸出表現將逐漸的達到材料之極限，近年來本研究團隊透過改變基板材料，大幅提升懸臂樑式壓電能量擷取元件之輸出功率，且有效的增強其結構之耐用性，故本研究認為唯有引入更新穎之材料，才能夠突破目前的壓電能量輸出極限，根據文獻指出鈮鎂酸鉛-鈦酸鉛(PMN-PT)陶瓷之壓電特性及機電耦合常數皆優於PZT陶瓷材料，其極有可能成為下一世代盛行之壓電能量擷取元件材料。 本論文將首先進行PMN-PT壓電陶瓷材料之研究，同時著手理解懸臂樑式壓電能量擷取元件之理論，並將焦點放在3-1及3-3工作模態之能量輸出表現，針對壓電懸臂樑式能量擷取元件之輸出功率關係式進行合理簡化，此簡化將有利於元件設計者可於短時間內完成元件之輸出功率估算，最終也將本論文所製作之元件參數代入關係式計算，所得之結果可概略的說明本實驗之結果。 實驗操作之部分，本論文中已成功的利用氣膠噴塗技術，沉積約為2.8 um厚之PMN-PT，並且對於陶瓷粉體及壓電膜進行微觀分析，目前已經初略了解氣膠噴塗技術之適合粉末條件，藉由微機電製程技術的協助，本論文順利的製作出PMN-PT懸臂樑式壓電能量擷取元件，並完成元件之退火條件、極化溫度以及極化電場條件之測試，所製成之元件於0.5g之振動環境中，共振頻率以及最大輸出功率分別為94.8 Hz及8.423 uW，此輸出表現優於同厚度之PZT壓電元件，而單位體積能量密度也優於過去本團隊所研發之PZT厚膜元件，故本研究認為若將來能夠突破PMN-PT之膜厚沉積極限，製作出之厚膜PMN-PT壓電能量擷取元件，將有極大可能取代現有之PZT壓電能量擷取器。

With the advent of the Internet of Things (IoT) era, more and more sensing units will be connected to the internet. While this improves quality of life, the extra sensors will, however, cost more electrical energy consumption. If each sensing unit has a self-powered generation system, whose power source is entirely from the environment, high cost batteries or cord connections will not be needed. According to past studies, the energy density of vibration sources is the highest available in our society and is practically inexhaustible. For this reason, this study is focused on the development of piezoelectric energy harvesters (EH) reaping energy from vibrations. Over the past few years, the majority of selected materials used to make EH are a type of lead zirconate titanate (PZT). As time progresses, research teams improve the output performance of EH through changing fabrication processes. Until now, the performance of EH energy output had gradually reached the limit of the chosen materials. In our previous research, a significant power output increase and durability improvements were caused by altering the EH substrate material. Therefore, this study suggests that only the introduction of innovative materials will allow a breakthrough in the limit of EH energy output. According to recently published literature, attention has been given to lead magnesium niobate–lead titanate (PMN-PT) material because of its high piezoelectric constant and electromechanical coupling factor. It has become highly desirable as the next-generation piezoelectric material. In this study, an introduction of piezoelectric ceramic material will be presented first. Theory regarding cantilever piezoelectric EH is elucidated with a focus on the 3-1 and 3-3 operation modes. The reasonable simplification of EH analysis is presented for the benefit of EH designers estimating the output performance in a practical amount of time. Next, measured parameters are used for EH analysis to show the theory corresponds to experimental results. To demonstrate EH performance by experiment, 2.8 um of PMN-PT film was successfully deposited on a stainless steel substrate by aerosol deposition. The microstructure of the ceramic powder and piezo-film were analyzed, assisting in the understanding of suitable powder conditions for aerosol deposition. With the help of micro electro-mechanical systems (MEMS) technology processes, this study produced PMN-PT based EHs and optimized the annealing temperature and poling condition of EH devices. The experimental results show that the device has a maximum output power of 8.423 uW with a resonant frequency at 94.8 Hz under 0.5 g acceleration. The output performance is better than the PZT-based EH with the same thickness. When given a comparison with previous work, the volumetric power density in this study is also better than those previously found.