多孔壓電駐極體的孔洞性質對聲阻抗與 壓電特性影響之研究

Abstract

本研究的主軸在於探討多孔壓電駐極體的孔洞性質對其聲阻抗性質與壓電性質的影響。使用了PVDF-TrFE 和 PVDF-HFP這兩種PVDF共聚物作為製程材料，採用蒸氣誘導式相分離法、非溶劑誘導式相分離法和混合製程三種方法產生具不同孔洞大小及結構的多孔壓電駐極體薄膜，再透過電暈放電極化使其完成駐電。本研究以掃描式顯微鏡研究製成參數對孔洞結構的影響，發現蒸氣誘導式相分離法的濕度條件是一項重要因素，孔洞大小能與環境濕度呈正相關，最大孔洞能從50 μm2提升到140 μm2。而非溶劑誘導式相分離法所產生的得孔洞分布較為集中，高濃度 的非溶劑能增加孔洞大小，使最大孔洞能從70 μm2提升到110 μm2。最後，混合製程法則可以透過放置時間增加，製備出具有700 μm2等級地巨型孔洞結構，以及同時包含0.01 μm2等級的極小型孔洞。本研究透過阻抗管法量測具不同孔洞結構的薄膜聲阻抗性質，發現其結果與孔洞形貌有高度相依性。以蒸氣誘導式相分離法製作的多孔壓電駐極體，以最高濕度及最低濕度製備的薄膜聲阻抗的等效彈簧係數達3.4倍的差距，而非溶劑誘導式相分離法與混合製程法則可以產生 3.9 倍以上的差距。在 壓電性量測方面，本研究以實驗驗證出以孔洞大小密度的調節，可以使壓電薄膜有6倍以上的壓電表現差距，並歸納出小而低占比的孔洞相較於大而高佔比，能有更優秀的壓電表現，d33值可達928.8 pC/N。此外，本研究並驗證將此多孔壓電駐極體進行乾燥後，能達到20倍以上的壓電表現，此壓電性能在受潮後乾燥，可復原至原有的95%，顯示本研究薄膜具有壓電準永久性。在比較不同製程的實驗結果得知，小孔洞及較低面積占比的孔洞結構能有較佳的壓電響應，且孔洞形貌的變化能透過不同製程參數進行調節，並與壓電性、聲阻抗性質之間有高度相依性，使得這些特性能夠透過製程靈活地進行調控。

This study investigates the influence of void structures of porous piezoelectric ferroelectric films on acoustic impedance and piezoelectric properties. Two types of PVDF copolymers, P(VDF-TrFE), and P(VDF-HFP), are used, including vapor-induced phase separation, nonsolvent-induced phase separation, and mixed-process. Fabricated films are polarized using corona discharge. After studying void structures using scanning electron microscopy, it is found that void size directly correlates with humidity in the vapor-induced phase separation method. The maximum pore size can increase from 50 μm² to 140 μm². A more concentrated void distribution is observed in the nonsolvent-induced phase separation method. A higher nonsolvent concentration leads to larger pores, increasing the maximum pore size from 70 μm² to 110 μm². The mixed-process method creates void structures with giant pores up to 700 μm² and extremely small pores down to 0.01 μm². On the other hand, the experimental results show a strong dependence on pore morphology for the acoustic impedance using the impedance tube measurement method. Furthermore, piezoelectric characteristics vary over six-fold by adjusting void size and density. Void structures containing smaller and lower-area percentage exhibiting superior responses, reaching a d33 value of 928.8 pC/N. It is also found that dehydrated porous piezoelectric films can achieved a 20-fold increase in piezoelectric performance, and a recovery of 95% performance can achieve by dehydrating a humid film. In summary, This study highlights the tunable nature of void morphology through different fabrication methods. The detailed study on the correlation between void structure and piezoelectric properties and acoustic impedance enables the adjustment of porous piezoelectric ferroelectric films