以釔鋇銅氧為犧牲層製作自支撐獨立單晶氧化物薄膜

Fabrication of Freestanding Single-Crystalline Oxide Thin Films Using YBa2Cu3O7-x as a Sacrificial Layer

近年來複雜性氧化物(Complex Oxide)因為其多樣的材料特性和可調控的功能性，受到許多的關注。為了充分發揮複雜性氧化物的潛力，堆疊的氧化物異質磊晶結構(heteroepitaxy)逐漸嶄露鋒芒。然而，在進行氧化物異質磊晶時，挑選合適的基板成為重要的課題，由於晶格不匹配的緣故，並不是所有的氧化物都能夠挑選到合適的基板並進行異質磊晶成長。若想使這些材料擁有的特性做更廣泛的應用和搭配，其中一個發想便是利用犧牲層及蝕刻法將原本經由磊晶形成的薄膜與基板分離，並利用轉移方法來整合磊晶薄膜與商用裝置及基板。此方法首先利用脈衝雷射沉積法將犧牲層材料與目標薄膜成長於單晶基板，利用相對較易被蝕刻的犧牲層材料，製備自支撐目標薄膜，再進行轉移。其中，La0.7Sr0.3MnO3和Sr3Al2O6便是兩種常見的犧牲層，與之配合的蝕刻液相對較溫和，可以確保目標薄膜不會被蝕刻液所破壞。但是相對的，欲蝕刻這兩種犧牲層需要花費較長的時間，以La0.7Sr0.3MnO3而言需要數小時，而Sr3Al2O6則需要數天。本研究以YBa2Cu3O7-x (YBCO)作為犧牲層，YBCO可以和許多複雜性氧化物堆疊進行磊晶成長，且該材料易與鹽酸為基底的溶液快速反應分解，很適合在濕式蝕刻轉移中作為犧牲層。且能應用於製備以La0.7Sr0.3MnO3為目標薄膜的樣品，在目標薄膜被蝕刻液嚴重破壞之前將La0.7Sr0.3MnO3和基板分離，大幅縮短了製作樣品所需要的時間，也提供了快速製備自支撐氧化物的新選擇。

Recently, complex oxide thin films have caught a lot of attention. They are known to possess rich physical properties with great potential to be commercially used. In order to bring complex oxides into practical application, heteroepitaxy was introduced and has been a widely adopted method to develop complex oxide thin films. However, due to the lattice mismatch, the chosen of a suitable substrate became a crucial issue and has hinder the development of oxide heteroepitaxy. To integrate complex oxide into commercial devices, freestanding membrane was proposed. With a sacrificial layer, freestanding thin film can be detached from the original substrate. Traditionally, La0.7Sr0.3MnO3 and Sr3Al2O6 are two common materials adopted as sacrificial layers. By etching the sacrificial layer, the thin film which was deposited on the sacrificial layer can be separated from the substrate. In this work, we proposed an alternative choice of the sacrificial layer, YBa2Cu3O7-x, which can be etched in a very short period, allowing the fabrication of high-quality freestanding thin films. Furthermore, such approach allows us to separate materials which is sensitive to acid etchant such as La0.7Sr0.3MnO3 because the etching time of YBa2Cu3O7-x is much faster than La0.7Sr0.3MnO3. Our goal is to develop a distinct method that could be a universal way to deliver freestanding thin films.