## 4 Conclusions  
In this work, we showed the procedure to fabricate free-standing membranes with remarkable crystallographic quality by using water-soluble SAO as a sacrificial layer. As an example, we reported on the preparation of STO/SAO/STO, GDC/SAO/STO, and SDC/SAO/STO heterostructures and then on the procedure to dissolve the SAO layer by sinking the heterostructure in distilled water at room temperature. Furthermore, the STO, GDC, and SDC layers detached from the STO substrate were transferred onto the polymer PDMS Gelpack, maintaining a good crystallographic quality. Free-standing membranes fabricated using SAO as a sacrificial layer offer a transformative pathway for transferring thin films onto diverse substrates. This approach not only preserves the crystalline structure and electrical properties of the films--even in the presence of minor imperfections such as cracks or flakes--but also demonstrates remarkable robustness and reliability. Such advancements allow the integration of high-crystallinity oxide thin films grown via PLD into established technologies, including silicon-based platforms, which are central to microelectronics and energy systems. For ionic and electronic conductors like SDC, this method provides a solid foundation for developing advanced electrochemical devices, such as micro-SOFCs and other miniaturized energy conversion systems. The retention of high-quality crystalline properties in transferred films is critical for achieving superior ionic conductivity, mechanical stability, and long-term reliability. Furthermore, the ability to fabricate free-standing membranes extends beyond SDC, enabling the exploration of a broad spectrum of multifunctional materials, including ferroelectric, piezoelectric, and magnetic oxides. These materials can be leveraged in next-generation MEMS sensors, actuators, and energy-harvesting devices, addressing key challenges in emerging technologies, such as wearables, IoT devices, and autonomous systems. A particularly promising avenue is the integration of ultrathin oxide films onto surfaces with tailored oxide terminations. This strategy enables precise control over interfacial properties, which are critical in designing heterostructures with novel functionalities. For instance, strain engineering at the interface can significantly enhance the transport properties of oxide thin films, such as ionic conductivity, electronic conductivity, and superconductivity. Such improvements are vital for applications in ionotronics, spintronics, and quantum devices. Additionally, the ability to create free-standing membranes expands opportunities for investigating phenomena such as flexoelectricity and strain-induced phase transitions, which are challenging to study in conventional substrate-bound systems. Figure 6: Electrochemical cell fabrication procedure with sacrificial layer method. Importantly, this technique paves the way for integrating oxide thin films into silicon-based technologies, bridging the gap between traditional semiconductors and functional oxides. This integration could drive the development of a new generation of micro-Solid Oxide Electrochemical Cells, micro-Solid Oxide Fuel Cells, and other multifunctional devices. These innovations hold the potential to revolutionize fields such as micro-scale energy harvesting, portable power systems, and environmental sensing. Moreover, the scalability and versatility of the sacrificial layer approach make it a promising candidate for industrial adoption. The costs associated with the sacrificial layer technique are primarily due to the fabrication of the SAO layer and the functional layers. These costs are comparable for various high-quality films. Moreover, the etching process is straightforward and does not require any specific solvents or equipment. Moreover, future research should focus on optimizing the transfer process to further minimize structural defects and improve scalability, as well as exploring its applicability to emerging material systems.