Ultrathin Membranes Fabricated with Water-Soluble Layer Enable Millimeter-Scale Flexible Electronics

The pursuit of flexible and miniaturised electronics hinges on developing advanced materials that can seamlessly integrate with silicon platforms, and freestanding oxide membranes represent a promising avenue for achieving this goal. Yuhao Hong, Yang Hu, and Jianyao Zheng, working at the MESA+ Institute for Nanotechnology at the University of Twente, lead a team that has now demonstrated a method for creating remarkably large and structurally perfect ultrathin oxide membranes spanning several centimetres. This breakthrough addresses a critical limitation in the field, where previous attempts to scale up membrane size resulted in cracking and wrinkling, hindering practical applications in areas like spintronics and energy technologies. By employing a water-soluble sacrificial layer, the researchers successfully fabricated membranes with exceptional structural integrity, opening up new possibilities for large-scale silicon integration and the development of truly flexible oxide-based devices, although challenges remain in preventing the introduction of defects during the fabrication process.

Freestanding Oxide Membranes Fabrication and Validation

These supplementary materials provide detailed supporting data for research describing the fabrication and characterization of freestanding oxide membranes, specifically strontium ruthenate and barium titanate. They validate claims regarding the quality, continuity, and structural perfection of these membranes, and offer more detailed information about the experimental procedures and data analysis techniques used. Data confirms layer-by-layer growth of both strontium ruthenate and the sacrificial layer, as evidenced by distinct oscillations and diffraction patterns observed during film growth monitoring. Images demonstrate the dissolution of the sacrificial layer, releasing the oxide membrane.

Optical microscopy reveals large-area, continuous strontium ruthenate membranes successfully integrated onto silicon substrates. Structural characterization of barium titanate membranes confirms their structural integrity and smooth surface morphology. High-resolution imaging visualizes the atomic structure of ultrathin strontium ruthenate membranes, confirming their structural perfection and continuity. Measurements demonstrate a clear magnetic response in the strontium ruthenate membranes, and ferroelectric properties in the barium titanate membranes. Investigations reveal the presence of oxygen vacancies within the membranes, which can influence their electronic and magnetic properties. Quantitative data from X-ray reflectivity measurements provides detailed information about the layer thicknesses and roughness of the samples.

Water-Assisted Lift-Off of Freestanding Oxide Membranes

Scientists have developed a new method for fabricating freestanding oxide membranes, overcoming a significant limitation in scaling up advanced materials for flexible electronics and spintronics. This study pioneers a water-assisted lift-off technique utilizing a super-tetragonal strontium aluminate layer as a sacrificial base, enabling the creation of ultrathin membranes spanning centimeter-scale areas. The fabrication process begins with the epitaxial growth of heterostructures, such as strontium ruthenate/strontium aluminate and barium titanate/strontium aluminate, on substrates using pulsed laser deposition. Real-time monitoring confirms layer-by-layer growth and the high quality of the strontium aluminate layer.

A soft cellulose acetate butyrate supporting layer is applied to the film surface and covered with a stamp, providing initial mechanical support. The key innovation lies in immersing the sample in deionized water, rapidly dissolving the sacrificial layer and releasing the oxide membrane, minimizing defect formation and enabling large-area, crack- and wrinkle-free membranes. Researchers demonstrate the versatility of this technique across a range of oxides, including ruthenates and ferroelectric titanates, and achieve membrane thicknesses as low as approximately 3 nanometers, aligning with the dimensional limits of advanced CMOS processes. The resulting membranes exhibit exceptional structural integrity and scalability, establishing a robust pathway for integrating complex oxides with semiconductor technologies.

Centimeter-Scale Freestanding Oxide Membranes Fabricated Successfully

Scientists have developed a new method for fabricating freestanding oxide membranes, achieving centimeter-scale areas with exceptional structural integrity. This breakthrough addresses a critical limitation in the field, where previous techniques were restricted to much smaller membrane sizes, hindering progress in flexible electronics and advanced device integration. Experiments reveal the key to this success lies in a water-soluble sacrificial layer of super-tetragonal strontium aluminate, which dissolves cleanly without damaging the overlying oxide film. Dissolution occurs rapidly and reproducibly, and is largely independent of the oxide composition.

Crucially, the use of a spin-coated cellulose acetate butyrate film, combined with a stamp, prevents bending and cracking during the release process, preserving the structural quality of the membranes. Detailed structural characterization confirms the exceptional crystalline quality of the freestanding films. Measurements demonstrate that the membranes remain coherently matched to the original substrate, with no unwanted secondary phases detected. Measurements confirm the thickness uniformity of the strontium ruthenate membranes, while barium titanate membranes were directly measured at approximately 40 nanometers thick. These results establish a robust pathway for integrating complex oxides with semiconductor technologies, potentially enabling next-generation devices with enhanced performance and functionality.

Ultrathin Oxide Membranes and Vacancy Formation

This work demonstrates a new method for fabricating freestanding oxide membranes, achieving centimeter-scale dimensions and thicknesses down to 3. 2 nanometers, while avoiding the cracks and wrinkles that typically limit the size of these structures. The technique utilizes a water-soluble sacrificial layer, offering a versatile route for constructing miniaturized devices directly on silicon platforms, with applicability extending to various oxide materials including ruthenates and titanates. However, the dissolution of the sacrificial layer introduces defects into the strontium ruthenate membranes, penetrating up to six unit cells and resulting in unusual transport behavior within the ultrathin films. While post-deposition annealing can eliminate these defects, the high temperatures required are incompatible with standard CMOS processing, presenting a significant obstacle to integrating these membranes into silicon-based devices. Future research should focus on developing alternative release strategies that minimize defect incorporation, or on identifying functional oxides that are inherently resistant to this issue, to fully realize the potential of freestanding oxide membranes in areas like flexible electronics, neuromorphic computing, and energy technologies.