Heterostructure membranes and their manufacturing process
The nanometric membranes of oxides allow to obtain new functionalities and to integrate the oxides in flexible electronics. The LaAlO3 / SrTiO3 interface represents, among the oxides, the counterpart to the highly mobile semiconductor heterostructures that play a crucial role in modern electronics. Our invention relates to a method for fabricating superconducting epitaxial membranes through pulsed laser deposition (PLD), by means of strain engineering. The membranes produced are transferable and contactable on Silicon wafers.
The patent describes a method to obtain the spalling of LaAlO3/SrTiO3 samples and manufacture self-formed micrometer sized membranes, showing structural and electrical properties identical to the bulk counterpart. This method is related to the control of the relaxation mechanism of the tensile strain, due to the difference of the lattice parameters between the two materials (3%). The epitaxial LaAlO3 films are grown by PLD on 5×5 mm2 SrTiO3 substrates, with appositely tailored experimental parameters (730°C, p=10-2mbar, λ=248nm 3Hz, F=2.0-2.5J/cm2). In such conditions, LaAlO3 films grow epitaxially in a strained tensile state for thickness (≤ 20nm) above the theoretical relaxation thickness. Relaxation finally happens thorough the formations of vertical cracks along the main crystallographic directions and, once exposed to air, horizontal cracks in the substrate. The result of this process is the fragmentation of the sample in a regular network of about 10^5-10^6 LaAlO3/SrTiO3 freestanding membranes with nanometer thickness and micrometer lateral dimensions. Each membrane is easily transferred and contacted on Si-chips, allowing the integration of the wide range of oxides functionalities on Si-based devices.
- Flexible electronics;
- Quantum technologies.
- High yield process (10^5 – 10^6 membranes for each sample growth);
- No need of sacrificial buffer layers removed by chemical process;
- Applicable to other oxides, semiconductors or metal systems.