Process optimization for waveguide fabrication by liftoff processing in layers deposited by pulsed laser

The realization of integrated active optical systems is crucial for the use of components such as amplifiers, lasers or photodetectors on a chip. Alumina (Al₂O₃) doped with erbium is a promising material for the realization of various active functions. Indeed, the low propagation losses of Al₂O₃, the rare earth compatibility and its wide transmission band makes Al₂O₃ suitable for a wide range of applications. Nevertheless, current methods for producing such waveguides are often costly and difficult, requiring complex and potentially loss-making processing steps like etching. In this context, Pulsed Laser Deposited (PLD) combined with lift-off is a relevant method for avoiding etchings. The process is composed of three main steps: photolithography, PLD and lift-off. In this work, we present how the different steps have to be optimized to make suitable waveguides for light propagation. Notably, photolithography needs a precise cross-section profile to obtain smooth sidewall, to ease lift-off and get high resolution patterning. For PLD, SEM images showed the importance of plume directivity and orientation in the PLD chamber to achieve a good control of the waveguide shapes. Finally, we also have shown that the Erbium photoluminescence is dependent on the annealing temperature. These results highlight the essential parameters which need to be precisely controlled to achieve accurate microstructures by liftoff processing performed in PLD layers, paving the way for the demonstration of low-loss waveguides and fully integrated erbium laser without etching.