Yttrium iron garnet, Y3Fe5O12 (YIG), is a ferrimagnetic insulator with unique properties, such as a very high Faraday rotation angle and record coherence for magnetization dynamics. It has many applications in electronics, serving in tunable microwave devices (for remote detection and transmission of information), microwave circulators, optical insulators, etc. The manufacture of integrated magnonic devices, which extend the above applications to micro- and nanometric scales, requires the epitaxial growth of magnetic insulators in thin (< 10 μm) and/or very thin (< 100 nm) films. Currently, LPE (Liquid Phase Epitaxy)-grown YIG thin films (thicknesses ranging from a few µm to a few nm) are at the heart of the needs of several research themes developed in the Grenoble environment, notably integrated microwave devices, microwave-optical transduction, or ultra-coherent magnonics at low temperatures, and are the key to numerous experimental breakthroughs. This thesis will focus on the growth of ultra-thin YIG layers by LPE in Pb-based and Pb-free solvents (technical services Cristaux Massifs (CM) and OPTIque et MAtériaux (OPTIMA) research team at the Institut Néel).