Magneto-Optical Bi-Substituted Yttrium and Terbium Iron Garnets for On-Chip Crystallization via Microheaters

Ferrimagnetic iron garnets enable magnetic and magneto-optical functionality in silicon photonics and electronics. However, garnets require high-temperature processing for crystallization which can degrade other devices on the wafer. Here bismuth-substituted yttrium and terbium iron garnet (Bi-YIG and Bi-TbIG) films are demonstrated with good magneto-optical performance and perpendicular magnetic anisotropy (PMA) crystallized by a microheater built on a Si chip or by rapid thermal annealing. The Bi-TbIG film crystallizes on Si at 873 K without a seed layer and exhibits good magneto-optical properties with Faraday rotation (FR) of -1700 deg cm-1. The Bi-YIG film also crystallizes on Si and fused SiO2 at 873 K without a seed layer. Rapidly cooled films exhibit PMA due to the tensile stress caused by the thermal expansion mismatch with the substrates, increasing the magnetoelastic anisotropy by 4 kJ m-3 versus slow-cooled films. Annealing in the air for 15 s using the microheater yields fully crystallized Bi-TbIG on the Si chip. In this study, magneto-optical and spintronic garnets that can be crystallized using a micro-heater built into a Si substrate are developed and the local crystallization of the garnets using the heater is demonstrated. Electron backscatter diffraction from a scanning electron microscope shows that the garnet on the heater is a polycrystalline film. image