Crystallization of bismuth iron garnet thin films using capacitively coupled oxygen plasmas

Abstract

It is demonstrated for the first time that amorphous bismuth iron garnet films can be crystallized within capacitively coupled oxygen plasmas at temperatures approximately 100 °C lower than required using conventional thermal annealing. We characterize the plasma optical emissions at high pressures (2 Torr–5 Torr) and high rf powers (500 W–800 W) and show that film crystallization is nevertheless related to thermal conditions generated in the plasma. It is demonstrated that these thermal conditions are related to the concentration of the dominant oxygen species O and O+ in the plasma, which, in turn, are a function of the rf power and pressure. The plasma treated garnet Faraday rotation and optical transmission are shown to be comparable with conventional oven or rapid thermal annealing.

Crystallization of Bismuth-Substituted Yttrium Iron Garnet under Low-Energy High-Repetition Rate Femtosecond Laser Pulses

“…Deposition of rare-earth-substituted YIG for monolithic magneto-optical isolators is typically performed by pulsed laser deposition. − However, it requires sophisticated equipment and deposition of a pure YIG buffer layer for further crystallization of rare-earth-substituted garnet during high-temperature annealing. On the other hand, materials that require thermal treatment at temperatures below 577 °C can be incorporated at the back-end of the CMOS process . Thus, the method of laser-induced crystallization of MOD-made rare-earth-substituted YIGs proposed in the present work can find applications in monolithic seed layer-free integration of magneto-optical garnets on the silicon platform for nonreciprocal photonic devices.…”

“…For example, the process may result in the decrease in a magnetophotonic crystal performance through occurrence of cracks and growth of microcrystals in layers composing Bragg mirrors. , The same annealing also restricts integration of magneto-optical rare-earth-substituted yttrium iron garnets on nongarnet substrates for photonic integrated circuits. − Thus, to overcome this issue, new approaches of Bi/YIG crystallization have to be developed. Jeffery et al suggested lowering temperature of bismuth iron garnet crystallization by approximately 100 °C below the temperature required to achieve crystallization via conventional thermal annealing using capacitively coupled oxygen plasmas . Local crystallization of the amorphous Bi/YIG film sputtered on a Bragg mirror made of Ta 2 O 5 and SiO 2 layers by continuous-wave green (λ = 532 nm) laser irradiation was demonstrated by Suzuki et al …”

“…temperature required to achieve crystallization via conventional thermal annealing using capacitively coupled oxygen plasmas. 29 Local crystallization of the amorphous Bi/YIG film sputtered on a Bragg mirror made of Ta 2 O 5 and SiO 2 layers by continuous-wave green (λ = 532 nm) laser irradiation was demonstrated by Suzuki et al 24 Ultrashort laser pulses delivered at a high-repetition rate are known to result in the heat accumulation effect that is observed when the interval between successive laser pulses is shorter than the time for heat diffusion out of the focal area. 30,31 Thus, high-repetition rate ultrashort laser pulses allow rapid and spatially confined temperature increase in an irradiated material even above its melting point.…”

Diffusion-Driven Exfoliation of Magneto-Optical Garnet Nanosheets: Implications for Low Thermal Budget Integration in Si Photonics

“…2 Notably, garnets can only be incorporated at the back end of the line in a CMOS (complementary metal-oxide-semiconductor) process if the crystallization temperature is below 577 °C without oxygen or below 515 °C if a capacitively coupled oxygen plasma is needed. 14 Therefore, high-temperature requirements of monolithic garnet integration are commonly cited as the basis for leaving integrated lasers unprotected by isolators, resulting in a lower performance and shorter lifetimes.…”

“…More recently, epitaxial bismuth-substituted yttrium iron garnet (Bi:YIG) thin films grown on the gadolinium gallium garnet (GGG) were shown to crystallize using a substrate temperature of only 560 °C, whereas technologically relevant Bi:YIG on Si required a seed layer and an ex situ rapid thermal annealing at 800 °C . Notably, garnets can only be incorporated at the back end of the line in a CMOS (complementary metal-oxide-semiconductor) process if the crystallization temperature is below 577 °C without oxygen or below 515 °C if a capacitively coupled oxygen plasma is needed . Therefore, high-temperature requirements of monolithic garnet integration are commonly cited as the basis for leaving integrated lasers unprotected by isolators, resulting in a lower performance and shorter lifetimes.…”