VP23-10 Large spin orbit torque induced by high temperature annealed BiSb topological insulator on oxidized Si substrates
Creators: Ho Hoang Huy
Li Wentao
Shigeki Takahashi
Yoshiyuki Hirayama
Yushi Kato
Pham Nam Hai
Publisher: name: IEEE
Year: 2025

BiSb topological insulator is a promising spin-orbit torque (SOT) material thanks to its colossal spin Hall angle θSH [1] and high electrical conductivity σ [2] for ultrafast [3] and ultralow power [4] SOT memory devices. Although hisgh crystal quality BiSb thin films have been studied so far on single crystalline substrates [2-7], realizing high quality of BiSb with high θSH and high σ on amorphous Si substrate is mandatory for realistic SOT spintronic applications. Furthermore, high temperature endurance during fabrication is also critical for integration with CMOS electronics. In this work, we aim to realize BiSb topological insulator thin films with high θSH and high σ on thermally oxidized Si/SiOx substrate using oxide buffer layers and high temperature post annealing. We first deposited a thick TiOx layer which can block O2 migration from SiOx to BiSb during annealing and an optional TaOx oxide buffer layer on Si/SiOx substrates. Both oxide layers are deposited by reactive sputtering of a Ti and Ta target. Next, we sputtered a 10 nm-thick BiSb on top of the oxide layers and a 3-nm Ti protection layer. After cooling the substrate in ultrahigh vacuum to room temperature, we deposited ferromagnetic multilayers for SOT evaluation. The schematic structure of sample A-TiOx/BiSb/Ti/Pt/Co/Pt, sample B-TiOx/TaOx/BiSb/Ti/Ta/CoFeB/MgO and their θ-2θ X-ray diffraction (XRD) spectra are shown in Fig. 1. Single phase BiSb (012) and (011) are confirmed in sample A and B, respectively. By high temperature annealing, we improved BiSb conductivity up to 1.1×105 Ω-1m-1 and achieved a relatively high θSH ~ 1.7 – 5. In Fig.2, we demonstrate type-z SOT magnetization switching of CoFeB in sample B with a low BiSb current density of 2.2 MA/cm2 which is an order smaller than that of heavy metals. Our results show that it is possible to achieve high performance BiSb on Si/SiOx substrates by employing oxide buffer layers and high temperature annealing.References: 1. N. H. D. Khang, Y. Ueda, P. N. Hai, Nature Mater. 17, 808 (2018). 2. Y. Ueda, N. H. D. Khang, K. Yao, et al., Appl. Phys. Lett. 110, 062401 (2017). 3. N. H. D. Khang, T. Shirokura, T. Fan, et al., Appl. Phys. Lett. 120, 152401 (2022). 4. H. Wu, A. Chen, P. Zhang, et al., Nature Commun. 12, 6251 (2021). 5. K. Yao, N. H. D. Khang, P. N. Hai, J. Cryst. Growth 511, 99 (2019). 6. T. Fan, M. Tobah, T. Shirokura, et al., Jpn. J. Appl. Phys. 59, 063001 (2020). 7. K. Ueda, Y. Hadate, K. Suzuki, et al., Thin Solid Films 713, 1383 (2020).
BiSb topological insulator is a promising spin-orbit torque (SOT) material thanks to its colossal spin Hall angle θSH [1] and high electrical conductivity σ [2] for ultrafast [3] and ultralow power [4] SOT memory devices. Although hisgh crystal quality BiSb thin films have been studied so far on single crystalline substrates [2-7], realizing high quality of BiSb with high θSH and high σ on amorphous Si substrate is mandatory for realistic SOT spintronic applications. Furthermore, high temperature endurance during fabrication is also critical for integration with CMOS electronics. In this work, we aim to realize BiSb topological insulator thin films with high θSH and high σ on thermally oxidized Si/SiOx substrate using oxide buffer layers and high temperature post annealing. We first deposited a thick TiOx layer which can block O2 migration from SiOx to BiSb during annealing and an optional TaOx oxide buffer layer on Si/SiOx substrates. Both oxide layers are deposited by reactive sputtering of a Ti and Ta target. Next, we sputtered a 10 nm-thick BiSb on top of the oxide layers and a 3-nm Ti protection layer. After cooling the substrate in ultrahigh vacuum to room temperature, we deposited ferromagnetic multilayers for SOT evaluation. The schematic structure of sample A-TiOx/BiSb/Ti/Pt/Co/Pt, sample B-TiOx/TaOx/BiSb/Ti/Ta/CoFeB/MgO and their θ-2θ X-ray diffraction (XRD) spectra are shown in Fig. 1. Single phase BiSb (012) and (011) are confirmed in sample A and B, respectively. By high temperature annealing, we improved BiSb conductivity up to 1.1×105 Ω-1m-1 and achieved a relatively high θSH ~ 1.7 – 5. In Fig.2, we demonstrate type-z SOT magnetization switching of CoFeB in sample B with a low BiSb current density of 2.2 MA/cm2 which is an order smaller than that of heavy metals. Our results show that it is possible to achieve high performance BiSb on Si/SiOx substrates by employing oxide buffer layers and high temperature annealing.References: 1. N. H. D. Khang, Y. Ueda, P. N. Hai, Nature Mater. 17, 808 (2018). 2. Y. Ueda, N. H. D. Khang, K. Yao, et al., Appl. Phys. Lett. 110, 062401 (2017). 3. N. H. D. Khang, T. Shirokura, T. Fan, et al., Appl. Phys. Lett. 120, 152401 (2022). 4. H. Wu, A. Chen, P. Zhang, et al., Nature Commun. 12, 6251 (2021). 5. K. Yao, N. H. D. Khang, P. N. Hai, J. Cryst. Growth 511, 99 (2019). 6. T. Fan, M. Tobah, T. Shirokura, et al., Jpn. J. Appl. Phys. 59, 063001 (2020). 7. K. Ueda, Y. Hadate, K. Suzuki, et al., Thin Solid Films 713, 1383 (2020).