[8p-N303-1~16] 10.2 Fundamental and exploratory device technologies for spin

4:15 PM - 4:30 PM JST(7:15 AM - 7:30 AM UTC)Presentation by Applicant for JSAP Young Scientists Presentation AwardEnglish Presentation

[8p-N303-11] Large spin Hall effect in BiSb topological insulator and perpendicularly magnetized CoFeB heterojunctions with oxide buffer and interfacial layers

〇(D)Thuan Van Pham¹, Hoang Huy Ho¹, Wentao Li¹, S. Takahashi², Y. Kato², S. Hirayama², Nam Hai Pham¹ (1.Science Tokyo, 2.Samsung Japan Corp)

Keywords:

topological insulator,Spin orbit torque,BiSb

BiSb topological insulator has emerged as a promising candidate for the spin-orbit torque (SOT) layer in ultrafast and ultralow power SOT-MRAM devices due to its giant spin Hall angle (theta_SH) and high electrical conductivity (sigma). Although large theta_SH has been demonstrated in BiSb/CoFeB heterojunctions deposited on sapphire with metallic Ti or Ru interlayers, BiSb is prone to evaporation during high-temperature annealing due to its low melting point. Therefore, an appropriate interfacial layer that suppresses BiSb loss is crucial to realize its full potential for practical applications.In this study, we fabricate BiSb/CoFeB heterostructures on thermally oxidized Si/SiO2 substrates with oxide buffer and interfacial layers to withstand 300⁰C post-annealing. Figure 1(a) illustrates the stack and annealing sequence. A TiOx (25 nm)/TaOx (5 nm) buffer layer was first deposited to suppress oxygen diffusion and promote BiSb crystallinity. A 10 nm BiSb layer was then sputtered, followed by a 1 nm TiOx or TaOx interfacial layer to protect BiSb during 1 hour annealing at 300⁰C. These oxide layers are insulating, thus reducing current shunting. Next, Ta (1 nm)/CoFeB (1 nm)/MgO (2.5 nm)/Ta (2 nm) layers were deposited, followed by a second annealing at 250 deg C for 30 minutes to induce perpendicular magnetic anisotropy (PMA), as shown in Figs. 1(b–c).Second harmonic Hall measurements confirmed large effective theta_SH > 4 [Figs. 1(d–e)]. XRF analysis showed BiSb thickness reduced to ~9.3 nm after annealing, suggesting the interfacial layer effectively suppresses material loss. Our results demonstrate that TiOx/TaOx buffer and TiOx or TaOx interfacial layers are effective in protecting BiSb and enabling high SOT performance on amorphous substrates.