Tohoku University · Physics and Astronomy
Professor Butsurin Jinnai's research lab specializes in advanced nanoscale spintronic devices and plasma processing technologies, with a primary focus on the development and scaling of magnetic tunnel junctions (MTJs) for next-generation spin-transfer torque magnetoresistive random access memory (STT-MRAM). The lab investigates fundamental mechanisms of material interactions under plasma irradiation, particularly UV/VUV and ion effects, to enable low-damage, high-selectivity processes essential for advanced CMOS integration. Key research directions include the engineering of multilayered ferromagnetic structures for enhanced thermal stability and switching performance at sub-10 nm scales, as well as innovative on-wafer monitoring techniques for real-time plasma diagnostics using machine learning. The lab also explores the compatibility of ArF photoresists and low-k dielectrics with plasma processes, aiming to overcome reliability challenges in nanofabrication.
Figures are computed from collected data and may differ slightly.
Magnetic tunnel junction (MTJ), a spintronics device, has been intensively developed in the past couple of decades because of its high potential in terms of non-volatility, fast operation, virtually infinite endurance, scalability, and compatibility with complementary metal-oxide-semiconductor (CMOS) integrated circuits as well as their process and circuits. Today, high-volume manufacturing of spin-transfer torque magnetoresistive random access memory based on MTJ has been initiated for embedded
UV radiation during plasma processing affects the surface of materials. Nevertheless, the interaction of UV photons with surface is not clearly understood because of the difficulty in monitoring photons during plasma processing. For this purpose, we have previously proposed an on-wafer monitoring technique for UV photons. For this study, using the combination of this on-wafer monitoring technique and a neural network, we established a relationship between the data obtained from the on-wafer moni
We show scalability down to 2.3 nm and high performance at single-digit nanometers of shape-anisotropy magnetic tunnel junctions (MTJs) employing a multilayered ferromagnetic structure. We reveal that a free layer with two ferromagnets separated by a MgO layer behaves as a single magnet at small device dimensions owing to magnetostatic coupling in addition to exchange coupling. This nature, in turn, leads to a notable performance increase of the MTJs in the single-digit-nm regime: thermal stabil
Plasma is extensively used for the etching/ashing of low-dielectric (low-k) films. However, since low-k films, such as SiOC films, are vulnerable to plasma irradiation, they are severely damaged during plasma processes, such as the extraction of methyl groups from low-k films. As a result, plasma irradiation increases the dielectric constant of low-k films and reduces the reliability of Cu/low-k interconnects. In previous work, the authors achieved highly selective and low-damage etching process
Abstract Making magnetic tunnel junctions (MTJs) smaller while meeting performance requirements is critical for future electronics with spin-transfer torque magnetoresistive random access memory (STT-MRAM). However, it is challenging in the conventional MTJs using a thin CoFeB free layer capped with an MgO layer because of increasing difficulties in satisfying the required data retention and switching speed at smaller scales. Here we report single-nanometer MTJs using a free layer consisting of
ArF excimer laser lithography was introduced to fabricate nanometer-scale devices and uses chemically amplified photoresist polymers including photoacid generators (PAGs). Because plasma-etching processes cause serious problems related to the use of ArF photoresists, such as line-edge roughness and low etching selectivity, we have to understand the interaction between plasma and ArF photoresist polymers. Investigating the effects of surface temperature and the irradiation species from plasma, we
Shape-anisotropy magnetic tunnel junctions (MTJs) are attracting much attention as a high-performance nonvolatile spintronic device in the X/1X nm regime. In this study, we investigate an energy barrier relevant to the retention property in CoFeB/MgO-based shape-anisotropy MTJs with various diameters at high temperatures and compare it with that in conventional interfacial-anisotropy MTJs. We find that the scaling relationship between the energy barrier and the spontaneous magnetization in shape
Spin-orbit torque (SOT) switching and retention properties in Co/Pt multilayer nanowire structures with various widths w down to 20 nm and the temperature dependences of the performance in the nanowire device with w = 20 nm are studied. Switching current Isw scales down as w is reduced. The nanowire devices show high thermal stability factor Δ > 100 for all the widths at room temperature. In the 20-nm-wide device, while a magnetization can be switched by current from –50 to 125 °C with a
The authors investigated charge accumulation in high-aspect-ratio contact-hole structures by using the new on-wafer monitoring device they fabricated on a Si substrate of 8in. in diameter by using a conventional production process for semiconductor devices. The device has high-aspect-ratio contact-hole structures that are comparable with the practical interconnect structures of recent dynamic random access memory devices. In this article they discuss charge accumulation and the electric conducti
Low plasma resistance and roughness formation in an ArF photoresist are serious issues in plasma processes. To resolve these issues, we investigated several factors that affect the roughness formation and plasma resistance in an ArF photoresist. We used our neutral beam process to categorize the effects of species from the plasma on the ArF photoresist into physical bombardment, chemical reactions and ultraviolet/vacuum ultraviolet (UV/VUV) radiation. The UV/VUV radiation drastically increased t
We show fast switching down to 3.5 ns while maintaining high data retention in sub-5-nm ultra-small magnetic tunnel junctions (MTJs) using multilayered ferromagnets (FMs). We engineer characteristic relaxation time, a critical factor for fast magnetization switching, by varying the number of CoFeB/MgO interfaces in multilayered FMs. We also find that switching efficiency improves with increasing the number of CoFeB/MgO interfaces. Harnessing the advantages of both the MTJ using multilayered FMs
A shape-anisotropy magnetic tunnel junction (MTJ) holds promise for its scaling into single-digit nanometers while possessing high data-retention capability. Understanding magnetization reversal mode is crucial to quantify the thermal stability factor Δ for data retention with high accuracy. Here, we study magnetization reversal mode in the shape-anisotropy MTJ with a 15-nm-thick CoFeB layer by evaluating Δ from two different methods: switching probability and retention time measurements. We fin
Major challenges associated with 193 nm lithography using an ArF photoresist are low plasma resistance and roughness formation in the ArF photoresist during plasma processes. We have previously found decisive factors affecting the plasma resistance and roughness formation in an ArF photoresist: plasma resistance is determined by UV/VUV radiation, and roughness formation is dominated by chemical reactions. In this study, based on our findings on the interaction between plasma radiation species an
Spin-orbit torque (SOT)-induced magnetization switching in Co/Pt multilayer structures with a Pt buffer layer is studied aiming to realize SOT-magnetic random access memory (MRAM) devices with high thermal stability. Current-induced magnetization switching and effective fields are measured using Hall-bar devices. The switching efficiency, defined as a ratio of the areal anisotropy energy density to switching current density, increases with increasing the number of Co/Pt stacks. This trend is in
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