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The CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) is the central element of any high performance perpendicular Magnetoresistive Random Access Memory (MRAM) device. The MgO tunnel barrier, in contact with CoFeB films at both sides in the magnetic tunnel junction, provides a high tunnel magneto resistance (TMR) and perpendicular magnetic anisotropy (PMA) thanks to the high crystalline quality of the MgO/CoFeB interface achieved upon post-deposition annealing. We study MgGa2O4 as an alternative barrier material due to its lower bandgap and show how to introduce it into state-of-the-art perpendicular MRAM stacks. We demonstrate that thin MgO films at both sides of the barrier are key to ensure a proper crystallization and induce reference layer and free layer perpendicular magnetic anisotropy. Consequently, a stack incorporating a MgGaxOy barrier with full PMA and TMR > 100% can be fabricated with a resistance-area (RA) product as low as 50 Ω μm2, which is of strong interest as a potential barrier in the field of voltage control magnetic anisotropy MRAM. [ABSTRACT FROM AUTHOR] more...

Voltage control of the magnetic anisotropy (VCMA) effect enables a voltage-mediated magnetization switching mechanism for lower-power applications. In this work, we experimentally investigate the characteristics of VCMA-induced switching and we observe a clear decrease in the critical switching voltage ( V c ) at elevated temperatures. A 50% reduction in V c is quantified when increasing the ambient temperature (T) from 300 K to 360 K. Such a T-dependence of V c is well explained with the variations of saturation magnetization ( M S ), interfacial anisotropy ( K i ), and VCMA coefficient (ξ). In addition, the dependences of these properties on temperature are well fitted and explained with the power law of M S (T). Our findings on the T-dependent magnetic and switching characteristics of VCMA are of technological importance for implementing VCMA in magnetic random access memory (MRAM) applications. [ABSTRACT FROM AUTHOR] more...

Co/LaSiO conducting bridge random access memory is a promising candidate for low power storage class memories due to its high endurance and short switching pulse width. Moisture has been hypothesized to be an important parameter in determining device retention. In this study, we anneal the LaSiO layers at different temperatures and pressures in order to reduce the absorbed moisture and improve retention. We evidence by Fourier transform infrared and x-ray reflectivity that the moisture content does not change with these anneal conditions. However, we find that increasing the amount of La–OH bonds is an effective way to improve the low resistance state retention. [ABSTRACT FROM AUTHOR] more...

Magnetic Random Access Memory (MRAM) targeting cache memory replacement consists of high density arrays of perpendicular Magnetic Tunnel Junctions (p-MTJs). One of the key advantages to MRAM is its non-volatility, where the measurement of retention is critical. However, evaluating the thermal stability of high density arrays is both time consuming and requires electric read out of many functional devices. It is shown that by using the Magneto-Optical Kerr Effect (MOKE) to measure the magnetic after-effect at fixed fields, efficient and in-line characterization of both the magnetic properties and data retention is possible. This is qualified through cross measurement of multiple dies using both MOKE and electrical readout of a Mbit array. Data from both techniques is then fitted using a macrospin model where the values of both Δ and Hk are shown to come within 10% of each other. [ABSTRACT FROM AUTHOR] more...

Free layers with double MgO/CoFeB interfaces are an established solution for improving the thermal stability at small device dimensions in perpendicular spin transfer torque-magnetic random access memory devices. A thin spacer layer, composed usually of Ta, W, Hf, etc., is used to ease crystallization and improve the perpendicular magnetic anisotropy. Here, we use ferromagnetic resonance to evaluate the impact of Ta or W containing spacer layers on the intrinsic anisotropy Hk and damping α parameters. While both spacer materials enable similar tunnel magneto-resistance and anisotropy values, W typically generates a higher damping. Ta-based spacers are therefore likely better candidates for very low switching current applications. [ABSTRACT FROM AUTHOR] more...

Alternative free layer materials with high perpendicular anisotropy are researched to provide spin-transfer-torque magnetic random access memory stacks' sufficient thermal stability at critical dimensions of 20 nm and below. We demonstrate a high tunnel magetoresistance (TMR) MgO-based magnetic tunnel junction stack with a hybrid free layer design made of a [Co/Ni] multilayer and CoFeB. The seed material on which the [Co/Ni] multilayer is deposited determines its switching characteristics. When deposited on a Pt seed layer, soft magnetic switching behavior with high squareness is obtained. When deposited on a NiCr seed, the perpendicular anisotropy remains high, but the squareness is low and coercivity exceeds 1000 Oe. Interdiffusion of the seed material with the [Co/Ni] multilayers is found to be responsible for the different switching characteristics. In optimized stacks, a TMR of 165% and low resistance-area (RA) product of 7:0Ωμm2 are attained for free layers with an effective perpendicular magnetic anisotropy energy of 1.25 erg/cm2, which suggests that the hybrid free layer materials may be a viable candidate for high density magnetic random access memory applications. [ABSTRACT FROM AUTHOR] more...

Spin-transfer torque magnetic random access memory (STT-MRAM) is considered as a replacement for next generation embedded and stand-alone memory applications. One of the main challenges in the STT-MRAM stack development is the compatibility of the stack with CMOS process flows in which thermal budgets up to 400 °C are applied. In this letter, we report on a perpendicularly magnetized MgO-based tunnel junction (p-MTJ) on a thin Co/Ni perpendicular synthetic antiferromagnetic layer with high annealing tolerance. Tunnel magneto resistance (TMR) loss after annealing occurs when the reference layer loses its perpendicular magnetic anisotropy due to reduction of the CoFeB/MgO interfacial anisotropy. A stable Co/Ni based p-MTJ stack with TMR values of 130% at resistance-area products of 9Ωµm² after 400 °C anneal is achieved via moment control of the Co/Ta/CoFeB reference layer. Thinning of the CoFeB polarizing layer down to 0.8 nm is the key enabler to achieve 400 °C compatibility with limited TMR loss. Thinning the Co below 0.6 nm leads to a loss of the antiferromagnetic interlayer exchange coupling strength through Ru. Insight into the thickness and moment engineering of the reference layer is displayed to obtain the best magnetic properties and high thermal stability for thin Co/Ni SAF-based STT-MRAM stacks. [ABSTRACT FROM AUTHOR] more...

Abstract: In this article we study the thermal stability of Al2O3\Cu–Te bi-layers up to temperatures used in the back-end-of-line integration process flow of conductive-bridging random-access-memory (CBRAM) technology. We investigate the temperature dependence of the microstructure and morphology of the CuxTe1−x layers for 0.20.7, phase separation is observed for as-deposited layers, resulting in rough morphology. Te-rich CuxTe1−x layers (x<0.5) show large segregation processes during post-deposition annealing. Cu–Te phase restructuration phenomena are also observed during annealing in the range 0.5 more...