Double-well potential energy surface in the interaction between h-BN and Ni(111)

ACS Appl. Mater. Interfaces

2021

Two-dimensional hexagonal boron nitride (h-BN) is studied as a tunnel barrier in magnetic tunnel junctions (MTJs) as a possible alternative to MgO. The tunnel magnetoresistance (TMR) of such MTJs is calculated as a function of whether the interface involves the chemi- or physisorptive site of h-BN atoms on the metal electrodes, Fe, Co, or Ni. It is found that the physisorptive site on average produces higher TMR values, whereas the chemisorptive site has the greater binding energy but lower TMR. It is found that alloying the electrodes with an inert metal-like Pt can induce the preferred absorption site on Co to become a physisorptive site, enabling a higher TMR value. It is found that the choice of physisorptive sites of each element gives more Schottky-like dependence of their Schottky barrier heights on the metal work function.

Section: Resultssupporting

confidence: 83%

Section: Resultssupporting

confidence: 74%

Ab Initio Study of Hexagonal Boron Nitride as the Tunnel Barrier in Magnetic Tunnel Junctions

Guo

ACS Appl. Mater. Interfaces

2021

“…Note the Moire models in (c,d) have a large interlayer distance (labelled as d ) and thus weaker interlayer interaction. (e) Calculated interface binding energy for chemisorptive and physisorptive sites of Ni on h-BN with optB88-vdw and optB86b-vdw functionals 32 for reference, showing a similar trend to ref ( 21 ).…”

Section: Introductionmentioning

confidence: 55%

“…This is readily seen for the second-row compound h-BN with lattice-matched metals such as Fe, Co, and Ni. Here, the chemisorptive site is the N on top of the metal site, whereas rotating the h-BN lattice to form the (√3×√3) orientation provides a physisorptive site with both B and N lying off-center and with a much larger interlayer spacing, 21 − 24 as schematically shown in Figure 1 e. The slope factor of h-BN contacts was found to be dramatically different for each site, S ∼ 0.26 for the chemisorptive site, while S ∼ 1 for the physisorptive site. 22 …”

Section: Introductionmentioning

confidence: 99%

Reduced Fermi Level Pinning at Physisorptive Sites of Moire-MoS₂/Metal Schottky Barriers

Zhang

Guo

ACS Appl. Mater. Interfaces

2022

Weaker Fermi level pinning (FLP) at the Schottky barriers of 2D semiconductors is electrically desirable as this would allow a minimizing of contact resistances, which presently limit device performances. Existing contacts on MoS 2 have a strong FLP with a small pinning factor of only ∼0.1. Here, we show that Moire interfaces can stabilize physisorptive sites at the Schottky barriers with a much weaker interaction without significantly lengthening the bonds. This increases the pinning factor up to ∼0.37 and greatly reduces the n-type Schottky barrier height to ∼0.2 eV for certain metals such as In and Ag, which can have physisorptive sites. This then accounts for the low contact resistance of these metals as seen experimentally. Such physisorptive interfaces can be extended to similar systems to better control SBHs in highly scaled 2D devices.

“…h-BN has a good lattice-match to the (111) surfaces of the three magnetic metals Fe, Ni and Co, taken in the fcc structures. [62][63][64] can adopt three different bonding sites on (111) Ni surfaces in density functional (DFT) calculations: the metal on N-top, B-top, and in the incommensurate ͱ7 Â ͱ7 structure, [62][63][64][65] as seen in Fig. 10(a)-10(c).…”

Section: Bonding Sites Of H-bn On Ni Co Fe Surfacesmentioning

confidence: 99%

Comparison of hexagonal boron nitride and MgO tunnel barriers in Fe,Co magnetic tunnel junctions

Applied Physics Reviews

Naganuma

2021

Magnetic tunnel junctions (MTJ) with MgO/Fe based interfaces and out-of-plane spin direction form the basis of present-day spin-transfertorque magnetic random-access memory (STT-MRAM) devices. They are a leading type of nonvolatile memory due to their very long endurance times and lack of reliability problems. Many semiconductor devices, such as the field effect transistor or nonvolatile memories, have undergone fundamental changes in materials design as dimensional scaling has progressed. Here, we consider how the future scaling of the MTJ dimensions might affect materials choices and compare the performance of different tunnel barriers, such as 2D materials like h-BN with the existing MgO tunnel barriers. We first summarize key features of MgO-based designs of STT-MRAM. We then describe general aspects of the deposition of 2D materials and h-BN on metals. We compare the band structures of MgO and h-BN with their band gaps corrected for the GGA band error. The different absorption sites of h-BN on Fe or Co are compared in terms of physisorbtive or chemisorbtive bonding sites and how this affects their spin-polarized bands and the transmission magneto-resistance (TMR). The transmission magnetoresistance is found to be highest for the physisorptive sites. We look at how these changes would affect the overall TMR and how scaling might progress.