Determination of probe spacings for the precise evaluation of electrical characteristics of a magnetic tunnel junction by in-house current-in-plane tunneling measurements

배태진,이상호,홍종일 한국물리학회 2014 Current Applied Physics Vol.14 No.3

Magnetic tunnel junctions have not been easily accessible for research because of not only their complicated fabrication processes but also side effects induced during the fabrication. The method utilizing arrays composed of in-line four-point probes with various spacings is promising as an alternative to the fabrication method. We found in the current-in-plane tunneling measurement that the determination of the probe spacing is the most important to evaluate the characteristics of magnetic tunnel junctions. Our simulation indicates that if one would choose at least more than three sets of an array with probe spacings centered at the spacing at which the maximum current-in-plane tunneling magnetoresistance is observed, the statistics should become improved resulting in the accurate evaluation of the properties of tunnel junctions. We also found that the suitable probe spacings with a change in the resistance of electrodes are not as sensitive as those with a change in the RA of the tunnel junction. Our results alert that the failure of selecting suitable probe spacings observes no tunneling signals because tunneling is very sensitive to the resistances of the tunnel junction and electrodes, which makes the current-in-plane tunneling method useless.

Determination of probe spacings for the precise evaluation of electrical characteristics of a magnetic tunnel junction by in-house current-in-plane tunneling measurements

Bae, T.,Lee, S.,Hong, J. Elsevier 2014 Current Applied Physics Vol.14 No.3

Magnetic tunnel junctions have not been easily accessible for research because of not only their complicated fabrication processes but also side effects induced during the fabrication. The method utilizing arrays composed of in-line four-point probes with various spacings is promising as an alternative to the fabrication method. We found in the current-in-plane tunneling measurement that the determination of the probe spacing is the most important to evaluate the characteristics of magnetic tunnel junctions. Our simulation indicates that if one would choose at least more than three sets of an array with probe spacings centered at the spacing at which the maximum current-in-plane tunneling magnetoresistance is observed, the statistics should become improved resulting in the accurate evaluation of the properties of tunnel junctions. We also found that the suitable probe spacings with a change in the resistance of electrodes are not as sensitive as those with a change in the RA of the tunnel junction. Our results alert that the failure of selecting suitable probe spacings observes no tunneling signals because tunneling is very sensitive to the resistances of the tunnel junction and electrodes, which makes the current-in-plane tunneling method useless.

Radio-frequency Shot-noise Measurement in a Magnetic Tunnel Junction with a MgO Barrier

Mushtaq Rehman,박정환,송운,이연섭,민병철,신경호,류상완,김정구,정연욱 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.4

We measured the noise power of a magnetic tunnel junction in the frequency range of 710 1200 MHz. A low-noise cryogenic HEMT amplifier was used to measure the small noise signal at a high frequency with wide bandwidth. The MgO-barrier tunnel junction showed large tunnel magnetoresistance ratio of 215% at low temperature, which indicates electronic transport through the tunnel barrier without any significant spin-flip scattering. In the bias-dependent noise measurement, however, the zero-bias shot noise was enhanced compared to the value expected from a perfect tunnel barrier or the value observed from a good Al-AlOx-Al tunnel junction. We assume that this enhanced noise comes from inelastic tunneling processes through the barrier, which may be related to the observed zero-bias anomaly in the differential resistance of the tunnel junctions. We present a simple phenomenological model for how the inelastic scattering process can enhance the zero-bias noise in a tunnel junction.

새로운 유사 원자층 증착 방법에 의한 산화막의 형성 및 터널링 자기 접합에의 응용

한신희,정원철,이장식,김병동,주승기 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.1

The tunneling barrier is crucial to the overall performance in magnetic tunnel junction. We have suggested a new formation method for the tunnel barrier, which has utilized pseudo atomic layer deposition with sputtering (PALDS). As is well known, all metallic thin films oxidize more or less under atmospheric conditions. With using this property of metallic thin films, we have prepared tunnel barrier by sputtering metallic thin film and exposing it to the oxygen ambience. From transmission electron microscopy (TEM) observation, the formed tunnel barrier has been confirmed to have clear and good interface between magnetic layers and tunnel barrier. From atomic force microscopy (AFM) observation, it has been also confirmed to have low surface roughness. The TMR MRAM cell manufactured using PALDS method has been shown to exhibit typical tunnel resistance of 86 KΩ·μm^2 and TMR ratio of about 40%. The 40% of MR is quite large. It is considered that this value is geometrically enhanced magnetoresistance due to the low junction resistance of MTJ.

Advantages of Prefabricated Tunnel Junction-Based Molecular Spintronics Devices

Pawan Tyagi,Edward Friebe,Collin Baker 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.4

Molecule-based devices may govern the advancement of the next generation's logic and memory devices. Molecules have the potential to be unmatched device elements as chemists can mass produce an endless variety of molecules with novel optical, magnetic and charge transport characteristics. However, the biggest challenge is to connect two metal leads to a target molecule (s) and develop a robust and versatile device fabrication technology that can be adopted for commercial scale mass production. This paper discusses distinct advantages of utilizing commercially successful tunnel junctions as a vehicle for developing molecular spintronics devices. We describe the use of a prefabricated tunnel junction with the exposed sides as a testbed for molecular device fabrication. On the exposed sides of a tunnel junction molecules are bridged across an insulator by chemically bonding with the two metal electrodes; sequential growth of metal–insulator–metal layers ensures that separation between two metal electrodes is controlled by the insulator thickness to the molecular device length scale. This paper highlights various attributes of tunnel junction-based molecular devices with ferromagnetic electrodes for making molecular spintronics devices. We strongly emphasize a need for close collaboration between chemists and magnetic tunnel junction (MTJ) researchers. Such partnerships will have a strong potential to develop tunnel junction-based molecular devices for futuristic areas such as memory devices, magnetic metamaterials, high sensitivity multi-chemical biosensors, etc.

Perpendicular Magnetization of CoZr/Pt Multilayers

길준표,Gi Yeol Bae,서동익,박완준,Won Joon Choi,Jae Sung Noh 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10

Recently, perpendicular magnetization of tunnel junctions has been proposed as a way to reduce the size of spin-transfer torque random access memory. In order to determine the free layer of a magnetic tunnel junction, we present a Co(90)Zr(10) alloy which is expected to have higher polarization than any other soft magnet. At a thickness of 0.6 nm, CoZr successfully forms perpendicular magnetization using interfacial anisotropy on CoZr/Pt interfaces. Unlike the Co/Pt multilayer, the CoZr/Pt multilayer shows magnetization recovery following 1.5 T field cooling after 300 ℃ annealing since the Zr insertion prevents the formation of a CoPt alloy. This work proposes CoZr as a free layer candidate for magnetic tunnel junctions due to its advantages of lower switching current and higher thermal stability.

Dependence of Conductance on the Magnetic-layer Thickness in Magnetic Tunnel Junctions

이병찬 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.10

The dependence of the conductance on the ferromagnetic (FM) layer thickness in magnetic tunnel junctions is investigated theoretically, and an analytical equation is derived with the reflection and transmission amplitudes of the separated interfaces. The conductance oscillates as the FM layer thickness increases, and the oscillation period is determined from the Fermi surface of the FM layer. Numerical calculations are carried out, and the analytical model is in a good agreement with the exact result. The experimental results of the Fe/MgO/Fe/Cr tunnel junctions are explained with the analytical model.

Current-driven Switching Property of MgO-based Magnetic Tunnel Junctions with a CoFeB Free Layer with In-plane Magnetization

길준표,Gi Yeol Bae,서동익,박완준,김기원,김광석 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.10

Spin-transfer torque enables magnetization switching by passing a spin-polarized current through nanostructures of spin valves or magnetic tunnel junctions. In this study, current driven switching is investigated for the magnetic tunnel junctions of CoFeB free layer having in-plane magnetization. It is found that the critical switching current depends on the feature of switching modes as well as the junction geometries. Especially, the long pulse mode switching generates the equilibrium remnant magnetization states before complete magnetization reversal. It results a robust switching by reducing the local magnetization anomalies. The current driven switching is understood by the combined effect of spin transfer and thermal activation.

Magnetoresistance in silicon based ferrite magnetic tunnel junction

S. Ravi,A. Karthikeyan,N. Angel Nesakumari,K.S. Pugazhvadivu,K. Tamilarasan 한국물리학회 2014 Current Applied Physics Vol.14 No.3

We report magnetoresistance for silicon based magnetic tunnel junction. We used cobalt ferrite & cobalt nickel ferrite as free layer and pinned layer. The magnetoresistance measured at room temperature through silicon by fabricating FM/Si/FM magnetic tunnel junction. Magnetoresistance shows a loop type behavior with 3.7%. We have successfully demonstrated spin tunneling through silicon with ferrite junction that opens the door for potential candidate for spintronics devices. The spin-filtering effect for this double spin-filter junction is also discussed.

Dependence of the tunneling conductance on the barrier thickness: effects of the complex-band structure

Lee B. C. 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.9

The dependence of tunneling conductance on the barrier thickness was investigated theoretically by using a tight-binding model. In order to calculate the tunneling conductance, full-band calculations were carried out with a model tunnel junction. In addition to an exponential decay, it was shown that the tunneling conductance may oscillate strongly as a function of the barrier thickness due to the complex-band structure of the barrier. The relation between the complex Fermi surface of the barrier and the oscillation period of the tunneling conductance was examined. The oscillation of the tunnel conductance is affected by the matching between the metal and the barrier bands.