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Investigation of ramped voltage stress to screen defective magnetic tunnel junctions
Choi, Chulmin,Sukegawa, Hiroaki,Mitani, Seiji,Song, Yunheub IOP 2018 Semiconductor science and technology Vol.33 No.1
<P>A ramped voltage stress (RVS) method to screen defective magnetic tunnel junctions (MTJs) is investigated in order to improve screen accuracy and shorten test time. Approximately 1500 MTJs with 1.25 nm thick tunnel barriers were fabricated for this evaluation, and normal MTJs show a 189% tunnel magnetoresistance ratio, a 365 Ω <I>μ</I>m<SUP>2</SUP> resistance-area product, and a 1.8 V breakdown voltage, which is enough for applying reliable screen tests. We successfully classified MTJs as normal MTJs having good characteristics or defective MTJs having insufficient endurance and showing resistance degradation after only short-term cycling. Using the RVS screen test with low ramp speed, it is demonstrated that remarkable screening performance and little dependence on temperature are obtained for short test time.</P>
TDDB modeling depending on interfacial conditions in magnetic tunnel junctions
Choi, Chul-Min,Sukegawa, Hiroaki,Mitani, Seiji,Song, Yun-Heub IOP 2017 Semiconductor science and technology Vol.32 No.10
<P>We investigated time-dependent dielectric breakdown (TDDB) modeling for MgO dielectrics with/without Mg insertion of MgO-based magnetic tunnel junctions (MTJs). The number of permanent trap sites at the no-Mg insertion interface was much larger than that at the Mg-inserted interface as determined by interval voltage stress (IVS) tests. The interfacial conditions related to trap sites at MgO dielectrics give rise to the different TDDB modeling. Here, we confirmed that the TDDB curves obtained from the constant voltage stress (CVS) tests for the Mg inserted interface case were well fitted by the power-law voltage V model, while the case of no-Mg inserted interface showed a good correlation to the 1/E model. The difference in the TDDB models related to interfacial conditions was understood based on theoretical and experimental results. Finally, we concluded that it is necessary to select an appropriate reliability model depending upon the presence or absence of the trap sites at dielectric interfaces.</P>
이정민,길규현,이개훈,최철민,송윤흡,Hiroaki Sukegawa,Seiji Mitani 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.8
The reliability of a magnetic tunnel junction (MTJ) based on a Co2FeAl (CFA) full-Heusler alloywith a MgO tunnel barrier was evaluated. In particular, the effect of a Mg insertion layer underthe MgO was investigated in view of resistance drift by using various voltage stress tests. Wecompared the resistance change during constant voltage stress (CVS) and confirmed a trap/detrapphenomenon during the interval stress test for samples with and without a Mg insertion layer. TheMTJ with a Mg insertion layer showed a relatively small resistance change for the CVS test anda reduced trap/detrap phenomenon for the interval stress test compared to the sample without aMg insertion layer. This is understood to be caused by the improved crystallinity at the bottomof the CFA/MgO interface due to the Mg insertion layer, which provides a smaller number of trapsite during the stress test. As a result, the interface condition of the MgO layer is very importantfor the reliability of a MTJ using a full-Heusler alloy, and the the insert of a Mg layer at the MgOinterface is expected to be an effective method for enhancing the reliability of a MTJ.
Time-dependent dielectric breakdown of MgO magnetic tunnel junctions and novel test method
Kim, Kyungjun,Choi, Chulmin,Oh, Youngtaek,Sukegawa, Hiroaki,Mitani, Seiji,Song, Yunheub IOP Publishing 2017 Japanese journal of applied physics Vol.56 No.4
<P>Time-dependent dielectric breakdown (TDDB), which is used to measure reliability, depends on both the thickness of the tunnel barrier and bias voltage. In addition, the heat generated by self-heating in a magnetic tunneling junction (MTJ) affects TDDB. Therefore, we investigated TDDB with the self-heating effect for a MgO tunnel barrier with thicknesses of 1.1 and 1.2nm by the constant voltage stress (CVS) method. Using the results of this experiment, we predicted a TDDB of 1.0nm for the tunnel barrier. Also, we suggested the use of not only the CVS method, which is a common way of determining TDDB, but also the constant current stress (CCS) method, which compensates for the disadvantages of the CVS method. (C) 2017 The Japan Society of Applied Physics</P>
Pressure-enhanced Giant Magnetoresistance in Fe/Cr Magnetic Multilayers
Gendo Oomi,Shuhei Higashihara,Kazufumi Suenaga,Kesami Saito,Koki Takanashi,Seiji Mitani 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
The magnetoresistance of Fe/Cr magnetic multilayers (MMLs) on the 1st and the 2nd peakshas been measured at high pressure up to 3 GPa at low temperature in order to make clear thecharacteristics of the giant magnetoresistance (GMR) under high pressure. The GMRs of the MMLson the 2nd peak are found to be enhanced strongly by applying pressure whereas those of 1st peakMMLs decrease with increasing pressure. The magnitude of GMR of the 2nd peak MMLs becomesabout twice or more at 2 GPa compared with the value at ambient pressure. The large differencein the pressure dependences is explained by assuming a pressure-induced crossover in the interlayerexchange coupling from the biquadratic to the bilinear spin arrangements.