Browsing by Author "Yao, Y. D."

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A highly reliable self-aligned graded oxide WOx resistance memory: Conduction mechanisms and reliability
(2007-01-01)
Ho, ChiaHua
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Lai, E. K.
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Lee, M. D.
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Pan, C. L.
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Yao, Y. D.
WOx formed by plasmas oxidation shows promising multibit/cell resistance memory characteristics [1]. The simple memory is completely self-aligned, requiring no additional masks and has a small 6F(2) cell size. In this work we introduce a graded oxide device that is highly reliable (250 degrees C baking for > 2,000 hrs). The conduction mechanism and factors affecting the memory reliability are examined extensively.
Analysis of diffusive interface resistance for measurements with perpendicular current in Fe/Nb multilayers
(2006-04-15)
Huang, S. Y.
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Lee, S. F.
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Yu, C. Y.
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Hsu, S. Y.
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Yao, Y. D.
In this study, we investigated the electron transport properties of interface between a ferromagnet and a superconductor with flowing current perpendicular to plan (CPP) at 4.2 K in Fe/Nb multilayers. The CPP resistance increased linearly with layer thickness and with bilayer number. We extracted the unit area resistance value of one pair of interface for superconducting and normal Fe/Nb by using a series resistor model. Hence, we can quantitatively analyze the interface resistance between Fe and Nb in the diffusive regime. (C) 2006 American Institute of Physics.
Bias-magnetic force for vibration reduction of magnetic bearing motors
(2007-06-01)
Wang, Chien-Chang
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Yao, Y. D.
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交大名義發表
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National Chiao Tung University
The objective of this paper is to propose a compact method using a novel bias magnet to induce an axial bias-magnetic force in order to reduce the radial vibration of a magnetic bearing (MB) motor. After applying the bias-magnetic force, the optimal radial vibration of the developed NIB motor is only around 0.197 g (peak-peak, 1 g = 9.8 m/s(2)) when the natural frequency of the bias magnet reaches the resonant frequency of 62 Hz. In this optimal condition, the ratio in the radial vibration of the MB motor with the bias-magnetic force to the original one is around 89%, and the driving power of 0.24 W is saved.
Characterization of a nano-oxide layer in a pseudo spin valve by complex magneto-impedance spectroscopy
(2006-10-01)
Chien, W. C.
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Peng, T. Y.
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Hsieh, L. C.
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Lo, C. K.
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Yao, Y. D.
The ac properties of a pseudo spin valve (PSV) consisting of NOLtop/Co/Cu/Co/Ni80Fe20/NOLbottom with a top and bottom nanooxide layer (NOL) were studied as functions of NOL and thickness, d, by magneto impedance spectroscopy. The NOLs were formed by natural oxidizing the top and bottom ferromagnetic or Ta layers in situ. The increase in the thickness of NOL resulting in the increment of caused the shift of roll-off frequency from low to high. The frequency dependence behavior of this NOLtop/PSV/NOLbottom system can be modeled by equivalent circuit theory. PSV with a different NOL structure can be checked by such a nondestructive analysis method.
Demonstration of edge roughness effect on the magnetization reversal of spin valve submicron wires
(2010-07-12)
Chiang, T. W.
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Chang, L. J.
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Yu, C.
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Huang, S. Y.
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Chen, D. C.
We prepared submicron wide trilayer spin valve wires designed with periodic "spikes" as artificial roughness. The height and the pitch of the spikes were varied systematically. No obvious dependence was found between the roughness and the domain wall velocity when the spikes were smaller than a threshold of 30 nm for NiFe. The average velocity was slowed down when the height of the spikes were larger than the threshold. In-plane transverse magnetic fields help to reduce the critical current density for current induced domain-wall motion. Our results could be attributed to the space modulation of the local magnetization. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3463459]
Determining vortex chirality in ferromagnetic ring by lateral nonlocal spin valve
(2008-04-01)
Chen, D. C.
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Yao, Y. D.
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Wu, J. K.
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Yu, C.
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Lee, S. F.
We demonstrate detecting chirality of vortex state in a magnetic ring by lateral nonlocal spin-valve (NLSV) measurement. A Permalloy (Py) ring, a Py narrow wire, and copper contacts were used as spin injector, detector, and the normal-metal diffusive channel, respectively. By comparing the anisotropic magnetoresistance loop of the individual ring with NLSV loop, the vortex chirality and the related switching field of the ring can be determined. Both onion-to-vortex transition field and vortex chirality were found to alternate in both the same and different current probe arrangements on the magnetic ring. (C) 2008 American Institute of Physics.
Effects of an Os buffer layer on structure and exchange bias properties of CoFe/IrMn fabricated on Si(100) and Si(111)
(2007-02-01)
Peng, Tai-Yen
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Lo, C. K.
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Chen, San-Yuan
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Yao, Y. D.
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材料科學與工程學系
The structural and exchange bias properties of CoFe/IrMn prepared on Si (100) and Si (111) with an Os/Cu buffer layer were investigated. Since the Os (0002) surface mesh has the same atomic arrangement as fcc (111) orientation, and the lattice mismatch between Os (0002) and IrMn (111) is as low as 2.6%, the CoFe/IrMn grown on H-Si(100) showed a strong IrMn (111) diffraction peak, while a very weak IrMn (111) peak appeared on H-Si (111). With increasing Os thickness (d(Os)), the IrMn (200) peak was weakened, while the IrMn (111) became strong on H-Si (100). For the CoFe/IrMn grown on H-Si(111), no obvious structural change appeared. Os plays an important role on tuning the IrMn to result in the exchange bias. On the other hand, CoFe/IrMn showed an exchange field (H-ex) on both H-Si(100) and H-Si(111) with the Os buffer layer; however, the magnetization switching process was different due to different the crystalline degree. A sharp magnetization switching process occurs for IrMn(111) on Os/Cu/H-Si(100) with a square hysteresis loop. A 370 and 310 Oe of H-ex was found in textured CoFe/TrMn on Os/Cu/H-Si(100) and Os/Cu/H-Si(111), respectively.
Endurance study of switching characteristics in NiO films
(2007-03-01)
Lee, M. D.
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Lo, C. K.
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Peng, T. Y.
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Chen, S. Y.
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Yao, Y. D.
Bi-stable switching effect has been studied in nickel oxide. lms with three different thicknesses. The best sample of our experiments was 150-nm NiO film. Its resistance ratio between high and low states was 3.6 in endurance measurement. The maximum resistance ratio in I-V curve could reach two orders of magnitude, and it could endure over 200 times of reverse processes with the ratio remaining about 1.46. This indicates that the nickel oxide has potential to be a promising material on resistance random access memory. (C) 2006 Elsevier B.V. All rights reserved.
Enhancement and inverse behaviors of magnetoimpedance in a magnetotunneling junction by driving frequency
(2006-11-13)
Chien, W. C.
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Lo, C. K.
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Hsieh, L. C.
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Yao, Y. D.
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Han, X. F.
The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al(1.2 nm)-oxide/CoFeB(4 nm)/Ru(5 nm). A huge change of more than +/- 17 000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1 MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency. (c) 2006 American Institute of Physics.
Enhancement of exchange field in CoFe/IrMn by Os/Cu buffer layer
(2007-05-01)
Peng, Tai-Yen
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Chen, San-Yuan
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Lo, C. K.
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Yao, Y. D.
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材料科學與工程學系
Enhancement of exchange field (H(ex)) and thermal stability of the textured CoFe/IrMn with Os/Cu buffer layer and Os diffusion barrier layer were studied. As revealed by x-ray Diffraction (XRD), an Os (0002) surface mesh was observed to form on Cu (100)/Si (100). The growth of CoFe (111)/IrMn (111) on such a template is parallel to the Os (0002). With the Os/Cu buffer layer, the CoFe/IrMn presents an enhancement of 70 Oe on H(ex) larger than that without Os/Cu. The H(ex) of the textured sample was 230 Oe at room temperature and it was increased to 330 Oe after 250 degrees C annealing. When the temperature reached 350 degrees C, H(ex) vanished. The increment of the temperature at which the textured and the nontextured sample obtaining their maximum H(ex) and the vanishing temperature of H(ex) were 50 and 75 degrees C, respectively. Furthermore, the CoFe/Os (d)/IrMn slowed down the H(ex) degradation. The sample with d=0.3 nm obtained its maximum H(ex) at 250 degrees C and vanished when it reached 400 degrees C. The combination of CoFe/IrMn with Os/Cu buffer layer and Os barrier layer made the H(ex) higher and also better thermal stability. (c) 2007 American Institute of Physics.
Epitaxial layer of MgO (001) grown on Si(001)wafer by e-beam evaporation
(2006-09-01)
Lee, M. D.
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Lo, C. K.
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Peng, T. Y.
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Yau, K. L.
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Chen, S. Y.
MgO(0 0 1) has been growing successfully on Fe/Pd/Cu/Si(1 0 0) by e-beam evaporation as examined by X-ray diffraction and high resolution transmission microscope. We present the magnetic peculiarity of crystal structure Fe(0 0 1)/Pd(0 0 1)/Cu(0 0 1) on Si(0 0 1) substrate. The magnetic properties of the sample were measured by magneto-optical Kerr effect which shows an in-plane magnetocrystalline anisotropy. (C) 2006 Elsevier B. V. All rights reserved.
Heteroepitaxial growth of sixfold symmetric osmium on Si (111) and Si (100)
(2007-03-19)
Peng, Tai-Yen
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Lo, C. K.
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Yao, Y. D.
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Chen, San-Yuan
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材料科學與工程學系
Growing sixfold symmetric osmium (Os) epitaxial films with suitable buffer layers was developed. Using a Cu buffer layer, the lattice mismatch between Os (0002) and Si (100) was significantly reduced from > 30% to similar to 7% to grow Os films with twin relationships and weak sixfold symmetries. On the other hand, the Cu/Au buffer layer was selected to form a fcc (111) surface mesh on H-Si (111)-1x1, and therefore sixfold symmetric Os films were grown due to the lower lattice mismatch. Such growth properties may be applied in the high density magnetic random access memory manufacturing processes to connect the magnetic tunnel junction growth and Cu metal line directly. (c) 2007 American Institute of Physics.
High frequency impedance inverse in MTJ junction
(2007-03-01)
Hsieh, L. C.
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Huang, Y. W.
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Han, X. F.
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Zeng, Z. M.
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Chien, W. C.
The magnetoimpedance effect of magnetic tunnel junction ( MTJ) was investigated at room temperature in the frequency ranged from 100 Hz to 15 MHz. The MR loop with a ratio of 9.49% at 5MHz switches to - 11.51% at 7 MHz, respectively. This indicates the MR loop reverse shape and sign around 6 MHz. This inverse MR effect is explained by the impedance competition among Resistor- Inductor series circuit and Capacitor part. (c) 2006 Elsevier B. V. All rights reserved.
High-temperature magnetoresistance study of a magnetic tunnel junction
(2006-09-01)
Chen, D. C.
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Yao, Y. D.
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Chen, C. M.
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Hung, James
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Chen, Y. S.
The thermal stability and the spin transportation phenomenon at room temperature and 140 degrees C of a series of magnetic tunneling junctions with the structure of bottom electrode/PtMn/Pinned layer/ AlO(x)/CoFe/NiFe/top electrode have been investigated. The MR ratio decreases from 33.5% at room temperature to 29% at 140 degrees C. The MR ratio at room temperature increases roughly 0.8% after thermal treatment at temperatures above 60 degrees C. This is related to the thermal relaxation of the strains existing in the samples. (C) 2006 Elsevier B.V. All rights reserved.
Interface resistance and transparency in ferromagnet/superconductor Co/NbxTi1-x multilayers (x = 1, 0.6, and 0.4)
(2007-07-01)
Huang, S.-Y.
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Lee, S. F.
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Hsu, S. Y.
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Yao, Y. D.
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電子物理學系
The quantitative interface resistance between polycrystalline ferromagnetic Co and NbxTi1-x, with x=1, 0.6, and 0.4, is measured and analyzed at 4.2 K. Both the superconducting and normal states of NbxTi1-x, respectively, above and below the superconducting critical thickness, are studied with current flowing perpendicular to the interface. A one-band series-resistance model is used to analyze our data. The interface transparencies in terms of the ratio between interface resistance and various physical quantities are discussed.
Kondo interactions and magnetic correlations in CePt2 nanocrystals
(2007-04-13)
Chen, Y. Y.
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Huang, P. H.
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Ou, M. N.
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Wang, C. R.
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Yao, Y. D.
The evolution of the Kondo effect and antiferromagnetic (AF) correlations with size reduction in CePt2 nanoparticles (3.1-26 nm) is studied by analysis of the temperature-dependent specific heat and magnetic susceptibility. The AF correlations diminish with size reduction. The Kondo effect predominates at small particle size with trivalent, small Kondo temperature (T-K) magnetic regions coexisting with strongly mixed-valent, large T-K nonmagnetic regions. We discuss the role of structural disorder, background density of states and the electronic quantum size effect on the results.
Magnetic Interaction in Domain Wall Depinning at Square Notch and Antinotch Traps
(2011-10-01)
Chang, L. J.
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Yao, Y. D.
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Lin, Pang
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Lee, S. F.
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材料科學與工程學系
In this paper, we report on domain wall (DW) pinning and depinning behavior using square notch and antinotch in NiFe nanowires. The presence of the DW in the samples was probed experimentally from focus magneto-optical Kerr effect (MOKE) measurement and anisotropic magnetoresistance (AMR). Pinning strengths as well as distribution of depinning field were measured. DW traps with antinotches were found to be more effective than notches, and the DW kept its structure during the depinning processes. Simulations of the magnetization orientation agreed with our results.
Magnetoresistance study of patterned permalloy nanostructures
(2008-05-01)
Chen, D. C.
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Mei, J. K.
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Wang, Y.
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Yao, Y. D.
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Wu, J. K.
We demonstrated the domain wall motion along the direction of the perimeter of a permalloy ring in the onion state. From the magnetoresistance (MR) measurement with a rotating ring at different constant fields, the critical field to form the onion state is near 200 Gauss and the lowest field that can still drag the domain wall is between 20 and 10 Gauss. The results also revealed a tendency for angle shifting and indicated that the lowest field component in the perimeter direction (the tangential component) was near 10 Gauss at an applied field of 20 Gauss.
MULTI-LEVEL OPERATION OF FULLY CMOS COMPATIBLE WOX RESISTIVE RANDOM ACCESS MEMORY (RRAM)
(2009)
Chien, W. C.
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Chen, Y. C.
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Chang, K. P.
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Lai, E. K.
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Yao, Y. D.
The multi-level operation of WOX based RRAM has been investigated. Improvement of our WOX process has produced an extended linear R-V region for our devices. By adding an electrical forming process and a program-verify algorithm we have demonstrated stable 2-bit/cell operation, with potential for 3-bit/cell. The reliability of the MLC operation has been examined and very stable high temperature retention, robust read disturb immunity and initial cycling endurance of >1,000 times have been demonstrated.
Oscillating voltage dependence of high-frequency impedance in magnetic tunneling junctions
(2007-06-01)
Chien, W. C.
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Hsieh, L. C.
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Peng, T. Y.
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Lo, C. K.
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Yao, Y. D.
Oscillating voltage (V-Os), which depends on the frequency dependence of the magnetoimpedance (MI) effect, was applied to study a magnetic tunneling junction (MTJ) of Ru(5 mn)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al-2 O-3/CoFeB(4 nm)/Ru(5 nm) at frequencies up to 40 MHz. The MI ratio decreased as the V-Os. was increased. The MI ratio turned from positive to negative at a certain frequency. An equivalent circuit model was employed to analyze the results. The fact that MTJ can be regarded as the composition of a resistance component and two sets of parallel resistance (R) and capacitance (C) components in series has been utilized to describe the individual impedance contribution from the lead of cross pattern, barrier, and interface. The resistance (R-barrier) and capacitance (C-barrier) of the barrier effect are functions of V-Os. The R-barrier decreases as the V-Os increases, However, Cbarrier behaves the opposite way. The tendency is for interfacial resistance R-interface and interfacial capacitance C-interface to have opposite results with increasing V-Os. This work provides a detailed investigation of high-frequency transport behavior subjected to V-Os, especially useful for MTJ characterization.