Browsing by Author "Lo, C. K."

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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.
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.
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.
The effect of Os interlayers on the thermal stability of magnetic CoFe/OsMn films
(2006-09-01)
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 thermal stability of a multilayer structure of protection layer/Co(90)Fe(10)/Os (d nm)/Os(20)Mn(80) has been studied as functions of annealing temperature (Tan) and thickness of Osmium (Os) layer. The insertion of a thin Os layer between the Co(90)Fe(10)/Os(20)Mn(80) interface shows better thermal stability. No diffusion evidence was found for samples with d >= 0:3 nm as examined by Auger electron spectroscopy depth profile at different annealing temperatures up to 400 degrees C. These samples with Os layer showed the same magnetic behavior and the hysteresis loop with squareness (S) larger than 0.9 were observed before and after annealing. (C) 2006 Elsevier B.V. All rights reserved.