-
C. H. Tsai,
F. T. Chen, H. Y. Lee,
Y. S. Chen,
K. H. Tsai,
T. Y. Wu,
S. Z. Rahaman,
P. Y. Gu,
W. S. Chen,
P. S. Chen,
Z. H. Lin,
P. L. Tseng,
W. P. Lin,
C.H. Lin,
S. S. Sheu,
M. -J. Tsai,
T. K. Ku
[show abstract]
[hide abstract]
ABSTRACT: Consumer gadgets make up the fastest growing market for electronic devices today. These products will rely more and more on embedded storage-type memory, which can store system and processing data without impacting standby power consumption. For embedded memory applications, including microcontrollers, automotive, and mobile code storage applications, NOR flash is a popular choice for its non-volatility and fast read time on the order of nanoseconds. However, its operation voltage is larger than 10V, and the write speed exceeds 10 microseconds. Although increasing density is not a key requirement for process scaling of embedded memory down to advanced nodes, the operation voltage needs to be reduced to continually lower power consumption and to match foundry offerings in the logic and mixed-signal sectors, both in the core voltages and the I/O voltages. Resistive random-access memory (RRAM) is proposed to be such a scalable embedded memory technology. RRAM offers the advantages of CMOS process compatibility, high speed, high endurance, low-voltage operation, and high cell density. In this article, we demonstrate that the operation voltage can be reduced to under 1V in the Ti/HfOx RRAM system with a multi-level RESET operation strategy, while keeping the write speed to less than 2 microseconds, opening up opportunities for RRAM in embedded memory applications.
China Semiconductor Technology International Conference (CSTIC) 2013; 03/2013
-
[show abstract]
[hide abstract]
ABSTRACT: Adsorption of ions on surfaces modified with brushes of polyampholytes J. Chem. Phys. 137, 074707 (2012) Perpendicular magnetic anisotropy induced by a cap layer in ultrathin MgO/CoFeB/Nb J. Appl. Phys. 112, 033910 (2012) Sharp transition from ripple patterns to a flat surface for ion beam erosion of Si with simultaneous co-deposition of iron AIP Advances 2, 032123 (2012) The effects of substrate size and temperature on the deposition of Cu clusters on a Si substrate J. Appl. Phys. 112, 024903 (2012) Study on low-energy sputtering near the threshold energy by molecular dynamics simulations AIP Advances 2, 032107 (2012) Additional information on Appl. Phys. Lett.
Applied Physics Letters 08/2012; 101. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper investigates the repeatable unipolar/bipolar resistive switching memory characteristics in a copper/germanium-oxide/tungsten (Cu/GeOx/W) structure. The switching mechanism occurs because of the lower barrier height for hole injection rather than electron injection. Therefore, Cu ions, as a positive charge, migrate before initiating growth at the GeOx/W interface and dissolving at the GeOx/Cu interface. The diameter of the Cu nanofilament increases linearly from 0.13 Å to 25 nm as current compliances increase from 1 nA to 10 mA, as calculated using the other approach. The crystalline Cu nanofilament was also confirmed by high-resolution transmission electron microscopy analysis under SET. Good data retention with high resistance ratios of 102–105 (and >104 at 85 °C) and ∼109 was obtained under the bipolar and unipolar modes, respectively. Therefore, a maximum memory size of 5000 Pbit/in2 can be designed in the future.
Applied Physics Letters 08/2012; 101(7):073106. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Background. Chronic urticaria (CU) is a common skin disorder that affects the well-being and quality of life (QOL) of patients. Recently, we developed and validated a questionnaire for measuring QOL in Korean patients with CU, called the Chronic Urticaria-Specific Quality of Life (CU-QOL) questionnaire. Aim. To evaluate the clinical significance of a computerized version of the CU-QOL, in adult patients with CU. Methods. This was a cross-sectional observational study that enrolled 249 Korean patients with CU from five university hospitals and measured computerized CU-QOL scores and Urticaria Activity Score (UAS) simultaneously. The internal consistency of the computerized CU-QOL was analysed using Cronbach α. To identify clinical correlations between the CU-QOL and patient characteristics, the atopic status and serum autoantibodies, including antinuclear, antithyroglobulin and antimicrosome antibodies, were measured. Multiple linear regression models were used to identify CU-QOL predictors. Results. Cronbach α was 0.94 for the overall computerized CU-QOL score. The CU-QOL scores correlated significantly with the UAS (r = -0.49, P < 0.001). Of the factors aggravating CU, delayed pressure, sunlight exposure and emotional stress significantly influenced the overall CU-QOL scores in the univariate analysis. Multivariate regression models indicated that UAS and emotional stress were significant predictors of the four domains and of the total CU-QOL scores. Conclusions. The computerized CU-QOL is a convenient and valid tool for measuring QOL in patients with CU. This study suggests that UAS, dermatographism and emotional stress are strong CU-QOL predictors in Korean patients with CU.
Clinical and Experimental Dermatology 06/2012; 37(7):722-8. · 1.20 Impact Factor
-
221st ECS Meeting, Seattle, WA; 05/2012
-
[show abstract]
[hide abstract]
ABSTRACT: This investigation examines the magnetorheological (MR) characteristics of Fe3O4 aqueous suspensions. Magnetite particles (Fe3O4) were synthesized using a colloidal process and their sizes were determined to be normally distributed with an average of
10nm by TEM. Experimental results reveal that the MR effect increases with the magnetic field and suspension concentration.
The yield stress increases by up to two orders of magnitude when the sample is subjected to a magnetic field of 146Oe/mm.
In comparison with other published results, concerning a concentration of approximately 10–15% v/v, this study demonstrates
that the same increase can be obtained with a concentration of nano-scale particles as low as 0.04% by volume. The viscosity
was increased by an order of magnitude while the shear rate remained low; however, the increase decayed rapidly as the shear
rate was raised. Finally, the MR effect caused by DC outperformed that caused by AC at the same current.
KeywordsMagnetorheological (MR)–Magnetite particles (Fe3O4)–Nano-scale particles–Yield stress–Fe3O4 suspensions
Colloid and Polymer Science 05/2012; 283(11):1253-1258. · 2.33 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Influence of GeOx layer on resistive switching memory performance in a simple and CMOS compatible W/WOx/GeOx:WOx mixture/W structure has been investigated for the first time. All layers are confirmed by both HRTEM and XPS. This memory device has enhanced performance in terms of the resistance ratio, uniformity, and program/erase cycles as compared to W/WOx/W structure. An excellent read endurance and program/erase cycles of >;10^6 at large Vread of ±1V are obtained. Furthermore, the memory device exhibits robust data retention at 85°C. This device can be operated as low current as 0.1 μA.
VLSI Technology, Systems, and Applications (VLSI-TSA), 2012 International Symposium on, Hsinchu, Taiwan; 04/2012
-
Journal of Applied Physics 03/2012; 111(6):063710. · 2.17 Impact Factor
-
Journal of Alloys and Compounds 03/2012; 530:18-21. · 2.29 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The influence of initial stress/strain state on ordering of FePt is studied. The internal stress of FePt thin films deposited at room tem-perature can be successfully controlled in a wide range from compressive 0.95 GPa to 1.1 GPa tensile by adjusting sputter distance and inserting SiO 2 underlayer with different thickness. Ordering process is triggered by rapid thermal annealing at 350 C for 15 min. Structural and magnetic results confirm that order transformation occurs within the stress range of 0 04 GPa 0 52 GPa. Highly stressed initial states (either compressive or tensile) suppress ordering in different ways. Large compressive stress increases the energy barrier of order reaction which results in volume expansion; strong tensile stress block the formation of 1 0 phase by preventing the densification, a vital process prior to ordering, which creates intensive tensile stress. The results provide an insight into the ordering process in the aspect of evolution of internal stress/strain.
IEEE Transactions on Magnetics 03/2012; 48. · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Design and fabrication of Dy-free sintered permanent magnets with high coercivity J. Appl. Phys. 111, 07A710 (2012) Structure and magnetotransport properties of epitaxial nanocomposite La0.67Ca0.33MnO3:SrTiO3 thin films grown by a chemical solution approach Appl. Phys. Lett. 100, 082403 (2012) Anisotropy study of garnet films grown over substrates populated with gold nanoparticles J. Appl. Phys. 111, 07A505 (2012) Study on the soft magnetic properties and high frequency characteristics of Co-M (M=Ti, Zr, and Hf) thin films J. Appl. Phys. 111, 07A333 (2012) Magnetism of BaB6 thin films synthesized by pulsed laser deposition Structure and magnetic properties of L1 1 CoPtCu thin films sputter-deposited on glass substrates were studied. Perpendicular coercivity (H c\) was largely enhanced by the replacement of Co with Cu with x ¼ 23 and 26, the magnetic properties obtained was better than the film grown on MgO(111) substrates. The enhancement of H c\ existed in a wide range of film thickness from 2 to 40 nm. A maximum value of H c\ of 2.7 kOe appeared in the films with thickness of 4 nm. The results of surface morphology indicated that the random distribution of the in-plane orientation of L1 1 grains induced by Pt(111) underlayer may create magnetic inhomogeneities acting as pinning site to domain walls, providing additional impedance for domain wall motion. V C 2012 American Institute of Physics. [doi:
Journal of Applied Physics 02/2012; 111(111):7-706. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Stress and texture development during sputtering of yttria, zirconia, and yttria stabilized zirconia films on Si substrates J. Appl. Phys. 112, 074910 (2012) Effect of Pt bottom electrode texture selection on the tetragonality and physical properties of Ba0.8Sr0.2TiO3 thin films produced by pulsed laser deposition J. Appl. Phys. 112, 044105 (2012) Focused ion beam induced structural modifications in thin magnetic films J. Appl. Phys. 112, 033901 (2012) Temperature dependence of nanometer-size metallic phase texture and its correlation with bulk magnetic and transport properties and defects of a (La0.4Pr0.6)0.67Ca0.33MnO3 film Appl.
Journal of Applied Physics 02/2012; 111(112):7-702. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Insulation and diffusion barrier characteristics of spin-on-glass layer on a stainless steel substrate J. Renewable Sustainable Energy 4, 011603 (2012) Effect of (O, As) dual implantation on p-type doping of ZnO films J. Appl. Phys. 110, 103708 (2011) Effect of the starting surfaces of GaN on defect formation in epitaxial Co thin films J. Appl. Phys. 110, 093501 (2011) Properties of defected one-dimensional terahertz plasmonic crystal films in a metal air-gap waveguide
Journal of Applied Physics 02/2012; 111(99):7-303. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Room-temperature-deposited FePt thin films with thickness ( t ) ranged from 5 to 100 nm treated by rapid-thermal annealing (RTA) were studied. With annealing condition of 900<sup>°</sup>C for 60 seconds at heating rate of 80<sup>°</sup> C/sec., a metastable phase of FePt was observed in the films with t ≥ 40 nm. The phase is chemically ordered with a face-centered-cubic (fcc) structure. The lattice parameter of it is found identical to the planar spacing of L 1<sub>0</sub> (100). The metastable structure is dominant in the film with t = 40 nm and gradually replaced by L 1<sub>0</sub> phase with increasing t . The fcc phase is soft magnetic with saturation magnetization similar to that of disordered FePt. Drastic changes were also observed in surface morphology. The results infer the connection between the metastable transformation and internal strain. The formation of the fcc structure is sensitive to processing parameters except t . Slower heating rate, lower annealing temperature, and longer annealing time, tend to suppress the formation of it. The interesting findings provide additional knowledge for FePt thin films.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Development of (001) texture in FePt thin films deposited on glass substrates with different thickness ( t ) treated by rapid thermal annealing (RTA) is studied. A critical thickness of 30 nm is characterized: below which the (001) preferred orientation of the films develops with increasing t ; when t >; 30 , the films become isotropic. Remarkable perpendicular anisotropy in magnetic properties is achieved in the 30 nm thick sample with the best (001) texture. Discontinuous changes are also observed in surface morphology, microstructure, magnetic domain structure, and internal stress. Direct evidences are presented relating the formation of (001) texture to abnormal grain growth. The internal stress/strain analysis indicates that the residual tensile (σ) stress is proportional to the degree of (001) preferred orientation. A large value of σ of about 8.9 GPa is obtained in the film with t = 30, suggesting the driving force forming the texture.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have characterized the dependence of residual strain/stress on annealing process (post-and in-situ annealing) in single-layer FePt films prepared by sputtering onto amorphous glass substrates. A remarkable difference of evolutions in residual strains between post-andin-situ annealed samples was observed by Sin 2 method using synchrotron radiation. The onset of ordering temperature for both series samples is almost identical (350 C), verified by x-ray diffraction. Crystalline domain size, measured by x-ray peak breadths, of FePt films indicates a difference between these two series samples, which is associated with evolution of residual strain. We believe that the dynamic stress relaxation is the major factor in discrepancy of the residual stress behavior, since the atomic mobility of adatoms during film deposition for in-situ annealing samples are much higher than that for post-annealed films. It is further deduced that residual strain mechanisms may influence the ordering behaviors and related microstructure of FePt films. Index Terms—Annealing process, FePt thin films, 1 0 , residual strain/stress.
IEEE Transactions on Magnetics 09/2011; 47. · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The stress state of FePt thin films deposited at room temperature was controlled within the range from 1.01 GPa compressive to 0.18 GPa tensile before taking rapid thermal annealing (RTA). After the order–disorder transformation triggered by RTA at temperatures (T a) from 650 to 800 C for 5 min, the tensile-stressed films exhibit significant preferred orientation of (001) of L1 0 structure. However, the compressive-strained ones show isotropic texture. Strong (001) texture with high Lotgering orientation factor of 0.9 is obtained at T a ¼ 800 C, resulting in enhanced perpendicular magnetic anisotropy. The results provide direct evidence of stress-induced (001) texture, which could be significant for future applications. V C 2011 American Institute of Physics. [doi:10.1063/1.3564950] L1 0 FePt (001) thin film has great potential use in advanced perpendicular magnetic recording media with ultrahigh density exceeding 1 Tbits/in. 2 The most crucial advantages of which are high magnetocrystalline anisotropy (K u $ 7 Â 10 7 erg/cm 3) and Curie temperature ($450 C), leading to stable magnetization of grains even though their grain sizes are reduced below 5 nm. Another advantage is its remarkable chemical stability, which enhances the durability of the device. From previous reports the (001) texture of L1 0 FePt films can be effectively induced by a variety of approaches, including epitaxial growth on single crystal sub-strates by either sputtering 1–3 or molecular beam epitaxy 4,5 techniques, underlayer induction, 6,7 multilayer deposition, 8,9 rapid thermal annealing (RTA), 10,11 etc. Among these meth-ods, RTA is the easiest one to use since it does not require epigrowth, single crystal substrates, multilayer or complex deposition process, or even in situ heating. However, the mechanism of forming (001) texture is still unclear. Although recent studies ascribed the development of FePt(001) texture to the coexistence of order–disorder trans-formation strain and biaxial tensile in-plane strain of the film, 12,13 direct experimental results are still lacking. In this study, the initial stress/strain state of FePt thin films depos-ited at room temperature were controlled to investigate the effect on forming the preferred orientation of L1 0 FePt after RTA. In our previous work, it was found that the sputter con-dition can significantly alter the stress/strain state of the FePt films deposited at RT. 14 With this approach, the initial stress can be well predetermined. Thin films with different stress state show distinct preferred orientation after RTA process. Strong (001) texture is present in the samples with tensile initial stress, which is direct evidence for the stress-induced (001) texture. The control of initial stress/strain states also manifests itself as an effective way to induce FePt (001) texture. FePt single layer thin films were deposited by rf sputter-ing at RT with a background vacuum less than 5 Â 10 À7 Torr on Corning 1737 glass substrates. The samples have constant thickness of 40 nm. A high-purity FePt alloy target was used. The chemical composition of the films analyzed by calibrated energy dispersive spectroscopy was Fe 52 Pt 48 . The initial stress of the RT-deposited FePt films was controlled by adjusting deposition conditions such as working distance, rf power, and argon pressure. The samples were then sub-jected to RTA at temperatures from 650 to 800 C for 5 min with heating rate of about 50 C/s. The phase structure and internal stress/strain were studied using x-ray diffractometry (XRD) with Cu Ka as well as synchrotron radiation light source at National Synchrotron Radiation Research Center (NSRRC) Beamline 17B. The beam energy at NSRRC is 8 keV with the corresponding wavelength k ¼ 0.15 nm and energy resolution on order of 10 À4 . The spot size is about 0.25 Â 0.8 mm and the step size is 0.025 . The in-plane stress/strain was determined by sin 2 w method 15 using planar spacing of fundamental peak (111). The diffraction geometry and definitions of various angles together with axes are shown in Fig. 1. The angular, w, dependence of the (111) peak was obtained by the rotation of v axis using a (6 þ 2) Huber goniometer from 0 to 75 . Magnetic properties were measured at RT using a vibrating sample magnetometer with a maximum external field of 2 T. Dependence of in-plane strain on sin 2 w for the RT-de-posited FePt films at working argon pressures of 5 and 25 mTorr is shown in Fig. 2. The in-plane strain e is defined as (d w À d 0)/d 0 ; d w is the planar spacing at w and d 0 is the unstressed planar spacing. When only in-plane strain exists, the strain lines will pass through the zero-strain point at
Journal of Applied Physics 04/2011; · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Equiatomic CoPt and FePt thin films grown on MgO(111) substrates at temperatures (Ta) from room temperature (RT) to 400 °C were studied. Distinct phase evolution was observed. In CoPt films, a metastable phase of L11 appears at Ta = 250 °C prior to the formation of thermodynamic equilibrium L10 phase; whereas no intermediate structure is found in the FePt films. Good epitaxial growth of CoPt films can be obtained at low Ta before ordering. However, in FePt films, high quality epitaxy appears after the occurrence of L10 ordering. Either L11 or L10 ordering induces magnetic hardening. Perpendicular magnetic anisotropy was obtained in the L11 films, yet the L10 sample exhibited isotropic magnetism. Corresponding evolution in magnetic domain structure was also reported.
Journal of Applied Physics 03/2011; 109(7):07B743-07B743-3. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study investigates structural and magnetic properties of the (Co 50-x Cu x)Pt 50 films deposited on the MgO(111) substrate. Experimental results indicate that adding Cu significantly improves the alignment of L1 1 [111] and decreases the structural defects of the epitaxial films. Additionally, a large increment of an order of magnitude in out-of-plane coercivity (H c\) from 0.2 to 2.2 kOe is achieved when x is increased from 0 to 23. Such an increase accompanies a reduction of in-plane coercivity (H c||) from 1.5 to less than 0.1 kOe. The enhancement in H c\ is attributed to the domain wall pinning effect induced by compositional segregation of Cu and Co. This study provides an effective approach to optimize the perpendicular magnetic properties of L1 1 CoPt. V C 2011 American Institute of Physics. [doi:10.1063/1.3545821] A decade ago Iwata et al. 1 identified CoPt L1 1 phase as a metastable superstructure based on molecular beam epitaxy (MBE) and MgO(111) substrates. The lattice structure is rhombohedral consisting of alternative stacked, close-packed atomic layers of Co and Pt with the sequence of ABC along the c-axis. This phase possesses a very high magneticocrys-talline anisotropy (K u) of 4 Â 10 7 erg/cm 3 and low formation temperature of around 300 C. 1 Huang et al. later indicated the feasibility of inducing L1 1 -ordering of CoPt on Al 2 O 3 substrates, as well as discussed the effect of substrate orien-tation. 2 A recent study demonstrated the ability to form L1 1 CoPt on glass substrates with a Pt(111) underlayer. 3 Addi-tionally, our previous study established that inserting a Pt underlayer between CoPt and MgO(111) substrate could fur-ther lower the onset temperature of L1 1 -ordering to 180 C and achieve high-quality epitaxial growth. 4 The L1 1 phase, a naturally perpendicular magnetically anisotropic material, can only be induced by the substrate texture or underlayer surface with a closed-packed plane (111) in face-centered-cubic lattice] perpendicular to the film plane. Although L1 1 CoPt holds various advantages for future perpendicular re-cording media with ultrahigh areal density of terabits/in. 2 , certain problems still persist. One of those is the low coerciv-ity. For epitaxially grown CoPt films with a continuous mor-phology, domain wall motion dominates the magnetic reversal. The absence of domain wall pinning sites signifi-cantly makes the impedance of wall motion very small, con-sequently causing low coercivity. This study attempts to create magnetic inhomogeneities in order to increase the re-sistance of domain wall motion. This objective is achieved by adding Cu to replace Co partially. This measure is taken because L1 1 CuPt is thermodynamically stable and has lat-tice parameters similar to those of L1 1 CoPt, possibly pre-serving or even stabilizing the L1 1 -ordering of CoPt. Another reason is that Cu is insoluble in Co, which is essen-tial for compositional segregation. Samples were fabricated by dc magnetron sputtering. The background pressure was lower than 5 Â 10 À9 Torr, and the working pressure was fixed at 10 mTorr. MgO(111) substrates were heated to 650 C for 30 minutes before thin film deposition for surface reconstruction and cleaning. (Co 50-x Cu x)Pt 50 films with thickness 50 nm were then de-posited by rotational co-sputtering after the substrate tem-perature was stabilized at 350 C. High-purity targets of Co, Cu, and Pt of 99.999 at. % were used. Once controlled by adjusting the sputtering powers of three targets, the chemi-cal composition of (Co 50-x Cu x)Pt 50 films was analyzed by calibrated energy dispersion spectroscopy (EDS). Next, the phase structure of the films was characterized at beamline 17B of National Synchrotron Radiation Research Center (NSRRC) (Hsinchu, Taiwan) by using x-ray diffractometry (XRD) with a synchrotron radiation light source. The beam energy is 8 keV with a wavelength of 0.15 nm. The step size of the h-2h scans was 0.01 , and the collection time was 3 s per step. Rocking curves were also evaluated for the L1 1 (111) peak ranging from À8 to 8 at a scan rate of 2 /min. Moreover, the magnetic domain structure was examined by magnetic force microscopy (MFM). The mag-netic properties were also determined using a vibrating sam-ple magnetometer (VSM) at room temperature. Figure 1(a) displays the XRD patterns for the 50-nm-thick (Co 50-x Cu x)Pt 50 samples with x ¼ 0, 10, 23, and 37 grown at 350 C. The average misalignment between
Journal of Applied Physics 03/2011; · 2.17 Impact Factor
-
H.Y. Lee,
Y.S. Chen,
P.S. Chen,
P.Y. Gu,
Y.Y. Hsu,
S.M. Wang,
W.H. Liu,
C.H. Tsai,
S.S. Sheu,
P.C. Chiang,
W.P. Lin,
C.H. Lin,
W.S. Chen,
F.T. Chen,
C.H. Lien,
M. Tsai
[show abstract]
[hide abstract]
ABSTRACT: The memory performances of the HfO<sub>X</sub> based bipolar resistive memory, including switching speed and memory reliability, are greatly improved in this work. Record high switching speed down to 300 ps is achieved. The cycling test shed a clear light on the wearing behavior of resistance states, and the correlation between over-RESET phenomenon and the worn low resistance state in the devices is discussed. The modified bottom electrode is proposed for the memory device to maintain the memory window and to endure resistive switching up to 10<sup>10</sup> cycles.
Electron Devices Meeting (IEDM), 2010 IEEE International; 01/2011
