Browsing by Author "Wu, Jong-Ching"

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Effect of ion-milled barriers on electron transport in micrometer-sized tunnel junctions
(2014-03-12)
Lee, Yen-Chi
;
Lin, Yong-Han
;
Wu, Jong-Ching
;
Lin, Juhn-Jong
;
電子物理學系
We studied the electron transport properties of micrometre-sized all-Al tunnel junctions (TJs) between 2 and 300 K, in which the AlOx layer grown by O-2 plasma was moderately Ar-ion-milled prior to top electrode deposition. In contrast to the direct tunnelling in the TJs whose barriers are intact (not ion-milled), the zero-bias conductances and the current-voltage characteristics of the TJs as processed are found to be best described by the fluctuation-induced tunnelling conduction mechanism. This observation indicates the formation of nanoscopic incomplete pinholes in the AlOx layer, owing to large junction-barrier interfacial roughness introduced by the ion-milling process. Topographical features revealed by the cross-sectional transmission electron microscopy imaging of the TJ stack conform to this result. This study is of relevance to cases in which ion-milling techniques are applied in tailoring the TJ properties.
Finite element analysis of antireflective silicon nitride sub-wavelength structures for solar cell applications
(2010-10-01)
Lee, Huang-Ming
;
Sahoo, Kartika Chandra
;
Li, Yiming
;
Wu, Jong-Ching
;
Chang, Edward Yi
We numerically calculate the spectral reflectivity of the silicon nitride (Si(3)N(4)) sub-wavelength structure (SWS) using a two-dimensional finite element simulation. The geometry-dependent effective reflectance of the Si(3)N(4) SWS over the wavelength ranging from 400 nm to 1000 nm is examined and the structure of Si(3)N(4) SWS is further optimized for the lowest effective reflectance. A p-n junction solar cell efficiency based on the optimized Si(3)N(4) SWS is also calculated, resulting in an improvement of 0.98% in efficiency than that of single layer antireflection coatings. (C) 2010 Elsevier B.V. All rights reserved.
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07)
Das, Bipul
;
Lee, Y. C.
;
Li, L. C.
;
Yi-Shiou, Liu
;
Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge\'s relation, S-V (f) = AV(2)/f(alpha) (A is Hooge\'s like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07-01)
Das, Bipul
;
Lee, Y. C.
;
Li, L. C.
;
Yi-Shiou, Liu
;
Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge's relation, S-V (f) = AV(2)/f(alpha) (A is Hooge's like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Observation of fluctuation-induced tunneling conduction in micrometer-sized tunnel junctions
(2012-09-01)
Lai, Yu-Ren
;
Yu, Kai-Fu
;
Lin, Yong-Han
;
Wu, Jong-Ching
;
Lin, Juhn-Jong
Micrometer-sized Al/AlOx/Y tunnel junctions were fabricated by the electron-beam lithography technique. The thin (approximate to 1.5-2 nm thickness) insulating AlOx layer was grown on top of the Al base electrode by O-2 glow discharge. The zero-bias conductances G(T) and the current-voltage characteristics of the junctions were measured in a wide temperature range 1.5-300 K. In addition to the direct tunneling conduction mechanism observed in low-G junctions, high-G junctions reveal a distinct charge transport process which manifests the thermally fluctuation-induced tunneling conduction (FITC) through short nanoconstrictions. We ascribe the experimental realization of the FITC mechanism to originating from the formations of "hot spots" (incomplete pinholes) in the AlOx layer owing to large junction-barrier interfacial roughness. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4749251]
Temperature Controlled Perfect Absorber Based on Metal-Superconductor-Metal Square Array
(2012-11-01)
Lee, Huang-Ming
;
Wu, Jong-Ching
;
物理研究所
;
Institute of Physics
The optical properties of a single-band near-perfect absorber are studied numerically by using a finite element method in conjunction with a two-fluid model. Based on a metal-superconductor-metal (MSM) scheme, the proposed structure comprises a lossless superconducting layer sandwiched by a silver square array and ground silver plane. The simulation results clearly show that near-perfect absorption band can be realized and promptly tuned from green light to red light by the temperature of the system. The designed MSM absorber also presents the characteristics of polarization insensitivity and wide-angle incidence up to 50 degree. This prompt manipulation of the near-perfect absorption band makes this MSM absorber a great potential candidate when designing an in-situ absorption band selector in the visible light wavelength regime.
Temperature Controlled Perfect Absorber Based on Metal-Superconductor-Metal Square Array
(2012-11-01)
Lee, Huang-Ming
;
Wu, Jong-Ching
;
物理研究所
;
Institute of Physics
The optical properties of a single-band near-perfect absorber are studied numerically by using a finite element method in conjunction with a two-fluid model. Based on a metal-superconductor-metal (MSM) scheme, the proposed structure comprises a lossless superconducting layer sandwiched by a silver square array and ground silver plane. The simulation results clearly show that near-perfect absorption band can be realized and promptly tuned from green light to red light by the temperature of the system. The designed MSM absorber also presents the characteristics of polarization insensitivity and wide-angle incidence up to 50 degree. This prompt manipulation of the near-perfect absorption band makes this MSM absorber a great potential candidate when designing an in-situ absorption band selector in the visible light wavelength regime.