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Phan Bach Thang,이재찬,정철호,최택집 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Current-voltage (I-V) characteristics of 0.2 % Cr-doped SrTiO3 (Cr-STO) thin film in a metalinsulator- metal (MIM), i.e., Pt/Cr-STO/La0.5Sr0.5CoO3, structure were measured, and the electrical conduction was investigated. The I-V characteristics exhibited hysteretic and asymmetric behaviors. The hysteretic behavior is attributed to bistable resistive switching between a highresistance state (HRS) and a low-resistance state (LRS) with voltage polarity. The voltages that induced the resistance switching were above ±3 V. The resistance ratio between the two conduction states was about two orders of magnitude. An analysis of the I-V characteristics revealed that the electrical conduction behavior followed a trap-controlled space-charge-limited current. The trap-filled limit voltage, VTFL, was .1.6 V.
AC Electrical Conduction of Cr-Doped SrTiO3 Thin Films
이재찬,Bach Thang Phan,김남철 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2
The ac conductivity of Cr-doped SrTio3 thin films has been studied as a function of frequency and temperature. The Cr-doped SrTio3 thin films exhibit a single relaxation process, which is a thermally activated process. The dielectric relaxation occurs in the bulk region and is governed by hopping of charge carriers between traps, resulting in trap-controlled ac conduction.
Jung, Chulho,Choi, Taekjib,Phan, Bach Thang,Lee, Jaichan Gordon and Breach Science Publishers 2007 Integrated ferroelectrics Vol.90 No.1
<P> The resistive switching of 0.2% Cr-doped SrTiO3 (Cr-STO) thin films grown on (La0.5, Sr0.5)CoO3/SrTiO3 (LSCO/STO) substrate have been investigated. The structure in a metal-insulator-metal (MIM) i.e., Pt/Cr-STO/LSCO, shows hysteretic and asymmetric behaviors in current-voltage (I-V) characteristics. The current-voltage characteristics are attributed to the resistive switching of Cr-STO thin films between high resistance state (HRS) and low resistance state (LRS) by applying pulsed or dc bias voltage stress. The current and voltage ramp sweeps in the I-V measurement reveal that threshold current is required to induce the resistive switching from HRS to LRS in the negative voltage region.</P>
Growth Mode of La0.5Sr0.5CoO3 Thin Films with Oxygen Pressure on Stepped SrTiO3 Substrates
김주호,이재찬,정철호,Phan Bach Thang,최택집 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
We have studied the growth mode of La0.5Sr0.5CoO3 (LSCO) thin films as a function of oxygen pressure on stepped SrTiO3 substrate by laser molecular beam epitaxy (Laser MBE). The growth behavior and mode of LSCO thin films are sensitive to oxygen ambient during growth. LSCO thin films grown at low oxygen pressures (<10.3 Torr) exhibited a two-dimensional layer-by-layer growth mode at the initial stage, followed by island growth mode within a few tenths of a unit-cell layer. When the ambient oxygen pressure reached 10 mTorr, the LSCO thin films exhibited a well-defined step-and-terrace structure with atomically flat surface roughness close to the SrTiO3 substrate, which suggests that two-dimensional layer-by-layer growth is obtained through the deposition. Further increasing the oxygen pressure degraded the growing surface, resulting in a gradual increase in surface roughness. This result indicates that two-dimensional growth was obtained in a certain degree of ambient oxygen pressure in the growth of oxide thin film whose oxygen nonstoichiometry is susceptible to oxygen ambient.P
Label-Free Optical Biochemical Sensors via Liquid-Cladding-Induced Modulation of Waveguide Modes
Tran, Nhu Hoa Thi,Kim, Jisoo,Phan, Thang Bach,Khym, Sungwon,Ju, Heongkyu American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37
<P>We demonstrated modulation of the waveguide mode mismatch via liquid cladding of the controllable refractive index for label-free quantitative detection of concentration of chemical or biological substances. A multi mode optical fiber with its core exposed was used as the sensor head with the suitable chemical modification of its surface. Injected analyte liquid itself formed the liquid cladding for the waveguide. We found that modulation of the concentration of analyte injected enables a degree of the waveguide mode mismatch to be controlled, resulting in sensitive change in optical power transmission, which was utilized for its real-time quantitative assay. We applied the device to quantitating concentration of glycerol and bovine serum albumin (BSA) solutions. We obtained experimentally the limit of detection (LOD) of glycerol concentration, 0.001% (volume ratio), corresponding to the resolvable index resolution of similar to 1.02 x 10(-6) RIU (refractive index unit). The presented sensors also exhibited reasonably good reproducibility. In BSA detection, the sensor device response was sensitive to change in the refractive indices not only of liquid bulk but also of layers just above the sensing surface with higher sensitivity, providing the LOD experimentally as similar to 3.7 ng/mL (mass coverage of similar to 30 pg/mm(2)). A theoretical model was also presented to invoke both mode mismatch modulation and evanescent field absorption for understanding of the transmission change, offering a theoretical background for designing the sensor head structure for a given analyte. Interestingly, the device sensing length played little role in the important sensor characteristics such as sensitivity, unlike most of the waveguide-based sensors. This unraveled the possibility of realizing a highly simple structured label-free sensor for point-of-care testing in a real-time manner via an optical waveguide with liquid cladding. This required neither metal nor dielectric coating but still produced sensitivity comparable to those of other types of label-free sensors such as plasmonic fiber ones.</P>
Correlation between crystallinity and resistive switching behavior of sputtered WO3 thin films
Thi Bang Tam Dao,Kim Ngoc Pham,Yi-Lung Cheng,김상섭,Bach Thang Phan 한국물리학회 2014 Current Applied Physics Vol.14 No.12
The as-depositedWO3 thin films were post-annealed at different temperatures (300 C and 600 C) in air to investigate a correlation between crystallinity and switching behavior of WO3 thin films. Associating the results of XRD, FTIR, XPS and FESEM measurements, the annealing-caused crystallinity change contributes to the variation of the switching behaviors of theWO3 thin films. The as-depositedWO3 films with low crystalline structure are preferred for random Ag conducting path, resulting in large switching ratio but fluctuating IeV hysteresis, whereas the annealedWO3 films with crystallized compact structure limits Ag conducting path, favoring the stable IeV hysteresis but small switching ratio. It is therefore concluded that electrochemical redox reaction-controlled resistance switching depends not only on electrode materials (inert and reactive electrodes) but also on crystallinity of host oxide.
Electrical Conduction and Resistance Switching Mechanisms of Ag/ZnO/Ti Structure
Nguyen, Trung Do,Pham, Kim Ngoc,Tran, Vinh Cao,TuanNguyen, Duy Anh,Phan, Bach Thang Institute of Korean Electrical and Electronics Eng 2013 전기전자학회논문지 Vol.17 No.3
We investigated electrical conduction and resistance switching behavior of the Ag/ZnO/Ti structures for random access memory devices. These films were prepared on glass substrate by dc sputtering technique at room temperature. The resistance switching follows unipolar switching mode with small switching voltages (0.4 V - 0.6 V). Two electrical conduction mechanisms dominating the LRS and HRS are Ohmic and trap-controlled space charge limited current, respectively. These both conductions are consistent with the filamentary model. Based on the filamentary model, the switching mechanism was also interpreted.
Electrical Conduction and Resistance Switching Mechanisms of Ag/ZnO/Ti Structure
Trung Do Nguyen,Kim Ngoc Pham,Vinh Cao Tran,Duy Anh TuanNguyen,Bach Thang Phan 한국전기전자학회 2013 전기전자학회논문지 Vol.17 No.3
We investigated electrical conduction and resistance switching behavior of the Ag/ZnO/Ti structures for random access memory devices. These films were prepared on glass substrate by dc sputtering technique at room temperature. The resistance switching follows unipolar switching mode with small switching voltages (0.4 V – 0.6 V). Two electrical conduction mechanisms dominating the LRS and HRS are Ohmic and trap-controlled space charge limited current, respectively. These both conductions are consistent with the filamentary model. Based on the filamentary model, the switching mechanism was also interpreted.