• Journal of Electrochemical Science and Technology
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• v.10 no.4
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• pp.424-432
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• 2019

Planar BiVO₄ and 3 wt% Mo-doped BiVO₄ (abbreviated as Mo:BiVO₄) film were prepared by the facile spin-coating method on fluorine doped SnO₂(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO₄ film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al₂O₃ layer, the ultra-thin Al₂O₃ layer with a thickness of approximately 2 nm was deposited on BiVO₄ film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO₄ and Mo:BiVO₄ films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al₂O₃ layer, the Al₂O₃ coated BiVO₄ (Al₂O₃/BiVO₄) film exhibited enhanced photoelectrochemical performance in 0.5 M Na₂SO₄ solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as V_RHE) than BiVO₄ film (0.12 mA/㎠ at 1.23 V_RHE). Moreover, Al₂O₃ coating on the Mo:BiVO₄ film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 V_RHE) than the Mo:BiVO₄ film (0.86 mA/㎠ at 1.23 V_RHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO₄ film and Al₂O₃/Mo:BiVO₄ film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (V_FB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al₂O₃ coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al₂O₃ layer.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.8
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• pp.340-346
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• 2002

Capacitor material utilized in the downsizing passive devices and integration of passive devices requires the physical and electrical properties at given area such as capacitor thickness reduction, relative dielectric constant increase, low leakage current and thermal stability. common capacitor materials, $Al_2O_3$, $SiO_2$, $Si_3N_4$, $SiO_2$/$Si_3N_4$, TaN and et al., used until recently have reached their physical limits in their application to integration of passive devices. $Ta_2O_{5}$ is known to be a good alternative to the existing materials for the capacitor application because of its high dielectric constant (25~35), low leakage current and high breakdown strength. Despite the numerous investigations of $Ta_2O_{5}$ material, there have little been established the clear understanding of the annealing effect on capacitance characteristic and conduction mechanism. This study presents the dielectric properties $Ta_2O_{5}$ MIM capacitor structure Processed by $O_2$ RTA oxidation. X-ray diffraction patterns showed the existence of amorphous phase in $600^{\circ}C$ annealing under the $O_2$ RTA and the formation of preferentially oriented-$Ta_2O_{5}$ in 650, $700^{\circ}C$ annealing and the AES depth profile showed $O_2$ RTA oxidation effect gives rise to the $O_2$ deficientd into the new layer. The leakage current density respectively, at 3~1l$\times$$10_{-2}$(kV/cm) were $10_{-3}$~$10_{-6}$(A/$\textrm{cm}^2$). In addition, behavior is stable irrespective of applied electric field. the frequency vs capacitance characteristic enhanced stability more then $Ta_2O_{5}$ thin films obtained by $O_2$ reactive sputtering. The capacitance vs voltage measurement that, Vfb(flat-band voltage) was increase dependance on the $O_2$ RTA oxidation temperature.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.290-294
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• 2000

ZnS:Mn TFEL devices were fabricated by electron-beam evaporation method and then the electro-optical properties were investigated. To investigate the capacitance which was due to oxygen vacancy at the $Ta_2O_5$ thin film, AES(Auger Electron Spectroscopy) and C-F(capacitance-frequency) measurements were used. It was found that the capacitance was decreased by annealing the $Ta_2O_5$ film in oxygen ambience. From EL emission measurement, we observed the EL emission spectrum which had the peak range from 550nm and 650nm. This emission is associated with the transition from $^4T_1(^4G)$ first excited state to $^6A_1(^6S)$ ground state in the $3d^5$ energy level configuration of $Mn^{2+}$ occurs. The threshold voltage of EL device with $Ta_2O_5$ insulator layer was found to be 24V~28V. The CIE color coordinates of these emission are X=0.5151, Y=0.4202 which is yellowish orange emitting. The EL device using $Ta_2O_5$ insulator layer can be driven with a low voltage which is beneficial to the practical application.

• Journal of IKEEE
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• v.22 no.4
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• pp.1025-1030
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• 2018

The proposed modulator is designed by utilizing a conventional structure employing time division technique to realize the 4th order delta-sigma modulator using one op-amp. In order to reduce the influence of KT/C noise, the capacitance in the first and second integrators reused was chosen to be 20pF and capacitance of third and fourth integrators was designed to be 1pF. The stage variable technique in the low power reconfigurable op-amp was used to solve the stability issue due to different capacitance loads for the reduction of KT/C noise. This technique enabled the proposed modulator to reduce the power consumption of 15% with respect to the conventional one. The proposed modulator was fabricated with 0.18um CMOS N-well 1 poly 6 metal process and consumes 305uW at supply voltage of 1.8V. The measurement results demonstrated that SNDR, ENOB, DR, FoM(Walden), and FoM(Schreier) were 66.3 dB, 10.6 bits, 83 dB, 98 pJ/step, and 142.8 dB at the sampling frequency of 256kHz, oversampling ratio of 128, clock frequency of 1.024 MHz, and input frequency of 250 Hz, respectively.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.308-313
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• 1997

TDS (Thermal Lkso~ption Spectroscopy)system, for diagnosis of CRT manufacturing process, was designed and constructed. Outgassings and themla1 desorptions from the part or materials of CRT can be measured and analysed with this system at various temperatures. The system is consisted of 3 pirrts. vacuum chamher and pumping system with variable conductance, sample heating stages & their controller, and outgassing measurement devices, like as ion gauge or quadrupole mass spectrometer. The ultimate pressure of the system was under $1\times10^{-7}$ Pa. With the variable conductance system, the effective pumping speed of the chamber could he controlled from sub 11s to 100 11s. The effective pumping speed values were determined by dynamic flow measurement principle. The temperatures and ramp rate of sample were controlled by tungsten heater and PID controller up to $600^{\circ}C$ within t $\pm 1^{\circ}C$$difference to setting value. Ion gauge & QMS were calibrated for quantitative measurements. Some examples of TDS measurement data ;ind application on the CRT process analysis were shown.

• Composites Research
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• v.31 no.5
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• pp.238-245
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• 2018

The hydrodynamic ram (HRAM) phenomenon is one of the main types of ballistic battle damages of a military aircraft and has great importance to airframe survivability design. The HRAM effect occurs due to the interaction between the fluid and structure, and damage can be investigated by measuring the pressure of the fluid and the dynamic strains on the structure. In this paper, HRAM test of a composite T-Joint was performed using a ram simulator which can generate HRAM pressure. In addition, calibration tests of PVDF sensor were performed to determine the circuit capacitance and time constant of the measurement system. The failure behavior of the composite T-Joint due to HRAM pressure was examined using the strain gauges and a PVDF sensor which were attached to the surface of the composite T-Joint.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.135-139
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• 2001

This paper describes a string resonator that is used for the interrogation system of a Fiber Bragg Grating(FBG) strain sensor. The strain on the fiber piece is calculated from the measured frequency based on that the natural frequency of a string is a function of the applied absolute strain. Existing research considered a fiber as a string, but a fiber is not a string in the strict sense due to its bending stiffness, thus the fiber should be modeled as a beam accompanied with an axial force. In the vibration modeling, the relationship between the strain and the natural frequency is derived, and then the resonance condition is described in terms of both the phase and the mode shape for sustaining resonant motion. Several experiments verify the effectiveness of the proposed model of the fiber. The performance of the string resonator is analyzed by measuring the frequency change according to the applied strains in the dynamic range of 1100$\mu\varepsilon$ referred to the displacement from capacitance sensor. From the experimental results, the implemented string resonator provides the accuracy of $\pm$3$\mu\varepsilon$, the quasi-static resolution of ~0.1$\mu\varepsilon$(rms) which amount to be $\pm$0.17$\mu\textrm{m}$ and ~6nm respectively, in case of fiber length of 56mm. For a dynamic strain, it can provide the accuracy of ~3$\mu\varepsilon$ until the frequency comes to 8Hz. As a consequence, the string resonator proposed for FBG sensor provides the high accuracy and the high resolution in strain measurement, and also it is expecting to be used, for the application, to not only strain but also displacement measuring device.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.47-53
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• 2016

Silicon nitride ($SiN_x:H$) films made by plasma enhanced chemical vapor deposition (PECVD) are generally used as antireflection layers and passivation layers on solar cells. In this study, we investigated the properties of silicon nitride ($SiN_x:H$) films made by PECVD. The passivation properties of $SiN_x:H$ are focused on by making the antireflection properties identical. To make equivalent optical properties of silicon nitride films, the refractive index and thickness of the films are fixed at 2.0 and 90 nm, respectively. This limit makes it easier to evaluate silicon nitride film as a passivation layer in realistic application situations. Next, the effects of the mixture ratio of the process gases with silane ($SiH_4$) and ammonia ($NH_3$) on the passivation qualities of silicon nitride film are evaluated. The absorption coefficient of each film was evaluated by spectrometric ellipsometry, the minority carrier lifetimes were evaluated by quasi-steady-state photo-conductance (QSSPC) measurement. The optical properties were obtained using a UV-visible spectrophotometer. The interface properties were determined by capacitance-voltage (C-V) measurement and the film components were identified by Fourier transform infrared spectroscopy (FT-IR) and Rutherford backscattering spectroscopy detection (RBS) - elastic recoil detection (ERD). In hydrogen passivation, gas ratios of 1:1 and 1:3 show the best surface passivation property among the samples.

• Journal of the Korean Vacuum Society
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• v.11 no.3
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• pp.135-140
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• 2002

In this paper, We deposited the BST thin-film on p-type (100)Si, (100)MgO and MgO/Si substrates respectively using RF magnetron sputtering method. After the BST thin-fil m was deposited, we performed RTA(rapid thermal anneal) at $600^{\circ}C$, oxygen atmosphere and 1 min. In the XRD measurement, we observed the (110) $Ba_{0.5}Sr_{0.5}TiO_3$ main peak in all samples and the peak intensity increased after post annealing. Then we manufactured a capacitor using Al Electrode and measured I-V, C-V. In C-V measurement result values for each substrate, dielectric constant was calculated 120 (bare Si), 305(MgO/Si), 310(MgO) respectively. A leakage current density was present less than 1 $\mu\textrm{A/cm}^2$ at applied fields below 0.3 MV/cm. In conclusion we confirmed that MgO/Si substrates give good results for BST thin-film deposition.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.205-206
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• 2000

The capacitance-temperature (C-T) measurement technique is proposed in the present work to investigate the thermal stability of organic and polymeric thin films for organic electroluminescent display (OELD). The single layer devices with the individual materials were subjected to the C-T measurement, prior to the examination of the complete OELD. The single layer devices with the small molecules destroyed below $180\;^{\circ}C$ depending on the kinds of materials. However, the device with the hole-transporting polyimide did not show any relaxation up to $200\;^{\circ}C$. The small molecule based OELDs failed to emit light after annealing, whereas that with the hole-transporting polyimide worked well in spite of large reduction in intensity.