• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.6
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• pp.293-297
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• 2009

In this paper, we made three kinds of porous silicon samples (single layer, distributed Bragg reflector, and microcavity) by electrochemical etching p-type silicon substrate. And then, we investigated their reflectance spectrum properties. We found that the number of fringe patterns and the maximum reflectivity of porous silicon multilayer increased compared with a porous silicon sinlge layer. In addition, we can observe that the DBR (distributed Bragg reflector) porous silicon has a full-width at half-maximum about 33 nm which is narrower than the porous silicon single layer and porous silicon microcavity.

• Journal of Integrative Natural Science
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• v.7 no.1
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• pp.1-4
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• 2014

Distributed Bragg reflector porous silicon of different characteristics were formed to determine their optical constants in the visible wavelength range using a periodic square wave current between low and high current densities. The surface and cross-sectional SEM images of distributed Bragg reflector porous silicon were obtained using a cold field emission scanning electron microscope. The surface image of distributed Bragg reflector porous silicon indicates that the distributions of pores are even. The cross-sectional image illustrates that the multilayer of distributed Bragg reflector porous silicon exhibits a depth of few microns and applying of square current density during the etching process results two distinct refractive indices in the contrast. Distributed Bragg reflector porous silicon exhibited a porosity depth profile that related directly to the current-time profile used in etch. Its free-standing film was obtained by applying an electro-polishing current.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.2
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• pp.250-254
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• 2003

A film bulk acoustic resonator (FBAR) device for 2 GHz radio frequency (RF) bandpass filter application is presented. This FBAR device consists of an aluminum nitride (AlN) film sandwiched between top(Al) and bottom(Au) electrodes and an acoustic multilayer reflector of a silicon dioxide/tungsten (SiO2/W). The A/N film deposited using a RF sputtering was observed to have small columnar grains with a strongly preferred orientation towards c axis. In addition to a high quality factor (4300), a large return loss of 37.19 dB was obtained.

• Current Optics and Photonics
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• v.2 no.2
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• pp.125-133
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• 2018

We report an in-depth analysis of the design and fabrication of multilayer dielectric (MLD) diffraction gratings for spectral beam combining at a wavelength of 1055 nm. The design involves a near-Littrow grating and a modal analysis for high diffraction efficiency. A range of wavelengths, grating periods, and angles of incidence were examined for the near-Littrow grating, for the $0^{th}$ and $-1^{st}$ diffraction orders only. A modal method was then used to investigate the effect of the duty cycle on the effective indices of the grating modes, and the depth of the grating was determined for only the $-1^{st}$-order diffraction. The design parameters of the grating and the matching layer thickness between grating and MLD reflector were refined for high diffraction efficiency, using the finite-difference time-domain (FDTD) method. A high reflector was deposited by electron-beam evaporation, and a grating structure was fabricated by photolithography and reactive-ion etching. The diffraction efficiency and laser-induced damage threshold of the fabricated MLD diffraction gratings were measured, and the diffraction efficiency was compared with the design's value.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.102-108
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• 2005

We have developed highly stabilized (p-i-n)-type protocrystalline silicon (pc-Si:H) multilayer solar cells. To achieve a high conversion efficiency, we applied a double-layer p-type amorphous silicon-carbon alloy $(p-a-Si_{1-x}C_x:H)$ structure to the pc-Si:H multilayer solar cells. The less pronounced initial short wavelength quantum efficiency variation as a function of bias voltage proves that the double $(p-a-Si_{1-x}C_x:H)$ layer structure successfully reduces recombination at the p/i interface. It was found that a natural hydrogen treatment involving an etch of the defective undiluted p-a-SiC:H window layer before the hydrogen-diluted p-a-SiC:H buffer layer deposition and an improvement of the order in the window layer. Thus, we achieved a highly stabilized efficiency of $9.0\%$ without any back reflector.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.2
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• pp.188-193
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• 2010

In this paper, SI(Signal Integrity) characteristic of the 4-layer PCB(Printed Circuit Boards) with a through-hole via was analyzed by impedance mismatching between the through-hole via and the transmission line, and deterioration of clock pulse response characteristic due to the P/G plane resonances which are generated between the power and the ground plane. The minimized impedance mismatching between the through-hole via and the transmission line for the improving of SI characteristic is confirmed by the TDR(Time Domain Reflector) simulation and lumped element modeling of the through-hole via. And the cancellation method of P/G plane resonances for improvement of the SI characteristic is represented by simulation result.

• Journal of information and communication convergence engineering
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• v.6 no.1
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• pp.34-37
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• 2008

Effects of the addition of Cr adhesion layer to $W/SiO_2$ multilayer Bragg reflectors on the resonance characteristics of film bulk acoustic wave resonator (FBAR) devices are presented. Main resonance peaks could be significantly shifted to higher frequency, mainly due to the addition of Cr adhesion layer to multilayer Bragg reflectors and control of the bottom electrode thickness as well. The FBAR devices with the Cr adhesion layer in Bragg reflectors could result in much more improved resonance characteristics at about 3 GHz in terms of return loss and Q-factor.

• Journal of Sensor Science and Technology
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• v.30 no.1
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• pp.56-60
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• 2021

In this study, the relationship between the transmitted light intensity and full-width-at-half-maximum (FWHM) of a Fabry-Perot filter was investigated. The measured refractive indices and absorption coefficients of the fabricated thin films were applied to the Fabry-Perot filter via simulations using optical software. Although considerable research has been conducted on Fabry-Perot filters, this study focused on the usefulness of 4.26-㎛ infrared filtering in carbon dioxide detection. Optical analysis was performed considering the effects of the thickness, refractive indices, and number of thin films in a distributed Bragg reflector. Ultimately, a clear trade-off relationship was observed wherein the transmitted light intensity decreased as the number of multilayers increased; however, the FWHM was observed to be narrower.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.437-440
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• 2007

This paper presents the improvement of the resonance characteristics of film bulk acoustic-wave resonator (FBAR) devices fabricated on multilayer Bragg reflectors (BRs) based on inserting ultra-thin chromium (Cr) adhesion layers into BRs and post-annealing processes. The measurements show excellent improvement of return loss $(S_{11})$ and Q-factor by the combined use of Cr adhesion layers and thermal treatments particularly for 120 minutes at $200^{\circ}C$.

• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.316-319
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• 2007

This paper presents some methods to improve the resonance characteristics of film bulk acoustic-wave resonator (FBAR) devices. The FBAR devices were fabricated on multilayer Bragg reflectors (BR) into which very thin chromium (Cr) adhesion layers were inserted, followed by several kinds of thermal annealing processes. These methods resulted in an excellent device improvement in terms of return loss and Q-factors.