Atomic-layer-deposited zinc oxide as tunable uncooled infrared microbolometer material

ZnO is an attractive material for both electrical and optical applications due to its wide bandgap of 3.37eV and tunable electrical properties. Here, we investigate the application potential of atomic-layer-deposited ZnO in uncooled microbolometers. The temperature coefficient of resistance is observed to be as high as -10.4%K-1 near room temperature with the ZnO thin film grown at 120 degrees C. Spectral noise characteristics of thin films grown at various temperatures are also investigated and show that the 120 degrees C grown ZnO has a corner frequency of 2kHz. With its high TCR value and low electrical noise, atomic-layer-deposited (ALD) ZnO at 120 degrees C is shown to possess a great potential to be used as the active layer of uncooled microbolometers. The optical properties of the ALD-grown ZnO films in the infrared region are demonstrated to be tunable with growth temperature from near transparent to a strong absorber. We also show that ALD-grown ZnO can outperform commercially standard absorber materials and appears promising as a new structural material for microbolometer-based applications

Galileo Galileo Galilei

that I have read this dissertation and that in my opinion it is full

Aqueous degradation and atomic layer deposition (ALD) stabilization of BaAl2O4: Eu2+, Dy3+long afterglow phosphors

MakaleWOS:000931990700001This paper presents the aqueous degradation mechanisms of BaAl2O4:Eu2+, Dy3+ phosphors and demonstrates an ability to prevent degradation via Al2O3 nano encapsulation of powders by atomic layer deposition (ALD) technique. Phosphor powder is synthesized from the solid-state reaction method. The aqueous degradation of this phosphor is systematically studied. This phosphor is found to hydrolyze and degrade within just 30 min of exposure in water. The degradation of BaAl2O4 host lattice directly affects the blue-green light emission at 497 nm, producing blue-and red-emissions that are peaked at 429 nm and 687 nm, respectively. Hydrated and structural decomposed BaAl2O4 reveals a continuous change in the phase assemblage over 30 days of immersion. To prevent this rapid degradation, use of a protective nanocoating was investigated. 10 nm Al2O3 coatings were applied to the surface of the phosphor powder via ALD. ALD coated BaAl2O4:Eu2+,Dy3+ phosphor retains its phosphorescence for at least 7 days of water exposure. Successful encapsulation of such phosphor particles will make them possible to use in aqueous applications or store in long-term humid environments.TUBITAK, International Doctoral Research Fellowship Programm

Broadband absorption enhancement in an uncooled microbolometer infrared detector

This paper introduces a method for a broadband absorption enhancement in the LWIR range (8-12 µm), in single layer microbolometer pixels with 35 μm pitch. For the first time in the literature, this study introduces a very simple and low cost approach to enhance the absorption by embedding plasmonic structures at the same level as the already existing metallic layer of a microbolometer pixel. The metal layer comprises the electrode and the arm structures on the body. Even though the periodicity of the plasmonic structures is slightly disturbed by the placement of the electrodes and the connecting metal, the metal arms and the electrodes compensate for the lack of the periodicity contributing to the resonance by their coupling with the individual plasmonic resonators. Various plasmonic structures are designed with FDTD simulations. Individual, plasmonically modified microbolometer pixels are fabricated, and an increase in the average absorption due to surface plasmon excitation at Au/Si3N4 interfaces is observed. Plasmonic structures increase the average absorption from 78% to 82% and result in an overall enhancement of 5.1%. A good agreement between the simulation and the FTIR measurement results are obtained within the LWIR range. This work paves the way for integration of the plasmonic structures within conventional microbolometer devices for performance enhancement without introducing additional costs

A Plasmonically Enhanced Pixel Structure for Uncooled Microbolometer Detectors

This paper introduces a method of broadband absorption enhancement that can be integrated with the conventional suspended microbolometer process with no significant additional cost. The premise of this study is that electric field can be enhanced throughout the structural layer of the microbolometer, resulting in an increase in the absorption of the infrared radiation in the long wave infrared window. A concentric double C-shaped plasmonic geometry is simulated using the FDTD method, and this geometry is fabricated on suspended pixel arrays. Simulation results and FTIR measurements are in good agreement indicating a broadband absorption enhancement in the 8 µm-12 µm range for LWIR applications. The enhancement is attained using metallic geometries embedded in the structural layer of the suspended microbridge, where the metallic-dielectric interface increases the average absorption of a 35 µm pixel from 67.6% to 80.1%. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Broadband One Way Propagation via Dielectric Waveguides with Unequal Effective Index

We present an efficient approach for broad band one way propagation of light by parallel and unequal dielectric waveguides leading different effective phase shifts. Three dimensional numerical simulations show that 30% operating bandwidth is achieved

Effect of Au nano-particles on TiO2 nanorod electrode in dye-sensitized solar cells

Au nano particles (NPs) were deposited on vertically grown TiO2 nanorod arrays on FTO substrate by hydrothermal process. Metal nanoparticles were loaded onto the surface of TiO2 nanorods via photochemical reduction process under ultraviolet irradiation. X-ray diffraction (XRD), electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis were used to characterize the as-prepared Au/TiO2 nanorod composites. Current density-voltage (I-V) measurements were obtained from a two-electrode sandwich type cell. The presence of Au nanoparticles can help the electron-hole separation by attracting photoelectrons. Addition of Au nanoparticles to the TiO2 nanorod significantly increased the fill factor and J(SC) (short circuit current density). The application of Au NPs TiO2 nanorods in improving the performance of DSSCs is promising

Terahertz Bandpass Frequency Selective Surfaces on Glass Substrates Using a Wet Micromachining Process

This paper presents terahertz (THz) frequency selective surfaces (FSS) implemented on glass substrate using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz. A fabrication process is proposed where a 100-mu m-thick glass substrate is formed through the HF etching of a standard 500-mu m-thick low cost glass wafer. Using this fabrication process, three separate robust designs consisting of single-layer FSS are investigated using high-frequency structural simulator (HFSS). Based on the simulation results, the first design consists of a circular ring slot in a square metallic structure on top of a 100-mu m-thick Pyrex glass substrate with 70% transmission bandwidth of approximately 0.07 THz, which remains nearly constant till 30A degrees angle of incidence. The second design consists of a tripole structure on top of a 100-mu m-thick Pyrex glass substrate with 65% transmission bandwidth of 0.035 THz, which remains nearly constant till 30A degrees angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100-mu m-thick Pyrex glass substrate with 70% transmission bandwidth of 0.051 THz, which remains nearly constant up to 20A degrees angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications, by using single layer FSS structures manufactured through a relatively simple fabrication process. Practically, these structures are achieved on a fabricated 285-mu m-thick glass substrate. Taking into account the losses and discrepancies in the substrate thickness, the measured results are in good agreement with the electromagnetic simulations