Browsing by Subject "Bolometers"
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Item Open Access An analysis for the broad-band absorption enhancement using plasmonic structures on uncooled infrared detector pixels(SPIE, 2012-05) Lüleç, S. Z.; Küçük, S. E.; Battal, Enes; Okyay, Ali Kemal; Tanrıkulu, M. Y.; Akın, T.This paper introduces an analysis on the absorption enhancement in uncooled infrared pixels using resonant plasmon modes in metal structures, and it reports, for the first time in literature, broad-band absorption enhancement using integrated plasmonic structures in microbolometers for unpolarized long-wave IR detection. Different plasmonic structures are designed and simulated on a stack of layers, namely gold, polyimide, and silicon nitride in order to enhance absorption at the long-wave infrared. The simulated structures are fabricated, and the reflectance measurements are conducted using an FTIR Ellipsometer in the 8-12 μm wavelength range. Finite difference time domain (FDTD) simulations are compared to experimental measurement results. Computational and experimental results show similar spectral reflection trends, verifying broad-band absorption enhancement in the spectral range of interest. Moreover, this paper computationally investigates pixel-wise absorption enhancement by plasmonic structures integrated with microbolometer pixels using the FDTD method. Special attention is given during the design to be able to implement the integrated plasmonic structures with the microbolometers without a need to modify the pre-determined microbolometer process flow. The optimized structure with plasmonic layer absorbs 84 % of the unpolarized radiation in the 8-12 μm spectral range on the average, which is a 22 % increase compared to a reference structure with no plasmonic design. Further improvement may be possible by designing multiply coupled resonant structures.Item Open Access Analytic modeling of patterned high-Tc superconductive bolometers: film and substrate interface effects(SPIE, 1998) Fardmanesh, Mehdi; Rothwarf, A.Superconducting film and substrate interface effects on the response of superconductive edge-transition bolometers are modeled with a one dimensional thermal model in closed form, for samples with large area patterns compared to the substrate thickness. The results from the model agree with experimental results on samples made of meander line patterned granular YBCO films on crystalline substrates, in both the magnitude and phase of the response versus modulation frequency up to about 100 KHz, the limit of the characterization setup. Using the fit of the calculated frequency response curves obtained from the model to the measured ones, values of the film-substrate and substrate-holder thermal boundary resistance, heat capacity of the superconducting film, and the thermal parameters of the substrate materials could be investigated. While the calculated magnitude and phase of the response of the SrTiO3 substrate samples obtained from the model is in a very good agreement with the measured values, the calculated response of the LaAlO3 and MgO substrate samples deviate slightly from the measured values at very low frequencies, increasing with an increase in the thermal conductivity of the substrate material. Using the fit of the calculated response to the measured values, film-substrate thermal boundary resistances in the range of 4.4* 10-3 to 4.4* 10-2 K-cm2-w-1 are obtained for different substrate materials. The effect of substrate optical absorption in the response of the samples is also investigated.Item Open Access Analytic thermal modeling for dc-to-midrange modulation frequency responses of thin-film high-Tc superconductive edge-transition bolometers(Optical Society of America, 2001) Fardmanesh, M.Thin-film superconductive edge-transition bolometers are modeled with a one-dimensional analytic thermal model with joule heating, film and substrate materials, and the physical interface effects taken into consideration. The results from the model agree well with the experimental results of samples made of large-meander-line Yba2Cu3O7-x films on crystalline SrTiO3, LaAlO3, and MgO substrates up to 100 kHz, the limits of the experimental setup. Compared with the results of the SrTiO3 substrate samples, the results from the model of the LaAlO3 and the MgO substrate samples deviate slightly from the measured values at very low modulation frequencies (below ∼10 Hz). The deviation increases for higher thermal-conductive substrate materials. When the model was used, the substrate absorption and the thermal parameters of the devices could also be investigated. © 2001 Optical Society of America.Item Open Access Atomic-layer-deposited zinc oxide as tunable uncooled infrared microbolometer material(Wiley-VCH Verlag, 2014) Battal, E.; Bolat, S.; Tanrikulu, M. Y.; Okyay, Ali Kemal; Akin, T.ZnO is an attractive material for both electrical and optical applications due to its wide bandgap of 3.37 eV 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 °C. Spectral noise characteristics of thin films grown at various temperatures are also investigated and show that the 120 °C grown ZnO has a corner frequency of 2 kHz. With its high TCR value and low electrical noise, atomic-layer-deposited (ALD) ZnO at 120 °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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access Broadband absorption enhancement in an uncooled microbolometer infrared detector(SPIE, 2014) Kebapcı, B.; Dervişoğlu, Ö.; Battal, Enes; Okyay, Ali Kemal; Akın, T.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.Item Open Access Digitally alloyed ZnO and TiO2 thin film thermistors by atomic layer deposition for uncooled microbolometer applications(AVS Science and Technology Society, 2017) Tilkioğlu, Bilge T.; Bolat, Sami; Tanrıkulu, Mahmud Yusuf; Okyay, Ali KemalThe authors demonstrate the digital alloying of ZnO and TiO2 via atomic layer deposition method to be utilized as the active material of uncooled microbolometers. Depositions are carried out at 200 °C. Crystallinity of the material is shown to be degraded with the increase of the Ti content in the grown film. A maximum temperature coefficient of resistance (TCR) of −5.96%/K is obtained with the films containing 12.2 at. % Ti, and the obtained TCR value is shown to be temperature insensitive in the 15-22 °C, thereby allowing a wide range of operation temperatures for the low cost microbolometers. © 2017 American Vacuum Society.Item Open Access Effect of the superconductivity transition on the response of YBCO edge transition bolometers(2003) Bozbey, Ali; Fardmanesh, Mehdi; Askerzade, I. N.; Banzet, M.; Schubert, J.Dependence of the phase and magnitude of the response of Y-Ba-Cu-O edge transition bolometers on the superconducting transition is studied. The responses of both large and small area devices were investigated and several anomalies are observed. The response of small area LaAlO3 devices considerably differed from that expected based on the dR/dT curve. This discrepancy is observed to be strongly dependent on the superconducting transition. Both the phase and magnitude/(dR/dT) of the response of the devices showed abrupt changes for below the Tc-onset when measured versus temperature, while the phase variation also showed strong dependence on the modulation frequency. We present the analysis and propose mechanisms responsible for the modulation frequency dependence of the response characteristics versus temperature, within the superconductivity transition region of the devices.Item Open Access Ge/SiGe quantum well p-i-n structures for uncooled infrared bolometers(IEEE, 2011-09-18) Atar, F. B.; Yesilyurt, A.; Onbasli, M. C.; Hanoglu, O.; Okyay, Ali KemalThe temperature dependence of current is investigated experimentally for silicon-germanium (Si-Ge) multi-quantum-well p-i-n devices on Si substrates as uncooled bolometer active layers. Temperature coefficient of resistance values as high as-5.8%/K are recorded. This value is considerably higher than that of even commercial bolometer materials in addition to being well above the previous efforts based on CMOS compatible materials.Item Open Access HTSC superconducting edge-transition infrared detectors; principles, fabrication, and characterization(Bilkent University, 2000) Akram, RizwanSince the discovery of High temperature superconductors, superconductivity became one of the fast emerging technologies being used in numerous applications ranging from large-scale to small-scale applications such as IR,-detectors. High temperature superconductors such as YBü'zCuíOj due to their properties are the prime candidates for the fabrication of detectors. Their responsivity and detectivity can be improved by changing the design and SC characteristics. In this thesis, one-dimensional thermal model has been considered to improve the characteristic parameters of the SC. Based on the model, the annealing profile and manufacturing process is modified to further enhance the responsivity and detectivity of the detectors. A characterization setup is established to perform dc & ac measurements at low temperatures. In order to improve the cryogenic setu]), a thermal equivalent model for the system is also proposed.Item Open Access LWIR all-atomic layer deposition ZnO bilayer microbolometer for thermal imaging(SPIE, 2017) Poyraz, M.; Gorgulu, K.; Sisman, Z.; Tanrikulu, M. Y.; Okyay, Ali KemalWe propose an all-ZnO bilayer microbolometer, operating in the long-wave infrared regime that can be implemented by consecutive atomic layer deposition growth steps. Bilayer design of the bolometer provides very high absorption coefficients compared to the same thickness of a single ZnO layer. High absorptivity of the bilayer structure enables higher performance (lower noise equivalent temperature difference and time constant values) compared to single-layer structure. We observe these results computationally by conducting both optical and thermal simulations. © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE).Item Open Access A plasmonically enhanced pixel structure for uncooled microbolometer detectors(SPIE, 2013) Erturk O.; Battal, Enes; Kucuk, S.E.; Okyay, Ali Kemal; Akin, T.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 SPIE.Item Open Access Temperature dependence of the phase of the response of YBCO edge-transition bolometers: effects of superconductivity transition and thermal parameters(Institute of Physics Publishing, 2003) Fardmanesh, M.; Askerzade, İ. N.The variation of the phase of the response of YBCO edge-transition bolometers on crystalline MgO substrate is found to be dependent on the normal-superconducting transition. The phase of the response for T < Tc increased at low modulation frequencies where the thermal diffusion length into the sample substrate from the top absorbing YBCO film is longer than the substrate thickness. The substrate/cold-head boundary resistance mainly dominates the thermal conductance of our samples at low frequencies. This transition-dependent change of the phase of the response is interpreted to be due to the effects of the order parameter of the YBCO material on the phonon spectrum and hence the determining Kapitza boundary resistance. The phase of the response decreased at high modulation frequencies where the thermal diffusion length into the substrate is less than the substrate thickness. The results of our analytical model for the low modulation frequencies agree well with the measured values for temperatures close to the Tc-zero.