Browsing by Subject "Microbolometers"

Now showing 1 - 4 of 4

Open Access
An all-ZnO microbolometer for infrared imaging
(Elsevier BV, 2014) Kesim, Y. E.; Battal, E.; Tanrikulu, M. Y.; Okyay, Ali Kemal
Microbolometers are extensively used for uncooled infrared imaging applications. These imaging units generally employ vanadium oxide or amorphous silicon as the active layer and silicon nitride as the absorber layer. However, using different materials for active and absorber layers increases the fabrication and integration complexity of the pixel structure. In order to reduce fabrication steps and therefore increase the yield and reduce the cost of the imaging arrays, a single layer can be employed both as the absorber and the active material. In this paper, we propose an all-ZnO microbolometer, where atomic layer deposition grown zinc oxide is employed both as the absorber and the active material. Optical constants of ZnO are measured and fed into finite-difference-time-domain simulations where absorption performances of microbolometers with different gap size and ZnO film thicknesses are extracted. Using the results of these optical simulations, thermal simulations are conducted using finite-element-method in order to extract the noise equivalent temperature difference (NETD) and thermal time constant values of several bolometer structures with different gap sizes, arm and film thicknesses. It is shown that the maximum performance of 171 mK can be achieved with a body thickness of 1.1 μm and arm thickness of 50 nm, while the fastest response with a time constant of 0.32 ms can be achieved with a ZnO thickness of 150 nm both in arms and body. © 2014 Elsevier B.V. All rights reserved.
Open Access
Atomic layer deposition based titanium alloying of zno for microbolometer applications
(2016-07) Temiz, Bilge
Microbolometers are attractive candidates for both military applications and consumer electronics among the uncooled thermal detectors due to their compactness, low cost, comparable performance with photon detectors and CMOS compatibility. The temperature sensitive active material is the most important part of resistive type microbolometers where change in electrical response occurs upon IR radiation. Typical active materials used for this purpose are YBCO and VOx. It was reported in several studies that ZnO has higher TCR value than commercially available active materials. However a temperature insensitive TCR property has not been achieved yet. To improve the TCR property of ZnO, doping with Titanium is proposed in this work. According to Ellingham diagram of oxides which is used generally in extractive metallurgy, it is obvious that titanium oxide is more stable than zinc oxide [1]. Therefore doping with Titanium may reduce oxygen related defects and improve TCR property. Atomic layer deposition (ALD) is used for digital alloying of ZnO with Titanium. Titanium doped ZnO (TZO) films with Ti concentrations 2.5%, 5.9% and 12.2% were deposited using precursors diethylzinc, mili-Q water and tetrekis(dimethylamido)titanium. Then intrinsic defect related elemental characterization were made. Effect of Titanium doping on structure of TZO thin films was discussed. After material characterization, planar microresistors were fabricated in UNAM cleanroom facility. Piranha-HF and solvent cleaning of silicon substrate were performed before microfabrication. Vaksis Handy Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to deposit insulation layer on silicon wafer. Photolithograpy steps were performed using Laurell Spinner system and EVG 620 mask aligner to pattern TZO thin film. Then contact material metallization was performed using Vaksis MIDAS Thermal Evaporator system. Current-voltage characterization of microfabricated resistors was performed before Temperature Coefficient of Resistance (TCR) measurements to see the contact type resistors. Then TCR measurements were done between 15oC and 25oC by applying constant current to the contact pads of resistor. Approximate resistivity values of 5 different samples were calculated. It is shown that proposed TZO active material for resistive type microbolometers has a temperature insensitive and high TCR value.
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.
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 Kemal
We 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).