Imaging in the Terahertz (THz) region has drawn attention in recent years, but the nature of the THz frequency regime causes some drawbacks in imaging such as long wavelength, high cost, and low emission levels at room temperature. Because of the high atmospheric absorption of THz waves, fabrication of a microbolometer pixel that works in the sub-1 THz frequency regime is necessary. Large pixel pitches due to longer wavelengths and the resulting higher thermal mass pose a difficult challenge. Due to those limitations, a unique design of an absorber is essential for THz microbolometers. This study investigates the use of absorbers based on novel materials and alloys with the goal of developing efficient absorbers in small pixel pitches. First, thin layer metal absorbers typically used in commercial IR microbolometers are characterized in terms of absorption performance in the sub-1 THz region. Thin films based on metal alloys such as TiAlV show a markedly lower absorption in this region than in the IR. To improve the performance of these absorbing layers and reduce pixel pitches. Use of effective media based on the mixture of dielectric materials and metals with patterned thin films are investigated to develop unique absorbing thin layers. It is seen that with the use of an effective medium whose complex dielectric constant is tailored appropriately, efficient absorption of sub-1 THz radiation can be achieved.
The microbolometer technology has proved its potential in the Infrared (IR) region due to its low fabrication costs, and room temperature operation, making this technology desirable to be used in various applications, and this interest has recently expanded into the Terahertz (THz) region as well. The detection in microbolometers is achieved through the absorption of THz radiation which subsequently heats up and is sensed by the temperature sensitive material at the core of the device. This temperature sensitive material is typically based on VOx, which exhibits a sufficient change in resistance with temperature. While this temperature sensitive material is useful in the IR, the low energy of the THz wave compared to the background radiation makes it a challenge to operate the device at room temperature and show a large change in resistance with respect to the slight change in temperature. Metal doped VOx films can show a better performance however these effects are not well understood in the THz region. In this study, Tungsten (W) doped and undoped VOx films are fabricated and then analyzed using Time Domain THz Spectroscopy. The DC electrical properties of the films as well as their optical behaviors in the region of 0.2-2.0 THz are analyzed as a function of temperature. The metal doping is seen to affect the overall electrical and optical response of the film. Understanding this dependence is key to achieving a better film for applications in the THz region.
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