| Terahertz (THz) detector is an important component in terahertz science and technologies, which paves the road for both weak terahertz signal detection and terahertz imaging. One of these terahertz detectors, the Nb5N6microbolometer, with its room temperature working conditions, easy fabrication, high sensitivity, short response time, and ease for super-large array integration, provides an excellent approach for terahertz detection. The main contents in this dissertation are classified as follows:1. A novel room-temperature microbolometer array chip consisting of a Nb5N6thin film microbridge and a dipole planar antenna and applied as a THz detector is described in this paper. Due to the high temperature coefficient of the resistance, which is as high as-0.7%K-1, of the Nb5N6thin film, such an antenna-coupled microbolometer is ideal for detecting signals from0.22THz to0.33THz. The dc responsivity, calculated from the measured Ⅰ-Ⅴ curve of the Nb5N6microbolometer, is about760V/W at the bias current of0.19mA. A typical noise voltage as low as10nV/VHz yields a low noise equivalent power (NEP) of1.3×10-11W/√Hz at modulation frequency above4kHz. This work could offer another way to develop a large scale focal plane array in silicon with simple techniques and low costs.2. We also researched the interference effects of the substrate on the performance of the device. With the above effects, we used substrates with different thicknesses to change resonant frequencies, and designed Nb5N6microbolometer devices with substrate resonant structures to further increase the coupling efficiencies of the devices.3. We designed and fabricated square diffractive microlens with five staircases in THz wave band for Nb5N6microbolometers. We calculated the power distribution at the focal plane of the microlens by a FDTD method. The results show the staircase square diffractive lens has a good ability of focusing, which can improve the coupling efficiency of the incident power into the Nb5N6microbolometers. We measured the voltage response of the Nb5N6microbolometer integrated with diffractive microlens. We find it has16.5times larger response than of the Nb5N6microbolometer fabricated on the silicon substrate. Preliminary results for THz radiation show that Nb5N6microbolometers integrated with diffractive microlens array as room-temperature detectors yield good optical voltage responsivity of74V/W and noise equivalent power (NEP) of1.1×10-10W/√Hz. Development of a focal plane array (FPA) using such devices as detectors is favorable since diffractive microlens array has many advantages,such as light weight, low absorption loss, high resolution, and the most important point is that the microlens array can be easily integrated by ready mass production using standard micro-fabrication techniques.4. The electric field distribution on the extended hemispherical silicon lens was analysised by the finite difference time-domain (FDTD) methold. Quasi-optical receivers were constituted by combining the extended hemispherical lens and antenna-coupled Nb5N6microbolometers. We present the experimental demonstration of a quasi-optical THz detector. It is based on the series connection of three Nb5N6microbolometers. This detector is of high responsivity and broadband response to THz signals. The maximum optical responsivity is428V/W at0.245THz, and the minimum is102V/W at0.367THz. The thermal time constant of the detector have been demonstrated to be1.3μs, which is similar to the ones obtained for single element microbolometers. These results make arrays of antenna-coupled Nb5N6microbolometers be promising for development of pixels in THz focal plane arrays.5. To further confirm the practicality of the Nb5N6microbolometer THz detectors, we applied detectors with several different structures to the THz imaging system, and obtained good imaging results of the imaged objects. This application laid the technological foundation for the application of Nb5N6microbolometer in THz fast and large-scale detection and imaging system. |
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