A thz focal plane imaging array using metamaterial-inspired bolometer and wafer-level integrated focusing elements

There is substantial interest in terahertz (THz) for applications in communications, sensing, spectroscopy, imaging, and security. Existing THz systems are built using quasi-optical setups. To reduce cost and make THz integrated circuits a reality, approaches to wafer level integration of components is critically needed. Among the many THz systems, imagers are most desirable as they can be immediately adopted for applications in medical-imaging, security, and non-destructive evaluation (NDE). Many types of detectors have been studied in the design and fabrication of THz focal plane arrays such as Schottky diode rectifiers and bolometers. A typical focal plane array (FPA) pixel element consists of a read-out circuitry, detector device and an antenna or a lens element. A 100x100 element FPA will require 10,000 of these individual elements. Pick-and-place of such a large number of elements within a small foot print is cost prohibitive and technically challenging. Wafer level integration of these elements is desirable to overcome this challenge. Among the many detector elements, bolometers are desirable as they are simple to implement and has the potential to provide high sensitivity. At THz frequencies a bolometer has to be directly coupled to an antenna element to achieve high coupling efficiency. However, antennas thermally load the bolometers and reduce the overall sensitivity. Thus, new approaches to integrating bolometer with antenna elements are needed to achieve high sensitivity. Furthermore, new approaches to improving intrinsic sensitivity of a bolometer in the THz spectral region are needed. Key focus of this research is towards the design and demonstration of THz metamaterial based absorbing structures and their utilization in the design of absorbers for packaging and bolometers for focal plane arrays (FPAs), with major research focus on the design and implementation of THz focal plane arrays. A range of bolometer designs based on metamaterial structures are investigated, including cross, circles, Minkowski, and slit ring resonator which are implemented using high resistive thin metal films. Minituarized unitcells are designed, fabricated and tested in order to improve the sensitivity of the bolometers. For beam focusing and enhanced coupling efficiency to the detector elements (bolometers), wide-band micro-lens array are designed and demonstrated. These microlens arrays can be fabricated at the wafer level using 3D printing. Furthermore, a new plasmonic antenna element is demonstrated that can also be utilized in place of the conventional micro-lens design. This antenna element is integrated in close proximity to the bolometer structures while avoiding thermal loading the detector element. Performance of this antenna element is presented in comparison to conventional antenna elements. A THz imaging array that integrates the detector elements and lens element at the wafer level is demonstrated as part of this research work. Apart from imaging array, under this research work, approaches to fabricating 3D THz components at the wafer level have been demonstrated through the use of 3D printing and deep metal etching processes.