Suspended GaN beams and membranes on Si as a platform for waveguide-based THz applications

Abstract

Epitaxial growth of ultra-thin NbN films on AlxGa1-xN buffer-layers S Krause, D Meledin, V Desmaris et al. IntroductionThe exploration of the THz frequency range is constantly gaining speed and numerous applications have emerged within research, security, astronomy, biomedicine and metrology in recent years [1][2][3]. The main reason for this relatively late development can be attributed to several technological challenges that had to be overcome. As the dimensions of microwave components usually scale with the wavelength, their size presents a serious issue when the device operation frequency is approaching the THz range. This manifests itself in certain performance limitations due to parasitic capacitances, thermal issues, the excitation of unwanted electromagnetic (EM) modes or excessive RF losses in conductors as the skin depth may approach the roughness of the metal surface. Waveguides for guiding THz EM waves offer wideband operation and full confinement of the fields, yet they are also miniaturized and demand high surface quality and accuracy on the waveguide dimensions and alignment. Several different micro fabrication techniques [4] were developed for this purpose and are based on copper electroforming over a thick sacrificial photo resist mold [5,6] or deep Si etching processes [7]. In waveguidebased THz components, the actual substrate becomes more of a delicate membrane-like structure, which reduces the electrical loading of the waveguide and excludes substrate modes. However, it is difficult to manipulate and to place such beams suspended inside the waveguide with high alignment precision. Typically beam leads [8] made of thick electro-plated gold are used for the electrical contacting, however, once the device is mounted it can neither be modified nor removed in a non-destructive matter. One possible approach to overcome the aforementioned issues is based on a Π-shaped Si support frame holder [9], which keeps a thin Si membrane hosting the active device suspended. This concept has been successfully AbstractWe demonstrate the suitability of employing suspended GaN beams on a Π-shaped Si frame for waveguide-based cryogenic THz components and systems. This concept addresses major challenges and provides eased device handling, cryogenic operation, micron-alignment possibilities, high integratability and allows the electrical contacting by using bonding wires. In particular, a balanced hot electron bolometer (HEB) mixer was implemented for frequencies at 1.3 THz with state-of-the-art IF performance, which combines micro-machined all-metal waveguide components in conjunction with a suspended GaN beam. In addition, in order to accomplish a proper design of active or passive components, the accurate knowledge of the effective dielectric constant at THz frequencies is crucial when such membranes are employed. Thus, a direct measurement method based on a resonance structure and an S-parameter measurement between 1 THz and 1.5 THz is also presented.Keywords: THz components, GaN on Si, HEB, waveguide (Some f...

Noise Characterization and Modeling of GaN-HEMTs at Cryogenic Temperatures

“…with gds=1/Rds. Tg and Td are the only unknowns in (5), and are treated as fitting parameters. Since the four noise paraments of the device are derived from its noise correlation matrix, they can also be expressed as function of Td and Tg.…”

“…In particular, the choice of the transistors can be a key determinant of the overall noise performance of the radio-astronomy receivers [4]. In addition to their potential natural integration with heterodyne mixers [5] [6], the superior linearity and dynamic range of GaN HEMTs over conventional technologies make them very attractive for radio-astronomy cryogenic instrumentation and inherently excellent robustness against Radio Frequency Interference (RFI). M.A.…”

Fabrication of GaN cantilever on GaN substrate by photo-electrochemical etching

“…3) Previous GaN MEMS devices reported to date were fabricated by the heteroepitaxial growth of a GaN film on a silicon (Si) substrate, which contains a higher dislocation density than that grown on a free-standing GaN substrate. [4][5][6][7][8][9][10] It was reported that the lower dislocation density increases the quality factor of MEMS devices. 11) Furthermore, GaN MEMS devices on free-standing GaN substrates are more advantageous MEMS devices for use in harsh environments than those grown on Si substrates.…”