Silicon Micromachined Heterodyne Array Receiver at 1.9 THz

We are proposing a new concept of integrated component development technology at submillimeter wavelengths that will dramatically simplify the fabrication, assembly, and integration of large focal plane arrays and imagers. This technology has the potential to significantly increase the pixel count of detector arrays and reduce the mass, volume, and complexity of array receivers for a broad range of applications in astrophysics and earth sciences. We will develop and demonstrate a highly integrated silicon-micromachined array receiver at 1.9 THz based on advanced dual-polarized, sideband-separating, balanced heterodyne mixers. The receiver front-end will be integrated with a novel micro-lens antenna array. We will design full-waveguide-band 90-degree quadrature hybrids, orthomode transducers (OMT), polarization twists, in-phase power splitters, and directional couplers at 1.9 THz; fabricate them using deep reactive ion etching (DRIE) based silicon micromachining, integrate them with existing HEB mixers at 1.9 THz; and test and fully characterize them in our laboratory. The scientific importance of high-resolution spectroscopic observations at submillimeter wavelengths is underscored by the key role of heterodyne spectrometers in the ESA cornerstone Herschel Space Observatory as well as the ground-based ALMA and airborne SOFIA. Star formation and key phases of galaxy evolution occur in region enshrouded by dust that obscures them at infrared and optical wavelengths, while the temperature range of the interstellar medium of ten to a few thousand Kelvin in these regions excites a wealth of submillimeter-wave spectral lines. With high-resolution spectroscopy, resolved line profiles reveal the dynamics of star formation, directly revealing details of turbulence, outflows, and core collapse. Observations of emission from ionized species such as C+ at 1900.53690 GHz (158 um), allow one to directly measure the cooling of the diffuse component of the interstellar medium, measure the amount of "dark gas" in which cannot be traced by CO, and analyze large-scale motions of this material from which giant molecular clouds form. The primary motivation to develop multi-pixel array technology arises from the need for future missions to study a wide range of astrophysical topics ranging from planet formation to the large-scale structure of the universe to the monitoring of the earth's atmosphere, this technology effort will also spawn synergistic systems involving other imaging sensors for reconnaissance usage and will help pioneer the emerging uses of the submillimeter-wave spectrum in the homeland security applications. Waveguide circuits have now become a necessity for receivers at terahertz frequencies for their low loss and guided wave properties. However, at frequencies beyond a few hundred gigahertz, the feature sizes of all but the simplest waveguide circuits are too small and the required tolerances are too demanding to be fabricated using conventional machining. In addition, the time-tested technique of building up complex microwave circuits from flanged waveguide components is not suitable for terahertz frequencies due to the losses they incur and reflections they produce. To deal with these issues, a new approach for integrated component development is needed that is compatible with the particular challenges of working at terahertz frequencies. Deep reactive ion etching (DRIE) based silicon micromachined integrated component development is the most promising technology to enable high-performance integrated circuits at terahertz frequencies. Silicon micromachining can achieve small feature sizes with large depths and excellent tolerances, making it ideally suited for fabricating waveguide components which require sharp vertical walls. Moreover, they will allow vertical integration of modular front-end components to a highly sensitive array which will increase pixel counts of heterodyne receivers by many counts. More »