TEASAR (TErahertz Active Source ARrays)An all-silicon reconfigurable terahertz source array for active imaging beyond 300 GHz
Final Report Abstract
Today’s battery-operated CMOS camera systems are in the need of efficient sources and illumination concepts for building an all-silicon solution for terahertz imaging. The aim of TEASAR was to develop low-cost single-chip source arrays in silicon process technologies above 300 GHz and to demonstrate global illumination scenarios for active terahertz imaging systems with angular, spatial, frequency and polarization diversity. The outcomes of this work are a milestone towards solving the issue of high power sub-mm CW radiation sources. Power combining of source arrays offers a novel opportunity of THz free space radiation sources with a mW-level output power. Conventional THz sources coherently lock all oscillators in phase. However, the circuit scheme of the investigated 4 × 4 source array locks the oscillators only on the pixel-level. The major challenge in the field of THz source arrays is to combine the beam of the individual source pixels into a final diffuse radiation beam. Integrated antennas in silicon process technologies are glued to the backside of a silicon lens. However, placing a source array chip into the elliptical focus of such a lens ensures a high directivity but generates under-sampling of the illuminated object plane. Within TEASAR, three approaches for providing a homogeneous object illumination have been investigated: i) super-array arrangement, ii) external diffusers and iii) reducing the silicon lens extension. For the first approach, two high directive source arrays have been rotated for 12.5 degrees which increased the 10-dB fill factor from 10.9 % to 61 %. Through the second approach, based on specially developed optical diffusers coupled to a single high directive source module, the object plane gets illuminated homogeneously. However, the third approach of decreasing the pixel-directivity holds the best efficiency performance and diffuseness of the radiated power compared to the usage of external optical diffusers. Furthermore, this solution allows a compact high output power diffuse radiation source above 300 GHz which can compete on output power with commercial discrete split-block systems. In addition, a global illumination concept was examined during TEASAR for which a 2 × 1 as well as a 2 × 2 super-array arrangement have been analysed. Along these lines, it has been shown for the very first time that radiation of multiple source modules can be combined to double / quadruple the illuminated area or the radiated power. Spatial, angular and polarization diversity have been characterized for these super-array arrangements. The results offer a milestone for THz active diffuse illumination scenarios in reflection mode, where an object can be multidirectionally illuminated through arranging several source modules in a circular way. During the project, an integrated 130 nm SiGe HBT source radiating 0.235 mW (-6.3 dBm) at around 430 GHz was also developed. A 3D-Huygens simulation demonstrated the concept of a 64-pixel source array for a directive as well as a diffuse radiation source module. The total radiated power can reach up to 15 mW (11.8 dBm). This source allows a smaller pitch caused by its single-ended structure compared to the investigated source module, where a differential topology was implemented. The occupied chip area would be 20 % larger in comparison to the investigated 16-pixel source module. The simulation results for a 8 x 8 source array coupled to a 20 mm silicon lens with an extension length of 2.92 mm show a pixel-directivity of at least 23.8 dBi by providing a diffuse radiation of the combined beam. The ray-tracing as well as the 3D-Huygens simulations, specially developed within TEASAR to solve the issue of inhomogeneous illumination at the object plane, will also be useful for future modelling of large 3D electromagnetic fields in an appropriate time.
Publications
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“A 0.53 THz reconfigurable source module with up to 1 mW radiated power for diffuse illumination in terahertz imaging applications,” IEEE Journal of Solid-State Circuits, vol. 49, no. 12, 2938–2950, 2014
U. R. Pfeiffer, Y. Zhao, J. Grzyb, R. Al Hadi, N.Sarmah, Neelanjan, W. Föster, H. Rücker, and B. Heinemann
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“SiGe transmitter and receiver circuits for emerging terahertz applications,” in Compound Semiconductor Integrated Circuit Symposium (CSICs), 2014 IEEE, IEEE, 2014, 1–4
U. R. Pfeiffer, J. Grzyb, R. Al Hadi, N. Sarmah, K. Statnikov, S. Malz and B. Heinemann
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“A 246 GHz fundamental source with a peak output power of 2.8 dBm,” in Microwave Integrated Circuits Conference (EuMIC), 2015 10th European, IEEE, 2015, 184–187
N. Sarmah, B. Heinemann and U. R. Pfeiffer
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“An antenna-coupled 0.49 THz SiGe HBT source for active illumination in terahertz imaging applications,” in 2015 10th European Microwave Integrated Circuits Conference (EuMIC), IEEE, Sep. 2015, pp. 180–183
P. Hillger, J. Grzyb, R. Lachner, and U. Pfeiffer
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“An antenna-coupled 0.49 THz SiGe HBT source for active illumination in terahertz imaging applications,” in Microwave Integrated Circuits Conference (EuMIC), 2015 10th European, IEEE, 2015, 180–183
P. Hillger, J. Grzyb, R. Lachner and U. R. Pfeiffer
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“A 210-270- GHz Circularly Polarized FMCW Radar With a Single-Lens-Coupled SiGe HBT Chip,” IEEE Transactions on Terahertz Science and Technology, vol. 6, no. 6, pp. 771–783, Nov. 2016
J. Grzyb, K. Statnikov, N. Sarmah, B. Heinemann, and U. R. Pfeiffer
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“A lens-integrated 430 GHz SiGe HBT source with up to -6.3 dBm radiated power,” in Radio Frequency Integrated Circuits Symposium (RFIC), 2017 IEEE, IEEE, 2017, 160–163
P. Hillger, J. Grzyb, S. Malz, B. Heinemann and U. R. Pfeiffer
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“A 65 Gbps QPSK one meter wireless link operating at a 225-255 GHz tunable carrier in a SiGe HBT technology,” in 2018 IEEE Radio and Wireless Symposium (RWS), IEEE, Jan. 2018, pp. 146–149
P. Rodriguez-Vazquez, J. Grzyb, N. Sarmah, B. Heinemann, and U. R. Pfeiffer
