Plasmonic Detection of Wide Band Modulated THz Radiations in GaAs Technology Shamsun Nahar ∗ , St´ ephane Blin † , Annick P´ enarier † , Philippe Nouvel † , Dominique Coquillat † , Wojciech Knap † and Mona M. Hella ∗ ∗ ECSE Department, Rensselaer Polytechnic Institute, Troy, NY, 12180 USA † Teralab, Universit´ e Montpellier 2 - CNRS, 34950 Montpellier, France Abstract—A fully integrated THz detection system consisting of an on chip dipole antenna, a plasmonic detector, and a wide band amplifier in 130 nm AlGaAs/InGaAs pHEMT technology is reported. The fabricated chip achieves an absolute responsivity of 3 V /W , while maintaining a 50 dB signal to noise ratio (SNR) over a modulation bandwidth of 8.5 GHz at ∼ 0.3 THz. I. I NTRODUCTION P LASMONIC field effect transistor (FET) based detection has shown a great potential for detecting modulated THz signals for low (< 1 kHz ) and high modulation bandwidths [1]–[4]. Such advances in THz detection combined with pos- sible THz generation in standard technologies using foundry services are expected to generate low cost, mass produced THz cameras, spectrometers, extreme bandwidth communication systems that would widely impact the biomedical, information technology, and security markets. This paper presents the design and measured performance of an on chip antenna- coupled plasmonic detector-amplifier system for wide band modulated THz detection. II. DESIGN OF THZ DETECTOR-AMPLIFIER CHAIN The THz detection chain is formed of an antenna, a plasma- wave FET detector and a wide bandwidth amplifier as shown in Fig. 1(a). The chip is fabricated in Triquint TQP13 tech- nology with unity gain frequency (f T ) of 95 GHz . The technology features two gold metal layers - one local and one air-bridge. The two metal layers are merged to realize the on chip dipole antenna whereas the 85 μm GaAs substrate works as the dielectric medium. A back metal plane has also been included to minimize the high dielectric loss in GaAs substrate with a dielectric constant (ε r ) of 12.9 [5]. The designed antenna is simulated in 3D EM simulator HFSS and the simulated return loss shows a bandwidth of 13 GHz (Fig. 2(a)) with a directivity and efficiency of 3.8 dB and 40% respectively. The plasmonic detector is realized using two depletion mode pHEMT devices with a gate width of 10 μm and a length of 130 nm. The minimum length is chosen to minimize the parasitic loss beyond the effective length (L ef f ) [2]. The low modulation frequency characterization results for the dipole antenna coupled differential HEMT have been reported in [1]. Given the square law behavior of the plasmonic detection, the output signals at the drains of the two detectors have the same polarity, hence, the drain terminals are tied together and connected to the wide band amplifier. The designed amplifier consists of two gain stages followed by a buffer. The stages are ac coupled and the dc bias tee is designed using an on chip metal-insulator-metal (MIM) capacitor (1 pF ) and Epi resistors (2 kΩ). Each stage employs shunt peaking through the resistor-inductor connected at the drains of transistors m 1 - m 3 as shown in Fig. 1(a). The use of shunt peaking extends the bandwidth of the common source amplifier stage. Simulation results show a bandwidth of 9 GHz with a 19 dB gain and 94 mW dc power consumption (Fig. 2(b)). III. MEASUREMENT RESULTS The proposed detector-amplifier chain is characterized for a sinusoidally modulated 295 GHz carrier signal with a 2 kΩ 10μm/ 130nm 2 kΩ 24μm 174.6μm 20μm 3.2nH 275Ω 6 V 3.2nH 300Ω 6 V 3.2nH 50Ω 6 V 1 pF 1 pF 2 kΩ 2 kΩ 2 kΩ 10μm/ 130nm 1 pF m1 m2 m3 Gate bias Gate bias Plasmonic detector Wide band amplifier On chip antenna (a) 700 μm 500 μm (b) Fig. 1. On chip dipole antenna coupled plasmonic detector followed by wide band amplification, (a) system block diagram, and (b) die micrograph.