Terahertz Electronics

Applications of terahertz technology include detection of biological and chemical hazardous agents, explosive detection, applications in building and airport security, radio astronomy and space research, and in biology and medicine, for example, in cancer diagnostics. These applications have stimulated a lot of interest in terahertz electronics technologies that have potential to replace or augment more traditional terahertz photonics techniques, such as Time Domain Spectroscopy, Fourier Transform Infrared Spectroscopy and THz dielectric spectroscopy. In addition to THz electronics technologies relying on the frequency multiplication using mostly Schottky diodes, THz transistor technology has emerged, since the device feature sizes have shrunk to the point, where ballistic mode of electron transport becomes important or even dominant. Both Heterostructure Bipolar Transistors (HBTs) and High Electron Mobility Transistors (HEMTs) have reached cutoff frequencies approaching 1 THz. Recently, THz emitters based on the excitation of two-dimensional electron gas (2DEG) plasmons at semiconductor heterointerfaces have been demonstrated opening up a new paradigm in the terahertz electronics. These sources are tunable and can be used together with THz plasmonic resonant and non-resonant detectors using the same technology. The challenge here is to increase efficiency and output power by orders of magnitude. Applications of terahertz technology [1-4] include detection of biological and chemical hazardous agents, explosive detection, applications in building and airport security[5] , earth and ozone hole [6,7] , monitoring, radio astronomy and space research [8,9] , in biology and medicine [10] , for example, in cancer diagnostics. These applications have stimulated a lot of interest in terahertz electronics technologies [11] that have potential to replace or augment more traditional terahertz photonics techniques, such as Time Domain Spectroscopy [12] , Fourier Transform Infrared Spectroscopy [13] and THz dielectric spectroscopy [14] . In addition to THz electronics technologies relying on the frequency multiplication mostly using Schottky diodes [15] , Gunn diodes, and IMPATT diodes (see Figures 1 and 2), THz transistor technology has emerged, since the device feature sizes have shrunk to the point, where ballistic mode of electron transport [16] becomes important or even dominant. Heterostructure Bipolar Transistors (HBTs) and High Electron Mobility Transistors (HEMTs) are capable of operation in the sub-terahertz region [17] , and recently have reached cutoff frequencies approaching 1 THz. University of Illinois group has recently reported on Type-II GaAsSb/InP HBTs with Record fT = 670 GHz and Simultaneous fT, fmax > 400 GHz (see Fig. 3) [18]. In these devices, the compositional grading was used to enhance the electron velocity, hence, increase speed. The Northrop Grumman group reported on Sub a 50 nm InP HEMT Device with fmax greater than 1 THz (see Figure 4). [19] They also demonstrated an amplifier with a 15 dB gain at 340 GHz and predicted that their technology will allow building MMIC amplifiers operating up to 600-700 GHz. The Seoul National University group reported on 610 GHz InAlAs/In0.75GaAs Metamorphic HEMTs with an UltraShort 15-nm-Gate and extracted ballistic velocity of 4.3 × 10 cm/s. [20] Figure 1: Power output versus frequency of available Continuous Wave (CW) Terahertz and Sub-terahertz sources. (From [21]). References: IMPATT, Gunn oscillators [22], BWO [23], frequency multipliers [24], photomixers [25,26] , OP laser [27] and QC lasers [28,29] CS MANTECH Conference, April 14-17, 2008, Chicago, Illinois, USA GaAs Silicon Silicon Carbide 1/f4