Emerging Electronic Devices for THz Sensing and Imaging

Continuing advances in scaling of conventional semiconductor devices are enabling mainstream electronics to operate in the millimeter-wave through THz regime. At the same time, however, novel devices and device concepts are also emerging to address the key challenges for systems in this frequency range, and may offer performance and functional advantages for future systems. In addition to new devices, advances in integration technology and novel system concepts also promise to provide substantial system-level performance and functionality enhancements. Several emerging devices and device concepts, as well as circuit-level concepts to take advantage of them, are discussed. Based on unconventional semiconductor device structures and operational principles, these devices offer the potential for significantly improved system sensitivity and frequency coverage. When combined in arrays, features such as polarimetric detection and frequency tunability for imaging can be achieved. As examples of emerging devices for millimeter-wave through THz sensing and imaging, heterostructure backward diodes in the InAs/AlSb/GaSb material system and GaN-based plasma-wave high electron mobility transistors (HEMTs) will be discussed. Based on interband tunneling, heterostructure backward diodes offer significantly increased sensitivity and extremely low noise for direct detection applications, and have been demonstrated with cutoff frequencies exceeding 8 THz. The plasma-wave HEMT is an emerging device concept that, by leveraging plasma-wave resonances in the two-dimensional electron gas within the channel of the HEMT, offers the prospect for both tunable narrowband detection as well as low-noise amplification at frequencies well into the THz. These emerging devices are both amenable to direct integration within compact planar radiating structures such as annular slot antennas for realization of polarimetric detection and frequency tuning for spectroscopy and imaging.