In recent years, the field of terahertz (THz) science and technology has entered a completely new phase of unprecedented expansion that is generating ever growing levels of broad-based international attention. In particular,there have been important advances in state-of-the-art THz technology and very enthusiastic growth in research activities associated with related scientific and industrial applications. One can legitimately argue that the potential payoffs of THz sensing and imaging (THz S&I) to application areas such as defense, security, biology and medicine are the major drivers of this new phenomenon. However, there remain major science and technology "gaps" in the THz regime that must be reconciled before many of the perceived payoffs ever become realizable. Therefore, it is natural to ask the question "Is now the time for THz?" or rather, are these recent events just a repeat of previous cycles in THz overenthusiasm that have been witnessed during the last century? The main goal of this paper is to consider some of the most promising THz S&I applications within the specific context of their particular science and technology challenges in an attempt to credibly judge (or speculate on) their future potential.

Terahertz Frequency Sensing and Imaging: A Time of Reckoning Future Applications?

Several research groups have been actively pursuing antimonide-based electronic devices in recent years. The advantage of narrow-bandgap Sb-based devices over conventional GaAs- or InP-based devices is the attainment of high-frequency operation with much lower power consumption. This paper will review the progress on three antimonide-based electronic devices: high electron mobility transistors (HEMTs), resonant tunneling diodes (RTDs), and heterojunction bipolar transistors (HBTs). Progress on the HEMT includes the demonstration of Ka- and W-band low-noise amplifier circuits that operate at less than one-third the power of similar InP-based circuits. The RTDs exhibit excellent figures of merit but, like their InP- and GaAs-based counterparts, are waiting for a viable commercial application. Several approaches are being investigated for HBTs, with circuits reported using InAs and InGaAs bases.

Antimonide-based compound semiconductors for electronic devices: A review

An antenna having at least one main element and a plurality of parasitic elements. At least some of the elements have coupling elements or devices associated with them, the coupling elements or devices being tunable to thereby control the degree of coupling between adjacent elements. Controlling the degree of coupling allows a lobe associated with the antenna to be steered.

Meta-element antenna and array

A switch arrangement comprises a plurality of MEMS switches arranged on a substrate about a central point, each MEMS switch being disposed on a common imaginary circle centered on the central point. Additionally, and each MEMS switch is preferably spaced equidistantly along the circumference of the imaginary circle. Connections are provided for connecting a RF port of each one of the MEMS switches with the central point.

Single-pole multi-throw switch having low parasitic reactance, and an antenna incorporating the same

InAs/GaSb nanowire heterostructures with thin GaInAs inserts were grown by MOVPE and characterized by electrical measurements and transmission electron microscopy. Down-scaling of the insert thickness was limited because of an observed sensitivity of GaSb nanowire growth to the presence of In. By employing growth interrupts in between the InAs and GaInAs growth steps it was possible to reach an insert thickness down to 25 nm. Two-terminal devices show a diode behavior, where temperature-dependent measurements indicate a heterostructure barrier height of 0.5 eV, which is identified as the valence band offset between the InAs and GaSb. Three-terminal transistor structures with a top-gate positioned at the heterointerface show clear indications of band-to-band tunnelling.

InAs/GaSb Heterostructure Nanowires for Tunnel Field-Effect Transistors

Small-area antimonide-based backward diodes for zero-bias millimeter-wave detection have been fabricated and tested. The devices were fabricated using high-resolution I-line stepper lithography, allowing accurate control of the small device active area required for operation at W-band. The devices exhibit excellent measured performance from 1-110 GHz, with responsivities when driven from a 50-/spl Omega/ source of 2540 V/W at 95 GHz. This translates to a projected responsivity of 11.5 /spl times/ 10/sup 3/ V/W at 95 GHz for a conjugately matched detector. The compression characteristics of the detectors have been measured, with 1.2 dB of responsivity compression for an input power of 8 /spl mu/W.

High-performance antimonide-based heterostructure backward diodes for millimeter-wave detection

We have performed accelerated temperature and bias lifetests on single-heterojunction AlInAs/GaInAs/InP bipolar transistors (HBTs) Discrete HBTs were fabricated and stressed at bias conditions of high collector-emitter voltage, typical operating current (V/sub CE/=3 V and J/sub C/=23 kA/cm/sup 2/), and at junction temperatures (T/sub j/) of 205/spl deg/C and 225/spl deg/C Previous lifetests had been presented at higher junction temperatures (T/sub j/>230/spl deg/C) and up to 2000 hours of stress In this work, we report results from stress tests up to 6000 hours Failure criteria defined by base-emitter turn-on voltage (V/sub BE/) and dc-gain (/spl beta/) degradation demonstrate a robust technology with activation energies (E/sub a/) greater than 11 eV and extracted median-time-to-failure (MTTF) in excess of 10/sup 7/ hours at T/sub j/=100/spl deg/C

Reliability and failure criteria for AlInAs/GaInAs/InP HBTs

The current against voltage characteristics of Sb-heterostructure zero-bias millimetre-wave diodes were measured from 15 to 81/spl deg/C. No significant variation in the zero-bias junction resistance or curvature coefficient was found. The new diode is the first that provides temperature independent direct detection capability at and beyond W-band.

Temperature dependence of Sb-heterostructure millimetre-wave diodes

We have developed a new zero bias millimeter wave diode based on quantum tunneling in an InAs/AlSb/GaSb nanostructure. It is ideal for square law radiometry and passive millimeter wave imaging. Excellent sensitivity has been demonstrated at present up to 110 GHz, with higher bandwidth predicted for smaller area diodes.

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S. Thomas

Papers

High-performance antimonide-based heterostructure backward diodes for millimeter-wave detection

Reliability and failure criteria for AlInAs/GaInAs/InP HBTs

Temperature dependence of Sb-heterostructure millimetre-wave diodes

High frequency performance of Sb-heterostructure millimeter-wave diodes