Highly scaled indium phosphide (InP) heterojunction bipolar transistor (HBT) technologies have been demonstrated with maximum frequencies of oscillation ( f max) of >1 THz and circuit operation has been extended into the lower end of the terahertz (THz) frequency band. InP HBTs offer high radio-frequency (RF) output power density, millivolt (mV) threshold uniformity, and high levels of integration. Integration with multilevel thin-film wiring permits the realization of compact and complex THz monolithic integrated circuits (TMICs). Circuit results reported from InP HBT technologies include: 200-mW power amplifiers at 210 GHz, 670-GHz amplifiers and fundamental oscillators, and fully integrated 600-GHz transmitter circuits. We review the state of the art in THz-capable InP HBT devices and integrated circuit (IC) technologies. Challenges in extending transistor bandwidth and in circuit design at THz frequencies will also be addressed.

We report on the development of a 0.25-μm InP HBT IC technology for lower end of the THz frequency band (0.3-3 THz). Transistors demonstrate an extrapolated fmax of >;800 GHz while maintaining a common-emitter breakdown voltage (BVCEO) >;4 V. The transistors have been integrated in a full IC process that includes three-levels of interconnects, and backside processing. The technology has been utilized for key circuit building blocks (amplifiers, oscillators, frequency dividers, PLL, etc), all operating at ≥300 GHz. Next, we report a series of fundamental oscillators operating up to 0.57 THz fabricated in a 0.25-μm InP HBT technology. Oscillator designs are based on a differential series-tuned topology followed by a common-base buffer, in a fixed-frequency or varactor-tuned scheme. For ≥400 GHz designs, a subharmonic down-conversion mixer is integrated to facilitate spectrum measurement. At optimum bias, the measured output power was -6.2, -5.6, and -19.2 dBm, for 310.2-, 412.9-, and 573.1-GHz designs, respectively, with PDC ≤ 115 mW. Varactor-tuned designs demonstrated 10.6-12.3 GHz of tuning bandwidth up to 300 GHz.

Two antimonide-based compound semiconductor (ABCS) microstrip MMICs, single-stage and three-stage ultra-low-power wideband 0.01-11 GHz low-noise amplifiers using 0.1-mum gate length InAs/AlSb metamorphic HEMTs, have been fabricated and characterized on a GaAs substrate. From 0.3-11 GHz, the single-stage wideband LNA demonstrated a typical associated gain of 16 dB with less than 1.7 dB noise figure (2-11 GHz) at 5mW DC power dissipation, and the three-stage wideband LNA demonstrated a typical associated gain of 30 dB with less than 2.6 dB noise figure (2-11 GHz) at 7.5mW DC power dissipation. We believe these low noise amplifier MMICs demonstrate the lowest DC power consumption with the highest gain-bandwidth product of any MMIC to date. These results demonstrate the outstanding potential of ABCS HEMT technology for ultra-low-power wideband applications

A 100-element 10-GHz grid amplifier has been developed. The active devices in the grid are chips with heterojunction bipolar transistor (HBT) differential pairs that include a resistive network to provide self-bias to the base. The planar metal grid structure was empirically designed to provide effective coupling between the HBTs and free space. Two independent measurements, one with focusing lenses, the other without, were used to measure the gain of the grid. In each case the peak gain of the grid was 10 dB at 10 GHz with a 3-dB bandwidth of 1 GHz. The input and output matches are better than 15 dB at 10 GHz. The maximum output power is 450 mW, and the minimum noise figure is 7 dB. Tests show that the grid is quite tolerant of failures-the output power dropped by only 1 dB when 10% of the inputs were detuned. The device amplifies beams with incidence angles up to 30 degrees with less than a 3-dB drop in power.< >

Although quasi-optical techniques are applicable to a large variety of solid-state devices, special attention is given to transistors, which are attractive because they can be used as either amplifiers or oscillators. Experimental results for MESFET bar-grid and planar grid oscillators are presented. A MESFET grid amplifier that receives only vertically polarized waves at the input and radiates horizontally polarized waves at the output is discussed. These planar grids can be scaled for operation at millimeter- and submillimeter-wave frequencies. By using modern IC fabrication technology, planar grid oscillators and amplifiers containing thousands of devices can be built, thereby realizing an efficient means for large-scale power combining. >

The authors present a Schottky diode grid mixer suitable for mixing or detecting quasi-optical signals. The mixer is a planar bow-tie grid structure periodically loaded with diodes. A simple transmission line model is used to predict the reflection coefficient of the grid to a normally incident plane wave. The grid mixer power handling and dynamic range scales as the number of devices in the grid. A 10-GHz 100-element grid mixer has shown an improvement in dynamic range of 16.3 to 19.8 dB over an equivalent single-diode mixer. The conversion loss and noise figure of the grid are equal to those of a conventional mixer. The quasi-optical coupling of the input signals makes the grid mixer suitable for millimeter-wave and submillimeter-wave applications by eliminating waveguide sidewall losses and machining difficulties. The planar property of the grid potentially allows thousands of devices to be integrated monolithically.< >

Keywords—low noise amplifier, antimonide-based compound semiconductor (ABCS) HEMT, InAs/AlSb HEMT. Abstract—Several antimonide-based compound semiconductor (ABCS) microstrip MMICs, an X-Band low-noise amplifier and an rf switch, using 0.1-µm gate length Antimonide Based Compound Semiconductor (ABCS) metamorphic InAs/AlSb HEMTs, have been fabricated and characterized on a 50 µm GaAs substrate. The compact 0.7 mm2 two-stage X-band LNA demonstrated a 1.25 dB noise-figure at 10 GHz with an associated gain of 22.3 dB. The measured dc power dissipation of the ABCS LNA was an ultra-low 1.6mW per stage, or 3.2 mW total which is less than one-tenth the dc power dissipation of a typical equivalent InGaAs/AlGaAs/GaAs HEMT LNA. Operation with degraded gain and noise figure at 0.98 mW total dc power dissipation is also verified. The compact 0.9 mm2 single- pole double-throw X-band RF switch demonstrated a 0.99 dB on-state insertion loss and an off -state isolation of > 32 dB. These results demonstrate the outstanding potential of the ABCS HEMT technology for low-power X-band applications. Fig. 1. A photomicrograph of the two-stage ABCS HEMT MMIC X-band LNA. The compact die measures 1.4mm by 0.7 mm with a thickness of 50 µm.