III-V microelectronics technology
These processes have been used to build a mHEMT portfolio featuring 100, 50 and 35 nm gate length technologies, which can be used to fabricate circuits operating at up to 220, 340 and 500 GHz, respectively. A 20 nm gate length process is currently under development, which will replace the 35 nm technology and enable the design of novel terahertz ICs operating at 750 GHz and beyond.
How fast?
In response to the fabrication of faster transistors by our team and others around the world, commercial suppliers are starting to develop and fabricate frequency extension modules for accurate S-parameter measurements of ICs and modules up to approximately 1.1 THz. In addition, RF probes are now available for frequency bands between 0 and 500 GHz.
Although these efforts are welcomed, there are still major challenges associated with ultra-high-frequency measurements. For example, increases in operational frequency come at the penalty of a reduction in the dynamic range of these measurement systems. This increases the noise floor, complicating system calibration, which in turn affects the measurement of both active devices and passive circuit components. The consequence is that as we push further into unchartered frequency domains, we have to devote far more time to accurate calibration, testing and device model extraction in order to ensure successful circuit design and fabrication.
Figure 5. Fraunhofer IAFs mHEMT amplifier modules produce a maximum gain of 21 dB at 300 GHz. Small-signal gain exceeds 19 dB between 295 and 320 GHz
In addition to small-signal amplifiers, we are developing all of the required functional blocks for transmitters and receivers. This ever-expanding portfolio encompasses frequency generation and multiplication, power amplification and frequency conversion.
One example of our efforts is an all-MMIC-based broadband heterodyne receiver front-end spanning 268 - 306 GHz (see Figure 3). The wideband receiver is formed by a monolithic chip set that combines a cascading low- noise amplifier; resistive mixer with integrated frequency- doubler; LO power amplifier; and frequency-multiplier-by- six. The result is a chip that delivers up to 8 dB of conversion gain and has a noise figure of 7.6 dB. These performance figures rival those of state-of-the-art Schottky receivers.
Recently, we have focused our development on sub- millimeter-wave ICs and modules for operation above 300 GHz. This hinges on the realization of TMICs, which is the short-term target. Progress in this direction includes the fabrication of a 320 GHz mHEMT amplifier package with a waveguide module in split-block configuration (see figure 4). The MMIC is thinned down to a substrate thickness of 50 µm, allowing the use of very short bond wires. This ensures low parasitics and low loss. To increase operational reliability, the power supply was integrated into the module.
Figure 4. Fraunhofer IAF’s sub-millimeter-wave amplifier module in split-block technology. The dissection plane divides the input and output rectangular waveguides along the centerline of the longer side. The monolithic 50 nm gate length amplifier circuit is mounted between two microstrip lines realized on 50 µm-thick quartz substrates. These two lines are serving as waveguide-to-microstrip transitions
Figure 6. The four-stage, 460 GHz mHEMT amplifier S-MMIC employs
transistors with a gate width of only 2 x 5 µm. Die size is only 0.37 x 0.63 mm2
October 2010
www.compoundsemiconductor.net 23
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