Teledyne and UCSB claim fastest DHBT MMIC
High-frequency InP transistors have made a key breakthrough for high-resolution, all-weather imaging, as they have been used to produce the first sub-millimeter wave DHBT monolithic amplifier.
Jonathan Hacker of Teledyne Scientific presented the InP DHBT MMIC, at the MTT-S International Microwave Symposium in Atlanta on June 18.
The device is able to amplify sub-millimeter wavelength signals, thanks to its record 324 GHz measured operation frequency, with 4.8 dB gain. The single-stage amplifier occupies an area of just 0.124 mm2 and produced a 1.3 mW saturated output power from 1.4 V, 12 mA DC input.
The device was developed with Mark Rodwell s group at the University of California, Santa Barbara, for the “SWIFT” program, which DARPA is running specifically to establish sub-millimeter wave imaging technology. One of SWIFT s aims is a single 340 GHz MMIC capable of producing at least 50 mW output power and 5 percent power added efficiency (PAE). The peak PAE of this MMIC is 0.6 percent.
Northrop Grumman, which is also involved in SWIFT, last year reported a three-stage InP HEMT MMIC that produces 15 dB gain at 340 GHz. Hacker points out, however, that these HEMT-based devices have low breakdown voltages that could limit their success as power amplifiers.
The Teledyne/UCSB MMIC exploits a 250 nm emitter junction width InP DHBT, which is based on devices reported by Rodwell in 2007. This device operates with a cutoff frequency, ft, of 373 GHz prior to being made into a MMIC and should avoid any breakdown voltage problems faced by HEMTs.
“250 nm InP DHBT devices are particularly promising because of their combination of high bandwidth and high breakdown voltage,” Hacker said. “That makes them ideally suited for output powers up to 10 mW and higher.”
In this case, the DHBT structure was fabricated on a 4-inch InP substrate, by growing a “high-quality” epistructure that consisted of a 30 nm carbon-doped base layer and a 150 nm nitrogen-doped InP collector region.
The team formed emitter contacts and first-level interconnects using electroplated gold, after a number of etching and lithography steps. They then laid down a 10 µm benzocyclobutene (BCB) layer on top of a ground plane deposited on the top side of the wafer. This arrangement allows Teledyne to make a MMIC with smaller transmission lines than one made from a device with the ground plane on the wafer backside.
“Low dielectric constant BCB allows for compact impedance matching and power-combining networks, reducing IC area and facilitating low-parasitic connections to the small active devices,” Hacker said.
