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WEIF-29: Student Paper: pHEMT and mHEMT Ultra Wideband Millimeter-wave Balanced Resistive Mixers
The session illustrates advances in integration methods for wireless LAN, CMOS for cellular base stations, SOI for WLAN, InP DHBT for high speed digital and MHEMT for broadband amplifiers.
WE4B-5: A GaAs MHEMT Distributed Amplifier with Greater than 250 GHz Gain-bandwidth Product for 40 Gbps Optical Applications
In the MHEMT, the device active layers are grown on a strain-relaxed, compositionally graded, metamorphic buffer layer which transforms the lattice constant from GaAs up through InP, allowing a high In content channel layer to be grown on low cost GaAs substrates.
The MHEMT's layer interfaces remain atomically smooth despite having twice the indium content and five times the total thickness as a typical GaAs PHEMT, demonstrating that metamorphic technology can successfully transform the lattice constant from GaAs.
The 300 K mobility of [In.sub.0.56]GaAs HEMT grown on a GaAs substrate measured within 5 percent of the mobility of an identical structure on an InP substrate,  demonstrating the high quality of the MHEMT channel.
MHEMT devices are typically mesa etched for isolation using a sulfuric- or phosphoric-based etchant.
The DC performance data for an [In.sub.0.60][Ga.sub.0.40]As MHEMT device shows a [G.sub.m] of 850 mS/mm, an [I.sub.max] of 630 mA/mm, a [V.sub.po] of -0.75 V and a [V.sub.dg BRK] = 8 V.
The MHEMT low noise results shown here [9,10] rival the best published MHEMTs,  as well as the best InP HEMTs.
The PHEMT shows approximately 8 dB [G.sub.assoc] near its minimum [F.sub.min], in contrast to the 33 percent In MHEMT with 10 dB.
Figure 8 shows the noise figure and gain of a 3-stage 60 percent In MHEMT Ka-band LNA with less than 1.5 dB noise figure and greater than 23 dB of associated gain from 31 to 32 GHz.
Drain bias limits of 3.5V have hampered the output power density of some MHEMT devices and most InP HEMTs, predominately due to low on-state breakdown governed by the small band gap of their high indium content channels.
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