Novel W-band monolithic push-pull power amplifiers

Monolithic W-band push-pull power amplifiers have been developed using 0.1-μm AlGaAs/InGaAs/GaAs pseudomorphic T-gate power HEMT technology. The novel design approach utilizes a push-pull topology to take advantage of a virtual ground between the device pair, eliminating the series feedback of the via hole inductance, and thus improving the performance of the power amplifier at millimeter-wave frequencies. For a two-stage design presented in this paper, the measurement results show a small signal gain of 13 dB and a saturated output power of 19.4 dBm at 90 GHz. The best power added efficiency of 13.3% has been achieved at an output power of 18.8 dBm under a lower bias condition. The gain and efficiency results represent state-of-the-art performance. These are the first reported monolithic push-pull amplifiers at millimeter-wave frequencies     

Design and Analysis of Broadband Dual-Gate Balanced Low-Noise Amplifiers

In this paper, we present three MMIC low-noise amplifiers using dual-gate GaAs HEMT devices in a balanced amplifier configuration. The designs target three different frequency bands including 4-9 GHz, 9-20 GHz, and 20-40 GHz. These dual-gate balanced designs demonstrate the excellent qualities of balanced amplifiers in terms of stability and matched characteristics, while demonstrating higher bandwidth than designs with a single-stage common-source device. Additionally, noise performance is excellent, with the 4-9 GHz LNA demonstrating <1.75 dB noise figure (NF), the 9-20 GHz LNA <2.75 dB NF and the 20-40 GHz LNA <2.5 dB NF. Demonstrating high gain and excellent bandwidth, the dual-gate devices seem a logical choice for the balanced amplifier topology.     

Physical identification of gate metal interdiffusion in GaAs PHEMTs

The Ti metal interdiffusion of Ti/Pt/Au gate metal stacks in 0.15-/spl mu/m GaAs PHEMTs subjected to high-temperature accelerated lifetest has been physically identified using scanning transmission electron microscopy. Further energy dispersive analysis with X-ray (EDX) analysis confirms the Ti diffusion into the AlGaAs Schottky barrier layer and the decrease of Schottky barrier height suggests the Ti-AlGaAs intermetallic formation, which is consistent with previous Rutherford backscattering spectroscopy/X-ray photoelectron spectroscopy studies. The Ti metal interdiffusion reduces the separation of the gate metal and InGaAs channel, thus leading to a slight Gm increase, positive shift in pinchoff voltage, and S21 increase during the preliminary portion of the lifetest. Accordingly, the Ti interdiffusion effect implies that the lifetime of GaAs PHEMTs subjected to high-temperature accelerated lifetest could be dependent upon the initial thickness of the Schottky layer underneath the gate metal.     

Submicron-gate InP power MISFET's with improved output powerdensity at 18 and 20 GHz

The microwave characteristics at 18 and 20 GHz of submicron-gate indium phosphide (InP) metal-insulator-semiconductor field-effect transistors (MISFETs) for high output power density applications are presented. InP power MISFETs were fabricated with 0.7 μm gate lengths, 0.2 mm gate widths, and drain-source spacings of 2, 3 and 5 μm. The output power density was investigated as a function of drain-source spacing. The best output power density and gain were obtained for drain-source spacings of 3 μm. At 18 GHz output power densities of 1.59 W/mm with a gain of 3.47 dB and a power-added efficiency of 20.0% were obtained for a drain-source spacing of 3 μm. At 20 GHz output power densities of 1.20 W/mm with a gain of 3.17 dB and a power-added efficiency of 13.6% were obtained for a drain-source spacing of 3 μm     

Innovative nitride passivated pseudomorphicGaAs HEMTs

A novel low-temperature nitride passivation technique using high-density inductively coupled plasma chemical vapor deposition (HD-ICP-CVD) with SiH/sub 4//N/sub 2/ chemistries to passivate 0.15 /spl mu/m pseudomorphic GaAs HEMTs has been developed for the first time. HD-ICP-CVD nitrides have higher density and lower hydrogen concentration than those of nitrides deposited by plasma-enhanced CVD (PECVD). Furthermore, HD-ICP-CVD passivated devices exhibit better performance in reverse breakdown voltage, transconductance, and cut-off frequency than those of PECVD passivated devices. The results achieved here warrant the applications of HD-ICP-CVD for next-generation nitride passivation in compound semiconductor technologies.     

Q-band high-efficiency monolithic HEMT power prematch structures

Monolithic Q-band high-efficiency prematch structures using 0.15 μm double-heterostructure pseudomorphic AlGaAs-InGaAs-GaAs HEMTs have been designed, fabricated and evaluated. The structures include a 400 μm and an 800 μm gate-width unit, demonstrating power-added efficiency of 41.6% and 37%, respectively, which represents state-of-the-art efficiency performance at this frequency. These building-blocks can be used easily to construct high-power, high-efficiency amplifiers. The circuit design, output power and efficiency performance of the prematch structures are also presented     

The effect of gate metal interdiffusion on reliability performance in GaAs PHEMTs

While Ti metal interdiffusion of Ti-Pt-Au gate metal stacks in GaAs pseudomorphic HEMT (PHEMTs) has been explored, the effect of Ti metal interdiffusion on the reliability performance is still lacking. We use a scanning transmission electron microscopy technique to correlate Ti-metal-InGaAs-channel-separation and Ti-sinking-depth with a threshold voltage V/sub T/. It has been found that Ti-sinking-depth is insensitive to V/sub T/. However, Ti metal interdiffusion reduces the separation of the gate metal and InGaAs channel, thus affecting the I/sub dss/ degradation rate. Accordingly, we observe the dependence of /spl Delta/I/sub dss/ on V/sub T/. Devices with less negative V/sub T/ exhibit inferior reliability performance to those devices with more negative V/sub T/. The results provide insight into a critical device parameter, V/sub T/, for optimizing reliability performance based on I/sub dss/ degradation.     

Ion-implanted high microwave power indium phosphide transistors

Encapsulated rapid thermal annealing (RTA) has been used in the fabrication of indium phosphide (InP) power metal-insulator-semiconductor field-effect transistors (MISFETs) with ion-implanted source, drain, and active channel regions. The MISFETs had a gate length of 1.4 μm. Six to ten gate fingers per device, with individual gate finger widths of 100 or 125 μm, were used to make MISFETs with total gate widths of 0.75, 0.8, or 1 mm. The source and drain contact regions and the channel region of the MISFETs were fabricated using silicon implants in semi-insulating InP at energies from 60 to 360 keV with doses from 1×10¹² to 5.6×10¹⁴ cm^-2. The implants were activated using RTA at 700°C for 30 s in N₂ or H₂ ambients using a silicon nitride encapsulant. The high-power, high-efficiency MISFETs were characterized at 9.7 GHz, and the output microwave power density for the RTA conditions used was as high as 2.4 W/mm. For a 1-W input at 9.7 GHz gains up to 3.7 dB were observed, with an associated power-added efficiency of 29%. The output power density was 70% greater than that reported for GaAs MESFETs