GaAs Pseudomorphic HEMT Research Articles

Q-band high conversion gain active sub-harmonic mixer

Abstract In this paper, we have designed and fabricated high conversion gain Q-band active sub-harmonic mixers for a receiver of millimeter-wave wireless communication systems. The fabricated active sub-harmonic mixer used second harmonic signals of a low local oscillator (LO) frequency. The fabricated mixer were successfully integrated by using a 0.1 μm GaAs pseudomorphic HEMT’s and a coplanar waveguide structure. We showed that the highest conversion gain of 4.8 dB has obtained at a LO frequency of 17.5 GHz and a RF frequency of 40 GHz. Conversion gain from the fabricated sub-harmonic mixer is one of the best reported thus far. The active sub-harmonic mixer also ensure a high degree of isolations, which are −35.8 dB from LO-to-IF and −40.5 dB from LO-to-RF, respectively, at a LO frequency of 17.5 GHz.

Thermal analysis of AlGaN-GaN power HFETs

In this paper, we present a thermal analysis of AlGaN-GaN power heterojunction field-effect transistors (HFETs). We report the dc, small-signal, large-signal, and noise performances of AlGaN-GaN HFETs at high temperatures. The temperature coefficients measured for GaN HFETs are lower than that of GaAs pseudomorphic high electron-mobility transistors, confirming the potential of GaN for high-temperature applications. In addition, the impact of thermal effects on the device dc, small-signal, and large-signal characteristics is quantified using a set of pulsed and continuous wave measurement setups. Finally, a thermal model of a GaN field-effect transistor is implemented to determine design rules to optimize the heat flow and overcome self-heating. Arguments from a device, circuit, and packaging perspective are presented.

Design and analysis of novel high-gain and broad-band GaAs pHEMT MMIC distributed amplifiers with traveling-wave gain stages

Using the concept of traveling-wave gain stages, novel GaAs pseudomorphic high electron-mobility transistor monolithic-microwave integrated-circuit (MMIC) distributed amplifiers (DAs) are demonstrated to achieve high gain and over several octaves of bandwidth performance simultaneously for microwave and millimeter-wave frequency applications. The cascaded single-stage distributed amplifier (CSSDA) is used as traveling-wave gain stages to improve the gain performance of the conventional distributed amplifier (CDA). By adopting the low-pass filter topology between the CDA and CSSDA and tuning the gain shape of CDA and CSSDA separately, a broad-band and high-gain DA, called CDA-CSSDA-2, was accomplished. The detailed design equations are derived for the broad-band matching design of this CDA-CSSDA-2. Two other MMICs, namely, a two-stage CSSDA called 2-CSSDA, and another two-stage design called CDA-CSSDA-1, are also included in this paper. This CDA-CSSDA-2 achieves 22/spl plusmn/1.5-dB small-signal gain from 0.1 to 40 GHz with a chip size of 1.5/spl times/2 mm/sup 2/. It also produces a gain-bandwidth product of 503 GHz, which is the highest among all reported GaAs-based DAs. The flat group delay also demonstrates the feasibility of this design for future digital optical communications and broad-band pulse applications.

Use of WNx as diffusion barrier for copper airbridged low noise GaAs PHEMT

A low noise pseudomorphic high electron mobility transistor (PHEMT) with copper airbridges using sputtered WNx as the diffusion barrier has been developed. Both the material system and the copper airbridged PHEMT with WNx as the diffusion barrier did not decay even after thermal annealing at 250°C for 20 h. The results show that the copper airbridges with WNx diffusion barrier can be used as the interconnects for low noise GaAs PHEMTs.

Design of an opto-electronic modulator driver amplifier for 40-Gb/s data rate systems

This paper describes the design and performance of a broad-band driver amplifier for 40-Gb/s noreturn-to-zero system applications. The function of the amplifier is to raise the output from a multiplexer (nominally 0.4 V peak to peak) to a level of /spl sim/5 Vp-p, which is suitable to drive a GaAs-based Mach-Zehnder optoelectronic modulator. The amplifier module contains two GaAs pseudomorphic high-electron mobility transistor traveling-wave MMICs fabricated on a 0.2-/spl mu/m gate process. The design issues relating to the specific requirements of a modulator driver amplifier and the techniques to resolve them are described.

Molecular beam epitaxial growth and characterization of strain-compensated Al0.3In0.7P/InP/Al0.3In0.7P metamorphic–pseudomorphic high electron mobility transistors on GaAs substrates

A novel metamorphic high electron mobility transistor (HEMT) structure was grown on GaAs substrates by solid-source molecular-beam epitaxy for potential microwave power applications. The HEMT device layers were strain compensated with pseudomorphic (tensile-strained) Al0.3In0.7P donor–barrier layers and a pseudomorphic (compressive-strained) InP channel layer. Atomic force microscopy measurements of the metamorphic structure yielded a root-mean-square surface roughness of 8 Å. Transmission electron micrographs of the device layers exhibited flat interfaces with the dislocation density estimated to be less than 1×106 cm−2. Room temperature photoluminescence measurements of metamorphic AlInP layers indicated large direct band gaps up to 2.10 eV. Due to the larger conduction band discontinuity at the Al0.3In0.7P/InP heterojunction than the AlGaAs/InGaAs heterojunction in GaAs pseudomorphic HEMTs, significantly higher channel sheet densities were obtained. For Al0.3In0.7P/InP HEMTs, channel sheet densities (cm−2) exceeding 3×1012 for single-pulse-doped, and greater than 4×1012 for double-pulse-doped, structures were readily obtained. Hall measurements on a double-pulse-doped Al0.3In0.7P/InP/Al0.3In0.7P HEMT gave mobilities (cm2/V s) of 4450 at 300 K and 18 500 at 77 K, which are consistent with a high quality InP channel layer. Secondary ion mass spectroscopy depth profiles of a double-pulse-doped structure displayed sharp doping pulses and interfaces indicating that metamorphic growth was not leading to enhanced diffusion or migration. Initial and nonoptimized devices with a gate length of 0.15 μm exhibited a maximum current density of 500 mA/mm and a transconductance of 520 mS/mm, which compare favorably to mature AlGaAs/InGaAs pseudomorphic HEMTs.

A broadband and miniaturized V-band PHEMT frequency doubler

We present the design and measured performances of a V-band frequency doubler fabricated using 0.15 μm GaAs pseudomorphic HEMTs and the three-dimensional (3-D) MMIC technology. Thank to the use of an improved 180/spl deg/ rat-race hybrid, the frequency doubler exhibits high spectral purity over a large bandwidth. Isolation better than 30 dB is achieved on a frequency range from 31.736 GHz and fundamental frequency rejection better than 35 dB is achieved between 31.5 GHz and 37.5 GHz. Conversion loss measured at 32.5 GHz is 8.5 dB for an input power of 14 dBm. Both the broadband spectral purity and the small size of 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> make it suitable for the realization of high-quality and widely tunable V-band frequency sources. For the future developments of millimeter-wave wireless communication systems, it offers good perspectives toward the fabrication of single-chip V-band transceiver including the frequency source.

Molecular beam epitaxial growth and device performance of metamorphic high electron mobility transistor structures fabricated on GaAs substrates

Single and double pulse doped metamorphic high electron mobility transistor (MHEMT) structures have been grown on GaAs substrates by molecular beam epitaxy. A linear indium graded buffer layer was used to expand the lattice constant. Transmission electron microscopy cross sections showed planar interfaces. Threading dislocations were not observed along both cleavage directions. For a single pulse doped MHEMT structure with an In0.56Ga0.44As channel layer, the mobilities (10 030 cm2/V s at 292 K; 32 560 cm2/V s at 77 K) and sheet density (3.2×1012 cm−2) were nearly equivalent to values obtained for the same structure grown on an InP substrate. Secondary ion mass spectroscopy measurements of a double pulse doped structure indicated no measurable migration of the silicon doping pulses. MHEMT devices with 0.15 μm gates were fabricated, tested, and compared to GaAs pseudomorphic HEMT devices of the same geometries. Above 9 GHz, the MHEMT devices exhibited lower noise figure. From 3 to 26 GHz, the associated gain was 3 dB higher with the MHEMT devices. Also higher linearity performance was obtained with the MHEMT devices. At 4 GHz MHEMT linearity measurements yielded third order intermodulation distortion intercepts, IP3, of 36–39 dBm with linearity figure of merits of 60–90. Due to the significantly lower cost and more robustness of GaAs substrates compared to InP substrates, MHEMT technology is very promising for low cost manufacturing of low noise amplifiers.

Breakdown in millimeter-wave power InP HEMTs: a comparison with GaAs PHEMT's

In spite of their outstanding transport characteristics, InP high-electron mobility transistors (HEMTs) deliver lower output power than GaAs pseudomorphic HEMTs (PHEMTs) throughout most of the millimeter-wave regime. However, the superior power-added efficiency of InP HEMTs when compared with GaAs PHEMTs makes this technology attractive for many applications. The reason for the relatively inferior power output of InP HEMTs lies in their comparatively small off-state and on-state breakdown voltages. This paper reviews the state of knowledge regarding the physics of breakdown voltage in InP HEMTs, placing it in contrast with GaAs PHEMTs. It also presents current understanding regarding burnout, a closely related phenomenon. This paper concludes by discussing strategies for improving the breakdown voltage and the power output of InP HEMTs.

GaAs PHEMT with 1.6 W/mm output power density

A very high power density GaAs pseudomorphic HEMT with a saturated output power density of 1.6 W/mm at 2 GHz is presented. To the authors' knowledge this is the highest reported value for GaAs HEMTs. A transistor with 2.5 mm gate width delivers a saturated output power of 4 W. The PAE at saturation is 62 %. The measurements are performed in CW mode on an unthinned GaAs wafer.

A new extraction method for the two-parameter FET temperature noise model

This paper presents a direct extraction method for the associated noise temperatures T/sub d/ and T/sub g/ in the field-effect transistor (FET) temperature noise model. The method is related to nodal analysis of circuits. T/sub d/ and T/sub g/ are extracted from the small-signal model parameters and the noise parameters of the device. It is also theoretically shown that there exist source admittances that cancel the thermal noise contribution at the output from either T/sub d/ or T/sub g/ in the model. Finally, a commercially available GaAs pseudomorphic high electron-mobility transistor (pHEMT) is measured and modeled for a wide range of bias points. Comparisons between measured and modeled noise parameters are presented in the 2-26 GHz frequency range.

60-GHz flip-chip assembled MIC design considering chip-substrate effect

In this paper, 60-GHz microwave integrated circuits (MIC's) with flip chip assembled 0.1-/spl mu/m-gate GaAs pseudomorphic high electron-mobility transistors (p-HEMT's) are demonstrated. To clarify the millimeter-wave characteristics of the flip-chip assembled structure, the parameters for the assembly equivalent circuit are examined using three-dimensional (3-D) electromagnetic-field analysis. The analytical results indicate that the optimum height of the bump is 30 /spl mu/m to minimize degradation of the millimeter-wave characteristics. A 60-GHz-band MIC two-stage amplifier and 30/60-GHz frequency doubler designed using the results of the field analysis have been fabricated. The amplifier has maximum gain of 12.8 dB at 58.6 GHz, P/sub 1dB/ of 12.9 dBm has been obtained at 60 GHz. A 30/60-GHz frequency doubler has maximum conversion gain of 0.4 dB and fundamental frequency suppression of -23.0 dB at the input frequency of 30.4 GHz. Good agreement between the measured and the simulated results demonstrates the potential of the structure and design method.

High-gain frequency-tunable low-noise amplifiers for 38-42.5-GHz band applications

High-performance tunable low-noise amplifiers for 38-42.5 GHz applications are presented based on a fully stabilized GaAs pseudomorphic high electron mobility transistor (PHEMT) 0.2 μm technology. A single 1.5×3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> chip, incorporating six amplifying stages, shows a measured gain of 36-42 dB depending on the center frequency. Both maximum gain frequency and input impedance of the amplifier are accurately tunable on the chip. This means that the amplifier provides a narrow-band filtering function and can be matched to a fast p-i-n photodiode as well as to a 50 /spl Omega/ load. This is the first time such performances are reported for single chip narrow-band tunable amplifiers using a GaAs PHEMT technology.

Effects of O2 addition to SiCl4/SiF4 and the thickness of the capping layer on gate recess etching of GaAs-pseudomorphic high electron mobility transistors

The effects of the addition of a small amount of O2 to SiCl4/SiF4 plasma and the thickness of the GaAs capping layer on gate recess etching of GaAs pseudomorphic high electron mobility transistor (p-HEMT) devices have been studied. During gate recessing of GaAs/AlGaAs p-HEMTs using a selective reactive ion etching (RIE) process in SiCl4/SiF4 plasma [see S. K. Murad, N. I. Cameron, P. D. Wang, S. P. Beaumont, and C. D. W. Wilkinson, Microelectron. Eng. 27, 439 (1995)], it was found that the profile of the gate changes dramatically from undercut to nearly vertical with no lateral etching when the thickness of the capping layer was reduced below 40 nm. This vertical profile puts the gate metal too close to the recess edges in devices with a ≤30 nm capping layer. The addition of a very small amount of O2 to SiCl4/SiF4 plasma was seen to increase GaAs etch rates remarkably, while maintaining the high selectivity over AlGaAs. This increase in the etch rate agrees well with optical emission spectroscopic observations which indicate that the Cl emission has increased by more than an order of magnitude for the addition of only 1.5% of O2 to SiCl4/SiF4 plasma. This selective RIE process of SiCl4/SiF4/O2 was applied to gate recess etching of GaAs/AlGaAs/InGaAs p-HEMTs with various capping layer thicknesses. The profile of the T gates changed from nearly vertical (with no undercut or gate offset) to undercut with a lateral etch rate depending on the thickness of the capping layer. The lateral etching rate also strongly depends on the O2 flow. The p-HEMT devices gate recessed using this process (SiCl4/SiF4/O2) exhibited an ft of 120 GHz, gm of 700 mS/mm and a gain of 9.5 dB at 94 GHz.

Temperature dependent study of the microwave performance of 0.25-μm gate GaAs MESFETs and GaAs pseudomorphic HEMTs

We report on the noise figure, associated gain, and the current gain cutoff frequency for comparable 0.25-/spl mu/m gate GaAs MESFETs and GaAs pseudomorphic HEMTs (p-HEMTs) as a function of cryogenic temperature. Contrary to previously published results which suggest that p-HEMTs should have a higher electron velocity and a lower noise figure than MESFETs due to the effects of the two-dimension electron gas (2-DEG), we have experimentally verified that this is not the case. We show clear evidence that the transport properties of the 2-DEG in p-HEMTs do not make a significant contribution to the speed enhancement and noise reduction during high-frequency operation of these devices. It is the fundamental InGaAs material properties, specifically the /spl Gamma/-L valley separation in the conduction band and associated effective mass of the electron in either GaAs or InGaAs channel, which limits the high-field electron velocity and thus the speed and noise performance of the devices.

Overview of recent development of HEMTs in the mm-wave range

Recent expansion in the demand for high frequency applications requires new transistors with better performance than the MESFETs, especially in the upper-microwave and mm-wave frequency ranges. To realize better transistors than the MESFET by utilizing features of the heterostructure, high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) are being developed. GaAs pseudomorphic HEMTs (PHEMTs) are currently the main type of low noise transistors being used in various microwave and mm-wave systems. Very low noise figures of 1.5 dB at 60 GHz and 2.1 dB at 94 GHz are achieved with GaAs PHEMTs. Furthermore, InP HEMTs, with better noise performance than GaAs PHEMTs, are being developed to replace the latter. State of the art noise figures for InP HEMTs are, for example, 0.8 dB at 60 GHz and 1.2 dB at 94 GHz. GaAs based power HEMTs show higher efficiencies than competing MESFETs for frequencies over 10 GHz, and are comparable to them below 10 GHz. In the higher frequency range, the state of the art in the output power of HEMTs gives a −6 dB/octave line connecting 4W at 20 GHz and 0.1 W at 100 GHz. As there are still reliability problems yet to be solved with the low noise InP HEMTs and the power HEMTs, further study of degradation mechanisms in AlInAs/InGaAs/InP systems, r.f. operation testing of really high power HEMTs, systematic reliable data, etc. would be necessary for them to be accepted as having been established to be reliable devices.

HEMT degradation in hydrogen gas

The effect of hydrogen treatment on both GaAs pseudomorphic HEMT's and InP-based HEMT's, in order to simulate the hermetic seal environment in a Kovar package, is reported for the first time. Under the 270/spl deg/C, 4% H/sub 2/ in Ar atmosphere, significant changes in both types of HEMT's were observed within several minutes. While the drain current at a fixed gate bias and the pinchoff voltage of the GaAs PHEMT consistently decreased under the influence of the hydrogen gas, they were found to either increase or decrease with the InP HEMT. The change of device characteristics resulting from exposure to the hydrogen environment is not permanent; partial recovery of device characteristics was observed under either nitrogen or hydrogen at both elevated and room temperatures. The change in HEMT DC characteristics seems to be primarily resulted from the change in the gate built-in potential. Any device changes due to the Si-donor neutralization by atomic hydrogen, and therefore a reduction in channel carrier concentration, were found to be insignificant.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A double-recessed Al/sub 0.24/GaAs/In/sub 0.16/GaAs pseudomorphic HEMT for Ka- and Q-band power applications

A double-recessed 0.2- mu m-gate-length pseudomorphic HEMT (PHEMT) has been demonstrated with 500 mW of output power (833 mW/mm of gate periphery), 6-dB gain, and 35% power-added efficiency (PAE) at 32 GHz. At 44 GHz, the device exhibited 494 mW of output power (823 mW/mm), 4.3-dB gain, and 30% PAE. This level of performance is attributed to excellent MBE material, optimized epitaxial layer design, and the use of individual source vias and of double recess with tight channel dimensions. Excellent 3-in-wafer uniformity was also observed: DC yield was greater than 95% and the interquartile range for all DC parameters was less than 20% of the median value (most are significantly lower). >

V-band high-efficiency high-power AlInAs/GaInAs/InP HEMT's

The authors report on the state-of-the-art power performance of InP-based HEMTs (high electron mobility transistors) at 59 GHz. Using a 448- mu m-wide HEMT with a gate length of 0.15 mu m, an output power of 155 mW with a 4.9-dB gain and a power-added efficiency of 30.1% were obtained. By power-combining two of these HEMTs, an output power of 288 mW with 3.6-dB gain and a power-added efficiency of 20.4% were achieved. This is the highest output power reported with such a high efficiency for InP-based HEMTs, and is comparable to the best results reported for AlGaAs/InGaAs on GaAs pseudomorphic HEMTs at this frequency. >

A super low-noise 0.1 mu m T-gate InAlAs-InGaAs-InP HEMT

It is reported that 0.1- mu m T-gate InAlAs-InGaAs-InP HEMTs have exhibited state-of-the-art noise and gain performance well up to 100 GHz. Minimum noise figures of 0.8 and 1.2 dB with gains of 8.9 and 7.2 dB have been measured at 60 and 94 GHz, respectively. A high-performance W-band three-stage amplifier has been built using these devices with noise figures between 3.2-3.5 dB and a gain of 17.5+or-0.4 dB from 91 to 96 GHz. A 6-dB improvement in the 1-dB compression characteristic of the amplifier had been achieved with a GaAs pseudomorphic HEMT in the third stage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>