Monolithic HEMT-HBT integration by selective MBE

We have achieved successful monolithic integration of high electron mobility transistors and heterojunction bipolar transistors in the same microwave circuit. We have used selective molecular beam epitaxy and a novel merged processing technology to fabricate monolithic microwave integrated circuits that incorporate both 0.2 μm gate-length pseudomorphic InGaAs-GaAs HEMTs and 2 μm emitter-width GaAs-AlGaAs HBTs. The HEMT and HBT devices produced by selective MBE and fabricated using our merged HEMT-HBT process exhibited performance equivalent to devices fabricated using normal MBE and our baseline single-technology processes. The selective MBE process yielded 0.2 μm HEMT devices with g_m=600 mS/mm and f_T=70 GHz, while 2×10 μm² HBT devices achieved β>50 and f_T=21.4 GHz at J_c=2×10⁴ A/cm². The performance of both a 5-10 GHz HEMT LNA with active on-chip HBT regulation and a 20 GHz Darlington HBT amplifier are shown to be equivalent whether fabricated using normal or selective MBE     

Antimonide-based compound semiconductors for electronic devices: A review

Several research groups have been actively pursuing antimonide-based electronic devices in recent years. The advantage of narrow-bandgap Sb-based devices over conventional GaAs- or InP-based devices is the attainment of high-frequency operation with much lower power consumption. This paper will review the progress on three antimonide-based electronic devices: high electron mobility transistors (HEMTs), resonant tunneling diodes (RTDs), and heterojunction bipolar transistors (HBTs). Progress on the HEMT includes the demonstration of Ka- and W-band low-noise amplifier circuits that operate at less than one-third the power of similar InP-based circuits. The RTDs exhibit excellent figures of merit but, like their InP- and GaAs-based counterparts, are waiting for a viable commercial application. Several approaches are being investigated for HBTs, with circuits reported using InAs and InGaAs bases.     

90 GHz basedband lumped amplifier

A broadband amplifier using InP-InGaAs single heterojunction bipolar transistors (HBTs) is presented. This modified Darlington amplifier exhibits a low-frequency gain of 6.2 dB with -3 dB bandwidth of 90 GHz. This wide bandwidth performance is compatible, or superior to, other lumped or distributed amplifiers based on HEMT and HBT technologies reported in the literature     

Integration of GalnP/GaAs heterojunction bipolar transistors andhigh electron mobility transistors

Integration of carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs) is demonstrated by growing an HBT on the top of a HEMT. A current gain of 60, a cutoff frequency of 59 GHz and a maximum oscillation frequency of 68 GHz were obtained for a 5×15 μm² self-aligned HBT. The HEMT, with a gate length of 1.5 μm has a transconductance of 210 mS/mm, a cutoff frequency of 9 GHz and a maximum oscillation frequency of 22 GHz. It is shown that the GaInP/GaAs HBT on the HEMT is a simple Bi-FET technology suitable for microwave and mixed signal applications     

A monolithically integrated HEMT-HBT low noise high linearityvariable gain amplifier

We report on a 1-6 GHz HEMT-HBT three-stage variable gain amplifier (VGA), which is realized using selective molecular beam epitaxy (MBE). The VGA integrates an HEMT low noise amplifier with an HBT analog current-steer variable gain cell and output driver stage to achieve a combination of low noise figure, wide gain control, and high linearity. The HEMT-HBT VGA MMIC obtains a maximum gain of 21 dB with a gain control range >30 dB, a minimum noise figure of 4.3 dB, and an input IP3 (IIP3) greater than -4 dBm over 25 dB of gain central range. By integrating an HEMT instead of on HBT preamplifier stage, the VGA noise figure is improved by as much as 2 dB compared to an all-HBT single-technology design. The HEMT-HBT MMIC demonstrates the functional utility and RF performance advantage of monolithically integrating both HEMT and HBT devices on a single substrate     

Reliability physics of compound semiconductor transistors for microwave applications

This paper reviews the reliability problems of compound semiconductor transistors for microwave applications. These devices suffer from specific failure mechanisms, which are related to their limited maturity, with the exception of the GaAs MESFETs, which exhibit a stable technology and an assessed reliability. The metallizations employed in high electron mobility transistors (HEMTs) already benefit from this assessment. However, HEMT are affected by concerns related to hot carriers and impact ionization. The trapping of carriers and the generation of defects in the different layers are responsible for the observed instabilities. The stability of the base dopant is the main reliability concern for heterojunction bipolar transistors (HBTs). Beryllium outdiffuses from the base into the emitter and causes device degradation. Carbon has a lower diffusivity, but is affected by the presence of hydrogen, which prompts gain variations. Finally the hot carriers reliability concern in SiGe HBTs is briefly reviewed.     

Analysis of multifinger power HEMTs supported by effective 3-D device electrothermal simulation

The influence of the metallization layer geometry on the electrothermal behavior of the multifinger power high-electron mobility transistors (HEMTs) is studied. The analysis of thermal and electrical behavior is supported by effective 3-D electrothermal device simulation method developed for Synopsys TCAD Sentaurus environment using mixed-mode setup. The proposed methodology allows fast simulation of complex systems from individual semiconductor layers at a frontend up to package and cooling assemblies at a backend. More accurate electrothermal model of power HEMT is proposed and validated by finite element method (FEM) simulations. The analysis points on significant influence of metallization geometry design on electrothermal properties and reliability of the multifinger power HEMTs. The unique identification and visualization of the critical regions allows effective device optimization. Very good comparison between simulation results and experimental data demonstrate validity of the proposed simulation methodology and HEMT structures analysis.     

All-active monolithic InP-based HBT VCO with tunable HEMT inductor

A novel HEMT-HBT VCO is presented; it is the first all-active analogue VCO demonstrated using InP HEMT-HBT integrated MMIC technology. The MMIC monolithically integrates an InP common-collector HBT oscillator with a tunable InP HEMT active inductor using selective MBE. The novel HEMT-HBT VCO can provide performance advantages over analogue VCOs such as the multi-vibrator, and has direct implications for high speed clock recovery circuits needed in InP based optoelectronic IC applications     

On-state distortion in high electron mobility transistor microwaveand RF switch control circuits

The origin of the distortion generating mechanism in microwave and RF control circuits using high electron-mobility transistors (HEMTs) is presented in this paper. A model is presented for predicting the distortion in series-connected HEMT switches. The theoretical discussion shows that turn-off voltages in the range of 1.0-1.5 V provide the lowest distortion in series switch configurations. A comparison of the HEMT snitch with MESFET switches shows that the HEMT switch generates more distortion than its MESFET counterpart. In addition, the frequency response of HEMT switches is the opposite of the MESFET switch, with less distortion at low frequencies. The model is validated with experimental data taken on a AlGaAs/GaAs HEMT in the series switch configuration     

AlGaN/GaN HEMTs on SiC for high power broadband applications up to 40 GHz

An overview of properties and recent achievements for AlGaN/GaN high electron mobility transistors (HEMT) on semi-insulating SiC substrate is given towards high power and broadband applications up to a frequency of 40 GHz. Starting from epitaxial growth and process technology we present state-of-the-art power results obtained at the Fraunhofer Institute (IAF) from AlGaN/GaN HEMTs on SiC. Further, a one-stage 16 GHz MMIC power amplifier circuit with 1.6 W output power is presented. This result represents the first AlGaN/GaN MMIC on SiC fabricated in Europe.     

Push-pull circuits using n-p-n and p-n-p InP-based HBT's for poweramplification

P-n-p heterojunction bipolar transistors (HBTs) have been combined with n-p-n HBTs in a push-pull amplifier in order to obtain improved linearity characteristics. Simulations of common-collector push-pull amplifiers demonstrate an improvement of 14 dB in second harmonic content at the onset of power saturation under class-B operation. Further improvement of 14 dB in the third harmonic content is shown by moving to class-AB operation at an expense of 4% decreased efficiency. A common-emitter push-pull amplifier was fabricated using both n-p-n and p-n-p HBTs with external matching and couplers. Testing of the circuit under class-AB conditions showed better third-order intermodulation (by ~9 dBc) and smaller second harmonic content (by ~11 dBc) compared with n-p-n HBTs alone. While the second harmonics were shown to combine destructively in the push-pull amplifier, total cancellation of the second harmonic was prevented by the wide difference in linearity characteristics of the n-p-n and p-n-p HBTs. In addition, the circuit produced over 2 dBm more output power than the n-p n HBT alone at 1 dB of gain compression     

The device characteristics of Ir- and Ti-based Schottky gates AlSb/InAs high electron mobility transistors

In this work, the InAs/AlSb high electron mobility transistors (HEMTs) on GaAs semi-insulating substrate using refractory iridium (Ir) gate technology was proposed. The Ir-gate exhibited a superior metal work function which was beneficial for increasing Schottky barrier height of InAs/AlSb heterostructures to 0.58 eV. Compared to the Ti-gate HEMT, the Ir-gate HEMT shows higher threshold voltage and lower gate leakage current owing to its higher Schottky barrier height and higher melting point. Moreover, the Ir-gated HEMT also shows the manifest stability improvement of DC characteristics under hot carrier stress as the Ti and As diffusion is alleviated.     

一种紧凑的GaN高电子迁移率晶体管大信号模型拓扑

GaN高电子迁移率晶体管（HEMT）以其复杂的器件特性使其大信号建模变得十分困难,尽管EEHEMT、Angelov等模型结构曾经成功应用于GaAs HEMT/MESFET的大信号模型,但当它们被用于GaN HEMT建模时却不再准确和完备.面向GaN HEMT器件的大信号模型,本文提出了一种紧凑的模型拓扑,此模型拓扑综合了GaN HEMT器件的直流电压-电流（I-V）特性、非线性电容、寄生参数、栅延迟漏延迟与电流崩塌、自热效应以及噪声等特性.经验证此模型拓扑在仿真中具有很好的收敛性,适用于GaN HEMT器件的大信号模型的建立,满足GaN基微波电路设计对器件模型的需求.     

Analysis of delta-doped and uniformly doped AlGaAs/GaAs HEMT's byensemble Monte Carlo simulations

Transport properties and device performance of delta-doped and uniformly doped AlGaAs/GaAs high electron mobility transistors (HEMTs) with identical threshold voltages and gate capacitors are investigated using two-dimensional self-consistent ensemble Monte Carlo simulations. The model includes the effects of real-space transfer and carrier degeneracy, as well as the influence of DX centers and surface states. A one-to-one comparison of simulation results for the two devices demonstrates superior performance for the delta-doped HEMT and provides a physical basis for the observed improvements. In particular, the delta-doped HEMT maintains its superior device performance as gate bias is increased. Reasons for these improvements are reported     

Improved performance of a cooled photoreceiver for high speedcommunication

An alternative method of improving photoreceiver sensitivity in a high-bit-rate optical transmission system is described. HEMTs have recently become commercially available and are known to generate mainly thermal noise and to exhibit transconductance enhancement at cryogenic temperatures. This suggests that a cooled photoreceiver with a HEMT in the first stage of the front-end amplifier could have an improved sensitivity with respect to that of room temperature operation. The DC transconductance variation between room temperature and 40 K for HEMTs of various technologies is presented. The signal-to-noise (S/N) ratios of a photoreceiver with a first-stage HEMT working at room temperature and 45 K are compared. The S/N improvement is currently about 4 dB (optical). It is found that HEMT noise generated in the frequency range considered does not seem to be of pure thermal origin. The results confirm that the proportion of MOCVD (metalorganic chemical vapor deposited) HEMTs exhibiting electrical characteristic degradation at low temperature is far less for MBE (molecular-beam epitaxial) HEMTs     

Design and performance of 20 dB gain two-tier matrix distributed amplifier

A matrix distributed amplifier, having a gain of 20 dB with a noise figure of 5 dB in the frequency range between 0.5-12 GHz, is presented. The amplifier, realised in hybrid technology using commercially available GaAs HEMTs, incorporates a novel scheme which allows the biasing of a single stage of the two tier amplifier (two rows of active devices) with a unique controlling resistance and, at the same time, the cascading of the two FETs of each stage. The computed results obtained using a small signal model for each FET fit rather well with the measurements in the whole frequency range.<>     

Very high-frequency small-signal equivalent circuit for shortgate-length InP HEMTs

A small-signal equivalent circuit for short gate-length InP high electron-mobility transistors (HEMTs) operating at very high frequency (HF) is proposed. First, the extrinsic parameters of the equivalent circuit are determined using a cold HEMT, but without forward gate bias. Then the intrinsic parameters of the equivalent circuit are extracted, including the frequency dependence of some of them. A fast and accurate method based on least-squares regressions is presented to obtain the extrinsic and intrinsic parameters from measured S-parameters. The improved equivalent circuit accurately fits the S-parameters of 0.25-μm InP HEMTs over the 500-MHz up to 40-GHz measurement bandwidth, for all gate-to-source and drain-to-source voltages     

Performance optimizing on multi-function MMIC design

Integration of GaAs BiFET (bipolar-FET) devices to obtain the optimum performance for multiple functions of MMIC design has been achieved. In this study, heterojunction bipolar transistors (HBTs), enhancement mode pseudomorphic HEMTs (E-pHEMTs), and depletion mode pHEMTs are developed for potential applications, including the integration of HBT power amplifier circuitry with pHEMT-based bias control, logic, RF switch, and low-noise amplifier circuitries. Critical processes including gate photolithography and gate recess control are presented and discussed in detail. The enhancement-depletion modes of pHEMT, HBT electrical performance, and uniformity are investigated comprehensively. In addition, power amplifiers and high power switches based on BiFET technology are investigated.     

一种基于微结构的GaAs HEMT的压阻系数

GaAs HEMT(高电子迁移率晶体管)位于微结构悬臂梁根部附近的最大应力处。介绍了GaAs HEMT和微结构的设计加工,并通过实验研究了GaAs HEMT在平行于HEMT生长方向(Z方向)单轴应力作用下的力电耦合特性。测试结果表明:GaAs HEMT不同偏压下压阻系数不同,且它的最大压阻系数为(1.72±0.33)×10-7Pa-1,比Si高出三个数量级。     

Characterization of surface-undoped In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

High-performance 0.3-μm-gate-length surface-undoped In_0.52 Al_0.48As/In_0.53Ga_0.47As/InP high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) have been characterized and compared with a surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMTs is obtained due to the improved g_m/g₀ ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3-×150-μm-gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. It is demonstrated that the surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance. Several millimeter-wave coplanar waveguide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. A high gain per stage distributed amplifier with 170-dB±1-dB small-signal gain across a frequency band of 24-40 GHz, a W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and a broad bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures