GaAs-based heterojunction bipolar transistors for very highperformance electronic circuits

This paper reviews the principles and status of AlGaAs/GaAs heterojunction bipolar transistor technology. Comparisons of this technology with Si bipolar transistor and GaAs field-effect transistor technologies are made. Epitaxial materials, fabrication processes, transistor DC and RF characteristics, and modeling of AlGaAs/GaAs HBT's are described. Key areas of HBT application are also highlighted     

Physics of degradation in GaAs-based heterojunction bipolar transistors

The GaAs HBT has recently become the technology of choice in particularly demanding wireless communications applications. However, controversy about HBT reliability is still widespread, with conflicting claims for lifetime and activation energy. Here, we detail the fundamental physics of HBT degradation, and describe the stress factors that drive it. Extensive testing shows that degradation is typically due to the formation of midgap traps associated with crystalline defects in the base. In addition, we describe the physical reasons for the superiority of the GaInP emitter in reliable HBT design. Finally, we show preliminary results of a stress test on large area (2 × 45 μm²) GaInP emitter HBTs which have lasted 5000 hours at 75 kA/cm², 215 °C with no discernable degradation in device characteristics yet.     

AlGaAs/GaAs heterojunction bipolar transistors for power applications: issues of thermal effect and reliability

AlGaAs/GaAs heterojunction bipolar transistor (HBT) has the advantages of superior switching speed, wide linearity, and high current handling capability. As a result, the device has gained popularity in designing power amplifiers for RF and microwave applications. However, the high power in the HBT, together with the poor thermal conductivity of GaAs, gives rise to significant thermal effect and reduced reliability in such a device. This paper presents an overview on the simulation, modeling, and reliability of AlGaAs/GaAs HBTs. Emphasis will be placed on the effects of thermal–electrical interacting behavior on the dc and ac performance of the HBT. The thermal-induced degradation process in the HBT will also be addressed and analyzed.     

Charge balance materials for homojunction and heterojunction OLED applications

In a homojunction device, a single organic layer assumes the multiple roles of hole, electron transportation, and emitter. Its ease in processing is highly desirable from the manufacturing point of view. In this paper, we shall describe the synthesis of a range of bipolar small molecules and conductive vinyl polymers for application in homojunction and heterojunction organic light emitting diodes (OLEDs). The bipolar materials, in general, consist of three basic building blocks: an arylamine, a 1,3,4-oxadiazole, and a polycyclic aromatic moiety. The achievement of charge balance can be validated either by direct measurement of electron/hole mobility or indirectly via optimization of device properties.A series of conductive vinyl copolymers containing hole transporting N-(4-methoxyphenyl)-N-(4-vinylphenyl)naphthalen-1-amine (4MeONPA) and electron transport-ing 2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (OXA) at different compositions was applied for heterojunction and homojunction OLEDs. For heterojunction devices employed the copolymers as the hole transporting layer and Alq3 as the electron transporting and emitting layer,a maximum luminance and current efficiency of over 23000 cd/m2 and 4.2 cd/A (PL of Alq3), respectively, were achieved at the charge balance composition. Homojunction devices for the copolymers were demonstrated by the addition ofrubrene as a dopant. The single layer devices at the optimal copolymer composition has ca 1500 cd/m2 and 0.74 cd/A.     

Measurement of the electron ionization coefficient at low electricfields in GaAs-based heterojunction bipolar transistors

Values of the electron ionization coefficient α_n in 〈100〉 GaAs extending the previously available data by two orders of magnitude, down to 1 cm^-1, are presented. The data are directly extracted from the multiplication factor, M-1, measured in lightly doped collector n-p-n AlGaAs/GaAs heterojunction bipolar transistors (HBT's). It is shown that the sensitivity of the technique is limited by the early effect, whose influence can be reduced by driving the device at constant emitter-base bias and by using heavily doped base regions. HBT's can provide simultaneously high base doping and current gain, and represent therefore an excellent tool for these measurements     

GaAs/AlGaAs heterojunction bipolar transistors for integrated circuit applications

Molecular-beam epitaxy (MBE) and ion implantation were used to fabricate GaAs/AlGaAs heterojunction bipolar transistors with buried wide bandgap emitters. Inverted-mode current gains of ∼ 100 were obtained, demonstrating the feasibility of this technology for I²L types of digital integrated circuits.     

InGaP/GaAs heterojunction bipolar transistor and RF power amplifier reliability

Electrothermal stress on advanced InGaP/GaAs heterojunction bipolar transistors (HBTs) was carried out experimentally. It showed a long-term stress-induced base current instability and a decrease in the DC current gain. A class-AB RF power amplifier (PA) was also considered to study the stress effect on the amplifier’s RF performance. The SPICE Gummel–Poon (SGP) model parameters were extracted from the pre- and post-stress HBT data and used in Cadence SpectreRF simulation. The amplifier’s post-stress RF characteristics, such as the output power and power-added efficiency (PAE), remained almost unchanged even though the post-stress HBT’s DC current gain had dropped to 73.6% of its initial value.     

SiGe heterojunction bipolar transistors and circuits toward terahertz communication applications

The relatively less exploited terahertz band possesses great potential for a variety of important applications, including communication applications that would benefit from the enormous bandwidth within the terahertz spectrum. This paper overviews an approach toward terahertz applications based on SiGe heterojunction bipolar transistor (HBT) technology, focusing on broad-band communication applications. The design, characteristics, and reliability of SiGe HBTs exhibiting record f/sub T/ of 375 GHz and associated f/sub max/ of 210 GHz are presented. The impact of device optimization on noise characteristics is described for both low-frequency and broad-band noise. Circuit implementations of SiGe technologies are demonstrated with selected circuit blocks for broad-band communication systems, including a 3.9-ps emitter coupled logic ring oscillator, a 100-GHz frequency divider, 40-GHz voltage-controlled oscillator, and a 70-Gb/s 4:1 multiplexer. With no visible limitation for further enhancement of device speed at hand, the march toward terahertz band with Si-based technology will continue for the foreseeable future.     

Modeling gallium arsenide heterojunction bipolar transistor ledge variations for insight into device reliability

It is widely known that under normal bias conditions, GaAs heterojunction bipolar transistor (HBT) device degradation proceeds by a gradual buildup of defects in the base and base–emitter junction depletion regions. The buildup of these defects is associated with a solid-state phenomenon known as recombination enhanced defect reaction, which is the formation and migration of defects associated with nonradiative electron–hole recombination events. These defects are often associated with midgap traps, which serve as additional recombination centers for electron–hole pairs. The resulting increased recombination current is an additional base leakage current, which reduces current gain. By extension, a high electron–hole recombination density in a region with an initially high defect density––such as an unpassivated or poorly passivated base surface––will lead to quick device degradation.This paper reports the modeling of the effects of various different extrinsic base passivation ledge parameters––material composition, thickness, width, and spacing from ledge to base contact––to determine the microscopic effects these parameters have on electron–hole recombination density. Through this we can qualitatively predict the effects these parameters will have on HBT reliability.     

The GaAs heterojunction bipolar transistor: an electron device with optical device reliability

GaAs-based heterojunction bipolar transistors (HBTs) are of interest for a wide variety of applications. However, concerns about the long-term stability of the device have recently arisen. This paper describes the physics of HBT degradation under bias stress as similar to GaAs light-emitting diode (LED) and laser diode (LD) degradation. TEM, electroluminescence, and electrical measurements support this model. Additionally, the model also indicates the factors in epitaxial growth and device processing that are critical to device reliability.     

A short-term high-current-density reliability investigation ofAlGaAs/GaAs heterojunction bipolar transistors

In high current and power density applications of AlGaAs/GaAs heterojunction bipolar transistors (HBT's), reliability is a critical issue. Therefore, in this letter we show results of a fundamental investigation on the temperature and current dependence of the fast initial rise of the dc-current gain (burn-in), which takes place during stress at current densities beyond those of today's applications. We find that the burn-in occurs at lower device junction temperatures (135°C) than previously reported in literature, and that it depends linearly on the current density. An activation energy of 0.4 eV is extracted for the burn-in effect     

GaAsSb for heterojunction bipolar transistors

The advantages of using GaAsSb in heterojunction bipolar transistors (HBT) are discussed with emphasis on two recent experimental results in the AlGaAs/GaAsSb material system. The performances of a prototype n-p-n AlGaAs/GaAsSb/GaAs double HBT (DHBT) that exhibits stable current gain with maximum collector current density of 5×10 ⁴ A/cm², and a p-n-p AlGaAs/GaAs HBT with a superlattice GaAsSb emitter ohmic contact which has a specific contact resistivity of 5±1×10^-7 Ω-cm² across the sample, are examined     

Significant operating voltage reduction on high-speed GaAs-based heterojunction bipolar transistors using a low band gap InGaAsN base layer

We report the fabrication of double heterojunction bipolar transistors (DHBTs) with the use of a new quaternary InGaAsN material system that takes advantage of a low-energy band gap E/sub G/ in the base to reduce operating voltages in GaAs-based electronic devices. InGaP/In/sub 0.03/Ga/sub 0.97/As/sub 0.99/N/sub 0.01//GaAs DHBTs with improved band gap engineering at both heterojunctions exhibit a DC peak current gain over 16 with small active emitter area. The use of the lattice-matched In/sub 0.03/Ga/sub 0.97/As/sub 0.99/N/sub 0.01/ (E/sub G/=1.20 eV) base layer allows a significant reduction of the turn-on voltage by 250 mV over standard InGaP/GaAs HBTs, while attaining good high-frequency characteristics with cutoff frequency and maximum oscillation frequency as high as 40 GHz and 72 GHz, respectively. Despite inherent transport limitations at the present time, which penalize peak frequencies, this novel technology provides comparable RF performance to conventional devices with a GaAs control base layer but at much lower operating base-emitter bias conditions. This technical progress should benefit to the next generation of RF circuits using GaAs-based HBTs with lower power consumption and better handling of supply voltages in battery-operated wireless handsets.     

Analysis of heterojunction bipolar transistor/resonant tunnelingdiode logic for low-power and high-speed digital applications

A high-speed digital logic family based on heterojunction bipolar transistors (HBTs) and resonant tunneling diodes (RTDs) is proposed. The negative differential resistance of RTDs is used to significantly decrease the static power dissipation. SPICE simulations indicate that propagation delay time below 150 ps at 0.09-mW static power per gate should be obtainable     

Insulated gate bipolar transistor reliability testing protocol for PV inverter applications

To decrease the cost of ownership of photovoltaic systems, less costly and more reliable photovoltaic inverters must be developed. Insulated gate bipolar transistors are a significant cause of inverter failures and system inefficiencies, so a thorough understanding of their strengths and weaknesses with regards to inverters is necessary. This paper summarizes the current state of experimentation surrounding the use of IGBTs in photovoltaic inverters and discusses their construction, use, lifetime, and reliability of IGBTs regularly used in photovoltaic inverters. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

GaAs heterojunction bipolar transistor device and IC technology forhigh-performance analog and microwave applications

GaAs-AlGaAs n-p-n heterojunction bipolar transistor (GaAs HBT) technology and its application to analog and microwave functions for high-performance military and commercial systems are discussed. In many applications the GaAs HBT offers key advantages over the alternative advanced silicon bipolar and III-V compound field-effect-transistor (FET) approaches. TRW's GaAs HBT device and IC fabrication process, basic HBT DC and RF performance, examples of applications, and technology qualification work are presented and serve as a basis for addressing general capability issues. A related 3-μm emitter-up, self-aligned HBT IC process provides excellent DC and RF performance, with simultaneous gain-bandwidth product, f_T, and maximum frequency of oscillation, f_max, of approximately 20-40 GHz and DC current gain β≈50-100 at useful collector current densities ≈3-10 kA/cm², early voltage ≈500-1000 V, and MSI-LSI integration levels. These capabilities facilitate versatile DC-20-GHz analog/microwave as well as 3-6 Gb/s digital applications, 2-3 G sample/s A/D conversion, and single-chip multifunctions with producibility     

Small H-shaped antennas for MMIC applications

A small short-circuited H-shaped GaAs monolithic microwave integrated circuits (MMICs) patch antenna is presented. Resonant at 5.98 GHz, it is the lowest frequency MMIC patch antenna reported that we are aware of and is intended for short-range communications (e.g., vehicular). Initial experimental and theoretical characterization of the proposed structure has been carried out on soft microstrip substrates. It has been shown that the size of an H-shaped patch antenna can be reduced to as low as one tenth of that of a half wavelength patch antenna resonant at the same frequency, saving valuable substrate space. The resonance frequency, radiation patterns and gain have been investigated. Ground plane truncation effects, which are important for MMIC applications, have been examined using the finite-difference time-domain (FDTD) method     

Miniaturised microstrip antenna for MMIC applications

A novel miniaturised quarter wavelength, H-shaped antenna which will find applications in monolithic microwave integrated circuit (MMIC) design is presented. The antenna occupies approximately one tenth of the substrate area of a half wavelength patch antenna. The effect on the resonance frequency, bandwidth and gain of the antenna are reported     

Re-engineering silicon: Si-Ge heterojunction bipolar technology

Thanks to refined techniques of material growth, circuits based on Si-Ge devices have made their way to market and bode especially well for wireless communications. The author reviews material properties, HBT technologies and circuit applications