Double Heterojunction Bipolar Transistors Research Articles

480-GHz $f_{\max}$ in InP/GaAsSb/InP DHBT With New Base Isolation $\mu$-Airbridge Design

Self-aligned 0.55×3.5 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> emitter InP/GaAsSb/InP double heterojunction bipolar transistors demonstrating an f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> of 310 GHz and an f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 480 GHz are reported. Common-emitter current gain of 24, together with a breakdown voltage of 4.6 V, is measured. The devices were fabricated with a triple-mesa process and easily fabricated with a new base isolation μ-airbridge design which, moreover, significantly reduced the base-collector capacitance C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BC</sub> .

Investigation of emitter size effect in InP/InGaAsSb/InGaAs double heterojunction bipolar transistors

The emitter size effect of a series InGaAsSb base series of InP/InGaAsSb/InGaAs heterojunction bipolar transistors (HBTs) with different emitter sizes is investigated. Compared to the InGaAs base HBTs, these devices exhibit much lower base surface recombination current. This is attributed to the surface Fermi level pinning near the valence band of the antimonide base. The effect of Sb composition and doping concentration of the base on the surface recombination current is well explained by the postulate.

InP/GaAsSb DHBTs Fabricated in a Low-Temperature Teflon Planarization Process

We demonstrate InP/GaAsSb/InP double heterojunction bipolar transistors (HBTs) fabricated in a low-temperature planarization process based on a spin-on Teflon amorphous fluoropolymer interlevel dielectric with ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 1.9 and a low dissipation factor. Devices with 0.3-μm-wide emitters show excellent junction characteristics, cutoff frequencies f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> = 362 GHz and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> = 450 GHz, a peak current gain β = 28, and a common-emitter breakdown voltage BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</sub> = 5.1 V. Teflon is seen to be an advantageous alternative to common benzocyclobutene and polyimide planarization dielectrics. A side-by-side comparison of devices fabricated in Teflon and airbridge processes shows nearly identical performances. The present approach is equally applicable to GaAs- and GaInAs-based HEMT and HBT technologies.

A 20-GHz ultra-high-speed InP DHBT comparator

An ultra-high-speed, master-slave voltage comparator circuit is designed and fabricated using InP/GaInAs double heterojunction bipolar transistor technology with a current gain cutoff frequency of 170 GHz. The complete chip die, including bondpads, is 0.75 × 1.04 mm2. It consumes 440 mW from a single −4 V power supply, excluding the clock part. 77 DHBTs have been used in the monolithic comparator. A full Nyquist test has been performed up to 20 GHz, with the input sensitivity varying from 6 mV at 10 GHz to 16 mV at 20 GHz. To our knowledge, this is the first InP based integrated circuit including more than 70 DHBTs, and it achieves the highest sampling rate found on the mainland of China.

Apparent base resistance decomposition by means of small-signal and high-frequency noise analyses of submicron InP/InGaAs HBTs

We present an original and reliable technique to elucidate the different contributions to the apparent base resistance (RB = RBx + XRBi) of double heterojunction bipolar transistors (HBTs) designed by Alcatel-Thales III–V Lab. The extrinsic base resistance (RBx) is quantified using small-signal measurements. The base-collector junction distribution factor (X) and the intrinsic base resistance (RBi) are extracted from high-frequency noise (HFN) measurements. This method was applied to three InP/InGaAs HBTs having different emitter surfaces (SE). The correct determination of RBx, X and RBi may be a useful tool for compact and/or linear electrical modelling and may give some guidelines to designers to improve operation frequencies. Moreover, this strategy can be applied to any layout and technological variation of HBT; it can be also applied to homojunction bipolar transistors. Our results show that HFN analysis should be included to fully characterize bipolar transistors.

Characterization of conduction band edge discontinuity for InAlAs/GaAsSb using InP/GaAsSb heterojunction bipolar transistors

AbstractIn this work, the temperature‐dependent DC performance of InP/GaAsSb double heterojunction bipolar transistors (DHBTs) with an InP/InAlAs composite emitter was characterized. The current transport mechanisms in DHBTs with a type‐I InAlAs/GaAsSb emitter–base junction interface and a type‐II GaAsSb/InP base–collector were studied. The experimental results reveal that electron injection at emitter–base junction could be affected by conduction barrier limited carrier transport. A conduction band edge discontinuity of 9.5 meV for InAlAs/GaAsSb heterojunction was experimentally estimated.

Physical modeling based on hydrodynamic simulation for the design of InGaAs/InP double heterojunction bipolar transistors

A physical model for scaling and optimizing InGaAs/InP double heterojunction bipolar transistors (DHBTs) based on hydrodynamic simulation is developed. The model is based on the hydrodynamic equation, which can accurately describe non-equilibrium conditions such as quasi-ballistic transport in the thin base and the velocity overshoot effect in the depleted collector. In addition, the model accounts for several physical effects such as bandgap narrowing, variable effective mass, and doping-dependent mobility at high fields. Good agreement between the measured and simulated values of cutoff frequency, ft, and maximum oscillation frequency, fmax, are achieved for lateral and vertical device scalings. It is shown that the model in this paper is appropriate for downscaling and designing InGaAs/InP DHBTs.

A collector current model for InAlAs/InGaAsSb/InGaAs double heterojunction bipolar transistors with non-ideal effects

A collector current model incorporating electron diffusion in the base and thermionic emission at the abrupt B–E heterojunction is derived and applied to InGaAsSb heterojunction bipolar transistors (HBTs). Parameters extracted from the model include effective base doping concentration, conduction band discontinuity (ΔEC) at the base-emitter junction, and emitter resistance. The calculated current from the model is consistent with the measured result. It is found that a high collector current ideality factor is resulted from a nonzero ΔEC and a low effective base doping concentration. Moreover, a nonzero ΔEC makes the high-injection effect almost invisible in collector current characteristics, even if it actually exists.

$\hbox{InGaP/GaAs}_{0.57}\hbox{P}_{0.28} \hbox{Sb}_{0.15}/\hbox{GaAs}$ Double HBT With Weakly Type-II Base/Collector Junction

We report on the dc characteristics of an InGaP/ GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.57</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.28</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> /GaAs double heterojunction bipolar transistor (DHBT). In comparison with control InGaP/GaAs single heterojunction bipolar transistors (SHBTs), the DHBT shows a lower turn-on voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE, on</sub> ) by ~ 70 mV, a lower knee voltage up to J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ~ 40 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and less temperature-sensitive current gain. The validity of reciprocity in the Gummel plot suggests no potential spikes at the emitter/base and base/collector (BC) junctions of the DHBT. By considering the differences, in terms of the built-in voltage of the BC junction, the Fermi level in the base, and the renormalized energy gap of the base, between the GaAsPSb DHBT and the control InGaP/GaAs SHBT, we conclude that the heavily p-doped GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.57</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.28</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> base and the lightly n-doped GaAs collector are in weakly type-II band alignment with a conduction and valence band offset of 44 and 221 meV, respectively. These findings indicate that GaAsPSb is a promising base material for DHBTs operating at high temperature and low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE, on</sub> conditions without suffering from the collector current blocking.

InP HBT Transferred to Higher Thermal Conductivity Substrate

We report the first demonstration of an InP double heterojunction bipolar transistor (HBT) transferred to a higher thermal conductivity substrate. This process allows lithographic access to both the frontside and backside of the device to minimize parasitic capacitances while transfer to a SiC substrate should reduce junction temperature by 42%, allowing for higher current density operation. The 0.20 × 3 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> emitter-area HBT has peak common-emitter current gain β = 22 and breakdown V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BR</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</sub> >; 4 V. No electrical degradation from the transferred-substrate process is observed. RF measurements show device peak <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">τ</sub> = 397 GHz, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ≥ 400 GHz, and maximum available gain (MAG) at 100 GHz is 15.3 dB.

RF performance of a novel all ternary InAlAs\\InGaAs DHBT

All ternary In0.52Al0.48As–In0.53Ga0.47As–In0.52Al0.48As double-heterojunction bipolar transistors (DHBTs) have been grown using solid-source molecular-beam epitaxy. The development of these DHBTs required epitaxial design trade-offs which culminated in an optimum structure achieving high-breakdown (5.5 V), and RF performance demonstrating unity cutoff frequency (ft) and maximum oscillation frequency (fmax) of 140 GHz and 95 GHz at relatively relaxed emitter dimensions of ∼1×5 µm2. This is the highest reported cutoff frequency for an all ternary In0.52Al0.48As–In0.53Ga0.47As–In0.52Al0.48As DHBT. The demonstration of the frequency performance at relaxed emitter dimensions shows potential for this material type.

Physical origins of nonlinearity in InP double heterojunction bipolar transistors

Two tone inter-modulation distortion measurements were performed at 18 GHz to characterize the nonlinearity of Type-I InP/InGaAs/InP and Type-I/II AlInP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs). Two-dimensional hydrodynamic (HD) simulations were also performed, showing that the base push-out and charge accumulation effects are the dominant physical origins of nonlinearity for the Type-I DHBT at high current densities. Comparatively, the Type-I/II DHBT exhibits no such effects. Hence, we conclude that DHBTs having a Type-I/II energy band alignment will have an inherent linearity advantage compared to DHBTs with the Type-I energy band alignment.

A Combined Model With Electrothermal Coupling and Electromagnetic Simulation for Microwave Multifinger InP-Based DHBTs

This paper presents a combined model with electrothermal coupling and electromagnetic (EM) simulation for multifinger InP-based double heterojunction bipolar transistors (DHBTs). The electrothermal coupling effect, which occurs in multifinger InP DHBTs, is characterized based on 3-D thermal simulation. In addition, EM simulation technique is presented to account for the distributed effect of interconnection of the fingers and their surroundings. A large-signal model for single-finger DHBTs is implemented as a seven-port symbolically defined device, which accounts for several physical phenomena, including the self-heating effect, Kirk effect, current blocking effect, mobile charge modulation of the base-collector capacitance, and velocity field modulation in the transit time. The combined model implemented in Agilent-ADS is verified by comparing the simulated and measured data in dc small-signal <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameters and large-signal microwave power characteristic. This approach allows a simple method to analyze and predict microwave multifinger InP DHBTs for power amplifier circuit design using commonly available computer-aided design tools such as Agilent-ADS.

GaN/InGaN heterojunction bipolar transistors with ultra‐high d.c. power density (&gt;3 MW/cm2)

AbstractWe report ultra‐high‐power performance on npn GaN/InGaN double heterojunction bipolar transistors (DHBTs) that is directly grown on a free‐standing (FS) GaN substrate. Measured common‐emitter current gain (hfe) reaches 80. A quasi‐static I–V measurement shows that JC &gt; 141 kA/cm2 and a power density of 3.05 MW/cm2 can be achieved for DHBTs grown on an FS‐GaN substrate. When the temperature is increased to 250 °C, a GaN/InGaN DHBT shows hfe = 43 and the offset voltage is reduced from 0.8 V at the room temperature to 0.3 V. Similarly, the knee voltage is reduced from 5.2 V at room temperature to 2.75 V at 250 °C. In this particular device, breakdown voltage (BVCEO) increases from 90 V at room temperature to 157 V at 250 °C.

Vertical-Gate Si/SiGe Double-HBT-Based Capacitorless 1T DRAM Cell for Extended Retention Time at Low Latch Voltage

A vertical-gate Si/SiGe double heterojunction bipolar transistor (VerDHBT)-based capacitorless 1T DRAM cell is proposed for improved storage performance with a fabrication feasibility through a selective epitaxy. It is verified through a TCAD device simulation for dc and transient characteristics of the proposed VerDHBT-based 1T DRAM. The off-state leakage current was significantly reduced, while the on-current was considerably increased with SIF/Bmid/DIF = SiGe/SiGe/Si as the interfacial source/middle body/interfacial drain. A large hysteresis window for the “read 1” from the “read 0” and a long retention time at low latch voltage could be also obtained.

Comparison of the performance for InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT

The characteristics of a double heterojunction bipolar transistor(DHBT) depend closely on the type of band alignment structure at the hetero-interface between emitter-base(E-B) heterojunction and base-collector(B-C) heterojunction. Based on thermionic-field-diffusion model, the comparisons are made of the DC and the RF characteristics between two novel HBTs, that is, InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT, of which the former has a type-I E-B junction and a type-II B-C junction and the later has a type-II E-B junction and a type-II B-C junction. The simulation results show that DHBT with a type-I E-B junction and a type-II B-C junction has much better current driving capability, DC gain and RF performance, although it has a slightly high turn-on voltage.

Characterization and Modeling of DHBT in InP/GaAsSb Technology for the Design and Fabrication of a Ka Band MMIC Oscillator

This paper presents the design of an MMIC oscillator operating at a 38 GHz frequency. This circuit was fabricated by the III–V Lab with the new InP/GaAsSb Double Heterojunction Bipolar Transistor (DHBT) submicronic technology (We=700 nm). The transistor used in the circuit has a 15 μm long two-finger emitter. This paper describes the complete nonlinear modeling of this DHBT, including the cyclostationary modeling of its low frequency (LF) noise sources. The specific interest of the methodology used to design this oscillator resides in being able to choose a nonlinear operating condition of the transistor from an analysis in amplifier mode. The oscillator simulation and measurement results are compared. A 38 GHz oscillation frequency with 8.6 dBm output power and a phase noise of −80 dBc/Hz at 100 KHz offset from carrier have been measured.

High breakdown voltage InGaAs/InP double heterojunction bipolar transistors with fmax = 256 GHz and BVCEO = 8.3 V

An InGaAs/InP DHBT with an InGaAsP composite collector is designed and fabricated using triple mesa structural and planarization technology. All processes are on 3-inch wafers. The DHBT with an emitter area of 1 × 15 μm2 exhibits a current cutoff frequency ft = 170 GHz and a maximum oscillation frequency fmax = 256 GHz. The breakdown voltage is 8.3 V, which is to our knowledge the highest BVCEO ever reported for InGaAs/InP DHBTs in China with comparable high frequency performances. The high speed InGaAs/InP DHBTs with high breakdown voltage are promising for voltage-controlled oscillator and mixer applications at W band or even higher frequencies.

65 GHz small-signal-bandwidth switched emitter follower in InP heterojunction bipolar transistors

Performances of two switched emitter follower structures for large bandwidth applications have been optimised, compared, implemented and measured. These circuits have been fabricated with a 320 GHz-FT InP double heterojunction bipolar transistor process. Measurements in track mode show a small-signal bandwidth over 65 GHz for one structure and over 50 GHz for the other. Track mode SFDR measured for 500 mVPP up to 15 GHz signal input is greater than 45 dBc.

Base charge accumulation and push-out effects on nonlinearity of Type-I InP/InGaAs/InP and Type-I/II AlInP/GaAsSb/InP double heterojunction bipolar transistors

The influence of energy band alignment on carrier transport and signal integrity is investigated on fabricated Type-I InP/InGaAs/InP and Type-I/II AlInP/GaAsSb/InP DHBTs. The Type-I double heterojunction bipolar transistor (DHBT) requires the use of a transition region (setback and superlattice layer) in base-collector hetero-interface to minimize the conduction band discontinuity that can cause current blocking in the collector I-V characteristics. Despite the effort, Type-I DHBT exhibits gain compression and base charge accumulation at high current injection, giving a nonlinear microwave operation. In contrast, the Type-I/II DHBT has a favorable band alignment and permits hot electron injection without impedance in both emitter-base and base-collector junctions, resulting in considerable microwave linearity improvement.