High Collector Current Density Research Articles

High-Gain Gated Lateral Power Bipolar Junction Transistor

We demonstrated a prototype Gated Lateral power bipolar junction transistor (GLP-BJT) on wide bandgap semiconductor. The device combined the intrinsic advantages of high current gain of a Gated Lateral-BJT and good current handling and voltage blocking capabilities of GaN material. As a result, the common-emitter current gain remained over 300 at a high collector current density of 2 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> despite a wide p-base region of 2 μm. The open base breakdown voltage BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</sub> was over 300 V corresponding to a high critical field of 2.5 MV/cm. These figures of merit show great promise of GaN-based GLP-BJT in power applications and also shed light on the development of state-of-the-art bipolar transistors based on other wide bandgap semiconductors.

Online monitoring of IGBT junction temperature based on Vce measurement

In this paper, an online junction temperature monitoring method based on the on-state voltage under high collector current density measurements for IGBT power modules is proposed. Unlike the conventional junction temperature monitoring method, the presented method can extract the junction temperature during operation without altering the modulation strategy or topology of the converter. The proposed method is verified by simulations and the JEDEC-51 standard recommended approach. To accurately extract the on-state voltage during operation, a measurement circuit that combines the advantages of both the active MOSFET clamp and the diode clamp is designed and tested. It has been shown to have good accuracy and a rapid response time. After the calibration results are obtained, the presented method is applied to a three-phase voltage source converter controlled by a closed-loop SVPWM modulation strategy.

Design and Development of InP DHBTs With High Breakdown Voltage for Ka-Band PA Applications

Type-I (straddled) InP DHBT devices have been fabricated to study the impact of different base-collector junction transition layer designs on the collector to emitter breakdown behavior, breakdown voltage, BVceo and the device output performance such as knee voltage, Vknee at high collector current densities, Jc. An abrupt breakdown behavior with BVceo of 11V and Vknee less than 1V at Jc>100kA/cm2 are achieved using an optimized base collector junction transition layer design. Using 2D numerical simulations, components of leakages dominating Iceo at low and high collector to emitter bias voltages are explained. It is further shown that the optimized device exhibits good RF and power performance achieving f $_{T}$ of 115GHz and f $_{max}$ of 150GHz at emitter width >1um. An MMIC power amplifier (PA) is also designed and fabricated using the optimized Type-I InP DHBT device. At 28GHz, good power performance is achieved with PAE of 54% and Psat of 26dBm. Thus, it is shown that InP DHBTs developed in this work are a good candidate for the next phase of 5G millimeter wave Ka-band power amplifier applications.

4H-SiC monolithic Darlington transistors with slight current gain drop at high collector current density

Profit from high current gain features, 4H-SiC power Darlington transistor has the capacity for handling high current transmission. In this paper, monolithic Darlington transistors were fabricated using a simultaneous formation process for both n-type (emitter) and p-type (base) ohmic contact. The isolated device shows current gain of 1061 and 823 with collector current density ( J C) increasing from 200 to 800 A/cm2, exhibiting a slight current gain drop at high J C. By extracting the interface state density ( D it) between SiO2 and p-type 4H-SiC, it is found that this advantage owes to the improvement of the shallow bulk minority carrier lifetime in base region. Furthermore, ISE-TCAD (technology computer aided design) simulation was carried out to study the relationship between base minority lifetime and the current gain, from which the total base minority lifetime is estimated to be 48 ns. The open base breakdown voltage ( BV CEO) is 850 V at a leakage current of 2 μA due to the electric filed crowding at the isolation bottom between drive bipolar junction transistor (BJT) and output BJT. To solve this, non-isolated devices were also fabricated with improved BV CEO of 2370 V, indicating the superior potential of 4H-SiC monolithic Darlington transistors for high power application, while the current gain is deceased to 420, which needs further improvement.

InP/InGaAs double heterojunction bipolar transistors with BV CEO = 12 V and f max = 470 GHz

0.25 μm emitter InP/InGaAs double heterojunction bipolar transistors (DHBTs) are presented that simultaneously exhibit a high collector current density (J c) of more than 3 mA/μm2 and high breakdown voltage (BVCEO) of 12 V. The DHBTs consist of a 30 nm-thick InGaAs base, 250 nm-thick InGaAs/InAlGaAs/InP collector and 150 nm-thick n-doped InP field buffer. Since the doping level of the InP field buffer is relatively high, only the InGaAs/InAlGaAs/InP collector is depleted at low V CE. Thus, the DHBTs can provide f t = 173 GHz and f max = 470 GHz at J c = 3.5 mA/μm2. On the other hand, at a high V CE, both the InGaAs/InAlGaAs/InP collector and InP field buffer are depleted. Therefore, the effective depletion thickness increases, which results in a BVCEO of 12 V. These results indicate that the use of the InP field buffer provides both high-speed performance and high BVCEO.

Investigation of the degradation mechanisms of InP/InGaAs DHBT under bias stress conditions to achieve electrical aging model for circuit design

The reliability of InP/InGaAs DHBT under high collector current densities and low junction temperatures is analyzed and modeled. From the Gummel characteristics, we observe several types of device degradation, resulting from the long term changes of base and collector current in both lower and higher base–emitter voltage ranges which impacts the reduction of DC current gain. In this paper, we investigate the underlying physical mechanism of base and collector current degradation with the help of TCAD device simulation. We chose the HICUM model level2 for the modeling purpose to evaluate the drift of model parameters according to stress time. The evolution of the model parameters is described with suitable equations to achieve a physics based compact electrical aging model. The aging laws and the parameter evolution equations with stress time are implemented in compact electrical aging model which allows us to simulate the impact of device failure mechanisms on the circuit in operating conditions.

High-Speed and High-Reliability InP-Based HBTs With a Novel Emitter

This paper describes InP HBTs with a novel emitter simply consisting of a degenerately doped n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs layer and an undoped InP thin layer. An n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InP layer is not necessary because the quasi-Femi level in the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs layer is high enough to exceed the conduction band discontinuity between the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs layer and the undoped InP layer. In the proposed structure, a thin ( ~ 10 nm) ledge structure can easily be fabricated by etching the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs layer. The fabricated HBTs with a 15-nm-thick ledge structure provide a high collector current density of over 6 mA/¿m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . There is almost no degradation of current gain, although the emitter width is reduced to as small as 0.5 ¿m. The HBTs also exhibit an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ft</i> of 324 GHz at a collector current density of 5.5 mA/¿m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is comparable with that of HBTs with a conventional emitter consisting of an n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs layer, an n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InP layer, and an n-InP layer. From the results of accelerated life tests, the activation energy of the degradation in HBTs is estimated to be around 1.8 eV, and the extrapolated mean time to failure is estimated to be over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> h at a junction temperature of 125°C.

In0.69Al0.31As0.41Sb0.59/In0.27Ga0.73Sb double-heterojunction bipolar transistors with InAs0.66Sb0.34 contact layers

Presented are the first DC and RF results for a double heterojunction bipolar transistor, at a 6.2 Å lattice constant, incorporating InAs0.66Sb0.34. These devices show excellent performance with a high collector current density of 1.9×105 A/cm2, high breakdown voltage over 2.5 V, high short-circuit current gain cutoff frequency of 59 GHz, and maximum frequency of oscillation of 34 GHz.

Composite-Collector InGaAs/InP Double Heterostructure Bipolar Transistors with Current-Gain Cutoff Frequency of 242 GHz

To eliminate the conduction band spike at the base-collector interface, an InP/InGaAs double heterostructure bipolar transistor (DHBT) with an InGaAsP composite collector is designed and fabricated using the conventional mesa structure. The DHBT with emitter area of 1.6 × 15 μm2 exhibits current-gain cutoff frequency ft = 242 GHz at the high collector current density Jc = 2.1 mA/μm2, which is to our knowledge the highest ft reported for the mesa InP DHBT in China. The breakdown voltage in common-emitter configuration is more than 5 V. The high-speed InP/InGaAs DHBT with high current density is very suitable for the application in ultra high-speed digital circuits.

Highly Reliable Submicron InP-Based HBTs with over 300-GHz ft

We have developed 0.5-μm-emitter InP-based HBTs with high reliability. The HBTs incorporate a passivation ledge structure and tungsten-based emitter metal. A fabricated HBT exhibits high collector current density and a current gain of 58 at a collector current density of 4mA/μm2. The results of dc measurements indicate that the ledge layer sufficiently suppresses the recombination current at the emitter-base periphery. The HBT also exhibits an ft of 321GHz and an fmax of 301GHz at a collector current density of 4mA/μm2. The ft does not degrade even though the emitter size is reduced to as small as 0.5μm×2μm. The results of an accelerated life test show that the degradation of dc current gain is due to thermal degradation of the interfacial quality of semiconductors at the passivation ledge. The activation energy is expected to be around 1.5eV, and the extrapolated mean time to failure is expected to be over 108 hours at a junction temperature of 125°C. These results indicate that this InP HBT technology is promising for making over-100-Gbit/s ICs with high reliability.

Effect of Mixed-Mode Electrical Stress on High-Frequency and RF Power Characteristics of SiGe Hetero-Junction Bipolar Transistors

In this study, we investigate the hot-carrier stress effects on the high-frequency and RF power characteristics of Si/SiGe hetero-junction bipolar transistors (HBTs). By simultaneously applying a high collector current density and a high collector–base voltage on Si/SiGe HBTs, because hot carriers will be induced; they will then degrade device performance. This is interesting because this stress condition is similar to the DC bias condition of a current source RF power amplifier, termed as the “mixed-mode” stress. We find that not only the high-frequency characteristic is adversely affected by but also the output power performance of Si/SiGe HBTs suffers from this electrical stress. In addition, we found that the degradations of the high-frequency and power characteristics of such HBTs are worse in constant-base-current measurement than in constant-collector-current measurement. We finally examined the degradations in terms of parasitic resistance and the ideality factors of base and collector currents using a large-signal model.

Kirk effect mechanism in type-II InP∕GaAsSb double heterojunction bipolar transistors

The Kirk effect mechanism is studied in type-II InP∕GaAsSb∕InP NpN double heterojunction bipolar transistors (DHBTs) both experimentally and through two-dimensional hydrodynamic numerical simulations. We show that the large valence band discontinuity ΔEV at the GaAsSb–InP base∕collector heterojunction does not allow hole injection into the InP collector as is the case in homojunction collectors. Instead, a blocking barrier is electrostatically induced in the base layer at high collector current densities: this barrier increases base recombination and decreases the current gain. We show that tunneling transport must be considered at the base∕collector heterojunction and that the induced barrier depends on the base layer doping level—effectively, InP∕GaAsSb DHBTs display high-current limitations that are also controlled to some extent by the base doping level.

Electrical stress effect on RF power characteristics of SiGe hetero-junction bipolar transistors

In this paper, we investigate the electrical stress effects on both the high-frequency and RF power characteristics of Si/SiGe HBTs. Simultaneously applying a high collector current density and a high collector–base voltage upon the Si/SiGe HBTs, their hot carriers will induce device performance degradation. This stress condition is similar to the DC bias conditions of a current source RF power amplifier, and is termed as a “mixed-mode” stress. We find that not only the maximum oscillation frequency but also the output power performance of Si/SiGe HBTs are suffered by this electrical stress. In addition, the degradations of high-frequency and power characteristics are also worse under a constant base-current measurement than those under a constant collector-current measurement. Finally, we developed a commercial large-signal model to examine the degradations of the parasitic resistances and ideality factors of base and collector currents to explain the RF power and linearity degradations.

English

The cutoff frequency performance of an NPN Si/SiGe/SiGe single-heterojunction bipolartransistor (SiGe SHBT) at high collector current densities has been analysed using a 2-D MEDICIdevice simulator. A conventional NPN Si/SiGe/Si double-heterojunction bipolar transistor(SiGe DHBT) having uniform 20 atomic per cent of germanium in the base region has beeninvestigated for comparison. The analysis shows the formation of a retarding potential barrierfor minority carrier electrons at the base-collector heterojunction of the DHBT structure. Whereas,the base-collector homojunction of the SiGe SHBT structure, having a uniform 15 atomic percent of germanium profile in its base and collector, inhibits the formation of such a retardingpotential barrier, the SHBT structure with a base-collector homojunction shows an improvedcutoff frequency at high collector current density in comparison with conventional SiGe DHBT,which makes it more promising for high speed, scaled down, field-specific applications.

Two-dimensional DC simulation methodology for InP/GaAs0.51Sb0.49/InP heterojunction bipolar transistor

This work describes a procedure to implement a two-dimensional hydrodynamic simulation of InP/GaAs0.51Sb0.49/InP double heterojunction bipolar transistor (DHBT). It concerns the DC characteristics and allows to fit some very sensitive but still unknown or uncertain parameters of GaAs0.51Sb0.49 material, such as the band gap energy and the minority carrier lifetime. In particular, the influence of the band gap narrowing on the DHBT DC operation is analyzed. Thereafter, the mechanisms of electron–hole recombination into GaAs0.51Sb0.49 are discussed and a typical value of the electron lifetime is calculated. Finally, the drop of DHBT performances at high collector current densities is highlighted.

Analysis and simulation of spectral regrowth in radio frequency power amplifiers

This work presents a novel method for efficiently analyzing the relationship between spectral regrowth and physical distortion mechanisms in radio frequency power amplifiers. It utilizes a Volterra series model whose coefficients are computed from basic SPICE parameters. The analysis uses a decomposition of the Volterra kernels into simpler subsystems in order to greatly reduce the computation times. The method is applied to the design of several bipolar-transistor power amplifiers after a series-based model is developed for representing the increase in active device forward transit time at high collector current densities. A number of single-stage SiGe power amplifiers have been designed, fabricated, and tested using the IEEE 802.11b and IS-95 modulation schemes at different carrier frequencies, and these results are compared with the theoretical analysis.

Study of Cutoff Frequency at High Collector Current Density in SiGe Single-Heterojunction Bipolar Transistor

The cutoff frequency performance of an NPN Si/SiGe/SiGe Single-heterojunction bipolar transistor (SiGe SHBT) at high collector current densities has been analyzed using a 2-dimensional MEDICI device simulator. A conventional NPN Si/SiGe/Si Double-heterojunction bipolar transistor (SiGe DHBT) having uniform 14%Ge in the base region has been investigated for comparison. The analysis shows the formation of a retarding potential barrier for minority carrier electrons at the basecollector heterojunction of the DHBT structure. Whereas, the base-collector homojunction of the SiGe SHBT structure, having a uniform 14%Ge profile in its base and collector, inhibits the formation of such a retarding potential barrier. The SHBT structure with a base-collector homojunction shows an Improved cutoff frequency at a high collector current density in comparison with conventional SiGe DHBT, which makes it more promising for high speed, scaled down, field-specific applications.

Study of improved reverse recovery in power transistor incorporating universal contact

The improvement in reverse recovery of power NPN bipolar transistor (BJT) through incorporation of “universal contact” in the base is studied in detail. It is shown that use of universal contact allows redistribution of base current in saturation from collector region where recombination lifetime is high to extrinsic base region where effective recombination lifetime is low. The reverse recovery time decreases as collector current density increases but increases as collector breakdown voltage increases. The improvement in reverse recovery is accompanied with an increase in collector–emitter voltage in the ON state. For low voltage transistors and high voltage transistors at low collector current densities, the increase is primarily due to reduction in reverse current gain. For high breakdown voltage transistors, the use of universal contact results in early onset of quasi-saturation effect and results in degradation in ON state voltage at high collector current densities.

Base transit time of an epitaxial n +pn −n + bipolar transistor considering Kirk effect

First an analytical expression for the base transit time in an epitaxial n +pn −n + bipolar transistor considering the field-dependent mobility and the electron velocity saturation before the onset of the Kirk effect is obtained. The base transit time is found to increase at the high collector current density. Whereas the existing analytical models show decrease of the transit time with the increase of the collector current density. The base transit time with the Kirk effect is also studied with a simple equation for transit time obtained after modifying De Graaff–Kloosterman formula for collector current. The Kirk effect is found to influence the base transit time of a bipolar transistor with highly doped base significantly at large collector current density.

AlGaN–GaN–AlInGaN induced base transistor

We have simulated an induced base transistor based on n-type GaN–AlGaN–GaN–AlInGaN heterostructure with a thin AlGaN emitter barrier and a thin GaN quantum well base. Our simulations show that such a majority carrier device should have a high collector current density, a low base resistance, a high current gain, and is expected to be a viable competitor to GaN-based heterostructure bipolar junction transistors.