Thermal coupling in 2-finger heterojunction bipolar transistors

We have previously analyzed the collapse phenomenon in heterojunction bipolar transistors (HBT's) when the mutual couplings among the transistor fingers are negligible. In this investigation, we derive the collapse loci equations in 2-finger HBT's in the presence of thermal coupling. It is found that the collapse loci equations are closely linked to a thermal instability condition best determined from the transistor regression characteristics. Unlike the previous derivation assuming zero thermal coupling, the collapse loci equations derived here are different depending on whether the HBT is driven by constant base current or constant base voltage bias     

Thermal properties and thermal instabilities of InP-basedheterojunction bipolar transistors

We investigate the physical parameters which are critical to the understanding of the thermal phenomena in InP-based heterojunction bipolar transistors. These parameters include thermal resistance, thermal-electric feedback coefficient, current gain, and base-collector leakage current. We examine the thermal instability behavior in multi-finger HBTs, and observe for the first time the collapse of current gain in InP-based HBTs. Based on both measurement and modeling results, we establish the reasons why the collapse is rarely observed in InP HBT's, in a sharp contrast to AlGaAs/GaAs HBT's. We compare the similarities and differences on how InP-based HBT, GaAs-based HBT, and Si-based bipolar transistors react once the thermal instability condition is met. Finally, we describe the issues involved in the design of InP HBTs     

Comparison of GaInP/GaAs heterostructure-emitter bipolartransistors and heterojunction bipolar transistors

Carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBT's) and heterostructure-emitter bipolar transistors (HEBT's) grown by MOCVD were fabricated. Experimental comparison of HBT's and HEBT's has been made based on the dc and the RF performance. HBT's have higher current gains than those of HEBT's in the high current regime, while HEBT's offer a smaller offset voltage and better uniformity in dc characteristics across the wafer. The current gain and cutoff frequency of the DEBT with a 150 Å emitter set-back layer are comparable to those of HBT's. DC (differential) current gains of 600 (900) and 560 (900) were obtained at a collector current density of 2.5×10⁴ A/cm² for the HBT and HEBT, respectively. The cutoff frequencies are 37 and 31 GHz for the HBT and HEBT, respectively. It is shown that there is negligible contribution of the diffusion capacitance to the emitter capacitance in HEBT's with a thin emitter set-back layer but not with a thick emitter set-back layer. The behavior of HEBT's both in dc and RF characteristics is similar to that of HBT's     

Compact multiple-valued multiplexers using negative differentialresistance devices

Quantum electronic devices with negative differential resistance (NDR) characteristics have been used to design compact multiplexers. These multiplexers may be used either as analog multiplexers where the signal on a single select line selects one out of four analog inputs, or as four-valued logic multiplexers where the select line and the input lines represent one of four quantized signal values and the output line corresponds to the selected input. Any four-valued logic function can be implemented using only four-valued multiplexers (also known as T-gates), and this T-gate uses just 13 devices (transistors) as compared to 44 devices in CMOS. The design of the T-gate was done using a combination of resonant tunneling diodes (RTD's) and heterojunction bipolar transistors (HBT's) with the folded I-V characteristic (NDR characteristic) of the RTD's providing the compact logic implementation and the HBT's providing the gain and isolation. The application of the same design principles to the design of T-gates using other NDR devices such as resonant tunneling hot electron transistors (RHET's) and resonant tunneling bipolar transistors (RTBT's) is also demonstrated     

Thermal stability of emitter ballasted HBT's

A simple analytical model is derived for thermoelectronic stability in heterojunction bipolar transistors (HBT's). An expression is presented for the value of emitter ballast resistor needed to stabilize the transistor. The result leads to a stability diagram on the current-voltage (I-V) plane which aids in the selection of emitter ballast resistors     

Thermal stability analysis of AlGaAs/GaAs heterojunction bipolartransistors with multiple emitter fingers

A numerical electro-thermal model was developed for AlGaAs/GaAs heterojunction bipolar transistors (HBT's) to describe the base current, current gain and output power dependence on junction temperature. The model is applied to microwave HBT devices with multi-emitter fingers. The calculated results of the common-emitter, current-voltage characteristics in the linear active region show a “current crush” effect due to inherent nonuniform junction temperature, current density and current gain distribution in the device. The formation of highly localized high temperature regions, i.e., hot spots, occur when the device is operating beyond the current-crush point. This thermally induced current instability imposes an upper limit on the power capability of HBT's. The dependence of this effect on various factors is discussed. These factors include the intrinsic parameters such as the base current ideality factor, the “apparent” valence band discontinuity, and the temperature coefficient of the emitter-base turn-on voltage, as well as the extrinsic factors such as the emitter contact specific resistance, the substrate thermal conductivity and the heat source layout     

Neutral base recombination and its influence on the temperaturedependence of Early voltage and current gain-Early voltage product inUHV/CVD SiGe heterojunction bipolar transistors

We present the first comprehensive investigation of neutral base recombination (NBR) in ultra-high vacuum/chemical vapor deposited (UHV/CVD) SiGe heterojunction bipolar transistors (HBT's), and its influence on the temperature characteristics of Early voltage (V_A ) and current gain-Early voltage product (βV_A). We show that a direct consequence of NBR in SiGe HBT's is the degradation of V_A when transistors are operated with constant-current input (forced-I_B) as opposed to a constant-voltage input (forced-V_BE). In addition, experimental and theoretical evidence indicates that with cooling, V_A in SiGe HBT's degrades faster than in Si bipolar junction transistors (BJT's) for forced-I_B mode of operation. Under the forced-V_BE mode of operation, however, SiGe HBT's exhibit a thermally-activated behavior for both V_A and βV_A, in agreement with the first-order theory. The differences in V_A as a function of the input bias and temperature for SiGe HBT's are accurately modeled using a modified version of SPICE. The performance of various practical SiGe HBT circuits as a function of temperature, in the presence of NBR, is analyzed using this calibrated SPICE model     

1 W Ku-band AlGaAs/GaAs power HBT's with 72% peak power-addedefficiency

High power and high-efficiency multi-finger heterojunction bipolar transistors (HBT's) have been successfully realized at Ku-band by using an optimum emitter ballasting resistor and a plated heat sink (PHS) structure. Output power of 1 W with power-added efficiency (PAE) of 72% at 12 GHz has been achieved from a 10-finger HBT with the total emitter size of 300 μm². 72% PAE with the output power density of 5.0 W/mm is the best performance ever reported for solid-state power devices with output powers more than 1 W at Ku-band     

In situ phosphorus-doped polysilicon emitter technology for veryhigh-speed, small emitter bipolar transistors

In situ phosphorus-doped polysilicon emitter (IDP) technology for very high-speed, small-emitter bipolar transistors is studied. The device characteristics of IDP transistors are evaluated and compared with those of conventional ion-implanted polysilicon emitter transistors. IDP technology is used to fabricate double polysilicon self-aligned bipolar transistors and the I-V characteristics, current gain, transconductance, emitter resistance, and cut-off frequency are measured. In conventional transistors, these device characteristics degrade when the emitter is small because of the emitter-peripheral-thick-polysilicon effect. In IDP transistors, the peripheral effect is completely suppressed and large-grain, high-mobility polysilicon can be used. The device characteristics, therefore, are not degraded in sub-0.2-μm emitter transistors. In addition, large-grain, high-mobility, and high phosphorus concentration IDP films increase current gain and lower emitter resistance. The use of IDP technology to build very small emitter transistors is evaluated and discussed     

无坑洞n-3C-SiC/p-Si(100)的LPCVD外延生长及其异质结构特性

在MBE/CVD高真空系统上,利用低压化学气相淀积(LPCVD)方法在直径为50mm的单晶Si(100)衬底上生长出了高取向无坑洞的晶态立方相碳化硅(3C-SiC)外延材料,利用反射高能电子衍射(RHEED)和扫描电镜(SEM)技术详细研究了Si衬底的碳化过程和碳化层的表面形貌,获得了制备无坑洞3C-SiC/Si的优化碳化条件,采用霍尔(Hall)测试等技术研究了外延材料的电学特性,研究了n-3C-SiC/p-Si异质结的I-V、C-V特性及I-V特性对温度的依赖关系.室温下n-3C-SiC/p-Si异质结二极管的最大反向击穿电压达到220V,该n-3C-SiC/p-Si异质结构可用于制备宽带隙发射极SiC/Si HBTs器件.     

Initial degradation of base-emitter junction in carbon-dopedInP/InGaAs HBTs under bias and temperature stress

Bias-temperature stress tests were performed to examine the stability of base-emitter junction characteristics of carbon-doped InP/InGaAs heterojunction biopolar transistors (HBT's). Two different kinds of degradation modes were observed from the Gummel I-V characteristics. One is characterized by the gradual increase in a nonideal base current. The generation of the nonideal current strongly depends on the crystallographic orientation of the emitter mesa. The other degradation mode was observed when a large current (200 kA/cm²) was injected under a high ambient temperature (180°C). This degradation is characterized by an initial decrease in turn-on voltage and significant drop in current gain     

The use of base ballasting to prevent the collapse of current gainin AlGaAs/GaAs heterojunction bipolar transistors

We propose the use of base-ballasting resistance to guarantee absolute thermal stability in AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Base-ballasted HBTs are fabricated and the measured I-V, regression and S-factor characteristics are discussed. We present a numerical model which elucidates the reasons why the base-ballasting scheme is helpful to HBTs but is damaging to silicon bipolar transistors. We compare measured small-signal and large-signal performances of unballasted, emitter-ballasted, and base-ballasted HBTs     

112-GHz collector-up Ge/GaAs heterojunction bipolar transistorswith low turn-on voltage

This paper reports small-sized collector-up Ge/Ga/As heterojunction bipolar transistors (HBT's) operating at low power and high frequency. A heavily B-doped Ge base-layer and a newly-developed self-aligned process reduce the base resistance and the parasitic elements. Intrinsic base resistance is 50 Ω/□; this is the lowest value reported for bipolar transistors. With limiting the active emitter area through B ion implantation, these collector-up HBT's with a collector size of 2×5 μm² exhibit a current gain of 60. They exhibit a maximum oscillation frequency f_max of 112 GHz with an associated current gain cutoff frequency f_T of 25 GHz. The large value of f_max, exceeding 100 GHz, is attributed to the extremely low base resistance caused by the heavily B-doped base-layer and the self-aligned process and to the low base-collector capacitance expected from the collector-up structure. The turn-on voltage of these HBT's is approximately 0.7 V smaller than that of AlGaAs/GaAs HBT's. These results show that these HBT's have excellent potential for low-power dissipation circuits     

Orientation effect on AlGaAs/GaAs heterojunction bipolartransistors

Orientation effects on N-p-n AlGaAs/GaAs heterojunction bipolar transistors (HBT's) have been demonstrated for the first time. We have observed that the current gains of HBT's fabricated on the same wafer are strongly dependent on the emitter direction. The HBT's with emitter direction of [010] show the highest current gain and the smallest emitter-size effect. This orientation effect could be attributed to the piezoelectric effect, which superposes the piezoelectric charges to the original emitter doping and generates the weak lateral electric field that drifts the injected carriers at the emitter periphery. The difference of the saturation voltage between collector-emitter of those HBT's corresponds to the superposed piezoelectric charges     

DC modeling and characterization of AlGaAs/GaAs heterojunctionbipolar transistors for high-temperature applications

The large signal dc characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBT) at high temperatures (27°-300°C) are reported. A high-temperature SPICE model is developed which includes the recombination-generation current components and avalanche multiplication which become extremely important at high temperatures. The effect of avalanche breakdown is also included to model the current due to thermal generation of electron/hole pairs causing breakdown at high temperatures. A parameter extraction program is developed and used to extract the model parameters of HBT's at different temperatures. Fitting functions for the model parameters as a function of temperature are developed. These parameters are then used in the SPICE Ebers-Moll model for the dc characterization of the HBT at any temperature between (27°-300°C)     

Microwave low-noise AlGaAs/InGaAs HBT's with p+-regrownbase contacts

This paper reports low-noise AlGaAs/InGaAs heterojunction bipolar transistors (HBT's) with p⁺-regrown base contacts. To reduce the thermal and shot noises, we have reduced R_B by using a p ⁺-regrown base contact and have reduced τ_B by using a compositionally-graded thin base layer. As a result, F_min values of 0.9, 1.1, 1.2, and 1.6 dB were obtained at 2, 6, 12, and 18 GHz, respectively. These low-noise characteristics of our HBT's show high potential for low-noise application     

MOS功率晶体管特性的温度效应

已设计的实验能够在同一仪器上方便地测量MOS功率管的脉冲I-V输出特性、直流I-V输出特性和器件内部的温度。对实验结果进行的综合分析表明,阈值电压随温度的增加而减小将引起MOS功率管的热不稳定,而表面迁移率随温度的增高而下降使MOS功率管的直流I-V特性在大电流区域呈观负阻。本文提出了反映热特性的两个特征点,给出了这两点处的栅源电压与器件设计参数的关系,作为MOS功率管热特性设计的依据。     

SiGe HBT器件的可靠性技术

介绍了SiGe异质结双极晶体管的特点,对SiGe异质结双极晶体管的物理机理进行了讨论,进而分析了影响其可靠性的各种可能因素,总结了目前SiGe HBT可靠性加速寿命试验方法,并进行了比较。     

Theory of electrothermal behavior of bipolar transistors: part II-two-finger devices

A thorough theoretical and numerical analysis of the electrothermal behavior of two-finger bipolar transistors is presented. It is shown that thermal feedback and coupling effects introduce an additional singularity in the output I-V characteristics, namely a current bifurcation, which manifests itself as multiple solution branches emanating from a branching point. As a result, when the bifurcation condition is reached, the device is triggered in an asymmetrical operation mode in which one device carries most of the current. A unified formulation for the electrothermal behavior of a two-finger device is derived for different bias conditions at the input port: constant voltage, constant base current and constant emitter current. The analysis proofs that the critical condition defining the onset of current bifurcation is the same for all kinds of bias conditions. While operation under a constant base-emitter voltage is limited by the flyback condition, the current bifurcation condition defines the boundary of the normal operation region for the constant base current and constant emitter current cases. Finally, a rigorous method for identifying the conditions of thermal instability for an arbitrary number of emitter fingers is outlined. As an example, the method is used to derive the thermal instability conditions for the general case of temperature dependent thermal conductivity in a two-finger device.     

Modulating HBT's current gain by using externally biased on-ledgeSchottky diode [GaAs devices]

The current gain of heterojunction bipolar transistors (HBT's) can be effectively modulated through Schottky diodes that contact the emitter passivation ledge directly. The behavior of the gain modulation is determined by the degree of the emitter ledge depletion. If the ledge is fully depleted, HBT's current gain can be modulated in the whole base-emitter bias voltage (V_BE) range up to 1.6 V. If the ledge is partially depleted, HBT's current gain can be modulated only in the low V_BE range (<1.35 V). This discovery leads to a simple method for monitoring the effectiveness of HBT's emitter ledge passivation and offers new insights to the mechanism of HBT gain degradation. It also creates a four-terminal HBT with an extra ledge electrode biased to control and modulate device's current gain at microwave frequencies