基于Matlab的基极电流理想因子提取方法研究

采用Matlab数字分析方法,结合多晶硅发射极双极器件基极电流的构成情况,阐述了不同理想因子电流成分分离的基本原理和数学方法。利用该方法分析了多晶硅发射极双极器件在正向大电流激励下的电参数退化过程中不同理想因子基极电流的变化情况,分析了导致各电流分量变化的物理机制。该理想因子提取方法普遍适用于各类双极型器件。     

Understanding the failure mechanisms of microwave bipolar transistors caused by electrostatic discharge

Electrostatic discharge(ESD) phenomena involve both electrical and thermal effects,and a direct electrostatic discharge to an electronic device is one of the most severe threats to component reliability.Therefore, the electrical and thermal stability of multifinger microwave bipolar transistors(BJTs) under ESD conditions has been investigated theoretically and experimentally.100 samples have been tested for multiple pulses until a failure occurred.Meanwhile,the distributions of electric field,current density and lattice temperature have also been analyzed by use of the two-dimensional device simulation tool Medici.There is a good agreement between the simulated results and failure analysis.In the case of a thermal couple,the avalanche current distribution in the fingers is in general spatially unstable and results in the formation of current crowding effects and crystal defects.The experimental results indicate that a collector-base junction is more sensitive to ESD than an emitter-base junction based on the special device structure.When the ESD level increased to 1.3 kV,the collector-base junction has been burnt out first.The analysis has also demonstrated that ESD failures occur generally by upsetting the breakdown voltage of the dielectric or overheating of the aluminum-silicon eutectic.In addition,fatigue phenomena are observed during ESD testing,with devices that still function after repeated low-intensity ESDs but whose performances have been severely degraded.     

Theory of electrothermal behavior of bipolar transistors: Part I -single-finger devices

A detailed theoretical and numerical analysis of the electrothermal behavior of single-finger bipolar transistors is proposed. Two models of different complexities are introduced to investigate self-heating effects in bipolar junction transistors (BJTs) and heterojunction bipolar transistors (HBTs) biased with a constant base-emitter voltage source or with a constant base current source. In the constant base-emitter voltage case, simple relations are derived for determining the onset of the flyback behavior in the output characteristics which defines the boundary of the safe operating region. The model indicates that the flyback behavior disappears at high V/sub BE/ values, and predicts a thermal hysteresis phenomenon at high currents. It is also shown that at high current levels the electrothermal behavior is dominated by ohmic base pushout. If a constant base current is applied, the model shows that both BJTs and HBTs are unconditionally thermally stable. The transient behavior is also considered, and the temperature evolution is investigated for different bias conditions. The model shows that, if the device is biased in the thermally unstable region, thermal breakdown occurs within a finite time instant in the limit case of a zero ballast resistance. Finally, the reduction in the safe operating area due to avalanche effects and to the temperature dependence of thermal conductivity is discussed, and a simplified model is proposed.     

Slow transients in polyimide-passivated InP-InGaAs HBTs: effects of UV irradiation, thermal annealing and electrical stress

The effects of UV irradiation, thermal annealing and electrical bias on the base current instability in polyimide (PI)-passivated InP-based heterojunction bipolar transistors (HBTs) have been studied. The base current transient could be effectively suppressed by UV irradiation. The suppression of current transient by UV irradiation can be attributed to the reduction of the near interface trap density in the PI, which has long-term stability at room temperature. However, baking the device at a temperature higher than 100 /spl deg/C may induce a significant increase in PI trap density as well as the broadening of spatial electron trap distribution causing the enhancement of current transient, and the current transient induced by electrical stress could be directly related to the device self-heating through thermal annealing effect.     

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     

Analysis of fast electrothermal dynamics in power BJT

It is well known that the self heating phenomenon in power bipolar devices strongly influences the electrical behavior. Heating phenomenon is a dynamic process ruled by different time constants. While the thermal dynamics associated to external heat exchange is an order of magnitude slower than the electrical one, the thermal dynamics occurring at the silicon level near the active junction is relatively faster and can interact with the electrical one. In this paper, it is proved that such a fast thermal dynamics is responsible for unstable oscillating electrical transients that can be detected in power bipolar transistors. An electrothermal resonance phenomenon Is theoretically and experimentally verified on a commercial power BJT. It is explained how such a phenomenon ran be operatively employed to extract the parameters of the fast thermal dynamics, difficult to measure with conventional procedures     

The collapse of current gain in multi-finger heterojunction bipolartransistors: its substrate temperature dependence, instability criteria,and modeling

One undesirable phenomenon observed when AlGaAs/GaAs heterojunction bipolar transistors (HBT's) are operated under high power density is the collapse (of current gain). The collapse manifests itself by a distinct abrupt decrease of collector current in the transistor common-emitter current-voltage (I-V) characteristics. In this investigation, we study the substrate temperature dependence of the collapse. A unified equation is introduced to relate the collapse instability criterion with other thermal instability criteria proposed for silicon bipolar transistors. The effects of the thermal instability on the collapse behavior of 2-finger and 1-finger HBT's are examined. We also present a numerical model to adequately describe the collapse in multi-finger HBT's having arbitrary geometry. The I-V characteristics and regression plots of both ballasted and unballasted HBT's are compared     

Bias dependence of high-frequency noise in heterojunction bipolar transistors

Hawkins' isothermal model developed to study noise in bipolar junction transistors (BJTs) is modified to investigate bias-dependent noise in heterojunction bipolar transistors (HBTs) by incorporating thermal effects. It is shown that the inclusion of thermal effects into the high-frequency noise model of HBTs is necessary as the temperature of the device may become very different from the ambient temperature, especially at high bias current. Calculation of the noise figure by including the thermal effect shows that the isothermal calculation may underestimate the noise figure at high bias current. It is observed that noise at low bias is ideality factor n dependent whereas high bias noise is insensitive to the variation of n. Moreover, the common base current gain plays a major role in the calculation of the minimum noise figure. The excellent fit obtained between the theoretical calculation and the measured data are attributed to the inclusion of the bias-dependent junction heating as well as C/sub De/ and C/sub bc/ into the present calculation.     

Thermal properties of very fast transistors

Recent predictions that thermal effects will limit future transistor speed improvement motivated an interest in predicting and measuring these effects. A mathematical model of the three-dimensional transient heat flow problem is presented which takes into account the physical structure of the device and the actual region of power dissipation. At any point within the device, the model predicts the time-dependent temperature response to a change in power dissipation. A new method of measuring the local time-dependent thermal behavior of small bipolar transistors is described and used to verify the model. It was found that the thermal spreading resistance becomes important in silicon transistors when the emitter stripe dimensions approach 1 µ. Furthermore, the thermal response is much slower than the electrical response. Also, it was confirmed that adjacent devices in integrated circuits are essentially thermally isolated as far as thermal spreading resistance is concerned.     

The effects of heavy impurity doping on AlGaAs/GaAs bipolartransistors

The effects of heavy impurity doping on the electrical performance of AlGaAs/GaAs heterojunction bipolar transistors are examined. Electrical measurements of GaAs diodes and transistors demonstrate that the electron current injected into p⁺-GaAs is unexpectedly large. These results provide evidence for a large effective bandgap shrinkage in p⁺-GaAs. The results are presented in a form suitable for device modeling. For the heavy p-type doping commonly used in the base of an n-p-n AlGaAs/GaAs heterojunction bipolar transistor, the effective bandgap shrinkage is comparable in magnitude to the bandgap variation designed into the device by its compositional variation. Two examples demonstrate that such effects must be considered when analyzing or designing such devices     

Double-interdigitated (TIL) bipolar power transistors with lightlydoped collectors

The results of an investigation concerning the implementation of the two-interdigitation-level (TIL) concept in TO-3-packaged, triple-diffused bipolar power n-p-n transistors with lightly doped collector are discussed. It is demonstrated that the TIL concept, which offers a fair balance between manufacturability ease/cost effectiveness and overall electrical performances, allows for an increase of both the DC and small-signal current gains and the voltage ratings of bipolar transistors. The peculiarities of the ON-state current carrying mechanism in TIL-type transistors was investigated and its impact on device behavior was also assessed     

Internal thermal feedback in four–poles especially in transistors

Thermal-electric interaction or "internal thermal feedback" occurs in temperature dependent devices and four-poles at low frequencies, if the thermal time constants are small. An electrical equivalent circuit which describes this thermal effect is generally derived and applied to transistors in common base and common emitter configuration. It consists of current sources and of resistance-inductance circuits which can be directly related to the thermal equivalent circuit of the device. It is shown that this thermal feedback should not be neglected in the measurement of high-frequency transistors, in the design of dc or video amplifiers and voltage or current regulators. Some measurements are reported and discussed. For instance, a strong frequency dependence of some four-pole parameters, especially of the forward trans-conductance y21and the short circuit output admittance y22eof high frequency transistors was found at frequencies below 1 Mc. These effects can be explained by the new equivalent circuit. Possible application of this thermal-electric interaction may include the realization of large low Q inductances for low frequency integrated circuitry, and perhaps the investigation of pinch-in and second breakdown effects. It appears that the low frequency noise figure of transistors may also be affected by this effect.     

Dislocation dynamics in heterojunction bipolar transistor under current induced thermal stress

Dislocation generation and multiplication in heterojunction bipolar transistors (HBTs) under electrical bias was studied using a finite element model. This model was developed to solve a physical viscoplastic solid mechanics problem using a time-dependent constitutive equation relating the dislocation dynamics to plastic deformation. The dislocations in HBTs are generated by the excessive stresses including thermal stress generated by the temperature change in the device during operation. It was found that the dislocation generation rate at the early stage and the stationary dislocation densities depend strongly on the current density.     

A closed-form delay expression for digital BiCMOS circuits withhigh-injection effects

A non-iterative formula is derived for calculating the delay time of digital BICMOS circuits with their bipolar transistors operating in high-current regime. Effects such as the base transit-time increase of minority carriers and the decrease of the current gain of the bipolar transistors are all incorporated in the model. This model can be used to investigate the effects of most device parameters such as transistor sizes and external loading on the performance of the circuits without resorting to any iterative procedures. This simplified model compares well with the original model to 10% over a wide range of operating conditions, and is especially accurate for situations where base widening affects the bipolar transistors     

Control of implant-damage-enhanced boron diffusion in epitaxially grown n-Si/p-Si1-xGex/n-Si heterojunction bipolar transistors

Boron out-diffusion in epitaxially grown n-Si/p⁺-Si_1-xGe_x/n-Si heterojunction bipolar transistors is significantly enhanced during 850°C, 10 s rapid thermal annealing following arsenic emitter contact implantation. In this paper, we introduce three techniques which dramatically reduce boron out-diffusion during implant activation. Limiting the post-implant processing to 600°C for 2 min results in minimal diffusion giving acceptable device performance. A second technique involves pulsed laser annealing of the As implant, which removes residual defects and eliminates enhanced diffusion during subsequent thermal processing. Finally, we show that high bulk concentrations of oxygen in the Si_1-xGe_x (∼10²⁰ cm^-3) dramatically reduce the implant-damage-enhanced boron diffusion. In addition to the depth profiles, electrical measurements performed on heterojunction bipolar transistors, incorporating these fabrication techniques, show ideal collector current characteristics and confirm the absence of deleterious boron out-diffusion effects.     

Emitter ballasting resistor design for, and current handlingcapability of AlGaAs/GaAs power heterojunction bipolar transistors

A systematic investigation of the emitter ballasting resistor for power heterojunction bipolar transistors (HBTs) is presented. The current handling capability of power HBTs is found to improve with ballasting resistance. An equation for the optimal ballasting resistance is presented, where the effects of thermal conductivity of the substrate material and the temperature coefficient of the ballasting resistor are taken into account. Current levels of 400 to 800 mA/mm of emitter periphery at case temperatures of 25 to -80°C for power AlGaAs/GaAs HBTs have been obtained using an on-chip lightly doped GaAs emitter ballasting resistor. Device temperature has been measured using both an infrared microradiometer and temperature-sensitive electrical parameters. Steady-state and transient thermal modeling are also performed. Although the measured temperature is spatially nonuniform, the modeling results show that such nonuniformities would occur for a uniform current distribution, as would be expected for an HBT with emitter ballasting resistors     

A study of L-band GaAlAs/GaAs HBTs for high-voltage RF-power

The feasibility of GaAlAs/GaAs heterojunction bipolar transistors as power output transistors for 24–28V cellular base station applications was studied. A 1W, 25V test vehicle was fabricated, with predictable and uniform electrical parameters. Maximum output power was 1.02W with 9.1dB gain at 2GHz and 18V supply voltage. Characterization at more than 22V destroyed all devices, even if emitter ballasting resistors were used for thermal balance. Analysis indicated that the failures were caused by too wide emitters in combination with the high supply voltage, causing current crowding and large temperature spikes. Small (<2-3µm) horizontal emitter dimensions are required even with low base sheet resistivity, otherwise leading to destructive temperature non-uniformities, unless special arrangements to drastically reduce the thermal resistance can be applied.     

静电放电作用下微波双极型晶体管的失效机理研究

通过理论建模和试验测试的方法研究了多指结构微波双极型晶体管在静电放电作用下的热稳定性和电稳定性。选择2SC3356作为受试器件,对100个测试样本进行人体模型静电放电注入实验,并从器件内部电场强度、电流密度和温度分布变化出发,用二维器件级仿真软件辅助分析了在静电放电应力下其内在损伤过程与机理。由于指间热耦合的存在,雪崩电流在各指上分布不均,局部的电流拥挤和过热效应会导致晶格损伤。试验结果表明,由于特殊的物理结构,受试器件对静电放电最敏感的端对并不是EB结,而是CB结,当静电放电电压增大到1.3KV时,CB结首先损坏。失效分析进一步表明静电放电引起的失效机理通常是介质层的击穿和局部铝硅共晶体的过热融化。静电放电注入实验的过程中存在积累效应,多次低强度的注入测试会导致潜在性失效并使器件性能大幅下降。     

Effects of rapid thermal processing on the current gain and emitterresistance of polysilicon emitter bipolar transistors

Results of measurements of base current and emitter resistance of polysilicon emitter transistors subjected to different rapid thermal anneal processes of the interfacial layer and different emitter drive-in times are presented. It is shown that a rapid thermal anneal for temperatures on the order of 1050°C leads to devices in which the base current is essentially independent of the emitter drive-in time. The emitter resistance obtained in devices given this interface anneal is considerably lower than that in devices without the anneal, and hence the values obtained are compatible with the requirements for realizing submicrometer bipolar circuits