Range Of Collector Currents Research Articles

Влияние топологии многокристальных IGBT-модулей на распределение тока между транзисторными чипами в статических режимах работы

Factors affecting the distribution of direct current among parallel transistor chips in a multichip IGBT module are experimentally investigated. The voltage-current characteristics (VCCs) of single-chip modules with the rated operating current equal to 200 A and voltage equal to 1200 V in the collector current range from 50 to 200 A at temperatures equal to 25, 90, 120 and 150°C were measured to evaluate the compensation ability of the saturation voltage positive temperature dependence. A comparative experiment on measuring the voltage drop across individual parts of the conductors system composed of samples of IGBT modules with different topologies based on the half-bridge circuit arrangement and having three parallel-connected chips in passing a 400 A direct current through the module was carried out. It has been found from the experimental results that the use of the saturation voltage positive temperature dependence for equalizing the current distribution between the chips has limited capabilities, and that one of possible methods for achieving this is to use the resistance of a system of aluminum conductors. Comparative tests were carried out for estimating the stability of modules with different topologies to the effect of cyclic current load in a mode facilitating accelerated degradation of the soldered seam between the chip and the DBC substrate. The experimental results confirm the importance of considering the factors affecting the static current distribution between the chips in designing the topology of multichip IGBT modules.

Comparisons between InGaP/GaAs heterojunction bipolar transistors with a sulfur- and an InGaP-passivated base surface

This paper reports on InGaP/GaAs heterojunction bipolar transistors (HBTs) with a sulfur-treated base layer, which are then compared to InGaP/GaAs HBTs with an InGaP-passivated base layer. Experimental results reveal that the improvement in base leakage current for InGaP-passivated HBTs is due to the inherent low surface recombination velocity associated with an InGaP layer while it is the electronic modification of the GaAs surface for sulfur-treated HBTs. The maximum dc current gain available is β = 75 with a base sheet resistance of R B = 220 Ω / □ for a sulfur-passivated HBT. The sulfur-passivated HBTs also exhibit very good linearity over a wide collector current range of 10 −5 to 10 −1 A. Furthermore, detailed sulfur treatment conditions and effects on device performances including post-treatment stability are investigated.

DC Characterization of InP/InGaAs Tunneling Emitter Bipolar Transistor

An InP/InGaAs tunneling emitter bipolar transistor (TEBT) is studied and demonstrated. From the simulation results, the band diagram, tunneling transmission, and carrier distribution of the device are analyzed as functions of barrier thickness. The higher the emitter injection efficiency, the higher the current gain and the larger the current drivability for the device studied by employing a tunneling barrier layer of suitable thickness. In addition, experimentally, InP/InGaAs TEBT has been fabricated successfully. Due to its excellent tunneling barrier structure, the studied device can be operated under an extremely wide collector current range. The operation range is larger than 11 decades of collector current (10-12 to 10-1 A). Moreover, the studied device exhibits a very small collector-emitter offset voltage (ΔVCE) of 40 mV and an extremely wide operation range of output current. Thus, the studied device is suitable for low-voltage and low-power circuit applications.

Non-local microscopic view of signal propagation times in BJTs biased up to high currents

This paper presents a microscopic analysis of signal propagation delay in bipolar transistors featuring relevant non-equilibrium transport effects. First, the physical mechanisms responsible of signal delay are reviewed. A novel technique to extract signal delays from self-consistent Monte Carlo device simulations is presented. These results are then used for a physically based comparison between compact quasi-static delay formulas and more accurate particle simulations carried out over a broad range of collector currents.

Radiation testing of fiber optic systems

Tests have been performed to examine the effects of radiation exposure on opto-electronic components that can be used in digital fiber optic data links. The response of fiber waveguides to ionizing radiation has been studied. Measurements of the growth and decay of the radiation-induced loss at 850 and 1300 nm have revealed that fibers are very sensitive to low γ-doses (2000 rad). The linear dependence of a short circuit current on a γ-dose rate, up to 380 rad/s for the photodiode has been shown. At very high dose levels permanent damage is noticed in the diode characteristics and its current decreases where a value of 1600 μA, measured at light intensity level of 8000 1x, was reduced to 1200, 950, 820, 700, 600 and 550 μA after γ-exposure up to 2.0, 16, 38, 70, 105 and 140 M rad respectively. The forward current gain factor of a phototransistor, measured as a function of operating collector current, shows a severe decrease due to γ-exposure. The minimum damage effects, usually correspond to the lower and higher ends of the operating collector current range of a device. Proposals using photodiodes for γ-dose and dose rate-dosimetry are given, tested and proved to be satisfactory.

Impact of Al composition on RF noise figure of AlGaAs/GaAs heterojunction bipolar transistors

The influence of Al content on the RF noise characteristics of Al/sub x/Ga/sub 1-x/As/GaAs heterojunction bipolar transistors (HBT's) is presented. It is shown that the minimum noise figure (F/sub min/) at 2 GHz is reduced by increasing the Al mole fraction (x). This observed improvement in noise figure is directly correlated to the differences in dc current gain. The lowest measured F/sub min/(2 GHz) of HBT's with emitter dimensions 2/spl times/(3.5/spl times/30) /spl mu/m/sup 2/, were 1.3, 1.61, and 2.1 dB for x=0.35, 0.30, and 0.25 devices, respectively at I/sub c/=3 mA. The measured results were found to agree well with calculated values over a wide range of collector currents.

SiGe-HBTs with high f T at moderatecurrentdensities

Silicon-germanium heterojunction bipolar transistors (HBTs) have been developed with regard to high cutoff frequencies within a wide collector current range. Unity current gain frequencies f/sub T/ high as 116 GHz were obtained at a collector current density of 2*10/sup 5/ A/cm/sup 2/. In addition, the FWHM of cutoff frequency f/sub T/ against collector current exceeds one and a half decades. Calculations indicate that the ratio of the collector to emitter area essentially determines the current density range of a high frequency HBT. >

Enhanced static performance of AlGaAs/GaAs HBTs by fluoride surface treatment

Using a combination of wet and dry chemical treatments, the parasitic surface current between the base and emitter of AIGaAs/GaAs heterojunction bipolar transistors (HBTs) has been suppressed by more than two orders of magnitude. This treatment opens up a variety of applications over a wide range of collector currents for selfaligned microwave AIGaAs/GaAs HBTs.

Characteristics of impact-ionization current in the advanced self-aligned polysilicon-emitter bipolar transistor

Using an algorithm to calculate the base current increase due to local thermal effects, the authors show that one can accurately measure the impact ionization current over the full range of collector current. From the measured impact ionization ratio, it was possible to quantitatively describe the characteristics of the space-charge modulation and base push-out effect over a wide range of collector current. Computer simulation results support the measured data. It is also shown that one can use the measured impact ionization ratio to distinguish small collector concentration variations and thickness differences. The characterization was performed for self-aligned polysilicon-emitter transistors in an advanced BiCMOS technology. >

Direct extraction of the AlGaAs/GaAs heterojunction bipolar transistor small-signal equivalent circuit

The authors describe a novel, direct technique for determining the small-signal equivalent circuit of a heterojunction bipolar transistor (HBT). The parasitic elements are largely determined from measurements of test structures, reducing the number of elements determined from measurements of the transistor. The intrinsic circuit elements are evaluated from y-parameter data, which are DC-embedded from the known parasitics. The equivalent-circuit elements are uniquely determined at any frequency. The validity of this technique is confirmed by showing the frequency independence of the extracted circuit elements. The equivalent circuit models the HBT s-parameters over a wide range of collector currents. Throughout the entire 1-18-GHz frequency range, the computed s-parameters agree very well with the experimental data. >

High Power Microwave Transistors

The characteristics and limitations of high power microwave transistors are discussed. The importance of the major parameters such as collector epilayer thickness and resistivity, base width, base-spreading resistance, contact resistances, collector-base feedback capacitance and emitter area, in determining current gain-bandwidth product (ft) and maximum frequency of oscillation (fmax) are pointed out and the design criteria are given. Fundamental limits of microwave power and gain set by semi-conductor material properties are presented.For a stripe geometry consisting of alternating fingers of base and emitter regions, design criteria leading to the selection of optimum finger dimensions are presented. A circular stripe geometry based on these design criteria is used to fabricate high power microwave transistors. Experimental results showing ft > 4 GHz and fmax > 2.5 GHz for a collector-current range of 20 to 200 mA and a collector-emitter voltage range of 2 to 15 volts are presented. The significance of...

Regulator to Control Current Sharing among Parallel-Connected Power Transistors

A current regulator is described that controls the peak current of a power transistor driving an inductive load, such as magnet coils. Presently, the current pulse has a 0.1- to I-ms adjustable duration with duty cycle to 5%. Ultimately, the pulse length must be ~ 7 ms with 50% duty cycle. The peak current nominally is 200 A, as set by a reference pulse. Several transistors, each controlled by an individual regulator, are connected in parallel to provide the total peak load current. The regulators compensate for differences between the power transistors and assure equal current sharing among the collectors. The regulator comprises an 8-bit multiplying digital-to-analog (D/A) converter that drives the base of the power transistor, an 8-bit up-down counter, an analog differencing circuit, and a comparator. For control purposes, a current-sensing resistor in the transistor's collector produces the second input to the differencing circuit. Regulation is accomplished over a collector current range of 200 ± 50 A per stage.

Double heterojunction AlxGa1-xAs/GaAs bipolar transistors (DHBJT's) by MBE with a current gain of 1650

Double heterojunction AlGaAs/GaAs bipolar junction transistors (DHBJT's) grown by molecular beam epitaxy (MBE) were fabricated and tested. Devices with 0.2-µm and 0.1-µm base thicknesses exhibited common emitter current gains of up to 325 and 1650, respectively, in a wide range of collector currents. To obtain such high current gains, growth conditions had to be optimized and controlled. These high current gains, compared with the previous best value of 120 obtained in a MBE-grown transistor, make the HBJT's very promising for low-power high-speed logic application.

Measurement and interpretation of the FT of planar transistors operating in the inverse mode

The problems of measuring the fT of upward-operating planar transistors are discussed. It is shown that accurate values of fβ may be determined by measuring the forward and reverse voltage transfer ratio of the transistor when connected in common-collector configuration. A simple, low-cost experimental system is described which gives excellent results over a wide range of collector currents (1 μA to 10μA). Results are presented for a discrete n-p-n transistor, but the method is also ideally suited to measurements on I2L transistors.

Remarks on the emission coefficient of a bipolar transistor

The extent to which it is necessary-and the collector current range over which it is valid-to characterize the base-emitter junction of a bipolar transistor by a nonunity emission coefficient is clarified by a simple theoretical argument based on a consideration of base majority carrier charge.

Experimental study of the effects of current crowding on noise of bipolar transistors at intermediate frequencies

In this paper a new transistor noise model taking into account current crowding and surface effects is proposed. The experimental methods characterizing the model elements are given. The model validity for an extended range of collector currents at intermediate frequencies is established. It is demonstrated that for high current values the transistor noise properties for low impedance sources tend to be determined by shot noise rather than by thermal noise as predicted by standard theories. A modulating effect which increases appreciably the equivalent input current noise generator and correlation terms is found. Methods determining the base resistance are discussed.

Method of obtaining accurate transistor data for the evaluation of computer models

The conventional manual method of obtaining simultaneous, measurements of Vce, Vbe and Ic for transistor modelling requires that the current gain be maintained at a fixed value over a wide range of collector current. A method is presented for accurately maintaining the current gain of the transistor constant to the required accuracy for over more than four decades of collector current.

Characteristics of silicon transistors

The d.c. and low-frequency a.c. characteristics of a number of silicon transistors have been measured over a collector-current range of 10 ?A?1 mA. The variations of d.c. and a.c. current gain, input resistance and mutual conductance with collector current are described by simple equations.

Design Tradeoffs for a Neutron Radiation-Tolerant Silicon Transistor

A detailed study was conducted of the tradeoffs involved in the design of silicon planar transistors tolerant to fast-neutron irradiation up to 1 × 1015 nvt. Initial measurements made on irradiated 2N918 transistors indicated that breakdown voltage and collector current range must be sacrificed in order to improve device radiation resistance. The tradeoffs relating post-irradiation hFE to transistor fT, saturation region characteristics to breakdown voltage, and usable collector current range to length of emitter periphery are discussed in detail. The cptirn design is a high frequency, lcw breakdawn voltage transistor with a narrow usable current range. Transistors were fabricated having hFE greater than 5 over a wide tenwrature range after irradiation to 1 × 1015 nvt.

Variation of l.f. noise figure of a junction transistor

Some results of measurement of l.f. noise component over a bandwidth of 300 c/s centred about a mid-band frequency channel of 1000 c/s are reported for a number of commercial transistors. Investigations cover a range of collector current (Ic) 0.3?l.6 mA and a temperature range ?20° to + 45°C. It is found that the noise increases with increasing values of Ic and decreasing values of temperature. Simultaneous measurement of lifetime ? of minority carriers in the base region shows that both 1/? and the l.f. noise vary in the same manner with temperature. Results are discussed in the light of the current ideas regarding the origin of 1.f. noise in semiconductor junction. It is shown that the major part of such noise in the transistors investigated may be attributed to surface recombination noise. It is tentatively suggested that the spectral distribution function ?(f) of surface recombination noise varies exponentially as the surface recombination velocity. Further, the value of ?(f) should, in general, depend on the current Ic and when this is taken into account the noise should vary as the square of Ic For a given Ic-value the l.f. noise figure depends very much on the functional relationship between ?(f) and Ic.