Emitter Current Crowding Effect Research Articles

Effect of Total Dose Irradiation on Parasitic BJT in 130 nm PDSOI MOSFETs.

In this work, the effects of total dose irradiation on the parasitic bipolar junction transistor (BTJ) in 130 nm PDSOI MOSFETs were investigated. The experimental results demonstrate that irradiation-induced oxide-trap charges can modify the E-B junction barrier, and thereby make the common-emitter gain β0 of the parasitic BJT in NMOS device increase, while decreasing it in a PMOS device. Additionally, irradiation-generated oxide-trap charges in shallow trench isolation (STI) elevate the surface electrostatic potential of the gate above the STI sidewall, thus providing an additional channel from the emitter to the collector. Moreover, these charges may generate parasitic reverse conductive paths at the STI/Si interface under high dose irradiation, thereby enhancing the leakage current in the front gate channel and diminishing the significance of the parasitic BJT. Under irradiation, the electric field intensity difference between two biases leads to higher β0 of the parasitic BJT in PG-biased devices than in ON-biased ones. Furthermore, the lifting effect of irradiation on β0 increases in wide or short channel irradiated devices, which can be explained using simulations and an emitter current crowding effect model.

The characterization of the built-in bipolar junction transistor in H-gate PD-SOI NMOS

The built-in bipolar junction transistor of H-gate partially depleted SOI NMOS was characterized by measuring the common-emitter output curve and calculating the common-emitter current gain. Unoptimized doping results in a low common-emitter current gain. The bias state of the front gate of the MOS has a significant influence on the characteristics of the built-in BJT. The geometry effect of the device is also studied. It is proved by mathematical analysis that the emitter current crowding effect also exists on the built-in BJT.

Modeling of the Lateral Emitter-Current Crowding Effect in SiGe HBTs

Two-section models for capturing the lateral ac emitter-current crowding effect, which is also known as the lateral nonquasi-static (NQS) effect, are presented following a consistent approach based on a model formulation for ac operating condition. Following the theoretical results, model formulations suitable for implementation in the large-signal domain are developed. The proposed two-section model performs better than the state-of-the-art model in both the large-signal and small-signal domains and appears to be suitable for accurately capturing the lateral NQS effect.

Non-ideal effect in 4H–SiC bipolar junction transistor with double Gaussian-doped base**Project supported by the National Natural Science Foundation of China (Grant Nos. 60876061 and 61234006), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2013JQ8012), and the Doctoral Fund of the Ministry of Education of China (Grant Nos. 20130203120017 and 20110203110010).

The non-ideal effect of 4H–SiC bipolar junction transistor (BJT) with a double Gaussian-doped base is characterized and simulated in this paper. By adding a specific interface model between SiC and SiO2, the simulation results are in good agreement with the experiment data. An obvious early effect is found from the output characteristic. As the temperature rises, the early voltage increases, while the current gain gradually decreases, which is totally different from the scenario of silicon BJT. With the same effective Gummel number in the base region, the double Gaussian-doped base structure can realize higher current gain than the single base BJT due to the built-in electric field, whereas the early effect will be more salient. Besides, the emitter current crowding effect is also analyzed. Due to the low sheet resistance in the first highly-doped base epilayer, the 4H–BJT with a double base has more uniform emitter current density across the base-emitter junction, leading to better thermal stability.

A New Extraction Technique for the Complete Small-Signal Equivalent-Circuit Model of InGaP/GaAs HBT Including Base Contact Impedance and AC Current Crowding Effect

In this paper, both ac current crowding and base contact impedance are considered and included in the T-type small-signal equivalent circuit of InGaP/GaAs heterojunction bipolar transistors. The ac current crowding effect and base contact impedance are modeled as a parallel RC circuit, respectively. Devices parameters of the equivalent circuit are obtained by a new parameters extraction technique. The technique is to directly analyze the two-port parameters of multibias conditions (cutoff-bias, open-collector, and active-bias modes). The parallel capacitances (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bi</sub> ), base resistances (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> and R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bi</sub> ), and base inductance (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) are especially determined under the active-bias mode without numerical optimization. In addition, the small-signal equivalent circuits of cutoff-bias and open-collector modes are directly derived from the active-bias mode circuit for consistency. By considering base contact impedance and intrinsic base impedance effects in the presented small-signal equivalent circuit, the calculated S-parameters agree well with the measured S-parameters. The observed difference in the slope for the unilateral power gain (U) versus frequency at high frequency is mainly attributed to the ac emitter current crowding effect and well modeled in this study

The effect of vertical emitter ballasting resistors on the emitter current crowding effect in heterojunction bipolar transistors

In order to improve thermal stability and extend their safe operation region, epitaxial emitter ballasting resistors have been incorporated into power heterojunction bipolar transistors (HBTs). In this report, we show that this lightly doped layer not only can function as ballasting resistors used in multi-finger power HBT cells, but also can reduce the emitter current crowding effect which is an important limitation in bipolar transistors operating at high emitter current densities.

Factors limiting the current gain in high-voltage 4H-SiC npn-BJTs

The dependence of the base current gain β on the collector current I C has been measured in high-voltage 4H-SiC bipolar junction transistors at collector current densities j C from 20 to 700 A/cm 2. With increasing collector current, the β value grows, reaching a maximum β max=23 at j C max of about 250 A/cm 2 and then decreasing sharply with further increase in current. The peculiarities of this dependence are analyzed in terms of a model taking into account the carrier recombination in the emitter space charge region (SCR), the surface recombination, and the emitter current crowding effect. It is shown that at relatively small j C the recombination in SCR plays a key role in limiting the β magnitudes. The decrease in β at high j C is mainly due to the surface recombination enhanced by the emitter current crowding effect. The effects of surface recombination and recombination in the SCR reduce the maximum current gain almost threefold: from 65 to 23.

MBE grown vertical emitter ballasting resistors to reduce the emitter current crowding effect in heterojunction bipolar transistors

In order to improve thermal stability and extend their safe operation region, epitaxial emitter ballasting resistors have been incorporated into power heterojunction bipolar transistors (HBTs). In this report, we show that this lightly doped layer not only can function as ballasting resistors used in multi-finger power HBT cells, but also can reduce the emitter current crowding effect which is an important limitation in bipolar transistors operating at high emitter current densities.

Transient characteristics of a 1.8 kV, 3.8 A 4H-SiC bipolar junction transistor

Transient switch-on and switch-off characteristics of 4H-SiC npn BJT'shave been studied in the temperature range 180-500 K.Both in common-base and in common-emitter configurations thetransistor switch-on times are governed by respective RC time constants.The switch-off processes are strongly affected by surface recombination.The role of the emitter current crowding effect has been discussed.The surface recombination velocity is estimated to be about 104 cm s-1.

Quantitative modelling of DC and transient characteristics at high injection level at 77 and 300K in silicon bipolar transistor

The current gain of a silicon bipolar transistor has been quantitatively modelled by the Early effect, the conductivity modulation effects in the base and in emitter, the effective base widening effect and the emitter current crowding effect at 77 and 300K involved in the carrier recombination currents in the emitter-base space charge region and in the base. On this basis, the transit times, the total transit time from the emitter to collector and the cutoff frequency are modelled as functions of the collector current at 77 and 300K. The results obtained are in agreement with the experimental data. Besides this, the influence of the maximum base doping concentration on the maximum current gain and the maximum cutoff frequency has been also analysed. The main results show that the current gain is mainly determined by the conductivity modulation effect and the emitter current crowding effect at high injection level at 77K, but at 300K it is mainly determined by the effective base widening effect. The cutoff frequency is mainly determined by the minority-carrier base transit time at 300K, and at 77K the minority-carrier emitter transit time may be dominant for the large bandgap narrowing effect in emitter. The bandgap narrowing effect is the main reason for the degradation of the cutoff frequency with lowering temperature, instead of the low-temperature trapping effect by the compensated impurities with the shallow energy levels.

Analysis of the high injection effects in silicon bipolar transistors at low temperatures

There are usually two explanations for the physical reasons of the high injection effects in silicon bipolar transistors: one is the effective base widening effect proposed by Kirk, the other is the base conductivity modulation effect proposed by Webster, the emitter current crowding effect intensifies these two effects. In this paper, low temperature characteristics of these three important effects are analyzed and the dominant physical mechanism which determines the high injection effects at low temperatures is presented. The obtained calculate results are in agreement with the experiments.

Investigation of emitter current crowding effect in heterojunction bipolar transistors

The emitter current crowding effect in heterojunction bipolar transistors (HBTs) has been investigated using a specific test device. This test device, which is a heterojunction bipolar transistor with two separate base fingers, also allows evaluation of the HBT base resistance. By use of this test device, the Letter demonstrate that a 3μm large HBT does not exhibit the emitter current crowding effect. An analysis of the saturated regime is also presented.

Low-temperature (77 K) BJT model with temperature dependences on the injected condition and base resistance

A low-temperature (77-K) bipolar transistor model based on physical analysis by considering the temperature dependences of the injection condition and base resistance modulation is described. A charge-based injection factor which describes the temperature dependence of the ideality factor n is introduced by taking into account the electron and hole concentration ratios at the edges of the emitter-base depletion layer. The temperature dependence of base resistance modulation is explained by using the temperature dependences of the conductivity modulation effect, the base pushout effect, and the emitter current-crowding effect. Calculations using the model are compared with measurements, revealing excellent agreement over a wide temperature range from 50 to 298 K. >

Early effect of high-current-gain heterojunction bipolar transistor

The current gain β of a high-β heterojunction bipolar transistor is usually limited, at normal operating range, by the ratio of the injected electron current to the recombination current in the space-charge region. The Early effect in these transistors is very important because the base layer is very thin in order to obtain high β. In this case, the classical transistor models are not very suitable, and an Early voltage smaller than for a homojunction bipolar transistor is commonly observed. In the letter an analysis has been carried out taking into account the emitter current crowding effect and heterojunction characteristics. A simple analytic equation of the Early voltage is derived, and experimental results are presented.

An accurate analysis of noise in rectangular bipolar transistors including current crowding

An accurate analysis of noise in rectangular bipolar transistors is developed from a distributed model using a collective approach and the transport noise theory. In this model, emitter current crowding effect are taken into account and noise behaviour at intermediate and low values of source impedance is precisely described. The structure of teh equivalent lumped circuit is established, and the analytical relationships characterizing its elements in an extended range of current and frequency are given. It is shown that; (a) the active base region must be represented by a nonlinear impedance with a generalized thermal noise source; (b) for low source impedances the equivalent input voltage shot noise generator is higher than predicted by low injection theories. Furthermore it is found that emitter crowding induces a uniform and important decrease in (a) base impedance (b) thermal noise and (c) the correlation between shot noise generators of the equivalent lumped circuit. Finally it appears that classical low injection theories are valid when crowding occurs in transistors biased with high source impedances.