Excess Base Current Research Articles

The effect of 63 MeV hydrogen ion irradiation on 65 GHz UHV/CVD SiGe HBT BiCMOS technology

Two thousand arrays of second generation (6HP) silicon–germanium heterojunction bipolar transistors (SiGe HBTs) were exposed to 63 MeV hydrogen ions at a fluence ranging from 1×1012 to 5×1013 cm−2. The dc electrical measurements, such as Gummel characteristics, excess base current (Δ I B=I Bpost−I Bpre), current gain (h FE), neutral base recombination, avalanche multiplication factor (M−1) and output characteristics (V CE–I C), were systematically studied before and after hydrogen ion irradiation. The SiGe HBT showed 80% degradation in forward-mode dc current gain after a total dose of 5×1013 cm−2 hydrogen ion irradiation.

Reliability studies on NPN RF power transistors under swift heavy ion irradiation

NPN RF power transistors were irradiated with 140 MeV Si 10+ ions, 100 MeV F 8+ ions, 50 MeV Li 3+ ions and Co-60 gamma radiation in the dose range from 100 krad to 100 Mrad. The transistor characteristics are studied before and after irradiation from which the parameters such as Gummel characteristics, excess base current (Δ I B = I Bpost − I Bpre), dc current gain ( h FE), transconductance ( g m) and collector-saturation current ( I CSat) are determined. The degradation observed in the electrical characteristics is almost the same for different types of ion irradiated NPN RF power transistors with similar total doses although there is a large difference in the linear energy transfer (LET) of the ions. Further, it was observed more degradation in DC I– V characteristics of ion irradiated devices than the Co-60 gamma irradiated devices for higher doses.

Effects of orientation of substrate on the enhanced low-dose-rate sensitivity (ELDRS) in NPN transistors

The radiation effects and annealing characteristics of two types of domestic NPN bipolar junction transistors, fabricated with different orientations, were investigated under different dose-rate irradiation. The experimental results show that both types of the NPN transistors exhibit remarkable Enhanced Low-Dose-Rate Sensitivity (ELDRS). After irradiation at high or low dose rate, the excess base current of NPN transistors obviously increased, and the current gain would degrade rapidly. Moreover, the decrease of collector current was also observed. The NPN transistor with 〈111〉 orientation was more sensitive to ionizing radiation than that with 〈100〉 orientation. The underlying mechanisms of various experimental phenomena are discussed in detail in this paper.

Application of advanced 200 GHz Si–Ge HBTs for high dose radiation environments

Third generation 200 GHz silicon–germanium Heterojunction Bipolar Transistors (Si–Ge HBTs) were irradiated with high dose Co-60 gamma radiation up to 100 Mrad. Pre-radiation and post-radiation DC figures of merits were used to quantify the radiation tolerance of the different geometry devices. The different electrical characteristics like Gummel measurements, excess base current, current gain, transconductance, neutral base recombination, avalanche multiplication of carriers and output characteristics were studied for different doses from 100 krad to 100 Mrad of total doses. The Si–Ge HBTs showed robust ionizing radiation tolerance up to a total dose of 100 Mrad.

An analysis of 100 MeV F 8+ ion and 50 MeV Li 3+ ion irradiation effects on silicon NPN rf power transistors

The dc characteristics exhibited by NPN power transistors are studied systematically before and after irradiation by 100 MeV F 8+ ions and 50 MeV Li 3+ ions in the dose range of 100 krad to 100 Mrad. The transistor parameters such as excess base current (Δ I B= I Bpost– I Bpre), dc current gain ( h FE), transconductance ( g m), and collector-saturation current ( I Csat) were studied before and after irradiation. The damage factors ( k) for h FE were calculated for ion irradiated transistors using Messenger–Spratt relation. The base current ( I B) was found to increase significantly after ion irradiation and this in turn decreases the h FE of the transistors. The g m decreases significantly after ion irradiation. Moreover, the output characteristics of irradiated devices also show that the collector current ( I C) in the saturation region ( I Csat) decrease with increase in ion dose. The observed change in these characteristics may be due to the ion induced generation–recombination (G–R) centers in emitter-base (E-B) spacer oxide and the ion induced point defects and their complexes in the transistor structure.

Conversion model of enhanced low-dose-rate sensitivity for bipolar ICs

A physical model is proposed for enhanced low-dose-rate sensitivity (ELDRS) in bipolar junction transistors. It is based on the conception of a shallow and a deep set of radiation-induced oxide traps that are converted into interface traps under irradiation at high or low dose rates, respectively. Excess base current is calculated by introducing an exponential or a power-law representation of the impulse response used in a convolution integral. The former representation makes it possible to define time constants of conversion at high or low dose rates, respectively. Values of fitting model parameters are determined that lead to close agreement with previously reported experimental results.

Study of electromagnetic field stress impact on SiGe heterojunction bipolar transistor performance

This paper deals with the various aspects of electromagnetic field impact modeling on the SiGe heterojunction bipolar transistor (HBT) device for microwave applications. This study differs from conventional HBT device reliability research associated with other stresses. The originality of this study comes from the generation of a localized electromagnetic field using the near-field bench. A coupling phenomenon between the electromagnetic field and the micro-strip lines connecting the transistor are evaluated by electromagnetic and electrical simulations. After stress, the input and the transmission scattering parameters are affected. This is primarily due to the deviation of the input impedance and the reduction of the transconductance, respectively. The stress effects have been related to a base current degradation. This degradation is due to a hot carrier introducing generation/recombination trap centers at the Si/SiO2 interface of the emitter–base spacer oxide, which leads to an excess recombination base current.

An investigation of electron and oxygen ion damage in Si npn RF power transistors

The effects of 8 MeV electrons and 60 and 95 MeV oxygen ions on the electrical properties of Si npn RF power transistors have been investigated as a function of fluence. The dc current gain (h FE), displacement damage factor, excess base current (Δ I B=I Bpost−I Bpre), excess collector current (Δ I C=I Cpost−I Cpre), collector saturation current (I CS) and deep level transient spectroscopy trap signatures of the irradiated transistors were systematically evaluated.

Characteristics of high- and low-dose-rate damage for domestic npn transistors of various emitter areas

There are many factors such as process technologies, dose rates and biased conditions which can affect radiation damage in npn transistors. High- and low-dose-rate radiation response of domestic npn transistors with three kinds of emitter areas were investigated in this article. The influence of emitter area on radiation damage was analyzed. The results show that the degradation of current gain was more severe at low dose rate, i.e. enhanced low-dose-rate sensitivity. Furthermore, radiation damage was more apparent at low current injection. Through the comparison of radiation damage for different emitter areas, it was found that greater perimeter-to-area ratio （P/A） would cause greater normalized excess base current （IB/IB0）. The damage mechanism for npn transistors is explained in detail, and the radiation hardness assurance is explored with respect to the emitter area and operating voltage of npn transistors.

An Investigation of Dose Rate and Source Dependent Effects in 200 GHz SiGe HBTs

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present an investigation of the observed variations in the total dose tolerance of the emitter-base spacer and shallow trench isolation oxides in a commercial 200 GHz SiGe HBT technology. Proton, gamma, and X-ray irradiations at varying dose rates are found to produce drastically different degradation signatures at the various oxide interfaces. Extraction and analysis of the radiation-induced excess base current, as well as low-frequency noise, are used to probe the underlying physical mechanisms. Two-dimensional calibrated device simulations are employed to correlate the observed results to the spatial distributions of carrier recombination in forward- and inverse-mode operation for both pre- and post-irradiation levels. Possible explanations of our observations are offered and the implications for hardness assurance testing are discussed. </para>

Swift heavy-ion irradiation effects on electrical and defect properties of NPN transistors

NPN transistors were irradiated by 95 MeV oxygen ions in a fluence ranging from 5 × 1010 to 5 × 1012 ions cm−2. The dc current gain (hFE), excess base current (ΔIB = IBpost − IBpre), excess collector current (ΔIC = ICpost − ICpre) and collector-saturation current (ICS) of the ion-irradiated transistors were studied systematically. We found that both hFE and ICS of the transistors decrease drastically after ion irradiation. Secondly, a significant increase in the collector current (IC) along with the increase in the base current (IB) after ion irradiation was observed. The radiation-induced trap levels in the collector–base depletion region of NPN transistors were studied by employing the deep level transient spectroscopy technique and different types of trap levels were observed. The results obtained on the activation energy, density of trap levels, apparent capture cross section of the defects, introduction rate and space charge layer lifetime of different defects for different total fluence are presented and discussed.

I– V and deep level transient spectroscopy studies on 60 MeV oxygen ion irradiated NPN transistors

NPN transistors have been irradiated by 60 MeV oxygen ions in a fluence ranging from 5 × 10 10 to 1 × 10 13 ions/cm 2. The DC current gain ( h FE), excess base current ( ΔI B =I B post −I B pre ), excess collector current ( ΔI C =I C post −I C pre ) and collector saturation current (I C Sat ) of the ion irradiated transistors were studied systematically. The h FE of the transistors were found to be decreased drastically after ion irradiation. A significant increase has been observed in the collector current ( I C) along with the increase in the base current ( I B) after ion irradiation. The I C Sat of the ion irradiated transistors were also decreased significantly after irradiation. The radiation induced trap levels in the collector base depletion region of NPN transistors were studied by deep level transient spectroscopy technique and different types of trap levels were observed. The results obtained on the activation energy, density of trap levels, apparent capture cross section, introduction rate and space charge layer lifetime of different defects for different total fluence are presented and discussed.

Passivation of InP-Based Heterostructure Bipolar Transistors in Relation to Surface Fermi Level

The effect of surface Fermi level position on dc-characteristics of InP-based heterostructure bipolar transistors (HBT) is reported. The Fermi level of an InP surface covered with silicon oxide was located at an energy position close to the conduction band minimum of InP. This implies that an electron accumulation layer forms at the interface, which acts as a surface leakage path. The HBT passivated with silicon oxide films showed large excess base current and poor current gain. In contrast, the Fermi level position at the silicon nitride/InP interface was found to be near the midgap, and no electron accumulation layer was formed at the interface. The HBT passivated with silicon nitride film showed excellent dc characteristics with very small, excess base current.

Modeling low-dose-rate effects in irradiated bipolar-base oxides

A physical model is developed to quantify the contribution of oxide-trapped charge to enhanced low-dose-rate gain degradation in bipolar junction transistors. Multiple-trapping simulations show that space charge limited transport is partially responsible for low-dose-rate enhancement. At low dose rates, more holes are trapped near the silicon-oxide interface than at high dose rates, resulting in larger midgap voltage shifts. The additional trapped charge near the interface causes an exponential increase in excess base current and a resultant decrease in current gain for some NPN bipolar technologies. Space charge effects also may be responsible for differences in interface trap formation at low and high dose rates.

Implementation of total dose effects in the bipolar junction transistor Gummel-Poon model

The effects of total dose on the SPICE model of bipolar junction transistors are investigated. The limitations of the standard Gummel-Poon model for simulating the radiation-induced excess base current are analyzed, and a new model based on an empirical approach is proposed. Four new SPICE rad-parameters are presented, and investigated for different dose rates. The relevant parameters are extracted using a new algorithmic procedure, combining a genetic approach and the standard optimization technique which minimizes the RMS error between measured and simulated excess base current. It is shown that the excess base current is accurately described by the same formula whatever the device type is. An empirical fitting of the rad-parameters as a function of total dose is proposed to use in hardening electronic circuits for space-like environments.

Modeling ionizing radiation induced gain degradation of the lateral PNP bipolar junction transistor

Ionizing-radiation-induced gain degradation in lateral PNP bipolar junction transistors is due to an increase in base current as a result of recombination at the surface of the device. A qualitative model is presented which identifies the physical mechanism responsible for excess base current. The increase in surface recombination velocity due to interface traps results in an increase in excess base current and the positive oxide charge moderates the increase in excess base current and changes the slope of the current-voltage characteristics. Analytical and empirical models have been developed to quantitatively describe the excess base current response to ionizing radiation. It is shown that the surface recombination velocity dominates the excess base current response to total dose.

Gain degradation of lateral and substrate pnp bipolar junction transistors

The effect of dose rate on radiation-induced current gain degradation at 20 krad(Si) was quantified for lateral and substrate pnp bipolar transistors over the range of 0.001 to 294 rad(Si)/s. Degradation increases monotonically with decreasing dose rate, such that, at an emitter-to-base voltage of 0.7 V, radiation-induced excess base current differs by a factor of approximately eight at the extreme dose rates. Degradation shows little dependence on dose rate below 0.005 rad(Si)/s, suggesting that further degradation enhancement at space-like dose rates may be negligible. In addition, the effect of ambient temperature on radiation-induced gain degradation at 294 rad(Si)/s was thoroughly investigated over the range of 25 to 240/spl deg/C. Degradation is enhanced with increasing temperature while simultaneously being moderated by in situ annealing such that, for a given total dose, an optimum irradiation temperature for maximum degradation results. Optimum irradiation temperature decreases logarithmically with total dose and is larger and more sensitive to dose in the substrate device than in the lateral device. Based on the measurement of midgap interface trap density in the base oxide, enhancement in transistor gain degradation due to elevated temperature is explained as an increase in surface recombination velocity in the base. Maximum high dose rate degradation at elevated temperature closely approaches low dose rate degradation for both devices. Based on high-temperature irradiations, a flexible procedure for the accelerated prediction of low dose rate gain degradation at 20 krad(Si) is developed for each of the devices studied.

Reliability Study of C-Doped AlGaAs/GaAs Heterojunction Bipolar Transistors with Half-Micron-Wide Emitters

The reliability of C-doped AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with emitter widths of 0.5 and 0.8 µ m is studied at base-emitter junction temperatures ranging from 240° C to 290° C with an emitter current density of 1.0×105 A/cm2. Although there is no difference between the initial current-voltage characteristics of HBTs fabricated using wet etching and dry etching processes, the bias stress increases the base current of the dry-etched HBTs. The excess base current has an ideality factor of two, which indicates that the damage caused during dry etching produces recombination centers during minority carrier injection. The activation energy for the current gain degradation is found to be 0.89 eV.

Non-ideal current - voltage characteristics in MBE-grown heterojunction bipolar transistors

The current - voltage characteristics of heterojunction bipolar transistors and Si homojunction bipolar transistors grown by MBE have been measured with the aim of elucidating the causes of degraded common-emitter gain and low . It is shown that high reverse diode leakage currents arising from Zener tunnelling contribute to low in all structures considered. In forward bias, recombination currents in the space charge layers are the dominant cause of excess base current at temperatures above . Below this temperature a defect-assisted tunnelling mechanism gives rise to diode non-ideality.

The base current degradation of poly-emitter BJTs under AC stress

A simple model for the analysis of the ac stress effect in poly-emitter bipolar transistors is presented. Apart from the reverse-bias induced hot-carrier effects, the forward-bias recovery effect is a key factor under ac stress, it obviously suppresses the base current degradation of the device which is caused during the reverse-bias periods. In this work, we derived the relationship between the excess base current and the stress time for different ac stress conditions. This model is verified with experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>