Base-collector Junction Research Articles

Design and Development of InP DHBTs With High Breakdown Voltage for Ka-Band PA Applications

Type-I (straddled) InP DHBT devices have been fabricated to study the impact of different base-collector junction transition layer designs on the collector to emitter breakdown behavior, breakdown voltage, BVceo and the device output performance such as knee voltage, Vknee at high collector current densities, Jc. An abrupt breakdown behavior with BVceo of 11V and Vknee less than 1V at Jc>100kA/cm2 are achieved using an optimized base collector junction transition layer design. Using 2D numerical simulations, components of leakages dominating Iceo at low and high collector to emitter bias voltages are explained. It is further shown that the optimized device exhibits good RF and power performance achieving f $_{T}$ of 115GHz and f $_{max}$ of 150GHz at emitter width >1um. An MMIC power amplifier (PA) is also designed and fabricated using the optimized Type-I InP DHBT device. At 28GHz, good power performance is achieved with PAE of 54% and Psat of 26dBm. Thus, it is shown that InP DHBTs developed in this work are a good candidate for the next phase of 5G millimeter wave Ka-band power amplifier applications.

12 GHz spontaneous optical bandwidth tunnel junction light-emitting transistor

In this report, a quantum-well based light-emitting transistor with an Al0.1Ga0.9As/In0.05Ga0.95As tunnel junction collector in a common-emitter configuration with a double-digit gigahertz optical −3 dB bandwidth (f−3 dB) is demonstrated. Both the electrical and optical characteristics and the corresponding carrier dynamics are investigated. From microwave measurements, a −3 dB bandwidth up to 12.6 GHz via direct voltage (field) modulation is exhibited when the device is operated in a negative differential resistance state. The voltage-modulated optical characteristics are sensitive to the operation of the base-collector tunnel junction. The “enhanced single-pole optical response” can be attributed to the modulation amplitude decay at low frequencies due to the high impedance at the base-collector junction.

Didactic model of a simple driven microwave resonant T-L circuit for chaos, multistability and antimonotonicity

A simple driven bipolar junction transistor (BJT) based two-component circuit is presented, to be used as didactic tool by Lecturers, seeking to introduce some elements of complex dynamics to undergraduate and graduate students, using familiar electronic components to avoid the traditional black-box consideration of active elements. Although the effect of the base-emitter (BE) junction is practically suppressed in the model, chaotic phenomena are detected in the circuit at high frequencies (HF), due to both the reactant behavior of the second component, a coil, and to the birth of parasitic capacitances as well as to the effect of the weak nonlinearity from the base-collector (BC) junction of the BJT, which is otherwise always neglected to the favor of the predominant but now suppressed base-emitter one. The behavior of the circuit is analyzed in terms of stability, phase space, time series and bifurcation diagrams, Lyapunov exponents, as well as frequency spectra and Poincaré map section. We find that a limit cycle attractor widens to chaotic attractors through the splitting and the inverse splitting of periods known as antimonotonicity. Coexisting bifurcations confirm the existence of multi-stability behaviors, marked by the simultaneous apparition of different attractors (periodic and chaotic ones) for the same values of system parameters and different initial conditions. This contribution provides an enriching complement in the dynamics of simple chaotic circuits functioning at high frequencies. Experimental lab results are completed with PSpice simulations and theoretical ones.

Effect of TLP rise time on ESD failure modes of collector-base junction of SiGe heterojunction bipolar transistors

Electrostatic discharge behavior of integrated SiGe heterojunction bipolar transistors is investigated by transmission line pulse (TLP) and transient interferometric mapping techniques. When stressing collector - base junction in reverse direction, two distinct non-thermal failure modes, depending on TLP pulse rise time (RT), have been found: For RT ≥ 10 ns the observed failure at a critical voltage is attributed to base corner breakdown as supported by failure analysis. For RT ≤ 5 ns the failure occurs due to parasitic capacitance coupling which virtually short-circuits the base-emitter junction at the pulse beginning and thus induces a parasitic bipolar action.

Degradation of non-linear optocouplers induced by 60 MeV proton irradiation

Abstract In this paper, the experiments of proton irradiation on optocoupler are presented. The degradations of current transfer ratio (CTR) are analyzed, and the mechanisms induced by radiation are also demonstrated. The degradations of primary photocurrent are analyzed, which may be attributed to the photoresponse degradation in collector-base junction of phototransistor. The parameter degradations of light-emitting diode (LED) after irradiation play a role too. The degradations of transistor gain change the dependence of CTR on forward current. Finally, integration research from the irradiation-sensitive parameter degradation to the CTR degradation of the optocoupler is achieved.

Operation of silicon-germanium heterojunction bipolar transistors with different structures at deep cryogenic temperature

In this work, the device performances of discrete and integrated SiGe heterojunction bipolar transistors (HBTs) with different device structures from 300 to 4.8 K were investigated. The turn-on voltages of base-emitter and base-collector junctions increased non-linearly with temperature cooled to 4.8 K. Energy bandgap engineering was taken into account for the analytical model of the turn-on voltage versus temperature. Incomplete ionization occurred in the base-collector junction because of the low doping concentration. The trap-assisted tunneling current in the forward base current was clearly observed below 20 K. The ideality factor and saturation current were shown to be temperature dependence. The ideality factor was much larger than 2 below 40 K, indicating that the current is not only contributed by drift, diffusion and recombination, but also by tunneling. The peak current gain of the discrete SiGe HBTs achieved the maximum value of 3,388 at 80 K, while that of the integrated was 546 at 140 K. The transconductance in logarithm was linearly dependent on reciprocal temperature above 50 K, but flattened below 50 K. Early effect was evidently observed below 77 K in the fixed base current output characteristics of the discrete SiGe HBTs, and it was not obvious for the integrated SiGe HBTs.

Theoretical analysis on optical frequency response of tunnel-junction transistor lasers operated in different configurations

The optical frequency responses of tunnel junction transistor lasers (TJTLs) in the presence of the intra-cavity photon-assisted tunneling (ICPAT) effect in different small-signal configurations are demonstrated. With the Franz-Keldysh (F-K) absorption, TLs can be modulated with the voltage across the base-collector junction in the reverse-bias regime. We simulate both the responses through current and voltage modulations of TJTLs based on the modified rate equations and small-signal model incorporating the F-K and ICPAT effects. The input electrical signal is transferred to both the base-collector junction voltage and base current through the equivalent circuit, leading to simultaneous modulations of voltage and current. It is shown that the resistance and capacitance of the base-collector tunnel-junction play essential roles in electrical transfer functions and modulation bandwidth. With the small-signal optical responses, the eye diagrams of TJTLs under current and voltage modulations are also calculated. The device can be potentially modulated at a speed over 20 Gb/s with clear eye-opening.

Extraction and Analysis of Gamma Irradiated Si BJT SPICE Model

The Simulation Program with Integrated Circuit Emphasis (SPICE) model parameters of pre and post-irradiated silicon bipolar junction transistor (Si BJT) were extracted with the use of Altium Designer (AD)/SPICE model wizard. The percentage changes (Δ%) between forward and reverse-bias parameters of existing BJT (ZETEX BCW72) SPICE model were estimated and also the degradation Δ% between the experimental data of pre and post-irradiated Si BJT were calculated. Then the new measured results by comparison were imported into AD/SPICE model wizard to extracts forward-bias parameters. The extracted forward-bias parameters were used to generate reverse-bias parameters through Δ%. The final extracted Si BJT SPICE model parameters were implemented in SPICE simulator to obtained forward and reverse Gummel plots. As expected, base current (IB) increases, the collector current (IC) increases slightly at low bias base-emitter voltage, leading to current gain degradation due to positive charge trapped in the oxide and interface of the BJT device. In addition, the results of the IB in the forward Gummel flows in parallel with base-emitter junction, while the IB in the reverse Gummel flows across the base-collector junction down to the back side collector contact through the collector region. Finally, the compared results of Si BJT forward Gummel simulation and experimental data showed good agreement.

Toward Nanowire HBT: Reverse Current Reduction in Coaxial GaAs/InGaP n(i)p and n(i)pn Core-Multishell Nanowires

In this work the reduction of reverse currents in Au-catalyzed, MOVPE grown coaxial GaAs nanowire diodes are reported. The reduction is achieved by introducing an interstitial, lattice-matched i-InGaP shell (spacer) as tunneling barrier inside the junction, which also functions as a selective etch stop. With increasing spacer thickness, rectification ratios of >1.57 × 106 at ± 1.65 V, ideality factors of 1.3, and dark saturation current densities as low as 20 pA cm−2 are extracted, which are related to a reduced tunneling probability. Temperature-dependent DC measurements of junctions with thin spacers show a correlation to a simple (trap-assisted) tunneling model. With absolute reverse currents in the pA range down to −3 V bias, the improved diode is implemented as a collector-base junction in a coaxial n(i)pn nanowire structure by growing an additional, outer n-doped InGaP shell as the emitter layer in a nanowire HBT.

Improved Modeling of High Injection Substrate Current in High Voltage Bipolar Transistors

A vertical NPN transistor is typically built on a p-type substrate, which gives rise to parasitic PNP transistor action when the NPN base-collector junction, which is also the PNP emitter-base junction, is forward biased. In Mextram and Hicum, the PNP base terminal is attached to the NPN collector node that corresponds to the epi layer / buried layer interface, with VB1C1 as the PNP control emitter-base voltage, as illustrated in Fig. 1. A long physics based derivation to justify this choice was given in [1]. In Vbic, an option is provided to use both VB1C1 and VBC2 as PNP control voltage, with VBC2 as default. Using B or B1 is insignificant typically, while the difference between C1 and C2 is. While such approach generally works well for high speed transistors, for high voltage transistors, we experience great difficulty in fitting the substrate current at high VBE when the electrical base pushes out towards the collector, causing the internal NPN base-collector junction to be forward biased despite a reverse bias on the NPN external base-collector junction. Holes injected from the base diffuse downward towards the buried layer, and are retarded by a high electric field near the epi/buried layer interface, making the actual physics of hole transport much more complex than in a standalone PNP transistor. Fig. 2 (a) shows the best results one can possibly get with the standard Mextram model for a typical VBE sweep at VBC=0, -2 and -5V, VBS=2V. It is important to note that the VB1C1 = VBC + ICRCC –IBRBC in Mextram terms, with RCC and RBC being extrinsic collector and base resistances, respectively. Fig. 2 (b) shows the simulated VB1C1. For VBC=-2 and -5V, VB1C1 is still largely negative, while in measurement substrate current starts to rise quickly around VBE of 0.8V, indicating a rapid turn on of PNP action. This clearly suggests that the theory of [1] does not apply to these transistors, and improved modeling of PNP is needed. An alternative is to use the intrinsic base-collector junction voltage VB2C2, i.e. VB2C2* in Mextram, as the PNP substrate current control voltage, which was suggested in [2]. This leads to a higher Isub as shown in Fig. 3 (a) and (b). However, the onset of Isub, and the high VBE values of IB are all overestimated. IC is underestimated due to overestimation of IBRBC. This, however, does suggest that the PNP action is in fact related to some kind of internal base-collector junction bias which relates to the epi layer state. Here we propose a new model for the effective PNP emitter-base junction voltage, based on Mextram’s epi layer model. To minimize coupling of PNP and NPN modeling, we create a separate VB2C2, denoted as VB2C2** , and calculate it exactly the same way VB2C2* is calculated from epi layer current IC1C2 and VB2C1, but with a set of dedicated epi layer model parameters, i.e. rcv, scrcv, ihc, axi and vdc. In parameter extraction, the regular epi layer model parameter set is used for fitting Gummel, output and fT curves, while this new set of Isub dedicated epi layer model parameters is used for fitting substrate current. Fig. 4 (a) and (b) show modeling results of our new model. IB and Isub are much better fitted, including accurate modeling of the onset of Isub. [1] W. D. Mack and M. Horowitz, “Measurement of series collector resistance in bipolar transistor,” IEEE J. Solid-State Circuits, vol. SC-17, pp. 767-773, Aug. 1982. [2] J. -S. Park, A. Neugroschel, V. de la Torre and P. J. Zdebel, “Measurement of collector and Emitter Resistances in Bipolar Transistors,” IEEE Transactions on Electron Devices, vol. 38, pp. 365-372, Feb. 1991. Figure 1

(Invited) Physics and Compact Modeling of Sige HBT Linearity

SiGe HBTs, like other semiconductor devices, are in general nonlinear circuit elements. The exponential IC-VBE nonlinearity common to all bipolar transistors represents the strongest possible nonlinearity for all devices in which currents are produced by drift and diffusion of electrons and holes. Nonlinearity is desired for frequency translation and oscillation, but undesired for signal reception, amplification and transmission. In this talk we will review the fundamentals of various physical nonlinearities in SiGe HBTs, their complex interactions, experimental biasing current and voltage dependence of 2nd and 3rd order intercept points, IP2 and IP3, as well as recent developments in compact modeling of linearity using Mextram, an industry standard transistor model we are developing, for both common-base and common-emitter configurations. From a circuit point of view, the consequence of nonlinear IC-VBE is to make effective transconductance gm,eff a function of small signal base-emitter junction voltage vbe , as opposed to a constant in a linear circuit. The nonlinear contributions in general increase with vbe, which in general decreases with increasing biasing current before high injection, making gm,eff closer to a constant. The linearity of a SiGe HBT amplifier can therefore generally be improved by increasing biasing current. At radio frequencies, however, at relatively higher current, the 3rd order current produced by the nonlinear base-collector junction capacitance becomes important, and can interact with the 3rd order currents produced by the nonlinear IC, leading to a peak of IP3. Likewise, at higher VCB, as found in the common-base stage of a cascode amplifier, avalanche multiplication current Iavl produces an important 3rd order current that interacts with 3rd order currents from IC (without avalanche) and CBC, which can lead to a peak of IP3 in VCB dependence. Such peaks of IP3 are important for transistor biasing and sizing in circuit design, but also pose more stringent requirements on compact modeling than DC I-V and linear s-parameters. While both CBC and Iavl are straightforward to characterize and model at low currents, difficulties in both characterization and modeling increase at higher currents of interest. Latest Mextram 505.00 provides several options for modeling VCB and IC dependence of CCB, which give similar y-parameters but different IP3, particularly for common-emitter configuration, as illustrated in Figure 1. New CCB model options for junction voltage and capacitance smoothing, swvjunc=1, swvchc=0, lead to much better modeling of peak OIP3 than swvjunc=2, swvchc=1, which reduces to 504.12. Recommendations of best options and parameters for accurate modeling of IP3 will be made. While CCB model also affects IC nonlinearity through Early effect, we will show that its impact on IP3 is primarily through capacitive current. We will also show that the IC dependence of CCB is import to include for IP3. Common-base transistors often operate at higher VCB and hence with significant amount of Iavl. Mextram 505.00 has a new Iavl model that allows better current dependence and temperature dependence. Figure 2 shows this new avalanche model (swavl=1) has improved current dependence modeling of OIP3 over 504.12 (swavl=2 reduces model to 504.12) for a common-base SiGe HBT. Figure 1

Optimized Ge1−<italic>x</italic>Sn<italic>x</italic>/Ge Multiple-Quantum-Well Heterojunction Phototransistors for High-Performance SWIR Photodetection

We present the design and analysis of three-terminal Ge1− x Sn x /Ge multiple-quantum-well (MQW) heterojunction phototransistors (HPTs) for high-performance short-wave infrared (SWIR) photodetection. The active layer incorporates Ge1− x Sn x /Ge MQW structures between base–collector junctions pseudomorphically grown on Ge-on-Si substrates, thereby providing compatibility with CMOS platforms for low cost and scalable manufacturing technology. Introducing Sn into the MQW structures can effectively reduce the direct bandgap, thereby considerably extending the photodetection range in the SWIR spectral range with improved absorption efficiencies. In addition, the use of MQW structures as the active layer can enhance the absorption coefficient via quantum-confinement effects, thus further enhancing the photoresponses. We develop theoretical models to calculate the strained electronic band structures and optical absorption coefficients for the Ge1− x Sn x /Ge MQW structures, and the current gain is evaluated as a function of the barrier/well thicknesses, number of periods of the MQW structures, and doping concentrations of the layers for the HPT structures. The calculation results show that the absorption coefficient can be significantly enhanced by increasing the Sn content in the Ge1− x Sn x /Ge MQW active layer, and the current gain can be considerably enhanced by optimizing the HPT structures. With the enhanced absorption coefficient and current gain, high-responsivity photodetection can be achieved in the SWIR spectral range, thus making this device very promising for a wide range of SWIR photodetection applications.

Control of radiative base recombination in the quantum cascade light-emitting transistor using quantum state overlap

The concept of the quantum cascade light-emitting transistor (QCLET) is proposed by incorporating periodic stages of quantum wells and barriers in the completely depleted base–collector junction of a heterojunction bipolar transistor. The radiative band-to-band base recombination in the QCLET is shown to be controllable using the base–collector voltage bias for a given emitter–base biasing condition. A self-consistent Schrodinger–Poisson Equation model is built to validate the idea of the QCLET. A GaAs-based QCLET is designed and fabricated. Control of radiative band-to-band base recombination is observed and characterized. By changing the voltage across the quantum cascade region in the QCLET, the alignment of quantum states in the cascade region creates a tunable barrier for electrons that allows or suppresses emitter-injected electron flow from the p-type base through the quantum cascade region into the collector. The field-dependent electron barrier in the base–collector junction manipulates the effective minority carrier lifetime in the base and controls the radiative base recombination process. Under different quantum cascade region biasing conditions, the radiative base recombination is measured and analyzed.

Graphene–Silicon-Based High-Sensitivity and Broadband Phototransistor

Graphene–silicon vertical junction is utilized here for fabrication of high-responsivity and broadband phototransistor. Graphene–silicon as a Schottky junction plays the role of collector–base junction in a bipolar junction phototransistor. We propose graphene–silicon-based phototransistor as a promising candidate for fabrication of high-gain photodetector with responsivity as high as 11 A/W. Gain and ON/OFF ratio of our fabricated device reach up to 18 and 100, respectively. Our results show that the graphene–silicon-based phototransistor is sensitive to a broad range of incident light from visible to IR spectrum. Our results open up a way to fabricate highly sensitive photodetectors suitable for silicon integrated electronics.

New proposal to the electrical representation of a solid oxide fuel cell

PurposeThe aim of this paper is to find the electrical representation of a solid oxide fuel cell (SOFC) that enables the application of typical exploitation characteristics of fuel cells for estimation of fuel cell parameters (for example, exchange current) and easy analysis of phenomena occurred during the fuel cell operation.Design/methodology/approachThree-layer structure of an SOFC, where a thin semi-conducting layer of electrolyte separates the anode from the cathode, shows a strong similarity to typical semiconductor devices built on the basis of P-N junctions, like diodes or transistors. Current–voltage (I-V) characteristics of a fuel cell can be described by the same mathematical functions as I-V plots of semiconductor devices. On the basis of this similarity and analysis of impedance spectra of a real fuel cell, two electrical representations of the SOFC have been created.FindingsThe simplified electrical representation of SOFC consists of a voltage source connected in series with a diode, which symbolizes a voltage drop on a cell cathode, and two resistors. This model is based on the similarity of Butler-Volmer to Shockley equation. The advanced representation comprises a voltage source connected in series with a bipolar transistor in close to saturation mode and two resistors. The base-emitter junction of the transistor represents voltage drop on the cell cathode, and the base-collector junction represents voltage drop on the cell anode. This model is based on the similarity of Butler-Volmer equation to Ebers-Moll equation.Originality/valueThe proposed approach based on the Shockley and Ebers-Moll formulas enables the more accurate estimation of the ion exchange current and other fuel cell parameters than the approach based on the Butler-Volmer and Tafel formulas. The usability of semiconductor models for analysis of SOFC operation was proved. The models were successively applied in a new design of a planar ceramic fuel cell, which features by reduced thermal capacity, short start-up time and limited number of metal components and which has become the basis for the SOFC stack design.

Impact of Breakdown Voltage on Gamma Irradiation Effects in 0.13- $\mu \text{m}$ and 0.25- $\mu \text{m}$ SiGe HBTs

We have investigated the ionization damage by 60Co gamma irradiation in 0.13- and 0.25- $\mu \text{m}$ SiGe heterojunction bipolar transistors (HBTs). Both technologies feature high-speed HBTs (HS-HBTs) together with high-voltage HBTs (HV-HBTs). Base current degradation with increasing total irradiation dose is studied. An identical behavior of corresponding HS-HBT and HV-HBT is found for operation in forward mode probing the emitter–base junction. In reverse mode where the collector base junction is determining the base current degradation, HV devices exhibit larger degradation than their HS counterparts. The increased width of the collector–base space charge region in HV devices leads to enhanced interface recombination at the adjacent Si/oxide interfaces and stronger base current degradation. TCAD simulations of device degradation suggest a linear relationship between total irradiation dose and radiation-induced interface state density $N_{\mathrm{ it}}$ .

Improved performance of bipolar charge plasma transistor by reducing the horizontal electric field

In this paper, we have proposed a modified lateral bipolar charge plasma transistor (BCPT). The appropriate work function engineering is used to induce the electron-hole concentrations under different regions. The reduced work function difference and absence of oxide layer (tox) in the proposed lateral BCPT reduce the horizontal electric field (EX) at the emitter. Also, reduced work function difference at base metal contact decreases the electric field at base-emitter and base-collector junctions. 2-D TCAD simulations of the proposed device reveal that there are evenly spaced output characteristic curves, improved cut-off frequency and breakdown voltage. The reduction in horizontal electric field about one-fourth compared to the conventional lateral BCPT results in realistic current gain (β) and reduced on-set voltage makes proposed device suitable for low power applications. The proposed device exhibits improved cut-off frequency (fT = 7.5 GHz) compared to the lateral BCPT (3.7 GHz) and improved current gain (37.67) and same cut-off frequency (= 7.5 GHz) compared to the conventional BJT (β = 26.5 &fT = 7.5 GHz).

An Analytical Model of Avalanche Multiplication Factor for Wide Temperature Range Compact Modeling of Silicon-Germanium Heterojunction Bipolar Transistors

SiGe BiCMOS technology is currently being used to develop electronics for space applications due to the excellent performance of SiGe HBTs over an extremely wide range of temperatures, e.g. from 93K to 393K as found on lunar surface [1]. We have previously developed a Mextram based compact model with extensions to enable wider temperature modeling [2]. In that work, avalanche multiplication factor (M-1) was modeled using standard Mextram M-1 model [3], together with empirical temperature dependences of the two Mextram avalanche parameters, WAVL and VAVL. This work presents a new analytical model of M-1 with improved performance in modeling both temperature dependence and current dependence, and fewer model parameters. The model equations are summarized in (1)-(3). VCB is collector-base voltage, IC is the collector current without avalanche effect. Voff is an offset voltage which can be made the same as the 300K collector-base junction built-in potential VdC in Mextram for the devices used. Interestingly, Voff is found to be temperature independent, which simplifies modeling. An and BnT are impact ionization coefficients. Like in standard Mextram, An is temperature independent, while BnT is temperature dependent. BnT extracted from our data can be approximately described by a linear temperature dependence between 393K and 93K. This differs from the parabolic temperature dependence in standard Mextram, which was based on fitting of measurements between 240K and 400K [4]. Voff, c, d are parameters needed for low current M-1, and current dependence is modeled through the IT0 parameter, in a similar manner as how current dependence is modeled in the room temperature M-1 model reported in [5]. For practical currents of interest, a single temperature independent IT0 is found to be sufficient. It is possible to lump BnT and d as a single parameter that varies with temperature linearly, one would also then need to make An model parameter as well. That will introduce two more model parameters, which we find unnecessary, at least for the device used. Fig.1 shows (M-1) – VCB modeling results at low current from 93K-393K obtained using the proposed model and standard Mextram model. The device used is a typical first generation SiGe HBT technology with 50GHz peak fT. A clear improvement in the temperature dependence modeling can be observed. The VCB dependence at each temperature is also improved. We have implemented this new avalanche model in the wide temperature range Mextram model of [2]. The same measurements and parameter extraction methods used in [2] are used here. Fig. 2 (a) - (e) show IC–VCE and VBE–VCE characteristics under forced IB base drive which are sensitive to the modeling of M-1 from 93-393K. The dash line in the IC–VCE plots indicates peak fT current. To illustrate the importance of current dependence modeling, all simulations are repeated by turning off the current dependence term in M-1. Observe that the decrease of M-1 with increasing IC is significant well below the peak fT current, as can be clearly seen from 300K and 223K IC-VCE plots. REFERENCES [1] J. D. Cressler, “On the potential of SiGe HBTs for extreme environment electronics,” Proc. IEEE, vol. 93, no. 9, pp. 1559-1582, Sept. 2005. [2] L. Luo, Z. Xu, G. Niu, P. Chakraborty, P. Cheng, D. Thomas, K. Moen, J. Cressler, A. Mantooth, “Wide temperature range compact modeling of SiGe HBTs for space applications,” Proc. IEEE Southeastern Symposium on System Theory, pp. 110-113, March 2011. [3] J. C. J. Paasschens et al., Model derivation of Mextram 504: The Physics behind the Model, Koninklijke Philips Electronics, 2004. [4] P. Cullen, H. C. de Graaff, and W. J. Kloosterman, A weak avalanche model to be incorporated into the compact transistor model Mextram, Technical Note 353/87, Philips Nat.Lab., 1987. [5] G. Sasso, M. Costagliola, N. Rinaldi, “Avalanche multiplication and pinch-in models for simulating electrical instability effects in SiGe HBTs,” Microelectronics Reliability, vol. 50, no. 9-11, pp. 1577-1580, 2010. Figure 1

In-suit investigation of DC characteristics degradation in SiGe HBT included by halogen lamp irradiation

In present work, the direct current (DC) characteristics degradation of SiGe HBT under halogen lamp radiation were systematically investigated. Characteristics such as forward Gummel, reverse Gummel, junction leakage current, neutral base recombination and avalanche multiplication were measured in-suit and used to quantify the irradiation tolerance. A considerable increase in collector current and substrate current were found when the transistors were exposed to irradiation. The radiation-generated electron-hole pairs in space charge region of reversed collector-substrate junction are strongly responded. Because of the additional irradiation-induce excess carriers in neutral base region and space charge region of reversed base-collector junction, the neutral base recombination and avalanche multiplication increase for the irradiated transistors. The underlying physical mechanisms are analyzed and investigated in detail.

A Pseudobipolar Junction Transistor for a Sensitive Optical Detection of Biomolecules

A new optical sensor system, called the pseudo-bipolar junction transistor (BJT) optical measurement system (PBOS), based on a pseudo-BVceo of the BJT is proposed by adding a back-to-back connection of a laser diode (LD) (or an LED) and a p-i-n photodiode (PD) in the conventional optical measurement system operated in the photoconductive mode. A back-to-back connection of two optoelectronic devices and illumination of the light from the LD to the PD generates an optical current gain in the PD. It is similar to the current flowing mechanism in the BJT under the base open condition, in which the forward emitter–base junction current generates an electrical current gain in the base–collector junction. Similar to the negative differential resistance (NDR) after BVceo of the BJT, the NDR is observed in the PBOS. Operating the PBOS in the NDR region, the system can provide much higher sensitivity and lower limit of detection compared with the conventional optical measurement system in the photoconductive mode with a p-i-n PD. We show a mathematical model of the sensitivity of the PBOS to the transmittance of the optical path and our initial data for glucose detection as a potential application of the system.