Common-emitter Mode Research Articles

Investigation of Bipolar Degradation of 1.2 kV BJTs under Different Current and Temperature Conditions

Bipolar silicon carbide devices are attractive for high power applications offering high voltage devices with low on-state voltages due to plasma flooding. Unfortunately, these devices suffer from bipolar degradation, which causes a significant degradation of the on-state voltage. To explore the generation of stacking faults, which cause the degradation, the impact of the current density and temperature on bipolar degradation is investigated in this work. The analysis is done by stressing the base-collector diode of 1.2 kV bipolar junction transistors (BJTs) as well as the BJTs in common-emitter mode operation with different current densities at different temperatures.

Investigation of built-in bipolar junction transistor in FD-SOI BIMOS

The built-in bipolar junction transistor (BJT) of a BIMOS fabricated in 28 nm ultra-thin body and BOX (UTBB) fully-depleted silicon-on-insulator (FD-SOI) high-k metal gate technology is investigated in common-emitter mode and in built-in metal-oxide-semi-conductor field effect transistor (MOSFET) off-state. In the weak VBE regime, field-effects dominate, generating a negative base current and making the current gain β0 meaningless. For VBE high enough, the BJT works normally but with a very low gain below 1.

All-organic bipolar vertical transistor with sulfonated polyaniline base energy barriers favoring recombination emitter-collector current

Abstract We report the development and characterization of an all-organic vertical transistor, with tris(8-hydroxyquinoline) aluminum (Alq3) as emitter, poly(bithiophene) (PBT), as collector material and a sulfonated polyaniline (SPAN) layer as base material in the structure Au/PBT/SPAN/Alq3/CsO/Al. A thin cesium oxide (CsO) layer provides improved electron injection from the Al into the Alq3. The transistor is operated in the usual common-emitter mode were the output characteristic evidences the modulation of the collector current through the applied voltage, showing common-emitter gain of 160 at 4.5 V. The incremented gain is due to an increased recombination current, consequence of the arrangement of the frontier orbitals of PBT, SPAN and Alq3, which favors the confinement of electrons and holes in the SPAN layer.

All-organic vertical transistor in an analogous n-semiconductor/metal/p-semiconductor trilayer structure

We report on the development and characterization of an all-organic vertical transistor, consisting of a p-type conjugated polymer, poly(bithiophene), as collector material, a poly(ethylene dioxythiophene)/poly(styrene sulfonate) layer as base material and a n-type molecule layer, Alq3, as emitter material. The transistor is operated under direct bias in the common-emitter mode, being its operation based upon charge recombination of the injected majority carriers at the emitter–base interface. Experimental results have yielded current amplification factors up to 7. We also demonstrate that tunneling controls the transport characteristics of the device.

Characterization of the Stability of Current Gain and Avalanche-Mode Operation of 4H-SiC BJTs

The stability of the electrical characteristics of SiC n-p-n bipolar junction transistors (BJTs) is investigated under long-term avalanche-mode, dc, and pulsed-current operation. There is absolutely no change in the blocking I-V characteristics after a 934-h repetitive avalanche stress test. Long-term operation of the base-emitter diode (open-collector mode) alone does not result in any degradation of the ON-state voltage drop V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> or current gain β. Long-term operation in common-emitter mode results in negligible V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> or β degradation, if the base plate is maintained at 25°C. A greater degradation of β results upon increasing the base-plate temperature. The same total electrical charge, if passed through the BJT as a pulsed current, instead of a dc current, results in smaller β reduction. It is also shown that the β degradation can be reversed by annealing at ≥200°C, suggesting the possibility of degradation-free operation of SiC BJTs, when operating in pulsed current mode at ≥200°C temperatures.

Modeling of current gain compression in common emitter mode of a transistor laser above threshold base current

We have obtained the expressions for the terminal currents in a heterojunction bipolar transistor laser the base of which contains a quantum well (QW). The emitter-base junction is assumed to be abrupt, leading to abrupt discontinuity in quasi-Fermi level at the interface. The expressions for the terminal currents as a function of collector-emitter and base-emitter voltages are obtained from the solution of the continuity equation. The current density in the QW located at an arbitrary position in the base is related to the virtual state current density. The threshold current density in the QW is calculated by using the expression for gain obtained from Fermi golden rule. The plot of collector current (IC) versus collector-emitter voltage (VCE) for different values of base current shows the usual transistor characteristics, i.e., a rising portion after a cut-in VCE, and then a saturation behavior. The dc current gain remains constant. However, as the base current exceeds the threshold, a stimulated recombination rate is added to the spontaneous recombination rate and the plots of collector currents become closer for the same increase in base current. This current gain compression is in agreement with the experimental observation. Our calculated values qualitatively agree with other experimental findings; however some features like Early effect do not show up in the calculation.

Temperature performance of the edge emitting transistor laser

The characteristic temperature (T0) of the edge emitting transistor laser (TL) is studied numerically. For the deep-ridge TL, the common base (CB) mode characteristic temperature (T0,CB) is a lot lower than the common emitter (CE) mode characteristic temperature (T0,CE), which is comparable to a conventional laser. This is resulted from the increase of the emitter to base current gain with the base current, which amplifies the increase of the CB threshold current with temperature. For the shallow-ridge TL, the T0,CE is found to be also rather low and is only slightly higher than the T0,CB. This can be attributed to the large fraction of electron current in the total base current, which is related to the large thickness of base layer and the insertion of quantum wells in the TL.

Large current gain and low operational voltage permeable metal-base organic transistors based on Au/Al double layer metal base

In order to realize the common-emitter characteristics of the tris(8-hydroxyquinoline) aluminium (Alq3)-based organic transistors, we used Au/Al double metal layer as the base, thus the vertical metal-base transistors with structure of Al/n-Si/Au/Al/Alq3/LiF/Al were constructed. It was found that the contact properties between the base and the organic semiconductors play an important role in the device performance. The utilization of Au/Al double layer metal base allows the devices to operate at high gain in the common-emitter and common-base mode at low operational voltage.

Hybrid Organic/Inorganic Transistors Utilizing an Indenofluorene Derivative as Emitter

The molecular semiconductors are widely used on a great diversity of electronic and optoelectronic devices. The incorporation of molecular semiconductors to semiconductor- metal-semiconductor transistors (SMS) simplified the required production technology and, more importantly, allowed the construction of devices in vertical architecture with nearly ideal common-base current gains. In this work we present the results of the construction of SMS transistors utilizing an organic semiconductor, an indenofluorene derivative (DPIF), as emitter. The base and collector are respectively tin (Sn) and p- doped silicon (Si-p). The devices were electrically characterized at three-terminal measurements and were operated in common-base and common-emitter modes, revealing a permeable- base characteristic. The base thickness was varied in order to investigate the influence on the device performance. High current gain (~1) was obtained in common-base mode, and in common-emitter mode a current gain of 120 was achieved for a base thickness of 23 nm.

Pentacene-Based Planar- and Vertical-Type Organic Thin-Film Transistor

Pentacene-based planar- and vertical-type organic thin-film transistors (OTFTs) are investigated in this paper. High operation voltages are observed for the planar-type OTFTs with top source/drain electrodes, which results from the limitations of channel length and low material mobility. With a reduced channel length, a LiF hole-injection enhancement layer, and a thin metal gate, the vertical-type pentacene OTFTs exhibit a low-voltage operation of less than 5 V and a compatible on/off ratio of larger than 102. The smaller current gain observed from the device under current modulation is attributed to the increase of base recombination current under the common-emitter mode.

Synthesis, morphology and device characterizations of a new organic semiconductor based on 2,6-diphenylindenofluorene

A new organic semiconductor, 2,6-diphenylindenofluorene (DPIF), was synthesized in four steps with a high overall yield of 49.3%. The morphology of thin films of DPIF that were formed under different substrate temperatures was examined by atomic force microscopy and X-ray diffraction analysis. Two different crystalline phases were found to exist depending on the deposition conditions. The DPIF thin film emits around 500–530 nm, while the OLED based on DPIF emits green light with a maximum output over 150 Cd/m2 under 35 V. Two typical transistor devices, thin-film transistor (TFT) and semiconductor-metal-semiconductor (SMS) transistor, were fabricated and characterized. DPIF shows a weak n-type character from the TFT device measurement, while SMS transistors using DPIF as an emitter behave like permeable-base transistors with low operating voltages in both common-base and common-emitter modes and a feature of current amplification. Our results demonstrate however, that further research efforts are necessary in order to prevent the observed instabilities. These are quite important, considering that the common-emitter mode is widely used in applications requiring not only switching capability, but also current amplification.

SiC BJT's for High Power Switching and RF Applications

ABSTRACTIn this paper, high performance, high voltage NPN bipolar junction transistors in 4H-SiC are presented for applications in low frequency (&lt; 5 MHz) power conversion systems as well as in RF (425 MHz) power amplifiers. The power BJTs for low frequency switching applications were designed to block 1300 V and showed a specific on-resistance of 8.0 mohm-cm2, which outperforms all SiC power switching devices ever reported. Moreover, these transistors show a positive temperature coefficient in the on-resistance and a negative temperature coefficient in the current gain, which enable easy paralleling of the devices. In addition, RF BJTs were designed, fabricated and tested for operation at UHF frequencies. The common emitter breakdown voltage was in excess of 500 V consistent with the 5 micron collector thickness. For VCC = 20 V, fT peaked at about 1.5 GHz. A single cell was measured in common emitter mode with a collector supply voltage of 80 V in class AB at 425 MHz. A 100 μs pulse width with 10% duty cycle was used. A maximum output power of 50 W for a single cell was achieved. The peak large signal power gain was 9.6 dB. The collector efficiency at the power output of 50 W was 51% with a power gain of 9.3 dB. This represents the first demonstration of a SiC RF BJT.

1800 V NPN bipolar junction transistors in 4H-SiC

The first high voltage npn bipolar junction transistors (BJTs) in 4H-SiC have been demonstrated. The BJTs were able to block 1800 V in common emitter mode and showed a peak current gain of 20 and an on-resistance of 10.8 m/spl Omega//spl middot/cm/sup 2/ at room temperature (I/sub C/=2.7 A @ V/sub CE/=2 V for a 1 mm/spl times/1.4 mm active area), which outperforms all SiC power switching devices reported to date. Temperature-stable current gain was observed for these devices. This is due to the higher percent ionization of the deep level acceptor atoms in the base region at elevated temperatures, which offsets the effects of increased minority carrier lifetime at high temperatures. These transistors show a positive temperature coefficient in the on-resistance characteristics, which will enable easy paralleling of the devices.

Prospects of bipolar diamond devices

The prospects of diamond bipolar devices are analysed theoretically and experimentally in respect to the problem of deep doping, especially the deep donor in diamond. For this purpose a set of p– n– p bipolar junction transistors (BJTs) is fabricated on p-type diamond substrates by epitaxial growth using boron ( E A=0.4 eV) and nitrogen ( E D=1.7 eV) as the p- and n-type dopants respectively. It is shown that at the boron/nitrogen junction a p– n junction is formed. The built-in potential of the junction is determined by the ionised boron/nitrogen impurities. The specific features of the fabricated devices are the high resistivity of the nitrogen doped base (10 GΩ·cm at 20°C) and a significant leakage current of the reverse biased p– n junctions. These factors limit the transistor action to d.c.-operation in the nA-current range and to temperatures below 200°C where leakage starts to dominate. The values of the static current gain I C/ I B are measured in the common base mode 200 and in the common emitter mode 1.1. The theoretical section of the paper deals with the calculation of the static current gain of diamond pnp transistor structures in dependence of the donor energy level, temperature and frequency. Both the theoretical and the experimental results indicate that diamond bipolar transistors with a nitrogen doped n-type base can exhibit a current gain β of up to 30,000 in the d.c.-regime provided the leakage of the p– n junctions is sufficiently low. High-gain diamond transistors operating in GHz-frequency can be expected as soon as n-doping by shallow donor like phosphorous ( E D<0.5 eV) becomes available.

GaN/SiC HBTs and related issues

This paper reviews recent progress in the field of GaN/SiC heterojunction bipolar transistors. Key issues are identified and discussed. These include the comparison of a double-mesa and a selectively grown emitter structure, the evaluation of the GaN/SiC heterojunction and the problems faced when operating the devices in a common-emitter mode. A circuit simulation is presented indicating that common-emitter operation can be obtained for devices with low leakage current and modest gain.

Room-temperature operation of a resonant-tunneling hot-electron transistor based integrated circuit

The first resonant-tunneling hot-electron transistor (RHET) EXCLUSIVE-NOR integrated circuit that operates at room temperature is demonstrated. The XNOR circuit consisting of a single resonant-tunneling transistor and four thin-film resistors, exhibits a 500-mV output voltage swing between the high- and low-logic levels when biased with a 1.8-V supply. The transistor, which features a novel InGaP collector barrier, has a peak current density of 4*10/sup 4/ A-cm/sup -2/, a common-base transfer coefficient of 0.9, and a peak-to-valley current ratio of 10:1 when operated in a common-emitter mode.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-efficiency Ku-band HBT MMIC power amplifier

A Ku-band monolithic HBT power amplifier was developed using a metal-organic chemical vapor deposition (MOCVD)-grown AlGaAs/GaAs heterojunction bipolar transistor (HBT) operating in common-emitter mode. At a 7.5 V collector bias, the amplifier produced 0.5 W CW output power with 5.0 dB gain and 42% power-added efficiency in the 15-16 GHz band. When operated at a single frequency (15 GHz), 0.66 W CW output power and 5.2 dB of gain were achieved with 43% PAE.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-efficiency Ku-band HBT amplifier with 1 W CW output power

A compact, high-voltage AlGaAs/GaAs HBT was developed for applications in the Ku band using carbon-doped base structures. A single unit-cell device, operating under common-emitter mode and 10 V collector bias, produced 1.0 W CW output power at 15 GHz with 5.0 dB gain and 42% power-added efficiency. The power density of the device was a record 5.6 W/mm of emitter length.

GaAs inversion-base bipolar transistor (GaAs IBT)

A completely new type of GaAs bipolar transistor with a base formed by a two-dimensional hole gas has been fabricated. The transistor has no metallurgical base layer but has an extremely thin inversion hole layer working as a base layer. The current gain β = 5.6 at 77 K and β = 17.1 at 300 K was obtained for the common emitter mode.

Switching transients in metal-insulator (tunnel) - silicon thyristor under base voltage drive

The transient switching characteristics of the metal-insulator (tunnel)-silicon thyristor under base voltage drive are examined. In the monostable common emitter mode measurements are carried out to establish the dependence of the turn-on delay and rise and fall times on base drive, pulsewidth and bias point. The turn-off delay time is also examined, and the results are explained qualitatively. The operation of the device in the monostable common collector mode and the bistable mode are also examined.