Increase In Current Gain Research Articles

Low-voltage bulk-driven flipped voltage follower-based transconductance amplifier

A low voltage high performance design of operational transconductance amplifier is proposed in this paper. The proposed architecture is based on bulk driven quasi-floating gate metal oxide semiconductor field effect transistor (MOSFET) which supports low voltage operation and improves the gain of the amplifier. Besides to this the tail current source requirement of operational transconductance amplifier (OTA) is removed by using the flipped voltage follower structure at the input pair along with bulk driven quasi-floating gate MOSFET. The proposed operational transconductance amplifier shows a five-fold increase in direct current (DC) gain and 3-fold increase in unity gain bandwidth when compared with its conventional bulk driven architecture. The metal oxide semiconductor (MOS) model used for amplifier design is of 0.18 um complementary metal oxide semiconductor (CMOS) technology at supply of 0.5 V.

Impact of Carriers Injection Level on Transients of Discrete and Paralleled Silicon and 4H-SiC NPN BJTs

The 4H-SiC vertical NPN BJTs are attractive power devices with potentials to be used as high power switching devices with high voltage ratings in range of 1.7 kV and high operating temperatures. In this paper, the advantages of the 4H-SiC NPN BJTs in terms of switching transients and current gain over their silicon counterparts is illustrated by means of extensive experimental measurements and modelling, including investigation of high level injection, as a common phenomenon in bipolar devices that influences the switching rates and DC current gain. The two device types have been tested at 800 V with maximum temperature of 175 °C and maximum collector current of 8 A. The turn-ON and turn-OFF transition in Silicon BJT is seen to be much slower than that of the SiC BJT while the transient duration will increase with increasing temperature and decreases with larger collector currents. The common-emitter current gain of SiC BJT is also found to be much higher than silicon counterparts, increasing with temperature in low injection levels but decreasing in higher injection levels in both devices. The rate of increase of current gain slows down toward stability as the collector current increases, known as the high-level injection. Current sharing imbalance among parallel connected devices is also investigated, which are shown to be evidently dependant on temperature and base resistance in Silicon BJT, while the current collapse in also seen in SiC BJT at high injection levels with high base resistance. The turn-OFF delay is seen to be temperature dependant in single and paralleled Silicon BJTs while almost non-existent in SiC device.

Effects of temperature and density evolution in MHD simulations of HIT-SI

The helicity injected torus-steady inductive (HIT-SI) experiment uses steady inductive helicity injection to form a spheromak equilibrium and sustain the structure against resistive decay. Helicity injection is performed using two half-tori “injectors” connected to the main plasma volume, whose fields are oscillated in an AC manner. The properties of the sustained spheromak equilibrium have been experimentally observed to vary with the frequency of the injector oscillation, producing higher current gains and more-symmetric and outwardly shifted current centroids with higher frequency. A computational scan of injector frequency using the 3D MHD code PSI-Tet, which models the entire HIT-SI plasma volume including the injectors, has been performed, including a comparison of the results using the full Hall MHD model to those obtained using a simplified “zero-beta” (constant temperature and density) model. The results of both PSI-Tet models are also compared with experimental data and with simulations using the NIMROD code, which does not model the injector regions. The results of the PSI-Tet simulations show that the average temperature and current gain increase with injector frequency, in agreement with experimental trends. The simulations also show qualitative changes in the dynamics of several quantities with increasing injector frequency, such as density oscillations and current evolution. However, the outward shift and symmetrizing of the current centroid, observed experimentally, are not observed in these MHD simulations, indicating that unresolved or excluded dynamics may be important.

Cap-layer and charge sheet effect in InP based pnp δ-doped heterojunction bipolar transistor

The effect of varying the cap layer and the δ doped charge sheet has been investigated for an InP based heterojunction bipolar transistor (HBT) using the SILVACO TCAD tool. At the outset the simulation method is validated by comparing with experimental reported results. The InGaAs cap layer is then replaced with InGaAsP. The device figures- of-merit are observed to be remarkable improved with the quaternary cap layer. Some of the noteworthy results include increase in DC current gain from 50 to 126 and the Early voltage is improved from 7.96 V to 19.23 V. The minimum noise figure is reduced from 7.3 to 3 dB. The unity gain cut-off frequency (fT) and the maximum frequency of oscillation (fmax) are improved from 7.3 MHz to 5.4 GHz and 1.59–12.33 GHz respectively. Now in the presence of InGaAsP cap layer the δ-doped charge sheet is varied from 2 × 1011 cm−2 to 2 × 1012 cm−2, and it is observed that it has little effect on these parameters except that the VCE,offset voltage decreases with increase in the sheet density.

Silicon carbide bipolar junction transistor with novel emitter field plate design for high current gain and reliability

A silicon carbide bipolar junction transistor with novel emitter field plate (EFP-BJT) design is proposed in this paper. The fabricated EFP-BJT features a metal plate of the extending emitter electrode with a 50-nanometer-thick oxide layer overlapped on the extrinsic base surface. The contrast of experimental results show that a 56% increase of maximum current gain is obtained by the EFP-BJT compared with a conventional SiC BJT (C-BJT), with the EFP-BJT’s current gain of 43 measured at the collector current density (JC) of 716 A cm−2 corresponding to a specific on-state resistance (RSP_ON) of 5.4 mΩ · cm2 and open-base breakdown voltage (BVCEO) of 1.5 kV. The novel EFP-BJTs are entirely compatible with the process and design considerations of the conventional ones. The in-depth mechanism comparisons between the proposed EFP-BJT and C-BJT are studied by the simulation tool TCAD Silvaco. The surface recombination effect of EFP-BJT is greatly reduced by the modulation of the emitter field plate. Additionally, due to the surface recombination suppression of the novel structure, EFP-BJTs have effectively enhanced reliability. Compared with C-BJTs, there is no significant degradation of the collector current for the fabricated EFP-BJTs under the forward current stress test.

Investigation on the Robustness During Short-Circuit Turn-off and Its Tradeoff Characteristics With Performance in IGBTs

Decreasing the chip thickness of insulated gate bipolar transistor (IGBT) to improve the performance makes the current crowding effect become more pronounced during short-circuit turn-off, especially in the self-clamping mode (SCM). Former researchers have investigated the failure mechanisms during short-circuit turn-off. But the measures to further improve the robustness of IGBT during short-circuit turn-off and performance simultaneously still need more investigations. This paper focuses on the influences of the major device parameters on the robustness of IGBT during short-circuit turn-off, especially in the SCM, and its tradeoff characteristics with performance via symmetrical multicell electrothermal simulations. The results show that wider drift region combined with higher doping concentration, lower saturation current, and larger cell pitch can achieve higher robustness during short-circuit turn-off, but the performance will degrade. Besides, as the current gain increases, there exists the optimum value at which the robustness of IGBT during short-circuit turn-off is the highest. In order to achieve high performance and high robustness during short-circuit turn-off simultaneously, combined with decreasing the chip thickness and current gain, the saturation current should be decreased without compromising the conducting voltage by novel device structure, such as trench shielded planar gate IGBT and high-conductivity IGBT.

High performance multi-channel MOSFET on InGaAs for RF amplifiers

In this paper, we propose a multi-channel MOSFET (MC-MOSFET) on In0.53Ga0.47As for the first time by utilising trenches in the conventional planar MOSFET (CP-MOSFET) for RF amplifier applications. The proposed multi-channel MOSFET (MC-MOSFET) has two vertical-gates placed in trenches creating multiple channels in p-body for parallel conduction of drain current. High-k Al2O3 having thickness of 2 nm is used as gate dielectric in the proposed device. The TaN gate electrodes are placed in two different trenches in the p-type InGaAs layer where multiple n-channels are formed. Simultaneous conduction from multiple channels enhances the drain current (ID) and gives higher transconductance (gm) leading to improvement in overall frequency response. Two-dimensional (2D) numerical simulations of both MC-MOSFET and CP-MOSFET are performed by using ATLAS device simulator and their different performance parameters are compared. The proposed multi-channel structure provides 6.79 times higher ID, 5.57 times improvement in gm, 2.5 times increase in unity current gain (ft), 15.85% higher unilateral power gain (fmax) and suppress the short-channel effects (SCEs) as compared with the CP-MOSFET.

Hot carrier effect on a single SiGe HBT's EMI response

This paper describes the rectification responses exhibited by two kinds of SiGe HBTs when electromagnetic interference (EMI) is injected at the base of the transistor. The variation of the EMI induced DC offset after hot carrier stress is also studied. The experimental results show that the EMI response of a single SiGe HBT is different from that of a Si BJT. With interference present, the DC current gain increases at low base-emitter (BE) bias and decreases at larger VBE values. The absence of AC crowding induced DC crowding along with the base recombination current accounts for the increase of current gain. The base-width effect and the high-injection effect tend to decrease the gain in presence of interference. The simulation results show that the Gummel–Poon model is able to quantitatively model the EMI response of a SiGe HBT.

Investigation of effective base transit time and current gain modulation of light-emitting transistors under different ambient temperatures

In this report, the modulation of current gain of InGaP/GaAs light-emitting transistors under different ambient temperatures are measured and analyzed using thermionic emission model of quantum well embedded in the transistor base region. Minority carriers captured by quantum wells gain more energy at high temperatures and escape from quantum wells resulting in an increase of current gain and lower optical output, resulting in different I-V characteristics from conventional heterojunction bipolar transistors. The effect of the smaller thermionic lifetime thus reduces the effective base transit time of transistors at high temperatures. The unique current gain enhancement of 27.61% is achieved when operation temperature increase from 28 to 85 °C.

The Effect of Magnetic Field on Thick Ir(ppy)$_{\bf 3}$: Ir(mpp)$_{\bf 3}$ Nonmagnetic Organic Transistor With Improved Performance by Film Deposition on Heated Substrate

In this paper, we examined the influence of magnetic field with different substrate temperatures during the deposition of the Ir(ppy):Ir(mpp) blend layer heterojunction organic nonmagnetic organic transistor. It is shown that substrate heating treatment during evaporation leads to a significant improvement in the nonmagnetic metal-base transistor performance mainly due to an increase in current gain and ON-to-OFF current ratio. This is attributed to the improvement of thermal energy. Upon heating the substrate to 110°C in the presence of magnetic field, current gain and ON-to-OFF current ratio of 281 and 3.30 × 106 were obtained compared to 219 and 2.06 × 106 for an identical device prepared at 26°C, respectively. Magnetocurrent effect of ~28% was obtained with applied 2 T and 110°C.

Surface passivation oxide effects on the current gain of 4H-SiC bipolar junction transistors

Effects of surface recombination on the common emitter current gain have been studied in 4H-silicon carbide (SiC) bipolar junction transistors (BJTs) with passivation formed by conventional dry oxidation and with passivation formed by dry oxidation in nitrous oxide (N2O) ambient. A gradual reduction of the current gain was found after removal of the passivation oxide followed by air exposure. Comparison of the measurement results for two different passivated BJTs indicates that the BJTs with passivation by dry oxidation in nitrous oxide (N2O) ambient show a half order of magnitude reduction of base current, resulting in a half order of magnitude increase of current gain at low currents. This improvement of current gain is attributed to reduced surface recombination caused by reduced interface trap densities at the base-emitter junction sidewall.

Passivation of InP-based HBTs

The surface effects, the (NH 4) 2S and low-temperature-deposited SiN x passivations of InP-based heterostructure bipolar transistors (HBTs) have been investigated. The surface recombination current of InP-based HBTs is related to the base structures. The (NH 4) 2S treatment for InGaAs and InP removes the natural oxide layer and results in sulfur-bonded surfaces. This can create surface-recombination-free InP-based HBTs. Degradation is found when the HBTs were exposed to air for 10 days. The low-temperature-deposited SiN x passivation of InGaAs/InP HBTs causes a drastic decrease in the base current and a significant increase in the current gain. The improvement in the HBT performance is attributed to the low deposition temperature and the effect of N 2 plasma treatment in the initial deposition process. The SiN x passivation is found to be stable. S/SiN x passivation of InGaAs/InP HBTs results in a decrease in the base current and an increase in the current gain. The annealing process can cause the base current to decrease further and the current gain increase.

Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors

ABSTRACTA diamond based insulated gate bipolar transistor is incorporated into a two-dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper.

TEMPERATURE DEPENDENT I-V CHARACTERISTICS OF AlGaN/GaN HBTS AND GaN BJTS

DC I-V characteristics of AlGaN/GaN heterojunction bipolar transistors (HBTs) and GaN homojunction bipolar transistors (BJTs) are analyzed in the temperature range of 200-450 K. At low current levels, the adverse effects of poor ohmic contacts coupled with paths of high leakage make it difficult to extract intrinsic device operation ["Explanation of anomalous current gain observed in GaN based bipolar transistors", Xing et al. IEEE Elect. Dev. Lett. 24(1) 2003:p.4-6]. At intermediate current levels, owing to enhanced ionization of Mg in the base, the HBTs show an increase in current gain resulting from mitigated current crowding, and the BJTs show a decrease in current gain resulting from reduction of emitter injection coefficient. The offset voltage dependence on temperature is also explained.

Current gain increase by SiN x passivation in self-aligned InGaAs/InP heterostructure bipolar transistor with compositionally graded base

Room-temperature deposited SiN x passivation of InGaAs/InP heterostructure bipolar transistors (HBTs) with graded base was investigated. The passivation indicated that the surface recombination significantly affected the HBT performances. Both the base current and the base current ideality factor were found to decrease drastically after the SiN x passivation. The passivation also resulted in the increase of the current gain. The ideality factor of the surface recombination current of 2 was identified by the analyses of emitter–base diodes with different sizes. The emitter-size-dependent current gain showed that the improvement was due to the reduction of surface recombination. The SiN x passivation also suppressed the dependence on the perimeter-to-area ratio of the emitter junction.

SiGe resonance phase transistor: active transistor operation beyond the transit frequency fT

For the first time it was possible to obtain a current gain increase to more than 0 dB at frequencies beyond the transit frequency f T by use of an SiGe resonance phase transistor (RPT). This was achieved by using a very thick base layer with a graded high content Ge profile and a thick low doped collector to get a large phase delay in the carrier drift and a delayed injection. Based on these ideas the so called RTP was fabricated. To get sufficient phase delay in the base, it is necessary to grow very thick base layers ( w B) with graded Ge content ( x) up to high Ge concentrations (i.e. w B=120 nm, x=5–30%). These structures were grown by MBE at low temperatures in the ultrametastable growth regime. The manufacturing of the transistors was performed by a low temperature process with temperatures below 450 °C, using a NiSi/Ag contact metallisation.

Suppression of the burn-in effect in InGaP/GaAs heterojunction bipolar transistors by constant period of voltage stress

Two significantly abrupt increases of dc current gain (β) at the opposite extremes of base-emitter voltages (Vbe) linked by a relatively slight increase of β in the range of 1.25⩽Vbe⩽1.75 V are found in InGaP/GaAs heterojunction bipolar transistors (HBT’s). It has been proved that the burn-in effect directly causes the second abrupt increase of β occurring at Vbe>1.75 V instead of elsewhere. In addition, choosing Vbe>1.75 V, a higher base-emitter voltage results in a faster increase rate with improvement in current gain transient. Based on these observations, a constant period of voltage stress (CPVS) with Vbe=2.0 V and Vce=3.0 V for 5 min with a specific choice of Vbe>1.75 V (the voltage range corresponding to the second abrupt increase of β) is thus applied to promote the electrical performance of HBT’s. After applying a CPVS, the burn-in effect is substantially suppressed without showing any second abrupt increase of current gain. Although the current measured under both reverse and forward biases is greatly reduced for the base-emitter junction, a CPVS slightly degrades the electrical properties of a base-collector junction. Also, it has been proved that bulk recombination, rather than the surface recombination current, the base contact recombination, or the space-charge recombination, is the dominant base current component causing the burn-in effect. The electrical improvement of the base-emitter junction is due to the annihilation of H-related traps in the base region after a CPVS. Once H− ions form, we propose that these ions are too fast to drift toward the base-collector junction under the reverse bias of the base-collector voltage. After migration through the extrinsic base region, H− ions are supposed to be trapped near the base-collector space region, which results in the degradation of the base-collector junction after a CPVS.

2D device-level simulation study of strained-Si pnp heterojunction bipolar transistors on virtual substrates

A novel strained-Si pnp heterojunction bipolar transistor (HBT) design, suitable for virtual substrate technology, is proposed that is inherently free from the detrimental valence band barrier effects usually encountered in conventional SiGe pnp HBTs on silicon. It takes advantage of the heterojunction formed between a strained-Si layer and a relaxed SiGe buffer (virtual substrate), whose associated valence band offset appears favorable for minority hole transport at the base/collector junction. From two-dimensional (2D) numerical simulation, it is found that the newly proposed strained-Si pnp HBT substantially outperforms the equivalent BJT on a silicon substrate in terms of DC and high-frequency characteristics. A threefold increase in maximum current gain β, a fourfold improvement in peak f t and a 2.5 times increase in peak f max are predicted for strained-Si pnp HBTs on a 50% Ge virtual substrate in comparison with identical conventional silicon pnp BJTs.

Burn-in effect on GaInP heterojunction bipolar transistors

The burn-in effect in metalorganic chemical vapor deposition grown GaInP/GaAs heterojunction bipolar transistors is explained as due to the passivation of hydrogen-related recombination centers in the emitter. Results show that the diffusion base current contribution is dominated by the recombination in the emitter neutral region. The recombination centers are deactivated through the capture of electrons, available under forward bias, increasing the hole diffusion length and decreasing the diffusion contribution of the base current producing the observed current gain increase. These processes produce an independent behavior of the diffusion ideality factors for holes and electrons at each side of the emitter junction.

Pnp AlGaN/GaN Heterojunction Bipolar Transistors Operating at 300 �C

We have fabricated Pnp AlGaN/GaN heterojunction bipolar transistors and investigated their common-emitter current-voltage (I-V) characteristics at the temperatures from room temperature to 300°C. Good saturation properties were observed in their common-emitter I-V characteristics. The current gain of 20 at room temperature increased with elevating the temperature. The maximum current gain was as high as 71 at 300 °C with the collector current from 20 to 200 μA. This increase in current gain is ascribed to the enhancement in the hole injection efficiency from the p-AlGaN emitter to the n-GaN base as well as the reduction of the device resistance and the improved Ohmic characteristics of the subcollector. These results indicate that Pnp HBTs have the potential for high temperature operation.