Collector Voltage Research Articles

Direct plasmadynamic conversion of plasma thermal power to electricity

The generation of electrical energy using direct plasmadynamic conversion (PDC) is studied experimentally for small-scale, chemically-assisted plasmas (CA-plasma) for the first time. Glow discharge and microwave-generated plasma sources are operated at power levels on the order of a few to 50 W in the discharge case and up to 12.83 W/cm/sup 3/ in the microwave case. Extracted power approaching 1/4 W has been achieved as a demonstration. It is envisioned that such a system may be readily scaled to a few hundred Watts to several tens of kilowatts output power for microdistributed commercial applications (e.g., household, automotive, light industry, and space based power). Three-quarter inch long by 0.040-in diameter cylindrical PDC electrodes have been tested in a 10-50 W direct current, glow discharge plasma device with He or Ar as the working gas at 0.3-3.0 torr. The PDC anode was magnetized in the range of 0-700 G with a 1.5-in water cooled Helmholtz electromagnet. Open circuit voltages up to 6.5 V were obtained across the PDC electrodes at 1 torr He and 350-G field. The collector voltage was shown to be a function of applied magnetic field strength B and peaking at about 300 G. A variety of resistive loads were connected across the PDC electrodes, extracting continuous electrical power up to 0.44 mW. The power/load curve peaks at 0.44 mW for a 20 k/spl Omega/ load indicating the impedance matching condition with the plasma source. The most severe limitation to collector output performance is shown to be plasma conductivity. Collector power drops sharply with increasing neutral gas fill pressure in the glow discharge chamber at constant discharge current indicating that electron collisions with neutral gas atoms are responsible for the reduction in conductivity. Scale-up to higher power has been achieved with the use of a microwave plasma generator. A 0.75-in long by 0.094-in diameter PDC anode was magnetized to /spl sim/140 G resulting in open circuit PDC voltages in excess of 11.5 V for He plasmas at /spl sim/0.75-1 torr and 50 sccm flow. Due to higher conductivity, load matching was now obtained at /spl sim/600 /spl Omega/. Langmuir probe results indicate good agreement between the conductivity change and the electron to neutral density ratio scale-up. For this source and electrode configuration, PDC power as high as /spl sim/200 mW was demonstrated in He at 0.75 torr for a microwave input power density of /spl sim/8.55 W/cm/sup 3/. Considering an electron mean-free path as the scale for collector probe influence in the plasma, the peak extracted power density is /spl sim/1.61 W/cm/sup 3/, corresponding to a volumetric conversion efficiency of /spl sim/18.8%.

Active-gate-control for Snubberless IGBTs connected in Series

High voltage IGBT converters require an IGBT series connection. To reduce converter loss and simplify converter configuration, snubber circuits should be omitted. In this paper we introduce our snubberless IGBT series connection technique with active-gate-control.In the active-gate-control IGBT, gate-voltage is set to increase with collector-voltage. Due to increased gate-voltage, IGBT impedance drops and the collector-voltage is limited. The collector-voltages of IGBTs connected in series can be balanced by uniting the collector-voltages of each single IGBTs independently. In the active-gate-control, the gate is charged before the collector-voltage reaches the clamping voltage. So fast control can be performed and surge voltages at the recovery state can be clamped. In the control the clamping voltage increases with tum-off current and it is saturated for further larger currents. By increasing the clamping voltage with tum-off current, the increase of tum-off loss caused by collector voltage clamping is limited. Saturating the clapping voltage for further higher currents prevents overvoltage failure.

Properties of the transient of avalanche transistor switching at extreme current densities

Avalanche transistor switching at extreme currents is studied under conditions in which the charge of the excess carriers drastically rebuilds the collector field domain, causing fast switching and a low residual voltage across the switched-on device. The dynamic numerical model includes carrier diffusion and considers different dependencies of the velocities and ionization rates for the electrons and holes in the electric field. These dependences determine the principal difference in the switching process between n/sup +/-p-n/sub 0/-n/sup +/ and p/sup +/-n-p/sub 0/-p/sup +/ structures. Reasonably good agreement is found between the simulated and measured temporal dependences of the collector current and voltage drop across the device for a particular type of avalanche transistor. Certain differences in the switching delay can partly be attributed to limitations in the one-dimensional (1-D) approach. It is now certain that collector domain reconstruction defines the transient in a n/sup +/-p-n/sub 0/-n/sup +/ transistor at high currents, but is not very pronounced in a p/sup +/-n-p/sub 0/-p/sup +/ transistor. Some nontrivial features of the device operation are found, depending on the semiconductor structure. In particular, it is shown that the thickness of the low-doped collector region affects mainly the switching delay, and does not significantly effect the current rise time.

A dual-voltage self-clamped IGBT for automotive ignition applications

Self-clamped inductive switching (SCIS) energy capability is a critical parameter of device performance for insulated gate bipolar transistors (IGBTs) used in automotive ignition applications. In this work, the authors propose a monolithic dual-voltage self-clamped IGBT to improve its SCIS energy capability. During an inductive turnoff process, the collector voltage of the proposed device is clamped first at a high level for a short period of time and then at a much lower level until the electromagnetic energy stored in the inductive coil is fully discharged. The concept has been verified and analyzed with extensive numerical device simulation. A monolithic prototype device based the concept has been designed and fabricated with a conventional eight-mask IGBT process. The preliminary experimental result is also reported.

Characterizing IGBT Losses for Switched Mode Operation

Accurate loss analysis of switch mode circuits that use IGBTs as a switching device is difficult. Switching losses are a function of switch current, collector voltage and junction temperature. These three-dimensional parameters increase equation complexity and are often time consuming in their determination. However, computer programs such as MathcadTM MatlabTM ExcelTM and Table CurveTM provide practical means of curve fitting empirical data. This paper outlines a methodology for recording and converting empirical IGBT performance data into accurate and useful equations. These equations may then be utilized as simple function calls for loss analysis calculations. The examples covered in this paper are the IGBT clamped inductive turn-off energy and VCE(SAT) on-state drop. The losses predicted by the empirical equations are compared with in-circuit measured losses. IGBTs representing two different technologies are modeled.

A 3.2-V operation single-chip dual-band AlGaAs/GaAs HBT MMIC power amplifier with active feedback circuit technique

This paper describes the design and experimental results for a 3.2-V operation single-chip AlGaAs/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (IMMIC) power amplifier for GSM900 and DCS1800 dual-band applications. The following two new circuit techniques are proposed for implementing the power amplifier. One is an on-chip HBT bias switch which in turn switches the amplifier between 900 and 1800 MHz. The proposed switch configuration allows the switch using a high turn-on voltage of 1.3 V of AlGaAs/GaAs HBT's to operate with a 3-V low supply voltage, because the switch circuitry needs no stacked configuration. The other is an active feedback circuit (AFB) to prevent permanent failure of HBT's in the output power stage even under severe conditions of oversupply voltage and strongly mismatching load. Experimental results revealed that the proposed feedback circuit, which works as a voltage limiter, can protect the output stage HBT's from an excessive collector voltage swing even when the amplifier is operated under a condition of a 5-V oversupply voltage and a 10:1 voltage standing-wave ratio (VSWR) mismatching load. Under a normal condition of 3.2 V and a 50-/spl Omega/ matching load, the IC is capable of delivering an output power of 34.5 dBm and a power-added efficiency (PaE) of 52% in a GSM900 mode, and a 32-dBm output power and a 32% PAE in a DCS1800 mode.

A note on low-frequency ion noise and its reduction in linear beam microwave tubes

A simple theory based on electron motion in the spatially periodic potential produced by beam scalloping due to focusing mismatch is presented to explain some key features of low frequency ion-induced phase noise. In particular, the theory presented here predicts: 1) relatively high sensitivity of phase noise levels to the strength of the magnetic focusing field and cathode voltage; 3) marginal sensitivity of phase noise to cathode heater filament voltage; and 3) relatively low sensitivity of phase noise to radio frequency (RF) drive level and collector voltage. It is shown that, in the event that beam scalloping due to mismatch cannot be avoided, a simple and effective way to suppress low-frequency phase noise is adjustment of the magnetic field so that the interaction length is an integral multiple of the scalloping wavelength. This conclusion is independent of the details of the dynamics of the ions, and therefore independent of the details of the ion noise spectrum.

Photoluminescence Study of Resonant Tunneling Transistor with p+/n-Junction Gate

We studied photoluminescence (PL) of a resonant tunneling transistor with a p+/n-junction gate. The excitation energy was selected to be close to the band-gap energy of the GaAs collector layer 1) so as not to excite the barrier layer and quantum well directly, and 2) in order to obtain a simple luminescence spectrum. The PL signal shows strong correlation with the resonant tunneling current. The PL peak position shows a redshift with increasing collector voltage, indicating the existence of the quantum-confined Stark effect. The collector voltage dependence of the PL linewidth suggests the existence of charge accumulation in the quantum well. The accumulated electron density and the charging time were estimated. It was also shown that the PL intensity could be controlled by the gate voltage without affecting the resonant tunneling behavior of electrons.

Concepts of light emission from a silicon MOS tunnel emitter Auger transistor

An interesting case of light emission from a silicon-based device, visible electroluminescence from an Auger phototransistor with a MOS tunnel emitter, has been analysed theoretically. A simple model of this luminescence is developed. The light originating from a tunnel MOS structure is shown to be a superposition of radiation produced by injected hot electrons (HE-radiation) and radiation from the space charge region (SCR-radiation). The shape of the spectrum and the total intensity can be changed by varying the collector voltage and insulator bias. The spectrum of HE-radiation has an apparent high-energy border, whose position depends primarily on the insulator voltage. A substantial contribution to the insulator voltage is provided by holes generated by Auger ionization.

Oscillation effects in IGBT's related to negative capacitance phenomena

Insulated gate bipolar transistors (IGBT's) are inherently unstable at high collector voltages due to negative gate capacitance values. We investigate IGBT gate voltage oscillations by experiment and through computer simulation. In addition, we show that under certain gate circuit conditions, gate voltage oscillations can lead to already observed collector current imbalance effects.

On the question of short-period oscillations of the collector voltage during transverse electron focusing

Giant short-period oscillations during transverse electron focusing at high emitter voltages have been observed in bismuth samples with a superlattice on the surface. A model is proposed which explains the onset of the oscillations, their position on the magnetic-field scale, and their intensification and shift along the magnetic-field scale with increasing current (this shift depending on the direction of current flow) and which can also account for the absence of oscillations in fields which are multiples of the field of the first oscillation. In this model the oscillations are attributed to the appearance of resonant surface (edge) states and their contribution to the electron transport.

Transmission through a quantum dot in a four-terminal phase-coherent system

Motivated by the recent experiment by Schuster et al (Schuster R, Buks E, Heiblum M, Mahalu D, Umansky V and Shtrikman H 1997 Nature 385 417), we study a four-terminal phase-coherent system, each arm having a quantum dot embedded in it (dot 1 for studying and dot 0 for reference). Using the nonequilibrium-Green-function method, the open-circuit collector voltage is derived. We find the following features. (1) The phase behaviours are similar for all of the resonance peaks. (2) In a single resonance peak, the phase increases by on a scale of about the half-peak-width . (3) An abrupt phase drop, by , occurs near the point half way between two consecutive peaks. These results agree well with experiment. We attribute the characteristic (3) to the off-diagonal linewidth of dot 1, which is a single-electron effect. In addition, the crossover of the phase behaviour in going from the four-terminal system to a two-terminal system is studied. Finally, another manifestation of this off-diagonal linewidth is also discussed.

Effect of Collector Current and Voltage Profiles on the Efficiency of Transistor Microwave Power Amplifiers of Class F(H) With Parametric Effects Taken Into Account

Effect of Collector Current and Voltage Profiles on the Efficiency of Transistor Microwave Power Amplifiers of Class F(H) With Parametric Effects Taken Into Account

Design considerations for millimeter-wave power HBTs based on gain performance analysis

Critical design issues involved in optimizing millimeter-wave power HBTs are described. Gain analysis of common-emitter (CE) and common-base (CB) HBTs is performed using analytical formulas derived based on a practical HBT model. While CB HBT's have superior maximum-gain at very high frequencies, their frequency limit is found to be determined by the carrier transit time delay. Thus, to fully exploit the potential gain in a CB HBT, it is essential to maintain a high f/sub T/ even at high collector voltages. The advantage of using CB HBT's in a multifingered device geometry is also discussed. Unlike CE HBTs, CB HBTs are capable of maintaining a high gain even if the device size is scaled up by increasing the number of emitter-fingers. Moreover, it is found that reducing the wire parasitic capacitance allows emitter ballasting resistance to be used without affecting the gain. Fabrication of HBTs based on these design considerations led to excellent power performance in a CB unit-cell HBT at 25-26 GHz, featuring output power of 740 mW and power-added efficiency of 42%.

The Double-surface Transistor

In a series of Letters to the Editor [1] appearing in a recent issue of this journal, there are described the physical construction and proposed theory of operation of a solid state semiconductor triode. This device, which is now called the type A transistor, comprises a block of high back-voltage germanium on one of the faces of which are two contacts, side by side with each other and close together. These contacts are called the emitter and collector, respectively. A large-area contact to the opposite face of the semiconductor block is called the base contact. The present communication describes another semiconductor triode, the double-surface transistor, in which the emitter and collector contacts bear on the two opposite faces of a thin wedge or slab of semiconductor. This slab is prepared from an ingot of high back-voltage germanium of N-type [2]. After being ground approximately to the desired shape, the slab is etched and provided with a suitable large-area base contact. For good gain characteristics it is advantageous that the thickness of the slab be no greater than about 0.01 cm at the place where the contacts bear upon it. These contacts should be within about the same distance of coming exactly opposite each other on the two faces of the slab. Tungsten, copper, and phosphor bronze have been used successfully as contact materials. This device, together with its electrical connections for use as a grounded-base amplifier, is illustrated schematically in Fig. 1. In operation a comparatively large dc reverse bias ( 50 to 100 V) is applied to the collector, while a comparatively small dc forward bias (a few tenths of a volt) is applied to the emitter. Because of positive feedback effects in the base contact and semiconductor body, the emitter bias voltage-to-base may in some cases be zero or even negative. The static characteristics of a double-surface transistor are presented in Fig. 2. Families of collector voltage versus collector current curves are given, with constant emitter current as parameter for the solid lines, and with constant emitter voltage as parameter for the dashed lines. Such a plot allows one to make judicious choice of dc operating point. It furnishes in addition complete information from which can be obtained, almost by inspection, the dynamic

IGBT negative gate capacitance and related instability effects

For high collector voltages, Insulated Gate Bipolar Transistors (IGBTs) exhibit a negative gate capacitance. In this condition, a p-channel inversion layer is formed on the N-base surface. The positive charges in the p-channel induce negative charges in the MOS gate electrode. This results in a negative gate capacitance. As a consequence of this negative capacitance, IGBT operation is inherently unstable, leading to current redistribution between cells or even chips.

Physical compact collector-emitter breakdown model for heterojunction bipolar transistors

Collector-emitter breakdown in npn HBTs is modeled using a base-collector current equal to I h = α i I c, where I c is the collector current and α i is the integral of the electron impact ionization coefficients over the base-collector depletion depth. We fit the α integrals for collector doping concentrations N d ∼ 0.08 to 1 × 10 17 cm −3 to functions of the collector voltage. The model is suitable for SPICE and harmonic balance simulators, is temperature dependent, and allows voltages to be swept above the collector-emitter breakdown limit without catastrophic effects to the model convergence.

Base and collector resistances in heterojunction bipolar transistors

In heterojunction bipolar transistors (HBTs), the reverse base currents flow from the outer base periphery to the collector. The reverse base and collector resistances are therefore dominated by contact resistance, which is inversely proportional to the outer base and inner collector periphery lengths which are larger than the emitter lengths when the base and collector electrodes surround the emitter element. These resistances can be extracted from reverse Gummel (current vs V bc with V bc = 0) and from measurements of output resistances at zero collector voltage sweeps. We compare models with measurements where the base and collector peripheries decrease with increasing emitter diameters.

Enhanced real-space transfer in δ-doped GaAs/In0.1Ga0.9As/In0.25Ga0.75As two-step channel heterojunctions

A two-step channel In0.1Ga0.9As/In0.25Ga0.75As heterostructure real-space transfer transistor grown by low-pressure metalorgonic chemical vapor deposition is implemented. By virtue of δ doping, shallow ohmic contacts and two-step channel, a high peak-to-valley current ratio up to 260 000 at 300 K can be obtained at low collector voltage (Vc=3 V). Moreover, from Shubnikov–de Haas (SdH) measurements, we observe a positive persistent-photoconductivity effect and variations of quantum lifetime. The SdH result is in good agreement with the critical drained-to-source onset voltage of negative differential resistance.

Monte Carlo Modeling of Transient Effects in Resonant-Tunneling Bipolar Transistors

Transient behavior of bipolar transistors with a quantum-well base and a resonant-tunneling structure in the collector is studied using the ensemble Monte Carlo particle method. The switch on/off processes as a response to trigger pulses of the collector voltage and the base current are simulated. The amplitudes and duration of the pulses providing reliable switching are obtained.