Alpha Cutoff Frequency Research Articles

A vertical silicon-graphene-germanium transistor

Graphene-base transistors have been proposed for high-frequency applications because of the negligible base transit time induced by the atomic thickness of graphene. However, generally used tunnel emitters suffer from high emitter potential-barrier-height which limits the transistor performance towards terahertz operation. To overcome this issue, a graphene-base heterojunction transistor has been proposed theoretically where the graphene base is sandwiched by silicon layers. Here we demonstrate a vertical silicon-graphene-germanium transistor where a Schottky emitter constructed by single-crystal silicon and single-layer graphene is achieved. Such Schottky emitter shows a current of 692 A cm−2 and a capacitance of 41 nF cm−2, and thus the alpha cut-off frequency of the transistor is expected to increase from about 1 MHz by using the previous tunnel emitters to above 1 GHz by using the current Schottky emitter. With further engineering, the semiconductor-graphene-semiconductor transistor is expected to be one of the most promising devices for ultra-high frequency operation.

Design graphs for the intrinsic alpha cut-off parameters ωα, ωTandmof bipolar transistors

Design graphs are developed for the intrinsic alpha cut-off frequencies ωα, and ωT, and for the excess phase m of bipolar transistors. The Kroemer equation giving the base transport factor in single-diffused transistors (constant aiding field in the base) is extended to cover double-diffused transistors (constant aiding and retarding fields in the base). The base retarding held is found to have an important degradation effect on the cut-off frequencies: a 2 kT/q retarding voltage extended along 20% of the base width diminishes ωα,to about half the value corresponding to a single-diffused transistor. A practical design criterion is given for optimizing the impurity-concentration profiles of double-diffused transistors.

Heterojunction GaAs/GaAlAs transistors with enhanced gain from avalanche multiplication

A GaAlAs/GaAs heterojunction transistor has been made using liquid-phase epitaxy. The emitter stripe was 10µm wide by 100µm long. The base and emitter had equal impurity content around 5 × 1023/m3 but, with the wide band gap GaALAs emitter, low-frequency current gains approaching 2000 were found. This is amongst the highest so far recorded for this type of transistor. The alpha-cutoff frequency was estimated to be around 1 GHz, but the unity gain frequency was experimentally as low as 100 MHz. This was attributed to high r.f. resistance, possibly caused by the Schottky barrier contact to the base region. When the basecollector region was driven close to primary breakdown, current densities in excess of 3 × 107 A/m2 could be obtained without secondary breakdown occurring, at least for the duration of the bias pulse. This appeared to be about an order of magnitude better than for a comparable Si transistor. Avalanche multiplication could then increase the unity gain frequency to 400 MHz.

Frequency properties of a Darlington composite transistor

Abstract In this paper the analysis of frequency properties of a Darlington composite transistor is given and such of its frequencies as alpha cut-off frequency, beta cut-off frequency and high-frequency power gain are obtained. It is shown that in the CB configuration the | α(ƒ)| function of this device has an extremum value greater than one

Radiation Resistance of Microelectronic Systems

The radiation resistance of microcircuit systems has been studied by testing separate microcircuits and using statistics based on known data of the transistor damage coefficients. The logic gates with bipolar transistors can be characterized by a transistor base transit time, tb, defined as tb=0.2/fα where fα is the alpha cutoff frequency. When tbø < 105ns/cm2 the separate gates almost certainly survive, failure almost certainly occuring when tbø > 107ns/cm2. The quantity ø is the fast neutron exposure of a reactor spectrum (E > 10 keV).

Schema equivalent du transistor allie resistance de base et tension de bruit ramenee a l'entree du transistor

Minority carriers injection in the base of a transistor modulates the conductivity and a dynamic base resistance must be added to the emitter-base diode impedance of the equivalent circuit. This resistance is strongly current dependent. A study of the transistor equivalent circuit at a frequency higher than the alpha cut-off frequency shows the current dependence of this element. Distributed elements can be located from a physical model and an equivalent circuit accounts for the observed phenomena in the complex plane. This method allows us to calculate from these measurements a noise voltage. This voltage is added to the input of the transistor which can now be considered noiseless.

Circuit Models to Predict Switching Performance of Nanosecond Blocking Oscillators

This paper presents circuit models for calculating the switching time of transistor blocking oscillators operating in the nanosecond time domain. The accuracy of the original theory proposed by Linvill and Mattson is tested using transistors with increasing alpha cutoff frequency. It is found that this theory gives close correlation between measured and calculated switching time for low-frequency transistors; however, for high-frequency units, differences as large as an order of magnitude exist. A new model is presented which adequately describes the oscillator performance with high-frequency transistors. Although large signals are involved in the circuit's operation, a large-signal transistor model is necessary only during a description of initial turnon. Switching time minimization is studied using the new models by examining the sensitivity of the oscillator switching time to variation in circuit model parameters. Graphs which show theoretical and measured sensitivity to parameter variation are presented. Three blocking oscillators have been constructed and tested to experimentally verify the accuracy of the new models. Measured results demonstrate that the equations derived from the new circuit models are quite adequate for calculating switching times of blocking oscillators in the nanosecond region.

Alpha cutoff frequency of junction transistors

The alpha cutoff frequencies of drift and diffusion transistors are analyzed and approximated by simple analytical expressions. The alpha cutoff frequency is determined in terms of the three major contributions: base-region transport cutoff, emitter cutoff due to the emitter capacitance, and the collector cutoff due to the base resistance and the collector capacitance. Denoting the respective cutoff frequencies by ω ∗ cα , ω E and ω c , and the resulting cutoff frequency by ω cα , it is found by computation that 1 ω cα = 1 ω ∗ cα + 1 ω E + 1 ω c In addition, a new expression is given for the base transport cutoff. The dependence of the frequency cutoff on the emitter current is also discussed for the current range where the built-in electric field is partially washed out by the high concentration of minority carriers injected into the base. A calculation is presented for the current level at which there is a maximum in the alpha cutoff. Experimental data are compared with the calculations.

Highly linear amplification with transistors

Highly linear amplification can be obtained with HF diffused-base transistors in the common base configuration. It is the purpose of this paper to 1) present experimental results to demonstrate this, 2) demonstrate the causes for this high degree of linearity and derive expressions for optimum bias voltages and currents (these results can be extended with certain restrictions to the common emitter and common collector configurations), and 3) present a general method for analytically treating nonlinearity in all transistor configurations. A push-pull amplifier using 2N509- or 2N1195-type transistors provided 13 db of gain, with signal-to-distortion ratios of 70 to 80 db for broad-band white noise signals with +3 dbm of average output power or sine wave signals with +15-dbm peak output power. The stability of this gain and linearity with temperature and interchange of transistors is high. This high degree of linearity is shown to be due to 1) cancellation of current sensitive nonlinearity in the emitter and collector resistances, 2) collector voltage bias adjusted so that the derivative of the collector conductance with respect to collector voltage is zero, and 3) the use of a high alpha cutoff frequency transistor. An expression derived for optimum bias was in good agreement with experiment. The nonlinear distortion in transistors is shown to be different from that found in most devices, in that there are frequency-sensitive and frequency-insensitive nonlinearities. A general analysis carried out including these terms was in good qualitative agreement with experiment.

Transistor Simulator

An apparatus allowing a straightforward determination of the π equivalent circuit of alloy junction transistors is described. The principle of measurement is based on the simulation of wave forms. The possibility of a simple determination of the equivalent circuit at any working point of the transistor enables a rapid evaluation of the current or voltage dependence of the circuit elements. The equipment, having an upper frequency limit of 10 Mc, can be used for transistors of much higher alpha cutoff frequencies, since for the measurements the common emitter configuration is chosen. Examples are given to demonstrate how some physical and dimensional values of the transistor can be calculated from the measured parameters.

Digital circuits operating at 1 Mc/s using transistors

The paper describes circuits for performing logical operations in data processing. They operate reliably at 1 Mc/s and at a maximum ambient temperature of 45° C. The logic circuits use an alloy-junction transistor with an alpha cut-off frequency exceeding 10 Mc/s and an aluminium-bonded diode. Complete digital systems can be built using a number of logic units called ‘bricks’, in conjunction with the circulating pulse stores described in a companion paper [Showell, H. A., Barrow, C. W. M., and Collis, R. E. (Convention paper*)]. A set of simple rules determine the interconnections that can be used between units.The logic units described are gates, buffer amplifiers, inhibit-inverter amplifiers, bistable triggers and monostable triggers. D.C. coupling is used between units in order to obtain uniform operation irrespective of the time pattern of the pulse signals. Each one-microsecond digit period is terminated by a common discharge pulse of short duration that restores all transistors, by removing minority carriers from the base regions. No regenerating amplifiers are used, because the circulating pulse stores perform the dual functions of storage and of regenerating pulses, which have suffered attenuation and delay in the logic circuits.Each circuit unit is on a small printed wiring card. These are assembled in the required combinations on larger cards which form convenient plug-in packages.

Structure-Determined Gain-Band Product of Junction Triode Transistors

This paper discusses some fundamental frequency limitations of the junction triode. It also describes briefly practical accomplishments with germanium diffused base transistors of the type reported by Lee. Finally, the frequency limitations of the junction triode are compared with those of the field effect transistor and the analog transistor. For transistors of the mesa type with linear emitter and base electrodes (i.e., an emitter stripe with parallel base contact stripes a fraction of the emitter width distant on each side), the (power gain)?(bandwidth) product is found to be about 7.5 × 106/s cps where s is emitter stripe width in centimeters. This is an order of magnitude better than the corresponding figures for field effect and analog transistors. For operation at or below the alpha cutoff fre quency, the gain-band product is shown to be nearly independent of the particular alpha cutoff frequency selected. This independence arises from the reciprocity between collector depletion layer capaci tance per unit area and collector depletion layer transit time. This transit time effectively determines alpha cutoff frequency in optimunm gain-band designs.

Receiver Video Transistor Amplifiers

The development of the transistor has progressed to the point where practical video amplifiers of quality comparable to those of vacuum tubes can be designed. Limitations such as collector-emitter voltage, power, and alpha cut-off frequency continue to pose problems in designing a one stage video amplifier.

70-MC silicon transistor

Grown-diffused silicon tetrode transistors are being produced which have power gains of 18-20 db at 70 mc and alpha cutoff frequencies up to 400 mc. A general description of the transistor construction is given accentuating those features which contribute to the high-frequency performance such as narrow diffused base, low collector saturation resistance, and low base resistance and collector capacity. The device specifications are presented and curves are shown depicting the distribution of parameters for pilot production transistors. Data are presented showing the variation of parameters and power gain with junction temperature for typical units.

A High Frequency Germanium Drift Transistor by Post Alloy Diffusion

ABSTRACT A new technique of Solid state diffusion, called here ‘ post alloy diffusion ’, is described with particular reference to the construction of a high frequency germanium drift transistor. In this post alloy diffusion technique two or more impurities of different conductivity type and alloyed into n-typo germanium to produce an alloyed pn junction. This structure is then modified by diffusion to produce a diffused pn junction, the graded n-typo region of which is suitable to act as the base and the p-type region the emitter of a drift transistor. The construction of a transistor made by this method is described and some of the design variables are discussed. Transistors with alpha cut-off frequency in excess of 200 Me/s, collector capacitance of 1·5 pF-and base resistance of 50 ohms, have been made

Measurement of high-frequency equivalent circuit parameters of junction and surface barrier transistors

Methods are described for the determination of the high-frequency parameters of junction and surface barrier transistors and involve, in addition to the knowledge of the usual low-frequency parameters, measurement of the product of C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> and the extrinsic base resistance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_{b0}</tex> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_{b0}</tex> itself, and the alpha cutoff frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</inf> . A previously described method is used to determine the product <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_{b0}C_{c}</tex> , but new methods are described for the measurement of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_{b0}</tex> and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</inf> . The measurements are of "bridge" type, involving simple circuit adjustments for a response null at a single frequency. Typical experimental results are given for transistors having f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</inf> values as high as 85 mc, C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values down to 2.3 pF and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_{b0}</tex> ranging from 45 to 400 ohms. The limits quoted for f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</inf> and C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> refer to surface barrier transistors. Comparison with results derived by alternative methods of measurement show good agreement.

Medium-power, high-speed N-P-N germanium alloy transistors

A Bell System application requires a complementary pair of medium-power, high-speed switching transistors which, among other requirements, must show an alpha cutoff frequency of greater than four megacycles/second and electrical punch-through voltage of twenty-five volts minimum. Units have been designed and produced which exhibit median values of these parameters of seven megacycles/second and seventy volts, respectively.

Behavior of Noise Figure in Junction Transistors

It is well-known that generator resistance and dcemitter current are two major factors in determining the noise figure of junction transistors. Other important factors are base resistance, low-frequency alpha, and alpha cutoff frequency. A method of calculating the noise figure in terms of these parameters, the frequency variation of the noise figure, and the conditions for minimizing the noise figure are presented. The results provide means for specifying transistor and circuit parameters to meet noise requirements. In the absence of "excess" or 1/f noise, the noise figure as a function of frequency for the common base, common collector, and common emitter configurations is constant up to √1-a0 fa. Here a0 is the low-frequency alpha and fa the alpha cutoff frequency. Above this frequency the noise figure increases toward an asymptote of 6 decibels per octave. Calculations show that for minimum noise figure the base resistance and emitter current should be small, a0 should be close to one, fa should be large, and the driving source resistance has an optimum value. This work is based on a simplified version of a transistor noise equivalent circuit developed by van der Ziel.

High-frequency silicon alloy transistor

The silicon alloy transistor is a high-frequency, p-n-p type transistor capable of operation at high temperatures. Its temperature characteristic, derived principally from the use of silicon as the semiconductor, permits operation from - 70°C to 150°C. It achieves its high-frequency characteristic through accurate control of the base geometry. The n-type base of silicon is accurately machined by jet electrochemical techniques. Alloy contacts of aluminum are fused into the bottoms of the etch pits without producing appreciable change in base geometry. The depth of alloy is limited by the thickness of the aluminum, by the temperature, and by the length of time for alloying. Lead wires are soldered to the aluminum contacts and the transistor hermetically sealed in glass-metal containers. The electrical characteristics of typical silicon alloy transistors include an I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">co</inf> of 0.005 µa, a common emitter forward current gain of 12, and an alpha-cutoff frequency of 12 mc.

Solution of a Transistor Transient Response Problem

The transient response of the exact current transfer function, \alpha(\omega) , of a grounded-base junction transistor operating in the short-circuited output condition is compared with the transient response derived from the conventional approximate form for \alpha(\omega) . The response to both a unit impulse and a unit step is calculated, and it is shown how the results may be readily adapted to yield a rapid oscilloscope method of determining the \alpha cutoff frequency and several of the transistor material and dimensional constants.