Unijunction Research Articles

An epitaxial planar structure for the unijunction transistor

A unijunction transistor with fast recovery time and high interbase resistance is made by growing a thin high-resistivity boron-doped epitaxial layer on a low-resistivity arsenic-doped substrate. Ring-and-dot base contacts are made directly on the p-type epitaxial layer with the beam-lead contact process. With the dot grounded and a negative bias on the ring, the most positive point along the edge of the space-charge region in the epitaxy is centered below the dot. When the substrate is adequately biased in the forward direction with respect to this point, conductivity modulation of the spreading resistance under the dot begins because of minority charge injection from the substrate. Experimental devices have been made by growing a 7.1-micron 53.1-Ω.cm epitaxial layer on a 5Ω.cm substrate. Interbase resistance was ∼ 100k Ω, intrinsic stand-off ratio ∼ 0.5, holding current ∼ 1 mA, and recovery time <20 ns. The paper concludes with possible memory array and shift register circuit applications that incorporate the unit described as well as a junction-isolated version that is free of parasitic transistors.

Theory of cylindrically symmetric unijunction transistors

A general theory for near-intrinsic homogenous semiconductor material is extended to the base region of an ideal cylindrical-geometry unijunction transistor. The theory predicts static emitter characteristics for planar geometries with cylindrical symmetry. These predicted characteristics include the effects of drift, diffusion, and simple recombination, and qualitatively agree with experimental data at high injection.

Linear voltage-amplitude to pulse-width conversion utilizing a controlled unijunction monostable multivibrator

A circuit that achieves linear wide-range voltage-amplitude to pulse-width conversion is presented. The circuit combines a unijunction transistor operating in an inverted mode, a field- effect transistor, and an integrated circuit flip-flop to obtain highly linear conversion. Other advantages are low-ments, excellent interface characteristics, asynchronous operation, simplicity, and a wide range of pulse-width variation. The circuit operation is discussed, and major design equations are derived. In the experimental circuit that is included, linearity of conversion is within 0.5 percent of full scale pulse width. The pulse width is controllable over the range of 85 to 6 ms for a control voltage variation of 0 to 1.6 volts.

Generalized Characterization of Unijunction Transistor Networks

The static characteristics of unijunction transistors are exhibited by two surfaces in three-dimensional space. This representation is employed to examine a general formulation of the problem of analysis and design with a device that is characterized by a nonlinear relationship among four variables.

The characterization of the static behavior of p-n junction devices

This paper examines the static behavior of certain p-n junction devices that are governed by Van Roosbroeck's differential equations. It is found that this set of first-order differential equations accurately predicts semiconductor static behavior in both the bulk and the transition regions. The purpose of this model is to find the hole and electron concentrations, hole and electron currents, and electric field as functions of position and external excitation. For part of the paper, use is made of the quasi-neutrality approximation in the bulk regions and the quasi-equilibrium Boltzmann relations (QEBR) which relate the hole and electron concentrations at transition region edges to the applied voltage across the transition region. The unijunction transistor with intrinsic base, p-i and p-in diodes, and a new current gain device are examined using these concepts, and the results are compared with experiment. By applying boundary conditions only at the ohmic contacts, a p-i diode problem is solved on a computer. One especially important point in this problem is that quasi-neutrality of the base and the QEBR are not imposed upon the problem. However, the final results indicate that these concepts are good approximations, except for extremely short devices.

An integrated unijunction structure

An integrated unijunction structure

Broadband AGC circuits

Two types of broadband AGC circuits are described, one using a PIN diode, the other using a unijunction transistor. Performance data are given for frequency response, group delay, and AM to PM conversion.

Controlled-potential coulometric titrator

Controlled-potential coulometric titrator and the titration cells have been deviced for the control analysis of semi-microgram quantities of uranium (VI) in nitric acid solutions.This instrument consists of transistorized potentiostat, and the coulometer, utilizing a pulse counter with a simple voltage-frequency converter composed of DC current amplifier and UJT (unijunction transistor).Between the range of 1 to 5 mg of uranium (VI), the precision was found to be 0.4 per cent of relative standard deviation.

Solid-State Controller for Air Conditioning Units

It is essential to maintain the condensing temperature of air-cooled air conditioning systems at certain minimum levels when operating during cold weather. Recent advances in solid-state technology have opened up new approaches to controlling condensing temperatures at any desired minimum level. The solid-state control system described uses an SCR with a unijunction transistor firing circuit to control directly the power to the specially designed fan motors. In designing such a control system, consideration has to be given to matching properly the solid-state control, fan motor, and the temperature sensing device with the air conditioning unit performance characteristics to obtain the desired reliability and stability.

Noise in silicon double-base diodes

The power spectrum of the current fluctuations (noise) in the double-base diode has been measured experimentally and calculated theoretically. It has been found that there are two sources of noise in the double-base diode. First, there is the thermal noise of the real part of the ac admittance. The second source of noise is fluctuations in numbers of electrons and holes in the conduction band and valence band, respectively. Noise measurements are also presented for a diode with a long, high resistivity base region. These measurements are discussed qualitatively.

Precise Temperature Controller for a Three-zone Diffusion Furnace

ABSTRACTThe paper deals with the design and construction of a precision temperature controller for use with a three-zone silicon diffusion furnace, to operate in the range 900–1400°C. Thermocouples are used as sensing elements. The controller utilizes adjustments of proportion bandwidth, rate action and reset action for precise control of the temperature. The power is controlled through silicon controlled rectifiers, phase controlled by the unijunction transistor oscillators.

An inexpensive solar pointing control

The theory, design and performance of an inexpensive, biaxial solar pointing control are presented and discussed. An altazimuth mount driven by fractional horsepower d.c. motors is used as the stable platform. Two identical error-sensing circuits are employed to drive the motors. A dual element photoconductive cell is used as the sensor in each circuit. The two elements form the variable arms of a simple a.c. bridge which is balanced when the two elements are equally illuminated. This condition prevails when the sensor is pointing at the sun. The off-balance voltage which results when the two are unequally illuminated is used to forward-bias the emitter junction of a unijunction transistor in a relaxation oscillator circuit which triggers a silicon controlled rectifier switching circuit. This circuit changes the polarity of the supply voltage to the d.c. motor which positions the altazimuth mount to restore the balance. Tracking accuracies of ?0? 30' of arc both in elevation and azimuth are easily attainable with loads up to 30 1b.

D.C. Theory of the Unijunction Transistor†

ABSTRACT The d.c. theory of the unijunction transistor is examined find calculations are carried out for an idealized, one-dimensional model neglecting diffusion currents but taking bulk recombination effects into account. This procedure leads to u simple set of equations relating the slope of the d.c. characteristics at low emitter currents to the inter-base voltage. Measurements of the peak point current as a function of inter-base voltage are compared with calculations for a unit with a geometry approaching that assumed in the calculations. Satisfactory agreement between theory and calculations is reported.

A thyristor operated electron emission regulator

The features of a thyristor operated electron emission regulator employing a unijunction transistor firing circuit for phase control are discussed, and a circuit described which was constructed to stabilize the electron current from a directly heated filament or an oxide-coated cathode at any value between 10 μA and 1 mA to 0.1 per cent for a 10 per cent variation in mains voltage. Long term drift, i.e. for periods up to 10 hours, was found to be <0.5 per cent. The regulator was designed for use with Bayard-Alpert type ionization gauges and positive ion sourced in mass spectrometers and has behaved very reliably. The inherent stability of the temperature-compensated firing circuit together with the control power gain of the order of 10 6 in the thyristor, makes this basic unit most attractive.

Unijunction transistors with tristable current/voltage characteristics

This letter describes unijunction transistors exhibiting unusual current/voltage characteristics with two independent negative-resistance regions.

Temperature Measurement in Thermogravimetry

A method is described whereby the temperature of a sample in a thermobalance may be determined directly without the large uncertainty that usually accompanies these measurements. The procedure consists of using a unijunction transistor relaxation oscillator with a thermistor as the resistive part. The entire primary circuit including the power supply is made part of the balance suspension and is weighed along with the sample. The frequency of oscillation which is a function of sample temperature is relayed to an events-per-unit-time meter via a mutual inductance between two suspended coils. The nonlinearity of the thermistor is removed to a considerable extent by a compensating circuit.

A unique current-controlled negative resistance generator

THE PHENOMENON of negative resistance is so well known that it requires only a cursory review. Negative resistance elements or networks are distinguished by driving-point resistance characteristics which exhibit, at least over a limited portion of the current-voltage (i-v) plane, a falling voltage with increasing current. In general, devices which exhibit a negative resistance region over some portion of their i-v characteristic curve may be separated into two classes. The first class includes all elements with an inherent negative resistance region, such as the point-contact transistor, unijunction transistor, p-n-p-n transistor, tetrode vacuum tube, and tunnel diode. The second class includes all the networks in which one or more active elements are used in conjunction with passive elements arranged to maintain a predetermined function of current and voltage. This group includes all the devices which may be synthesized by utilizing positive feedback and such circuits as the complementary transistor cascade and the negative impedance converter. It should be understood that a physically realizable negative resistance is not the opposite of a positive resistance. For a positive resistance, the i-v relationship is an interdependent one, but for a negative resistance, the element utilizes an internal phenomenon which depends only on the potential or only on the current. Therefore, a 2-terminal negative resistance device comprises an internal energy source which is controlled either by the current through or the potential across its terminals, but not by both.

Solid frequency-selective circuit with double-base diode

Solid frequency-selective circuit with double-base diode

Integrated unijunction transistor oscillators

The unijunction transistor (UJT) is being considered as the active element in an integrated harmonic oscillator realization. Necessary and sufficient conditions for oscillation in the harmonic mode have been determined. The dependence of the frequency constancy factor, \frac{1 d\omega_{o}}{\omega_{o} dT} , on device temperature and bias-conditions is derived. These results depend on an a.c. perturbation analysis of the UJT. The analysis brings out in detail the known behavior of the UJT input port as a -R, L network at low frequcndcs. The input port is also shown to function as a +R, C network at high frequencies. A natural resonance in the diffusion process at medium frequencies is pointed out. An intrinsic UJT oscillator is proposed, based upon this resonance. Experimental work with commercially available UJT structures substantiates analytical results. Experimental studies of prototype oscillator circuits are used to design an integrated oscillator realization which is optimized with regard to temperature stability and waveform distortion.

Reactive effects in semiconductor filaments due to conductivity modulation and an extension of the theory of the double-base diode

The effects of conductivity modulation on the terminal characteristics of a semiconductor device are analyzed. Considerable attention is paid to the accompanying reactive effects. The solution for the flow of added carriers is based upon the assumption of quasi-charge neutrality and absence of trapping effects. A double-base diode structure is selected to investigate the transient and ac steady-state effects associated with conductivity modulation, since conductivity modulation by injected carriers proves to be strong in this device. The input characteristics of the double-base diode are considered in this paper. Reactive effects (both inductive and capacitive) in p-n junction diodes, previously reported by other researchers, are easily derived as a special case of the more general structure studied here. Two models are employed in the analysis. One model is used to study double-base diodes made of extrinsic filaments. Here, due to the externally applied electric field, injected carriers are transported essentially by the drift mechanism. The second model describes devices constructed of high resistivity material such that excess carriers are transported primarily by diffusion, as in an intrinsic structure. However in both models drift currents are responsible for inductive and negative resistive effects. The input static characteristics, transient effects and impedance predicted from theory are in good agreement with those observed experimentally.