Numerical analysis of a double avalanche region IMPATT diode on the basis of nonlinear model

The analysis of the n⁺pvnp⁺ avalanche diode structure has been realized on the basis of the nonlinear model. This type of the diode that was named as double avalanche region (DAR) IMPATT diode includes two avalanche regions inside the diode. The phase delay which was produced by means of the two avalanche regions and the drift region v is sufficient to obtain the negative resistance for the wide frequency band. The numerical model that is used for the analysis of the various diode structures includes all principal features of the physical phenomena inside the semiconductor structure. The admittance characteristics of the DAR diode were analyzed in very wide frequency band. The obtained results contradict to the before performed analysis on basis of the approximate models and show that only diode with a sufficiently short drift region can produce active power in some frequency bands.     

Microwave phase shifting with gain using IMPATT diodes

The use of an IMPATT reflection amplifier to produce phase modulation at microwave frequencies has been demonstrated. By operating the IMPATT diode near to avalanche resonance frequency, phase-switching through 180° can be obtained, and the drive current can be set to give equal gain in the two phase states so that no amplitude modulation is produced. Possible application to high-frequency data-transmission systems is envisaged.     

A simplified field analysis of a distributed IMPATT diode usingmultiple uniform layer approximation

A small-signal field analysis of a distributed IMPATT diode is presented. The active region of the diode is assumed to consist of a uniform avalanche layer and avalanche-free drift layers. The propagation constant and field distributions are obtained without numerical solution of differential equations. The effects of losses caused by the presence of inactive layers are included in the analysis. Numerical examples of GaAs double-Read distributed IMPATT diodes are given which show the dependence of the amplification characteristics on the thicknesses of the avalanche and drift layers     

GaN based transfer electron and avalanche transit time devices

A new model is developed to study the microwave/mm wave characteristics of two-terminal GaN-based transfer electron devices (TEDs), namely a Gunn diode and an impact avalanche transit time (IMPATT) device. Microwave characteristics such as device efficiency and the microwave power generated are computed and compared at D-band (140 GHz center frequency) to see the potentiality of each device under the same operating conditions. It is seen that GaN-based IMPATT devices surpass the Gunn diode in the said frequency region.     

An Investigation of Parametric Noise in Millimeter-Wave IMPATT Oscillators

The IMPATT oscillator used as an LO source in a receiver has often been found to contribute a large amount of excess noise to the system (sometimes more than 40 dB compared to a klystron). Often the IMPATT noise has been referred to as avalanche noise, but theoretically this should only reduce the carrier-to-noise ratio by 10-15 dB when compared to a klystron. In the following paper, we show that the excess noise far from the carrier frequency (i.e., sideband noise) is much more dependent on parametric oscillations excited below the cutoff frequency of the mount than, on avalanche noise. By modifying the Hines equation for parametric stability, we have been able to investigate the parametric noise properties of realistic millimeter-wave IMPATT oscillators. Using theoretical waveguide models, we have investigated how the sideband noise depends on various mount configurations, avalanche currents, and IMPATT diodes, The calculated curves show good correlation with the measured noise at 4 GHz from the carrier. It often has been found to be very difficult to completely reduce the parametric noise in avalanche oscillators. In these cases, the method of comparison between different mounts presented here for finding the diode-mount configuration which gives least parametric noise can be an aid in the construction of low-noise IMPATT oscillators.     

A comparative study of noise properties of Si IMPATT diodes operating at 80 GHz

The oscillator-noise properties of three kinds of Si IMPATT diodes operating at 80 GHz are measured. A DDR type of diode is superior in FM noise measure to the other two SDR types, one of which operates in the fundamental frequency mode and the other in the second harmonic frequency mode.     

Effect of finite current multiplication factor in the avalanche zone on the high-frequency noise properties of read diodes

The high-frequency noise properties of a Read diode, whose current multiplication factor in the avalanche zone can be controlled and is finite, has been analyzed. The analysis indicates that the open-circuit noise voltage and the noise figure of the diode are reduced with the lowering of the current multiplication factor. It is also found that the open-circuit noise voltage exhibits a finite peak at the avalanche frequency for finite but large values of M which, however, disappears at lower values of M(≤100).     

200-Megabit-pulsed avalanche oscillation with Ge silver- bonded diode in 50-GHz region

Some experimental results with an IMPATT diode operating in the 50-GHz region are presented, including 200-megabit- pulsed avalanche oscillation, injection locking, frequency spectra of the free running oscillation and the locked oscillation, and the noise spectra around the avalanche oscillation.     

Thermal runaway of IMPATT diodes

A simple one-dimensional computer model of the dc-thermal behavior of a Schottky-barrier GaAs IMPATT diode has been formulated to compute the conditions for thermal runaway in IMPATT diodes of various designs. The model has been used to determine the thermal stability conditions for three designs of GaAs IMPATT's. The computations lead to several conclusions, the most important of which are the following. a) Junction thermionic emission (leakage) current is thermally unstable, whereas avalanche multiplication is thermally stabilizing. Diode thermal stability at high junction temperature requires that the thermionic emission current be low and the avalanche multiplication be large. b) Lowering of the barrier height caused by contaminants or defects at the junction increases the likelihood of thermal runaway. c) For a given barrier height, the higher the doping of the IMPATT diode, the more resistant it will be to thermal runaway.     

Double-drift-region ion-implanted millimeter-wave IMPATT diodes

A detailed experimental comparison between double-drift-region (DDR) and single-drift-region (SDR) millimeter-wave avalanche diodes is presented. For 50-GHz CW operation, DDR diodes have given a maximum of 1-W output power compared to 0.53 W for the SDR diodes, while maximum efficiencies of 14.2 percent for the DDR and 10.3 percent for the SDR diodes have been obtained. These results are in agreement with the theory of Scharfetter et al. [1] for DDR IMPATT diodes. Both the DDR and SDR diode measurements were made on room temperature, metal heat sinks. The DDR diodes were shown to operate at significantly lower junction temperatures for the same value of output power, indicating a potential reliability advantage. Ion implantation was used to make the p drift region of the p⁺p-n-n⁺50-GHz DDR devices. Otherwise the fabrication (which includes diffusion and epitaxial technologies) and the microwave measurement methods were identical for both types of diodes. Capacitance measurements were compared with calculations to determine the desired doping concentrations for frequencies from 43 to 110 GHz. Experimental results for the higher frequency millimeter-wave region have been obtained on DDR structures with both p and n drift regions implanted. At 92 GHz an output power of 0.18 W and an efficiency of 7.4 percent have been obtained.     

Power-noise characterization of phase-locked IMPATT Oscillators

IMPATT diode characterization on the basis of output power and the corresponding FM noise figure over a range of operating conditions is presented. The characterization consists of families of power noise curves obtained for a phase-locked IMPATT oscillator where the supply current, load conductance, and the operating frequency are parameters. It is shown that the maximum output power and minimum FM noise are not achieved concurrently. In particular FM transmitter application, it is shown that the best performance for each type of diode was obtained when operated at less than maximum power (and at reduced efficiency) where the system benefits from the attending lower noise. Better system performance, this application, was obtained with the GaAs IMPATT diode. The power-noise characterization defines the optimum operating conditions for an IMPATT diode and provides a valid basis for the comparison of diodes for specific applications.     

IMPATT operation below the avalanche frequency

Very high output powers are obtained with double drift IMPATT diodes at current densities which shift the avalanche frequency above the oscillation frequency: 30-40 W pulsed around 90 GHz. This operation mode cannot be explained in terms of the conventional READ theory. A numerical large signal simulation shows that avalanche multiplication over the whole diode takes place. At high current densities the double drift device behaves like a pin diode without the unfavourable breakdown of the ionisation process in the centre of the diode.<>     

Optimum Noise Measure of IMPATT Diodes

An attempt is made to determine some of the factors responsible for the noise performance of avalanche diodes. In particular we are interested whether there are any lower lids in the noise measure. We derive a theorem which shows that there is a lower limit M/sub opt/ = 1/2 q/ /spl alpha'/kT for an IMPATT diode which has a constant value of a', where M/sub opt/ is the optimum noise measure, q is the electronic charge, a' is the derivative with respect to the electric field of the carrier generation rate, k is Boltzmann's constant, and T is the standard absolute temperature. Even though the optimum noise measure is derived for a diode with constant a' in extensive numerical calculations of structures with sections of different a', we never found cases where the overall diode noise figure was lower than calculated by the above formula using the largest value of a'. Detailed calculations show that the lowest noise measure is achieved for carrier transit angles near 2/spl pi/. The negative real part of the impedance becomes rather small when both the transit angle is near 2/spl pi/ and when a' is made large. In practical cases it is therefore often not possible to reach noise measures close to M/sub opt/. The paper also investigates how the amplifier noise determines amplitude and frequency noise of the corresponding avalanche oscillators.     

Ion-implanted planar-mesa IMPATT diodes for millimeter wavelengths

A process has been developed that combines ion-implantation doping with planar and mesa-etching techniques for the fabrication of fully passivated millimeter-wave IMPATT diodes. The device geometry consists of an IMPATT diode surrounded by a two-layer annular region of passivation: one layer of high-resistivity semiconductor and the other of thick insulator material. Devices constructed with this new geometry have sufficient mechanical strength to allow direct mounting into microwave circuits without the use of an insulator standoff and metal ribbon package arrangement. A simple model of the diode-circuit interaction is used to estimate the degradation in microwave performance as a function of the passivation parasitics. These results are compared to a diode with no parasitic losses. Based on the I²-PLASA process, a fully passivated silicon IMPATT diode was fabricated for V-band (50-75-GHz) operation. Degradation factors of approximately 50 percent are predicted for the present devices. A continuous-wave output power of 100 mW was obtained at 62 GHz from an I²-PLASA IMPATT diode with an implanted p⁺-n-n⁺doping profile. Mechanical tuning characteristics of these devices were found to be more broad-band than standard packaged diodes. The measured AM and FM noise spectra close to the carrier were representative of standard single-drift silicon millimeter-wave IMPATT diodes.     

Low noise wide bandgap SiC based IMPATT diodes at sub-millimeter wave frequencies and at high temperature

We have presented a comparative account of the high frequency prospective as well as noise behaviors of wide-bandgap 4H-SiC and 6H-SiC based on different structures of IMPATT diodes at sub-millimeter-wave frequencies up to 2.18 THz. The computer simulation study establishes the feasibility of the SiC based IMPATT diode as a high power density terahertz source. The most significant feature lies in the noise behavior of the SiC IMPATT diodes. It is noticed that the 6H-SiC DDR diode shows the least noise measure of 26.1 dB as compared to that of other structures. Further, it is noticed that the noise measure of the SiC IMPATT diode is less at a higher operating frequency compared to that at a lower operating frequency.     

A small signal analysis of an impatt device having two avalanche layers interspaced by a drift layer

A small signal analysis of an IMPATT device (p?n?i?p?n structure) having two avalanche layers interspaced by a drift layer is carried out. When the widths of the two avalanche layers are different the device exhibits discrete negative conductance frequency bands separated by positive conductance frequency bands. Oscillations are expected to occur more favourably in the lowest frequency band where the maximum and minimum values of magnitudes of negative conductance and negative Q occur, respectively. When the two avalanche layer widths are equal, the device impedance is a high Q-reactance whose magnitude depends on the d.c. current.     

Large-signal noise, frequency conversion, and parametric instabilities in IMPATT diode networks

A theoretical treatment is presented of some of the nonlinear properties of the IMPATT or Read avalanche diode, a negative-resistance semiconductor device that is now coming into wide-spread use for microwave oscillators and power amplifiers. Based upon the somewhat idealized Read model, this theory presents a qualitatively meaningful explanation of certain "parametric" effects that are often troublesome to the designers of amplifier and oscillator networks. First, an analytic treatment is given for frequency-conversion effects that appear when the device is strongly driven by one continuous signal, and simultaneously perturbed by a weak signal at another frequency or by noise. From this theory, stability criteria are derived for spurious oscillations of the "parametric" type which frequently appear in these devices under large-signal conditions. The noise-generation mechanism is reviewed, and it is shown that the noise is enhanced by strong signals and the spectral distribution is modified by frequency conversion. Some measurements of noise and frequency-conversion gain are presented which indicate substantial qualitative agreement with the theory.     

Modes of avalanche oscillations in silicon diodes

A computer program which includes both electronic and thermal processes has been used to study avalanche oscillations in a diode which is punched through only well above breakdown. IMPATT, relaxing avalanche, and MULTIPATT oscillations have been studied. The MULTIPATT mode is shown to be a superpesition of transit-time oscillations upon a relaxation oscillation. It is postulated that the TRAPATT mode is initiated by the IMPATI mode via the MULTIPATI mode. The frequency of the IMPATT oscillations was found to vary with the square root of the current over a factor of 100 in current. For parallel operation of TRAPATT diodes, it is shown that nonpunched-through diodes should be used.     

Noise theory for the read type avalanche diode

An analysis is presented for the noise current spectrum of an avalanche diode under assumed conditions of ideal uniform avalanche behavior in a zone which is thin compared with the total high-field depletion zone. The result is applied to the Read diode amplifier. For a typical set of operating parameters, the theory predicts a noise figure on the order of 40 dB. Depending upon particular device parameters, lower noise figures may be possible.     

Frequency conversion in IMPATT diodes

A large-signal model of the Read-type IMPATT diode has been used to analyze the frequency-mixing properties of the oscillating diode. The self-oscillating, two-port frequency converter is described in terms of its short-circuit admittance parameters. It is shown that in the proper circuit, parametric frequency conversion may result in a negative conductance at the input and output ports of the converter. Therefore, high-gain frequency conversion and parametric amplification are possible. Under some conditions, spurious oscillations may occur due to this negative conductance. Experimental circuits have been built which demonstrate conversion gain and parametric amplification and confirm qualitatively the theoretical results. It is also shown experimentally that some of the sideband noise of the IMPATT oscillator is due to low-frequency noise which is up converted from the bias circuit. Some of this noise can be eliminated by proper circuit design.