Effect of heavier doped junction side on efficiency of Si IMPATT diodes

For n- and p-type Si IMPATT diodes, the effect of the doping profile of the heavier doped junction side was calculated in terms of the dc-to-RF efficiency. In p-type diodes, the electric field existing within this region leads to a decrease in efficiency. This effect is assumed to be one reason why the theoretically expected high efficiencies of these diodes have not been obtained experimentally.     

Effect of p-n junction overheating on degradation of silicon high-power pulsed IMPATT diodes

The thermal limits of the two-drift impact avalanche and transit-time (IMPATT) diode operating in the pulsed mode in the 8-mm wavelength region with a microwave power as high as 30–35 W have been estimated. It is shown that p-n junction overheat at an operating pulse length of 300 ns and a supply current amplitude of 11.3–15 A amounts to 270–430°C relative to an ambient medium. The temperature limit of junction overheating, above which IMPATT diodes rapidly degrade, was determined as 350°C. The presented results of X-ray phase analysis and depth profiles of Au-Pt-Ti-Pd-Si ohmic contact components confirm thermal limits of the IMPATT diode operating in the pulsed mode.

     

Gunn diodes with different cathode contacts oscillation on harmonic frequencies

The studies of Gunn diodes on the basis of GaAs with different types of cathode contacts, the profile of doping, the active area length and temperature at frequencies of the second and third harmonics were carried out to obtain effective oscillation in the millimeter and submillimeter ranges.     

High-efficiency continuous oscillations in silicon IMPATT diodes below the transit-time frequency

C.W. room-temperature operation of silicon IMPATT diodes at the first subharmonic of the transit-time frequency has been observed in a high-efficiency mode. Efficiencies as high as 8.8% at 5GHz with 1.2 Wc.w. have been achieved with current densities no more than 1480A/cm2.     

Junction-temperature measurement of IMPATT diodes

The breakdown voltage VB of an IMPATT diode is a function of the junction temperature. Pulse techniques are applied to measure VB directly during actual operation, thus giving the temperature within an accuracy of a few per cent. The method also provides a display of 'space-charge resistance at the operating temperature.     

High-speed modulation of IMPATT diodes

A high-speed bias circuit modulation process which occurs in Gunn oscillators by virtue of their equivalent circuit is shown to also occur in IMPATT oscillators.     

Properties of millimeter-wave IMPATT diodes

A study of the effect of the doping profile on the properties of IMPATT devices has been carried out and the results of a small-signal analysis for different ram-wave Si IMPATT-diode structures are presented. Properties of single-drift abrupt-junction diodes of both Si complementary structures with different punch-through factors (PTF) are described and compared to those of symmetrical and asymmetrical double-drift diode structures. Since the initiation of the TRAPATT mode may be related to the IMPATT performance, these results should also be useful in assessing the effects of the doping profile on TRAPATT initiation.     

Accelerated ageing of IMPATT diodes

An investigation conducted to determine suitable reliability test methods for IMPATT diodes has shown that elevated temperature accelerated their normal degradation in a predictable way only when the diodes were stressed with normal d.c. power applied and controlled in a constant-voltage mode. Normal degradation was manifested initially by an increase in thermal resistance and ultimately by short-circuits, both of which were caused by the progressive interaction of the constituents of the contact metallizations. Initial instabilities and infant mortalities had to be eliminated by burning-in the diodes before overstress results could be related to long-term wearout. Thereafter, simple d.c. was adequate to assess life expectancy because the changes in thermal resistance could be used to estimate consequent changes in r.f. performance.     

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.     

The relationship of frequency of operation to large-signal noise degradation in IMPATT diodes

A singly tuned X-band IMPATT amplifier is simulated on a hybrid computer and results are given for the amount of conduction current modulation present in the device as a function of the period, T, with the ac voltage across the diode held fixed, Using Sjolund's large-signal noise theory which relates the conduction current modulation to the noise measure, M, curves are presented showing a logarithmic relation between M and the period, T, with M increasing for larger T. An approximate theory is given to explain this behavior. These noise measure results are compared to the IMPATT power-output data to give a qualitative understanding of the rate of noise degradation with power output in relation to frequency of operation. It is shown that, for minimum noise degradation, the IMPATT should be operated at or above the frequency corresponding to maximum power output for a given ac voltage across the diode. This information can be used to establish a criterion for minimum noise degradation during intermediate and large signal operation.     

High-power IMPATT diodes on diamond heat sinks

This paper presents calculated and experimental results which demonstrate that the performance of IMPATT diodes is significantly improved by the use of diamond heat sinks. Oscillator test results on germanium IMPATT diodes at 6.2 GHz indicate about 50 to 100 percent increase in power output for diamond versus copper heat-sinked units without compromising other oscillator characteristics. An increase in thermal conductance of about 40 percent is realized for diodes mounted on selected high-conductivity diamonds compared to units mounted on copper. Considerations of IMPATT wafer design for optimum power performance on high thermal conductance heat sinks are discussed. Thermal conductivity of naturally occurring diamonds ranges from 1.0 to 5.0 times that of copper which necessitates selection of stones to realize maximum thermal conductance. This paper presents the results of a study of diamond thermal conductivity, its measurement, and its relationship to diamond optical properties. The dependence of diode thermal conductance on die area for diamond heat-sinked devices has been obtained by computer solution of the heat flow equations for the relevant geometries. These calculations have been corroborated by measurement of the thermal conductance of diodes with various die diameters.     

Coupling coefficient dependence on oscillation frequency stability of self-pulsating DFB laser diodes

Grating coupling strength effects in self-pulsating distributed feedback lasers were investigated. Choosing the coupling coefficient appropriately, improvements in the timing jitter as well as the injection locking sensitivity were observed experimentally. The results are attributed to a co-ordination of optical feedback strengths between dual lasing modes.     

A series connection of IMPATT diodes

A microwave oscillator using a series combination of three packaged IMPATT diodes has been successfully operated. Since the series combination increases the power output of IMPATT oscillators without decreasing the impedance level, the 1/f²limitation of the power-impedance product for IMPATT diodes can be avoided. This type of series combination is suited for use at millimeter-wave frequencies.     

Batch fabrication of integral-heat-sink IMPATT diodes

A new technique for IMPATT-diode fabrication is described, in which the critical portion of the diode heat-flow path is formed as an integral part of the diode. The technique has economic advantages over conventional methods in that all processing steps are performed while diodes are still in wafer form. In addition, the technique permits passivation using standard dielectric deposition techniques, and the diode geometrical shape is such as to suppress premature edge breakdown. Typical experimental results are shown.     

Computer optimisation of double-drift-region IMPATT diodes

Design parameters for double-drift-region silicon IMPATT diodes for frequencies from 10 to 100 GHz are presented. The design is based on extensive large-signal computer simulations at one frequency of two different diode structures in a simple circuit. From these simulations, a simple design criterion was derived which permits the calculation of optimised impurity profiles for any desired frequency, with a small computer effort.     

Effects of tunneling on high-efficiency IMPATT avalanche diodes

A theoretical and experimental study is presented of the effects of tunnel injection on high-efficiency IMPATT avalanche diodes characterized by a high low-doping profile. Some characteristics usually observed in such high-efficiency IMPATT oscillators are explained, taking into account the effects of tunneling.     

Computer study on GaAs Schottky barrier IMPATT diodes

Oscillation characteristics of GaAs Schottky barrier IMPATT diodes are studied by computer simulation. For a Schottky barrier-n-n⁺ structure, the Read condition and the just-punch-through condition are found to be optimum with respect to the efficiency and power at 30 GHz. In order to improve the efficiency, a superabrupt doping profile is proposed and a high efficiency of 32 per cent is predicted. Calculation of the frequency dependence of the efficiency shows that GaAs IMPATT diodes still have the potentiality of high efficiency oscillator at 100 GHz and they are a promising microwave source in mm-wave region.