Frequency chirp in W-band pulsed IMPATT oscillators

An analytical device-circuit interaction model to compute the frequency chirp bandwidth in W-band pulsed DDR IMPATT diodes is presented. The measured chirp agrees reasonably well with the calculated values.     

GaAs IMPATT diodes for 60 GHz

High-performance GaAs double-drift Read IMPATT diodes have been demonstrated at 60 GHz. 1.24-W CW output power at 11.4-percent dc to RF conversion efficiency was obtained with a junction temperature rise of 225°C. The doping profiles and test circuits have not yet been optimized and we expect that still higher power and efficiency should be achievable.     

Millimeter-wave GaAs Schottky-barrier IMPATT diodes

Recent experimental observations on a Schottky-barrier GaAs IMPATT diode for F-band operation are presented. The diode slices were thinned to 10 to 20 µm by removing the substrate by precision polishing. Output power of 304 mW at 50 GHz with 4.58 percent efficiency was observed. The highest efficiency was 4.72 percent at 55 GHz.     

High-efficiency X-band GaAs IMPATT diodes

Epitaxial GaAs diodes have been fabricated giving 65¹mW CW output power at 10 GHz under room temperature operation. A dc to RF efficiency of 10.1 percent was obtained from a diode operating CW while the measured output of another diode was over 20 mW for 3 mA dc with 70-volt biasing.     

High-efficiency proton-isolated GaAs IMPATT diodes

The fabrication and c.w. operation of planar proton-isolated diffused junction and Schottky-barrier GaAs IMPATT diodes are described. The diodes have shown a maximum efficiency of 13.5% and output power of 315 mW in the Q band. Planar diodes appear to be superior to mesa devices formed from identical material.     

Millimeter-wave GaAs read IMPATT diodes

We have designed, fabricated, and evaluated gallium arsenide Read IMPATT diodes for Ka-band (36-38 GHz)operation. The devices were packaged units intended for manufacturability and high yield. Oscillator output power as high as 710-mW CW was obtained at 9-percent efficiency. This paper describes design and fabrication techniques employed and discusses the potential and limitations of such devices.     

High-efficiency V-band GaAs IMPATT diodes

Double-drift GaAs IMPATT diodes were designed for V-band frequency operations and fabricated using molecular-beam epitaxy. The diodes were fabricated in two configurations: (a) circular mesa diodes with silver-plated (integrated) heat sinks; (b) pill-type diodes bonded to diamond heat sinks. Both configurations utilised a miniature quartz-ring package. Output power greater than 1 W CW was achieved at V-band frequencies from diodes on diamond heat sinks. The best conversion efficiency was 13.3% at 55.5 GHz with 1 W output power.     

High-efficiency monolithic GaAs IMPATT diodes

Impedance-matching circuits were integrated on the same chip as the IMPATT diodes to produce monolithic impatt diodes for millimetre-wave applications. A drastic reduction of device-to-circuit parasitic elements was achieved by placing the external circuitry very close to the device. Oscillators fabricated in this fashion gave the highest efficiencies reported so far in the 30?35 GHz range with 28% conversion efficiency using hybrid-Read structures.     

Millimeter-wave GaAs distributed IMPATT diodes

Millimeter-wave oscillations were obtained in distributed GaAs IMPATT diodes prepared by molecular beam epitaxy (MBE). Both single-drift-region and double-drift-region structures were used to fabricate various length devices, up to 1.25 mm, to investigate oscillation frequency dependence on device length. Output power levels of 1.5 and 0.5 W were obtained at 22 and 50 GHz, respectively, using 500-ns pulses. The highest frequency of oscillation observed was 89 GHz.     

Design considerations of low-noise high-efficiency silicon IMPATT diodes

The noise and efficiency of p⁺-n1-n2-n⁺and n⁺-p1- p2-p⁺high-low silicon IMPATT diodes have been studied as a function of doping ratio n1/n2or p1/p2. In contrast to GaAs IMPATT diodes whose efficiency can be improved with some degradation of noise performance, both the efficiency and noise of Si IMPATT diodes can be improved. As an example, for a 6-GHz silicon n⁺-p1-p2-p⁺IMPATT structure with a doping ratio of 10, the efficiency is 21 percent and the incremental noise as compared to a uniformly doped structure is about -6 dB. These results indicate that silicon high-low structures can compete favorably with GaAs structures in both efficiency and noise performances.     

140 GHz GaAs double-Read IMPATT diodes

CW GaAs double-Read IMPATT diodes for D-band frequencies are designed and tested. For reproducible RF impedance matching, the module encapsulation technique is applied. Ohmic losses of the active device are reduced by a titanium-Schottky contact instead of an alloyed ohmic n ⁺-contact. At 144 GHz 100 mW RF power with a conversion efficiency of 5% is realised     

GaAs 50 GHz Schottky-barrier IMPATT diodes

Technological improvements have been made to realise high-efficiency GaAs Schottky-barrier IMPATT diodes in the 50 GHz band. Efficiency and output power have been increased by a factor of 1.5 over previous best results. Efficiency as high as 11.0% at 51 GHz and an output power of 420 mW at 53 GHz have been obtained.     

Compensation degradation mechanism for high-efficiency GaAs IMPATT diodes

The reliability of Cr Schottky-barrier high-efficiency (hi-lo) GaAs IMPATTs has been investigated. Devices operated under d.c. conditions degraded due to compensation of the electron concentration in the avalanche region of the devices. This degradation was not observed in diodes oven-tested with no bias applied.     

Design considerations of high-efficiency GaAs IMPATT diodes

The efficiency and noise of p⁺n1n2n⁺GaAs IMPATT diodes have been studied as functions of the doping ratio n1/n2(when n1=n2we have a conventional abrupt p-n junction). For n1/n2>1 there are tradeoffs between efficiency and noise. At 12 GHz, for example, with a ratio of 4 the efficiency is 25 percent and the noise measure is 3 dB higher then that of a conventional IMPATT diode.     

0.7 W single-drift GaAs IMPATT diodes for millimetre-wave frequencies

Single-drift flat-profile GaAs IMPATT diodes with diamond heat sinks have been fabricated in the 50 GHz band. The design of the diodes is based on a lower value of effective saturated drift velocity of electrons at high electric fields. Output power as high as 0.7 W at 53 GHz and an efficiency of 12.3% at 51 GHz have been obtained.     

Ferrite bias lines for use with GaAs IMPATT diodes

Lowpass ferrite-bead bias filters are used to suppress high-frequency bias oscillations and enhanced noise components obtained when high-efficiency GaAs IMPATT diodes (uniformly doped n-type and Read) are operated as free-running oscillators and saturated amplifiers in broadband (low Q factor) r.f. coaxial circuits with distributed-line bias arms. The impedance properties of the ferrite beads have been measured up to a frequency of 2 GHz, which has resulted in a 4-stage bias-filter prototype being realised. Also incorporated is a simple r.f. low-shunt-capacitive choke that reduces the loss on the main coaxial r.f. cavity to less than 0.2 dB over the frequency range 7?12 GHz.     

Optimum design for high-power and high-efficiency GaAs Hi-Lo IMPATT diodes

Optimum structure parameters of GaAs hi-lo IMPATT diodes to give a high-efficiency and a high-output power are experimentally determined in the frequency range from 7 to 18 GHz. The highest efficiency is obtained at any frequency when a diode has a punch-through factor of about 0.6 and is depleted with an electric field strength of 10 kV/cm at the end of the lo region under operation. The optimum lo-region carrier concentration to achieve the highest efficiency and the upper limit of a junction area to obtain a high-output power without decreasing efficiency are found to be simply related to frequency by the following equations:(N_{L})_{opt} = (4 times 10^{14}) cdot (f/7)^{3}cm^-3and(S_{j})_{max} = (20 times 10^{-4}) cdot (f/10)^{-1.9})cm²), respectively, wherefis in gigahertz.     

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.     

Large-signal operation of PIN IMPATT diodes for pulsed oscillators at millimetre-wave frequencies

The specific RF power generation mechanism of PIN-IMPATT diodes at high current density as applied in pulsed operation is described and confirmed by a realistic computer model. It is shown that these devices can be operated at large-signal avalanche resonance, where they deliver relatively high output power at high impedance level.     

Conduction current injection delay in Read GaAs IMPATT diodes

We find experimentally that, for GaAs Read avalanche diodes, the optimal drift region width is not simply inversely proportional to optimum frequency. This finding can be understood by noting that the injection phase of the avalanche current into the drift region is not 90° with respect to the voltage maximum, but varies as a function of frequency. The experimental observations are in reasonable agreement with solutions of the Read equation which include the reverse junction saturation current. The theoretical fit to the data is relatively insensitive to the avalanche intrinsic response time, and thus we cannot make an independent determination of its value at present.