Effect of Temperature on Device Admittance of GaAs and Si IMPATT Diodes

The effect of temperature on the small-signal admittance of IMPATT diodes with uniformly doped and high-low doped (Read) structures is investigated experimentafly and theoretically. Small-signal admittance characteristics of X-band Si p+-n-n+, GaAs M-n-n+ (Schottky-uniform), and GaAs M-n+-n-n+ (Schottky-Read) IMPATT diodes are measured at various junction temperatures for different dc current levels. Small-signal analysis is performed on GaAs IMPATT diodes of uniformly doped and high-low doped structures, and the calculated results on temperature dependence of the device admittance are compared with the experimental results. Reasonable agreement is found between theory and experiment. It is shown that GaAs IMPATT diodes are superior to Si diodes in admittance temperature characteristics and that the uniformly doped structure has a small admittance temperature coefficient in magnitude, compared to the high-low doped structure. It is also shown by calculation that the admittance temperature coefficient of a punch-through diode is small in magnitude, compared to that of a non-punch-through diode.     

Degradation of the power- and frequency-temperature performance of IMPATT diodes at lower frequencies

Investigations of the effect of ambient temperature on the RF power and frequency ofX-band p+-n-n+ Si IMPATT diodes at frequencies and temperatures below their optimum conditions show considerable degradation of performance. A simple model is presented to explain these effects in terms of a lower limit to the instantaneous terminal voltage of the diode. Values of diode negative conductance are derived from the measurements and good agreement is obtained with independent measurements. The effects are relevant to both amplitude and frequency stability in wide band applications of IMPATT diodes.     

一种新的非均匀减薄法选择阳极氧化法

提出了一种新的非均匀减薄法,即选择阳极氧化法。用于n+-n-n++GaAs高低结雪崩二极管的n+层厚度的控制,使器件的效率达到理论值。     

IMPATT oscillators with enhanced leakage current

The behavior of IMPATT oscillators with enhanced leakage current has been experimentally evaluated by irradiating operating diodes with transient ionizing radiation. Leakage current was induced in diffused junction GaAs and silicon X-band IMPATT diodes by irradiation with 100 nsec pulses of 10 MeV electrons. With increasing leakage current, the oscillator RF power decreases and the frequency of oscillation increases. A large signal circuit model of the IMPATT diode is developed which correlates well with experimental measurements.     

Measurement of series resistance in IMPATT diodes

A new method is given for determining the electrical series resistance of an IMPATT diode. The measurement is based on observation of the oscillation threshold bias current for a diode in a standard circuit. The method is applied to GaAs diodes near 40 GHz. The values obtained are used to quantitatively explain other performance characteristics of the diodes.     

GaAs TUNNETT diodes on diamond heat sinks for 100 GHz and above

Single-drift GaAs TUNNETT diodes were mounted on diamond heat sinks for improved thermal resistance and evaluated around 100 GHz in a radial line full height waveguide cavity. The diodes were fabricated from MBE-grown material originally designed for diodes that operate in CW mode around 100 GHz on integral heat sinks. An RF output power of more than 70 mW with a corresponding DC to RF conversion efficiency of 4.9% was obtained at 105.4 GHz. This is the first successful demonstration of GaAs TUNNETT diodes mounted on diamond heat sinks. To the authors' knowledge, these DC to RF conversion efficiencies and RF power levels are the highest reported to date from TUNNETT diodes and exceed those of any single discrete device made of group III-V materials (GaAs, InP, etc.) at this frequency. Free-running TUNNETT diode oscillators exhibit clean spectra with an excellent phase noise of less than -94 dBc/Hz, measured at a frequency off-carrier of 500 kHz and an RF output power of 40 mW     

Potentials of GaP as millimeter wave IMPATT diode with reference to Si, GaAs and GaN

This paper presents the simulation results of DC,small-signal and noise properties of GaP based Double Drift Region( DDR) Impact Avalanche Transit Time( IMPATT) diodes. In simulation study we have considered the flat DDR structures of IMPATT diode based on GaP,GaAs,Si and GaN( wurtzite,wz) material. The diodes are designed to operate at the millimeter window frequencies of 94 GHz and 220 GHz. The simulation results of these diodes reveal GaP is a promising material for IMPATT applications based on DDR structure with high break down voltage( V_B) as compared to Si and GaAs IMPATTs. It is also encouraging to worth note GaP base IMPATT diode shows a better output power density of 4. 9 × 10~9 W/m~2 as compared to Si and GaAs based IMPATT diode. But IMPATT diode based on GaN( wz) displays large values of break down voltage,efficiency and power density as compared to Si,GaAs and GaP IMPATTs.     

GaAs Schottky—Read diodes for x-band operation

High-efficiency performance of GaAs Schottky-Read IMPATT diodes has been observed at X-band frequencies. The highest efficiency measured was 26.1 percent with 2.5-W continuous-wave (CW) output power at 8.8 GHz for a single-mesa diode while multiple-mesa diodes have delivered more than 7 W at X band. The diodes were fabricated from multiple-layer epitaxial material with gold-plated heat sinks. Details of materials preparation and diode fabrication are presented. Theoretical calculations of diode breakdown voltage and efficiencies have been made as a function of the structural properties of the diodes. Good agreement has been obtained between the experimental microwave oscillator performance and the theoretical calculations.     

Symmetry Experiments with Four-Mesa IMPATT Diodes (Letters)

Experiments with four-mesa silicon p+-n-n+ IMPATT diodes have shown power saturation and reduced efficiency when connected and packaged in electrically asymmetrical configurations. The need for electrical symmetry is illustrated by experiments wherein seemingly trivial asymmetries caused severe saturation of the power output.     

Sweep oscillation mode of GaAs IMPATT diode

Properties of the sweep oscillation mode of GaAs IMPATT diodes in the millimeter-wave region are studied in comparison with Si IMPATT diodes. In spite of their narrower depletion width, the GaAs diodes oscillate at lower frequencies than the Si devices. This can be explained by using the newly measured drift velocity of GaAs.     

IMPATT diode quasi-static large-signal model

A quasi-static large-signal model of an IMPATT diode with general doping profile is derived. The numerical solution of this model has been implemented in a Fortran IV program which executes economically. This model has been used to analyze large-and small-signal admittances of GaAs double-drift and quasi-Read IMPATT diodes. The small-signal results are in good agreement with calculations done using a linearized small-signal model. The large-signal calculations exhibit power and efficiency saturation when reasonable values of parasitic resistance are included and are in good agreement with experimental GaAs diode performance. The generalized quasi-static formulation simplifies analysis of IMPATT structures with arbitrary doping profiles, specifically those with distributed avalanche zones, by providing the correspondence between these devices and the Read diode model.     

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.     

Noise characteristics of GaAs and Si IMPATT diodes for 50-GHz range operation

Direct comparison of noise behaviors between GaAs Schottky-barrier junction and Si diffused p⁺-n junction diodes operating in the 50-GHz range is reported by using the same circuitry. In the oscillator operation, the GaAs diode exhibits excess "1/f^m" noise near carrier, whereas the Si diode shows flat spectrum. Far from the carrier, and AM-DSB-NSR of -133 dB in a 100-Hz bandwidth and an FM noise measure of 27.1 dB are observed for GaAs diodes. Corresponding values obtained for Si diodes are -125 and 36.2 dB, respectively. As a reflection amplifier, minimum noise figures of 27.5 and 38 dB are achieved for the GaAs and Si devices, respectively. These results indicate that the GaAs IMPATT is superior in noise behavior to the Si diode also in the 50-GHz frequency range by about 10 dB. It is emphasized that the noise induced in the bias circuit of the IMPATT oscillator is a replica of the sideband noise of the output power and can be used as an indicator to obtain a low-noise tuning condition of the oscillator.     

IMPATT Diode Circuit Design for Parametric Stability

A new approach to IMPATT diode circuit design to achieve freedom from parametric instabilities is described. Necessary and sufficient conditions are described in the frequency domain for the load impedance presented to the diode terminals. A number of unconditionally stable circuits have been developed for flat-profile GaAs diodes using this approach. Three of these circuits have been built and tested experimentally in 11-GHz IMPATT oscillators and amplifiers. These experimental circuits have been free of parametric instability, even when driven into full RF saturation. In a systems application practical constraints such as cost, RF loss, and tunability will require compromises which will degrade the stability, and it may not always be possible to achieve complete stability for a given diode.     

Broad-Band Small-Signal Impedance Characterization of Silicon (Si) P+-N-N+ Impatt Diodes

A method is described that permits a broad-band small-signal characterization of an IMPATT diode mounted in a package. From automatic-network-analyzer measurements on a package-shaped metal dummy, an empty package, and the diode under test biased below and above breakdown, the method allows first determination of a coupling-circuit parameter, bonding-wire inductance, and diode series resistance, and then evaluation of junction admittance above breakdown. Experimental results on silicon (Si) p+-n-n+ diodes over 2.5-15 GHz are shown. Nearly frequency-independent bonding-wire inductance is observed. Avalanche frequency squared (f/sub a//sup 2/) is found to be sublinear with respect to dc current density (I/sub d), possibly due to a variation of junction temperature (T/sub i/). An experimental formIda for (f/sub a//sup 2/) / (I/sub d) is obtained in terms of (T/sub i/).Detailed comparisons of the measured junction admittance with an existing analytical theory indicate a good agreement, if a suitable amount of saturation current is postulated, and also suggest that the estimated amount is in excess of the prebreakdown saturation current.     

Pulsed measurement of BARITT-diode impedance against current and temperature

The small-signal impedances of M?n?p and p?n?p BARITT diodes have been measured as a function of bias current and diode temperature. A bridge method, developed by Van Iperen and Tjassens, has been adapted so that measurements can be made during short current pulses. In this way, the diode temperature can be kept close to the heatsink temperature. The method is equally suited for other microwave diodes, e.g. IMPATT and Gunn diodes.     

Circuit Conditions to Prevent Second-Subharmonic Power Extraction in Periodically Driven IMPATT Diode Networks

The small-signal characteristics at the second subharmonic (half-frequency) of a periodically pumped IMPATT diode are presented. Theoretical analysis using an appropriate model indicates these characteristics can be interpreted as a "phase-sensitive admittance" which clarifies subharmonic oscillation conditions and suggests a method for their measurement. Measured data on silicon and GaAs diodes de-embedded to the active wafer are in good agreement with theoretical predictions based on the equivalent nonlinear model for each device. Circuit conditions that eliminate second subharmonic and thus prevent fundamental power robbing are given which can be readily obtained for existing devices. An example demonstrating the efficiency-limiting properties of subharmonic is given.     

GaAs W-band IMPATT diodes for very low-noise oscillators

W-band single-drift flat-profile IMPATT diodes were fabricated from GaAs MBE material and tested in a full-height waveguide resonant cavity with resonant cap. A quasi-optical parabolic Fabry-Perot resonator was used to determine the FM noise of the GaAs IMPATT oscillator. With a minimum noise measure of 20 dB at power levels around 20 mW, IMPATT diode oscillators can compete well with oscillators using Gunn devices. The (N/C)/sub FM/=-82 dBc measured at 100 kHz frequency off-carrier and at Q/sub EX/=95 is comparable to the value obtained from Gunn devices. The maximum available output power of 270 mW, however, markedly exceeds that of Gunn 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.     

High-power millimeter wave IMPATT oscillators with both hole and electron drift spaces made by ion implantation

CW powers of 640 mW at 50 GHz have been obtained from double-drift region IMPATT diodes. This result represents the highest product of CW power times frequency squared obtained to date from any IMPATT diode. The diodes are p⁺pnn⁺structures and have both hole and electron drift spaces. The systematic fabrication (by ion implantation) and the evaluation of the dc and millimeter wave characteristics are presented.