Low noise, high efficiency GaAs IMPATT diodes at 30 GHz

Low noise, very high efficiency IMPATT diodes provide an attractive alternative to Gunn diodes for many millimetre-wave applications. GaAs hi-lo single-drift IMPATT diodes are demonstrated. The diodes are fabricated using molecular beam epitaxy and (at approximately 30 GHz) exhibit exceptional efficiencies (>20%), very low FM noise (-88 dBc/Hz at 100 kHz off-carrier) and simultaneous CW power levels in excess of 300 mW.<>     

A study of the power handling ability of gallium arsenide and silicon,single and double drift IMPATT diodes

The concept of a critical current density effect on the operation of silicon and gallium arsenide IMPATT diodes is examined using large signal analysis. This critical current density effect does not appear to exist in the form that is generally thought of to-date. However, other physical processes develop at high current densities which gradually degrade diode efficiencies. These processes are worse in silicon diodes than in gallium arsenide diodes because at a given frequency of operation silicon diodes need a lower doping density than gallium arsenide diodes due to the lower saturated drift velocities of carriers in gallium arsenide. Reasons are suggested which explain why these other processes develop before a true critical current density limit is seen. New scaling data for limits on power handling ability vs frequency of gallium arsenide IMPATT diodes are presented. In addition the advantages of double drift structures over single drift structures are re-examined in the light of the suggestion that silicon and gallium arsenide IMPATT diodes are thermally and impedance limited rather than current density limited at high frequencies. The problem of tunnelling is also examined and is shown to be unimportant at all frequencies up to 120 GHz.     

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.     

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.     

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.     

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.     

High-Power 50-GHz Double-Drift-Region IMPATT Oscillators with Improved Bias Circuits for Eliminating Low-Frequency Instabilities

Low-frequency instabilities in millimeter-wave double-drift-region (DDR) IMPATT diodes are investigated and new oscillator circuits with the improved bias circuits for eliminating the low-frequency instability are developed. DDR IMPATT diodes mounted in these circuits exhibited a maximum free-running oscillation power of 1.6 W at 55.5 GHz with 11.5-percent conversion efficiency. A highly stabilized oscillator was also constructed with the maximum output power of 1 W and the frequency stabflity 0.3 ppm/mA at 51.86 GHz.     

A new concept for high-efficiency operation of high-low-type GaAs IMPATT diodes

A new operation mode, the "surfing mode," is proposed as an explanation for the high-efficiency operation of high-low-type GaAs IMPATT diodes. This mode is characterized by the concept that the avalanche charge pulse drifts synchronously with the movement of the front edge of the depletion layer at a velocity higher than the saturation velocity. The design chart of high-low-type GaAs IMPATT diodes is determined on the basis of the concept of the "surfing mode." The high-low-type GaAs IMPATT diodes designed using this chart exhibited output powers of 15.3 W (Delta T_{j}= 210°C) at 6.1 GHz with 25-percent efficiency.     

Analysis of Nonlinear Characteristics and Transient Response of IMPATT Amplifiers

Nonlinear characteristics, large-signal effects, and transient response of IMPATT amplifiers are analyzed leading to clear understanding of various nonlinear and large-signal phenomena which are often observed experimentally on IMPATT diodes operated as stable (linear) amplifiers or injection-locked oscillators. Effects of bandwidth on transient response of the IMPATT amplifiers as applied to phase-modulated signals and amplitude-modulated signals are investigated in detail. The relationship between the transition (switching) time and the amplifier bandwidth is derived. Capabilities and limitations of IMPATT diodes operated as stable amplifiers or injection-locked oscillators are discussed.     

GaAs TUNNETT Diodes

The tunnel-injection-transit-time (TUNNETT) diode is operated at a high frequency and has a low-noise level compared to the IMPATT diode. The tunnel injection in a thin carrier generating region of the TUNNETT depends strongly on the electric-field intensity over 1000 kV/cm where the ionization of carriers can be neglected, leading to a higher efficiency performance than that of the IMPATT. GaAs TUNNETT diodes with p+-n and p+-n-n+ structures have been fabricated by a new LPE method (the temperature-difference method under controlled vapor pressure). The fundamental oscillation at frequencies from about 100 up to 248 GHz has been obtained from the pulse-driven p+-n-n+ diodes. This paper describes the details of the oscillation characteristics of GaAs TUNNETT diodes.     

Microstrip Varactor-Tuned Millimeter-Wave IMPATT Diode Oscillators

Varactor-tuned millimeter-wave IMPATT diode oscillators in microstrip form using chip-mounted diodes are described. A nearly level output power of 28 /spl plusmn/ 8 mW was achieved over a 6-GHz tuning range. Tunable bandwidths as high as 8 GHz with 6-26 mW of power were obtained from a single source. P-type epitaxial silicon IMPATT diodes were used for both the active device and the tuning varactor functions.     

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.     

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.     

A comparison of silicon and gallium arsenide large signal IMPATT diode behaviour between 10 and 100 GHz

A large-signal computer simulation of an IMPATT diode has been used to investigate the differences between gallium arsenide and silicon IMPATT diodes. The variations of efficiency with frequency, current density, series resistance, amount of punch-through and reverse saturation currents are all investigated.With no ‘parasitic’ effects the silicon diode efficiency remains almost constant between 10 and 100 GHz, whereas the efficiency of gallium arsenide diodes is higher than that of silicon diodes at 10 GHz but decreases to the silicon diode efficiency at 100 GHz. A lower residual avalanche particle current in gallium arsenide diodes results in a higher susceptibility to reverse saturation currents. In silicon diodes the higher material resistivity affects the efficiency more than in gallium arsenide diodes, the removal of series resistance by having a punched-through diode does not necessarily increase the efficiency. The difference between experimental results quoted in the literature and the theoretical calculations are considered in terms of these effects. By considering the differences in ionization coefficients and velocities between the materials the lower efficiency of silicon diodes compared to gallium arsenide diodes is explained, also the lower breakdown voltage of gallium arsenide diodes compared to silicon diodes of the same frequency, and the ‘forward-bias’ effect found at high frequencies in gallium arsenide diodes.     

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.     

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.     

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.     

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.     

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.