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.     

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.     

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.     

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 Two-Stage IMPATT-Diode Amplifier

The system aspects and packaging of a two-stage FM IMPATT-diode amplifier are described. The amplifier combines the output power of 4 IMPATT diodes in the final stage to provide an output power of greater than 4 W at 6 GHz. The system has a locking bandwidth of greater than 200 MHz with a 16-dB gain and a noise figure of less than 50 dB. Both the design and the experimental performance of the amplifier and each of its stages are discussed. The noise characterization of IMPATT-diode amplifiers, operating as injection-locked oscillators or stable amplifiers, determined the mode of operation for each stage. Included in the paper are experimental results of large-signal noise characterization of both Si and GaAs IMPATT diodes, as are the noise characteristics related to the output power and gain.     

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.     

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.     

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.<>     

10-W and 12-W GaAs IMPATT's

Hi-lo and lo-hi-lo GaAs Schottky-barrier IMPATT diodes have generated CW power outputs over 12 and 10 W, respectively, at 6 GHz. Noise measurements indicate a decreasing FM noise measure with increasing power output. The diodes are less susceptible to tuning-induced burnout than are flat-profile GaAs Impatts, having repeatedly survived input power surges over 70 W.     

HIgh-Power C-Band Multiple-IMPATT-Diode Amplifiers

The design considerations and performance characteristics of two high-power microwave reflection amplifiers that use multiple silicon IMPATT diodes are presented. The amplifiers employ microstrip hybrid-circuit-type power combiners to combine the individually matched IMPATT diodes. The first unit, a single-stage 4-diode amplifier, produced 8-W output with 6-dB gain while the second 12-diode amplifier gave 15.8-W output at about 9-dB gain. FM and AM noise added by these amplifiers has been measured with each amplifier driven to nearly full output. Use of microstrip hybrid-circuit power combiners appears to offer a simple and economical design approach for the implementation of microwave solid-state power amplifiers using multiple active devices.     

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.     

Noise in IMPATT diodes: Intrinsic properties

The design of low-noise IMPATT diodes has been aided by theories describing the noise generation under small-signal conditions. A major deficiency in this procedure has existed in that there is no apparent connection between the small-signal behavior and the great increases in the noise observed in large-signal operation. As a remedy a theory has been developed for the noise generation at arbitrary signal levels by using a Read diode model. The theory is based on a linearization technique for calculating the spectrum of homogeneous noise with linear damping resulting in a separation of the large-signal and noise problems. The open-circuit noise voltage increases strongly at high signal levels due to nonlinear parametric interactions and gives rise to a rapid increase in the noise measure as a function of the generated microwave power. Operating parameters are derived that optimize the power-noise ratio. A long intrinsic response time is found to be beneficial in achieving high power as well as low noise. Other factors affecting the design and choice of material for IMPATT diodes are discussed. An important feature of the presented theory is that a complete design optimization with respect to the power-noise characteristics can be carried out provided reliable information exists about the ionization rates and the drift velocities. A simpler alternative is to obtain the physical quantities governing the power-noise behavior from small-signal admittance and noise measurements. Good agreement has been obtained with experimental power-noise measurements by this method. As an application of this procedure a state of the art comparison is given for GaAs, Ge, and Si diodes at 6 GHz.     

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.     

Effect of doping profile on avalanche noise of silicon IMPATT diodes

The open-circuit spectral noise-voltage density e2/?f of silicon IMPATT diodes with different punchthrough factors has been measured. A noise reduction has been obtained for diodes with punchthrough factors > 1. This is in agreement with theoretical curves calculated on the basis of the noise theory of Gummel and Blue.     

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.     

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.     

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.     

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.     

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.