A sensitivity analysis of millimeter wave characteristics of SiC IMPATT diodes

Ionization rate coefficients and saturation drift velocities for electrons and holes are the vital material parameters in determining the performance of an IMPATT diode. We have performed a sensitivity analysis of the millimeter wave characteristics of 4H-SiC and 6H-SiC IMPATT diodes with reference to the above mentioned material data and an operating frequency of 220 GHz. The effect of a small variation in the ionization rate and drift velocity on the device characteristics like break down voltage, efficiency, noise measure and power output has been presented here.     

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 optical illumination on DDR IMPATT diode at 36 GHz

A reverse biased p-n junction diode with proper resonant cavity and boundary conditions is able to generate rf power and shows normal DC and small signal properties designed with semiconductor materials like 4H-SiC, GaAs, InP, Si-based DDR IMPATT structure at Ka band with dark condition. But when it is exposed to optical illumination through a proper optical window for both top mounted (TM) and flip chip (FC) configuration, it shows the influence on the oscillator performances in that band of frequency. The simulated results are analyzed for 36 GHz window frequency in each of the diodes and relative differences are found in power output and frequency of all these diodes with variable intensities of illumination. Finally it is found that optical control has immense effect in both FC and TM mode regarding the reduction of output power and shifting of operating frequency from which optimization is done for the best optically sensitive material for IMPATT diode.     

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.     

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.     

Characterization of hard- and soft-switching performance of high-voltage Si and 4H-SiC PiN diodes

This paper presents a study of the performance of high-voltage Si and 4H-SiC diodes in a DC-DC buck converter. Device operation in both hard- and zero-voltage switching conditions is presented with the help of measurements and two-dimensional (2-D) mixed device-circuit simulations. Experimental results show that SiC PiN diodes have a strong potential for use in high-speed high-voltage power electronics applications operating at high temperature. A combination of low excess carrier concentration and low carrier lifetime results in superior switching performance of the 4H-SiC diode over ultrafast Si diodes. Soft switching is shown to minimize the switching loss and allow operation at higher switching frequencies using Si diodes. The power loss of 4H-SiC diodes is dominated by conduction loss. Consequently, soft-switching techniques result in a marginal reduction in power loss. However, the low overall power loss implies that SiC diodes can be used at very high switching frequencies even in hard-switching configurations.     

Experimental demonstration of a silicon carbide IMPATT oscillator

Silicon carbide (SiC) is an excellent material for high-power and high-frequency applications because of its high critical field, high electron saturation velocity, and high thermal conductivity. In this letter, we report the first experimental demonstration of microwave oscillation in 4H-SiC impact-ionization-avalanche-transit-time (IMPATT) diodes. The prototype devices are single-drift diodes with a high-low doping profile. DC characteristics exhibit hard, sustainable avalanche breakdown, as required for IMPATT operation. Microwave testing is performed in a reduced-height waveguide cavity. Oscillations are observed at 7.75 GHz at a power level of 1 mW     

High frequency noise properties of a double avalanche region (DAR) IMPATT diode

The high frequency noise properties of a double avalanche region (DAR) IMPATT diode consisting of two avalanche layers interspaced by a drift layer have been studied. In view of the fact that SDR IMPATT diode shows a high value of noise figure, one may think that the presence of two avalanche layers in DAR IMPATT diode may lead to a noise figure of the order of 2 or 3 times larger than that of the SDR (or SAR) IMPATT. However, from the study, it has been observed that the DAR IMPATT has the same order of noise as that of SDR IMPATT under operating condition. Since the DAR IMPATT diode with unequal avalanche layer width can be used as microwave oscillator with minimum coupling between the harmonically related frequencies [1], the device may be very useful in the microwave frequency range.     

The potential of diamond and SiC electronic devices for microwaveand millimeter-wave power applications

The potential of SiC and diamond for producing microwave and millimeter-wave electronic devices is reviewed. It is shown that both of these materials possess characteristics that may permit RF electronic devices with performance similar to or greater than what is available from devices fabricated from the commonly used semiconductors, Si, GaAs, and InP. Theoretical calculations of the RF performance potential of several candidate high-frequency device structures are presented: the metal semiconductor field-effect transistor (MESFET), the impact avalanche transit-time (IMPATT) diode, and the bipolar junction transistor (BJT). Diamond MESFETs are capable of producing over 200 W of X-band power as compared to about 8 W for GaAs MESFETs. Devices fabricated from SiC should perform between these limits. Diamond and SiC IMPATT diodes also are capable of producing improved RF power compared to Si, GaAs, and InP devices at microwave frequencies. RF performance degrades with frequency and only marginal improvements are indicated at millimeter-wave frequencies. Bipolar transistors fabricated from wide bandgap material probably offer improved RF performance only at UHF and low microwave frequencies     

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.     

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.     

Large-Signal Equivalent Circuits of Avalanche Transit-Time Devices

A large-signal analysis for IMPATT diodes is derived, which allows carrier multiplication by impact ionization to occur at every point in the diode. Therefore, the operating characteristics of IMPATT diodes with a wide range of realistic doping profiles can be investigated. For a given operating frequency, RF voltage, dc bias current, and doping profile, the admittance, power output, efficiency, bias voltage of a diode can be obtained. An equivalent circuit the diode package, microwave circuit mount and diode, is obtained experimentally. Using this circuit, the admittance of the diode is measured by a reflection-type circuit and an oscillator circuit as a function of the RF voltage, dc bias current, and frequency.     

Noise in IMPATT-diode oscillators at large-signal levels

A theory is formulated which describes the noise properties of IMPATT-diode oscillators operating at large-signal levels. This theory is based directly on the work of Convert [17] and Hines [18]. The theory takes into account the signal dependence of the noise generation process, and also the intermodulation effects occurring between the various frequency bands. The equations are conveniently arranged in matrix form; such a formulation provides physical insight and facilitates the obtaining of quantitative results in terms of measurable noise parameters. The AM, FM, and low-frequency noise of low-Q IMPATT-diode oscillators operating at high output power levels has been measured and compared with the values predicted by this theory. Si p⁺-n, Si n⁺-p, and n-GaAs S.B. IMPATT diodes have been used. Agreement between the measured and theoretically predicted values is good. Special experimental evidence for the signal dependence of the noise-generating mechanism is obtained by considering the ratio of the AM and FM noise. The Comparatively few measurements published on the correlation between AM, FM, and low-frequency noise have been compared with our theoretical results; as far as can be judged, the trends are similar. Finally, an experiment is described in which a Si n⁺-p diode was used in a high-Q Kurokawa circuit. The experimental value of the rms frequency deviation of 0.8 Hz in a 100-Hz bandwidth was found to be in reasonable agreement with the present theory, extended with an equivalent circuit describing the high-Q circuit.     

Noise effect in oscillators using multiple active devices connected in series or in parallel

The effect of noise in an IMPATT or Gunn diode oscillator on a phase or frequency fluctuation can be reduced when the oscillator is constructed of multiple diodes connected in series, compared with the oscillator using a single diode.     

The influence of high-temperature annealing on SiC schottky diode characteristics

The influence of high temperature (up to 800C) annealing on the current-voltage characteristics of n-type 6H-SiC Schottky diodes is presented. Our experimental results indicate that high-temperature annealing can result in the improvement of the forw ard and reverse electrical characteristics of SiC Schottky diodes by repairing any leaky low barrier secondary diode parallel to the primary diode that may be present due to the barrier inhomogeneities at the Schottky contact interface.     

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.     

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.     

SiC power Schottky and PiN diodes

The present state of SiC power Schottky and PiN diodes are presented in this paper. The design, fabrication, and characterization of a 130 A Schottky diode, 4.9 kV Schottky diode, and an 8.6 kV 4H-SiC PiN diode, which are considered to be significant milestones in the development of high power SiC diodes, are described in detail. Design guidelines and practical issues for the realization of high-power SiC Schottky and PiN diodes are also presented. Experimental results on edge termination techniques applied to newly developed, extremely thick (e.g., 85 and 100 μm) 4H-SiC epitaxial layers show promising results. Switching and high-temperature measurements prove that SiC power diodes offer extremely low loss alternatives to conventional technologies and show the promise of demonstrating efficient power circuits. At sufficiently high on-state current densities, the on-state voltage drop of Schottky and PiN diodes have been shown to be comparable to those offered by conventional technologies     

Computer Experiments on TRAPATT Diodes

Simplified analytical treatments of the TRAPATT mode of operation in avalanche diodes do not consider in sufficient detail the initial starting conditions for this mode. This paper examines this question in greater detail by analyzing a number of diode structures using a large-scale computer program. The results of these computer experiments have indicated that the requirements for efficient TRAPATT operation and the requirements for IMPATT operation diverge with increasing frequency. Since the IMPATT oscillation is required to start the TRAPATT mode, self-starting TRAPATT oscillators are increasingly difficult to fabricate as the operating frequency is increased. A novel diode structure is proposed which eliminates this problem and is capable of high-frequency CW TRAPATT operation.     

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.