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     

Estimation of power density in IMPATT using different materials

ABSTRACT

The RF output power dissipated per unit area is calculated using Runge-Kutta method for the high-moderate-moderate-high (n⁺-n-p-p⁺) doping profile of double drift region (DDR)-based impact avalanche transit time (IMPATT) diode by taking different substrate at Ka band. Those substrates are silicon, gallium arsenide, germanium, wurtzite gallium nitride, indium phosphide and 4H-silicon carbide. A comparative study regarding power dissipation ability by the IMPATT using different material is being presented thereby modelling the DDR IMPATT diode in a one-dimensional structure. The IMPATT based on 4H-SiC element has highest power density in the order of 10¹⁰ Wm^?2 and the Si-based counterpart has lowest power density of order 10⁶ Wm^?2 throughout the Ka band. So, 4H-SiC-based IMPATT should be preferable over others for the power density preference based application. This result will be helpful to estimate the power density of the IMPATT for any doping profile and to select the proper element for the optimum design of the IMPATT as far as power density is concerned in the Ka band. Also, we have focused on variation of power density with different junction temperatures and modelled the heat sink with analysis of thermal resistances.     

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.     

SiC/GaN IMPATT二极管的交流性能研究

利用p型宽带隙材料SiC替代p型GaN,制作了一种p-SiC/n-GaN异质结双漂移(DDR)IMPATT二极管.对器件的交流大信号输出特性进行数值模拟仿真.结果表明,相比传统GaN单漂移(SDR)IMAPTT二极管,p-SiC/n-GaN新结构DDR器件的击穿电压、最佳负电导、交流功率密度和直流-交流转换效率都获得了...     

A simplified field analysis of a distributed IMPATT diode usingmultiple uniform layer approximation

A small-signal field analysis of a distributed IMPATT diode is presented. The active region of the diode is assumed to consist of a uniform avalanche layer and avalanche-free drift layers. The propagation constant and field distributions are obtained without numerical solution of differential equations. The effects of losses caused by the presence of inactive layers are included in the analysis. Numerical examples of GaAs double-Read distributed IMPATT diodes are given which show the dependence of the amplification characteristics on the thicknesses of the avalanche and drift layers     

Drift-free 10-kV, 20-A 4H-SiC PiN diodes

As impressive as the advancement in 4H-SiC material quality has been, 4H-SiC PiN diodes continue to suffer from irreversible, forward-voltage instabilities. In this work, we describe PiN diodes designed to block 10 kV and conduct 20 A at less than 4.5 V, which were fabricated on 4H-SiC PiN epitaxial layers that were grown with an innovative epitaxial process that has been developed specifically to suppress V_F drift. The diodes fabricated on epitaxial layers that implemented this new epitaxy process showed excellent V_F stability, with 86% of the diodes drifting less than 0.1 V during forward current stressing at 10 A (50 A/cm²) for 30 min. However, these improvements in V_F drift come with a cost in blocking yield, as the surface morphology and other crystal defects imparted by the epitaxial process resulted in only 1 of 50 diodes reaching the 10-kV blocking specification. Nevertheless, the remarkable progress in V_F drift yield brings us closer to commercialization of high-power 4H-SiC PiN diodes.     

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.     

Computer-aided analysis of double drift region impatt diode

The results calculated by computer for the double drift region IMPATT diode oscillator on the 8 mm waveband are reported in this paper. A comparison between single and double drift devices concerning the power output and efficiency is given. The effect of doping profile, current density and RF voltage on the performances of these devices have also been investigated. The theoretical data of these double drift IMPATT oscillator and amplifier are provided.     

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.     

4H-SiC射频功率MESFET大信号直流I-V特性解析模型

根据 4H - Si C高饱和电子漂移速度和常温下杂质不完全离化的特点 ,对适用于 Si和 Ga As MESFET的直流I- V特性理论进行了分析与修正 .采用高场下载流子速度饱和理论 ,以双曲正切函数作为表征 I- V特性的函数关系 ,建立了室温条件下 4H - Si C射频功率 MESFET直流 I- V特性的准解析模型 ,适于描述短沟道微波段 4H- Si CMESFET的大信号非线性特性 ,计算结果与实验数据有很好的一致性 .同时与 MEDICI模拟器的模拟结果也进行了比较 .     

Premature collection mode in IMPATT diodes

Experimental efficiencies of up to 35.5 percent have been reported for Read-type GaAs diodes, whereas theoretical calculations have predicted an upper limit of approximately 30 percent for the conversion efficiency of IMPATT diodes. The concept of a premature collection mode is shown to resolve this discrepancy by predicting maximum efficiencies close to 40 percent. Premature collection refers to large-signal conditions where the modulation of the drift width is sufficiently large to result in collection of the avalanche current pulse at drift angles smaller than the small-signal angle. It is shown that a discontinuous transition between the IMPATT and the premature collection modes takes place when the drift angle in the small-signal limit is greater than π. Designing the diode for close to punchthrough conditions in small-signal operation extends the practical frequency range for inducing premature collection by avoiding long drift angles and corresponding rapid conductance saturation in the IMPATT mode. The onset of premature collection is accompanied by a substantial increase in power output because of a more favorable drift angle, and in high noise because of the high RF levels involved. The jump in transit angle causes a discontinuous increase in negative conductance. The hysteresis in the tuning characteristic resulting from this discontinuity has been observed experimentally. Noise measures in the range 60-70 dB have been measured and calculated for the premature collection mode compared to 40-50 dB under large-signal conditions for the IMPATT mode. Therefore, the high efficiencies available with the premature collection mode are expected to be usable only in applications where high noise levels can be tolerated.     

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.     

Matching of active millimetre-wave slot-line antennas

The matching of a radiating, resonant structure to an active millimetre-wave device is investigated. As an active device, an IMPATT diode is considered to be matched to a planar slot-line structure. An analytical IMPATT diode model and an equivalent circuit of the slot line are used to calculate possible oscillation frequencies and large-signal modulation parameters of the diode. In the case of matching the output power is predicted. The results are in satisfactory agreement with experimental data and suggest a diode design with shorted drift regions and reduced diode area for optimum impedance matching.<>     

High efficiency GaInAs/InP heterojunction IMPATT diodes

Heterojunction IMPATT diodes make it possible to produce new high conversion efficiency devices, combining a low bandgap semiconductor for the avalanche zone with a large bandgap material for the drift region. In this study, the heterojunction GaInAs/InP which seems particularly attractive is used in various structures. The theoretical predictions of performances are determined by a computer simulation which takes into account the main limitation effects of IMPATT diodes and the influence of particular physical phenomena due to the use of heterojunctions and semiconductors, mainly the influence of injection currents. Potential performances of the proposed structure appear very attractive especially in the millimeter-wave range using a MITATT mode (Mixed-Tunneling-Avalanche-Transit-Time) by combining tunneling current and avalanche multiplication injections.     

4H-SiC双层浮结肖特基势垒二极管温度特性研究

为了增强器件高温条件下的适应性,对4H-SiC双层浮结肖特基势垒功率二极管的温度特性进行了研究.结果表明,当温度变化时,器件的阻断电压、通态电阻、反向漏电流及开关时间等电学性质均要发生一定的变化.作为一种基于浮结技术的sic新器件,通过数值模拟方法对其特征参数进行优化,可使其承载电流能力、阻断特性和开关速度等得到进一步...     

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.     

A simple approximate method of estimating the effect of carrier diffusion in IMPATT diodes

Most large-signal analyses of IMPATT diodes neglect the diffusion of charge carriers in the drift region. A correction can be introduced to include the effect of diffusion in the negative conductance or the efficiency of the IMPATT diode calculated from such analyses. An approximate method of estimating a simple correction factor is presented using the Read model of the diode.     

Effect of undepleted high-resistivity region on microwave efficiency of GaAs IMPATT diodes

Degradation of the microwave efficiency due to the undepleted high-resistivity epitaxial region was experimentally found to be remarkably, small on GaAs X-band conventional-type IMPATT diodes. The result seems to be consistent with large low-field drift mobility for electrons in GaAs. Present study confirms the superiority of n-GaAs over other materials for IMPATT diode use.     

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.     

Measurement of high-field electron transport in silicon carbide

We report recent measurements of the drift velocity of electrons parallel to the basal plane in 6H and 4H silicon carbide (SiC) as a function of applied electric field. The dependence of the low field mobility and saturated drift velocity on temperature are also reported. The saturated drift velocities at room temperature are approximately 1.9×10⁷ cm/s in 6H-SiC and 2.2×10⁷ cm/s in 4H-SiC