Terahertz planar antennas for future wireless communication: A technical review

In this paper the potentiality of impact avalanche transit time (IMPATT) devices based on different semiconductor materials such as GaAs, Si, InP, 4H-SiC and Wurtzite-GaN (Wz-GaN) has been explored for operation at terahertz frequencies. Drift–diffusion model is used to design double-drift region (DDR) IMPATTs based on different materials at millimeter-wave (mm-wave) and terahertz (THz) frequencies. The performance limitations of these devices are studied from the avalanche response times at different mm-wave and THz frequencies. Results show that the upper cut-off frequency limits of GaAs and Si DDR IMPATTs are 220 GHz and 0.5 THz, respectively, whereas the same for InP and 4H-SiC DDR IMPATTs is 1.0 THz. Wz-GaN DDR IMPATTs are found to be excellent candidate for generation of RF power at THz frequencies of the order of 5.0 THz with appreciable DC to RF conversion efficiency. Further, it is observed that up to 1.0 THz, 4H-SiC DDR IMPATTs excel Wz-GaN DDR IMPATTs as regards their RF power outputs. Thus, the wide bandgap semiconductors such as Wz-GaN and 4H-SiC are highly suitable materials for DDR IMPATTs at both mm-wave and THz frequency ranges.

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Prospects of IMPATT devices based on wide bandgap semiconductors as potential terahertz sources

In this paper, we have presented the simulation results of a rectangular microstrip patch antenna at terahertz (THz) frequency ranging from 0.7 to 0.85 THz. THz electromagnetic wave can permit more densely packed communication links with increased security of communication transmission. The simulated results such as gain, radiation efficiency and 10 dB impedance bandwidth of rectangular microstrip patch antenna at THz frequencies without shorting post configuration are 3.497 dB, 55.71% and 17.76%, respectively, whereas with shorting post configuration, corresponding parameters are 3.502 dB, 55.88% and 17.27%. The simulation has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the method of finite difference time domain technique.

Rectangular Microstirp Patch Antenna Design at THz Frequency for Short Distance Wireless Communication Systems

In this paper we review THz radiation properties, generation methods, and antenna configurations. This paper suggests some new class of antennas that can be used at THz frequency, like optical antennas or Carbon nanotube antennas. THz technology has become attractive due to the low energy content and nonionizing nature of the signal. This property makes them suitable for imaging and sensing applications. But at the same time detection and generation of THz signals has been technologically challenging. This paper presents a comparative study of the generation techniques for THz frequency signals giving emphasis to the some new techniques like Quantum Cascade lasers which has created significant research interest. The main aim for this study is to find out the materials suitable for fabricating THz devices and antennas, a suitable method for generation of high power at THz frequency and an antenna that will make THz communication possible.

Terahertz (THz) Frequency Sources and Antennas - A Brief Review

Potentiality of Impact Avalanche Transit Time (IMPATT) devices based on different semiconductor materials such as InP, 4H-SiC, and Wurtzite-GaN (Wz-GaN) has been explored for operation at terahertz (THz) frequencies. Drift-diffusion model is used to design double-drift region (DDR) IMPATTs based on above mentioned materials at different millimeter-wave (mm-wave) and THz frequencies and the upper cut-off frequency limits of those devices are obtained from the avalanche response times at those mm-wave and THz frequencies. Results show that the upper cut-off frequency limits of both InP and 4H-SiC DDR IMPATTs are 1.0 THz; whereas, the same is 5.0 THz in Wz-GaN DDR IMPATTs. The Wz-GaN DDR IMPATTs emerge as the most suitable devices for generation of THz frequencies due to their small avalanche response time, high DC to RF conversion ratio, and sufficiently high RF power output at THz frequencies. But, it is observed that up to 1.0 THz, 4H-SiC DDR IMPATTs excel Wz-GaN DDR IMPATTs due to their higher ou...

Potentiality of IMPATT Devices as Terahertz Source: An Avalanche Response Time-based Approach to Determine the Upper Cut-off Frequency Limits

Reliability of terahertz-frequency (~1.0 THz) characteristics of wide-bandgap (WBG) wurtzite (Wz)-GaN- and 4H-SiC-based p++nn++-type single-drift-region (SDR) impact avalanche transit time (IMPATT) devices (normal and photoilluminated) is compared through a simulation scheme. The simulation experiment reveals that an RF power density of 3.37 times 1011 W middotm-2 (efficiency of 18.2%) at around 1.126 THz may be realized from the optimized unilluminated GaN IMPATT device, whereas the unilluminated 4H-SiC IMPATT device is expected to generate an RF power density of 1.35 times 1011 W middotm-2 (efficiency of 9%) at 1.05 THz. However, the parasitic series resistance reduces the maximum exploitable power density from the terahertz devices. Under optical illumination, additional photogenerated carriers are created in the devices, and these carriers change the admittance and negative resistance properties of the terahertz IMPATT diodes. The performance modulation of the terahertz devices is simulated, and the results are compared in this paper. Under external radiation, the operating frequencies of the GaN- and SiC-based diodes are found to shift upward by 6.0 and 40.0 GHz, respectively, with degradation of maximum output-power density level and device negative resistance. The extensive simulation experiments establish that, although the photosensitivity of the 4H-SiC-based IMPATT device is better than its GaN counterpart, the overall terahertz performance of the unilluminated GaN IMPATT device is far better than the 4H-SiC-based device, particularly in terms of output power and efficiency. The simulation results and the proposed experimental methodology presented here can be used for realizing optically tuned WBG IMPATT oscillators for terahertz communication.

Photosensitivity Analysis of Gallium Nitride and Silicon Carbide Terahertz IMPATT Oscillators: Comparison of Theoretical Reliability and Study on Experimental Feasibility

The dynamic performance of wide-bandgap 4H-SiC based double drift region () IMPATT diode is simulated for the first time at terahertz frequency (0.7 Terahertz) region. The simulation experiment establishes the potential of SiC based IMPATT diode as a high power ( ) terahertz source. The parasitic series resistance in the device is found to reduce the RF power output by 10.7%. The effects of external radiation on the simulated diode are also studied. It is found that (i) the negative conductance and (ii) the negative resistance of the diode decrease, while, the frequency of operation and the quality factor shift upward under photoillumination. Holes in 4H-SiC based IMPATT are found to dominate the modulation activities. The inequality in the magnitude of electron and hole ionization rates in the semiconductors may be correlated with these findings.

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Prospects of 4H-SiC Double Drift Region IMPATT Device as a Photo-Sensitive High-Power Source at 0.7 Terahertz Frequency Regime

The dynamic properties of a 4H-SiC DDR (p + p n n + type) IMPATT diode operating at 0.5 THz region are studied through DC and smallsignal analysis. The study indicates that 4H-SiC IMPATT is capable of generating high RF power (P RF ) (2.70 W) at 0.515 terahertz with high efficiency (12 %). However, the parasitic series resistance is found to produce a 7 % reduction in the negative conductance and the P RF of the diode. The effect of photo-illumination on the device is also investigated by studying the role of enhanced saturation current on the THz frequency performance of this IMPATT device. A modified double iterative simulation technique developed by the authors is used for this purpose. It is found that (i) the negative conductance and (ii) the negative resistance of the device decrease, while, the frequency of operation and the device quality factor shift upward with increasing saturation current. The upward shift in operating frequency is found to be more (~ 65 GHz) when the device performance is controlled by the hole saturation current rather than by the electron dominated saturation current. These results thus indicate that 4H-SiC DDR IMPATT diode is highly photo-sensitive even at THz range of frequencies.

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Optically Illuminated 4H-SiC Terahertz IMPATT Device

Extensive simulation experiments have been carried out on the DC and high-frequency characteristics of α-(4H) Silicon Carbide based double-drift (p++ p n n++ type) impact avalanche transit time (IMPATT) diodes at two important millimeter-wave window frequencies (35 and 140 GHz). The studies reveal that the IMPATT diode designed at Ka-band (at around 35.0 GHz) may yield an RF power density of 10.72 × 1012 Wm−2 with an efficiency of 21.5%, whereas the D-band (at around 140.0 GHz) IMPATT is capable of delivering an RF power density of 0.38 × 1012 Wm−2 with an efficiency of 15.0%. These results are very encouraging to choose SiC as a suitable base material for developing high-power and high-frequency IMPATT diodes. Impurity charge spikes are introduced in the flatly doped n and p regions of the double-drift diodes in the form of single low-high-low (p++ p p+ p n n+ n n++ type) bump. The effects of this charge bump on the mm-wave characteristics of the double-drift 4H-SiC IMPATTs are analyzed for the f...

Effects of Charge Bump on High-Frequency Characteristics of α-SiC-based Double-drift ATT Diodes at Millimeter-wave Window Frequencies

The effects of elevated junction temperature on the terahertz (THz) frequency characteristics of α-(hexagonal, 4H and 6H) silicon carbide (SiC) based double-drift region (DDR, p++ p n n++ type) impact ionization avalanche transit-time (IMPATT) devices are studied and compared for the first time through simulation experiments. This study reveals that at 300 K < T < 600 K, a 4H-SiC IMPATT diode may yield 3.5 W of output power (efficiency (η) ~ 8.6%) at 1.3 THz, while its 6H-SiC counterpart can deliver 3 W of output power (η = 6.3%) at 1.2 THz. It is interesting to observe that at elevated temperature, the performance of a 6H-SiC IMPATT diode degrades more in comparison with its 4H-SiC counterpart. These comparative analyses reveal the superiority of 4H-SiC diodes over their 6H-SiC counterparts, and thus establish the potential of the former as a high-power THz IMPATT oscillator even in harsh environments. Mobile space charge effects and the effect of positive series resistance on the high-temperature performance of the THz devices are also simulated, and it is found that series resistance reduces the output power level of the diodes by at least 15.0%. Moreover, the effects of increased junction temperature on the photo-sensitivity of top mounted (TM) and flip chip (FC) α-SiC IMPATTs are also investigated using a modified simulation technique. The device operating frequencies, under TM illumination configuration, shifts upward by at least 40.0 GHz, whereas the operating frequency shifts upward by at least 100.0 GHz under FC illumination configuration. The simulation results and the proposed experimental methodology presented here may be used for realizing optically controlled α-SiC transit-time devices for application in THz communication.

https://iopscience.iop.org/article/10.1088/0268-1242/25/5/055008/pdf

Nilratan Mazumder

Papers

Photosensitivity Analysis of Gallium Nitride and Silicon Carbide Terahertz IMPATT Oscillators: Comparison of Theoretical Reliability and Study on Experimental Feasibility

Prospects of 4H-SiC Double Drift Region IMPATT Device as a Photo-Sensitive High-Power Source at 0.7 Terahertz Frequency Regime

Optically Illuminated 4H-SiC Terahertz IMPATT Device

Effects of Charge Bump on High-Frequency Characteristics of α-SiC-based Double-drift ATT Diodes at Millimeter-wave Window Frequencies

α-SiC nanoscale transit-time diodes: performance of the photo-irradiated terahertz sources at elevated temperature