Terahertz Microstrip Elevated Stack Antenna Technology on GaN-on-Low Resistivity Silicon Substrates for TMIC

In this paper we demonstrate a THz microstrip stack antenna on GaN-on-low resistivity silicon substrates (ρ < 40 Ω.cm). To reduce losses caused by the substrate and to enhance performance of the integrated antenna at THz frequencies, the driven patch is shielded by silicon nitride and gold in addition to a layer of benzocyclobutene (BCB). A second circular patch is elevated in air using gold posts, making this design a stack configuration. The demonstrated antenna shows a measured resonance frequency in agreement with the modeling at 0.27 THz and a measured S11 as low as −18 dB was obtained. A directivity, gain and radiation efficiency of 8.3 dB, 3.4 dB, and 32% respectively was exhibited from the 3D EM model. To the authors' knowledge, this is the first demonstrated THz integrated microstrip stack antenna for TMIC (THz Monolithic Integrated Circuits) technology; the developed technology is suitable for high performance III-V material on low resistivity/high dielectric substrates

Novel Shielded Coplanar Waveguides on GaN-on-Low Resistivity Si Substrates for MMIC Applications

Shielded-Elevated Coplanar Waveguides (SE-CPWs) with low loss have been successfully developed for the first time for RF GaN on low-resistivity silicon (LR-Si) substrates (σ < 40 Ω.cm). Transmission losses (S 21 ) of less than 0.4 dB/mm at X-band and better than 2 dB/mm at K-band with less than 20 dB return loss were exhibited by the developed SE-CPW, making them comparable in performance to those on traditional (semi-insulating) SI substrates. The developed waveguides use air-bridge technology to suspend CPW tracks above the HEMT GaN layer on LR-Si, directly above an additional thin layer of SiN and shielded ground planes. EM simulation was used to adjust structure parameters for performance optimization. In this work, we eliminated RF energy coupled into the substrate, paving the way for a cost-effective and higher integration GaN MMICs on LR-Si.This work was supported in part by the EPSRC III-V national center pump-priming scheme

High-performance MMIC inductors for GaN-on-low-resistivity silicon for microwave applications

Novel MMIC spiral inductors on GaN-on-low-resistivity silicon (LR-Si) substrates ( σ<40 Ω⋅cm ) are demonstrated with enhanced self-resonance frequency ( fSRF ) and Q -factor. The developed technology improves inductor performance by suppressing substrate coupling effects using air-bridge technology above benzocyclobutene dielectric as an interface layer on the lossy substrate. A 0.83-nH spiral inductor with peak Q -factor enhancement of 57% ( Q=22 at 24 GHz) and maximum fSRF of 59 GHz was achieved because of the extra 5- μm elevation in air. An accurate broad-band model for the fabricated inductors has been developed and verified for further performance analysis up to 40 GHz. The proposed inductors utilize cost-effective, reliable, and MMIC-compatible technology for the realization of high-performance RF GaN-on-LR Si MMIC circuits for millimeter-wave applications

Low-Loss MMICs Viable Transmission Media for GaN-on-Low Resistivity Silicon Technology

In this work a novel ultra-low loss transmission media for RF GaN-on-low-resistivity silicon (LR-Si) substrates (σ < 40 $\Omega$.cm) has been successfully demonstrated. The developed shielded-microstrip lines achieve comparable performance to those on semi-insulating (SI) GaAs substrates with transmission loss of 0.9 dB/mm for frequencies up to 67 GHz. Line performance was further enhanced by additional elevation of the shielded-microstrip lines using air-bridge technology above a 5 μm layer of benzocyclobutene (BCB) on shielded metalized ground planes. Transmission loss of 0.6 dB/mm for frequencies up to 67 GHz was obtained as a result of the extra elevation. Structure parameters were designed and optimized based on EM simulation for best performance. The work shows that the RF energy coupled into the substrate was eliminated, indicating the suitability of III-V-on-LR Si technology for millimeter-wave applications.This work was supported by the EPSRC under grant EP/N014820/1 and III-V national center pump-priming scheme

Multi-channel AlGaN/GaN lateral schottky barrier diodes on low-resistivity silicon for sub-THz integrated circuits applications

This paper presents novel multi-channel RF lateral Schottky-barrier diodes (SBDs) based on AlGaN/GaN on low resistivity (LR) (σ = 0.02 Q.cm) silicon substrates. The developed technology offers a reduction of 37 % in onset voltage, V ON (from 1.34 to 0.84 V), and 36 % in ON-resistance, R ON (1.52 to 0.97 to Q.mm) as a result of lowering the Schottky barrier height, Φn, when compared to conventional lateral SBDs. No compromise in reverse-breakdown voltage and reverse-bias leakage current performance was observed as both multi-channel and conventional technologies exhibited VBV of (VBV > 30 V) and I R of (I R <; 38 μA/mm), respectively. Furthermore, a precise small-signal equivalent circuit model was developed and verified for frequencies up to 110 GHz. The fabricated devices exhibited cut-off frequencies of up to 0.6 THz, demonstrating the potential use of lateral AlGaN/GaN SBDs on LR silicon for high-efficiency, high-frequency integrated circuits applications

High Performance GaN High Electron Mobility Transistors on Low Resistivity Silicon for X -Band Applications

This letter reports the RF performance of a 0.3-μm gate length AlGaN/AlN/GaN HEMT realized on a 150-mm diameter low-resistivity (LR) (σ <; 10 Ω · cm) silicon substrate. Short circuit current gain (fT) and maximum frequency of oscillation (fMAX) of 55 and 121 GHz, respectively, were obtained. To our knowledge, these are the highest fT/fMAX values reported to date for GaN HEMTs on LR silicon substrates.This work was supported by the Pump-Priming Scheme–EPSRC National Centre for III–V Technologies

Quantifying Temperature-dependent Substrate Loss in GaN-on-Si RF Technology

Intrinsic limits to temperature-dependent substrate loss for GaN-on-Si technology, due to the change in resistivity of the substrate with temperature, are evaluated using an experimentally validated device simulation framework. Effect of room temperature substrate resistivity on temperature-dependent CPW line loss at various operating frequency bands are then presented. CPW lines for GaN-on-high resistivity Si are shown to have a pronounced temperature-dependence for temperatures above 150{\deg}C and have lower substrate losses for frequencies above the X-band. On the other hand, GaN-on-low resistivity Si is shown to be more temperature-insensitive and have lower substrate losses than even HR-Si for lower operating frequencies. The effect of various CPW geometries on substrate loss is also presented to generalize the discussion. These results are expected to act as a benchmark for temperature dependent substrate loss in GaN-on-Si RF technology.Comment: 7 pages (double-column), 10 figure

Buffer Induced Current-Collapse in GaN HEMTs on Highly Resistive Si Substrates

We demonstrate that the highly resistive Si substrate in GaN-on-Si RF HEMTs does not act as an insulator, but instead behaves as a conductive ground plane for static operation and can cause significant back-gate-induced current collapse. Substrate ramp characterization of the buffer shows good agreement with device simulations and indicates that the current collapse is caused by charge-redistribution within the GaN layer. Potential solutions, which alter charge storage and leakage in the epitaxy to counter this effect, are then presented

Novel slotted mmWave CPW branch line coupler for MMIC and sub-THz applications

This paper presents a novel mm-wave branch line coupler with an enhanced isolation up to 72dB between the input ports, whereas a conventional branch line coupler usually gives less than 40dB of isolation. Similarly, there was also a small increase in the return loss. The two slots are situated a half wavelength apart acting as resonators and bandpass filters. The shape of the slot is rectangular with smaller sides equal to a half of the transmission line (TL) it is placed on (whether the Z0 or Z0/√2ohmTL). The two slots must be identical to output symmetrical resonance frequencies. This is a promising coupler design particularly in an integrated microwave circuit such as, mixer or multiplier circuits at high frequencies (mmWave)