Passive Components Technology for THz-Monolithic Integrated Circuits (THz-MIC)

In this work, a viable passive components and transmission media technology is presented for THz-Monolithic Integrated Circuits (THz-MIC). The developed technology is based on shielded microstrip (S-MS) employing a standard monolithic microwave integrated circuit compatible process. The S-MS transmission media uses a 5-μm layer of benzocyclobutene (BCB) on shielded metalized ground plates avoiding any substrate coupling effects. An insertion loss of less than 3 dB/mm was achieved for frequencies up to 750 GHz. To prove the effectiveness of the technology, a variety of test structures, passive components and antennas have been design, fabricated and characterized. High Q performance was demonstrated making such technology a strong candidate for future THz-MIC technology for many applications such as radar, communications, imaging and sensing

Terahertz Monolithic Integrated Circuits (TMICs) Array Antenna Technology On GaN-on-Low Resistivity Silicon Substrates

In this paper, we have demonstrated a viable microstrip array patch antenna technology for the first time on GaN-on-low resistivity silicon (LR-Si) substrates (ρ <; 40 Ω.cm) at H-band frequencies (220-325 GHz). The developed technology is compatible with standard MMIC technology with no requirement for high temperature processes. To mitigate the losses presented by the substrate and to enhance the performance of the integrated array antenna at THz frequencies, the driven patch is shielded by silicon nitride and gold layer in addition to a layer of benzocyclobutene (BCB). The demonstrated 4×1 array integrated antenna showed a measured resonance frequency in agreement with our simulation at 0.27 THz; a measured S11 as low as -41 dB was obtained. A directivity, gain and radiation efficiency of 11.2 dB, 5.2 dB, and 20% respectively was observed from the 3D EM model for a 5 μm BCB inset. To the authors' knowledge, this is the first demonstration of a THz integrated microstrip array antenna for TMIC technology; this developed technology is promising for high performance III-V electronic material on low resistivity/high dielectric substrates

Optimization of ohmic contact for AlGaN/ GaN HEMT on low resistivity silicon

In this article, we report the optimization of ohmic contact formation on AlGaN/GaN on low-resistivity silicon. For achieving this, a strategy of uneven AlGaN/GaN was introduced through patterned etching of the substrate under the contact. Various pattern designs (holes, horizontal lines, vertical lines, grid) and varied etch depth (above and below the 2-D electron gas) were investigated. Furthermore, a study of planar and nonplanar ohmic metallization was investigated. Compared to a traditional fabrication strategy, we observed a reduced contact resistance from 0.35 to 0.27 Ω · mm by employing a grid etching approach with a “below channel” etch depth and nonplanar ohmic metallization. In general, measurements of “below channel” test structures exhibited improved contact resistance compared to “above channel” in both planar and nonplanar ohmic metallizatio

Pseudo-planar Ge-on-Si Single-photon Avalanche Diode Detector with Record Low Noise-equivalent Power

Single-photon avalanche diode (SPAD) detectors are of significant interest for numerous applications, including light detection and ranging (LIDAR), and quantum technologies such as quantum-key distribution and quantum information processing. Here we present a record low noise-equivalent-power (NEP) for Ge-on-Si SPADs using a pseudo-planar design, showing high detection efficiency in the short-wave infrared; a spectral region which is key for quantum technologies and hugely beneficial for LIDAR. These devices can leverage the benefits of Si avalanche layers, with lower afterpulsing compared to InGaAs/InP, and reduced cost due to Si foundry compatibility. By scaling the SPAD pixels down to 26μm diameter, a step change in performance has been demonstrated, with significantly reduced dark count rates (DCRs), and low jitter (134ps). Ge-on-Si SPADs were fabricated using photolithography techniques and characterised using time-correlated single-photon counting. The DCR reaches as low as kilocount/s at 100K for excess bias up to ~5%. This reduction in DCR enables higher temperature operation; e.g. the DCR of a 26μm diameter pixel at 150 K is approximately equivalent to a 100 μm diameter pixel at 77 K (100s of kilocounts/s). These low values of DCR, coupled with the relatively temperature independent single photon detection efficiencies (SPDE) of ~29% (at 1310nm wavelength) leads to a record low NEP of 7.7×10−17WHz−1/2. This is approximately 2 orders of magnitude lower than previous similarly sized mesa-geometry Ge-on-Si SPADs. This technology can potentially offer a lowcost, Si foundry compatible SPAD operating at short-wave infrared wavelengths, with potential applications in quantum technologies and autonomous vehicle LIDAR

Millimeter-wave and terahertz technology for integrated circuits

In recent years, there has been rapid growth in the use of millimeter-wave or Terahertz-wave frequencies for various applications like communication, imaging, medical sciences and space instrumentation. As the semiconductor processing technologies have enhanced from past years and with state of the art TMIC (Terahertz Monolithic Integrated Circuits) offering increased cut-off frequencies (>1 THz) of HEMT / HBT transistors, these applications have become even more feasible and can now be integrated onto a single chip for low cost and compact production. The work carried out in this thesis mainly deals with the development of passive structures such as transmission lines, antenna, couplers and power dividers, which are compatible to available TMIC processes using GaN on low resistivity silicon as a substrate. Techniques to reduce ohmic contact resistance for GaN HEMT technology was also investigated. To reduce losses caused by the substrate and to enhance performance of the integrated antenna at THz frequencies, passive structures were shielded using silicon nitride and metal, in addition to a layer of low dielectric material. Transmission lines were designed with operational frequencies up to 1 THz, in order to demonstrate losses presented by several dielectric mediums- air, BCB (Benzocyclobutene) and SiO2 (Silicon-dioxide). BCB and SiO2 were also investigated to evaluate antenna performance. For this, various types of antenna were designed - rectangular, circular, three variants of stack antenna (double rectangular, double circular, rectangular-circular), array antenna and stack array antenna. These designs were studied at two different frequencies, 300 and 650 GHz. Both simulated and measured results are presented, which show the importance of using low dielectric materials at THz frequencies. Other passive structures, such as couplers and power dividers were designed using the shielding technique mentioned above. Here, four different hybrid junction couplers (branch line, cascaded branch line, rat race, curved rat race) and one power divider (Wilkinson) were designed at three frequencies: 90, 300, and 650 GHz. The results presented by both antenna and couplers showed the viability of the shielding technique used. The optimisation of ohmic contact formation on AlGaN/GaN layers on LR Si has been studied by way of etching into the substrate under metal contacts. This investigation compared various etch patterns to standard, unetched, contacts. The depth of these patterns was varied to be above and below the substrates conductive channel and Ti/Al/Ni/Au metal schemes was used. A contact resistance below 0.3 Ω.mm was achieved using a grid etch pattern

RF and microwave oscillator design using p-HEMT transistor

This paper presents a systematic approach to designing negative-resistance and Colpitts oscillators using p-HEMT transistor. Various models such as, common source and common gate configuration in negative-resistance oscillators, common source series feedback in Colpitts oscillator is selected to analyze the output power and stability presented by the p-HEMT transistor. These oscillators are designed at 2.45 GHz frequency for which we find application in Bluetooth and Wi-Fi. In this paper, these designs are studied and tested, with their results analyzed below. Further, study proved that the Colpitts oscillator designed gave more output power and stability than the negativeresistance oscillators

Design and performance comparison of various terahertz microstrip antennas on GaN-on-low resistivity silicon substrates for TMIC

In this paper we demonstrate various configurations of THz microstrip antenna on GaN-on low resistivity silicon substrates (ρ <; 40 Ω.cm). To reduce the losses caused by the substrate and to enhance the antenna performance, the driven patch is shielded by a ground plane and silicon nitride, with BCB as the inset layer between them. Second patch (elevated patch) is suspended in air using gold posts, which makes the design stack configuration. Here, study of various design performances has been represented by changing the shape of the antenna between rectangular and circular, optimising the BCB and stack height and evaluating performance of stack using air and BCB as dielectric. Better fabricated performance was obtained when the patch was elevated in air and by using rectangular-circular stack configuration with BCB and elevation height of 5 μm. 3D EM model showed directivity, gain, and radiation efficiency as high as 8.3 dB, 3.4 dB, and 32 % respectively, a significant improvement over single or stack configuration antenna. Better simulated gain (6.7 dB) was obtained with the BCB height of 30 μm using a single antenna and highest gain and directivity (7.5 dB and 8.8 dB respectively) for stack antenna of height 15 μm. To the authors' knowledge this is the first time such a study has been carried out at Terahertz frequency and this developed technology is suitable for high performance III-V material on low resistivity/high dielectric substrates