Substrate-attachment voids are critical defects in high-reliability RF assemblies, yet their quantitative impact on passive circuit performance is underreported. This study investigates the correlation between AuSn solder voiding and the RF performance (VSWR and insertion loss) of miniature hybrid semi-monolithic microstrip lines and bandpass filters across C through Ka bands. Full-wave 3D FEM (Ansys HFSS) and MoM planar EM (Keysight ADS Momentum) simulations were validated experimentally for microstrip-line and bandpass-filter test vehicles, respectively. Results show that even substantial voiding (up to 44.9%) causes a negligible worst-case insertion loss deviation of 0.33 dB. Reliability testing via a 144-hour thermal bake at 125 °C confirmed high electrical stability, with minor fluctuations tied to stress relaxation. These findings advocate distinguishing active-device thermal paths from passive ground paths to avoid unnecessary rework and reduce manufacturing costs.

Robust Air-bridge structures are essential for high-performance GaN high-electron-mobility transistors (HEMTs), particularly when implementing multi-finger architectures, yet fabrication complexities frequently compromise yield and structural integrity. This work presents an optimized arc-shaped air-bridge fabrication method that employs a process sequence of two-step mask-aligner photolithography, thermal treatment, DC magnetron sputtering (for seed-layer deposition), electroplating, and lift-off, with fine-tuned resist thickness, curvature control, seed-layer thickness, and plating parameters. Applying this technique to multi-finger GaN HEMTs, with configurations featuring up to eight fingers, all fabricated air bridges remained intact after lift-off across multiple (>20) samples. Field Emission Scanning Electron Microscope (FE-SEM) inspection confirms precise lift-off and well-defined structural formation. These results demonstrate a high-yield arc-shaped air bridge fabrication methodology in GaN HEMTs with >11 times arc height to length ratio, offering enhanced structural robustness and enabling multi-finger configuration.

This article is focused on automatic eutectic, die and wire bonding process parameter optimizations respectively for precision micro-assembly of multi-chip modules (MCM) over multilayer Low Temperature Co-Fired Ceramic (LTCC) substrate. Basically, this article focuses on various aspects of process optimization including, multi-stage brazing, controlled epoxy dispensing, automatic die and wire bonding respectively for mass production of space grade modules. Statistical process control (SPC) is carried out for wire bonder to narrow down the statistical variation window. Here, epoxy dispense process has been analysed thoroughly and a new equation is proposed to predict volume flow. Parameter optimization of temperature profile (TP) for auto eutectic bonding (using AuSn preform) is discussed in this article. Statistical analysis is carried out to estimate the process capability in brief. Assembled samples have passed critical tests and the data for same is presented.

This paper presents the design and implementation of a dual channel loss-compensated filter bank utilizing mid-loss Transversely Coupled Resonator Filters (TCRFs). It addresses the challenges encountered in achieving optimal return loss and passband flatness within the filter bank. The configuration includes a two-way power divider at the input, followed by two narrowband TCRFs, power combiner and concludes with output amplifier. A lumped component Wilkinson power divider and combiner, constructed on an FR4 substrate, has been designed for this filter bank. The TCRFs employed offer a highly selective filtering response, characterized by a fractional bandwidth of less than 0.1% and significant out-of-band rejection, with bandwidth requirements being consistent across both filters.

Micro-acoustic radio frequency (RF) filters have become the technology of choice for precise frequency band selection in modern mobile communication equipment. Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) are the two variants of this technology that fulfil the filtering requirements up to sub- 6 GHz bands. SAW filters are easier to fabricate, because of lesser number of lithographic mask layer requirements than BAW filters. Quartz and Lithium Tantalate are the most commonly used piezoelectric substrates for SAW filter fabrication. To reduce their form factor, a lot of research has been carried out for developing processes for the Wafer Level Packaging (WLP) of SAW filters. However, most of these efforts, have been directed towards WLP of SAW filters made on Lithium Tantalate. This paper, for the first time, discusses unit processes related to WLP of SAW filters fabricated on Quartz, which is a difficult material to process because of its hardness and chemical inertness. Processes pertaining to deep via etching, via filling and planarization, wafer thinning and polishing, wafer bonding and dicing of bonded wafers are discussed. Challenges in each of these unit process steps are highlighted and ways to overcome them are discussed along with practical results.

Low Temperature Co-fired Ceramic (LTCC) technology has emerged as an extremely useful Multi-Chip-Module (MCM) platform for the heterogeneous integration of multi-technology Monolithic Microwave Integrated Circuits (MMICs). However, the fabrication of LTCC-based MCMs operating at microwave and millimetre-wave frequencies presents a range of complex challenges. Foremost among them, is the ability to have tight control over high frequency transmission line impedances by reducing dimensional tolerances. Controlling the cavity dimensions, that house the bare dies, is also critical, as the same can impact bond wire length assumptions. Planarity of the cavity tops is key to achieving hermeticity. Module thickness at high frequencies, can be thinner than that at lower frequencies. Achieving good flexural strength ensures that these thin modules survive downstream die assembly processes. Dicing of thin high frequency ceramic modules presents additional challenges. This paper systematically investigates these key challenges and presents practical solutions to address them. The proposed methodologies include optimized Vertical Interconnect Access (VIA) punching and filling techniques, planar transmission line dimensional control strategies, cavity structure enhancement methods, sintering profile optimization, and a modified dicing approach to mitigate structural defects. The results support the advancement of robust and high-performance LTCC-based packaging solutions for next-generation RF and microwave systems

Design and implementation of a SIW-based five-pole wideband bandpass filter (BPF) in low-temperature co-fired ceramic (LTCC) technology have been completed. In-depth discussion is given of the issues with LTCC technology for designing high frequency BPF, such as in the K and Ka bands. The K-band filter is implemented at 20.2 GHz with a fractional bandwidth of 975 MHz. A back-to-back CPW-to-SIW transition is implemented into the filter for measuring purposes. At 20.2 GHz, which is the passband center frequency, the transition integrated filter's measured passband IL is 1.58 dB. When the transition losses are taken into account, the passband IL is similar to that of waveguide filters, but much lighter and smaller. An outstanding out-of-band response is offered by the filter, with rejection being greater than 30 dB below 17.95 GHz and above 22.95 GHz over the passband.

This paper presents the design and implementation of a high performance Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) based Low Noise Amplifier (LNA) for space-borne X-band radar applications, fabricated using the UMS foundry's 0.25 mu m GaN-on-SiC process. The LNA demonstrates exceptional performance metrics, achieving a noise figure (NF) of less than 1.6 dB, gain greater than 18.5 dB and gain flatness of +/- 0.25 dB across the frequency range of 9 to 10 GHz. The high linearity of GaN LNAs is exhibited through a P1dB of 20.5 dBm. The entire design is implemented in a compact die size of 2.46mm X 1.79mm. A total of 27 dies were fabricated and measured, and the performance results were consistent across all samples, affirming the reproducibility and high yield of the design. This combination of low noise figure, high gain, good gain flatness, high linearity and compact chip size, which are otherwise contradictory requirements, represents the best-in-class performance reported to date for GaN LNAs operating in the specified frequency range.

A high-quality In0.17Al0.83N/GaN heterostructure with a record high mobility of 11370 cm(2) V-1 s(-1) is achieved at 2 K using the metal oxide chemical vapor deposition (MOCVD) technique, where enhanced Shubnikov-de Haas (SdH) oscillations of two-dimensional electron gas (2DEG) are observed at low temperatures up to 20 K. In this study, we explore the quantum transport properties induced by 2DEG using perpendicular magnetic (B-perpendicular to) field strengths up to 14 T. Excellent crystalline and structural quality of the ultrathin InAlN/GaN heterostructure was revealed by high resolution X-ray diffraction (HRXRD) and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). From the temperature-dependent oscillation amplitude, we have derived effective mass m* approximate to 0.247m(e). Furthermore, the dominance of small-angle scattering in the 2DEG channel is evidenced by a quantum lifetime (tau(q)) to Hall transport lifetime (tau(t)) ratio of less than unity (tau(q)/tau(t) << 1). These findings offer a robust foundation for exploration into fundamental physics and emergent phenomena in quantum transport within the InAlN/GaN 2DEG, leading to better suitability and a way forward to high power-high frequency GaN high electron mobility transistor (HEMT) development.

In Low Temperature Co-Fired Ceramic (LTCC) technology, lamination of green ceramic tapes is one of the most pivotal steps. Lamination process, if not properly optimized, can affect the final strength as well as integrity of three-dimensional (3-D) structures and printed patterns in LTCC. In this work, we have conducted lamination experiments using Ferro A6M-E LTCC tapes and addressed several challenges. Optimization of lamination process parameters was done with the help of Design of Experiments (DOE) to arrive at a lamination density of 1.80 gms/cm 3 , sintered density of 2.5 gms/cm 3 and post fired flexural strength of 177 MPa. The effect of lamination pressure on density and shrinkage is studied. Prevention of cavity distortion is proposed through precise design and use of silicone-based inserts. Occurrence of conductor pattern cracks accruing from the use of silicone inserts is eliminated through the use of Poly-Eutherene sheets. Inspection, post micro-sectioning of laminated tapes and 3-D X-ray microscopy were used for characterization at various experimental stages.

This work presents a model for GaN HEMT devices using a broad width-scaling approach, considering the geometrical changes in threshold voltage, mobility and drain-induced barrier lowering (DIBL). To achieve the best performance in circuit design, a weighted optimization of the device periphery is required. In this work, we demonstrate a gate-width scalable model for DC-IV and RF characteristics up to 43.5 GHz. A single SPICE model card for the three devices of different gate widths $((W\times NF)-200\times 10\mu m, 220\times 10\mu m$ and $250 \times 10 \mu m)$ is generated using the proposed model implemented in the ASM-HEMT framework.

Low Temperature Co-fired Ceramic (LTCC) is the technology of choice for realization of high frequency Multi-Chip-Modules (MCMs). Transitions are an integral part of these MCMs providing an effective means of connecting two different types of transmission lines. This paper discusses the design and fabrication of a DC-Ku band Co-planar Waveguide with Ground (CPWG) to Stripline (SL) transition in LTCC technology. The deleterious effects of standard fabrication tolerances on transition performance are presented. Changes in screen-printing process parameters are subsequently proposed to improve achievable tolerances and thereby satisfy target specifications.

Gallium-Nitride High Electron Mobility Transistors (GaN-HEMTs) are susceptible to trapping effects, signifi-cantly degrading device performance. The degradation can be seen in the current-voltage characteristics and also manifests in the form of a shift in the dynamic on-resistance and threshold voltage. In this paper, we present pulsed characterization and empirical modeling of a 250 x 10 mu m RF GaN HEMT device. To study the impact of drain-induced trapping, pulse I-V characterization is performed at a fixed quiescent gate voltage of -7 V with varying drain quiescent voltage. An empirical RC network approach is proposed to accurately model the trapping in the device. The model effectively captures the impact of trapping and takes into account the self-limiting behavior of traps. The model is implemented in Verilog-A within the Advanced SPICE Model for High Electron Mobility Transistors (ASM-HEMT) framework. Validation of the model is done with six different quiescent conditions of pulse measurement with on-state drain bias varying from 0 V to 20 V.

Surface acoustic wave (SAW) filters provide an efficient and compact means of narrow band channelization in Satellite Communication payloads. The efficiency of this narrow band filtering is critically dependent on temperature and fabrication induced frequency shifts in the filter centre frequency. The temperature induced drifts can be minimized by the choice of a suitable piezoelectric substrate. However, tolerances associated with the fabrication processes, especially the thin film metallization thickness, can have a deleterious effect on the repeatability and accuracy of the centre frequency. Here, we present results demonstrating a reliable and repeatable fabrication process for SAW narrow band pass filter (BPF) development. We have achieved precise thickness tolerance of 1% for NiCr/Al metallization, using e-beam evaporation. The thickness characterization is conducted using stylus profilometer and X-ray reflectivity (XRR) measurement, using high resolution x-ray diffraction (HRXRD) system. We have showcased that a change of just ±120 Å in the metal thickness, about the nominal value, leads to a deviation of approximately ∓ 146 kHz in the centre frequency of a UHF SAW filter. Process details to minimize the metallization thickness tolerance are discussed and the ensuing benefits in achieving the desired centre frequency is presented through fabrication and measurement.

This paper presents the design and realization of a X-Band GaN HEMT based high-power Single Pole Double Throw (SPDT) switch for a space based phased array RADAR front ends. The switch is designed using the space qualified 0.25um GaN-on-SiC process of United Monolithic Semiconductors. The switch is designed using series-shunt configuration and its performance is measured and evaluated over the frequency band of 9 GHz – 11 GHz. and fits in a size of 1.3mm X 1.79mm. The switch exhibits state-of-art performance with an insertion loss of less than 0.85dB, isolation> 25 dB and on-state power handling capability of better than 42 dBm at 0.5 dB insertion loss compression point. The input return loss is better than 20dB and the output return loss of both the on and off states are better than 17dB over the entire bandwidth.

A SIW based five-pole narrowband bandpass filter (BPF) has been designed and implemented in low-temperature co-fired ceramic (LTCC) technology. The problems associated with a narrowband BPF in LTCC technology are discussed in detail. An X-band filter with a fractional bandwidth of 230 MHz is implemented at 11.575 GHz. The filter is integrated with a back-to-back CPW-to-SIW transition for measurement purposes. The measured passband insertion loss of the transition integrated filter at the passband center frequency of 11.38 GHz is 3.194 dB. The filter provides an excellent out-of-band response, rejection being more than 30 dB below 11.13 GHz and above 11.63 GHz the passband.

In this paper, we present a production-ready DC, small- and large-signal model for large-periphery GaN HEMTs. The Device Under Test (DUT) is a 200 μm × 10 HEMT based on a GaN-on-SiC stack. DC measurements were performed on the device up to a drain bias of 30 V – typical of conventional amplifier applications. S-Parameter measurements were performed up to 43.5 GHz to account for most 5G New Radio bands. A high-pass feedback network between the gate and drain port was used to obtain a better fit for the output RF characteristics – leading to better matching network design.

Impedance Element RF SAW filters have come to be the mainstay of all modern wireless receivers, including cell phones. The basic performance of these filters is governed by the acoustic response of the constituent resonators. However, there are a host of other secondary factors, viz. impact of resonator pads, interconnecting lines in the filter, grounding connections, housing package parasitics and mounting board layout, that play a significant role in determining the overall response of the filter. This paper, for the first time, presents a comprehensive discussion on the effect of these secondary factors on the final filter response. These factors, when accounted for, enable the accurate design of Impedance Element SAW factors. The findings are exemplified by means of design of a L1 band GPS SAW filter.

In principle BB84 protocol supports secure quantum communication by assuming transmitter and receiver devices to be ideal. However, practically it is very challenging to build an ideal single photon source and detector. These imperfections in practical devices (i.e., wavelength mismatch, full width at half maximum (FWHM) pulse width mismatch and different arrival times of photon) leads to side channel attacks. In this work, we have analyzed the wavelength mismatch issue associated with four laser diode based practical BB84 transmitter. An asymptotically achievable rate of extraction of secure key (also known as key generation rate) is estimated from side-channel leakage calculation between transmitter (Alice) and adversary (Eve).

High power operation of AlGaN/GaN HEMTs leads to a high channel temperature and heat dissipation issues which severely degrade the device reliability and power performance. Self-heating effects cannot be ignored when estimating the power performance of HEMTs, and have been an active area of research for a long time [1], [2]. Several methods used for thermal resistance measurements have been proposed in the literature, including techniques to generate comprehensive temperature profiles like infrared thermography, high-resolution Raman thermography [3], [4], etc. These thermography approaches are not always practical as they frequently require specific device samples and prohibitively expensive laboratory equipment. Pulsed measurements enable the determination of thermal resistance across a wide range of ambient temperatures [5], [6] and have been used in this work. The industry standard compact models [7]–[9] account for the self-heating effect using a thermal circuit approach involving parallel RC circuits to represent thermal time constants as shown in Fig 2(c). However, these self-heating models are valid for a narrow range of geometries and are not scalable in the truest sense (as shown in Fig. 1(a)). In this paper we presents a complete SPICE model capable of emulating the geometry-dependent self-heating behavior using a single model card.