Future telecommunication systems are set to revolutionize connectivity, driven by advancements in technologies like 6 G, artificial intelligence, and the Internet of Things (IoT). However, this evolution brings significant challenges. Traditional silicon-based transistors struggle to meet demands for efficiency and power handling. Indium Phosphide (InP)-based Double Heterojunction Bipolar Transistors (DHBTs) deliver excellent performance at sub-mm-wave frequencies while minimizing power loss and heat generation. Additionally, achieving reliable large-signal performance in high-frequency applications requires accurate large-signal modelling and advanced testing techniques, such as load-pull measurements. In this paper, we report the comparison between two InP/GaAsSb Double Heterojunction Bipolar Transistors (DHBTs) with different collector epitaxial designs in terms of their small- and large-signal performance. The effect of the epitaxial design on the small- and large-signal performances is investigated and load-pull measurements in G-band are performed to assess the great power-handling and efficiency capabilities of the InP/GaAsSb DHBT technology. For both of the designs, THz cut-off frequencies with Power-Added Efficiency (PAE) > 30% are achieved. Moreover, the value of PAE = 39.2% reached in G-band represents the highest among any technology. Finally, the two different epitaxial designs are thermally characterized to investigate the effect of different layers on the thermal and RF-performances.

In this paper, we consider the possibilities of the stimulated infra-red thermography for local metallic sample thermal characterization. At first we introduce the measurement principle, which is based on the local measurement of the thermal diffusivity parameter. Then, using simulations, we demonstrate the feasibility of the method. We then present the experimental device implemented for the study. Finally, we show that this approach allows a good estimation of the thermal diffusivity of a metal sample.

Dispersions containing 1 mg/mL of several carbon nanomaterials were used to deposit films containing 1 to 20 layers. The electrical properties of the composite films were characterized via impedance spectroscopy along two directions: in-plane on the film topmost surface and also through the thickness. It was found that carbon black nanoparticles never achieved full in-plane interconnection while the multiwalled carbon nanotube (MWNT) and single-walled carbon nanotube were already percolated at one layer. Graphite flakes showed a complete percolation curve that allowed its resistance to change by 6–7 orders of magnitude. The differences in the microstructure, electrical response, and thermal decomposition behavior of these carbon nanomaterial–paper substrate films were explained by detailed equivalent circuit analysis of the impedance spectra. Interpretation was supplemented by scanning electron microscopy images and thermal analysis via Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA). Thru-plane electrical properties were for the most part similar, although only films with short MWNT showed a clearly infiltrated network structure.