The advancement of wireless communications technologies has had a profound impact on mankind’s way of life, reducing the constraints of both time and space also bringing about many conveniences. In terms of mobile communication development history, the research and development of 6th Generation Mobile Communication/6th Generation Wireless Systems (6G) has already begun. Considered an extension of the current 5G technology, it is expected to see commercialization by 2030. This will lead the way for the upgrade from the 5G mobile Internet of Things to the 6G Internet of Everything.
The goal of 6G is to provide a highly reliable, low-latency Low Earth Orbits (LEO) global communications network with high-speed transmissions (100Gbps~1Tbps) in the ultra-high frequency band (~1THz). It will be able to overcome the limitations that 5G faces in remote areas, oceans and deserts and improve network performance to achieve greater bandwidth, lower latency and higher connection densities to create an intelligently connected world that fully integrates the virtual and the real.
6G technology is an important focus of technological development in advanced countries, and semiconductor materials are bound to play in important role in key 6G components, such as power amplifiers, array antennae, radio frequency modules, high frequency communication chips and more. RF components made from III-V materials such as indium phosphide (InP) have the potential to 100GHz, which in the 6G frequency band. At a conference at the end of 2020, Interuniversity Microelectronics Centre (imec) presented its development of InP/CMOS heterogeneous stacking technology for 6G RF components.
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Indium phosphide, a second generation semiconductor with high frequency characteristics superior to those of gallium arsenide (GaAs) and silicon germanium (SiGe), will be the key to the development of 6G technology! |
InP Heterojunction Bipolar Transistors (HBTs) have excellent high-speed performance and high breakdown voltages and can be used in future fiber-optic communications systems. In fact, they are already being used today in most ICs that operate at speeds of over 100 Gbit/s. InP HBTs are often used in Laser Diodes (LD) and Photodiodes as optical receivers. The typical InP HBT structure uses InP/InGaAs/InP as an Emitter/Base/Collector. Generally, an emitter width greater than 1 um can meet the output power required for the 5G millimeter wave.
The InP HBT is considered one of the most promising technologies for the enabling of THz operations and the continued setting of new records for speed. Examples include the InP/InGaAs Pseudomorphic Heterojunction Bipolar Transistor (PHBT) being developed by the Snodgrass research team. Its structure uses a 12.5nm Base and a 55nm Collector to achieve a Transit Frequency (fT) of up to 845GHz. The methods for enhancing the performance of HBTs being researched include continuing to scale down the components (thinning the base and collector layers), reducing emitter contact resistivity, and reducing the emitter and collector junction widths, etc..
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Laser Diodes (LD) are made of semiconductor materials. Their conductivity can be changed by introducing different impurities into the lattice. They are often used in optical fiber communication components. Below, we will describe each of the materials analysis techniques that can be used for these materials. |
With its atomic-level resolution, the Transmission Electron Microscope (TEM) is able to observe the hierarchical structure of semiconductor components. The principle is to project a high-energy electron beam onto an ultra-thin sample to generate a solid-angle scattering image. This is suitable for observing the fine structure of a sample. Note that optical fiber communications components need to undergo TEM sample preparation before they are suitable for TEM imaging and analysis. Figure 1 is a TEM image of an LD under progressive magnification. It displays the position and number of P and N-type doped layers and Multiple Quantum Wells (MQW). Through TEM image comparison, it can be seen that adopting the stacking method of heterogeneous structures for MQWs can increase the probability of LD radiative recombination.
Figure 1. TEM Image of the LD |
Secondary Ion Mass Spectrometry (SIMS) is suitable for analyzing the structure of thin films, the concentration of doping elements and the trace contamination in processes. Process problems can be understood through the examination of changes in element concentrations and the corresponding epitaxial layers. The principle behind SIMS is to generate secondary ions by bombarding the surface of the sample with energetic incident ions. After acceleration, the ions enter the secondary ion mass spectrometry system, which uses deflection by electric and magnetic fields to separate ions according to the mass-to-charge ratio in order to complete component analysis. Secondary ion intensity can be used to determine the concentrations of elements, and the ion bombardment time can be converted into the depth of the impurity distribution.
SIMS has excellent detection limits and can measure element contents in solid materials down to parts per million. Figure 2 is the SIMS analysis diagram of an InP-based InGaAsP MQW LD. The structure is shown to be InP/InGaAsP/InP. The diffusion of Zn, Si and S doping concentrations between different layers affects the performance of the component. In addition, InGaAsP MQW epitaxial layers with nanometer thicknesses can be clearly distinguished.
  Figure 2. SIMS Diagram of an InGaAsP MQW LD |
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Scanning Capacitance Microscopy (SCM) is often used for the analysis of IC components, such as power electronic components, GBT/FRD, triodes, laser diodes, DRAM components, and MOSFETs, as well as for optoelectronic industry applications, such as CMOS Image Sensors, VCSEL, optical communications components and LEDs, etc... SCM can observe two-dimensional doping images and distinguish between N-type and P-type regions, which is very helpful for analyzing failures caused by abnormal doping distributions and reverse engineering. It can also measure the dimensions of various regions, such as doping thickness, Channel Length, Trench doping depth, Source/Drain size and N/P Well interfaces, etc.. SCM analysis technology can make up for the deficiencies of other analysis techniques. For instance, SIMS and Spread Resistance Profiling (SRP) can only show one-dimensional distributions, and it is difficult to control the etching rate when combining SEM with chemical etching and staining analysis, etc.. Figure 3 is the SCM image of an LD cross section. It clearly shows the relative changes in the carrier concentration of the LD structure as well as the distribution of doping activation. |
Figure 3. SCM Image of the LD |
MA-tek has accumulated years of experience in the testing of optical fiber communications components and has already begun to analyze the needs of B5G (Beyond 5G)/6G new materials research and development. MA-tek has cutting-edge analysis equipment and skills. We are committed to supporting research and development in the industry, government and academia and striving to provide even more comprehensive analysis services.
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