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DuPont MCM | Demonstration of high-frequency 5G modules using LTCC



Brian J. Laughlin, Ph.D.




While the infrastructure, devices, and applications of 5G telecommunications are evolving, the need for circuits which operate at the higher frequency millimeter wave (mmWave) bands is clear. High-frequency circuit operation presents many challenges, including the need to create efficient RF signal processing and wireless transmission which can generally be achieved via increased integration that allows shorter communication paths. Also, advanced materials that enable both heterogenous integration of disparate active devices (e.g., Si, GaAs, GaN, and SiC) and passive devices (e.g., SMD, antennae, filters, etc.) while providing stable operation and low losses in a variety of environments are critical performance considerations. DuPont™ GreenTape™ Low-Temperature Co-fired Ceramic (LTCC) tape and silver (Ag) metallization delivers excellent high-frequency performance in designs optimized for high reliability and long life—even in the most challenging environments.



Figure 1: GreenTape™ dielectric constant (Dk) and dielectric loss (Df) measured by a Fabry Perot from 20 to 100 GHz.



As part of an initiative to demonstrate the high performance of GreenTape™ and create a reference design that goes beyond a basic material datasheet, DuPont Microcircuit and Component Materials (MCM) partnered with Dr. Chun-An “Ivan” Lu at the Material and Chemical Research Laboratories (MCL) of the Industrial Technology Research Institute (ITRI) in Taiwan. This joint effort resulted in creating a wireless communication system featuring an Antenna-in-Package (AiP) which integrates a beam steerable antenna array in a Radio Frequency Front-End module (RFFE) operating at 28 GHz. The basis of this demonstration is GreenTape™ ceramic dielectric which has excellent dielectric properties through 100 GHz while maintaining Dk of 7.1 and Df of <0.0010 (see Figure 1). Additionally, GreenTape™ ceramic’s dielectric properties are stable throughout the extreme temperature range (-50°C to 150°C) a deployed radio head may be exposed to (see Figure 2). Using a full suite of high conductivity Ag metallization pastes for ground planes, via fills, signal lines, and solderable pads, a multilayer module can be made using standard LTCC processing† that is co-fired and then can be further processed to surface mount passives, connectors, and active semiconductors.


Figure 2: GreenTape™ dielectric properties measured at 28 GHz in-situ from -50°C to 150°C


An RFFE AiP module was designed to incorporate Anokiwave phasor integrated circuit (IC) chipsets and utilize a 2 x 4 patch antenna array. (Figure 3 shows images of the top and bottom of the LTCC module, an illustration of the fully assembled module, and a schematic of the system architecture.) The module design and prototyping started with the radiating antenna patches, followed by the feedline network and power divider, and, finally, the integration and operation with the phasor IC with all the required passives and connectors.



Figure 3: (top) Images of the LTCC module with the antenna side on the left and the SMD/Connector/IC pad on the right. (middle) Illustration of the multilayer module fully assembled. (bottom) A schematic representation of the AiP RFFE module and system architecture.


The fabricated LTCC device shows excellent agreement between the simulations of the design using the material properties measured previously and the measured performance as shown by the return loss of the antenna elements (Figure 4). The module was evaluated by over-the-air measurements at 28 GHz where the Effective Isotropic Radiated Power (EIRP) of greater than 18 dBm was observed while steering the radiated beam by the array and the phasor ICs over ±35°. Less than 1 part per million error vector magnitude (~0.7 ppm EVM) was observed in a 64-quadrature amplitude modulation (64 QAM) scheme. These results were achieved due to the excellent high-frequency properties of GreenTape™ LTCC material and the highly integrated design of the system.




Figure 4: (top right) Simulated verses measured data for the antenna elements showing excellent agreement. (top left) Antenna array performance over ±35° of beam steering. (bottom) Photograph of the transmitter component and the EVM data showing <1ppm of error.


The AiP demonstration successfully shows how DuPont™ GreenTape™ LTCC can be used to create devices for 5G telecommunications operating in the mmWave regime. After building a software system and components to simulate the signal processing functions, 4K resolution video was transmitted reliably over 10 meters.


Our reference design is analogous to several use cases in the real-world 5G buildout from customer premise equipment (CPE) including:

· small cells installed indoors

· connected factories

· municipal- or provider-owned small cells for coverage in densely populated areas like smart cities or arenas and performance centers

· mmWave base station radio heads


In small and macro cells deployed outdoors, LTCC has unique advantages over organic laminate material platforms due to a significantly greater thermal conductivity of the dielectric which helps with thermal management in milliwatt to >1W operation power. Plus, LTCC is established as a highly reliable material with >200 MPa flexural strength. Unlike other materials, it is hermetic, and therefore impervious to moisture that can degrade performance. The thermal expansion of LTCC is also a close match to critical ICs that are active components in the modules. These data and the reference design are provided to encourage hardware designers to consider how LTCC properties and high-frequency performance can enable devices that provide greater access to 5G mmWave bands. The DuPont team welcomes inquiries from industry players who want to collaborate on antenna applications for GreenTape™.


For more information and to view a short video of this demonstration please visit: https://www.youtube.com/watch?v=gJcwya3HLzs




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