Modeling, Design and Fabrication of Miniaturized, High Performance and Integrated Passive Components for 5G and mm-Wave Applications

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Ali, Muhammad
Tummala, Rao R.
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The objective of this research is to model, design, fabricate and characterize integrated passive components for 5G and mm-wave applications on advanced substrates such as ultra-thin laminated glass. These passive components include filters, power dividers, antenna arrays, diplexers and their integrated versions. The target frequency range of these passive components are the 5G new radio (NR) bands: 28 and 39 GHz and the bands of interest are in the Frequency range 2 (FR2) as defined by 3GPP: n257, n258 and n260. Both circuit-level simulation and full-wave electromagnetic (EM) simulation are employed to design these passive components for 5G and mm-wave applications. Glass substrate is emerging as an ideal candidate to realize mm-wave technologies. This is mainly because of its low loss, superior dimensional stability, ability to form fine-pitch through-vias, stability to temperature and humidity, matched coefficient of thermal expansion (CTE) with devices, and availability in large-area, low-cost panels. Passive components such as filters, power dividers, antenna arrays and diplexers can benefit from the aforementioned advantages of glass substrates along with precision redistribution layers (RDL) to enable miniaturization. These components can be designed and fabricated to achieve dimensions of less than twice the free space wavelength corresponding to the operating frequency and can be integrated in electronic packages such as RF front-end modules (FEM), as integrated passive devices (IPD). Precision linespace capabilities also empower the designer to opt for higher-impedance structures for filters, reducing the footprint. The demonstrated filters exhibit low loss, low standing wave ratio (VSWR) and high selectivity. Similarly, the power dividers are designed and fabricated in two-, three- and four-way equal-split ratios, and they can used in low-power on-device antenna-to-chip chain to provide power to corresponding antenna array configurations. Moreover, they utilize minimal matching techniques to efficiently cover the entire 28 GHz 5G band and exhibit low VSWR as well as minimal phase shift variation between the output ports. Yagi-Uda antennas are used to demonstrate antenna arrays utilizing the designed power dividers. The diplexers are designed using the filters for 5G NR bands and they exhibit low insertion loss, high stopband rejection, high selectivity, ease-of-integration in packages as well as small footprint. The diplexers are also integrated with couplers to emulate a power detection and control circuitry in a modern RF power amplifier (PA) FEM. The coupler covers the entire 5G mm-wave bands: from 24.25 GHz to 40 GHz. Using this integrated passive component block as an example, a system performance analysis using a co-simulation technique is presented to quantify the distortion in amplitude and phase produced by the fabricated passive component block. Moreover, the scalability of this approach to compare similar passive components based on their specifications and evaluation of their signature using a system-level performance metric such as error vector magnitude (EVM) is discussed. For the fabrication of these passive components, semi-additive patterning (SAP) process is utilized using a glass substrate as a core. Unlike subtractive patterning process, where a thick copper foil is etched off from the undesired areas to form circuit patterns, SAP yields better dimensional and copper sidewall control. Finally, dimensional analysis is performed to find the discrepancy between desired and obtained feature dimensions. All of the demonstrated passive components have a footprint which is a fraction of the unit free-space wavelength of their operating frequencies. It is observed that the feature dimensions do not vary by more than 5%, resulting in an excellent model-to-hardware correlation of fabricated passive components. Thus, the superiority of glass based IPDs for RF FEMs is demonstrated.
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