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INEMI PROJECT REPORTS BENCHMARK NEW AND EMERGING TEST AND MEASUREMENT METHODOLOGIES FOR 5G/MMWAVE MATERIALS

The transition of 4G LTE based communication to 5G/mmWave-based protocols is expected to drive disruptive changes in the communications industry. For mmWave product designers it is critical to start with correct electrical material models. Fast, easy and accurate methods for characterizing materials at mmWave frequencies are critical for enabling functional designs on the first cycle. To date, however, there is a lack of standard reference materials and characterization test methods for materials at mmWaves.

iNEMI members organized the 5G/mmWave Materials Assessment and Characterization project to address this industry challenge collaboratively. The project is developing guidelines and best practices for a standardized measurement and test methodology that can be shared with industry and relevant standards organizations. The initial focus is to benchmark currently available — as well as emerging — test methods and provide pro/con analyses, identify any gaps for extending test methods to 5G/mmWave frequencies, and develop reliable reference standard materials for setup and calibration.

There are currently 26 members in this project, spanning the entire communications industry value chain. The team has completed significant work to date and has published two reports that are now available to iNEMI members. The reports are summarized in this article.

Report 1: Benchmark current industry best practices for low loss measurements

Each new material for mmWave 5G applications requires careful consideration to determine the best measurement methodology, fixturing requirements, sample fabrication methods and test instrumentation. There are dozens of different methodologies that could be used, but which to choose is often not obvious. Report 1 focuses on the following measurement techniques and their merits: rectangular cavity resonator (RCR), split-post dielectric resonator (SPDR), split cylinder resonator (SCR), balanced circular disk resonator (SCR), and Fabry-Perot open resonator (FPOR). Figure 1 maps these available techniques against frequency.

5G Fig 1-1

Figure 1. Selected measurement capabilities versus frequency.

The report also discusses standard reference materials, outlines best practices and identifies key sources of uncertainty. Significant focus is given to the importance of reference standard material and the need for national metrology institutes, such as NIST, to develop and supply new standards reference materials to the 5G sector. The impact of the existing traceability gap is shown in Figure 2. Proposed standard reference materials considered by the project team are shown in Table 1.
 

5G Fig 2

Figure 2. Traceability gap for complex permittivity of 5G materials.

 

Table 1. Proposed Standard Reference Materials

Material Type

Approximate Thickness

Structure

Approx. Er,Tand

Important Notes

Cyclo olefin polymer (COP/ Zeonex®)

100 um

Isotropic, homogeneous

2.3, 5e-4

Can degrade with finger oil - avoid handling unless using gloves

Cross linked polystyrene (Rexolite®)

700 um

Isotropic,

homogeneous

2.534, 4.6e-4

Easy to machine, difficult to make flat, stable with temperature and humidity

PTFE / Teflon®

 

Isotropic, homogeneous

2.1, 2e-4

Easy to machine

Fused silica

500 um

 

3.8 / 1e-4

Easy to machine, preferred by project team

Sapphire

365 um

Anisotropic (c-plane)

9.4 / 11.6, 5e-5

Hard to machine

Alumina

100 um

Isotropic, homogeneous

9.8, 1e-4

Easy to machine, preferred by project team

 

Report 2: Benchmark emerging industry best practices for low loss measurements

The second report discusses emerging measurement techniques that will become increasingly relevant as new spectrum auctions open up additional communication bands above 5G/mmWaves. These techniques are in the research and development stages and can be commercially deployed for next generation material characterization, especially at frequencies >100GHz. Discussions include two separate wafer-level measurement techniques pioneered at Georgia Institute of Technology and NIST, respectively. It also includes information about time domain spectroscopy-based measurement techniques extending the frequency ranges to higher than 100 GHz to 6G and next generation communication technologies. It is important for industry groups to monitor the new research being pioneered at universities and research institutions.

Ongoing work

The project team will be spending the next several quarters conducting extensive round robin measurements, spread amongst volunteer test sites globally, to assess critical concerns of sensitivity and repeatability of the standard reference materials and provide recommendations to the industry. The project team would welcome new participants who are interested in collaborating and contributing to these developments. If interested in getting involved with the project, contact Urmi Ray (urmi.ray@inemi.org).

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