Enhancing GaN MMIC Design Verification Through Highly Reproducible On-Wafer Measurements

[Editor's Note] The Electronics and Telecommunications Research Institute (ETRI) has built an evaluation platform for GaN MMIC by utilizing Anritsu vector network analyzers (VNA). This platform enables consistent design verification by supporting highly reproducible measurements across the millimeter-wave and sub-terahertz (sub-THz) bands.

■ Overview

The Electronics and Telecommunications Research Institute (ETRI) is a leading domestic research institute in the fields of information and communications technology (ICT), electronics, and semiconductors. ETRI conducts research on compound semiconductor technology for millimeter-wave and sub-terahertz (sub-THz) applications and next-generation communication technologies.

The development of GaN MMIC-based high-frequency devices requires broadband characterization evaluation that extends beyond the operating frequency band. To increase design accuracy and performance predictability, evaluation of harmonic frequency bands is also important. For this purpose, on-wafer measurements are widely utilized. However, in the millimeter-wave and sub-terahertz bands, measurement results are highly sensitive to probe contact conditions and the effects of the measurement system, making it difficult to maintain measurement reproducibility and data consistency. As operating frequencies continue to increase, the importance of an evaluation platform that can secure accurate correlation between simulation results and measurement data is growing.

To address these challenges, ETRI introduced the Anritsu VectorStar™ ME7838G broadband vector network analyzer, which supports single-sweep measurements up to 220 GHz. Using a single measurement platform, ETRI has established an on-wafer evaluation platform that enables device characterization from millimeter-wave to sub-terahertz bands under consistent test conditions.

This article introduces the challenges of on-wafer measurements in high-frequency device development, the evaluation platform established by ETRI, and the contributions this platform makes to GaN MMIC design verification.

■ Challenges in High-Frequency On-Wafer Characterization Evaluation

As device operating frequencies expand into the millimeter-wave and sub-terahertz bands, it becomes increasingly difficult to secure consistent measurement results.

In on-wafer measurements, minor differences in probe contact or alignment, impedance discontinuities, and parasitic effects can directly influence S-parameter results. This can make it difficult to obtain consistent results even from identical devices. Such variations can also hinder correlation between simulation results and measurement data.

In frequency bands above 100 GHz, the effects of reference-plane definition and probe contact reproducibility become more pronounced. Therefore, minimizing measurement variation becomes a key challenge in device characterization evaluation. This requires broadband measurements under strictly controlled test conditions.

■ Building a Broadband On-Wafer Evaluation Platform

To address these challenges, ETRI introduced the Anritsu VectorStar™ ME7838G broadband vector network analyzer.

The ME7838G supports single-sweep measurements up to 220 GHz on a single measurement platform, eliminating the need to switch measurement systems between frequency bands. This enables device characterization from millimeter-wave to sub-terahertz bands under consistent test conditions, and comparison and analysis of measurement data becomes more convenient.

In addition, this system supports advanced calibration techniques and is compatible with industry-standard measurement environments.

Furthermore, through 4-port measurement, differential S-parameter analysis, and TDR functionality, the characterization evaluation scope can be expanded beyond individual devices to include packages and interconnect structures. These capabilities allow evaluation of both devices and their connected interconnect structures on the same platform.

■ Evaluation Platform for Reliable Design Verification

Following the introduction of the ME7838G, ETRI established calibration protocols, applied de-embedding techniques, and standardized measurement conditions and procedures. Through these efforts, reproducible measurement data under consistent test conditions can now be secured regardless of the operator or measurement session.

■ Measurement Data for More Reliable Design Verification

High-frequency device design relies on comparison between simulation results and measurement data to improve models and optimize design parameters. When large variations exist in measurement data, it becomes difficult to determine whether the difference originates from the device itself or from measurement conditions.

The evaluation platform established by ETRI provides highly reproducible measurement data, enabling more accurate correlation between simulation results and measurement data. Through this, the accuracy of device performance characterization and model verification is improved.

■ Broadband Evaluation for More Efficient Design and Analysis

The ME7838G enables characterization evaluation from millimeter-wave to sub-terahertz bands on a single platform.

With the elimination of the need to switch measurement systems between frequency bands, comparison and analysis of acquired data becomes more convenient. 4-port measurement, differential S-parameter analysis, and TDR functionality expand the evaluation scope beyond individual devices to include packages and interconnect structures.

Accordingly, design verification, characterization evaluation, and analysis can be performed on a common platform.

■ For Future High-Frequency Device Development

Research and development for 6G and next-generation satellite communications is expanding into frequency regions beyond the millimeter-wave band. Accordingly, the importance of measurement data that can accurately correlate with simulation results is increasing.

The evaluation platform established by ETRI can be applied not only to current GaN MMIC characterization but also to future device development in the millimeter-wave and sub-terahertz bands.

As development shifts to higher frequency bands, this platform provides the measurement capabilities needed to verify design results throughout the entire development cycle.

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