Improving the quality factor of the coplanar waveguide resonator

At a Glance

Metadata	Details
Publication Date	2015-03-27
Journal	Microwave and Optical Technology Letters
Authors	Mohamed Ismaeel Maricar, Ata Khalid, David R. S. Cumming, Christopher H. Oxley
Institutions	University of Glasgow, Durham University
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Q Diamond Resonators

Executive Summary

This analysis leverages the research on enhancing Coplanar Waveguide (CPW) resonator quality factors (Q) through ground plane notching, specifically highlighting the superior performance and miniaturization potential of diamond stub resonators.

Core Achievement: A novel method using a ground plane notch successfully increased the loaded Q-factor of CPW diamond stub resonators by approximately 28%.
Miniaturization Advantage: Diamond stub resonators demonstrated a significant size reduction, occupying 55% less chip area compared to traditional radial stub designs.
Frequency Range: The methodology is validated for high-frequency applications, with characterization performed across the microwave and millimeter-wave spectrum (100 MHz to 110 GHz).
Material Opportunity: While the study used Gallium Arsenide (GaAs), the application demands the ultra-low loss tangent and high thermal conductivity inherent to 6CCVD’s Single Crystal Diamond (SCD) for optimal Q-factor performance and power handling.
Custom Fabrication: The successful implementation relies on precise micro-scale feature definition (25 x 50 µm notches) and thin-film metallization (0.4 µm), capabilities offered by 6CCVD’s advanced processing services.

Technical Specifications

The following hard data points were extracted from the research paper detailing the physical and electrical parameters of the CPW resonators:

Parameter	Value	Unit	Context
Substrate Material Used	Gallium Arsenide (GaAs)	N/A	Semi-insulating, used for fabrication
Substrate Thickness	620	µm	Thickness of the GaAs wafer
Substrate Relative Permittivity (ε_r)	12.9	N/A	Used for ADS simulation
Metallization Thickness (t)	0.4	µm	Thickness of the CPW lines and resonators
CPW Line Width (W)	60	µm	Dimension for 50 Ω transmission line
CPW Gap (G)	40	µm	Dimension for 50 Ω transmission line
Resonator Sectorial Angle	60	°	Constant angle for both radial and diamond designs
Optimal Notch Dimensions	25 x 50	µm	Dimensions yielding maximum Q-factor increase
Q-Factor Improvement	~28	%	Maximum increase in loaded Q for diamond resonator
Operating Frequency Range	100 MHz to 110 GHz	N/A	Range of S-parameter characterization
Diamond Resonator Area Savings	55	%	Reduction in chip area vs. radial stub resonator

Key Methodologies

The experiment focused on the design, fabrication, and RF characterization of CPW radial and diamond stub resonators on a semi-insulating GaAs substrate.

Design and Simulation: Resonator structures were designed using the Advanced Design System (ADS-2009) software, optimizing the inner radius (R) or length (L) (0.1 mm to 1.0 mm) and the ground plane notch dimensions (e.g., 25 x 50 µm) to maximize the loaded Q-factor.
Substrate Preparation: Semi-insulating GaAs wafers (620 µm thick, relative permittivity 12.9) were selected as the supporting material.
Fabrication: Resonators were fabricated using standard nanofabrication techniques, including the deposition of a 0.4 µm thick metallization layer to form the CPW lines and resonator structures.
RF Characterization: Two-port S-parameter measurements were conducted using an Agilent E8364b network analyzer (100 MHz to 110 GHz) coupled with calibrated Cascade Microtech ACP11-100 RF probes.
Q-Factor Measurement: The loaded Q-factor was experimentally determined from the measured S₂₁ data using the standard definition: Q = f_o / Δf_-3dB.

6CCVD Solutions & Capabilities

The research confirms the viability of diamond stub resonators for high-frequency miniaturization. To replicate or extend this work, particularly to achieve higher power handling and superior Q-factors beyond the limits of GaAs, 6CCVD’s MPCVD diamond materials are the ideal solution.

Applicable Materials

The transition from GaAs to diamond is critical for maximizing performance in this millimeter-wave application.

Application Requirement	6CCVD Material Recommendation	Technical Rationale
High-Q Factor Substrate	Optical Grade SCD Diamond	SCD offers the lowest known dielectric loss tangent (tan δ < 10^-4) and high purity, minimizing energy dissipation and maximizing the intrinsic Q-factor at frequencies up to 110 GHz and beyond.
Thermal Management	High Thermal Conductivity SCD	Diamond’s thermal conductivity (> 2000 W/mK) is vastly superior to GaAs (46 W/mK), enabling high-power operation necessary for oscillators and filters without frequency drift.
Large-Area Production	High-Quality PCD Plates	For scaling production, 6CCVD offers Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, suitable for high-volume manufacturing of integrated circuits.

Customization Potential

6CCVD provides comprehensive engineering services necessary to meet the precise dimensional and material requirements demonstrated in this research.

Paper Requirement	6CCVD Customization Capability
Custom Dimensions & Thickness	We supply SCD and PCD plates in custom sizes up to 125 mm (PCD) and thicknesses ranging from 0.1 µm to 500 µm (SCD/PCD), allowing precise control over substrate thickness (e.g., matching the 620 µm GaAs thickness or optimizing for diamond).
Precision Feature Definition	Our advanced laser cutting and etching services can define the required micro-scale features, such as the 25 x 50 µm ground plane notches, with high accuracy.
Surface Finish	We guarantee ultra-smooth surfaces (SCD Ra < 1 nm; PCD Ra < 5 nm) crucial for minimizing conductor losses and surface scattering effects at millimeter-wave frequencies.
Metallization Layer	6CCVD offers internal, high-quality deposition of thin-film metals (Au, Pt, Ti, W, Cu) to achieve the required 0.4 µm metallization thickness and ensure robust adhesion for CPW structures.

Engineering Support

6CCVD’s in-house PhD team specializes in applying MPCVD diamond to demanding RF, optical, and thermal applications. We can assist researchers in optimizing material selection and design parameters for similar millimeter-wave integrated resonator projects, ensuring the maximum benefit from diamond’s unique properties.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

A novel method of introducing a notch at a point of high magnetic field in a coplanar\nwaveguide (cpw) radial and diamond stub resonator to increase the quality factor (Q) was\nanalysed. For comparison both radial and diamond shaped cpw resonators with and without\nnotches were fabricated on gallium arsenide (GaAs) semi-insulating substrate at the James\nWatt Nanofabrication Centre and tested in the milli-metric laboratory at University of\nGlasgow. The notch increased the loaded Q factor of the diamond resonator by approximately\n28% and good agreement was obtained between the measured and simulated loaded Q for\nboth cpw radial and diamond resonators.

Tech Support

Original Source

DOI: https://doi.org/10.1002/mop.29082

References

1993 - Coplanar waveguide radial line double stub and application for filter circuits [Crossref]
2001 - Microstrip filters for RF/microwave application [Crossref]
1966 - Miniature X band Gunn oscillator with a dielectric-tuning system [Crossref]
1984 - InGaAs Gunn oscillators [Crossref]
1993 - Coplanar waveguide radial line stub
2014 - Design and characterization of a novel diamond resonator [Crossref]