Electromagnetic properties of polycrystalline diamond from 35K to room temperature and microwave to terahertz frequencies

TL;DR

This study investigates the electromagnetic properties of polycrystalline diamond across a wide temperature range and frequencies, highlighting its potential as a low-loss dielectric material for high-frequency applications.

Contribution

It provides high-resolution measurements of polycrystalline diamond's electromagnetic properties from 35K to room temperature at microwave to terahertz frequencies, suggesting its suitability for millimetre wave oscillators.

Findings

Loss tangent decreases with frequency

Polycrystalline diamond shows promising low-loss characteristics

Potential application in stable millimetre wave frequency sources

Abstract

Dielectric resonators are key components for many microwave and millimetre wave applications, including high-Q filters and frequency-determining elements for precision frequency synthesis. These often depend on the quality of the dielectric material. The commonly used material for building the best cryogenic microwave oscillators is sapphire. However sapphire is becoming a limiting factor for higher frequencies design. It is then important to find new candidates that can fulfil the requirements for millimetre wave low noise oscillators at room and cryogenic temperatures. These clocks are used as a reference in many fields, like modern telecommunication systems, radio astronomy (VLBI), and precision measurements at the quantum limit. High-resolution measurements were made of the temperature-dependence of the electromagnetic properties of a polycrystalline diamond disk at temperatures between 35 K and 330 K at microwave to sub-millimetre wave frequencies. The cryogenic measurements were made using a TE01{\delta} dielectric mode resonator placed inside a vacuum chamber connected to a single-stage pulse-tube cryocooler. The high frequency characterization was performed at room temperature using a combination of a quasi-optical two-lens transmission setup, a Fabry-Perot cavity and a whispering gallery mode resonator excited with waveguides. Our CVD diamond sample exhibits a decreasing loss tangent with increasing frequencies. We compare the results with well known crystals. This comparison makes clear that polycrystalline diamond could be an important material to generate stable frequencies at millimetre waves.