The Dielectric Constant of Silicon Nitride – What Makes It Unique?

High strength and low dielectric loss are a rare combo for a material to possess, making silicon nitride an attractive option for a wide range of applications.

What is Dielectric Constant?

A dielectric material is an electrically insulating material that stores an electrical charge when subjected to an external electric field. The dielectric constant for a given dielectric material is the ratio of the capacitance, formed by two plates with that material sandwiched between them, to the capacitance of the same plates with only a vacuum between them. This electrical property is a unitless, dimensionless quantity with a value always greater than 1, that provides a measure of the ability of that material to store electric energy in an electrical field. For high-frequency electromagnetic applications where a signal (e.g. radar) is passing through the material, the dielectric constant needs to be low.

What is Dielectric Loss?

Dielectric loss quantifies a dielectric material’s inherent dissipation or loss of electromagnetic energy typically in the form of heat that takes place as the material absorbs electrical energy. (The three main forms of electromagnetic loss mechanisms for dielectric loss materials are interfacial polarization, dipolar polarization, defect-induced polarization, and conductive loss.) Dielectric losses depend on the frequency of the electrical field and the dielectric material, which means that for any given application, it is important to know the values of dielectric loss at the frequencies of interest.

The Dielectric Constant of Silicon Nitride

The dielectric constant of silicon nitride is between 8.0 and 10.071, whereas many other high-temperature ceramics have higher values. This makes silicon nitride a good choice when you need a material with radio transparency that can also withstand high temperatures.

An RF Transparent Material Option for Extreme Environments

Due to its rare combination of high strength, high oxidation resistance, low dielectric constant, and low dielectric loss, silicon nitride is a superior material choice for components that need a radio frequency (RF) transparent material that is durable at high temperatures and speeds.

It is an attractive material option for technical, industrial, and structural applications. Specific applications in which the dielectric properties of silicon nitride show promise include rocket components, antenna windows, high-speed missile radomes, and electrical insulators for fusion reactors72

Our blog post, Silicon Nitride – An Advanced Aerospace Material, contains more information about how the dielectric properties of silicon nitride are applied in the aerospace and aviation industries.

Silicon Nitride Vs Other Low Dielectric Loss Materials

High strength and radio transparency at high temperatures are not usually exhibited in tandem by a single material. A material may possess high strength or low dielectric loss but rarely both, making silicon nitride especially unique.

Silicon nitride material properties include not only high strength and RF transparency but high hardness and thermal resistance as well. The material is incredibly light for the strength it provides, making it ideal for aerospace and other applications where both weight and strength are critically important.
In addition, the thermal properties of silicon nitride offer low thermal conductivity and a high melting point, which allows it to withstand extreme temperatures. It also offers a low thermal expansion coefficient, leading to fewer dimensional changes compared to metal components.

Dielectric Properties of Ceramics

Ceramic dielectrics are characterized by high heat resistance, stability and reliability, and particularly, resistance to the effects of high energy radiation. Due to these properties, dielectric ceramics are widely used in telecommunication and aerospace.

While there are ceramics with lower dielectric constants than silicon nitride (such as fused silica) these other ceramics cannot withstand high-temperature performance. Therefore, silicon nitride is the best choice for achieving good radio transmission at high temperatures73

Dielectric Constant of Plastic

Most plastics resist a current flow, thus making them dielectrics or insulators. However, the dielectric strength of a plastic material generally decreases with increased temperature. Thus, while plastics perform well at room temperature, they do not stand up to high-temperature use, especially for aviation or aerospace.
Silicon nitride is one of the few materials capable of surviving the severe thermal shock and thermal gradients generated in hydrogen/oxygen rocket engines. Unlike plastics, it offers a high melting point and the ability to maintain performance at high temperatures.

Factors Influencing Dielectric Constant

Many different factors can influence a material’s dielectric constant, including:
● Frequency of the electrical field
● Moisture and temperature of the environment
● Voltage
● Structure and morphology of the dielectric
● Presence of other materials for plastics
● Weathering and deterioration of the dielectric

Electronic environments can be challenging to ordinary plastics. Beyond the high-temperature environment, often chemical exposure is a potential threat to a material’s survival. Silicon nitride offers both excellent chemical and thermal resistance.

OEM Partnerships with SINTX

If you need an RF transparent material that can withstand high temperatures and thermal shock, talk to SINTX about silicon nitride components.

SINTX is a flexible partner that can deliver high-quality silicon nitride products, perfected by years of experience. Our unrivaled in-house manufacturing capabilities allow for intricate designs and shapes that can be rapidly developed, prototyped, and tested across a wide variety of applications, including aviation and aerospace.

Our leading R&D and manufacturing teams are ready to collaborate with you on specialized application development for your company. Get started on your custom silicon nitride components by requesting a quote from SINTX.

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