Electronics engineers continually look for better insulating materials to use in their projects. Finding the right ones leads to a longer product lifespan, along with improved performance and reduced heat during use. Over the last several years, researchers have achieved particularly promising results while using boron nitride to insulate electronics.
Boron nitride is a synthetic ceramic material available in solid and powder forms. Since it has a similar microstructure to graphite, some people refer to it as "white graphite." Unlike graphite, boron nitride performs well as an electronics insulator with a higher oxidation temperature than that material.
Scientists are working hard to test and verify boron nitride's usefulness as an electronics insulator. What follows are some of the recent achievements associated with it.
A Team Treats Boron Nitride to Make It Bind to Other Materials
Besides its insulating properties, boron nitride is strong, lightweight, and electrically conductive. However, its natural chemical resistance and lack of molecular binding sites at the surface level posed obstacles for those who wanted to use boron nitride with other materials.
A research team discovered that treating boron nitride with chlorosulfonic acid introduced positive charges. The acid's repelling property made boron nitride's layers separate into sheets and created binding sites on each one. Those results could lead to opportunities to interface boron nitride with nanoparticles, molecules, and other two-dimensional nanomaterials.
Vikas Berry, the lead author of a research paper published on the findings, explained, "We showed that the positive charges on the surfaces of the separated boron-nitride sheets make it more chemically active. The protonation—the addition of positive charges to atoms—of internal and edge nitrogen atoms creates a scaffold to which other materials can bind."
Berry also sees potential for using boron nitride in composite materials. If further experiments show the desired effects, researchers could conclude that the possibilities of using it as an insulator are broader than they initially believed.
Engineering Boron-Nitride Pellets to Overcome a Previous Challenge
When professionals who design electronics get to the stage of selecting their insulating material, they must consider various performance-related properties to make the best choices. For example, G10/FR4 is an option made from an electrical glass cloth treated with epoxy resin. It has a 70,000 pound-force per square inch flexural strength. There's also polyester film, which is a highly stable insulator that tolerates high temperatures and moisture.
When choosing an insulator, engineers take care to pick the option with most of the characteristics they need and want. Since using boron nitride as an insulating material is a relatively new and still emerging possibility, researchers often come across some surprises that initially seem limiting, and they require innovative approaches to tackle these things.
As researchers began learning more about the hexagonal form of boron nitride, some wondered if its electrical insulating properties and high thermal conductivity could lead to it becoming an alternative material for heatsinks and heat spreaders. However, while using the material for that purpose, scientists discovered boron nitride had uneven thermal conductivity in different directions.
It didn’t allow for heat to transfer from hot spots by vertically crossing a film made of boron nitride. Instead, it spread along the film horizontally, which became inefficient. By using a pioneering process based on a spark plasma sintering technique, scientists turned powdered boron nitride into a solid mass as a pelleted form.
That new form showed thermal conductivity and efficient heat dissipation in three directions. Most importantly, for the scope of this topic, the pellets retained their electrically insulating properties. The scientists also found them safer than most metal materials, allowing for placement as close as possible to hot devices without damaging them.
A Feasible Way to Remove Impurities
During the more than two decades since creating this material in a lab, researchers have learned that boron-nitride nanotubes (BNNTs) are electrical insulators with a projected thermal conductivity over 10 times that of copper. However, the purity levels of BNNT using conventional production methods varied widely. They could range from 30% to 70%, making BNNT unsuitable for industries with stringent requirements.
Researchers devised a new method of purifying BNNT nanotubes that removes more than 99% of impurities. It involves using a mild hydrocarbon called heptane, plus a temperature below that of boiling water. Previous methods tried by other scientists required using temperatures as high as 1,400°F, which damaged the BNNT. This more recent method doesn’t harm them, and the researchers believe their approach offers industrial-level scalability.
The approach led to the development of the purest BNNTs ever made. The applications for them range from defense and aerospace to the manufacturing of better solar panels or smaller electronics. As teams continue to successfully create new processes like this one, it becomes likelier that more electronics will feature boron nitride, due to its insulating properties and other advantages.
Boron Nitride Lends Itself to Smaller, Superior Electronics
When it comes to electronics, size does matter. Consumers want progressively tinier, slimmer products, and they usually don't consider the difficulties that can arise when meeting their demands. One goal for creating smaller-scale devices relates to minimizing the size of the wires—the interconnects—linking each part of a chip. Smaller dimensions for those accelerate performance and device responsiveness.
Choosing insulating materials for interconnects is a key to making them smaller. However, succeeding isn’t always straightforward. Besides having thermal, chemical, and mechanical stability, the materials selected for interconnects should also act as diffusion barriers that prevent metals from migrating into nearby semiconductors.
In addition, there’s a parameter called a dielectric constant that defines a material's insulating properties. A suitable choice for interconnects must have a dielectric constant no higher than two. Scientists have worked for decades to find better options for interconnect materials. However, many ultimately fail after integration due to poor mechanical properties or a lack of chemical stability.
However, when scientists achieved the large-scale synthesis of a film made from amorphous boron nitride, they found it offered a record-low dielectric constant of 1.78 at 100 kHz. Scientists created it on a silicon substrate, resulting in a film as thin as 3 nm. Moreover, lab tests showed how the material stopped metal atoms from moving from the interconnects to the insulator.
The researchers' findings pave the way for a future of enhanced, high-performance electronics. Even if they encounter unforeseen difficulties during further tests, the advances made so far strongly suggest that amorphous boron nitride could address many of the must-have necessities for smaller interconnects.
A Promising Future for Boron Nitride
As scientists verified boron nitride's electrical insulation properties, many realized it had other characteristics that suited it to high-tech electronics' demands. Developments are ongoing, but it may not be long before you hear of electronics manufacturers using boron nitride in the real world. Transitioning from the lab is often not a simple process, but boron nitride's potential gives scientists and engineers plenty of reason to put in the effort to make that happen.
Megan R. Nichols is a STEM writer and blogger.