ADELPHI, Md. – For future Army battlefields, the ability to maintain and control large amounts of energy will help Soldiers achieve technological superiority over their adversaries.
Researchers from the U.S. Army Combat Capabilities Development Command, known as DEVCOM, Army Research Laboratory demonstrated a new method of anti-ferroelectric thin film production that takes advantage of the widespread availability of hafnium.
The resulting lead hafnate, or PbHfO3, thin film created with this Army technique could potentially open new doors for researchers who want to capitalize on the unique properties of anti-ferroelectric materials in order to create even more powerful energy technologies.
“When you need a burst of electrical power like in a defibrillator or a railgun, anti-ferroelectrics are a good way to get raw watts of pulse power out,” said Dr. Brendan Hanrahan, Army materials engineer. “Anti-ferroelectrics also naturally absorb oscillating signals, which make them excellent electronic filters.”
According to Hanrahan, this breakthrough signifies the first time that researchers produced antiferroelectric thin films with lead hafnate, a relatively unknown compound that wasn’t even confirmed to have antiferroelectric properties until 2019.
Researchers had theorized about lead hafnate’s anti-ferroelectric properties as early as 1953, two years after they identified lead zirconate, or PbZrO3, as an anti-ferroelectric material.
Due to the high cost of hafnium and years of inconclusive results, however, lead hafnate fell into obscurity while lead zirconate surged in popularity as the quintessential anti-ferroelectric material.
“Lead hafnate is almost absent from the literature, because getting pure enough hafnium at the time was incredibly difficult,” Hanrahan said. “Lead zirconate and lead hafnate were almost in equal esteem at the very outset, but lead zirconate was the only one anyone ever used because zirconium was a lot easier to come by than hafnium.”
Hafnium remained largely inaccessible until the early 2000s when it became an important component in semiconductor devices.
Once Army researchers realized that hafnium-related materials no longer struggled with the same supply chain issues that they once faced in the past, the researchers began to seriously consider hafnium as a potential ingredient for new materials.
From these deliberations emerged the possibility of an anti-ferroelectric thin film made from lead hafnate.
Around the same time, Army materials scientist Dr. Nicholas Strnad had recently discovered how to fabricate piezoelectric lead-based compounds with a technique called atomic layer deposition.
Given the favorable conditions, Hanrahan and Strnad seized the opportunity to determine whether they could use atomic layer deposition, a process commonly employed by semiconductor industry giants such as Intel and Samsung, to create anti-ferroelectric thin films for silicon wafers.
“ARL has been a leader in atomic layer deposition of ferroelectrics for the past five years,” Hanrahan said. “If you combine this capability with the current ubiquity of hafnium, it’s very easy to imagine why we should try tackling this anti-ferroelectric lead hafnate from the old literature.”
With the development of a lead hafnate thin film, Army researchers believe that lead hafnate has another chance to show its full potential as an anti-ferroelectric material and even outperform lead zirconate.
Hanrahan and his colleagues plan to further tailor the unique properties of lead hafnate in order to transition this technology to small businesses.
Their research paper, The other model anti-ferroelectric: PbHfO3 thin films from ALD precursors, appeared in the peer-reviewed scientific journal Applied Physics Letters Materials as part of the 100-year anniversary special issue celebrating the discovery of ferroelectrics.
“We have proven the anti-ferroelectric property, but now there is a lot of application-specific tuning that needs to happen,” Hanrahan said. “Lead hafnate can be used for applications in energy storage, thermal sensors, radio and more. It all depends on how we want to use it.”
As the Army’s corporate research laboratory, ARL is operationalizing science to achieve transformational overmatch. Through collaboration across the command’s core technical competencies, DEVCOM leads in the discovery, development and delivery of the technology-based capabilities required to make Soldiers more successful at winning the nation’s wars and come home safely. DEVCOM Army Research Laboratory is an element of the U.S. Army Combat Capabilities Development Command. DEVCOM is a major subordinate command of the Army Futures Command.