A new way to deposit thin layers of atoms as a coating on substrate material at near room temperatures was invented at the University of Alabama at Huntsville (UAH), part of the University of Alabama system.
Dr. Munhyung Zhang, a doctor of research, came up with the idea of using ultrasonic nebulizer technology to evaporate the chemicals used in the deposition of the atomic layer (ALD) while shopping for a home humidifier.
Dr. Zhang works in the laboratory of Dr. Yu Lei, an associate professor in the Department of Chemical Engineering. They both published an article about their invention, which was chosen to be the editor of Journal of Vacuum Science and Technology A.
“ALD is a three-dimensional thin film deposition technique that plays an important role in the production of microelectronics, in the production of elements such as CPUs, memory and hard drives,”
Each cycle of ALD deposits a layer of several atoms deep. The ALD process repeats the deposition cycle hundreds or thousands of times. The homogeneity of the thin films depends on a superficial self-limiting reaction between the vapors of the chemical precursor and the bases.
“ALD offers exceptional control over nanometer performance while applying materials evenly over large silicon wafers for high volume production,” says Dr. Leigh. “This is a key technique for producing powerful and small smart devices.”
While surfing the web for a safe and easy-to-use home humidifier, Dr. Zhang notes that humidifiers on the market use either direct high-temperature heating or ultrasonic vibration at a room temperature nebulizer to generate water mist.
“Moon suddenly realized that the latter could be a safe and easy way to generate money for reactive chemicals that are thermally unstable,” says Dr. Leigh.
“The next day, Luna came to discuss the idea, and we created the experiments to prove the concept in our research lab. The whole process took almost a year. But the great idea came to Luna like lightning.”
ALD processes typically rely on heated gas phase molecules to evaporate from their solid or liquid form, similar to room humidifiers that use heat to evaporate water. However, in this ALD process, some chemical precursors are not stable and may decompose before reaching sufficient vapor pressure for ALD.
“In the past, many reactive chemicals were considered unsuitable for ALD because of their low vapor pressure and because they were thermally unstable,” says Dr. Leigh. “Our study found that the ultrasonic nebulizer technique allows the evaporation of reactive chemicals at low temperatures to room temperature.”
The ultrasonic invention of UAH scientists makes it possible to use a wide range of reactive chemicals that are thermally unstable and not suitable for direct heating.
“Ultrasonic nebulizer, developed by our research team, supplies low-vapor precursors because precursor evaporation occurs through ultrasonic vibration of the module,” says Dr. Leigh.
“Like a household humidifier, ultrasonic spraying generates a mist consisting of saturated vapors and micro-sized droplets,” he says. “Micro-sized droplets continuously evaporate as the mist is delivered to the carrier gas substrates.”
The process uses a piezoelectric ultrasonic transducer placed in a liquid chemical precursor. Once started, the transducer begins to vibrate several hundred thousand times per second and generates a mist from the chemical precursor. The small droplets of liquid in the mist quickly evaporate into the gas collector under vacuum and soft heat treatment, leaving an even coating of the depositing material.
“Using the room temperature ultrasound spraying reported in our manuscript, new ALD processes using low volatility and unstable precursors can be developed,” says Dr. Leigh. “This will open a new window for many ALD processes.”
In their report, UAH researchers demonstrated proof of concept by comparing titanium oxide ALD using thermally vaporized and ultrasonic atomized chemical precursors at room temperature, respectively.
“TiO2 the quality of the thin film is comparable, ”says Dr. Leigh.
New chemistry for ultrathin gas sensors
Henrik H. Sønsteby et al. tert-butoxides as precursors for the atomic deposition of alkali metal containing thin films, Journal of Vacuum Science and Technology A (2020). DOI: 10.1116 / 6.0000589
Provided by the University of Alabama at Huntsville
Quote: Researchers develop new atomic layer deposition process (2020, October 27), retrieved on October 28, 2020 from https://phys.org/news/2020-10-atomic-layer-deposition.html
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