Plasma Enhanced Atomic Layer Deposition of TiN for plasmonic films by Boston and Purdue collaboration.

A Plasma Enhanced Atomic Layer Deposition for Plasmonic Films by Boston and Purdue :

In work published in the journal Materials of MDPI (Basel, Switzerland), Dr. Katherine Hansen (lead author), Dr. Melissa Cardona, Dr. Armatya Dutta, and Professor Chen Yang have produced an ultrathin film composed of a transition metal nitride for plasmonic films. To achieve this, these researchers from Boston University and Purdue University have used plasma-enhanced atomic layer deposition (ALD).

Transition metal nitrides, like the titanium nitride (TiN) which was produced in this work, are considered a promising alternative to noble metal plasmonic materials. In contrast to the widespread use of noble metals such as gold, the transition metal nitrides are durable, compatible with integrated circuits, and low cost.

In fig. 1. A list of materials suitable for plasmonic materials is shown:

Fig. 1 from Prof. Alexandra Boltasseva: Emerging Materials for Nanophotonics and Plasmonics, video available in https://youtu.be/heYhkc_MPrE?t=1187

Plasmonics is a field of research and study that explores the interaction of light waves and metallic surfaces. When light waves interact with metallic surfaces, waves of electrons can be generated and can oscillate. 

The electrons that oscillate are then called surface plasmons (SPs). SPs can exhibit strong variations by resonance, making it possible to confine specific light wave frequencies. The length of these plasmon waves is much shorter than the wavelengths of light, making it possible to use light indirectly in the very small dimensions of today’s integrated circuits.

By transforming wavelengths of light into waves of electrons, it has become possible for scientists to merge the speed of optics with the dimensions of electronic devices. However, plasmonics has remained mired in a proof-of-concept state despite many practical devices having been experimentally demonstrated for on-chip circuitry.

The light confinement at the nanoscale is one of the special properties of SPs, making them unique when thinking about optical properties.

Prof. Alexandra Boltasseva, who is also from Purdue University, has made a very nice review about emerging materials for nanophotonics and plasmonics. In her presentation, she also explores the potentiality of TiN associated with atomic layer deposition, as a plasmonic material. Not only that, a wide range of applications for plasmonic technology is presented in Fig. 2:

Fig. 2 Image from Prof. Alexandra Boltasseva: Emerging Materials for Nanophotonics and Plasmonics, video available in https://youtu.be/heYhkc_MPrE?t=1187

Thus, devices that use plasmonic technology can exploit the optical properties of nanostructures to permit sending and handling of light at the nanoscale. By integrating conventional electronics and plasmonics in, for example, chips, ultra-fast and ultra-compact modulators, and detectors can be produced.

Now, Katherine Hansen et. Al have demonstrated ultrathin plasmonic TiN that was synthesized by plasma-enhanced atomic layer deposition (PE-ALD). This was done by using dimethyl amido titanium IV (TDMATi) and ammonia (NH3).

The TiN films were synthesized in a Gemstar XT plasma enhanced atomic layer deposition system using ultra-pure Argon (Ar) as a carrier and purging gas. All steps of the TiN film synthesis were carried out in the ALD reaction chamber under vacuum at 250oC, which is considered a low temperature for such a technique.

When using precursors, TDMATi was first exposed to the chamber, followed by 1000 milliseconds, followed by NH3:Ar plasma. Briefly, this completes one deposition cycle, which was repeated until the desired film thickness. The authors also did a post-deposition hydrogen plasma treatment on TiN.

To confirm the successful synthesis of titanium nitride thin film from TDMATi and NH3 plasma in low temperatures, techniques such as Raman spectroscopy and X-ray photoelectron spectroscopy were applied.

Fig. 3 Image from article: Real (solid lines) and imaginary (dashed lines) values of permittivity of ultrathin TiN (100 cycles) on MgO as prepared (green) and after hydrogen plasma anneal (blue).

The TiN was found to be optically metallic for both thick (42 nm) and thin (11 nm) films on MgO and Si <100> substrates, with visible light plasmon resonances in the range of 550–650 nm. 

They also demonstrated that a hydrogen plasma post-deposition treatment improves the metallic quality of the ultrathin films on both substrates, increasing the ε1 slope by 1.3 times on MgO and by 2 times on Si (100), to be similar to that of thicker, more metallic films. In addition, the post-deposition was found to tune the plasmonic properties of the films, resulting in a blue-shift in the plasmon resonance of 44 nm on a silicon substrate and 59 nm on MgO (Fig. 3).

About the authors:

Authors in clockwise, from the top left to bottom left: Dr. Katherine Hansen (top left), Dr. Melissa Cardona, Dr. Amartya Dutta, And Prof. Chen Yang (bottom left)

Dr. Katherine Hansen, the lead author, is a chemist, with a Ph.D. in chemistry from Boston University (2017-2020). Nowadays, she works as Staff Scientist in thin film processing at RMD.

Dr. Melissa Cardona worked at Boston University as a Research Fellow from 2017 to 2019, and has her Ph.D. from Purdue University (2013-2017), working at Prof. Chen Yang Dr. Research Laboratory, Department of Chemistry. Today she works as a MOCVD Scientist at Masimo Semiconductors.

Dr. Amartya Dutta is an electrical engineer and photonics specialist, and got his Ph.D. in Physics and Electrical Engineering from Purdue University and Boston University, respectively (2015-2020).

Prof. Chen Yang graduated from the University of Science and Technology of China (USTC), Hefei, Anhui, P. R. China, with a bachelor’s degree in Chemical Physics in 1999. She obtained a Master of Philosophy in 2000 by studying theoretical chemistry with Professor. Yijin Yan at Hong Kong University of Science and Technology. Then, she received her doctoral degree in Chemistry at Harvard University in 2006 under the supervision of Prof. Charles M. Lieber. Prof. Yang then worked as an associate in McKinsey & Co, a business consulting company, from June 2006 to July 2007. Prof. Yang joined the Department of Chemistry and Department of Physics as an Assistant Professor at Purdue University in August 2007 and was promoted to Associate Professor in 2013. She is currently an Associate Professor in the Department of Electrical and Computer Engineering and the Department of Chemistry at Boston University.

Prof. Yang’s research interest focuses on nanomaterials for their potential applications in nanoscale devices and biological applications. Her previous research has been published in high-profile journals, including Science and Nature, and has been featured in many public press releases, including Chemical and Engineering News and Harvard Gazette magazine. She has won the NSF Career Award and Purdue Seed of Success. Prof. Yang is Associate Chair for the Master Program in the Department of Electrical & Computer Engineering at Boston University. She is also directing a research experience for an undergraduate (REU) program partnering between Boston University and Zhejiang University. 

Her research group focuses on developing new nanomaterials with functionality gained from low dimensionality, structural and compositional complexity, and novel optical and electrical properties for great societal impact. They have adopted the “Design and Develop” strategy where we design the new nanostructures based on unique understanding gained through experiments and theories for the targeted application.

The research programs in her department are currently focused on three major areas: (1) Interfacing Nanomaterials with Biology; (2) Understanding and designing new nanomaterials with unique optical properties for photonics and solar energy applications; (3) Nanowire architecture for electronics and photonics applications. Reflecting the interdisciplinary feature of her research, Dr. Yang holds a faculty position at the Department of Electrical & Computer Engineering and the Department of Chemistry.

About the lecturer:

Alexandra Boltasseva is an associate professor at the School of Electrical and Computer Engineering, Purdue University. Boltasseva received the 2013 IEEE Photonics Society Young Investigator Award, 2013 Materials Research Society (MRS) Outstanding Young Investigator Award, MIT Technology Review Top Young Innovator (TR35) award. She is a Fellow of the Optical Society (OSA), a member of MRS Board of Directors and Editor-in-Chief for OSA's Optical Materials Express.

You can find more information on:

Hansen, K.; Cardona, M.; Dutta, A.; Yang, C. Plasma Enhanced Atomic Layer Deposition of Plasmonic TiN Ultrathin Films Using TDMATi and NH3. Materials 2020, 13, 1058. https://doi.org/10.3390/ma13051058

Professor Yang webpage: https://sites.bu.edu/yanglab/

Prof. Alexandra Boltaeva webpage: https://engineering.purdue.edu/~aeb/