Growth, properties, and applications of Al1-xScxN thin films
Paul Muralt
Electroceramic Thin Films Group, EPFL
Lausanne, Switzerland
The discovery of enhanced piezoelectricity in solid solutions of AlN and ScN [1] is certainly one of the most important events in piezoelectric MEMS. As compared to pure AlN, it brought a crucial factor 2 to 3 improvement in a number of figures of merit governing the performance of MEMS devices. The aim of this talk is to give an overview of the present knowledge about this material, its properties, and demonstrated device performance. Growth issues, phase stability of metastable AlScN, and the disturbing formation of abnormally oriented grains in otherwise perfect (0001)-textured columnar microstructures are addressed. Piezoelectric and dielectric properties obtained from experiments are compared with results from density functional theory .[2] Figure of merits for a number of applications are presented and compared with the ones of AlN and PZT thin films.[3] In ultrasonic devices for communication and sensors, AlScN will replace in many cases AlN. The higher coupling factors allow for the exploitation of new resonator types that previously did not reach a high enough coupling. This is the case for instance with Lamb wave resonators. The strong coupling will also help to push thin film SAW devices for wireless sensors with identification tags. Latest results in these areas will be presented. A darker side of AlScN lies in its strong chemical stability. It is in fact difficult to etch the material in a selective way. This hampers for the time being the achievement of precisely patterned structures in microsonic devices with micron feature sizes. But most likely, enough industrial efforts will be spent to overcome this problem.
[1] M. Akiyama, T. Kamohara, K. Kano, A. Teshigahara, Y. Takeuchi, N. Kawahara, Adv.Mat. 2009, 21, 593.
[2] S. Mertin, B. Heinz, O. Rattunde, G. Christman, M.-A. Dubois, S. Nicolay, P. Muralt, Surf Coat Technol 2018, 343, 2.
[3] R. Matloub, M. Hadad, A. Mazzalai, N. Chidambaram, G. Moulard, C. Sandu, T. Metzger, P. Muralt, Appl.Phys.Lett. 2013, 102, 152903.
European perspective on lead-free piezoceramics
Rödel, J., Koruza, J., Lalitha, K.V.
We will start with a broad industrial perspective by contrasting the case of functional ceramics in Europe and Japan. This will include annual production values in ceramics with a focus on functional ceramics and will compare the businesses with respect to size, strategy, marketing etc.
To make the talk more directly applicable to attendees we will then focus on piezoceramics and especially on lead-free piezoceramics. We will suggest guidelines for future work, for the academic as well as the industrial sector 1,2,3.
Apart from the legislation providing a driving force for the replacement of lead-containing piezoceramics, new lead-free piezoceramics also offer distinct advantages in select application fields. These include the ability to co-sinter (K0.5Na0.5)NbO3 with nickel electrodes 4, improved high-power characteristics 5 and enhanced fracture toughness of Na1/2Bi1/2TiO3 in comparison to Pb(Zr,Ti)O3.
A specific focus will be on the recent work on NBT-based piezoceramics, specifically the composite approach to tailor the properties. It has been found that NBT-based composites can be tailored with enhanced depolarization temperature 6 and increased electromechanical hardness 7. The underlying mechanisms will be outlined, supported by structural, mechanical and electromechanical characterization. A comparison with PZT will further establish the potential of NBT-based composites for high-power application.
References
[1] J. Rödel, K. G. Webber, R. Dittmer, W. Jo, M. Kimura and D. Damjanovic, J. Eur. Ceram. Soc., 35, 1659-81 (2015).
[2] J. Koruza, A. J. Bell, T. Frömling, K. G. Webber, K. Wang and J. Rödel, J. Materiomics, 4, 13 (2018).
[3] J. Rödel and J.-F. Li, mrs Bulletin, 43, 576-560 (2018).
[4] S. Kawada, M. Kimura, Y. Higuchi, H. Takagi, Appl. Phys. Express, 2, 111401, (2009)[5] T. Tou, Y. Hamaguti, Y. Maida, H. Yamamori, K. Takahashi, Y. Terashima, Jpn. J. Appl. Phys., 48, 07GM03(2009).
[6] L. Riemer, L. K. Venkataraman, X. Jiang, N. Liu, C. Dietz, R. Stark, P. B. Groszewicz, G. Buntkowsky, J. Chen, S.-T. Zhang, J. Rödel and J. Koruza, Acta Materialia, 136, 271-280 (2017).
[7] Lalitha, K. V., L. Riemer, J. Koruza and J. Rödel, Appl. Phys. Let., 111, 022905 (2017).
Epitaxial integration of PZT thin films with Si and III/V substrates
Guus Rijnders
MESA+ Institute for Nanotechnology, University of Twente, The Netherlands
Recently there has been an increased demand for high performance piezoelectric and ferroelectric thin films for electronics, sensors and actuators, such as high-power FET, ink jet printing and adaptive optics. For such applications, lead zirconate titanate (PZT) thin films have received much attention because of the strong intrinsic piezoelectric and ferroelectric properties. It has been shown that the control of the microstructure and orientation of the PZT film is very important for device performance. In film growth processes, the microstructure of a film is usually determined by the nucleation and initial growth phase. The former is mainly controlled by the substrate used, such as crystallinity, surface orientation, and lattice mismatch, while the latter is usually controlled by the process conditions.
In this contribution, I will highlight recent work on the epitaxial integration of PZT with Si and III/V semiconductors. The epitaxial integration of PZT with Si and for instance GaN is hampered by the difference in crystal structure and large lattice mismatch. Using epitaxial buffer layers and optimized growth with pulsed laser deposition, we are able to obtain epitaxial growth of PZT on MgO-buffered GaN [1]. The thickness of the MgO can be lowered down to single monolayers while maintaining the high quality and good properties of epitaxial PZT films, which enable practical applications for high power FET’s and non-volatile ferroelectric controlled electronics devices.
I will furthermore show epitaxial integration of (001)-oriented PZT with glass using nanosheet Ca2Nb3O10 (CNOns) layers buffer layers [2]. The PLD deposition temperature and repetition frequency used for the deposition of the PZT films were found to play a key role in the precise control of the microstructure and therefore of the ferroelectric and piezoelectric properties.
[1] Li, L., Liao, Z., Gauquelin, N., Nguyen, M. D., Hueting, R. J. E., Gravesteijn, D. J., Lobato, I., Houwman, E. P., Lazar, S., Verbeeck, J., Koster, G. & Rijnders, G. “Epitaxial Stress-Free Growth of High Crystallinity Ferroelectric PbZr0.52Ti0.48O3 on GaN/AlGaN/Si(111) Substrate” ,Advanced materials interfaces., 2018, 5, 2, 1700921
[2] Minh D. Nguyen, Evert P. Houwman, Huiyu Yuan, Ben J. Wylie-van Eerd, Matthijn Dekkers, Gertjan Koster, Johan E. ten Elshof, and Guus Rijnders, “Controlling Piezoelectric Responses in Pb(Zr0.52Ti0.48)O3 Films through Deposition Conditions and Nanosheet Buffer Layers on Glass”, ACS Appl. Mater. Interfaces, 2017, 9 (41), pp 35947–35957, DOI: 10.1021/acsami.7b07428
APPLICATIONS OF ULTRASONIC TRANSDUCERS FOR NON-DESTRUCTIVE TESTING IN THE NUCLEAR INDUSTRY
Jean François Saillant
Nuclear power plants play an important role in the supply of electricity of today’s developed countries. They allow to produce a large amount of energy while still complying with the consensus on climate change regarding the reduction of greenhouse gas emission.
When thinking of a nuclear reactor, the first thing that comes to mind is nuclear safety. Non-Destructive Testing (NDT) techniques based on ultrasound are a key technology for assessing the integrity of nuclear reactors and to ensure their safe operation. These techniques rely on ultrasonic transducers that are exclusively made from ferroelectric materials. This invited conference aims at presenting some of the techniques that are presently used on site and some of the R&D that is carried out for present and future reactors.
This conference will be divided in two parts. The first part will present some of the automated ultrasonic inspections carried out on the primary components of so-called Generation 3 reactors, representing a majority of today’s nuclear reactor parks. Different technologies will be presented such as focused ultrasound, phased array or conformable probes. The topic of standards for nuclear inspections will also be raised. The second part of this conference will present NDT for tomorrow’s Generation 4 reactors. These reactors will be sodium-cooled reactors, which will require new ultrasonic transducers capable of surviving in a very severe environment while still requiring high acoustic performances. State of the art results will be presented, showing the feasibility of performing NDT in such a difficult environment.
