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Projects / Programmes source: ARIS

Growth of high quality piezoelectric thin films on silicon using pulsed laser deposition

Research activity

Code Science Field Subfield
2.04.00  Engineering sciences and technologies  Materials science and technology   

Code Science Field
T150  Technological sciences  Material technology 

Code Science Field
2.05  Engineering and Technology  Materials engineering 
Keywords
Pulzed laser deposition, reconstruction of silicon surface, Sr-based interface, piezoelectric thin films, MEMS, energy harvesting
Evaluation (rules)
source: COBISS
Researchers (12)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  29158  PhD Elena Chernyshova  Physics  Researcher  2014 - 2017  127 
2.  37842  David Fabijan    Technical associate  2016 - 2017 
3.  00582  PhD Miran Gaberšček  Materials science and technology  Researcher  2014 - 2017  902 
4.  34441  PhD Dejan Klement  Chemistry  Junior researcher  2014 - 2015  24 
5.  25630  PhD Jakob Konig  Materials science and technology  Researcher  2014 - 2017  132 
6.  22281  PhD Špela Kunej  Materials science and technology  Researcher  2014 - 2017  111 
7.  28561  PhD Jože Moškon  Materials science and technology  Researcher  2014 - 2017  87 
8.  29547  PhD Mojca Otoničar  Materials science and technology  Researcher  2014 - 2016  173 
9.  24273  PhD Matjaž Spreitzer  Materials science and technology  Head  2014 - 2017  369 
10.  08012  PhD Danilo Suvorov  Materials science and technology  Researcher  2014 - 2017  1,050 
11.  15600  MSc Maja Šimaga    Technical associate  2014 - 2016 
12.  25379  Damjan Vengust  Physics  Technical associate  2014 - 2017  222 
Organisations (2)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0104  National Institute of Chemistry  Ljubljana  5051592000  21,237 
2.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,855 
Abstract
The aim of the proposed project is to perfectly join oxides with silicon in a fast and reliable way using pulsed laser deposition (PLD). With such perfect joining many diverse properties of oxides will be successfully brought to the well-developed silicon technologies and can thus be fully exploited in a number of devices. The reason for performing this research is the lack of commercially acceptable technologies that are capable of joining such dissimilar materials. Molecular beam epitaxy (MBE), which enables the high-quality growth of oxides on silicon wafers, demonstrates a very slow growth speed with extremely sensitive deposition. In the project we propose to use PLD technology, which can successfully solve MBE-related problems, keeping growth control at the atomic level. However, the change of technology is corroborated by the fact that automated large-area PLD system are now already commercially available and enable homogeneous growth across 6-inch wafers with a very high growth speed of 50 nm/min. Due to the dissimilar properties of oxides and silicon and consequently extremely delicate growth it is necessary to develop templates, which can be easily overgrown with different oxides. The first objective of the project thus aims at the delivery of a high-quality SrTiO3 thin films on silicon substrates. A number of advanced, in-situ, analytical techniques will be applied to follow the growth of the initial oxide layer, which plays the most important role in achieving full epitaxy. Such in-situ analyses enable the transfer of samples in ultra-high vacuum (UHV) and are a prerequisite for profound understanding of the silicon-oxide interfaces due to their high reactivity. The realization of in-situ measurements is the most complex part of the project and is enabled by the delicate clustering of corresponding UHV systems. The present structures will also be analyzed using state-of-the-art aberration corrected scanning transmission electron microscopy to reveal an exact termination plane of the silicon and adjust the deposition process correspondingly. This study is the first of its kind and is believed to give an unprecedented insight into unique properties and enable the successful engineering of PLD-derived silicon-oxide interfaces. Microelectromechanical systems (MEMS) is among the most rapidly developing silicon-based technology and exhibits a great potential for advanced devices when integrated with piezoelectric material. Among a number of options, we target energy harvesting (EH) devices, which can generate electricity from waste vibrations with countless applications. For instance, they can be powered by a heartbeat to operate a pace-maker. State-of-the-art EH exploit fully epitaxial Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) layers, grown on silicon using a combination of sputtering and MBE. However, due to MBE-related drawbacks the developed EHs cannot be commercialized and therefore the functionalization of as-prepared templates with high-quality PMN-PT thin films using PLD technology is proposed for the second objective. As an environmentally friendly substitute for PMN-PT, lead-free piezoelectric systems based on Na0.5Bi0.5TiO3 will also be investigated. For the project we also propose to collaborate with two international organizations, SINTEF from Norway and National Taiwan University from Taiwan. At SINTEF the up-scale of growth to 6-inch wafers is planned based on our protocols using a recently installed piezoFlare 1200 system, which is the first automated large-area PLD system in the world. Based on as-prepared films SINTEF will also model and fabricate a corresponding transducer, which will be integrated into EH devices using an interfacing circuit and finally validated at the National Taiwan University.
Significance for science
Integration of oxide thin films with silicon represents an important research aim from the perspective of both basic and applicative science. From the perspective of basic science the results of the research are interesting, due to an improved understanding of the Si-Sr (or SrO) interactions and surface reconstructions and other structural peculiarities. These phenomena had already been studied, but only in MBE deposition processes, where the source material is evaporated from effusion cells and slowly condensed on the substrate surface. PLD, on the other hand, in its essence, is a technique that uses laser light to form a plasma with high-energy particles, which can damage the surface of the sample, especially, if the deposition is carried out in vacuum. With the intention of protecting the surface and controlling the surface reconstruction, we have studied the deposition parameters for Sr and SrO, such as the substrate temperature, pressure and atmosphere, energy and frequency of the laser pulses, etc. We analyzed the samples by various in-situ analysis techniques to obtain a comprehensive insight into the structure and chemical composition of the surface and the Sr-Si interface. We have shown that the quality of the PLD-derived chemically stable surface of Si with 1 ML Sr coverage is comparable to ones prepared by MBE, which represents an important result also from the applicative perspective, as PLD is a much more industrially-appropriate tool than MBE. In order to integrate the as-prepared substrates with functional oxides, a buffer layer is needed, which is simultaneously compatible with the Sr/Si surface and the active layer. For this reason, we have precisely studied the growth of STO on Sr/Si, using state-of-the-art techniques, in order to ensure the growth of a stoichiometric STO layer with low surface roughness, which is necessary for the overgrowth of functional oxides. In the scope of the second aim of the project, we deposited active PMN-PT layers on the as-prepared STO/Sr/SI templates. PMN-PT is a well-known piezoelectric system, which exhibits high piezoelectric coefficients. However, its preparation is complex and its structure has not yet been fully explained, especially in thin films in the vicinity of the MPN. We have systematically optimized the preparation of PMN-PT films on single-crystal STO substrates, in order to achieve a high degree of phase purity and the appropriate crystal structure. In one case, PMN-PT was deposited directly onto STO substrates, while in the other case, thin-film LNO electrodes were deposited between the substrate and the PMN-PT. This way, the heterostructures prepared in the first case were appropriate for the 3-3 mode of EH operation, and in the other case, the 3-1 mode could be implemented. Such a comprehensive study offers insight into the correlation between the crystal, chemical and domain structure of the films, as well as their functional properties on different templates. Understanding this correlation is indispensable for engineering oxide layers for specific applications. The knowledge obtained in the study on a research PLD system, was transferred onto an industrial PLD system at SINTEF, obtaining important information regarding the process transfer onto a larger scale. Therefore, the use of the PLD technique for the preparation of the entire heterostructure for the EH device offers numerous advantages in comparison to a combination of techniques such as MBE and sputtering.
Significance for the country
The majority of contemporary electronics is based on silicon. Mass production of silicon wafers enables the operation of supercomputers, smartphones and numerous other devices. Nevertheless, the functionality of Si itself is limited. Its integration with oxide materials opens the gate for new electronic components and devices. Si-oxide heterostructures are developing in two main directions: i) growth of polycrystalline or textured functional layers on SiO2/Si substrates, with an emphasis on the speed and simplicity of the synthesis and ii) growth of epitaxial layers on Si with an emphasis on the preparation of a sharp interface, which enables overgrowth of high-quality functional films. In the latter case, usually a long and complicated MBE procedure is used to prepare a Si template with an oxide buffer layer. Afterward, a different, faster technique is used to synthesize the thicker active layer. The results of our research represent a major contribution to the comprehensive integration of functional oxide layers with silicon using the PLD technique, which enables faster mass production, while maintaining the high quality of the layers. The results of the project specifically contribute to the development of piezoelectric thin films, which can be utilized in the form of transducers, actuators or sensors in numerous MEMS devices. As the developed technology is compatible with existing production processes, the transfer of the obtained knowledge into the industrial sphere can be very swift. Such advanced devices can be produced in SMEs, which would enable them to participate in the growing market of the MEMS industry. Opportunities and concepts have been presented to several Slovenian companies. Alongside the general development of the MEMS industry and smart systems, there is an increasing demand for EH devices, which were the center of focus in this project, as there is a strong motivation for self-powering these systems. The development of advanced EH devices would help Slovenia to establish a network for the Internet of Things. One of the more important accomplishments of the project is the transfer of knowledge and skills between the participating members, among which are also post-doctoral fellows, and doctoral and master students. The students have been educated via transfer of knowledge within the group, as well as via communication with collaborating organizations from an international environment. All participating members have had an opportunity to work with state-of-the-art equipment and collectively solve one of the key research problems in the field of oxide electronics. This has provided the members with wider visibility in the research community concerned. As the project was highly interdisciplinary, it enabled a deeper understanding of the issues, focusing on finding solutions for practical applications. The project brought together different research groups within JSI. An especially strong collaboration was developed on the basis of a UHV connection between the PLD, XPS and JT-STM systems, as it enabled a comprehensive characterization of the heterostructures. The project also strengthened the collaboration between JSI and the National Institute of Chemistry. International collaborations were also established within the project, namely with the research organization SINTEF and National Taiwan University. Both organizations are established members of the MEMS community with outstanding results in the field of applied research. Collaborations with the members of these organizations have greatly contributed to our understanding of issues, related to modelling, production and integration of MEMS devices. Further cooperation with all of the involved research organizations is foreseen. The results of the project have been reported on numerous international conferences and in publications in scientific journals. We have also prepared promotional materials and organized informative visits on JSI.
Most important scientific results Annual report 2014, 2015, final report
Most important socioeconomically and culturally relevant results Annual report 2014, 2015, final report
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