Projects / Programmes
Engineering of oxides on silicon for future electronics
| Code |
Science |
Field |
Subfield |
| 2.09.00 |
Engineering sciences and technologies |
Electronic components and technologies |
|
| Code |
Science |
Field |
| T150 |
Technological sciences |
Material technology |
| Code |
Science |
Field |
| 2.05 |
Engineering and Technology |
Materials engineering |
Epitaxy, oxide electronics, silicon, pulsed laser deposition
Researchers (16)
Organisations (2)
Abstract
The aim of the proposed research project is to develop technological procedures for industrially-appropriate fabrication of epitaxial oxide layers on silicon substrates. With such perfect integration, many diverse properties of oxides and their heterostructures will be successfully brought to the well-developed silicon technologies and can thus be 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 high run-to-run instability. In the project, we propose to use Pulsed Laser Deposition (PLD) technology, which can successfully solve MBE-related problems, while keeping the atomic-scale control of the growth. The change of technology is corroborated by the fact that large-area PLD system are now commercially available and enable homogeneous growth across 8-inch wafers with a very high growth speed of 50 nm/min.
Due to the dissimilar properties of oxides and silicon their corresponding interfaces have to be first well understood in order to join them perfectly, which defines the first objective of the project. This makes it necessary to develop templates, which can be easily overgrown with different oxides. The first result of the project thus aims at the delivery of a high-quality SrTiO3 thin film on silicon substrates. Since the growth of the initial oxide layer is extremely delicate due to the high reactivity of the silicon-oxide interfaces and plays the most important role in achieving full epitaxy, interfaces will be optimized by applying a number of advanced, in situ analytical techniques, like reflection high-energy electron diffraction, X-ray photoelectron spectroscopy and scanning tunnelling microscopy. The thermodynamic stability of different stoichiometry models from the silicon-oxide interface will be investigated using Density Functional Theory calculations. This will enable us to engineer the buffer layer beyond the state-of-the-art with more lasting and atomically abrupt contact between the constituents. This study is the first of its kind and is believed to give an unprecedented insight into unique properties of PLD-derived silicon-oxide interfaces.
Microelectromechanical systems is among the most rapidly developing technology and exhibits a great potential for advanced devices. Among a number of options, we target energy harvesting (EH) devices, which can generate electricity from waste vibrations with many possible applications. State-of-the-art EH exploits 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 materials cannot be commercialized and therefore functionalization of as-prepared templates with high-quality PMN-PT thin films using PLD technology is proposed for the second objective. Because of the environmental issues of lead-containing compounds, lead-free heterostructures based on Na0.5Bi0.5TiO3 will also be investigated. Furthermore, as-grown piezoelectrics will be processed and integrated into prototype EH devices and validated with application-specific electronic circuit. As a part of the second objective, functionalization of silicon with LaAlO3-SrTiO3 heterostructures that enable formation of two-dimensional electron gas at their interface is also proposed. The electric-field dependent interface conductance in this system will be tested as the drain-source channel in n-type field-effect transistors, which will be further constructed into more complex circuits. The second result of the project is thus to deliver guidelines for successful functionalization of silicon substrates using relevant piezoelectrics and heterostructures and to demonstrate novel oxide-based devices on silicon platform for next generation electro
Significance for science
A major scientific breakthrough is expected in the field of the heteroepitaxial growth of oxides on silicon using PLD technology, required for exploitation of rich properties of oxides for next generation electronics. Growth of oxides on Si has been studied by many research groups in the past, but the progress in epitaxial integration has always been hindered by the problem of the materials’ incompatibility.
Our preliminary results demonstrate possible path for single-crystalline growth of oxides on silicon using PLD. However, compared to MBE-grown layers, their structural quality is significantly smaller, which might be due to the intrinsically different nature of the corresponding two deposition techniques. In the MBE chamber, elements are evaporated from effusion cells and gently arrive to the surface, while in the PLD system a high-energy laser pulses generate a plume of supersaturated species with much higher kinetic energies. Related to the first objective of the project various oxide layers will be prepared using PLD and analyzed in situ with a number of techniques, like STM, XPS, and TPD. Surface defects, step edges, bonding site and wetting of the deposited material will be investigated. Additionally, aberration-corrected STEM will be used to gain atomistic insight into the unique structures of oxide and their interfaces with silicon. The proposed methodology will enable us to better understand integration of such dissimilar materials and to prepare epitaxial STO on Si platform with optimized stoichiometry and minimized concentration of structural defects.
For the second objective, the STO templates will be overgrown with piezoelectrics and heterostructures with 2DEG. The main purpose of this part of the project is to successfully integrate the well-established material systems with silicon and to maintain values of piezoelectric coefficients and electron mobilities that are as high as possible. By growing high-quality films we expect to exactly correlate their functional response with the crystal-structural properties of the films deposited on silicon, the lattice mismatch, and the compositional disorder. Furthermore, as-prepared structures will be tested on the device level, specifically for energy harvesting applications and field-effect transistors, to estimate their applicability in oxide electronics.
In addition to materials science, the proposed project also addresses various issues related to applied physics and electrical engineering. In response to that an interdisciplinary research team is proposed, connecting different national and international research departments and institutes, as described in the work programme. Thus a research cluster of scientist with complementary expertise will be created, which will help us to direct research activities and deliver a better understanding of complex interfaces and electronic circuits.
Significance for the country
A major scientific breakthrough is expected in the field of the heteroepitaxial growth of oxides on silicon using PLD technology, required for exploitation of rich properties of oxides for next generation electronics. Growth of oxides on Si has been studied by many research groups in the past, but the progress in epitaxial integration has always been hindered by the problem of the materials’ incompatibility.
Our preliminary results demonstrate possible path for single-crystalline growth of oxides on silicon using PLD. However, compared to MBE-grown layers, their structural quality is significantly smaller, which might be due to the intrinsically different nature of the corresponding two deposition techniques. In the MBE chamber, elements are evaporated from effusion cells and gently arrive to the surface, while in the PLD system a high-energy laser pulses generate a plume of supersaturated species with much higher kinetic energies. Related to the first objective of the project various oxide layers will be prepared using PLD and analyzed in situ with a number of techniques, like STM, XPS, and TPD. Surface defects, step edges, bonding site and wetting of the deposited material will be investigated. Additionally, aberration-corrected STEM will be used to gain atomistic insight into the unique structures of oxide and their interfaces with silicon. The proposed methodology will enable us to better understand integration of such dissimilar materials and to prepare epitaxial STO on Si platform with optimized stoichiometry and minimized concentration of structural defects.
For the second objective, the STO templates will be overgrown with piezoelectrics and heterostructures with 2DEG. The main purpose of this part of the project is to successfully integrate the well-established material systems with silicon and to maintain values of piezoelectric coefficients and electron mobilities that are as high as possible. By growing high-quality films we expect to exactly correlate their functional response with the crystal-structural properties of the films deposited on silicon, the lattice mismatch, and the compositional disorder. Furthermore, as-prepared structures will be tested on the device level, specifically for energy harvesting applications and field-effect transistors, to estimate their applicability in oxide electronics.
In addition to materials science, the proposed project also addresses various issues related to applied physics and electrical engineering. In response to that an interdisciplinary research team is proposed, connecting different national and international research departments and institutes, as described in the work programme. Thus a research cluster of scientist with complementary expertise will be created, which will help us to direct research activities and deliver a better understanding of complex interfaces and electronic circuits.
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