Wafer-Scale High-Quality Microtubular Devices

Fabricated via Dry-Etching for Optical and Microelectronic Applications

Significance 

Hierarchical structures ranging from microscale to nanoscale sizes are ubiquitous in nature. Although there are numerous building structures, self-assembly provides a more feasible and robust approach for building high-performance hierarchical structures. Self-assembly, especially at the nanoscale level, can be driven by the interactions between chemical functional groups. However, the mechanical engineering strain formed at the interfaces of thin films is crucial for fabricating self-assembled three-dimensional (3D) microarchitectures. Examples include cubes and microcylinders, which have found applications in various fields such as in photonics and electronics.

Similarly, self-assembly by rolling-up of structured thin-film stacks has been extensively investigated. In particular, it has been used to create micromachined devices such as roll-up microtubes with unique three-dimensional geometry desired for various applications. Typically, the fabrication of these microtubular architectures involves using wet-release techniques, which have several drawbacks. It reduces the yield, uniformity and quality of the resulting microtubular architectures as well as the overall deterioration of the device performance. These problems can be attributed to the presence of aggressive reagents and capillary forces.

Dry release methods have been identified as a promising solution due to their ability to delaminate the layer stacks during thermal annealing or when selectively under etched in the gaseous atmosphere. Equipped with this knowledge, a group of researchers at the Institute for Integrative Nanosciences in Germany: Christian Saggau (PhD candidate), Felix Gabler, Dr. Dmitriy Karnaushenko, Dr. Daniil Karnaushenko, Dr. Libo Ma and Professor Oliver Schmidt developed a wafer-fabrication of high quality and high-performance microtubular devices via dry rolling of dielectric, metallic and dielectric/metallic hybrid thin films. The authors purposed to use this method in different microelectronic and optical applications. Their work is currently published in the research journal, Advanced Materials.

In their approach, the process was divided into two: patterning of the thin films in a controlled wafer-scale fashion and dry release of the films in a gas or plasma atmosphere. Self-assembly of prestrained nanomembers was triggered in a controlled manner by etching a thin sacrificial silicon layer on an insulator using dry fluorine chemistry. The potential practical applications of this method in photonics and electronics as well as its complementary metal oxide semiconductor (CMOS) compatibility and integration, were discussed in detail.

The authors successfully demonstrated a simultaneous self-assembly process of thousands of integrated microcapacitors on a single wafer. The fabrication on a wafer-scale resulted in a high yield of devices with improved performance, uniformity and reproducibility desirable for broad applications in phonics and electronics. For instance, 84% and 91% yield of microcapacitors within the E24 and E12 IEC/EN 60062 industrial standard, respectively. For photonic devices, active microtubular optical cavities were fabricated on a wafer-scale. The optical microtube resonators exhibited optical resonances with a wide spectral range with Q-factors exceeding 7800 which is the highest reported for this kind of optical cavities. Furthermore, it was worth noting that the process quality could be improved in an industrial fabrication line due to its superior optimization deposition and cleanliness.

In a nutshell, a well-controlled and CMOS compatible method for the fabrication of high-quality and high-performance rolled-up microdevices on a wafer-scale is reported. The process addressed the limitations of the conventional wet-etching methods commonly used in the self-assembly techniques and is advantageous because it can be realized using standard tools like those used in the commercial production of photonics and electronic devices. Moreover, the approach can also be applied to other materials used to fabricate electronic and optical devices. In a statement to Advances in Engineering, the authors explained that the guided self-assembly provides opportunities for on-chip large-scale integration of high-performance 3D photonic, electronic and optoelectronic devices.

Wafer-Scale High-Quality Microtubular Devices Fabricated via Dry-Etching for Optical and Microelectronic Applications - Advances in Engineering
Figure 1. Microscope image showing wafer scale fabrication of rolled-up microbe capacitor arrays compared with a commercial multilayer-ceramic-chip-capacitor. Inset shows a zoom-in view of rolled-up microtubes for both microelectronic and optical applications.

About the author

Christian N. Saggau obtained his bachelor in nanoscience from the University of Hamburg. Afterwards he moved to Barcelona, where he obtained his master degree in photonics at the Polytechnic University of Catalunya (UPC) and the Institute of photonic science (ICFO). Since then he works as a PhD student at the Institute of Integrative Nanosciences, at the Leibniz Institute for Solid State Research and Material Science, under the supervision of Prof. Oliver G. Schmidt. His main field of interest are: nanophotonics, optical microcavities, strain engineering and nanofabrication.

About the author

Libo Ma is a research group leader in the Institute of Integrative Nanosciences, Leibniz IFW Dresden. He received his B.S. degree in physics from Shandong Normal University in 2001. He obtained his Ph.D. degree from the Institute of Physics, Chinese Academy of Sciences in 2007. His current research interests include cavity photonics, plasmonics, light–matter interactions, on-chip photonic integration, and topological photonics.

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About the author

Oliver G. Schmidt is the director of the Institute of Integrative Nanosciences, Leibniz IFW Dresden. He holds a full professorship for Materials Systems for Nanoelectronics at Chemnitz University of Technology, Germany. His interdisciplinary activities bridge across several research fields, ranging from nanophotonics and nanoelectronics to materials design and system engineering. His special interest lies with nanomembrane materials which can be strain-engineered and employed in multifunctional devices both on and off the chip.

Reference

Saggau, C., Gabler, F., Karnaushenko, D., Karnaushenko, D., Ma, L., & Schmidt, O. (2020). Wafer‐Scale High‐Quality Microtubular Devices Fabricated via Dry‐Etching for Optical and Microelectronic ApplicationsAdvanced Materials, 32(37), 2003252.

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