Physics-based virtual coherence scanning interferometer for surface measurement
Rong Su, Richard Leach
Published Published online: 01 April 2021,  doi: 10.37188/lam.2021.009
Virtual instruments provide task-specific uncertainty evaluation in surface and dimensional metrology. We demonstrate the first virtual coherence scanning interferometer that can accurately predict the results from measurements of surfaces with complex topography using a specific real instrument. The virtual instrument is powered by physical models derived from first principles, including surface-scattering models, three-dimensional imaging theory, and error-generation models. By incorporating the influences of various error sources directly into the interferogram before reconstructing the surface, the virtual instrument works in the same manner as a real instrument. To enhance the fidelity of the virtual measurement, the experimentally determined three-dimensional transfer function of a specific instrument configuration is used to characterise the virtual instrument. Finally, we demonstrate the experimental validation of the virtual instrument, followed by virtual measurements and error predictions for several typical surfaces that are within the validity regime of the physical models.
[HTML FullText](398) [PDF 7262KB](85)
3D printed micro-optics for quantum technology: Optimised coupling of single quantum dot emission into a single-mode fibre
Marc Sartison, Ksenia Weber, Simon Thiele, Lucas Bremer, Sarah Fischbach, et al.
Published Published online: 31 March 2021,  doi: 10.37188/lam.2021.006
Future quantum technology relies crucially on building quantum networks with high fidelity. To achieve this challenging goal, it is of utmost importance to connect individual quantum systems such that their emitted single photons overlap with the highest possible degree of coherence. This requires perfect mode overlap of the emitted light from different emitters, which necessitates the use of single-mode fibres. Here, we present an advanced manufacturing approach to accomplish this task. We combined 3D printed complex micro-optics, such as hemispherical and Weierstrass solid immersion lenses, as well as total internal reflection solid immersion lenses, on top of individual indium arsenide quantum dots with 3D printed optics on single-mode fibres and compared their key features. We observed a systematic increase in the collection efficiency under variations of the lens geometry from roughly 2 for hemispheric solid immersion lenses up to a maximum of greater than 9 for the total internal reflection geometry. Furthermore, the temperature-induced stress was estimated for these particular lens dimensions and results to be approximately 5 meV. Interestingly, the use of solid immersion lenses further increased the localisation accuracy of the emitters to less than 1 nm when acquiring micro-photoluminescence maps. Furthermore, we show that the single-photon character of the source is preserved after device fabrication, reaching a \begin{document}$ g^{(2)} (0)$\end{document} value of approximately 0.19 under pulsed optical excitation. The printed lens device can be further joined with an optical fibre and permanently fixed.This integrated system can be cooled by dipping into liquid helium using a Stirling cryocooler or by a closed-cycle helium cryostat without the necessity for optical windows, as all access is through the integrated single-mode fibre. We identify the ideal optical designs and present experiments that demonstrate excellent high-rate single-photon emission.
[HTML FullText](596) [PDF 4203KB](100)
3D-printed miniature spectrometer for the visible range with a 100 × 100 μm2 footprint
Andrea Toulouse, Johannes Drozella, Simon Thiele, Harald Giessen, Alois Herkommer
Published Published online: 04 February 2021,  doi: 10.37188/lam.2021.002
The miniaturisation of spectroscopic measurement devices opens novel information channels for size critical applications such as endoscopy or consumer electronics. Computational spectrometers in the micrometre size range have been demonstrated, however, these are calibration sensitive and based on complex reconstruction algorithms. Herein we present an angle-insensitive 3D-printed miniature spectrometer with a direct separated spatial-spectral response. The spectrometer was fabricated via two-photon direct laser writing combined with a super-fine inkjet process. It has a volume of less than 100 × 100 × 300 μm3. Its tailored and chirped high-frequency grating enables strongly dispersive behaviour. The miniature spectrometer features a wavelength range of 200 nm in the visible range from 490 nm to 690 nm. It has a spectral resolution of 9.2 ± 1.1 nm at 532 nm and 17.8 ± 1.7 nm at a wavelength of 633 nm. Printing this spectrometer directly onto camera sensors is feasible and can be replicated for use as a macro-pixel of a snapshot hyperspectral camera.
[HTML FullText](2182) [PDF 9794KB](508)
Non-destructive thickness characterisation of 3D multilayer semiconductor devices using optical spectral measurements and machine learning
Hyunsoo Kwak, Sungyoon Ryu, Suil Cho, Junmo Kim, Yusin Yang, et al.
Published Published online: 12 January 2021,  doi: 10.37188/lam.2021.001
Three-dimensional (3D) semiconductor devices can address the limitations of traditional two-dimensional (2D) devices by expanding the integration space in the vertical direction. A 3D NOT-AND (NAND) flash memory device is presently the most commercially successful 3D semiconductor device. It vertically stacks more than 100 semiconductor material layers to provide more storage capacity and better energy efficiency than 2D NAND flash memory devices. In the manufacturing of 3D NAND, accurate characterisation of layer-by-layer thickness is critical to prevent the production of defective devices due to non-uniformly deposited layers. To date, electron microscopes have been used in production facilities to characterise multilayer semiconductor devices by imaging cross-sections of samples. However, this approach is not suitable for total inspection because of the wafer-cutting procedure. Here, we propose a non-destructive method for thickness characterisation of multilayer semiconductor devices using optical spectral measurements and machine learning. For > 200-layer oxide/nitride multilayer stacks, we show that each layer thickness can be non-destructively determined with an average of approximately 1.6 Å root-mean-square error. We also develop outlier detection models that can correctly classify normal and outlier devices. This is an important step towards the total inspection of ultra-high-density 3D NAND flash memory devices. It is expected to have a significant impact on the manufacturing of various multilayer and 3D devices.
[HTML FullText](1788) [PDF 2903KB](239)
Three-Dimensional Direct Laser Writing of PEGda Hydrogel Microstructures with Low Threshold Power using a Green Laser Beam
Haoyi Yu, Haibo Ding, Qiming Zhang, Zhongze Gu, Min Gu
Published Published online: 12 January 2021,  doi: 10.37188/lam.2021.003
Three-dimensional (3D) direct laser writing (DLW) based on two-photon polymerisation (TPP) is an advanced technology for fabricating precise 3D hydrogel micro- and nanostructures for applications in biomedical engineering. Particularly, the use of visible lasers for the 3D DLW of hydrogels is advantageous because it enables high fabrication resolution and promotes wound healing. Polyethylene glycol diacrylate (PEGda) has been widely used in TPP fabrication owing to its high biocompatibility. However, the high laser power required in the 3D DLW of PEGda microstructures using a visible laser in a high-water-content environment limits its applications to only those below the biological laser power safety level. In this study, a formula for a TPP hydrogel based on 2-hydroxy-2-methylpropiophenone (HMPP) and PEGda was developed for the fabrication of 3D DLW microstructures at a low threshold power (0.1 nJ per laser pulse at a writing speed of 10 μm·s−1) in a high-water-content environment (up to 79%) using a green laser beam (535 nm). This formula enables the fabrication of microstructures with micrometre fabrication resolution and high mechanical strength (megapascal level) and is suitable for the fabrication of water-responsive, shape-changing microstructures. These results will promote the utilisation of low-power 3D DLW for fabricating hydrogel microstructures using visible lasers in high-water-content environments.
[HTML FullText](1370) [PDF 7859KB](197)
Review of geometric error measurement and compensation techniques of ultra-precision machine tools
Zongchao Geng, Zhen Tong, Xiangqian Jiang
Published Published online: 08 May 2021,  doi: 10.37188/lam.2021.014
Inevitable machine motion errors change the cutting tool trajectory and degrade the machined surface quality. Compared to the mature error measurement technologies developed for traditional precision CNC machine tools, the increasing use of ultra-precision machine tools (UPMTs) has shown some distinctive characteristics in error modelling, measurement, and compensation. This paper attempts to summarise state-of-the-art research in the calibration of geometric errors of UPMTs. A general routine for a UPMT error calibration is proposed in this literature review. Various error modelling methods, instruments, and measurement methods applicable to the geometric error measurement of both the linear and rotary axes are discussed using typical case studies. With respect to these achievements, there is a real concern regarding the reproducibility of measurement sensors used for the calibration of UPMTs and it remains challenging to decompose the volumetric motion error of UPMTs. Owing to the high flexibility in practice, trial cutting and a sensitivity analysis-based error measurement and compensation provide a promising solution to achieve a fast UPMT calibration.
[HTML FullText](72) [PDF 7943KB](15)
Extracellular scaffold design for ultra-soft microtissue engineering
Jiaqi Wang, Xiaowei Tang, Zitian Wang, Jiawei Li, Shaohua Ma
Published Published online: 10 April 2021,  doi: 10.37188/lam.2021.011
Soft and ultra-soft extracellular scaffolds constitute a major fraction of most human internal organs, except for the skeletal system. Modelling these organs in vitro requires a comprehensive understanding of their native scaffolding materials and proper engineering approaches to manufacture tissue architectures with microscale precision. This review focuses on the properties of soft and ultra-soft scaffolds, including their interactions with cells, mechanical properties (e.g. viscoelasticity), and existing microtissue engineering techniques. It also summarises challenges presented by the conflict between the properties of the materials demanded by cell behaviours and the capacities of engineering techniques. It proposes that leveraging the engineering ability of soft and ultra-soft scaffolds will promote therapeutic advances and regenerative medicine.
[HTML FullText](221) [PDF 6915KB](45)
Metasurfaces for manipulating terahertz waves
Xiaofei Zang, Bingshuang Yao, Lin Chen, Jingya Xie, Xuguang Guo, et al.
Published Published online: 22 March 2021,  doi: 10.37188/lam.2021.010
Terahertz (THz) science and technology have attracted significant attention based on their unique applications in non-destructive imaging, communications, spectroscopic detection, and sensing. However, traditional THz devices must be sufficiently thick to realise the desired wave-manipulating functions, which has hindered the development of THz integrated systems and applications. Metasurfaces, which are two-dimensional metamaterials consisting of predesigned meta-atoms, can accurately tailor the amplitudes, phases, and polarisations of electromagnetic waves at subwavelength resolutions, meaning they can provide a flexible platform for designing ultra-compact and high-performance THz components. This review focuses on recent advancements in metasurfaces for the wavefront manipulation of THz waves, including the planar metalens, holograms, arbitrary polarisation control, special beam generation, and active metasurface devices. Such ultra-compact devices with unique functionality make metasurface devices very attractive for applications such as imaging, encryption, information modulation, and THz communications. This progress report aims to highlight some novel approaches for designing ultra-compact THz devices and broaden the applications of metasurfaces in THz science.
[HTML FullText](634) [PDF 16800KB](277)
Miniaturising artificial compound eyes based on advanced micronanofabrication techniques
Lin Zhu, Yong-Lai Zhang, Hong-Bo Sun
Published Published online: 25 February 2021,  doi: 10.37188/lam.2021.007
Compound eyes (CEs) are advanced optical visual systems with distinct features of large view-fields, infinite depth of field, and dynamic imaging capability, revealing their significant potential in applications including robot vision, unmanned aerial vehicle detection, and medical diagnosis. Compared with macroscopic CEs, which primarily comprise multicamera arrays, compact integrated CEs have garnered significant attention because of their portability and possibility of flexible integration with microrobots and in-vivo medical facilities. To date, considerable effort has been devoted to this field, in which manufacturing technologies are vital to the development of artificial CEs (ACEs) capable of large field-of-view imaging, depth information collection, and three-dimensional imaging. Challenges and opportunities exist for the practical application of advanced ACEs. This paper reviews state-of-the-art technologies for manufacturing ACEs, and then briefly summarises their potential applications in different fields. Finally, the current challenges and perspectives of ACEs are discussed.
[HTML FullText](928) [PDF 11437KB](214)
Recent Progress in Heterogeneous III-V-on-Silicon Photonic Integration
Di Liang, John E. Bowers
Published Published online: 24 February 2021,  doi: 10.37188/lam.2021.005
Silicon (Si) photonics is a disruptive technology on the fast track to revolutionise integrated photonics. An indispensable branch thereof, heterogeneous Si integration, has also evolved from a science project 15 years ago to a growing business and compelling research field today. We focus on the scope of III-V compound semiconductors heterogeneously integrated on Si substrates. The commercial success of massively produced integrated optical transceivers based on first-generation innovation is discussed. Then, we review a number of technological breakthroughs at the component and platform levels. In addition to the numerous new device performance records, our emphasis is on the rationale behind and the design principles underlying specific examples of materials and device integration. Finally, we offer perspectives on development trends catering to the increasing demand in many existing and emerging applications.
[HTML FullText](1137) [PDF 7935KB](348)
Recent progress of skin-integrated electronics for intelligent sensing
Dengfeng Li, Kuanming Yao, Zhan Gao, Yiming Liu, Xinge Yu
Published Published online: 12 January 2021,  doi: 10.37188/lam.2021.004
Skin-integrated electronics are a novel type of wearable devices that are mounted on the skin for physiological signal sensing and healthcare monitoring. Their thin, soft, and excellent mechanical properties (stretching, bending, and twisting) allow non-irritating and conformal lamination on the human skin for multifunctional intelligent sensing in real time. In this review, we summarise the recent progress in the intelligent functions of skin-integrated electronics, including physiological sensing, sensory perception, as well as virtual and augmented reality (VR/AR). The detailed applications of these electronics include monitoring physical- and chemical-related health signals, detecting body motions, and serving as the artificial sensory components for visual-, auditory-, and tactile-based sensations. These skin-integrated systems contribute to the development of next-generation e-eyes, e-ears, and e-skin, with a particular focus on materials and structural designs. Research in multidisciplinary materials science, electrical engineering, mechanics, and biomedical engineering will lay a foundation for future improvement in this field of study.
[HTML FullText](1539) [PDF 13494KB](312)
Letter to the Editor
Author Correction
Bigger, Stronger and More Open, the “Engineering, Manufacturing” Category in SCI
Bi Ning
Published Published online: 02 July 2020,  doi: 10.37188/lam.2020.003
The number of journals and papers in “Engineering, Manufacturing” category is getting bigger. Bibliometrics indicators of this category reveals the positive trend of robust and open, however it lags the advance of Open Access in the whole SCI database.
[HTML FullText](1534) [PDF 1369KB](113)