Article

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: 10 January 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.
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.
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.