Three-dimensional microfabrication through a multimode optical fiber

3D printing based on additive manufacturing is an advanced manufacturing technique that allows the fabrication of arbitrary macroscopic and microscopic objects. Many 3D printing systems require large optical elements or nozzles in proximity to the built structure. This prevents their use in applications in which there is no direct access to the area where the objects have to be printed. Here, we demonstrate three-dimensional microfabrication based on two-photon polymerization (TPP) through an ultra-thin printing nozzle of 560 mu m in diameter. Using wavefront shaping, femtosecond infrared pulses are focused and scanned through a multimode optical fiber (MMF) inside a photoresist that polymerizes via two-photon absorption. We show the construction of arbitrary 3D structures built with voxels of diameters down to 400 nm on the other side of the fiber. To our knowledge, this is the first demonstration of microfabrication through a multimode optical fiber. The proposed printing nozzle can reach and manufacture micro-structures in otherwise inaccessible areas through small apertures. Our work represents a new area which we refer to as endofabrication. (C) 2017 Optical Society of America

Growth and characterization of single quantum dot devices for fiber-based quantum communications

Blandine Alloing

Single photon sources have recently attracted significant interest for their potential role in the future applications of quantum cryptography, and in the longer term, quantum computing. Among the different types of single photon emitters, semiconductor quantum dots (QDs) are good candidates as they combine discrete electronic transitions with the possibility of electrical excitation. Self-assembled InAs QDs on GaAs substrate are by far the most studied system as they can easily be grown into a microcavity structure. Embedding these into a microcavity is important as it increases the extraction efficiency, directionality and speeds up the photon emission. Until now, most studies have concentrated on QDs emitting in the λ

EPFL2006

Characterisation and applications of stencil lithography

Jürgen Brugger, Nao Takano, Marc Antonius Friedrich van den Boogaart, Oscar Vazquez Mena

Increased flexibility of patterning methods is important for the engineering of multimaterial and multifunctional nano/micro-electro-mechanical systems (NEMS/MEMS), such as polymer-based electronic and sensor devices, 3D microfluidic systems, and bio-analytical systems. Stencil lithography is a good candidate as it is a resistless, single step patterning method based on direct, local deposition of material on an arbitrary surface through a solid-state membrane, e.g. a 200-nm thick silicon nitride (SiN) membrane. We present two new stencil membrane stabilisation geometries and associated MEMS processes that allow for advancing further towards a well-controlled full-wafer (100 mm) nanostencil process for reproducible, high-throughput, large-area nanopatterning of mesoscopic structures (10-9 - 10-3 m). In fact, the major challenges for well-controlled and reproducible nanostencil lithography are to control stress-induced membrane deformation, clogging of membrane apertures and the gap between stencil and substrate. The stabilized membranes show improved membrane stability (i.e. reduced out-of-plane deformation) up to 94%, resulting in an improved pattern definition of stencil-deposited structures. We have also systematically characterized the clogging of membrane apertures and the influence of the gap between stencil and substrate on the deposited structures as a function of aperture size and deposited material. A method is presented to recover nominal dimensions of stencil-deposited structures over a gap. To integrate nanomechanical structures with CMOS circuits, stencil lithography was used as a clean, CMOS-compatible method to define the mechanical structures on a CMOS circuit, using the stencildeposited metal patterns as a mask for silicon reactive ion etching (RIE). When the stencil and the CMOS wafer are put in contact, a gap exists between the layer to be structured and the stencil. We have been able to correct the blurring effect by developing a controlled dry Al etch process. The results obtained provide a clear remedy to overcome one of the major challenges in nanostencil-based surface patterning. Stencil lithography is also used in the development of novel nanotemplates of anodic porous alumina (APA). To obtain APA structures with high regularity, a method to pre-pattern the surface of the aluminum substrate before conventional anodization is a prerequisite. A pre-patterned arrangement of dots or holes on Al plates is obtained by evaporation, sputtering, electrodeposition, or chemical etching through stencils. It should result in a high regularity mono-domain APA with pore spacing comparable with the visible wavelength for large area photonic crystals for optical applications and luminescence devices.

2005

Inkjet printing and high aspect ratio structuring for polymer-based micro and nano systems

Vahid Fakhfouri

Inkjet printing of functional materials, photolithography and micromolding are 3 different techniques largely used in the field of micro-electromechanical systems (MEMS) with increasing interest for the fabrication of new devices and the development of new applications. This Ph.D. thesis provides new insights into each of these fields and, by combining them, aims to enable the access to new application fields. Complementary to photolithography, inkjet printing is increasingly considered a cost-effective and flexible microfabrication method to structure functional materials. The ease of mass fabrication and the inherent flexibility of inkjet technology make it a suitable method for the manufacturing of microsystems and components. The results presented in this dissertation summarize recent achievements in this relatively new technology for the development of miniaturized devices. First the piezo-acoustic inkjet printing technology is described and a theory to explain the drop generation process is developed and evaluated. The experimental work was focused on the drop-on-demand inkjet printing of viscous polymers, particularly SU-8, a negative tone photo-resist epoxy. It validates the theoretical predictions and shows the shortcomings of the existing theories. The camera-assisted high accuracy alignment (< 3 µm misalignment) technique developed in the frame of this work enables the precise positioning of microdrops on pre-structured substrates and accurate filling of high aspect ratio micromolds. Additionally, polymeric microlenses were also Inkjet-printed and characterized. The highly reproducible optical properties of such microlenses, i.e. the focal length in the range of 40-150 µm and the numerical aperture in the range of 0.25-0.75, can be adjusted for different applications in micro-optical systems. An innovative technique, based on micromolding, for the microfabrication of high aspect ratio ceramic structures using polymeric precursors is also presented. Polyureasilazane, a precursor for silicon-carbide-based ceramics was investigated. Pipettes and inkjet printers were used to fill high-aspect ratio SU-8 molds. The micromolded structures were released using a sacrificial layer. After a pyrolysis step which enables the polymer-to-ceramic transformation in a simple tube furnace, the final structures showed that this process is very reliable as the mold shapes were perfectly replicated and a smooth surface was obtained. This technique is an interesting candidate for the fabrication of ceramic devices for harsh environments and high temperatures. Incorporation of luminescent nanocrystals (NCs) in SU-8 is another contribution of this thesis. For this purpose, the selection of an appropriate solvent for both NCs and the epoxy-resist formulation is fundamental in directing the nanocomposite resist preparation. The NC-modified SU-8 was successfully patterned and high aspect ratio structures with micrometer resolution were fabricated, showing that the overall UV-structuring capability of the modified resist was not affected by the NC incorporation. The obtained microstructures were shown to retain the NC emission properties. Finally the possibility to combine inkjet printing, micromolding and photopolymerization for the fabrication of Hybrid AFM probes by a single-plane surface-micromachining technique was demonstrated. Hybrid AFM probes, with a tip made of a hybrid organic/inorganic polymer and a cantilever and a holder made of SU-8 were micro-structured, characterized and tested for AFM imaging. The results were compared with a commercial silicon probe and a SU-8 AFM cantilever. This technology can be used to convey new properties to scanning microscopy probes for new sensing applications or to improve the quality of the existing devices. Functional materials can be inkjet-printed to form the tips with a minimum material waste. This thesis is intended to contribute to the advancement of micromachining technologies in the area of micro-devices with enhanced properties. In particular, it shall contribute to the cost effective fabrication of hybrid components made of different functionalized materials.