Microstructure Devices Research Articles

Comparative analysis of direct laser writing and nanoimprint lithography for fabrication of optical phase elements.

We report a comparison between two commercially available methods for printing phase shaping optical microstructures. Phase elements that convert a zero-order Hermite-Gaussian (HG00) mode into higher-order modes (HG10, HG01, HG20, and HG02) were fabricated by 3D-direct laser writing (3D-DLW) and nanoimprint lithography (NIL). The structures in each method were characterized and the corresponding beam qualities were analyzed. The direct comparison of equivalent optical devices enables us to reveal the limitations and advantages of the two fabrication methods in order to optimize the fabrication of useful optical microstructure devices. 3D-DLW enables sharper edges and a straightforward lithography process, while NIL enables fabrication of thinner elements, and allows using a larger variety of optical materials including sol-gel glasses, which possess better surface optical quality.

A Review of Magneto-Optical Microstructure Devices at Terahertz Frequencies

Recent research work on magneto-optical micro- structure devices in terahertz (THz) regime has been reviewed. Some magneto-optical materials responding at THz frequency range were introduced. Based on these magneto-optical materials, MO microstructures devices were reviewed, including magnetic photonic crystals, magneto-plasmonics, and magneto-metasurface all in the submillimetre scale. These devices can realize several functions of isolating, modulation, sensing, and directional beam scanning. Moreover, the necessary conditions of forming THz nonreciprocal transmission in magneto-optical microstructure devices were concluded, and the tunability of these devices was also analysed, which strongly depends on the magneto-optical property of material and the symmetry of structure. The unique magneto-optical effects make it play an irreplaceable role in the high performance THz applications of communication, imaging, and sensing systems.

Femtosecond laser internal manufacturing of three-dimensional microstructure devices

Potential applications for three-dimensional microstructure devices developed rapidly across numerous fields including microoptics, microfluidics, microelectromechanical systems, and biomedical devices. Benefiting from many unique fabricating advantages, internal manufacturing methods have become the dominant process for three-dimensional microstructure device manufacturing. This paper provides a brief review of the most common techniques of femtosecond laser three-dimensional internal manufacturing (3DIM). The physical mechanisms and representative experimental results of 3D manufacturing technologies based on multiphoton polymerization, laser modification, microexplosion and continuous hollow structure internal manufacturing are provided in details. The important progress in emerging applications based on the 3DIM technologies is introduced as well.

Microstructure devices for process intensification: Influence of manufacturing tolerances and design

Process intensification by miniaturization is a common task for several fields of technology. Starting from manufacturing of electronic devices, miniaturization with the accompanying opportunities and problems gained also interest in chemistry and chemical process engineering. While the integration of enhanced functions, e.g. integrated sensors and actuators, is still under consideration, miniaturization itself has been realized in all material classes, namely metals, ceramics and polymers. First devices have been manufactured by scaling down macro-scale devices. However, manufacturing tolerances, material properties and design show much larger influence to the process than in macro scale. Many of the devices generated alike the macro ones work properly, but possibly could be optimized to a certain extend by adjusting the design and manufacturing tolerances to the special demands of miniaturization. Thus, some considerations on the design and production of devices for micro process engineering should be made to provide devices which show reproducible and controllable process behavior. The aim of the following publication is to show the importance of considerations in manufacturing tolerances and dimensions as well as design of microstructures to avoid negative influences and optimize the process characteristics of miniaturized devices. Some examples will be shown to explain the considerations presented here.

Microstructure Devices for efficient Evaporation of Liquids

Different microstructure devices used for evaporation and generation of steam are described in this publication. Starting with simple liquid-heated devices, electrically powered devices containing micro channels as well as non-channel microstructures are shown. An electrically powered device for optical inspection of the microstructures and the processes inside has been designed and manufactured. Exchangeable metallic micro channel array foils as well as an optical inspection of the evaporation process by high-speed videography have been integrated into this test system. Fundamental research onto the influences of the inlet flow distribution system geometry and the geometry and dimensions of the micro channels have been performed. A pre-calculation sheet for micro evaporators with micro channel arrays based on the measurement of inlet parameters for the liquid only was generated. While evaporation of liquids in micro channel devices of more or less conventional design is possible, it is, in many cases, not feasible to generate superheated steam due to certain boundary conditions. Therefore a new design was proposed to obtain complete evaporation and steam superheating, consisting of an arrangement of numerous circular blanks with connecting nozzles. A maximum power density of 1400 kW · m−2 has been transferred while water could be completely evaporated and the generated steam superheated.

Comparative study of photonic band gaps of germanium-based two-dimensional triangular-lattice and square-lattice and decagonal quasi-periodic photonic crystals

Photonic band gaps (PBGs) of germanium-based two-dimensional (2D) triangular-lattice and square-lattice and decagonal quasi-periodic photonic crystals (PCs) with the scatterer radius in the range of [0,0.3a] and within two cases of the construction (germanium cylinders being placed in air, air cylinders being placed in germanium) have been calculated by using the plane wave expansion (PWE) method. Germanium-based 2D triangular-lattice PC and 2D decagonal quasi-periodic PC are more easily to generate PBG than 2D square-lattice PC. 2D decagonal quasi-periodic PC is more easily to generate complete band gap than the other two kinds of PCs. The PBG properties of the three PCs are similar to the properties of silicon-based system as the radius of the scatterer cylinder increases. Nevertheless, the germanium-based system is more likely to generate PBG than silicon-based system. These findings will guide the design of PBG-type microstructure devices.

Endpoint Detection Strategy in Bosch Process Using PCA and HMM

Bosch process is developed for advanced microstructure devices and etch endpoint detection (EPD) is demanded for 'notching' (as feature profile degradation) or reducing thickness of the underlying stop. One method commonly used to detect plasma process endpoint is utilizing optical emission spectrometry (OES) sensor. OES analyzes the light emitted from plasma source to draw inferences about the chemical and physical state of the plasma process. In this paper, an endpoint detection algorithm conjunction with Principal Component Analysis (PCA) and extended Hidden Markov Model (eHMM) using OES signal in Bosch process is proposed. PCA is used to reduce dimension of data without information loss and eHMM is applied to correctly detect endpoint. In 120 um TSVs, this work shows excellent performance.

Microstructure Evolution and Device Performance in Solution-Processed Polymeric Field-Effect Transistors: The Key Role of the First Monolayer

Probing the role of the first monolayer in the evolution of the film polymer microstructure is essential for the fundamental understanding of the charge carrier transport in polymeric field-effect transistors (FETs). The monolayer and its subsequent microstructure of a conjugated polymer [poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT] film were fabricated via solution deposition by tuning the dip-coating speed and were then studied as accumulation and transporting layers in FETs. Investigation of the microstructure of the layers prepared at different coating velocities revealed that the monolayer serves as an important base for further development of the film. Significant improvement of the charge carrier transport occurs only at a critical multilayer network density that establishes the required percolation pathways for the charge carriers. Finally, at a low dip-coating speed, the polymer chains are uniaxially oriented, yielding pronounced structural anisotropy and high charge carrier mobilities of 1.3 cm(2) V(-1) s(-1) in the alignment direction.

Microstructure devices for water evaporation

Microstructure devices for water evaporation

Deformation Mode Construction Using Photoresist Microstructure Devices Produced with Nanoindention Technology

In this study, we try to produce SU-8 photoresist microstructure devices using nano-imprint technology, and try to conduct nano-indention tests on SU-8 photoresist with nano-indention detector, in order to describe the behaviors and characteristics of nano-indentions on SU-8 microstructure devices and establish the deformation mode for the indention under nano-meter level. The tests tell us that, after nano-indention tests, the result indention hardness increases with the loading rate, indention repeats, and reduction of load or depth. Similarly, the indention hardness decreases because of reduction of loading rate, extension of loading time, and increase of load, and depth. Finally, we propose a deformation mode for nano-indention. This mode can also be used to explain the deformation behavior of SU-8 under nano-indention.

Development and Characterization of Quasi-Optical Mesh Filters and Metastructures for Subterahertz and Terahertz Applications

We review our recent results on development of passive quasi-optical selective devices based on metallized subwavelength microstructure arrays designed for controlling radiation beams at frequencies from a few tens GHz up to ten THz: filters, polarizers, metasurfaces, ET-metamaterial lenses. The methods of electromagnetic simulation, technological implementation and (sub)THz-characterization of microstructure devices, as well as their applications, are discussed.

Cu deficiency in multi-stage co-evaporated Cu(In,Ga)Se 2 for solar cells applications: Microstructure and Ga in-depth alloying

The objective of this work is to study the influence of the maximum Cu content during the deposition of Cu(In,Ga)Se 2 (CIGSe) by multi-stage co-evaporation on the phases present in the final film, the film structure and the electrical properties of resulting solar cell devices. The variation of the composition is controlled by the Cu content in stage 2 of the deposition process. The different phases are identified by Raman spectroscopy. The in-depth Ga gradient distribution is investigated by in-depth resolved Raman scattering and secondary neutral mass spectroscopy. The morphology of the devices is studied by scanning electron microscopy. Efficiencies of 9.2% are obtained for ordered-vacancy-compound-based cells with a Cu/(In + Ga) ratio = 0.35, showing the system’s flexibility. This work supports the current growth model: a small amount of Cu excess during the absorber process is required to obtain a quality microstructure and high performance devices.

A novel device for the optical investigation of phase transition in micro channel array evaporators

Abstract Evaporation is one of the most important unit operations in thermal and chemical process engineering. Microstructure devices are especially well-suited to act as evaporators. Due to the extraordinary heat exchange performance, electrically powered micro heat exchangers are predestinated to act as evaporators in order to provide sufficient thermal energy for evaporation. Phase transition in micro channels, especially in micro channel arrays, is accompanied by phenomena like vapor clogging, vapor slugging or pressure drop, mass flow and temperature fluctuations. These arrays consist of a multitude of micro channels, which are connected to a collective fluid inlet and outlet. The main objective of this research is to investigate phase transition in micro channel arrays through identify the dependence of phase transition on microstructure geometry. In this publication, a novel electrically heated device which enables the optical investigation of processes inside micro channels is presented and compared to a previous design. The device generates a nearly homogeneous temperature distribution in micro channel arrays and additionally provides various degrees of freedom concerning the microstructure geometry. Methods of investigation as well as equipment required for characterization are presented. The optical investigation of multiphase flow composed of water and steam is performed by an optical microscope and a CCD-based digital high-speed camera with recording frequencies in the range of several 1000 up to a few 100,000 pictures per second.

Microstructure devices for efficient heat transfer

Microstructure devices provide unique properties with regard to heat and mass transfer. Due to the tremendously high surface-to-volume ratio they are very well suited for many thermal and chemical processes in which large amount of heat has to be transferred. Metal microstructure devices also provide very high stability against high pressure, combined with an adjustable mass flow range of up to several thousand kg of liquid per hour and per passage, depending on the size and number of the integrated microstructures. Aside of fluid driven metallic microstructure devices like the famous Karlsruhe Cube, electrically powered devices have been developed and applied for temperature ranges where thermoliquids reach their limits or the use of gases may be disadvantageous due to their high viscosity and the arising pressure drop. In this publication several microstructure devices for heating and evaporation of fluids as well as for chemical reactions are presented in overview style. Details on manufacturing and device properties are given. Some process examples and experimental data for different types of microstructure devices are shown. Fouling problems are discussed briefly by an example.

Forced periodic temperature cycling of chemical reactions in microstructure devices

In this publication, several stainless steel microstructure reactors specially designed to obtain rapid and periodic temperature changes are presented. Different microstructure reactor designs have been manufactured and tested for their thermal behaviour and equally by running a test reaction under stationary and non-stationary temperature conditions. The devices were continuously electrically heated and periodically cooled by a deionized water flow. The objective of the experimental measurements was to demonstrate that non-stationary temperature conditions may lead to an increase in the reaction rate compared to the stationary conditions. The heterogeneously catalysed oxidation of CO was chosen as the test reaction. The catalyst used was a dispersion of platinum on a porous alumina support generated by sol–gel technology. The experiments realized under non-stationary temperature conditions with a temperature oscillation amplitude of 41 K and a period duration of 21 s show an increase in the mean CO 2 concentration of a factor 1.72 compared to the mean concentration under quasi-stationary temperature conditions. The simulations of a simple monomolecular reaction under non-stationary temperature conditions indicate that the presence of a transitional surface coverage generated by the temperature oscillations may be a possible explanation for the observed phenomenon.

Microstructure Heat Exchanger Applications in Laboratory and Industry

In this article, heat transfer in microstructure devices and its application in laboratory and industry will be described. Basic principles of microstructure heat exchangers made of metal, ceramics, and polymers will be presented. A variety of laboratory prototype applications will be shown, as well as some examples for industrial use of not only microstructure heat exchangers, but also microstructure devices as chemical reactors. A brief outlook will describe possible future application fields.

Testing and simulation of ceramic micro heat exchangers

Abstract Ceramic microstructure devices in form of counterflow and crossflow microchannel heat exchangers have been manufactured to be used in thermal and chemical process engineering. The performance has been tested using water as a test fluid with maximum flow rates of 120 kg/h. The results of the measurements are compared with global estimations using standard correlations for heat exchangers and a more detailed simulation using a local porous body approach of the micro structured region. The devices show stronger heat transfer and pressure loss than predicted by theoretical considerations. This result is mainly explained by effects of channel blockages arising from the joining process.

Reducing side product by enhancing mass‐transfer rate

AbstractFast mass transfer rate and short reaction time are required to reduce side product of the premixing reaction, in the SNIA Viscosa process, as a liquid‐liquid competitive consecutive system. In order to obtain high selectivity, a microstructure device, named a membrane dispersion mini‐reactor, was designed and tested at several operation conditions. The mass transfer rate of cyclohexanecarboxylic acid (CCA) was significantly increased by membrane dispersion in this mini‐reactor compared with a traditional batch reactor and a membrane free one, just with a residence time less than 80 ms. The results showed that the nominal yield of side product was lower than 10% in the reaction products and about 5% lower than the traditional stirring method. Additionally, a theoretical model was developed to eliminate the mass transfer flux in this mini‐reactor, and the calculation results fit well with the experimental data. © 2006 American Institute of Chemical Engineers AIChE J, 2006

3D Optical microstructure fabrication and its bonding to micro IR detector using elastomeric polymer

This paper describes polidimethylsiloxane(PDMS) based bonding for assembly of microstructure device, an UV lithography applications for fabricating a 3-dimensional (3D) feed-horn-shaped structure mold array, and obtaining parallel light by using a mirror-reflected parallel-beam illuminator (MRPBI) system. A 3D feed-horn-shaped micro-electro-mechanical systems (MEMS) antenna has some attractive features for array applications, which can be used to improve microbolometer performance and to enhance the optical efficiency for thin film transistor-liquid crystal display (TFT-LCD) and other display devices but currently, MEMS technology has faced many difficulties in the fabrication of a 3D feed-horn-shaped MEMS antenna array itself. The purpose of this paper is to propose a new fabrication method to realize a 3D feed-horn-shaped MEMS antenna array by using a mirror-reflected parallel-beam illuminator (MRPBI) System with a very slowly rotated, inclined x-y-z stage. With a conventional UV lithography apparatus, it is very difficult to fabricate high-aspect-ratio structures (HARS) because a typical UV lithography apparatus cannot produce perfectly parallel light. From a theoretical analysis, a columnar illuminator over 6 m in height is required to achieve parallel light, but generally a laboratory height is not 6 m. Also, a novel method of lithography was tried to make a 3D structure array by exposing a planar wafer to the generated parallel light and rotating an inclined x-y-z stage at an ultra-slow rate. An optimization of the 3D structure array can be achieved by simulating a 3D feed-horn MEMS antenna. The feasibility of fabricating both a 3D feed horn MEMS antenna and assembly of detector with 3D feed-horn MEMS antenna was demonstrated. As a result, it seems possible to use a 3D feed-horn-shaped MEMS antenna to improve microbolometer performance and to fabricate several optical microstructure applications.

Fast temperature cycling in microstructure devices

For a couple of years, unsteady state processing has been discussed to be possibly advantageous for chemical process engineering. Specifically periodic changes of reaction parameters are expected to enhance the rates of certain reactions [Chem. Eng. Commun. (1973) 111]. For different reaction systems, concentration cycling has been performed [P.L. Silveston, Composition Modulation of Catalytic Reactors, Gordon and Breach, Amsterdam, 1998]. In contrast, a fast periodic modulation of the reactor temperature, even though potentially beneficial, has long been considered to be beyond reach because of the large thermal masses and the poor surface-to-volume ratio which restrict the heat exchange between conventional reactor systems (e.g. fixed bed reactors) and heating/cooling systems. Recently, microstructure devices for fast temperature cycling have been described [J.J. Brandner, G. Emig, M. Fichtner, M.A. Liauw, K. Schubert, A new microstructure device for fast temperature cycling for chemical reactions, in: M. Matlosz, W. Ehrfeld, J.P. Baselt (Eds.), Proceedings of the Fifth International Conference on Microreaction Technology, IMRET 5, Springer, Berlin, 2001, pp. 164–174; Chem. Eng. Sci. 56 (2001) 1419; Gen. Eng. News 22 (11), 42]. The devices make it possible to obtain a periodic temperature change by 100 K in the second to subsecond range. A method for catalyst integration into microstructure devices will be described briefly. First results on the stability of catalyst carrier layers with respect to fast temperature changes are very promising. The oxidation of carbon monoxide was chosen as model reaction. Under fast temperature cycling conditions, a considerably higher yield compared to the steady state could be observed.