The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near-edge region can be fitted to a simple expression in which the intercept gives the band-gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called “Tauc” plots). While the technique is powerful and simple, the accuracy of the fitted band-gap result is seldom stated or known. We tackle this question by refitting a large number of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examination of the band gap values and their distribution leads to a discussion of some experimental factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure-of-merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single crystalline material.

Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies We present in this paper the technology of hot embossing as a flexible, low-cost microfabrication method for polymer microstructures, which uses the replication of a micromachined embossing master to generate microstructures on a polymer substrate With this fabrication technology high aspect ratio structures can be fabricated over large surface areas, which allows a commercially successful manufacturing of polymer microcomponents

Hot embossing as a method for the fabrication of polymer high aspect ratio structures

Very deep treches (up to 200 um) with high aspect ratios (up to 10) in silicon are etched using a fluorine-based plasma (SF6/O2/CHF3). Isotropic, positively and megatively (i.e. reverse) tapered as well as fully vertical walls with smooth surfaces are achieved by controlling the plasma chemistry. A convenient way to find the processing conditions needed for a vertical wall is described: the Black Silicon Method. This new procedure is checked for three different Reactive Ion Etchers (RIE); two parallel plate reactors and a hexode. The influence of the r.f. power, pressure, and gas mixture on the profile will be shown. Scanning Electron Microscope (SEM) photos are included to demonstrate the Black Silicon Method, the influence of the gases on the profile, and the use of this method in fabricating Micro Electro Mechanical Systems (MEMS).

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The black silicon method: a universal method for determining the parameter setting of a fluorine-based reactive ion etcher in deep silicon trench etching with profile control

Microfluidics is an emerging field that has given rise to a large number of scientific and technological developments over the last few years. This review reports on the use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems. It also presents the main application fields concerned with the different technologies and the most significant results reported by academic and industrial teams. Finally, it demonstrates the advantage of developing approaches for associating polymer technologies for manufacturing of fluidic elements with integration of active or sensitive elements, particularly silicon devices.

https://iopscience.iop.org/article/10.1088/0960-1317/17/5/R01/pdf

Lab-on-chip technologies: making a microfluidic network and coupling it into a complete microsystem : a review

This paper show that under optimized deposition condition, films can be grown having a full width at half maximum (FWHM) value of the (002) x-ray diffraction (XRD) line a factor of 4 smaller than the previously published results using PLD and among the best reported so far by any technique. Under optimized conditions, c-axis oriented ZnO films having a FWHM value of the (002) XRD reflection line less than 15°, electrical resistivities around 5 × 10-2 Ω cm and optical transmittance higher than 85% in the visible region of the spectrum were obtained. Refractive index was around 1.98 and the Eg = 3.26 eV, values characteristic of very high quality ZnO thin films.

Characteristics of high quality ZnO thin films deposited by pulsed laser deposition

The mechanisms causing stiction of polysilicon structures fabricated by surface micromachining techniques have been investigated. It is found that during drying from rinse liquids attractive dynamic capillary forces are responsible for bringing micromechanical structures into contact with the underlying substrate. Measured adhesion energies of sticking microbridges indicate that van der Waals forces are responsible for the stiction of hydrophobic surfaces and that hydrogen bridging is an additional adhesion mechanism for hydrophilic surfaces. Methods to reduce the stiction problem are indicated.

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Stiction of surface micromachined structures after rinsing and drying: model and investigation of adhesion mechanisms

Several thin-film deposition and etching techniques of the polymer fluorocarbon are investigated and the resulting thin-film properties will be compared with those of commercially available bulk polytetrafluoroethylene. The most promising deposition technique is performed in a conventional reactive ion etcher using a carbonhydrotrifluoride (CHF3) plasma. By changing the deposition parameters, control of the properties and step coverage of the deposited thin films within a certain range is possible, eg., uni-directional and conformal step coverage of deposited thin films can be obtained. Etching is performed with the help of an evaporated aluminium oxide mask using an oxygen, nitrogen, or sulfurhexafluoride plasma for isotropic etching, or a CHF3 plasma giving a directional etch profile. The combination of the unique properties, deposition and etching techniques make fluorocarbon thin films a promising tool for micromachining; a number of applications will be discussed and demonstrated.

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Applications of fluorocarbon polymers in micromechanics and micromachining

https://ris.utwente.nl/ws/files/6858268/Craciun95growth.pdf

Growth of ZnO thin films on GaAs by pulsed laser deposition

https://ris.utwente.nl/ws/files/6406745/Craciun95effects.pdf

J. Elders

Papers

Characteristics of high quality ZnO thin films deposited by pulsed laser deposition

Stiction of surface micromachined structures after rinsing and drying: model and investigation of adhesion mechanisms

Applications of fluorocarbon polymers in micromechanics and micromachining

Growth of ZnO thin films on GaAs by pulsed laser deposition

Effects of laser wavelength and fluence on the growth of ZnO thin films by pulsed laser deposition