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This chapter presents an overview of the key methods and process recipes commonly employed in the deposition of semiconductor
and dielectric thin films used in the fabrication of microelectromechanical systems (MEMS). These methods include chemical
vapor deposition, epitaxy, physical vapor deposition, atomic layer deposition, and spin-on techniques...
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AlN epilayers were grown directly on sapphire (0001) substrates using a combined growth scheme, consisting of a low-temperature nucleation layer and a second layer grown by high-temperature pulsed atomic layer epitaxy via metalorganic chemical vapor deposition. With an emphasis on the nucleation layer, its growth temperature was varied from 470°C t...
Citations
... For silicon oxide, a larger variety of growth and deposition procedures exist. However, the residual stress range is much smaller than for silicon nitride and is typically compressive around 150 MPa [103]. A MEMS Handbook [104] can be consulted for an overview and details on LPCVD and PECVD recipes and materials commonly deposited using these processes. ...
Microelectromechanical systems (MEMS)-based sample carriers became a breakthrough for in situ inspection techniques, especially in transmission electron microscopy where the sample carrier functions as a microsized laboratory and enables dynamic studies on samples, such as nanoparticles, nanowires, lamellas, and 2-D materials. Microheaters allow for in situ manipulation of samples by applying heat stimuli such that sample properties and interactions can be studied in real time at elevated temperatures. However, currently developed microheaters still suffer from undesired effects such as mechanical deflection and limitations in temperature range, accuracy, and homogeneity. This review discusses advancements in the technological development of microheaters. Methods and results found in the literature are categorized to provide an overview of optimization methods for thermoelectromechanical design aspects. The knowledge from various application fields, including a critical reflection on mesoscopic material properties, is combined into a series of design guidelines. These compose instructions for developing and optimizing microheater characteristics, such as mechanical and thermal stress, temperature accuracy and homogeneity, power consumption, response time, and sample drift. Although this review and guide are applicable to many application fields that require a microheater, an emphasis is laid on aspects most relevant to the microheater as a high-temperature sample carrier for in situ experiments. [2017-0149]
... Passivation is an inevitable process for nearly every MEMS device, and the passivation layer can prevent the existing elements from being damaged in the subsequent processes [52]. Passivation layers, usually made of SiO 2 and Si 3 N 4 , are often realized by thermal oxidation, plasma enhanced chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD) [53]. However, the passivation layer frequently suffers from process-induced stress, whose state may vary with the layer material and fabrication process. ...
The field of piezoresistive sensors has been undergoing a significant revolution in terms of design methodology, material technology and micromachining process. However, the temperature dependence of sensor characteristics remains a hurdle to cross. This review focuses on the issues in thermal-performance instability of piezoresistive sensors. Based on the operation fundamental, inducements to the instability are investigated in detail and correspondingly available ameliorative methods are presented. Pros and cons of each improvement approach are also summarized. Though several schemes have been proposed and put into reality with favorable achievements, the schemes featuring simple implementation and excellent compatibility with existing techniques are still emergently demanded to construct a piezoresistive sensor with excellent comprehensive performance.
A large-area and ultrathin MEMS (microelectromechanical system) mirror can provide efficient light-coupling, a large scanning area, and high energy efficiency for actuation. However, the ultrathin mirror is significantly vulnerable to diverse film deformation due to residual thin film stresses, so that high flatness of the mirror is hardly achieved. Here, we report a MEMS mirror of large-area and ultrathin membrane with high flatness by using the silicon rim microstructure (SRM). The ultrathin MEMS mirror with SRM (SRM-mirror) consists of aluminum (Al) deposited silicon nitride membrane, bimorph actuator, and the SRM. The SRM is simply fabricated underneath the silicon nitride membrane, and thus effectively inhibits the tensile stress relaxation of the membrane. As a result, the membrane has high flatness of 10.6 m−1 film curvature at minimum without any deformation. The electrothermal actuation of the SRM-mirror shows large tilting angles from 15° to −45° depending on the applied DC voltage of 0~4 VDC, preserving high flatness of the tilting membrane. This stable and statically actuated SRM-mirror spurs diverse micro-optic applications such as optical sensing, beam alignment, or optical switching.
This paper describes and applies a methodology to determine the elastic properties of freestanding thin membranes by means of a bulge test and a numerical approach. The numerical procedure is based on the combination of two standard methods i.e. finite element analysis and classical analytical solutions to calculate elastic properties of thin films. Bulge tests were conducted on silicon nitride (Si3N4) monolayer of 2x2 mm (square) and 1.5x3.5 mm (rectangular) membranes with the aim to determine elastics properties (Young’s modulus (E) and Poison’s ratio (v)) that define the load-deflection curves of both membranes. With this purpose, an error function was constructed for each membrane which involved finite element solutions, analytical solutions and experimental measurements. Error functions were found and minimized by mapping a set of elastic parameters for the two membranes (square and rectangular). A unique solution was determined in the intersection of both linear approximations, obtaining 236 GPa for E and 0.264 for v. It is well known that in a traditional bulge test analysis only one of both biaxial modulus can be determined and not a combination of E and v. Numerical results show that calculated load-deflection curves agree well with the measurements obtained for both square and rectangular membranes experimentally. The proposed methodology is only applicable in thin films with elastic behavior, however generalization for more complicated geometries is possible.
This research is a survey on characterization of partial oxides of silicon. In this study some coatings with X, whose values represents the ratio of oxygen to silicon, were deposited on an n type silicon wafer using the physical vapor deposition method. In morphology studies, first the structures of the created coatings were analyzed applying such techniques as SEM, FTIR, XPS, and AFM. The results showed that the increase of the parameter x could minimize the structural defects as well as increase the texture density. In addition, optical properties of the created coatings were investigated demonstrating that with an increase of the parameter X, the transmission properties diminished, while reflective characteristics improved.
This chapter covers processes for doping
and surface modification of silicon. Technologies described for doping silicon are diffusion and ion implantation, the latter requiring a thermal process to accomplish properly doped material. A process for thermally modifying silicon into the dielectric, amorphous silicon dioxide (SiO2) is oxidation, using either a dry or a wet process. Due to stoichiometric relationships and differences in density between Si and SiO2, the film volume increases during the reaction. While doping and surface modification are key technologies in the semiconductor industry, MEMS and NEMS devices also use these technologies, although on a much smaller scale.
Silicon carbide (SiC) is a leading material for both semiconductor devices and harsh environment micro- and nano-electromechanical systems (MEMS/NEMS) due to a combination of exceptional electrical, mechanical and chemical properties. SiC is also an excellent structural material for micromechanical transducers because of its high Young's modulus and mechanical strength. Suspended thin film diaphragms have been used in a wide range of applications, ranging from fundamental materials characterization to structural elements in high temperature pressure transducers. This paper reviews some of our efforts to develop SiC as a structural material for diaphragm-based MEMS, highlighting recent advances by our group in developing these structures for use in electromechanical microsensors and microactuators.
We developed a tunable surface-micromachined Fabry–Pérot interferometer for the thermal infrared spectral region of wavelengths 7–11 µm. The device is controlled through capacitive actuation with the maximum applied voltage near 30 V. The transmission characteristics, as a function of the tuning actuation, were recorded for several samples with a Fourier-transform infrared spectrometer. Two different device designs are compared in terms of the transmission peak width and height evolution along the actuation. Numerical simulations and the established analytical Airy expression are exploited in order to bridge the gap between an ideal-model performance and the measurement results. Emphasis in the analysis is on the movable mirror unidealities and their implications in the performance. Finally, we present example data recorded with a laboratory setup of a gas spectrometer, based on the device under study.
Final capping insulation layer is a critical step in the microfabrication process that determines the lifetime of analytical microsensors in real fluids. Actual processes encounter considerable limitations as (i) organic passivation layers do not provide a satisfying long-term protection against liquids and (ii) inorganic passivation processes (dielectric materials deposition and patterning) are very aggressive for the underlying layers, imposing severe constraints on the integration of sensitive materials. We present here a low temperature deposition process of high quality silicon nitride Si3N4 using ICP-CVD technique combined with a lift-off based process to pattern conformal deposition, in order to avoid harsh treatments such as wet or dry etching. High-density SiNx films with low H content (5 × 1020 at/cm3) were synthesized at 100 °C with controlled uniformity (5%), refractive index (2.025 at 830 nm), etch rate in buffered hydrofluoric acid (8 nm/min), residual stress (−500 MPa), breakdown field (3.9 MV/cm) and dielectric constant (6.0). In order to validate the compatibility of this passivation process with long-term fluids analysis, microelectrodes were fabricated and their lifetime in natural seawater was evaluated. Their active surfaces were defined by patterning the insulation layer. Special care was given to their accurate estimation through the modelling of chronoamperometric curves. Reproducible and stable electrochemical response was obtained for months (>50 days), demonstrating a considerably extended lifetime in harsh liquid media.
