Processing of MEMS structures

As physical structures used in technological applications have been reduced in size, there has been an increasing need to understand the limiting processes of adhesion and to try to minimize them. For example, adhesion due to humidity is known to have a major effect on the durabihty and friction forces experienced at the recording head/disk interface. Microelectromechanical systems (MEMS) are also detrimentally affected by nanoscale adhesion, with their motion being perturbed or prevented. 

In the MEM/Rietveld analysis, each of the observed structure factors of intrinsically overlapped reflections (for instance, 333 and 511 in a cubic system) can be deduced by the structure model based on a free atom model in the Rietveld refinement. In such a case, the obtained MEM charge density will be partially affected by the free atom model used. In order to reduce such a bias, the observed structure factors should be refined based on the deduced structure factors from the obtained MEM charge density. The detail of the process is described in the review article [9,22-24]. In addition, the phased values of structure factors based on the structure model used in Rietveld analysis are used in the MEM analysis. Thus, the phase refinement is also done for the noncentrosymmetric case as P2, of Sc C82 crystal by the iteration of MEM analysis. The detail of the process is also described elsewhere [25]. All of the charge densities shown in this article are obtained through these procedures. 

Figure 5.2.1 shows a photograph of an integrated surface-micromachined accelerometer, and Figure 5.2.2 is a close-up of the surface-micromachined polysilicon MEMS structure near the center of Figure 5.2.1. The structural material is 3 pm thick polysilicon and the IC process is bipolar and CMOS (BiCMOS) with thin film resistors. This structure thus combines bipolar transistors, CMOS, precision laser-trimmed resistors, and mechanical polysilicon [4],...

The fluid control MEMS is composed of a microdiaphragm and micro-channel. Figure 5.31 shows the fabrication process of a multilayer diaphragm structure. 

Due to the complexity of MEMS devices and the multitude of materials used, there is no one-size-fits-all solution to successfully integrating ceramics into MEMS structures as each of the thermal, chemical and mechanical issues interact with one another. Generally three types of approaches can be employed to overcome the issues increased resistance, avoidance or management. In the resistance approach materials that are thermally, chemically or mechanically more resistant are employed. With avoidance, the integration issues are avoided through the selection or modification of processing routes so that the deleterious effects do not arise and in management the effects are controlled so as to minimise any issues that arise. 

In the early days of CMP, when the process engineers had recognized that the planarization technology developed for very large-scale integration devices could also be of benefit for their MEMS structures, they transferred the processes almost one-to-one to their applications. But it showed very quickly that they had to adjust these processes to the specific manufacturing requirements of their structures. 

Electrochemical and photoelectrochemical control of semiconductor anodic decomposition reactions allow for controlled fabrication of fine structures on semiconductor surfaces, for example, diffraction gratings, lenses, and MEMs structures [13-22]. These processes are usually carried out under conditions where the oxidation products are soluble in the electrolyte. Patterns are... 

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