Effect of Process Parameters on TED-Based Q-Factor of MEMS

2007 ◽  
Author(s):  
Ryszard J. Pryputniewicz ◽  
Dariusz R. Pryputniewicz ◽  
Emily J. Pryputniewicz
Keyword(s):  
Internal Friction ◽  
Microelectromechanical Systems ◽  
Coefficient Of Thermal Expansion ◽  
Operating Conditions ◽  
Q Factor ◽  
Accuracy And Precision ◽  
Mems Technology ◽  
Q Factors ◽  
Application Specific

Continued advances in microelectromechanical systems (MEMS) technology have led to development of numerous applications including, but not limited to: automotive, communication, information technology, deep-space, medical, safety, national security, etc. These developments are being made possible because of creative designs and novel packaging based on use of some of the most sophisticated analytical and experimental tools available today. These tools are also employed to overcome limitations due to inherent behavior of materials fabricated into miniature shapes subjected to extremely harsh operating conditions while satisfying very challenging specifications/requirements of their applications. Thermoelastic internal friction is present in all structural materials and has been found experimentally in miniature silicon resonators (e.g., microgyroscopes, accelerometers, as well as biological, chemical, and other sensors/actuators) that rely on vibrations of either sensing elements or application-specific elastic suspensions that resonate. Regardless of their applications, sensors are always designed to provide the most sensitive responses to the signals they are developed to detect and/or monitor. One way to describe this sensitivity is to use the Quality (Q) factor. Most recent experimental evidence indicates that as the physical sizes of sensors decrease (especially because of continued advances in fabrication, e.g., by surface micromachining) the corresponding Q-factors become more and more dependent on thermoelastic damping (TED). This form of damping depends on material properties such as coefficient of thermal expansion, thermal conductivity, specific heat, density, and modulus of elasticity. It is also related to such design/operating parameters as resonator dimensions and temperature. This paper reviews a theoretical analysis of the effects that thermoelastic internal friction has on the Q-factor of microscale resonators and shows that the internal friction relating to TED is a fundamental damping mechanism in determination of quality of high-Q resonators over a range of operating conditions. Furthermore, the analysis also shows that the Q of resonators can be critical to the development of modern sensors. Microscale resonators are often used as basic sensing elements in the modern micromachined sensors. These sensors are frequency-modulated devices and exhibit a change in output frequency that is related to measurements and/or control of a physical variable. Accuracy and precision of these measurements/controls are inherently dependent on the frequency stability of the sensor/device output. This, in turn, greatly depends on damping in the resonating element itself.

Optoelectronic Methodology for Development of MEMS

2007 ◽  
Author(s):  
Ryszard J. Pryputniewicz ◽  
Ryan T. Marinis ◽  
Adam R. Klempner ◽  
Peter Hefti
Keyword(s):  
Computer Technology ◽  
Microelectromechanical Systems ◽  
Design Analysis ◽  
Operating Conditions ◽  
Functional Characteristics ◽  
Optimum Performance ◽  
Recent Advances ◽  
Challenging Tasks ◽  
Optoelectronic Method

Development of microelectromechanical systems (MEMS) constitutes one of the most challenging tasks in today’s micromechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of MEMS to enable refinement and optimization of their designs. Until recently, this characterization was hindered by lack of a readily available methodology. However, building on recent advances in photonics, electronics, and computer technology, we have developed an optoelectronic methodology particularly suitable for development of MEMS. In this paper, we describe the optoelectronic methodology and illustrate its use with representative examples. By quantitatively characterizing performance of MEMS, under different vibration, thermal, and other operating conditions, we can make specific suggestions for their improvements. Then, using the optoelectronic method, we can verify the effects of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS, which will ensure that they are operated at optimum performance, are reliable, and are durable.

Mechanical and Environmental Degradation of Self-Assembled Monolayer Coatings for Microelectromechanical Systems

2007 ◽  
Author(s):  
Shannon J. Timpe
Keyword(s):  
Microelectromechanical Systems ◽  
Extreme Environments ◽  
Operating Conditions ◽  
Sliding Contact ◽  
Great Promise ◽  
Self Assembled Monolayer ◽  
Normal Loading ◽  
Assembled Monolayers ◽  
Mems Technology ◽  
Self Assembled

Self-assembled monolayer coatings have shown great promise for dramatically reducing the tribological forces of adhesion and friction in microelectro-mechanical systems (MEMS). However, monolayer coatings often display significant degradation when exposed to extreme environments, dynamic sliding contact, and dynamic impact loading. This degradation is coupled with a corresponding increase in the tribological properties. In this study, the degradation of tridecafluorotri(dimethylamino)silane is examined under the typical operating conditions of MEMS technology using a specialized microdevice designed for characterizing the tribological behavior surface micromachines. Results of friction and adhesion degradation under normal loading and sliding contact are interpreted in relation to the primary degradation mechanisms of self-assembled monolayers.

Simulation and Contrast Analysis of tem Images of Cracks

1990 ◽  
Vol 48 (1) ◽  
pp. 578-579
Author(s):  
D. Goyal ◽  
A. H. King
Keyword(s):  
Displacement Vector ◽  
Crack Tip ◽  
Perfect Crystal ◽  
Operating Conditions ◽  
Displacement Fields ◽  
Fringe Contrast ◽  
Orthogonal Geometry ◽  
Moire Fringe ◽  
Moiré Fringe

TEM images of cracks have been found to give rise to a moiré fringe type of contrast. It is apparent that the moire fringe contrast is observed because of the presence of a fault in a perfect crystal, and is characteristic of the fault geometry and the diffracting conditions in the TEM. Various studies have reported that the moire fringe contrast observed due to the presence of a crack in an otherwise perfect crystal is distinctive of the mode of crack. This paper describes a technique to study the geometry and mode of the cracks by comparing the images they produce in the TEM because of the effect that their displacement fields have on the diffraction of electrons by the crystal (containing a crack) with the corresponding theoretical images. In order to formulate a means of matching experimental images with theoretical ones, displacement fields of dislocations present (if any) in the vicinity of the crack are not considered, only the effect of the displacement field of the crack is considered.The theoretical images are obtained using a computer program based on the two beam approximation of the dynamical theory of diffraction contrast for an imperfect crystal. The procedures for the determination of the various parameters involved in these computations have been well documented. There are three basic modes of crack. Preliminary studies were carried out considering the simplest form of crack geometries, i. e., mode I, II, III and the mixed modes, with orthogonal crack geometries. It was found that the contrast obtained from each mode is very distinct. The effect of variation of operating conditions such as diffracting vector (), the deviation parameter (ω), the electron beam direction () and the displacement vector were studied. It has been found that any small change in the above parameters can result in a drastic change in the contrast. The most important parameter for the matching of the theoretical and the experimental images was found to be the determination of the geometry of the crack under consideration. In order to be able to simulate the crack image shown in Figure 1, the crack geometry was modified from a orthogonal geometry to one with a crack tip inclined to the original crack front. The variation in the crack tip direction resulted in the variation of the displacement vector also. Figure 1 is a cross-sectional micrograph of a silicon wafer with a chromium film on top, showing a crack in the silicon.

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