Reference/link list for MEMS related information.
This work is a highly collaborative venture involving faculty from both chemistry and engineering (in our Department of Chemistry and Biochemistry: Dr. Eric V. Anslyn, Dr. John T. McDevitt, and Dr. Jason B. Shear; in our Department of Electrical Engineering: Dean Neikirk). One example of this work is the demonstration of a Fabry-Perot microcavity structures for use as a chemical sensor, fabricated using a single-wafer surface micromachining sacrificial layer process. We have also begun work on a new type of sensor array that will function as an "electronic tongue" using a combination of state-of-the-art micromachining, novel photochemical sensing schemes, molecular engineering of receptor sites, and pattern recognition protocols. The development of such smart sensors capable of discrimination of different analytes, toxins, and bacteria has become increasingly important for real time identification of water-borne contaminants. These sensors should allow for the simultaneous detection of multi-analyte systems, while also properly "rejecting" irrelevant chemicals, biochemicals and bacterial agents. The ultimate goal would be the evaluation of promising sensor suites in clinical virology and biomedical engineering settings to attack detection problems of crucial importance in commercial, medical, and military areas.
References for other work on chemical sensors.
In this project we are working on a new class of optically interrogated pressure microsensors with tailored dielectric film mirrors. The sensors are based on the well-established combination of a pressure sensitive membrane serving as the sensing element with an optical fiber as the interconnect. The pressure sensitive element consists of a Fabry-Perot cavity monolithically built by etching a polysilicon sacrificial layer that lies between dielectric film stacks. The size of the cavity can be precisely adjusted by controlling the thickness of the sacrificial layer grown using LPCVD. Using LPCVD, multiple dielectric films (typically consisting of silicon dioxide and silicon nitride) can be deposited to form wavelength selective dielectric mirrors. A guiding structure for the optical fiber can also be formed using anisotropic silicon etching. The structure allows accurate alignment between the pressure sensitive Fabry-Perot cavity and the fiber. Similar fabrication techniques can be applied to construct a tunable optical filter that allows the use of optical wavelength modulation detection techniques, which are much less sensitive to light loss during interrogation. The batch fabrication and surface micromachining techniques used here allow excellent alignment and parallelism of the two mirrors in the cavity, which has been a problem in devices using hybrid assembly. We have also studied the impact of film thickness variations on such Fabry-Perot interference-based devices, and have found that the layer design has a profound impact on the yield of manufactured sensors. We have also begun to study the use of micromachined Fabry-Perot devices for chemical sensing.
Eddy-current sensors have been studied for a number of years as a method of non-destructive testing and non-contact measurement. Macroscopic proximity sensors based on the eddy-current techniques are commercially available. However, these proximity sensors are not conducive to scaling to conventional integrated circuit levels. This is because most conventional eddy current proximity sensors use a single inductor. For miniature inductors fabricated using integrated circuit techniques, as the inductor is scaled down the inductance decreases while the resistance of the coil increases dramatically. This means that the sensor needs to be operated at much higher frequencies for which the inductance of the coil dominates its resistance, i.e., [[omega]]L >> R. We have developed a new inductive proximity sensor design that makes use of two coupled coils, forming a planar transformer. This device produces a phase shift between input and output that is insensitive to changes in coil resistance (due to either temperature change or change due to scaling to IC levels). This is a critical requirement for the successful operation of a miniature IC inductive proximity sensor. Using our two coil approach, the sensor can be operated at lower frequencies than those required for a single coil eddy-current sensor. Potential applications using two-coil planar inductive devices include bearing wear sensors, small gap measurement, and accelerometers.
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Microdynamical systems have been studied for a number of years, with concentration on sensors and, more recently, actuators. Very little work has been done on integrating microdynamical components into systems that satisfy mechanical tasks on macroscopic scales. In this work we are studying microdynamical components to produce a surface which is actively deformable. Active surfaces can operate on global or local surface characteristics. In local surface control, sensing, control and actuation all are accomplished locally in order to produce either a purely local or a global effect. For example, local control could be used to minimize local pressure gradients across a surface or to produce a global wave which propagates along the surface. Our work concentrates on creating micron-scale surface deformations of critical machine elements to produce macro-scale system responses. In particular, our focus is on the design and demonstration of smart journal and thrust bearings capable of using embedded sensors and actuators to dynamically change the surface geometry of the bearing. The ability to actively deform bearing surfaces allows for the design of bearings which are less prone to failure, the design of bearings with greater load carrying abilities, and a fundamental study of the effect of surface geometries and fluid conditions on bearing performance, such as start-up and shut-down conditions.
