Fabrication and characteristics of MEMS sensors for the particle detection in the air/fluid

Abstract

Recently, various micro/nano-sized particles are synthesized or produced for the affluent goods of human life or the effluent byproduct of industrial contaminants. These micro/nano-sized particles are only classified benefit or harmful for human life by the functional aspect, it has to be researched the affection of particles by size to human body. The research had been reported the affection to the lung by the general inflow path in the air, and recently the affections to DNA and genetic instability of mice are reported by the injection TiO2 nano-sized particles to the drinking water, but the few reported about the affection in the real human life. Particle analyses are the basics for the confirm and predict of the material's optical, electrical, magnetic, chemical, physical properties in the air or fluid. The analyzed targets(factors) are important to recognize the properties of particles in the air/fluid. For the airborne particles, it is very important to detect the mass/number concentration by size and the compositions of the particles. For the case of the particles in fluid(or liquid, water), the particles is not limited to the precipitates or floating contaminants; the bio particles include synthesized bio markers, cells, bacterium, etc. For the bio particles, it is important not only to detect the mass/number concentration but also the to trap individual particles for the bio/medical analyses, or to sort by size for incubations. In this thesis, the conventional equipments of the particle analyses are introduced and we suggest the MEMS sensors as the particle analyzers in the air/fluid. Thesis are consisted of two parts; the airborne particle mass detection and the subaqueous particle trap. Each parts include the several sub topics; the introductions of conventional equipments, the theoretical backgrounds, the fabrication process flow, the equipment setup for fabrication and measurement, the results of measurements and conclusions. First, the basic theoretical backgrounds of the MEMS resonators and sensors are studied to design the MEMS structure. The paddle-type MEMS structures are suggested and the resonant frequencies and the minimum mass loading resolutions are simulated and calculated to confirm the dimensions of MEMS devices; spring: 700 μm (L) × 100 μm (W), paddle: 1000 μm × 1000 μm. The actuating methods of MEMS resonators are introduced and the piezoelectric actuating method is adapted to MEMS resonators and sensors for particle mass detection. Second, the basic MEMS fabrication process flows are studied in order to fabricate the MEMS resonators for airborne particle mass detection and the fluidic MEMS devices for subaqueous particle trap. Two major micromachining processes are introduced and the fundamental equipments are designed and manufactured to fabricate chip-sized MEMS devices; LPCVD for the silicon nitride layer deposition as the hard mask when bulkk etching, chemical etching reactor for the bulk etching of silicon. Third, the basics of front-ends are introduced, we suggest the laser interferometric measurements based on the optical fiber in order to basically detect the displacement The several measurement equipments are arranged in order to adaptively measure the mass change using the optical fiber laser interferometer. The MEMS resonators and fluidic MEMS devices are fabricated using the previously manufactured fabrication equipments and the optical fiber laser inteferometric measuring systems. Basically, the basic properties of airborne particles are studied in order to confirm the relationship of airborne particles and the electrostatically attracting paddle. The airborne particles are collected on the oscillating MEMS sensor by electrostatic attraction, the mass change is detected by laser interferometer by mass-loading effect resulted from the change of the resonant frequencies and the phase of oscillating frequencies. The total mass concentration of airborne particles are detected by various conditions; humidity, electrostatic strength, oscillating frequency(the physical energies of oscillating MEMS structures). The basic hydrodynamics in the fluidic MEMS devices are studied to trap the subaqueous particles(bio particles). The controlling of volumetric flow rate can trap the particles in the well or drive the particles to be bypassed through another path. The fabricated MEMS devices are treated by the oxygen plasma in order to confirm the laminar flow in the fluidic channel. The particle entrapment is demonstrated by observing and image-capturing through the microscope when the volumetric flow rate is controlled.