Optimization of piezoelectric MEMS process on Sr and La co-doped PZT thin films

Doped lead-zirconate-titanate(PZT)thin films are preferred for the development of micro-electro-mechanical systems(MEMS)-based acoustic sensors because of their inherent higher dielectric and piezoelectric coefficients.Patterning process is used to develop such MEMS devices which is highly complex even for undoped PZT thin films;therefore,the problem is further cumbersome for doped PZT thin films due to the presence of added dopant elements and their associated chemistry.This paper presents patterning of strontium(Sr)and lanthanum(La)co-doped PZT thin film(PSLZT)deposited on platinized silicon substrate using wet and dry etching processes for fabricating a diaphragm structure with thickness of 15-25μm and diameter of 1.4-2 mm,suitable for acoustic sensing applications.The effects of various etching conditions have been studied and the results are reported.It is found that the dry etching is the most suited process for realizing the piezoelectric MEMS structure due to its higher etching resolution.An appreciable etching rate of 260-270 nm/min with smooth vertical sidewalls is achieved.The silicon diaphragm with patterned PSLZT thin film is found to retain more than 80%of its dielectric and piezoelectric coefficients and has a resonance of 1.43 MHz.

Coastal upwelling off the southwest coast of India:observations and simulations

Spatial hydrographic data collected from August 2007 through May 2008 and the Princeton Ocean Model(POM)are utilized to explain and document the upwelling in the south eastern Arabian Sea(SEAS).The decrease in the magnitude of winds towards the coast favors local anticyclonic vorticity,resulting in the formation of cyclonic eddy and reversal of coastal currents.The Ekman transport due to alongshore winds,Ekman pumping due to wind stress curl,cyclonic eddy and southward West Indian Coastal Currents play different roles in the SEAS upwelling.In the offshore,wind stress curl leads to the formation of meso-scale eddies,resulting in Ekman pumping at the center and consequent upwelling.The rapid depth variation on the western side of Quilon Mount intensifies upwelling in the offshore.The upwelling Kelvin waves generated at the equator terminates in the Bay of Bengal and do not contribute to the SEAS upwelling.The possible role of local and remote winds,especially around Sri Lanka on the upwelling dynamics of SEAS is described utilizing POM.The Kelvin waves generated off the coast of Sri Lanka during the active phase of the summer monsoon also contribute to the upwelling dynamics off the west coast of India.