Student Project Abstracts 2005 - Pluto - University of Washington

Moisture Uptake of Thin Polymer FilmsEphriam LucasGeorgia Institute of TechnologyDr. Sue-Ann Bidstrup Allen and Dr. Paul KohlGeorgia Institute of TechnologyAte HeFort Valley State UniversityThin films are layers of either conductive or non-conductivefilms that are added to the top surface of wafers. These filmsmay be used to form interconnects between devices or insulatorsbetween interconnects layers. A variety of materials can be depositedon a wafer. Three main categories of thin films materialsare conductors, insulators, and semiconductors. In this researcha polymer “insulator” is used as the thin film. This polymer filmis used and tested to see how much moisture it absorbs underdifferent circumstances. These films can later be used to coatmicrochips for computer, cell phones etc.A slide of quartz crystal with a gold electrode on each sideis used in this project. After coating the quartz with a thin polymerfilm on one side, the quartz crystal is attached in a sealedglass cell. The cell is connected to nitrogen to test the moistureabsorption. The nitrogen enters into the cell in two forms: wetnitrogen and dry nitrogen. The nitrogen that has been condensedwith water is called wet nitrogen, and the direct nitrogen flow isdry nitrogen. While using dry nitrogen, the relative humidity iszero, which means that there is no water at all in the cell. Whena voltage is applied to the quartz, it vibrates and the frequency isproportional to the mass of the film. Once the mass of the film ischanged by moisture uptake, the frequency reflects that change.The more moisture the film absorbs the heavier the film will becausing the frequency to be lower. The theory behind this is thehigher the condenser temperature, the higher the moisture contentinside the cell, which increasing the relative humidity. The higherthe relative humidity, the more moisture the polymer film willuptake, which increases the mass of the thin polymer film.There has not been much progress in this research as of yetdue to inaccurate data. The data recorded show that there was a2.5% increase in weight when changing from dry nitrogen to wetnitrogen and a 2.21% decrease in weight when changing backfrom wet to dry. This tells us that all the moisture is not beingreabsorbs. We believe the frequency values are inaccurate due tothe fact that the nitrogen flow is not constant. The nitrogen flowrate constantly fluctuates when changing from wet to dry and dryback to wet. A way to stabilize the nitrogen flow at a slow steadyrate is needed before this research can be continued.ACKNOWLEDGEMENTSResearch support is gratefully acknowledged from the NationalScience Foundation Center on Materials and Devices forInformation Technology Research (CMDITR), DMR-0120967.CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 75