Student Project Abstracts 2005 - Pluto - University of Washington

Enhanced Heat Dissipation Substrates for Organic Semiconductor DevicesAaron MontgomeryUniversity of VirginiaDr. Samuel GrahamGeorgia Institute of TechnologyAshante Allen, Erik Sunden and Adam Christensen`Many electronic devices are susceptible to overheatingwhich can result in failures of the device. This can be exemplifiedthrough electronic chips located inside a computer. To addressthese failures, much research has been performed to developthermal management solutions for microelectronic devices.These solutions have generally been geared towards Si-basedmicroelectronics and have achieved cooling capabilities of 100W/cm 2 or greater. While such power densities are not expected inorganic semiconductors, these devices have unique thermal managementchallenges arising from their inherent low thermal conductivity(results in high thermal resistance), the use of thermallyresistive substrates for flexible electronics, and the need to havetransparent materials for photon transfer. Thus, new concepts forboth active and passive thermal management of organic semiconductordevices (OSD) must be explored.In this work, I will primarily concentrate on developing newschemes for the removal of thermal energy through both activeand passive mechanisms by “thermally connecting” the OSD tohigh thermal conductivity substrates. The thermal connection willbe based on carbon nanotubes (CNTs) which will act as a thermalinterface material (TIM) with superior properties to conventionalTIMs. These CNTs possess a very high thermal conductivity(900-10,000w/mk). I will investigate the use of multilayercatalysts to produce highly aligned CNTs on metal substrates andthe creation of actively cooled PMMA and Si (gold coated) substratesusing various bonding techniques. There is a severe lackof attention on the thermal characterization and heat dissipationin OSD. Much of what I do here will be new and provide muchneeded contributions to the challenges of thermal management inOSDs. In addition, with overheating of chips stalls the advancementof better electronic devices.The multilayer catalysts deposition onto metal substrateshas proven successful in producing some CNT growth (Figure1). Some parameters that contribute to this growth are the typeof catalyst deposited onto the metal, the maximum temperatureduring the procedure, and the length that the sample is exposed tothe gases. By changing these parameters I am hoping to producea recipe that will generate better quality CNT growth with fewerdefects. Also, success was achieved at bonding Si (gold coated)to Si and PMMA to PMMA. Using a furnace, Si bonding canbe accomplished at 460 degrees Celsius for 5 minutes and is usedto for creating microfluidic channels for active cooling. Concerningpolymers, a hydraulic press successfully bonded PMMAwith a carbon nanofiber interlayer at 250 degrees Fahrenheitwhile maintaining 400lbs of force for 5 minutes (Figure 2). Thislaminated structure was used to create a flexible heat spreaderin polymer substrates for improve heat dissipation. Future workwill involve finding a feasible bonding method for PET which ismore commonly used for flexible organic semiconductors and tocontinue to produce CNT growth onto metal substrates with theleast amount of defects.Figure 1. Growth of carbon nanotubes on a copper substrate (left) and ascanning electron microscope image showing the details of the growth (right).Figure 2. Growth of carbon nanofibers (left) which werelaminated between sheets of PMMA to create a flexible heatspreader (right) integrated into a polymer substrate.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 83