Organic Light Emitting Material Direct Writing by Nanomaterial Enabled Laser Transfer
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Organic Light Emitting Material Direct Writing by Nanomaterial Enabled Laser Transfer Seung H. Ko1,2*, Heng Pan1, Nipun Misra1, Costas. P. Grigoropoulos1, Hee K. Park3 1 Department of Mechanical Engineering, University of California, Berkeley, California 947201740, USA. 2 Department of Mechanical Engineering, KAIST, Daejeon, Korea. 3 AppliFlex LLC, 320 Logue Ave., Suite 104, Mountain View, California 94043, USA. ABSTRACT Organic light emitting material direct writing is demonstrated based on nanomaterial enabled laser transfer. Through utilization of proper nanoparticle size and type, and the laser wavelength choice, a single laser pulse could transfer well defined and arbitrarily shaped tris-(8hydroxyquinoline)Al patterns ranging from several microns to millimeter size. The unique properties of nanomaterials allow laser induced forward transfer at low laser energy (0.05 J/cm2) while maintaining good fluorescence. The technique may be well suited for the mass production of temperature sensitive organic light emitting devices. The combined effects of melting temperature depression, lower conductive heat transfer loss, strong absorption of the incident laser beam, and relatively weak bonding between nanoparticles during laser irradiation result in the transfer of patterns with very sharp edges at relatively lower laser energy than commonly used, thus inducing minimal damage to the target organic light emitting diaode material with no evidence of cracks. This technique can be applied to a broad range of laser wavelengths with proper selection of nanoparticle size and size distribution, as well as the material type. Additionally, nanomaterial enabled laser transfer may be particularly advantageous for the mass production of temperature sensitive devices. INTRODUCTION Organic light emitting diodes (OLED) displays have a number of desirable features such as high contrast and brightness, wide color range, thin structure and light weight, among others. [1] OLED displays have several manufacturing requirements such as large area scalability and an increasing push towards smaller feature sizes, tighter feature shape control, high yield and low cost. However, traditional lithography and thermal evaporation deposition techniques have significant disadvantages, including the need for masks that are typically difficult to make to the required specifications at a reasonable price. Therefore, OLED display manufacturing employs direct write techniques for patterning the various materials. Examples of direct write technologies include ink jet printing,[2-4] laser chemical vapor deposition (LCVD),[5] and laser induced forward transfer (LIFT).[1,6-7] The LIFT technology may be further subdivided into processes such as matrix assisted pulsed laser evaporation direct writing (MAPLE DW),[6] laser induced thermal imaging (LITI),[7] and laser induced pattern-wise sublimation (LIPS).[1] Many of the direct write technologies mentioned above are subject to a number of limitations such as the need for solvent removal and contamina
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