Patterning and integration of polyfluorene polymers on micropixellated UV AlInGaN light emitting diodes B. Guilhabert 1 , Z. Gong 1 , C. Belton 2 , A. MackIntosh 3 , E. Gu 1 , P. Stavrinou 2 , D.D.C. Bradley 2 , R.A. Pethrick 3 , and M.D. Dawson 1 1 Institute of Photonics, University of Strathclyde, 106 Rottenrow, Glasgow G4 0NW, UK 2 Experimental Solid State Physics, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK 3 Pure and Applied Chemistry Department, University of Strathclyde, Glasgow G4 0NW, UK Benoit.guilhabert@strath.ac.uk Abstract: The integration of polyfluorene polymer micro-pixels onto GaN-based micropixellated UV Light Emitting Diodes is demonstrated. Polymer down-converted visible emission from these hybrid organic/inorganic electroluminescent micro-arrays is achieved. ©2007 Optical Society of America OCIS codes: (250.3680) Light Emitting Polymers; (230.3670) Light Emitting Diodes 1. Introduction: Conjugated light emitting polymers (LEPs) offer high photoluminescence efficiencies and are thus attractive materials for use as gain media and optical amplifiers across the visible spectrum [1,2]. Their ability to be blended together makes them attractive candidates for white light generation [3]. Benefits of combining these materials with AlInGaN UV Light Emitting Diode (LED) excitation have been identified recently and hybrid structures demonstrated with unpatterned polyfluorene polymer films [3]. Here, we report the patterning and full integration of polyfluorenes onto a 64x64-elements matrix-addressable micropixellated LED array emitting at 370 nm [4]. Each pixel of the integrated LED array has a diameter of 20 μm on a 50 μm pitch. The UV micro-LEDs are covered with a 2.5 μm thick UV-transparent polymer interlayer and a 30 nm thick polyfluorene film. Polyfluorene micro-pixels were fabricated by standard photolithography techniques and Reactive Ion Etching (RIE). Figure 1 is a cross-sectional schematic of the hybrid device. Fig 1. Scheme of the integration of polyfluorene polymer onto 64x64 matrix-addressable microstructured LEDs 2. Polyfluorene polymer and integration process: The integration process starts with spin-coating of the GaN device using a novel UV-transparent polymer material developed in-house [5]. To polymerize the thin polymer film, a UV (258 nm) photocuring step is performed followed with post-baking in an oven at 150 ºC, resulting in a film transparent down to ~230nm. This layer acts as a planarization interlayer between the UV emitters and the light emitting polymer which is spin coated subsequently. The polyfluorene LEP polymer used in this work is a generic PFO synthesized by Sumitomo. The maximum absorption wavelength of PFO is at 390 nm and it exhibits vibronic peaks at 439 nm, 466 nm and 495 nm [6]. From a solution of 20 mg PFO in one mL of toluene, the thickness of the spin coated PFO film is 30 nm. Photo-resist is then spin-coated on top of PFO layer and patterned into micro-disks aligned with the emitters of the UV LED pixels underneath. These photoresist disks are used as a sacrificial mask for dry etching in a O 2 /CF 4 plasma Reactive Ion Etching (RIE) step. By etching down to the deep UV-transparent polymer layer, PFO pixels are created on top of each UV emitter of the array. Finally, an O 2 plasma RIE step clears off the materials over the connection pads of the device. Figure 2a is a microscope image of a part of the integrated LED array and figure 2b shows the same area imaged under UV light illumination, revealing well resolved fluorescing light emitting polymer pixels. Figure 2c shows a representative image of 2 LED pixels of the array turned on under 1.6 mA injected current. a2247_1.pdf JTuA98.pdf