Pixel-to-point transfer: a process for integrating individual GaN-based light-emitting devices in t o heterogeneous microsystems Z. S. Luo 1 , T. Sands 1,5 , N.W. Cheung 2 , J. A. Chediak 1 , J. Seo 3 , and L. P. Lee 4 1 Department of Materials Science & Engineering, 2 Department of Electrical Engineering, 3 Applied Science & Technology Graduate Group and 4 Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720. 5 School of Materials Engineering and School of Electrical & Computer Engineering, Purdue University, W. Lafayette, IN 47907. ABSTRACT A novel ultra-low-thermal-budget pixel-to-point transfer process based on the excimer laser lift-off and Pd-In transient-liquid-phase bonding scheme was developed for flexible and precise placement of single pixels of GaN-based light-emitting diodes (LED) on target substrates. The transfer was accomplished by (1) temporarily bonding the light-emitting diode (LED) pixel to a specially designed pick-up rod with sapphire substrates facing up using Super Glue  , (2) removing the sapphire substrates using laser lift-off, and (3) registering and permanently bonding the LED pixel to the designated area in the target substrates using Pd-In transient-liquid-phase bonding. An oxygen plasma was employed to remove the Super Glue  residue before further microfabrication and system integration was performed. The capability of this technique was demonstrated in the integration of GaN-based LED pixels with pre-fabricated PIN photodiode chips and thin-film bandedge filters, which formed the non-disposable subsystems of a fluorescence-based lab-on-a-chip system. The performance of these integrated LED pixels and the integrated microsystems has been assessed by evaluating the fluorescence intensity as a function of equivalent fluorescein dye concentration using disposable polydimenthyl siloxane(PDMS) microfluidic channels. GaN LEDs with peak emission at 463 nm were used to excite 515nm fluorescence from FluoSpheres® carboxylate-modified fluorescent microspheres (40nm in diamters). INTRODUCTION In order to achieve multiple functionality on a chip, intimate integration of a broad spectrum of high-performance materials and devices is desirable. GaN-based light-emitting devices have been extensively studied due to their potential applications in areas such as full-color displays, full-color indicators and high-efficiency lamps. [1-4] The wide-bandgap nature also makes GaN- based light-emitting devices promising candidates as excitation light sources for biological applications such as fluorescence detection. Fluorescence detection, combined with microfluidic systems, enables the rapid analysis and manipulation of biological samples. The system is usually implemented using laser-induced fluorescence (LIF), microfluidic chips and confocal microscopy. One drawback for this type of scheme is that the size of the associated optics and detector is large relative to the size of the microfluidic chip. Therefore, the ability to integrate optical components, detector and microfluidic device into a microsystem is a major challenge in the development of microanalytical systems. We envision such heterogeneous integration of microsystems will lower cost and enhance portability, thereby broadening the utility of fluorescence detection for both bioassay and chemical detection in the field as well as in the lab [5]. Mat. Res. Soc. Symp. Proc. Vol. 768 © 2003 Materials Research Society G4.8.1