Pixel-to-point transfer: A process for integrating individual GaN-based light-emitting devices in o heterogeneous microsystems

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 pro-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).