Scaling a Fluorescent Detection System by Polymer-Assisted 3-D Integration of Heterogeneous Dies

Scaling by 3-D integration of various heterogeneous components enables miniaturized systems. However, the heterogeneous system integration is challenging due to the dissimilarities in materials and process used in fabrication of individual components. In this paper, we demonstrate a simple 3-D integration method for miniaturization of systems. Various components of the system were stacked using SU-8-based planarization and epoxy-based bonding. Spacer dielectric (SU-8) was patterned using photolithography for the formation of interconnect vias. Electrical interconnects over the large topography between the layers was formed by the screen printing of silver nanoparticle epoxy. Using this integration technique, we demonstrate a fluorescence-sensing platform consisting of a silicon photodetector, plastic optical filters, commercial LED, and a glass microheater chip. This paper resolves several fabrication challenges of planarization, stacking and interconnection of these divergent chips. For example, the process incompatibility of the plastic optical filters was resolved by additional passivation using parylene-C. The functionality of the demonstrated system is verified by detecting the fluorescence property of Rhodamine B and Rhodamine 6G dyes. Rhodamine B's sensitivity to temperature was also demonstrated using the on-chip microheater. This process flow can be scaled to stack a larger number of layers for demonstrations of more complicated systems with enhanced functionality and applications.