Aligning Chips Face-to-Face for Dense Capacitive and Optical Communication

We report a new method that precisely self-aligns face-to-face semiconductor chips or wafers to enable communication between the chips using electromagnetic waves. Our alignment mechanism takes advantage of miniaturized versions of two of nature's idealized shapes: an inverse pyramidal shape defined by a self-terminating wet-etch process in silicon and micro-spheres with radii accurate to submicron accuracy. This approach allows chips to be packaged using passive alignment that is self locating and reaches nearly one micron level of chip misalignment tolerance. Packages for applications to capacitive and optical connections are presented. Additionally, we describe a physical architecture for a multi-chip array packages with ¿bridge¿ and ¿island¿ chips where the function of the bridge is to transfer electromagnetic signals between island chips using either capacitive or optical proximity communication. The bridge chip can provide a predetermined amount of compliance to help maintain alignment and thereby accommodate topology variants in first level package or in chip thickness when required. Experimental packages providing precise alignment between 1-D arrays and 2-D arrays of chips are presented. We show that our precision alignment mechanism enables high fidelity 10 Gb/s optical-proximity-communication with reflecting mirrors micro-machined into Silicon and co-integrated to low loss silicon-on-insulator waveguides for chip-to-chip communication. The alignment mechanism was also applied to a demonstration of chip-to-chip capacitive proximity communication in a linear array of six chips. Alignment measurements on a 4 × 4 array of chips are reported.