Flip-chip fabrication of advanced micromirror arrays

This paper describes the design, fabrication, and testing of advanced micromirror arrays created using a novel, inexpensive, simple, reliable, and repeatable flip-chip assembly technique. The arrays are assembled by flip-chip bonding the upper structural layers of a micromirror array chip to the lower structural layers of a submount receiving chip using a custom built flip-chip bonding machine. Each chip is commercially prefabricated in the MUMPS process and then flip-chip bonded to form the working arrays such that many of the typical adverse effects of surface-micromachining were removed. Several arrays of piston and cantilever micromirror devices were flip-chip fabricated using this technique. These arrays demonstrated unprecedented features including 98% active surface area, five structural layers, less than 2 nm of RMS surface roughness per device, less than 80 nm of peak planarity variance across 1 mm arrays, address potentials compatible with CMOS control electronics and built-in masking capabilities for deposition of reflective materials. This work demonstrates that the demanding requirements of most micromirror applications can be met using a fast, simple, and low-cost technique that produces devices superior to those fabricated using far more costly techniques.