Test system for micro mirror arrays
Over the last few years, high resolution spatial light modulators (SLMs) have been developed at the IMS Dresden. These are fabricated using one of two different technological processes. In one version a flexible, highly reflecting aluminum coating of about 50nm is evaporated onto a elastic layer, while the other version has quite rigid aluminum mirrors that are suspended by flexible hinges above the substrate. Both versions are fabricated on top of a CMOS DRAM matrix, which allows the addressing of individual pixels. So far SLMs with over 2 million pixels have been produced. In order to ensure a high quality of these SLMs a map of the SLM under test is needed showing the exact position of defective pixels together with the type of defect e.g. not responding, always deflected, wrong spring constant, poorly reflecting surface. Additionally information on the local and global flatness is required. This task can only be handled by an automated test stitching together many single measurements. A test system has been set up using a white light interferometer (WLI). This allows to measure the response of each and every SLM pixel to applied voltages.