Characterization of MEMS piston mirror arrays with comb drive actuator

Nowadays virtual, augmented and mixed reality applications are becoming more and more widespread. With this, the requirements for image quality are getting more demanding, leaving room for improvement of the user experience of the existing systems. While many research groups and companies try to improve on fixed-focus stereo image systems, we propose to make use of real holography as the best possible solution providing all depth cues automatically in a consistent way. Within such holographic display systems, a spatial light modulator (SLM) is re-shaping the incident light generating the desired images. As SLMs with the required properties are not commercially available today, a novel device is being developed within the Horizon 2020’REALHOLO’ project funded by the European Union: a MEMS micromirror Array (MMA) with 8 million phase-shifting pixels based on a novel comb drive micro actuator concept. Earlier theoretical work and simulations had showed clear perspectives for a superior performance in comparison to other SLM technologies allowing high frame rates and high precision wave front modulation. By now the first samples of proof-of-concept MMA chips have been fabricated and in this paper we present experimental characterization results: microscope and SEM images, quasi-static response curves measured by white light interferometry (WLI) as well as the dynamic properties like resonance frequency and damping measured by laser doppler vibrometry (LDV). In addition an addressing approach for a minimum mirror settling time is also investigated. We discuss the impact of fabrication tolerances on the overall precision together with the response curve dependency on design parameters and compare the experimental results to simulations.