A spatial light modulator using moving liquid mirrors (MLM) on a CMOS active-matrix
Die-sized spatial light modulators (SLM) are gaining importance as microdisplays for projection systems and in other fields of application including direct-writing systems for lithographic patterning and optical processing. The IMS has developed micromechanical SLMs with viscoelastic control layers (VCL) and with cantilever beam mirrors (CBM) on a silicon backplane with complete CMOS addressing circuitry. Here, we report on a third micromechanical actuator technology which is under development. The moving liquid mirror (MLM) empoys surface deformations of an oil film to modulate the phase of the reflected light. The liquid actuator promises low mechanical degradation, and process control is easy due to electrode preparation in standard CMOS-technology. The high-voltage CMOS-technology for the silicon backplane is optimized for surface-micromechanics and guarantees a highly planar chip surface. Pixel voltages of up to 40V are supported. The developed circuit with pixel sizes of 16µm, 20µm and 24µm allows 16 voltage levels for gray-scaling and has a TTL-compatible digital data interface. Matrix sizes can be customized preferably with blocks of 256-256 pixels. Images were observed using a simple projection setup with Schlieren optics. Contrast ratios of 43:1 in the 0th diffraction order have been measured. Switching times are typically around 5ms.