SOI-CMOS-MEMS electrothermal micromirror arrays

A fabrication technology called SOI-CMOS-MEMS is developed to realize arrays of electrothermally actuated micromirror arrays with fill factors up to 90% and mechanical scan ranges up to +/-45°. SOI-CMOS-MEMS features bonding of a CMOS-MEMS folded electrothermal actuator chip with a SOI mirror chip. Actuators and micromirrors are separately released using Bosch-type and isotropic Si etch processes. A 1-D, 3 x 3 SOI-CMOS-MEMS mirror array is characterized at a 1 mm scale that meets fill factor and scan range targets with a power sensitivity of 1.9 deg·m W-1 and -0.9 deg·m W-1 on inner and outer actuator legs, respectively. Issues preventing fabrication of SOI-CMOS-MEMS micromirror arrays designed for 1-D and 3-D motion at scales from 500 microm to 50 microm are discussed.;A unified model for aspect ratio dependent etch modulation is developed that achieves depth prediction accuracy of better than 10% up to 160 microm depth over a range of feature shapes and dimensions. The technique is applied extensively in the SOI-CMOS-MEMS process to produce deep multi-level structures in Si with a single etch mask and to control uniformity and feature profiles.;TiW attack during release etch is shown to be the driving factor in mirror coplanarity loss. The effect is due to thermally accelerated etching caused by heating of released structures by the exothermic reaction of Si and F. The effect is quantified using in situ infrared imaging. Models are developed that predict suspended device temperatures based on a power balance model using a single parameter, the proportion of etch heat carried away by volatile species, as the sole fitting parameter.;Electrothermomechanical analytic models of power response of a generic folded actuator topology are developed that provide insight into the trends in actuator behavior for actuator design elements such as beam geometry and heater type, among others. Adverse power and scan range scaling and favorable speed scaling are demonstrated. Mechanical constraints on device geometry are derived. Detailed material, process, test structure and device characterization is presented that demonstrates the consistency of measured device behavior with analytic models.