Digital Light Processing (DLP) Mirror

Coventor offers a comprehensive suite of software tools for designing integrated MEMS+IC devices. SEMulator3D is used to build 3D models of complex MEMS structures and CMOS circuits and to visualize the electrical connectivity between them. One of the best known examples of a monolithically integrated CMOS circuit and MEMS device is the Texas Instruments Digital MicroMirror Device, wherein MEMS digital light switches are rotated by electrostatic attraction depending on the state of an underlying SRAM cell.

Figure 1: Isometric and cross-section view of single pixel model created with SEMulator3D

The images below are SEM photomicrographs (courtesy of Texas Instruments) on the left with the equivalent SEMulator3D model view on the right.

Figure 2: Ion Mill and SEMulator3D model cross section

Figure 3: SEM of DMD with mirror removed and SEMulator3D model

Each DMD is addressed by an SRAM memory cell. SEMulator3D can accurately model both the underlying CMOS circuit as well as the MEMS device integrated above it.

Figure 4: Example of 6T SRAM CMOS model before the micromirror is built. (Top left) Exploded view of DLP mirror and memory cell. (Bottom left) 6T SRAM. (Top right) 3D model of circuitry. (Bottom right) Top view of MEMS DLP 3D model.

Additionally, SEMulator3D is able to discretize the voxel model with mesh elements to generate simulation-quality meshes. Both triangle surface and tetrahedral volume meshes can be exported from SEMulator3D.

Figure 6: SEMulator3D voxel model and mesh model

Advanced options in SEMulator3D allow for meshes to be refined in areas where a denser mesh is required.

Figure 7: Meshed model with a much finer mesh on the hinge element, wherein the maximum stresses are expected to develop.

SEMulator3D meshes can be used with the FEA tool of choice. Surface meshes are exported in .ans, .dxf, .stl and .obj formats with volume meshes exported in .unv and .ans formats. The image below is a .unv mesh imported into the CoventorWare Preprocessor.

Figure 8: Discrete model from SEMulator3D in CoventorWare Preprocessor. The model has been rendered to reflect separate conductor regions for analysis in CoSolve.

Once the discrete model has been imported, surfaces, parts, conductors, etc. can be named for boundary conditions to be assigned as part of electrostatic-mechanics simulations.

Figure 9: Face selection shows that model edges are well defined and correctly identified in the CoventorWare Preprocessor.

A CoSolveEM voltage trajectory analysis predicts the mechanical response of the device from electrostatic actuation, including deflection until contact is achieved.

The geometric fidelity of the SEMulator3D model improves simulation accuracy with FEA results based on the device expected from the actual microfabrication process rather than the idealized geometry customary to FEA analyses. Obtaining mechanical analysis details such as predicting regions of stress concentration for realistic MEMS device geometry is simple and intuitive with SEMulator3D.

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