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Multilayered CMOS Image Sensor structure created with Sentaurus Process. The microlens on top of the structure is designed to focus light onto the active silicon substrate. The color contour plot in the bottom silicon layer shows a typical optical generation rate distribution, as calculated by Sentaurus Electromagnetic Solver.
Electrical response of the CMOS Image Sensor as simulated with Sentaurus Device. The blue curve shows the change in the electrostatic potential in the active region as the gate voltage is switched on and off (black curve). The top plots show corresponding 3D potential distribution.
Overview
As the device dimensions continue to scale down, simulations become more and more important in the design process allowing for reduced costs and time savings during the development cycle. Modeling of a CMOS image sensor (CIS) is a particularly challenging task which often requires a full three-dimensional approach. Furthermore, three aspects of the simulation are important for predictive simulations of the CMOS image sensors. These components are simulation of the process flow, modeling of the light propagation and the excitation of the carries, and carrier transport in the device. TCAD Sentaurus provides all the necessary components for such three-dimensional simulations in an integrated simulation flow.
The application example this month presents such a simulation flow. It uses Sentaurus Process, Sentaurus Structure Editor, Sentaurus Electromagnetic Solver, and Sentaurus Device. Sentaurus Structure Editor and Sentaurus Process are used to create a realistic three-dimensional CIS structure. The so-called paint-by-numbers technique is used for the 3D process simulation. Since the typical dimensions of the CIS structures are on the micrometer scale, the light exposure simulation has to account for the diffraction-limited propagation of light. The finite-difference time-domain (FDTD) Sentaurus Electromagnetic Solver is used for this purpose. Sentaurus Mesh now supports the automatic generation of fine sub-wavelength meshes optimized for the FDTD calculation, so one can seamlessly integrate the simulation of the light propagation with simulation of the electrical response, which requires a different (coarser) mesh. Once the optical carrier generation rates are calculated by the Sentaurus Electromagnetic Solver they are imported into Sentaurus Device and electrical characteristics of the device are calculated.
If you are interested in accessing this Application Example, please fill out the Example Request Form and you will be emailed download instructions.
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