Layout Data Structure
In the realm of chip and PCB (Printed Circuit Board) design, layout data plays a fundamental role. This data defines how components and connections are arranged on a semiconductor chip or circuit board.
Representation as Vector Graphics
Layout data is primarily represented as vector graphics. Unlike raster graphics which are composed of individual pixels, vector graphics are mathematical calculations between points, forming lines and shapes. This vector format is preferred for several reasons:
Efficiency: Vector graphics are memory-efficient compared to raster images, making them suitable for complex layouts.
Processing Speed: They can be processed quickly and easily due to their information-rich nature.
Flexibility: Vector shapes can be resized or modified without losing accuracy.
Graphics elements within layout data, such as structures for doped regions or interconnects, are known as shapes. Each shape is associated with a specific layer. This layer assignment is crucial for generating masks during fabrication and for performing graphical operations. It’s important to note that these layers in layout data do not always directly correspond to fabrication layers on a semiconductor wafer. Some layers may have no direct wafer counterpart, adding complexity.
Drawn Layers vs. Fabricated Layers
To clarify layer terminology, we distinguish between two types: drawn layers and fabricated layers. Drawn layers refer to the layers in the layout data’s data structure, while fabricated layers correspond to physical layers in the fabrication process. While they often align, this isn’t always the case. For instance, certain layers in layout data may not directly relate to wafer structures. These distinctions are primarily for clarity and context.
Shapes within layout data are invariably polygons, which are two-dimensional, continuous graphics elements with straight edges. They are efficiently stored in vector format as a list of successive corner coordinates. This allows polygons to be defined using whole numbers, conserving computer memory and ensuring model accuracy. Layout data also supports polygons with holes (donuts) and shapes with rounded boundaries (conics), though approximations are made due to the inherent limitations of polygonal representations.
Special Shapes in Layout
In addition to general polygons, layout data includes two specialized shapes: rectangles and paths.
Rectangles: Rectangles are polygons with four sides and right angles, often represented by coordinates of two diagonally opposed corners. This efficient data structure aligns with how rectangles are created during layout design.
Paths: Paths are polylines with a specified width (w). They are commonly used for interconnects, ensuring a consistent cross-sectional area for electrical current. Paths are represented by their centerlines and path width in the data structure. This efficient representation simplifies modification and reduces data volume.
In summary, layout data is a critical element in chip and PCB design, encompassing vector graphics representations, layer assignments, polygonal shapes, and specialized shapes like rectangles and paths. The data’s efficiency and flexibility play a pivotal role in efficiently designing and manufacturing intricate semiconductor chips and circuit boards.
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