Physical design (electronics)

In integrated circuit design, physical design is a step in the standard design cycle which follows after the circuit design. At this step, circuit representations of the components (devices and interconnects) of the design are converted into geometric representations of shapes which, when manufactured in the corresponding layers of materials, will ensure the required functioning of the components. This geometric representation is called integrated circuit layout. This step is usually split into several sub-steps, which include both design and verification and validation of the layout.

Modern day Integrated Circuit (IC) design is split up into Front-end design using HDLs, Verification, and Back-end Design or Physical Design. The next step after Physical Design is the Manufacturing process or Fabrication Process that is done in the Wafer Fabrication Houses. Fab-houses fabricate designs onto silicon dies which are then packaged into ICs.

Each of the phases mentioned above has Design Flows associated with them. These Design Flows lay down the process and guide-lines/framework for that phase. Physical Design flow uses the technology libraries that are provided by the fabrication houses. These technology files provide information regarding the type of Silicon wafer used, the standard-cells used, the layout rules (like DRC in VLSI), etc.

Typically, the IC physical design is categorised into Full custom & Semi-Custom Design.

One can refer ASIC for Full Custom design and FPGA for Semi-Custom design flows.The reason being that one has the flexibility to design/modify design blocks from Vendor provided libraries in ASIC. This flexibility is missing for Semi-Custom flows like FPGA (e.g. Altera).

The main steps in the ASIC physical design flow are:

These steps are just the basics. There are detailed PD flows that are used depending on the Tools used and the methodology/technology. Some of the tools/software used in the back-end design are :

A more detailed Physical Design Flow is shown below. Here you can see the exact steps and the tools used in each step outlined.

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