To know what is the role that device modelling plays in IC industry. A top-down design approach should be made to have a global view.It comprises of three levels in hierarchy, including: circuit-level, device-level, fabrication-level. IC design is in the circuit-level. Device modelling is in the device-level. IC process technology or namely IC manufacturing process is in the fabrication-level.

(Pin Characteristics) includes terminal voltages, currents or charges, are featured as the input and output ports values.The unknown ports values of a device are solved by an external simulator ADS when circuit analysis is being carried out. The simulator employees KCL and KVL to create a set of nonlinear differential equations. The nonlinear equations are not solved directly, but with approximation and iterative methods. Under certain approximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis. IC design engineers work on a higher abstraction level than the device(transistor) level. In other words, transistors are the primitive components in the eyes of IC designers. The primitive component appears as an analog functional block with 4 pins or a symbol with 4 pins.The virtual symbol is the representative of a real semiconductor device or an electronic component.

Advanced Design System(ADS), as a widely used IC design EDA tool, has three design types: schematic, symbol, and layout. Those designs can all be stored in a small container names "cell" and a big container names "library". So, they can be stored in and reused from component library. IC designer works with the connection of some symbols in a schematic.Each symbol represents a semiconductor device or an electronic component. Little knowledge of a device's internal structures and behaviours are required for IC designers. Because a device works as a functional block. In stead, a device's external structures (connection) and behaviours are of concerns.

On the fabrication-level, a compact model gives the internal description of the device characteristics by means of a set of physics-based expressions with technology dependent model parameters. The physic-based model parameters values accounts for the actual behaviours and properties of a device, defined by its process variables such as: geometrical dimensions and doping profiles.

After the structure and behavior of the individual compact model is specified, the description(structure and behavior) are submit to the simulator.Thus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis