元件模型在IC設計產業的角色

DaShiaSun@FB

A top-down design approach in IC industry comprises of three levels which includes:
IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
On the circuit-level,
a compact model provides the external terminal electrical characteristics
2 W" u/ V- x* [, i! ~6 L7 m/ P, R5 Qresulted from the mathematic expressions of an electronic device.
The external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
; A8 s( {* c7 O. rare featured as the input and output ports values.
The unknown ports values of a device are solved by a simulator when performing circuit analysis.
( ~1 y; |8 P2 F$ ~After the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
submit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
The nonlinear differential 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 eye of IC designer.
A virtual symbol is the representive of a real device(component).
5 q- |) U- g1 c& t' ZFor instance, transistor's compact model is seen as a 4 pins symbol.
In Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
Those designs can all be stored in a small containner names "cell" and a big containner names "library".
IC designer works with the connection of some symbols in a schematic.
# X# A# e. q4 d' f5 c9 P4 kEach symbol represents an electronic device (component).
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Little knowledge of a device's internal structures and behaviours are required for IC designers. Because a device works as a funtional block. In stead, a device's external structures (connection) and behaviours are of concerns.
On the fabrication-level,
a compact model has 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 behavior and properties
of a device are defined by its process variables such as: geometrical dimensions and doping profiles.
9 x  c$ S9 X: B2 d' IThe true parameters values need to be carefully measured by the experimental setup of device characterization.
Accordingly,
the verified compact models are expected to be implemented in simulators.
/ k- e/ x2 v( M8 ^0 }Thus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
! ]2 c0 h) G+ }1 q' Q, Zis the same as its implemented compact model. Meanwhile, a compact model is the most crucial process design kit, which plays as the interface between circuit designers and device developers.
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