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).
- O9 k5 q% r: O' TOn the circuit-level,
. M- x( J4 [9 m: l* H7 W& ca compact model provides the external terminal electrical characteristics
8 h; Y6 k2 |1 V! E" y7 y2 `3 _resulted from the mathematic expressions of an electronic device.
* J0 a7 J$ V6 aThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
9 w' G  \8 a9 \; L! Xare featured as the input and output ports values.
" T" i  X- Y4 [: N: ?; ZThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
/ O' y" k" x6 N; {# ^* L  F4 iAfter 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
6 D4 V( T2 H" e4 ?: @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).
For 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".
0 {5 k) Q) ?" l) d  XIC designer works with the connection of some symbols in a schematic.
% P- B2 d  k4 ~3 j. rEach symbol represents an electronic device (component).

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1 |) d* C# W- N! @' V6 [3 u9 gLittle 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,
* K5 J* b# e; w3 J8 e' Da compact model has the internal description of the device characteristics by means of a set of physics-based expressions with
* Z  `2 }; I0 r# u# h$ {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.
/ Q( o& l+ }. OThe true parameters values need to be carefully measured by the experimental setup of device characterization.
: |2 B* [( v) |, [* B5 \. LAccordingly,
the verified compact models are expected to be implemented in simulators.
Thus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
is 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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