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:
: C9 B% N# R% ?1 P; x9 }IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
. k; i  ^! |- E" t# _On the circuit-level,
3 r9 r5 {2 c" D( ga compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
The external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
7 R1 `+ T# q' @+ d; u; {are featured as the input and output ports values.
0 e7 o9 z  r9 b7 cThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
After the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
9 Y* R" i- c" a% Y( _; ?; t  ^4 Xsubmit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
& a/ B, O' ]; i: Q. y8 K2 uThe 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.
) y% \) {# |$ U0 X9 UIn other words, transistors are the primitive components in the eye of IC designer.
A virtual symbol is the representive of a real device(component).
& z2 p8 U6 d% ]- }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".
IC designer works with the connection of some symbols in a schematic.
Each symbol represents an electronic device (component).

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/ E- p% X2 W" h; c4 |: RLittle 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
- Z5 a4 w7 u) A: K( ^3 M$ C% S/ vtechnology 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.
" ]- ~3 {* E! }1 Z4 p$ ~6 LThe true parameters values need to be carefully measured by the experimental setup of device characterization.
7 s0 W) q: A* O! g& ~' {. P1 uAccordingly,
the verified compact models are expected to be implemented in simulators.
: d  N8 Q- G0 M! F. K/ LThus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
/ e! c* a. C" L$ L3 \8 t3 Kis 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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