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).
4 H' h1 f+ o/ Y( h3 h4 \On the circuit-level,
a compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
- a, _5 p/ @- L1 P) B+ BThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
; U/ W- F; @7 r7 ~) A9 y; sare featured as the input and output ports values.
4 @2 S: s+ H/ t$ B7 N1 RThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
. {9 t  V7 I2 V/ Y4 \* [1 LAfter 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
4 x! k% H4 N: D6 d$ y& D0 @2 I2 E" \approximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis.
. x# h* O& R4 P3 B$ z; y. A3 j7 `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.
5 g( x, ?3 u8 b9 L+ U6 ]- c2 t4 I' ?$ e, ^: [A virtual symbol is the representive of a real device(component).
+ d% r, k$ g/ v% ~! A2 kFor instance, transistor's compact model is seen as a 4 pins symbol.
9 b+ l( k! Z* ^/ kIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
# L: u* ?& U' nThose designs can all be stored in a small containner names "cell" and a big containner names "library".
7 H1 \" S: }0 \. j+ _' _! EIC designer works with the connection of some symbols in a schematic.
Each symbol represents an electronic device (component).
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! D9 q" S" e- L/ C0 n6 f1 p* s: FLittle 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.
; h$ `$ W: g: o$ P4 HOn the fabrication-level,
) m2 K# j& q# Z- L+ ]a compact model has the internal description of the device characteristics by means of a set of physics-based expressions with
4 [+ p0 r, }# a; Z- X: s9 |technology dependent model parameters. The physic-based model parameters values accounts for the actual behavior and properties
$ `* |& y/ Y9 A8 ?of a device are defined by its process variables such as: geometrical dimensions and doping profiles.
' c& w2 @" p+ I! `* m- O. n$ lThe true parameters values need to be carefully measured by the experimental setup of device characterization.
* L# o* W; U9 Z, v- G# LAccordingly,
the verified compact models are expected to be implemented in simulators.
8 J9 j/ l5 }# C* H* xThus 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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