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:
! B3 s  v4 A% U. K* i- J. h- BIC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
! N; o1 w- `/ i' e0 V  }0 _3 B* K/ UOn the circuit-level,
a compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
1 q* T" V: _# c8 q$ S9 q5 IThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
, _8 x. Z) M/ K8 A8 Care featured as the input and output ports values.
The unknown ports values of a device are solved by a simulator when performing circuit analysis.
, l; h4 U# I0 c0 {4 [, Y$ Y, v; EAfter 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.
( v/ X5 ?0 w) U; z. ]) x5 y- EIC 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).
8 _& u& j" K+ C# p/ E9 Q* S7 V$ gFor instance, transistor's compact model is seen as a 4 pins symbol.
% z( C# L3 K3 R5 V: f, [! U1 i6 KIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
( N" k# m: \. O) D6 bThose designs can all be stored in a small containner names "cell" and a big containner names "library".
! R4 y% ^9 H1 B/ u# `# F8 wIC designer works with the connection of some symbols in a schematic.
" E+ |* z5 b" D! n. X( i- ?, UEach symbol represents an electronic device (component).

* n; [9 [* S! L# _7 m5 L

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.
; z$ C2 `! F1 `4 [. ROn the fabrication-level,
& d* u4 R; G& M! W' u" w/ ~0 za 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
. E, r8 m8 ]  P+ @! ]4 Pof a device are defined by its process variables such as: geometrical dimensions and doping profiles.
9 M& Y4 p7 l7 y; v1 s( f8 }; TThe true parameters values need to be carefully measured by the experimental setup of device characterization.
: k' E! l: u# V. {" I% O! Q$ N4 R% AAccordingly,
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.



* B7 ~, K2 U8 [/ f


, U8 s0 p+ L* f% d2 Q
+ T- p3 q; g# N
% }# ]; W( O3 H
: Y2 q, C9 L0 g# Z3 o