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,
: C# P0 Z" N2 Ha 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,
! Q* k7 u' x# eare featured as the input and output ports values.
The unknown ports values of a device are solved by a simulator when performing circuit analysis.
9 R# ^7 d) C# rAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
9 f9 Y4 s0 l5 S: ysubmit 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.
5 J' [$ V) \9 I: _5 EIn other words, transistors are the primitive components in the eye of IC designer.
9 M) w( `! O5 y) kA virtual symbol is the representive of a real device(component).
7 _  n4 t: X9 X: H" t7 T! \  b3 xFor instance, transistor's compact model is seen as a 4 pins symbol.
6 f: X+ |9 A# lIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
8 k# R0 J* X, ]) `8 jThose designs can all be stored in a small containner names "cell" and a big containner names "library".
6 Q+ u9 G. Z9 _. n3 f4 s, PIC designer works with the connection of some symbols in a schematic.
Each symbol represents an electronic device (component).
4 `1 c4 S4 P/ ]& E1 b" j, n9 N+ T
2 _4 P( Z3 U7 n

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.
) m( ?$ A2 D. k. J2 \The true parameters values need to be carefully measured by the experimental setup of device characterization.
8 S0 C; @5 I. {/ o: y0 y( j8 uAccordingly,
% M. S5 y9 m: g$ J# F8 a# \. s, }" Mthe 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.
- m  _9 `/ Z- O8 P4 c+ ^
/ P: S' I6 b4 O- y
* n; A5 i# a2 o2 e  z; T; d1 M0 [8 M

: V% L1 X0 @3 E4 A+ P- b



+ L$ ~$ S* S) V, [1 O
1 l) c# h3 r# q