Mextram
General Purpose Bipolar Model

New Level 504 Improvements

From the older Mextram level 503, the new version has been upgraded regarding the following features :

• Mextram now includes self-heating, allowing device temperature to be dynamically computed. Self-heating calculations use only analytical derivatives, reducing simulation times (no need to compute numerical derivatives)
   
• Modeling of SiGe is now possible, using a dedicated set of parameters
   
• The set of parameters has been reviewed to make extraction procedure easier
   
• Two constant overlap capacitances have been added
   
• First and higher order derivatives have been smoothed, resulting in better accuracy and convergence ability

Evolution of cut-off frequency with smoothing parameter AXI.

Forward DC characteristics.

Mature Bipolar Model

Mextram provides several features that Gummel-Poon model lacks:

• Bias-dependent Early effect
   
• High injection effects
   
• Ohmic resistance of the epilayer
   
• Velocity saturation effects on the resistance of the epilayer
   
• Hard and quasi saturation (including Kirk effect)
   
• Split base-collector and base-emitter depletion capacitance
   
• Substrate effects and parasitic PNP
   
• Current crowding and conductivity modulation of the base resistance
   
• First order approximation of distributed high frequency effects in the intrinsic base (high frequency current crowding and excess-phase shift)
   
• Recombination in the base (for SiGe transistors)
   
• Early effect in the case of a graded bandgap (for SiGe transistors)
   
• Temperature scaling
   
• Self-Heating

Simucad Implementation

• Mextram is compatible with VZERO and BYPASS options in order to achieve great speed performance
   
• Internal warnings and diagnostics provide valuable information to help finding convergence issues
   
• User-friendly parameters checking: user is kept aware of every clipped parameter
   
• Device internal variables (currents, conductances, charges...) can easily be accessed like any other parameter
   
• Mextram model is part of the SmartLib product-independent model library. It can be accessed within SmartSpice as level 503 or 504

Advanced Applications

Mextram’s second version is now well suited to high technology:

• Advanced processes such as double poly or even SiGe can be modeled
   
• Mextram can be used for high-voltage power applications
   
• Uncommon situations like simulating the NPN device in LDMOS technology behave correctly with Mextram

Rev. 101807_04