2.1.1 Tool Integration

Since not all available tools and simulators are explicitly designed to work inside a TCAD framework, compatibility with external TCAD tools must be ensured by facilitating their migration into the framework through the use of appropriate data level concepts. These concepts relate to tool integration methodologies and mechanisms available in a TCAD framework.

Tools available in a TCAD framework may be divided into two groups:

Conventional Tools
These tools are classical standalone tools (``point tools'') often written long before the TCAD system itself existed. They employ their own specialized file formats, since they have no need to cooperate with other tools or a framework. Therefore they usually have their own pre- and postprocessing facilities (e.g. for grid generation and visualization) and solve isolated design problems.

Framework Tools
These tools are explicitly designed to work within the framework, and are written when the framework either exists already or is engineered in parallel. They rely heavily on framework services, and the more of those services they use, the tighter they are integrated into the framework. The classical conception of a tool being an executable file is no longer valid for framework tools, which may be realized as an advanced framework library or even a single function.

For a conventional simulator, two methods of integration can be applied:

   
Wrapping
This method integrates a conventional tool by running a conversion program before and after running the tool itself. The program performing the conversions and controlling the simulator is then called the wrapper. There is no need for the source code to be available, since the simulator itself remains unchanged, and just the input and output files are converted to TCAD compliant data (PIF, in the case of VISTA). Fig. 2.1 depicts this integration method. The advantages of this integration method are that there is no need to change the simulator itself. Therefore this method can be applied to any simulator whose executable and data format descriptions are available. However, one drawback is that any change in data formats involves changing the wrapper. Additionally, if the conversion process is time and space consuming, it may seriously affect overall simulator performance in the framework.

Direct Integration
Through substituting (or augmenting) the simulator's input and output code with the TCAD system's data level library calls, the simulator will directly read and write framework compliant data. The advantage is that this simulator will then behave like a native framework tool without any performance drawbacks through conversion. A prerequisite is that the source code of the simulator has to be available, and that a suitable data level interface is provided by the framework for the programming language the simulator is coded in and for the data structure the simulator uses. Fig. 2.2 shows how a simulator is directly integrated into a framework.

  
Figure 2.1: Simulator integration by wrapping

  
Figure 2.2: Direct simulator integration

  
Figure 2.3: Total simulator integration by splitting into functional modules