8.14 Sspd_chapter 6_part 7_device simulation2  (Page 2/3)

7.4.2.: Interface FromDevEdit

A 2D or 3D structure created by DEVEDIT (device edit) can be read into ATLAS using the following statement.

MESH INF=<structure filename>

This statement loads in the mesh, geometry, electrode positions, and doping of the structure. ATLAS will automatically determine whether the mesh is 2D for S-PISCES or BLAZE, or 3D for DEVICE3D or BLAZE3D.

If the structure coming from DEVEDIT were originally created by ATHENA, the electrodes should be defined in ATHENA as described in the previous section. If the structure is created in DEVEDIT, the electrode regions should be defined in the Region/Add menu of DEVEDIT.

7.4.3. : Using The Command Language To Define A Structure

To define a device through the ATLAS command language, you must first define a mesh. This mesh or grid covers the physical simulation domain. The mesh is defined by a series of horizontal and vertical lines and the spacing between them. Then, regions within this mesh are allocated to different materials as required to construct the device. For example, the specification of a MOS device requires the specification of silicon and silicon dioxide regions. After the regions are defined, the location of electrodes is specified. The final step is to specify the doping in each region.

When using the command language to define a structure, the information described in the following four sub-sections must be specified in the order listed.

Specifying the Initial Mesh

The first statement must be:

MESH SPACE.MULT =<VALUE>

This is followed by a series of X.MESH and Y.MESH statements.

X.MESH LOCATION =<VALUE>SPACING =<VALUE>

.

Y.MESH LOCATION =<VALUE>SPACING =<VALUE>

.

The SPACE.MULT parameter value is used as a scaling factor for the mesh created by the X.MESH and Y.MESH statements. The default value is 1. Values greater than 1 will create a globally coarser mesh for fast simulation. Values less than 1 will create a globally finer mesh for increased accuracy. The X.MESH and Y.MESH statements are used to specify the locations in microns of vertical and horizontal lines, respectively, together with the vertical or horizontal spacing associated with that line. At least two mesh lines must be specified for each direction. ATLAS automatically inserts any new lines required to allow for gradual transitions in the spacing values between any adjacent lines. The X.MESH and Y.MESH statements must be listed in the order of increasing x and y. Both negative and positive values of x and y are allowed.

After an initial mesh has been defined, you can remove grid lines in specified regions. This is typically done in regions of the device where a coarse grid is expected to be sufficient such as the substrate. The removal of grid lines is accomplished using the ELIMINATE statement. The ELIMINATE statement removes every second mesh line in the specified direction from within a specified rectangle. For example, the statement: