
		ISOLATION STRUCTURE FOR PIN DIODE


The structure in this example is an isolation structure that basically 
is supposed to stand off up to 110 volts.  Such a capability is obtained
by having a series of reverse biased pn junctions that drop part of the
voltage each such that the total voltage drop is shared.  This structure
is large (450um x 300um) and as such requires a large number of grid
points for an accurate solution.  

The mesh is produced by a file called pinmesh.p2 and is written to a file
called isol13.mesh.  As usual, the unnecessary points are eliminated from
the grid.  The appropriate electrodes are defined.  The background doping
is p-type of concentration of 1e12.  First an n-type diffusion is defined, 
and then the p-type several p-type diffusions are added.  These pn junctions
will be used to stand off the voltage.  After the pn junctions are defined,
a regrid is done to ensure more grid points around the junctions for better
resolution and more accurate results.

The simulation of this structure is done by a file called pin.p2.  This file
loads in the mesh and then uses the two carrier newton method to solve for
the initial solution.  Please note that the impact ionization model is 
used here since in this simulation it is critical to determine where the
structure breaksdown and more important to make sure it doesn't breakdown
before 110 volts.  The iteration limit has also been raised from its 
default value of 15 to 25 to guarantee convergence.  In order to keep
consistency with the semiconductor chosen for this simulation, the SRH
lifetimes have been increased from their default value of 100ns to 1ms.
With a couple of parameter changes, the initial solution is again obtained.
A log file called IVisol13 is started to save the large quantity of  
simulation data.  The substrate in this example is grounded and the 
electrodes 1 and 2 are supposed to be connected together, as such, in this
simulation they are both maintained at the same potential.  Outfiles at
10, 20, 30, 42, 50, 62, 70, 82, 90, 102, and 110 volts are saved for
possible post processing.  Due to the large number of nodes and several
solve statements, this simulation is quite lengthy.  Appropriate quantities
are then plotted, but in this case its best to do post processing.


