HEAT solver - Simulation object

General tab

Simulation region

The simulation region contains several settings:

• SOLVER REGION: Select the simulation region the solver will use.
• SOLVER MODE: Steady state mode for steady-state simulations and transient mode for time dependent simulations. The color of the simulation region will change depending on which option is picked.
• SOLVER PHYSICS: Thermal only performs a thermal simulation only, thermal and conductive option runs an electro-thermal simulation using a conductive model for the electrical part. For more details about the two simulation options go to the HEAT solver introduction page.
• NORM LENGTH: The length of the device in the direction perpendicular to the plane of the simulation; any normalizations length will be with respect to this value.

Mesh tab

Global Mesh Constraints

The global mesh settings section contains several settings:

• MINIMUM EDGE LENGTH: The minimum length of an edge of a triangle (in 2D) used in the mesh.
• MAXIMUM EDGE LENGTH: The maximum length of an edge of a triangle (in 2D) used in the mesh.

Auto Refinement Settings

The auto refinement settings section contains several settings:

• MAX REFINE STEPS: The automatic refinement proceeds in multiple stages, creating a quality triangulation and refining the mesh according to the change in doping density and, if present, optical generation rate. This setting limits the number of refinements at each stage, and corresponds to the number of vertexes that can be added to the mesh at each stage.
• SENSITIVITY: This setting controls the threshold at which the mesh will be refined due to the gradient in the doping density or optical generation rate. The default value will roughly correspond to a limit of a factor of 2 change in the doping density or generation rate over the span of an element in the mesh.

Advanced Options

Geometry Options

• DEFLECTION TOLERANCE (UM):  Controls how curved surfaces are broken up into multiple linear segments.  A smaller deflection tolerance will force the geometry builder to break up a curved surface into smaller segments. Only available in 2D simulations and 3D simualtions with vertex insertion volume meshing.

• MAX PLC EDGE LENGTH (UM):  Forces the solver to break long objects into smaller segments in order to help with the geometry building with long and narrow structures. This is only available in 3D simulations with vertex insertion volume meshing.

Mesh Options

• TRIANGLE QUALITY: The quality of mesh triangle, defined the minimum angle used in the triangular mesh cells. The higher the angle, the higher the quality of the triangle.
• VOLUME MESHING: The meshing algorithm used by the solver for 3D simulations.
• Vertex insertion: This method forms vertices within boundaries of the volume to generate a 3D mesh and refines the mesh in a volume based on variations in parameters such as imported heat generation across the volume  This is the default option and suitable for most cases.
• Advancing front: This method forms a surface mesh before generating a volume mesh which can result in a better mesh than vertex insertion method for geometries with thin features. Note that this method doesn't refine the mesh based imported parameters variations and doesn't support directly defined mesh constraints.
• Hybrid: This is a combination of vertex insertion and advancing front techniques useful for structures with thin features and import based mesh refinement. It should only be used if vertex insertion method fails generating the mesh and the accuracy of the results should be verified.

Transient tab

Transient Simulation Controls

The transient simulation controls section contains several settings:

• MIN TIME STEP: The smallest time step that will be used in the transient simulation (used as the initial time step)
• MAX TIME STEP: The largest time step that will be used in the transient simulation.
• ABS LTE LIMIT: If the absolute error is less than this value then the solver increases the time step.
• REL LTE LIMIT: If the relative error is less than this value then the solver increases the time step.

Downsampling

• DOWN SAMPLE MODE: The type of downsampling to use, None, for no downsampling, count, for specifying the number of point to downsample at, and interval to specify the downsample step size.

Global Source Shutter

The global Source shutter will apply a shutter to all the heat source objects in the simulation.

• SHUTTER MODE: disabled, for no shutter, step on and step off for step functions, pulse on and pulse off for a pulse with on and off times. The time shutter function will be plotted as the option is chosen for ease of use. The on and off times can then be specified.
• SHUTTER TON: Sets the on time of the shutter.
• SHUTTER TOFF: Sets the off time of the shutter.
• SHUTTER TSLEW: Sets a slew in the stepping of the shutter.  This feature is useful in helping the solver to converge where a sharp step in the shutter tend to makes the solver diverge.
• SHUTTER SLEW FUNCTION: linear for a linear transition between off and on states, log for an exponential change between the off and on states.
• SHUTTER SLEW CUTOFF: The shutter uses the logarithmic function to step from this value to 1 (for turning on) and from 1 to this value (for turning off).  The stepping from zero to the slew cutoff value (and back) is abrupt (within one time step).
• ILLUMINATION POWER SCALING: This option can be used to scale the amplitude of the source. By default the value is set to '1' which means no scaling.

Results tab

This tab contains a list of all the spatial results that can be recorded throughout the simulation. One can pick to enable or disable one or more of the results to save memory as needed.  The tab also contains basic information about the available results such as their units and descriptions.  Please see the results section below for more information on the available results.

Mesh

Once the simulation region has been meshed, the HEAT simulation object returns the mesh grid as an  unstructured dataset which shows the returns  area of the mesh cells, and the unique ID of the partitioned regions.

Spatial

After the simulation is run the grid object will be overwritten; however, the grid can be viewed from any of the new results. Each result is returned as an unstructured dataset.  If the simulation is transient the results will be a function of time, and in steady state the results will have the boundary condition values as parameters.  

Boundary Conditions

The thermal solver returns one matrix dataset called boundaries with the results from each boundary as an attribute. For transient simulations the dataset parameter is time, and in steady state simulations the boundary condition set-points are the parameters.

Advanced tab

Global Solver Controls

• MULTITHREADING: If enabled, the user can choose to divide up and run the simulation over multiple threads

Iteration Controls

• USE DEFAULTS: checked by default, will use an iteration limit of 40, absolute tolerance of 1e-06 volts and a maximum update value of 5 volts.
• ITERATION LIMIT: Takes a value between 1 and 10000. This limits the number of iterations of the Poisson or drift-diffusion solver that may be run.

ABSOLUTE TOLERANCE: For a calculation to be considered converged, this determines the maximum absolute change between iterations that can exist. For the Poisson solver, the step converges when

$$\parallel V^{k+1}-V^k\parallel_\infty<\delta$$

where δ is the tolerance and V is the electrostatic potential. For the drift-diffusion solver, both the electron and hole quasi-Fermi levels must converge:

$$\parallel E_{Fn}^{k+1}-E_{Fn}^k\parallel_\infty<\delta$$

$$\parallel E_{Fp}^{k+1}-E_{Fp}^k\parallel_\infty<\delta$$

 MAXIMUM UPDATE: To help the calculation converge, the maximum change that will be applied to estimate the (thermal) solution at the next step can be clamped. This value is in units of Kelvin.

 MAX VOLTAGE UPDATE: To help the calculation converge, the maximum change that will be applied to estimate the (electrostatic) solution at the next step can be clamped. This value is in multiples of the thermal potential (kT/q).