SYMMIC Users Manual CapeSym

Device Parameters

Parameters allow device dimensions and operating conditions to be quickly changed. Each parameter value is stored in the template, along with an allowable value range. The minimum and maximum values that define the allowable range for a parameter have usually been chosen by the template creator to make sure that the model will not have overlapping components or other geometrical problems, and to ensure that the mesh resolution will be reasonable. Changing these minimum and maximum values is not recommended. When parameter changes are made through the Device menu, parameter values are restricted to the allowed range.

Note: To retain parameter modifications between sessions the template must be explicitly saved.

Editable parameters in a template are mostly listed in the Device menu, but some parameters (e.g. whether the solution is steady-state or transient) are accessed from the Configure Run submenu of the Solve menu. For information on the Configure Run parameters see the separate sections on Solutions Through Time and Recording Run Values.

Navigating Parameter Lists

Device parameters can be modified using one of the lists of the Device menu. Parameter lists can be accessed with the mouse or with the keyboard. To open the Device menu with the keyboard use Alt-D. A parameter list can then be selected by using the down arrow key or by using the first letter of the list name. For example, to quickly access the Components list use Alt-D-C in the main window. For most parameter lists only one list may be opened at a time. The exceptions to this are the Components, Materials, and History lists which may be open concurrently with other lists. (These are also the lists that are present for all templates; parameter lists may vary from template to template.)

Once a list is open, an item can be modified by using the down arrow key, followed by the Enter key. To abandon a parameter dialog without changing anything use the Escape key or the Cancel button. To access another list from the keyboard it is necessary to first set the focus back to the main window. Press the Alt and Tab keys at the same time and release them to activate the main window, then use Alt-D to again open the Device menu.

Changing Parameter Values

Parameters are unique to a particular template, but modifying parameter values is done in the same way for all parameters. As an example consider the parameter list of Drain Lengths for the Generic FET Template. Double-clicking on the parameter name in the list opens a dialog that allows a new value to be entered. If the entered value is outside the allowable range it will be set to the nearest limit.




List items displayed in red text indicate parameters that currently have fixed values. These may be fixed because they are constrained by other parameters or because they are not applicable to the current model. In the case of drain lengths, only those drains that are present in the device have modifiable lengths; drains not present are just given the Default Drain Length. For example, only drains #1 and #2 are present in a 3-gate generic FET, so only these would be modifiable. When the number of gates is large enough, all the drains are present and all the lengths are individually modifiable.

Modifying certain parameters may change the minimum and maximum allowable values of other parameters, because the dimensions are interdependent. For example, it is not possible to increase the width of the source vias beyond the widths of the source fingers themselves. Therefore, Finger Width may have to be modified before Source Via Width to enlarge the vias successfully. The order of parameter modification may be important in cases of interdependent parameter values.

The “Allow value to equalize between devices check box has to do with the sharing of parameters between devices in a layout. If the box is checked on the same parameter for two devices in a layout, then changing the value on one device will automatically cause the same change on the other device. The two parameters will always have the same value whenever BOTH of the devices have the equalize flag set to true. Although the user is free to change these flags on any parameters, sometimes they are important for proper modeling and analysis of layouts. For example, in a MMIC layout containing two or more generic FETs, common layers are the substrate, solder, shim, and adhesive layers. All FETs in the layout should have the same thicknesses of these layers to form a consistent MMIC model. Therefore, the thickness parameters for these common layers should all remain equalized.

The “Record this parameter with run values” check box at the bottom of the dialog can be used to automatically record the parameter value after each simulation run. For more details, see the section on Recording Run Values.

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