SYMMIC Users Manual CapeSym

Editing Layouts

A layout is edited using Edit layout... from the File menu, which opens the Device Layout Table dialog.



The layout can be given a title in the first edit box at the top of the dialog. As with all strings entered in SYMMIC, quotation marks, commas, less than signs (<) and greater than signs (>) are not allowed. These illegal characters will be replaced with underscores.

The Length and Width boxes specify the extent of the rectangular layout area. Like all dimensions in the Device Layout Table these have units of micrometers (microns). If the arrangement of devices extends beyond the Length and Width values, then these values are ignored and the layout area is extended to cover all the devices. So setting Length and Width values to zero results in the layout being sized to fit the devices. A blank entry is interpreted as zero.

The Meshsize parameter is used for meshing the areas of the layout outside of the devices. (The device meshing parameters are specified in the device templates.) The Meshsize parameter does not affect finite element calculations during superposition, but it determines the mesh of the final solution. A smaller value will result in smoother plot surfaces, while a larger value will produce smaller solution files and faster graphics. Appropriate values should be in the range of one tenth to one hundredth of the Length and Width dimensions. The bias parameter sets the “borderbias” attribute, a multiplicative bias that grows the size of mesh elements away from each device during superposition. A larger value will tend to produce somewhat smaller meshes during the finite element calculations, and reduce accuracy in the temperature coupling between devices. The default bias is 1.25. Larger values may reduce simulation times but the value should be kept below 2 in most cases.

Devices are listed in the Device Layout Table in the order they are specified in the layout template file. Each device is numbered sequentially with the same numbers used in the Select submenu of the Device menu. Empty table rows have no device numbers and all the edit boxes are blank. If there are more than 16 devices in the layout, the scrollbar to the right of the dialog is enabled to allow scrolling through all the devices. There is no limit to the number of devices that can be entered in the layout table, however the Select submenu will display only the first 256 devices.

Pressing the Apply button causes all of the entries of the table to be read and the actual layout in the main window to be updated. All of the device files will be reloaded from disk during this update, so any changes to device parameters will need to be saved prior to this update. The dialog attempts to detect device changes (in the main window) prior to an update, and displays the following message box if changes are suspected. Replying Yes will cause the device files to be overwritten, but No will result in loss of the device changes since the original devices will simply be reloaded.



Please be aware that device files are not renamed when saved from the Device Layout Table dialog. All devices are resaved to their original files. This means that if a change is made to a parameter in one device but not to a later device (in the table) loaded from the same file, then the later device will overwrite the file for the device with the changed parameter, effectively erasing this change. Best practice is probably to save all device changes before opening the Device Layout Table dialog.

Unlike the device template files, the layout template file is not reloaded or updated by the Apply button. It will need to be explicitly saved to permanently store the new layout by using one of the Save menu items from the File menu.

The Quit button will exit the Device Layout Table dialog without re-reading the table entries or further updating the layout in the main window. Quit will NOT cause device files to be saved or reloaded.

Editing a Device Entry

Changing the Device Template File in a row of the table will cause a new device file to read when the table is applied, and the information in this device file will then be used update the Device title. A device may be removed from the layout by erasing the filename from the Device Template File box. The deletion will be displayed after the Apply button is pressed and the devices have been reloaded. The remaining devices will be renumbered sequentially.

The X Position and Y Position determine where the lower left corner of the device (as seen from a top view) is placed relative to the (x,y) origin. However, if the Center at box is checked the center of the device will be placed at (X Position, Y Position). Device positions must be in increments of 0.5nm. Values not at 0.5nm intervals will be shifted to the nearest, smaller 0.5nm interval. For example, setting the X Position to 100.000778 will place the device at 100.000500 microns.

No devices in the layout may overlap. If a layout contains overlapping devices when the Apply button is pressed, the Device Layout Table will be redisplayed with (one of) the offending X Position and Y Position entries highlighted in red. The offending device will be removed from the actual layout, but not from the table. Failure to correct the entries that caused the overlap will cause the error to recur each time the Apply button is pressed.

The Mirror X check box selects whether the device will be mirrored about its maximum x-value. Device templates for symmetrical devices usually define only half of the full device, with the axis of symmetry placed at the maximum x extent of the half-device. Use of the full device in the layout requires that the half-device model be copied and reflected about this axis of symmetry. A half-device without mirroring should only be used in a layout when an edge of the layout corresponds to the axis of symmetry. That is, the half-device's maximum x-value should occur at the edge of the layout's rectangular area.

The Flip Y checkbox flips the device vertically about an x-axis through the device center. A horizontal flip can be realized by combining the flip checkbox with 180-degree rotation. The Rotation pull-down list allows the orientation of the device to be changed from its definition in the device template. A device in a layout can be rotated (about the positive z-axis) by ±90 or 180 degrees. The flip and rotation are applied after the device is mirrored but before (x,y) positioning. The lower left corner of the device AFTER rotation is positioned at X Position and Y Position.

Adding a Device

To add a device to the table, enter the filename of the device template in the Device Template File box of an empty row. This can be done by either typing the filename or by clicking on the browse button (...) next to the edit box and selecting the file. To insert a blank row above an existing row, place the cursor in the Device Template File box of the row and then hit the Insert key. To insert a device at the bottom of the layout, scroll down until the first blank row is encountered and then enter the device filename. Fill in the remaining entries in the row to complete the device specification. The device template is not loaded until the Apply button is pressed. If the file cannot be found, the Device Layout Table will be automatically reopened with the filename highlighted in red.

Device Selection Check Boxes

The check boxes on the left side of the dialog are for selecting single or multiple devices. The top-most check box selects (or unselects) all of the devices in the layout, even those not currently visible in the dialog. Selected devices may then be operated on as a group using the operations available through the For selected... button. This button opens the Action for Selected dialog, as shown in the next figure.

The Action for Selected dialog allows fields of the table rows to be modified simultaneously across all of the selected rows. For example, each of the Center at check boxes in the selected rows may checked by using the X,Y at Centers operation, or unchecked by the Do not center operation. An entire group of devices may be moved to a different place in the table with the Move to row operation. A group of devices may be deleted by Delete rows. Most of these changes can be recovered by the Undo button (see below).

Copy rows to end takes the selected rows, duplicates them, and adds the duplicate rows to the end of the table. Note that the duplicate devices will exactly overlay the existing devices in the layout, so do not Apply these changes to the layout until after the duplicates have been moved to new, non-overlapping locations. To facilitate moving the duplicates as a group, the selection is automatically changed from the existing rows to the duplicated ones. Any of the group movement operations can thus be immediately used.

There are four group movement commands: Switch X and Y, Shift by dX dY, Reflect all over dX, and Reflect all over dY. The other commands may move each device in a group by a different amount, but these four commands will keep them all together. The Switch X and Y operation exchanges the X Position value with the Y Position value on every selected device row. This will rotate the group 180 degrees while also shifting it to a different side of the layout. The Shift by dX, dY operation adds the offsets in the dX and dY boxes to all of the X Position and Y Position values, respectively. The Reflect operations flip the group across an axis of symmetry. Reflect all over dX applies a horizontal flip to the group and then shifts the group to the other size of the line x = dX, so that group appears mirror reflected around that line of symmetry. Likewise, Reflect all over dY applies a vertical flip to the group and then shifts the group to the other side of y = dY to become a symmetrical reflection about that line.




The Undo Button

The Device Layout Table dialog maintains an undo stack of entries prior to each Apply. The Undo button may be used to retrieve and apply these old entries to return to a prior layout. Please note: there is no redo operation. Once the Undo button is pressed all of the previous changes are permanently lost. The only way to regain that layout is to repeat all of the changes in the table again and Apply them. The undo stack applies only to layout table entries, not to changes made in device parameters and saved in the device files. The undo stack will remember only the 24 most recent layouts. Quiting the Device Layout Table dialog erases all of the undo stack memories.

Equalizing Components or Parameters

At the bottom of the Device Layout Table two groups of radio buttons are available for setting the equalization flags globally on all devices. Leaving the selections at “As Is on both groups means that no change will be made when the OK button is pressed. Most users will want to leave these settings “As Is.

When the equalization flag is set on the same parameter in two devices in a layout, the parameter will always have the same value in both devices. For example, if the equalization flag is set on the Number of Gates parameter on two devices then these two devices will always have the same number of gates. Selecting “All parameter settings in the Device Layout Table sets the equalization flags on all parameters on all devices, so any parameters with the same name will have the same values on all the devices. In contrast, selecting “No parameter settings” resets the equalization flags. This means that any changes to parameters on one device will not be automatically repeated on another device. Selecting “No parameter settings” will not effect the layout because no parameters are actually changed, whereas selecting “All parameter settings” will cause parameters to be equalized as soon as the OK button is pressed.

The second group of radio buttons provides similar global control over the equalization of the materials of the components in the devices. When “All component materials” is selected, all components with the same names will be set to use the same materials in all devices. If the Gates of the first device are made of gold, then so will the Gates of all the other devices. When “No component materials” is selected, the components of the devices will be free to assume different material settings. It would then be possible to change the Substrate material to GaAs on one device and to SiC on another, making a rather unrealistic layout. So care should be used when making global changes to equalization flags.

Copying Parameters between Devices

The Device Layout Table can be used to copy parameter and material settings from one device to several others. To copy the parameter settings from device template src.xml to device template dest.xml, open src.xml and create a layout from it, then add dest.xml as the second device in the Device Layout Table. Select “All parameter settings” to set all the equalization flags on both devices, and press the OK button. All the parameter values from device 1:src.xml will then be copied to device 2:dest.xml. Use Save device as... from the File menu to save the modified dest.xml to a new file. (The src.xml template will be unchanged except all its equalization flags are now set. To avoid destroying the original flag settings, hit Cancel when prompted to save it.) A similar process can be used to copy all the materials of all components from one device template to another by selecting “All component materials”.

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