1 Introduction to Fluid Guard Rings

The Virtuoso Layout Suite L (Layout L) provides an innovative infrastructure with capabilities to create and implement layout designs. One of the important offerings of Layout L includes a menu-driven programmable feature for installing, creating, and editing fluid guard ring (FGR) devices, which are a type of fluid Pcells.

This user guide covers information about how to create and manage FGR devices. For information about how to use the Layout L tool, refer to the Virtuoso Layout Suite L User Guide.

You can also refer to the Virtuoso Fluid Guard Ring Frequently Asked Questions manual.

This user guide is aimed at developers and designers of integrated circuits who want to harness the usability and productivity benefits of FGR devices in Layout L. It assumes that you are familiar with:

Virtuoso Studio design environment and application infrastructure mechanisms designed to support consistent operations between all Cadence® tools
Applications used to design and develop integrated circuits in the Virtuoso Studio design environment, notably Virtuoso Layout Suite and Virtuoso Schematic Editor
Design and use of parameterized cells
OpenAccess version 2.2 technology file
Component description format (CDF)

Virtuoso automatically loads a set of implementation files (vfo*.ils) at the time of initialization. These files provide the Virtuoso Fluid Object (VFO) infrastructure that enables you to install, create, and edit VLS-based FGRs as described in this user guide.

In addition, Virtuoso allows you to work with customized FGRs developed using the VFO infrastructure that adheres to the added or modified user-defined capabilities or features. In other words, the customized FGRs are based on capabilities that are not shipped as part of Virtuoso.

As it is difficult to ascertain the scope of customizations done by a PDK developer, which can differ from PDK to PDK, this user guide covers only the information about VLS-based FGRs. The information about customized FGRs pertains only to ‘how to customize an FGR’. If you are using the customized FGRs and need assistance in configuring or troubleshooting, contact your PDK provider for information.

A good understanding of creating parameterized cells (Pcells) using Cadence® SKILL language is a prerequisite for the concepts discussed below. For detailed information on Pcells, see the Virtuoso Parameterized Cell SKILL Reference.

Introducing Fluid Pcells

Fluid Pcells provide an infrastructure to develop new Pcells that can be edited graphically (like shapes), and whose behavior in response to editing commands can be defined and customized using SKILL language.

Fluid Pcells offer to a Pcell developer complete control over the graphical editing functionality of a Pcell super master shape object.

You can draw the shapes in a fluid Pcell based on its fluid shape’s points or any additional Pcell parameters. You can select a fluid shape from the top-level in Virtuoso Layout Suite L. In addition, you can edit designated fluid shapes within a sub-master like any other top-level shape. A set of SKILL updater functions, associated with the fluid Pcell super master, are called in response to the top-level editing commands, such as Chop, Merge, Split, Reshape, Convert To Polygon, Abut, and Obstruct.

The following figure shows an example of a fluid Pcell:

Features of Fluid Pcells

Fluid Pcells have the following features:

You can Chop, Merge, and Convert To Polygon a fluid Pcell just like any other shape.
You can stretch, split, or reshape a fluid shape within a fluid Pcell instance sub-master:
- The edited shape is then passed to the correct SKILL updater function which in turn reflects the modified fluid shape edit back to the Pcell instance as a parameter value change.
- The editing is done from top-level. There is no need to use the Edit In Place or Descend command.
You can use the Tunnel command to connect through the fluid Pcell instances.
You can partially select an edge, centerline, or end point in a fluid Pcell.
The content of the fluid shape is specified in the hidden Pcell parameters.
Fluid Pcells are useful for guard rings, space filling capacitors, and filling structures.
cdsGuardRing or FGR is the first application of fluid Pcells.

For detailed information about fluid Pcells, refer to the Creating Fluid SKILL Pcells application note available on the Cadence Online Support website.

Introducing Fluid Guard Rings

Fluid guard rings are a type of fluid Pcells that can be used to enclose one or more objects, such as devices or device chains.

There are two types of FGRs, p-diffusion or n-diffusion. These are the new generation fluid Pcell devices that comprise the following parts:

Diffusion Layer: Encloses all other parts of the guard ring, except the implant or well layer when one is required.
Contact Layer: A set of sub-rectangles, which are vias. The layer specified as the Contact layer is entirely enclosed by the Metal and the Diffusion layers; the vias are centered within the Metal layer.
Metal Layer: Encloses the vias, which are centered within the Metal layer. The Metal layer is entirely enclosed by the Diffusion layer.
Implant/Well Layer: An optional layer. You can define multiple implant and/or well layers for a guard ring.

The following figure shows a cross-section of an FGR device.

Launching the Old or New Fluid Guard Rings GUI

When you open a design, by default, the new Fluid Guard Rings GUI is launched. In case, your design meets the following conditions, the old Fluid Guard Rings GUI is launched:

The technology file has a custom device.
Any of the Fluid Guard Ring forms have been customized.

You can refer to the following chapters for detailed procedural information:

Toolbar for Creating and Editing Fluid Guard Rings

From the Window – Toolbars menu, click the Guardring submenu. The following toolbar gets displayed:

This toolbar has the following icons that enable you to create and edit FGR instances:

Toolbar Command	Toolbar Icon	Alternative Access from Layout L Menu	Description
Create Guardring by Wrapping		Create – Fluid Guard Ring – Wrap tab	Creates an FGR instance in wrap mode around a selected device. For more information, refer to the Wrap Mode section in Chapter 4, “Creating Fluid Guard Rings (Old GUI).”
Create Guardring from Path		Create – Fluid Guard Ring – Path tab	Creates an FGR instance in path mode. For more information, refer to the Path Mode section in Chapter 4, “Creating Fluid Guard Rings (Old GUI).”
Create Guardring from Rectangle		Create – Fluid Guard Ring – Rect tab	Creates an FGR instance in rectangle mode. For more information, refer to the Rectangle Mode section in Chapter 4, “Creating Fluid Guard Rings (Old GUI).”
Create Polygon Contact Fill		Create – Fluid Guard Ring – Polygon tab	Creates an FGR instance in polygon mode. For more information, refer to the Polygon Mode section in Chapter 4, “Creating Fluid Guard Rings (Old GUI).”
Convert to Polygon		Edit – Fluid Pcell – Convert to Polygon	Converts the selected FGR instance into a polygon. For more information, refer to the Converting a Fluid Guard Ring to a Polygon section in Chapter 5, “Editing Fluid Guard Rings.”
Chop		Edit – Fluid Pcell – Chop	Removes a part of an FGR instance or cut it into pieces. For more information, refer to the Chopping a Fluid Guard Ring section in Chapter 5, “Editing Fluid Guard Rings.”
Merge		Edit – Fluid Pcell – Merge	Merges FGRs and create a new FGR device. For more information, refer to the Merging Fluid Guard Rings section in Chapter 5, “Editing Fluid Guard Rings.”
Tunnel		Edit – Fluid Pcell – Tunnel	Creates a tunnel through an FGR. For more information, refer to the Creating a Tunnel Through a Fluid Guard Ring section in Chapter 5, “Editing Fluid Guard Rings.”
Heal		Edit – Fluid Pcell – Heal	Removes one or more tunnels from an FGR. For more information, refer to the Healing a Fluid Guard Ring section in Chapter 5, “Editing Fluid Guard Rings.”
Reshape		Edit – Advanced – Reshape	Alters the fluid shape points and re-generates the underlying guard ring based on the new points. For more information, refer to the Reshaping a Fluid Guard Ring section in Chapter 5, “Editing Fluid Guard Rings.”
Split		Edit – Advanced – Split	Splits the fluid shape of a guard ring. For more information, refer to the Splitting a Fluid Guard Ring section in Chapter 5, “Editing Fluid Guard Rings.”
Clean Overlapping Contacts		Edit – Fluid Pcell – Clean Overlapping Contacts	Cleans all the overlapping contacts from an FGR, or just from an area on the canvas that you draw based on the option you select. For more information, refer to the Cleaning Overlapped Contacts from Fluid Guard Rings section in Chapter 5, “Editing Fluid Guard Rings.”

Fluid Guard Ring Context-Sensitive Menu

Right-click any FGR instance to display the context-sensitive Instance – Fluid Pcell menu that provides a quick access to the FGR editing commands.

This Instance – Fluid Pcell context-sensitive menu provides the following options:

Editing Command	Menu Icon	Alternative Access from Layout L Menu	Description
Convert to Polygon		Edit – Fluid Pcell – Convert to Polygon	Converts the selected FGR instance into a polygon.
Chop		Edit – Fluid Pcell – Chop	Removes a part of an FGR instance or cut it into pieces.
Merge		Edit – Fluid Pcell – Merge	Merges FGRs and create a new FGR device.
Tunnel		Edit – Fluid Pcell – Tunnel	Creates a tunnel through an FGR.
Heal		Edit – Fluid Pcell – Heal	Removes one or more tunnels from an FGR.

A few more options in the Instance context-sensitive menu are described in the table below:

Editing Command	Menu Icon	Alternative Access from Layout L Menu	Description
Copy		Edit – Copy	Enables you to place a copy the selected FGR instance to the same cellview or to another cellview. For more information, refer to the Copying Objects section in the Editing Objects chapter of the Virtuoso Layout Suite L User Guide.
Move		Edit – Move	Lets you move the selected FGR instance to another location in the current or another cellview. For more information, refer to the Moving Objects section in the Editing Objects chapter of the Virtuoso Layout Suite L User Guide.
Stretch		Edit – Stretch	Stretches the FGR instance by using the center line or the vertex of the path. For more information, refer to the Stretching a Fluid Guard Ring section in Editing Fluid Guard Rings
Delete		Edit – Delete	Deletes the selected FGR instance.
Freeze Pcell			Enables you to perform Pcell editing that is normally not supported by the Pcell parameters. This means you can avoid geometry changes in the FGR instances using this menu option. For more information, refer to the Freezing and Unfreezing Pcell Instances section in the Working With Hierarchical Designs chapter of the Virtuoso Layout Suite L User Guide. Clicking this menu option opens the Freeze Pcell Instance form. On this form, specify a new cell name with which the FGR instance should be saved as a non-fluid Pcell instance of a new master created on the disk. By default, the new cell is named in the format, `CDN_<`DEVICE_NAME`>_FROZEN_#`, where `#` denotes the unique number assigned to the frozen copy of the selected FGR instance. For example, `CDN_CONT_FROZEN_1`.s
(De)Select Under Cursor			Lists the FGR instances under the cursor. You can deselect or select the check box next to each FGR instance name. As a result, it gets ignored or considered for the edit actions you perform.
Properties			Displays the Edit Instance Properties form that has separate tabs for changing the editable Attribute, Connectivity, Parameter, Property, and ROD. For more information, refer to the Edit Instance Properties Form section in Fluid Guard Ring Form Descriptions

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Virtuoso Fluid Guard Ring User GuideProduct Version IC23.1, November 2023

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Introduction to Fluid Guard Rings