Layout Conventions for CIF and GDSII
MOSIS accepts layout in CIF or GDSII format. This document reviews conventions for these formats as they relate to procedures for submitting and checking files
CIF Conventions:
CIF layer names for each TECH-CODE are available from MOSIS by connecting to the MOSIS Technology Codes web page and selecting first a technology, and then a layer map file. Please note that CIF specifications permit some practices that the MOSIS Service disallows.
The following are MOSIS conventions for CIF:
- Polygons (P) must have at least three points. Other than this, arbitrary polygons are accepted.
- Wires (W) must have at least one point.
- Round Flashes (R) must have a non-zero diameter.
- Delete Definition (DD) is not allowed.
- Symbols may not be redefined.
- Lines are limited to 509 characters of text.
- User extensions are allowed but ignored.
- Wires extend beyond the two extreme endpoints by half the wire-width ("square extensions").
- The comment layer has a name ending with the letter "X", e.g., CX for SCMOS. All data on this layer is read by MOSIS but is totally ignored; however, any syntax error may cause CIF file rejections.
- Projects designed using MOSIS SCMOS rules can use an an optional layer (called XP in CIF) to define which pads are to be bonded and which are not. This layer is valid ONLY in MOSIS SCMOS rules. For more information, see the MOSIS SCMOS Rules (search for XP Layer).
- Any layer not contained in the TECH-CODE mapping (plus the comment and bonding pad layers) will cause the CIF file to be rejected.
- The file's "outer block" (external to all DS/DF cell parentheses, but before the file's final "E") should contain a single call (without rotation, mirroring or translation) to the project's top cell. Most CAD tools will include this provided you have specified the top cell.
- When a CIF symbol is scaled (DS #42 a / b;), where a and b are integers, the evaluation of the distance values in that symbol (distance * a / b) uses floating point arithmetic to produce a real value in centi-microns, not an integer value. Scaling is the only way to achieve CIF resolutions below one centi-micron (or 10 nanometers).
GDSII Conventions:
The MOSIS layer names for each TECH-CODE are available from MOSIS by
connecting
to the
MOSIS Technology Codes web page and selecting first a technology,
and then a layer map file.
The following are MOSIS conventions for GDS:
- Any layer not contained in the TECH-CODE mapping is considered a comment (non-fabrication) layer. However, we strongly urge that all extra layers be removed before submission.
- The entire layout for a project must reside in a single library file; the submission documentation must indicate the name of the top-level structure that is the project. Multiple projects submitted simultaneously may all reside in the same library and specify separate top-level structures. The inclusion of extraneous structures is strongly discouraged.
- NODE and BOX elements are read but ignored.
- ELFLAGS, PLEX, and ELKEY modifiers are read but ignored.
- TEXT of any width is treated as commentary and is not fabricated.
- Fixed-width PATHs (those whose specified width is less than zero) cannot be magnified during instantiation.
- All referenced structures must be defined in the file.
- For GDS layout files submitted on tape, the file formats should be fixed length 512- or 2048-byte records.
- Projects designed using MOSIS SCMOS rules can use an an optional layer (number 26 in GDSII) to define which pads are to be bonded and which are not. This layer is valid ONLY in MOSIS SCMOS rules. For more information, see the MOSIS SCMOS Rules (search for XP Layer).
- In GDS format, a mask layer is specified by a layer number between 0 and 255, and possibly by a datatype between 0 and 255. For MOSIS SCMOS designs (only), MOSIS reserves layer numbers from 21 to 62 for mask specifications and future extensions. Layers 1 to 20 can be used by designers for their own purposes.