Design rules for non-Manhattan shapes
Résumé
An approach to MEMS Computer Aided Design tools has been to make use of Integrated Circuits CAD suites with specific enhancements for MEMS designs. Extending the IC Design Rule Checkers to non-Manhattan shapes is one of these needed enhancements. IF anecdotally used in IC designs, non-manhattan shapes are intensively used in todays state of the art MEMS products. High performance gyroscopes and yaw rate sensors made in surface micromachining processes feature spiral springs and torsional combdrives made of toroidal fingers. Applying classical DRCs to these layouts generate thousands of false errors. The errors are false because they do not affect the manufacturability of the device. But because of their number, they prevent the designers from detecting real errors in their layout. Most false errors are generated by rounding floating point vertices' coordinates, translating different data types and snapping points to a grid. This paper presents a new methodology to eliminate false errors generated by the DRC of non-manhattan shapes. This methodology includes adding a tolerance factor to Microsystem design rules with respect to the geometric properties of non-manhattan shapes and the manufacturing grid parameters, closely controlling the vertices coordinates when automatically generating the non manhattan shapes and controlling the snapping on the grid. This methodology has been implemented in MEMSCAP Microsystem engineering kits and has been validated for three foundry design rules: BOSCH, SensoNor, and AMS