CMOS Layers n nwell process pwell process Twintub
CMOS Layers n n-well process p-well process Twin-tub process
n-well process Gate NMOS PMOS NMOS FOX n+ n+ p+ p+ n-well p-substrate MOSFET Layers in an n-well process p+ p+
Layer Types n n n n p-substrate n-well n+ p+ Gate oxide Gate (polycilicon) Field Oxide q q Insulated glass Provide electrical isolation
Top view of the FET pattern NMOS n+ n+ PMOS NMOS n+ n+ p+ PMOS p+ n-well p+ p+
Metal Interconnect Layers n n Metal layers are electrically isolated from each other Electrical contact between adjacent conducting layers requires contact cuts and vias
Metal Interconnect Layers Ox 3 Via Metal 2 Active contact Ox 2 Metal 1 Ox 1 n+ n+ n+ p-substrate n+
Interconnect Layout Example Gate contact Metal 1 Metal 2 MOS Metal 1 Active contact
Designing MOS Arrays A B C y x
Parallel Connected MOS Patterning A x x B A X B X X y y
Alternate Layout Strategy x x A X X B A y y B
Basic Gate Design n Both the power supply and ground are routed using the Metal layer n+ and p+ regions are denoted using the same fill pattern. The only difference is the nwell Contacts are needed from Metal to n+ or p+
The CMOS NOT Gate Vp Contact Cut Vp X n-well X X X Gnd
Alternate Layout of NOT Gate Vp Vp Gnd X X
NAND 2 Layout Vp Vp X X X Gnd X
NOR 2 Layout Vp Vp X X Gnd X X X
NAND 2 -NOR 2 Comparison Vp X X X Gnd Vp X MOS Layout Wiring X Gnd X X X
General Layout Geometry Vp Shared drain/ source Individual Transistors Gnd Shared Gates
Graph Theory: Euler Path Vp x x Vertex Edge b c a Out y y c Vertex a b Gnd
Stick Diagram
Stick Diagrams • Cartoon of a layout. • Shows all components. • Does not show exact placement, transistor sizes, wire lengths, wire widths, boundaries, or any other form of compliance with layout or design rules. • Useful for interconnect visualization, preliminary layout compaction, power/ground routing, etc.
Stick Diagrams Metal poly ndiff pdiff Can also draw in shades of gray/line style.
Stick Diagrams Buried Contact Cut
5 V 5 v Dep Vout Enh Vin 0 V 0 V
Stick Diagram - Example I A OUT B NOR Gate
Stick Diagram - Example II Power A Out C B Ground
Points to Ponder • be creative with layouts • sketch designs first • minimize junctions but avoid long poly runs • have a floor plan for input, output, power and ground locations
The End
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