The document explains stick diagrams used in VLSI design, emphasizing their role in visually representing circuit layout and component relationships through color coding. It outlines the conventions and rules governing stick diagrams, such as representing electrical contacts and transistors, as well as providing design rules critical for ensuring functional circuit layouts. Additionally, it discusses the limitations of stick diagrams and the necessity of adhering to design guidelines for optimal yield and circuit reliability.

1. Basics of Stick Diagrams

2. • VLSI design aims to translate circuit concepts
onto silicon.
• Stick diagrams are a means of capturing
topography and layer information using simple
diagrams.
• Stick diagrams convey layer information
through color
encoding).
codes (or monochrome
• Acts as an interface between symbolic circuit
and the actual layout.
Stick Diagrams

3. • Does show all components/vias.
– Via is used to connect higher level metals from metal connection
• It shows relative placement of components.
• Goes one step closer to the layout
• Helps plan the layout and routing
A stick diagram is a cartoon of a layout.
Stick Diagrams

4. • Does not show
– Exact placement of components
– Transistor sizes
– Wire lengths, wire widths, tub boundaries
– Any other low level details such as
parasitics
Stick Diagrams

5. Stick Diagram Colour Code
P diffusion Yellow/Brown
N diffusion Green
Polysilicon Red
Contacts Black
Metal1 Blue
Metal2 Magenta/Purple
Metal3 Cyan/L.Blue

6. Metal 1
poly
ndiff
pdiff
Can also draw
in shades of
gray/line style.
Stick Diagrams – Notations
Buried Contact
Contact Cut

7. Component Colour Use
metal 1 Power and signal wires
metal 2 Power wires
polysilicon Signal wires and transistor
gates
n-diffusion Signal wires,source and drain of
transistors
p-diffusion Signal wires,source and drain of
transistors
contact Signal connection
via Connection between metals

8. NMOS transistor

9. PMOS transistor

10. Stick Diagrams – Some Rules
Rule 1:
When two or more ‘sticks’ of the same type cross or touch
each other that represents electrical contact.

11. Stick Diagrams – Some Rules
Rule 2:
When two or more sticksof different type cross or touch each
other there is no electrical contact.
(If electrical contact is needed we have to show the connection
explicitly)

12. Stick Diagrams – Some Rules
Rule 3:
When a poly crosses diffusion it represents a transistor.
Note: If a contact is shown then it is not a transistor.

13. Stick Diagrams – Some Rules
Rule 4:
In CMOS a demarcation line is drawn to avoid touching of p-diff
with n-diff. All PMOS must lie on one side of the line and all
NMOS will have to be on the other side.

14. INVERTER- STICK DIAGRAM

15. Twohorizontal wires are used for connection with VSS and
VDD. This is done in metal2, but metal1can be use instead.
Step 1

16. Step 2
Two vertical wires (pdiff and ndiff) are used to represent the
p-transistor (yellow) and n-transistor (green).

17. Step 3
The gates of the transistors are joined with a
polysilicon wire, and connected to the input.

18. Step 4
. The drains of two transistor are then connected with
metal1 and joined to the output. There cannot be direct
connection from n-transistor to p-transistors.

19. Step 5
The sources of the transistors are next connectedto
VSS and VDD with metal1. Notice that vias are used, not
contacts

20. metal1 is used instead of metal2 to connectVSS
and VDD supply
Alternative inverter

21. NAND Gate

22. NOR Gate

23. Examples of Stick Diagrams
Gnd
VDD
x x
X
X
X
X
VDD
x x
Gnd

24. Examples of Stick Diagrams

25. Examples of Stick Diagrams
Vout
Vdd =5V
Vin
* Note the depletion mode device

26. Examples of Stick Diagrams

31. Design Rules
• The limitations of the patterning process give rise to a set of mask design
guidelines called design rules
• Design rules are a set of guidelines that specify the minimum dimensions and
spacings allowed in a layout drawing
• Violating a design rule might result in a non-functional circuit or in a highly
reduced yield
The design rules can be expressed as:
»A list of minimum feature sizes and spacings for all the masks required in a
given process
»Based on single parameter λ that characterize the linear feature (e.g. the
minimum grid dimension). λ base rules allow simple scaling

32. λ based design rules

33. λ based design rules

34. λ based design rules

35. λ based design rules

37. Contact Cuts

49. Double Metal MOS Process

50. Yield

51. General Observations of design values
1. Every dimensions must be rounded up to whole lambda
2. The goal of any set of design rules should be to optimized yield while keeping
the geometry as small as possible without compromising the reliability of the
finished circuit.
3. The 3λ metal rules
4. Metal to metal separation is too large.
5. Lambda based rules try “to be all things to all people” they do suffer from
least common denominator effects and from the upward rounding of all
process line dimension parameters into integrer values of lambda.

52. Design Rules Reality

55. Micron Based Rules