Layout Design Rules Questions and Answers

Q: Most of the VLSI foundries specify Design Rule files. These design rules however do not specify :

Design rules do not specify layer colours.Design rules are the geometric constraints a foundry sets so that a layout can be manufactured reliably: minimum line widths, minimum separations between patterns on the same or different layers, and minimum extensions and overlaps (for example, how far polysilicon must extend beyond the active region). Mead and Conway's lambda-based rules express them in multiples of a unit length.Colours are merely a convention of layout editors and stick diagrams for telling layers apart on screen; they have no effect on fabrication and are not part of the rules.

Q: As per lambda design rules for wires minimum width of metal 2 is ............ and separation between two metal 2 layers .....................

Metal 2 has a minimum width of 4 lambda and a minimum separation of 4 lambda.In the lambda-based wire rules given in Pucknell and Eshraghian's Basic VLSI Design, first-layer metal is 3λ wide with 3λ spacing, while second-layer metal is given 4λ for both width and separation. Metal 2 lies over a rougher surface, after more layers have been deposited and etched, so its rules are relaxed to keep the lines continuous and free of shorts.Option B repeats the metal 1 figures. Options C and D mix the two, so neither matches the rule for metal 2.

Q: Which gives scalable design rules ?

Scalable design rules are given by lambda rules.Mead and Conway's lambda-based rules express every layout dimension, such as minimum widths, spacings and overlaps, as a multiple of a single unit \(\lambda\), roughly half the minimum feature size. When the process shrinks, only the value of \(\lambda\) changes, and the same layout can be scaled to the new technology.Micron rules give absolute dimensions in micrometres for one particular process, so they are more precise but not scalable. 'Layer rules' and 'thickness rules' are not names of a scalable rule system.

Most of the VLSI foundries specify Design Rule files. These design rules however do not specify :

A.Line widths
B.Interpattern separations
C.Layer colours
D.Pattern extensions

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: C

Design rules do not specify layer colours.

Design rules are the geometric constraints a foundry sets so that a layout can be manufactured reliably: minimum line widths, minimum separations between patterns on the same or different layers, and minimum extensions and overlaps (for example, how far polysilicon must extend beyond the active region). Mead and Conway's lambda-based rules express them in multiples of a unit length.

Colours are merely a convention of layout editors and stick diagrams for telling layers apart on screen; they have no effect on fabrication and are not part of the rules.

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The minimum width of n-diffusion and p-diffusion layer should be :

A.3λ
B.2λ
C.λ
D.4λ

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

The minimum width of the n-diffusion and p-diffusion layers is 2λ.

In the Mead-Conway lambda-based design rules, as taught in Pucknell and Eshraghian's Basic VLSI Design, every dimension is a multiple of \(\lambda\), half the minimum feature size. The rules give diffusion (n and p) a minimum width of 2λ, polysilicon a minimum width of 2λ, and first-layer metal a minimum width of 3λ.

So 3λ is the metal 1 rule, not the diffusion rule, 4λ is the rule for second-layer metal, and a single λ is below the minimum width allowed for any layer.

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As per lambda design rules for wires minimum width of metal 2 is ............ and separation between two metal 2 layers .....................

A.4 lambda, 4 lambda
B.3 lambda, 3 lambda
C.4 lambda, 3 lambda
D.3 lambda, 4 lambda

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

Metal 2 has a minimum width of 4 lambda and a minimum separation of 4 lambda.

In the lambda-based wire rules given in Pucknell and Eshraghian's Basic VLSI Design, first-layer metal is 3λ wide with 3λ spacing, while second-layer metal is given 4λ for both width and separation. Metal 2 lies over a rougher surface, after more layers have been deposited and etched, so its rules are relaxed to keep the lines continuous and free of shorts.

Option B repeats the metal 1 figures. Options C and D mix the two, so neither matches the rule for metal 2.

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Which gives scalable design rules ?

A.Lambda rules
B.Micron rules
C.Layer rules
D.Thickness rules

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: A

Scalable design rules are given by lambda rules.

Mead and Conway's lambda-based rules express every layout dimension, such as minimum widths, spacings and overlaps, as a multiple of a single unit \(\lambda\), roughly half the minimum feature size. When the process shrinks, only the value of \(\lambda\) changes, and the same layout can be scaled to the new technology.

Micron rules give absolute dimensions in micrometres for one particular process, so they are more precise but not scalable. 'Layer rules' and 'thickness rules' are not names of a scalable rule system.

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Layout Design Rules Questions and Answers

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