Process nodes (28nm→7nm→5nm→3nm→2nm)

4.3.18 · Hardware › Semiconductor Fabrication

Process node KYA hota hai?

Number ka physical meaning KYUN khatam hua:

• 1970s–2000s mein, "node" ≈ sabse chhoti gate length ≈ half-pitch. Sab kuch saath shrink hota tha (Dennard scaling).
• 22nm ke aaspaas, flat (planar) transistor ko shrink karna kaam karna band ho gaya — leakage badh gayi. Manufacturers ne sirf shrink karne ki jagah transistor ka shape badla (FinFET, phir GAA). "nm" label marketing continuity ke liye girnaa jaari raha, bhaale gate length ~15–20nm par ruk gayi thi.

Hum shrink kyun karte hain — teen drivers (PPA)

1. Area / density — asli metric

Scratch se derivation: ek logic cell width $w$ aur height $h$ occupy karta hai, dono roughly pitch $p$ se set hote hain. Cell area $A=w\cdot h\propto p^2$. Har linear pitch ko $k$ se shrink karo: $A_{\text{new}}=k^2{A}_{\text{old}}$. Fixed die area mein cells ki ginti = (die area)/$A$, toh yeh $1/k^2$ se multiply ho jata hai. "0.7× linear shrink" per node se $1/0.7^2\approx 2\times$ density milti hai — yeh wahi classic doubling hai jo Moore's Law ke peeche hai.

2. Power — har switch mein dynamic energy

Derivation: capacitor $C$ ko voltage $V$ tak charge karne se charge $Q=CV$ move hota hai aur energy $E=\frac{1}{2}C{V}^2$ store hoti hai. Usi energy ko discharge mein dissipate kiya jaata hai, isliye ek pura switch cycle $C{V}^2$ dissipate karta hai. Yeh $f$ baar per second karo, jab $\alpha$ fraction of time node switch kar raha ho, toh $P_{\text{dyn}}=\alpha C{V}^{2}f$ milta hai.

KYUN nodes power kam karti hain: chhote transistors → chhota $C$; naye nodes $V$ bhi kam karte hain. Kyunki power $V^2$ par depend karti hai, $V$ ko 0.9 V se 0.7 V tak giraane se akela dynamic energy $(0.7/0.9{)}^2\approx 0.60$ ho jaati hai — 40% saving.

3. Leakage — woh wall jisne planar transistors ko kill kiya

Nodes ke paas transistor ka shape KAISE badla

KYUN zyada gate coverage help karta hai: gate ka kaam channel ko on/off switch karna hai. Zyada surrounding surface = zyada strong electric field control = transistor bahut chhota hone par bhi poori tarah OFF (low leakage) aur poori tarah ON (high current) hota hai.

Worked examples

Common mistakes (steel-manned)

Flashcards

Connections

• FinFET and GAA transistors
• Dennard scaling aur Moore's Law
• EUV Lithography
• Subthreshold leakage / MOSFET threshold voltage
• Dynamic vs static power
• Backside power delivery (2nm era)
• CMOS fabrication steps

Concept Map