## June 09, 2014

### Feature Size of Transistors

The feature size of any semiconductor technology is defined as the minimum length of the MOS transistor channel between the drain and the source. The technology node has been scaling year by year. From early 2000s it has shrunk from 180nm to 22nm designs today (2014).

You would have probably noticed that the technology scaling has followed:

180nm -->> 130nm -->> 90nm -->> 65nm -->> 40nm -->> 28nm --> 22nm...

Ever wondered who decides these numbers? Are these arbitrary or there's some inherent logic behind these numbers? Let's see.

In early 1970s, Gordon Moore of Intel Corp. predicted that the number of transistor on a an integrated circuit would double itself in approximately 18-24 months. This prediction has proven to be accurate as scaling of technology continues unabated even after 40 years! Well, it's mainly because Moore's law has set out a challenge and a roadmap for designers to keep the scaling going!

You might ask yourself, why scaling? Here's why:
• If double number of transistors can be incorporated on the same area, it means we get double (roughly) functionality for the same cost!
• Alternatively, with scaling of technology, the same functionality will be available at roughly half the cost!
• Moreover, smaller the channel length, faster would be the transient response of the transistors which would translate into better performance!

The goal of every design company now is to double the number of transistors on their integrated circuits with each technology. As you would notice, the numbers above from 180nm to 130nm to 90nm scale down by roughly a factor of 0.7. What's so special about 0.7?

If the feature size of the transistor is scaled by 0.7, the area would be scaled by a factor of 0.72=0.49 =~ 0.5. That means if we scale our feature sizes by a factor of roughly 0.7, we would be able to pack twice the number of transistors on the same area as the previous technology!

1. Thanks. I asked this question to many people but no body answered it clearly. My long standing doubt has been cleared.

2. Really useful! Thanks!

3. Hi Naman,

With one side of explanation its true. But according to my understanding its relative to the lithography techniques. As the number of lens used to focus the light source 193nm and its respective NA (numerical aperture) this dimensions are set. The Lenses of Lithography machine can't be manufactured with NA as required, but based on NA of these lenses the node is decided.

I visited after a longer time and your blog is enriched with much knowledge. Thanks for the same.

1. thanks a lot karan

can you give much information regarding how to decide a node based on NA of lense

thank you

4. Thanks a lot of for giving this valuable information ! it is realy very helpful

5. how do u say that the area is scaled by that factor ???

6. I dont know why but this is the best post on your blog! Unique and rare topic.

7. 180*0.7=126 ==>aprox 130
130*0.7=91 ==>aprox 90
90*0.7= 63 ==>aprox 65 etc.....
hence can say scaled by factor of 0.7

1. Thanks, Amish. I think I should have probably explained this part more explicitly. Thanks for doing so, and helping many readers grasp the logic better.

-Naman

8. Ty all.. Especially Naman for this posting, Mihika for his Question which was raised same for me while reading post and Amish for clearing the doubt.

I'm really thankful to Naman for such a excellent knowledge sharing blogspot.

1. Hello, Unknown! :P
Thanks you much so much. I'm glad people find my posts useful. Really gives me a great feeling. :)

Thanks,
Naman

9. thank you for the explanation. I'm dying looking for the answer about what feature size is on the internet, then i came across this helpful blog. thank you Naman.

1. Hi Megurine,