Sep 05 2006
About
Blog
This blog will document my life as an EE grad student. I think my life will be interesting, I hope I will make it sound interesting, and I hope you will enjoy reading my blog.
You may also find my other blog interesting: http://charts.vdsat.com
Picture
Credit: Myself. Shapes drawn in MS Paint. Shapes blurred with The GIMP.
The picture above is a transistor at the edge of saturation, a condition such that no inversion layer exists at the drain end of the channel and only at that point in the channel. According to simple device models, this phenomenon occurs when the drain to source voltage is equal to the gate to source voltage minus the threshold voltage. (Vds = Vgs - Vt) This particular Vds is known as Vdsat.
The pictured transistor is an NMOS transistor. The dark green regions are the n-type source and drain while the pink bottom is the p-substrate. The border between these n-type and p-type regions is blurred and it represents the depletion region of the pn junction. Note that the drain of the transistor has a larger blur area, or depletion region, which is caused by a high drain voltage that more negatively biases the pn junction.
The light green region is supposedly the inversion layer. In reality, the inversion layer does not have the triangular shape as portrayed in the picture, but rather only exists extremely close to the gate oxide which is represented by light gray in the picture. However, the inversion layer is often represented by a triangular shape to demonstrate the relative carrier concentration.
The red rectangle is the polysilicon gate, the blue shapes are metal 1 that contact the source and drain, and the dark gray stuff is field oxide.
If you wish to learn more about transistors, Wikipedia has a nice article on MOSFETs.
Contact
current_saturates@vdsat.com
When Vds is increased beyond Vdsat, the current (ideally) stops increasing. Therefore it can be said that the current saturates at Vdsat.
About the Categories
Blast from the Past
Some of the posts on my old blog are classics. I will repost some of them occasionally.
Blog Junk
Posts in this category point out things in the blog and keep track of the blog’s visibility.
Chicks
Loser Ph.D. student + chicks = strange things happen. Stay tuned.
Class
I hate my classes and I like to blog about how much I hate them. However, sometimes I have a bit too much fun in my classes and I blog about that too.
Research
As long as I keep my advisor happy, life is good. Learn the art of keeping an advisor happy by reading this category.
Stocks
If I can’t rationalize a trade on this blog, then it’s probably a stupid trade. Blogging about stocks will also help me figure out what trading strategies work and which ones don’t.