News and Views: Nature Nanotechnology

A. M. Ionescu

Electronic devices: Nanowire transistors made easy

Nature Nanotechnology, vol. 5, iss. 3, pp. 178 – 179, March 2010

Figure (a) A junction FET is turned on in the (strong) inversion condition, when a channel of minority carriers is formed just under the gate, and junction barriers to their flow are reduced. The off state of the junction FET corresponds to high junction barriers and the suppression of the inversion channel. The horizontal red line shows the bottom of the depletion region, and the slanted red lines indicate the limits of the depletion region controlled by the gate. (b) In contrast, the on state of a junctionless FET is obtained in 'flat band' conditions, with majority carriers travelling through a highly doped film. The device (which requires a thin-film silicon-on-insulator substrate) turns off when the gate-controlled depletion extends over the whole film. Both devices operate with the source grounded and a positive potential applied to the drain. Vt denotes the threshold voltage (positive for the n-type devices). Similar descriptions apply to the operation of complementary p-type FETs. Blue and red colours depict electron and hole doping respectively, with a darker colour indicating heavier doping. The white regions correspond to the depletion regions, and the green colour represents the gate oxide.

References

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An interesting (educative?) post in EDN by Paul Rako :

Op-amp Spice macro-models article from Intersil

June 16, 2010

Former EDN analog editor Bill Schweber has published a good article from Tamara Schmitz and Jian Wong about developing Spice macromodels for voltage-feedback op-amps. Part 1 (pdf), and part 2 (pdf). All the youngsters like to use Spice for op-amp circuit design but I am more like Bob Pease and Jim Williams, you have to build the circuit to know what is going on. I will never forget being perfectly happy with a Spice run, until I built the circuit and realized that the quad op amp was running way too hot. I did not notice the power consumption of each of the amps was about ¼ W. That was a newbee mistake, sure, but even if Spice does not lie, it is the product of digital and software minds, so rather than flashing a big red sign that warns you that you are going to burn up the quad op amp, they just require you to define a power variable and display it and then print the result in the same tiny test and the blizzard of other information. Then software people smile and fold their arms and tell us everything is our fault, since the information was right there if only we asked for it.  The one thing about analog is that is has a sense of importance. That’s why steering wheels and shift levers are big and prominent and radio treble controls are tiny little buttons. If software people designed cars everything would be a tiny little icon and the crash warnings would be in 10-point text.
So anyway, Spice does not necessarily lie like Bob Pease says, but I guarantee you that if you give it poor models it will give you the wrong answer. This is the big hassle with op amp models. Some of them, like the old National Semi Comlinear models (pdf) published by Mike Steffes before he left for Burr Brown and now Intersil were essentially transistor-level models. An IC designer could infer the design of the part from them. Mike told me that he knew that, but it was just so important to give an accurate model that he felt he had to release those great models. If someone wanted to copy the circuits, well, they had a lot more work to do-anyone can de-cap an op amp and reverse engineer it in a day. That still does not give you the process or the testing regime or the design secrets and tricks.
That is why this Intersil article is so important. Anything that helps you make good models is important in a world where kid engineers trust a computer rather than a breadboard. The article give some history of op amp models and that will tip you off as to what you can expect from a simulation. If the model you use does not model for 1/f noise, and most vendor models do not, you cannot get a meaningful simulation of low-frequency noise performance of the circuit. If the model does include flat-band noise and you are designing and ac-coupled video circuit, well that is fine for your needs. I have yet to see a Spice op-amp model that accurately tells you what happens if you bang the output into the rails and saturate the transistors. I will ask Mike Steffes if his old Comlinear models would do that, and leave a comment.

Modeling The Bipolar Transistor (Book)

Modeling The Bipolar Transistor (*)
By Ian Getreu

(2009; Paperback, 286 pages)

The book describes the bipolar transistor model and parameter measurement techniques for the SPICE circuit simulator. Originally published by Tektronix in 1974, this is a slightly modified revision republished in 2009 by the original author.

Read the review by Colin McAndrew

(*) There is a $4.00 discount if people order it by June 30 - use the coupon code: SUMMERREAD305.

IEEE Awards 2010

Takayasu Sakurai, has got the 2010 IEEE Donald O. Pederson Award in Solid-State Circuits, for pioneering contributions to the design and modeling of high-speed and low-power CMOS logic circuits.

Note that this is not compact modeling, but his alpha power law model has had a big impact!


Gennady Gildenblat has got promoted to IEEE Fellow for his "contributions to modeling of metal-oxide semiconductor field effect transistors".

Yasuhisa Omura has got promoted to IEEE Fellow for the contributions made to the SOI technology, analysis and modelling.

Thomas Piotr Skotnicki also got the promotion to IEEE Fellow for contributing to the development of MOS models.



Congratulations to all of them!

Physicists from Mainz University develop a quantum interface between light and atoms

Ultra-thin glass fiber enables the controlled coupling of light and matter / publication in Physical Review Letters:

E. Vetsch, D. Reitz, G. Sagué, R. Schmidt, S. T. Dawkins, and A. Rauschenbeutel
Optical interface created by laser-cooled atoms trapped in the evanescent field surround-ing an optical nanofiber
Physical Review Letters, May 21, 2010
DOI: 10.1103/PhysRevLett.104.203603