Wednesday, 28 February 2007

David M. Cardamone, from the Department of Physics, Simon Fraser University, and Charles A. Stafford and Sumit Mazumdar Department of Physics, from the Department of Optical Sciences, University of Arizona talk in the SPIE Newsroom about a novel kind of transistor. They claim that their device is not based on field-effect, but on quantum interference. They show some results obtained using a benzene molecule as device, and, frankly, the results are not bad at all. However, I have my doubts that this can be practical in a medium range, because many problems (mainly the interconnections, from my point of view) are left open. Moreover, I'd like to see a digital gate made using these devices. Or, better, an analog amplifier. That could be a real test.

Tuesday, 27 February 2007

S-Parameters

I've been sent a white paper from RF-globalnet on S-parameter extraction. For those of you who do not know what a S-parameter is, I shall recommend to read it. For the rest, it can be interesting reading another point of view. The paper is from Richard Wang, Applications Engineering Manager, RF Micro Devices, Inc., and Ming-Hsiang Cho, Ph.D. Candidate, National Chiao-Tung University (Taiwan). You can download it from this link (it's free!).

Hint: S-parameters are used in RF circuits...

Monday, 26 February 2007

Thin-film design guidelines

Did you ever wondered how thin-film transistors are made or what are the design rules you should use? I'm asking because, in order to get a proper model or to explain it to a designer (the final user of our models, let me remind you), you should be aware of all these things and how they affect to your model, because they are important. Diablo Industries, Inc. now has made available on-line a set of design rules and material description that is very interesting to read, even it you only perform a quick lecture.

Friday, 23 February 2007

Reliability

Another not-quite-in-topic entry. Today I was looking for information on a kind of defects (GOS) to get some information on how people do model them. I know this is not quite compact modeling, but you would be surprised on how much related they are. In fact, a GOS defect is usually modeled using a parasitic transistor. However, this is only an approximation, and a true physical model is still to come. I won't be the one developing it, though. I was only looking for some model that I could use with my transistor models. And, then, I found a gem. I've found a review paper (more than 20 pages!) about reliability. I think I'm going to use it as a textbook. You can access it here. The paper is:

Electronic circuit reliability modeling

Pages 1957-1979
J.B. Bernstein, M. Gurfinkel, X. Li, J. Walters, Y. Shapira and M. Talmor

Thursday, 22 February 2007

European Microwave Week 2007 (EMW 2007) just after Oktoberfest!

This year the European Microwave Week (EMW) will take place in Munich, from October 8 to 12,...just after Oktoberfest!

The European Microwave Week is the main Microwave symposium in Europe. Besides, the European Microwave Exhibition constitutes the largest trade show on RF and microwaves in Europe.

EMW 2007 is composed of four conferences: the European Microwave Conference (EuMC), the European Conference on Wireless Technology (ECWT), the European Radar Conference (EuRAD), and the European Microwave Integrated Circuits (EuMIC).

EuMIC 2007 will be a very interesting conference and forum to present results on high-frequency compact modelling of semiconductor devices. Many of the indicated EuMIC topics can be related to compact modelling: Physics Based Device Modelling and Simulation, CAD Oriented Device Modelling, Noise Modelling, Linear and Non-linear CAD Techniques for Devices, Circuits & Systems (incl. Behavioural Modelling) (common Topic with EuMC), Linear CAD Techniques, Non-Linear CAD Techniques, Mixed-Signal Modelling.

Important: the deadline to submit summaries to EuMIC 2007 is February 25 2007!

I suggest high frequency compact model researchers to come one week earlier to Munich and start the compact modelling discussions while enjoying at the same time the Oktoberfest! For sure nice ideas can come then...

Monday, 19 February 2007

Monte Carlo or Montecarlo?

I've had some nomenclature problems with this. To solve them, I've recurred to the easiest solution: I've 'googled' for it...

I've found a very interesting page at riskglossary. It seems that the first time it was cited explicitely was in this paper:
Metropolis
, Nicholas and Stanislaw Ulam (1949). The Monte Carlo method, Journal of the American Statistical Association, 44 (247), 335-341

So, following the criteria that the first one to use it has the right to name it, I'll use "Monte Carlo" from now on.

Friday, 16 February 2007

And more papers

It seems that this is my week to read papers. Well, it's a good exercise... I strongly recommend it!

Another quite interesting paper: Analytical Charge and Capacitance Models of Undoped Cylindrical Surrounding-Gate MOSFETs. This time, it is from Oana Moldovan et al. This is a quite good paper, that continues their work on DG MOSFETs.

Another one from the same journal: Modeling of Surrounding Gate MOSFETs With Bulk Trap States. It is also interesting to read. Anyway, the approach is different to the previous one, and it is good to keep an open mind.

And the last one from this journal: Surface-Potential Solution for Generic Undoped MOSFETs With Two Gates. The topic has been discussed before, and I still think that the approach by Francisco and Adelmo is easier to understand. However, this is only an opinion.

Thursday, 15 February 2007

Miscellanea

More of my personal obsession: plastic electronics. This week, in the 3GSM Conference, in Barcelona, Polymer Vision has presented (some people would say 'again') the Readius, which is a mobile phone with an integrated roll-up display. It seems that this time they are serious, thanks to Plastic Logic....

Another curious thing: for all those of you that love playing sudoku, you now may have a hard competitor: a quantum computer. I don't know how actually serious this is. However, I think that it may be indicative that people is starting to crave for quantum computers. The first step to be able to produce them should be letting people (engineers) how they work. So we need compact models for that. Anyway, I think that we're still a long way from the point where computers designers can actually use this.

Wednesday, 14 February 2007

More papers

Another paper: Arbitrary Density of States in an Organic Thin-Film Field-Effect Transistor Model and Application to Pentacene Devices. After reading it, I've been left with the feeling that they have done a lot of very good work, but that the results are somehow quite similar to those that one can obtain with the old good RPI model. Probably it is my fault, but it seems too much work to end up with a gds that is not accurate, and with a fitting comparable to RPI. However, I repeat, the work is quite good and the problems I mention are mainly due to problems with the parameter extraction.

Tuesday, 13 February 2007

More Organic Circuits

I'm sorry, but this is quite out of topic. One of my personal obsessions are organic circuits, and this month the IEEE Journal of Solid-State Circuits publishes two very promising papers:
A 13.56-MHz RFID System Based on Organic Transponders
and the other one:
An Organic FET SRAM With Back Gate to Increase Static Noise Margin and Its Application to Braille Sheet Display
This means that it is more and more important having good models for plastic electronics. And this does not mean that we should be able to predict (more or less) the static curves, but also the gm and gds and, more and more important, the capacitances. This must be done if we are to implement full systems-on-display, as it seems to be the trend.

Monday, 12 February 2007

Some papers

I've been reading some new papers, and I've found some worth noticing:

The first one (Statistics of Grain Boundaries in Polysilicon),from H. Watanabe, is a quite interesting paper, discussing the application of statistics to a MOSFET model. I believe that the idea is applicable not only to bulk MOS, like he does, but it is somehow the path to follow for all the models devoted to devices where a signifiant parameter dispersion is expected. In fact, I think that this is a better way to face the problem than the one proposed by the EKV model, where they proposed a model for the deviations of the parameters.

And tomorrow, more...

Thursday, 8 February 2007

SISPAD 2007

The 2007 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) will be held this year in Vienna (Sept 25-27 2007), organized by TU-Wien (Technische Universität Wien). SISPAD is considered one of the top conference on device and process simulation.

You can find all the information in:

www.sispad.org

The topics of SISPAD include all kinds of modeling techniques.

I want to remark that, according to the CFP, one of the topics is "Compact device modeling for circuit simulation".

For compact model developers, SISPAD can be a very attractive forum to present new developments and results, and to interact with researchers working in numerical and predictive process and device simulation.

Besides, there are two interesting companion workshops:
1) Workshop on Electromigration Reliability (Sept 24)
2) Workshop on Organic Electronics (Sept 28)

Of course, it is also a good opportunity to enjoy the wonderful city of Vienna!

How many angels can dance on top of a pin?

Two weeks ago I was in Rome, in the ITC. As you can guess from the title, I had a quite interesting, but byzantine, discussion. I was presenting a paper (with B. Iniguez, M. Shur and some other people) about a universal procedure to model TFT. The core idea of the procedure is using a compact model to model an intrinsic device, and then model all the rest of the parasitic elements as lumped elements. The other guy was telling me that this is not physical. Obviously, I don't agree. Moreover, I think that using lumped elements is near as physical as it can get.
My point is: it is OK trying to put everything inside your equations. However, this usually leads to a loss of insight on what is happening in the field-effect device. I think it is better to model the device with as much accuracy as possible and without losing the insight, and then add as many elements as necessary as lumped elements. Thus, the resulting model will have a quite straight physical representation, easy to grasp by intuition, and will not lose precision due to any approximation. Moreover, the simulator will handle quite effectively the model, because it has been programed to do so. Probably, it will even behave better, because the equations will be easier to handle.
Anyway, it is only my opinion, and there are some argements in the other side that I'll discuss another day.

Tuesday, 6 February 2007

RF Simulators

I've seen that Agilent Technologies announces a breakthrough in high-frequency SPICE simulation technology for high-speed digital board design. It seems that they have just realized that simulation in the frequency domain is faster than that in time domain. I don't grasp the novelty of the news, because they have been doing so for a long time. However, the point I'd like to make is that a good model for RF design not only has to be accurate, etc.... but it also has to take into account the possibility of being used in a simulator oriented to frequency.
It seems then that in a good model to be used in an RF environment, we should be careful enough as to explicitly state the equations for the S parameters, and not only for the capacitances. Thus, we should present both versions of the model: one with the capacitances, and another one with the S-parameters. It would be then a question of choosing the most appropriate set of equations to simulate.

Monday, 5 February 2007

Back to work

Here I am, back to real world after two weeks of conferences. I must confess that I'm happy to be at home again. Well, to the point. The last one of the conferences was a bit disappointing, because it was mainly dedicated to solar cells in the oral sessions. This is so because it was organized by the Solar Energy Institute. The poster sessions were more interesting, with many different topics, though the only ones dedicated to compact modeling were some posters from B. Iñiguez and Toni Lazaro, dedicated mainly to double gate and RF modeling. Quite interesting, even if they didn't win the best paper award (by the way, only five of the six awards went to people related to the organizers).
Another poster I was happy to see was one about pi-gate FETs, where they were modeling the transistor using some device simulator. The funny thing was to see the double threshold effect, with some explanantions about it.