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.

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.

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...

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.

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.

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.