I gave a presentation last year at the MOS-AK workshop in San Francisco. The people attending this workshop are all interested in simulation models for semiconductors. One of the comments made during the workshop, was that circuit designers blame the models when their circuits do not work right. In most cases what is meant as model, is really the model parameters that are created by a foundry for a specific simulation model.
The real models go by names such as BSIM, PSP, Gummel-Poon, HICUM. These models are the sets of equations that mimic the electrical behavior of a device. The model is of itself useless without a set of parameters that are process and geometry unique. These parameters are created (fitted) from test circuits the foundry creates. A circuit simulator implements the particular models equations, this coupled with the model parameters, and a netlist describing the desired circuit will give a simulation of how the circuit should work.
A great deal of work goes into the model. This work is reviewed by many people. While mistakes can occur in the model, because of their wide adoption and peer review they tend not to be buggy. The model parameters on the other hand do not experience the same peer review process. The methods of extracting data to fit to the model may vary greatly, how well the data is fitted to the model is variable. Some foundries have very accurate model parameters, some not so accurate. When circuit designers talk of model problems most often they mean model parameter problems.
Model versus Model, really is Model versus Parameters.
I went to the Intel International Science and Engineering Fair (ISEF) on Thursday. This will be the last time it will be in San Jose for many years. Thirty Five years ago I competed in the ISEF when it was held in Oklahoma City. I won first place in Chemistry back then. There were probably 400 more entries than when I competed, and there was certainly many more countries sending students than 35 years ago, when international meant 4 other countries besides the US. When I competed I got to meet Dr. Glenn Seaborg; noble prize winner, and co-discoverer of Plutonium and nine other trans-uranium elements (the element Seaborgium is named after him).
2010 Intel Intenational Science and Engineering Fair, San Jose Ca
1975 International Science and Engineering Fair - Oklahoma City, Awards Ceremony
1975 International Science and Engineering Fair - Oklahoma City, David Schwan (left) and Dr. Glenn Seaborg (right)
Finally finished reading this book. This book describes the history of Avante-Garde music in San Francisco. The cast of characters include Ramon Sender, Pauline Oliveros, Morton Subotnick, Terry Riley, Lucianio Berio, John Cage, Stewart Brand (of the “Whole Earth Catalog” and the Long Now Foundation), Don Buchla (Synthesizer pioneer), Ken Kesey (and the Trip Festivals), Phil Lesh and the Grateful Dead. Most of these people started their careers in the Bay Area, and many later went on to jobs on the east coast. This book describes the intersection of the Avante-Garde music scene and the “West Coast Sound” of the psychedelic bands. The whole notion of light shows during a concert was created by these people. Definitelya book worth reading.
As feature size is reduced in chip design life for digital design gets way more complicated. We are building 45 and 32nm chips using 193nm light sources. This is like using a 4 inch wide brush to paint 1 inch lines, something doable, but inherently limiting. Double patterning is beginning to be used to achieve the small feature sizes, by using two large feature masks, and printing each separately, the intention is to create the smaller feature size through two large steps[1]. By having two patterning steps, there are two alignment steps. This means that there will be misalignment, and this will be part of the inherent variation of the transistor. While this may be ok for digital design, is analog design going to be feasible? My feeling is this will make analog design so hard, so low performance, that it will force the push to using deep UV, from 193nm.
[1] – http://en.wikipedia.org/wiki/Double_patterning
On this weeks Science Magazine Podcast they reported a study that collected saliva samples from 120 people, with 12 regions of the world and 10 people in each region. Out of these samples they found 64 bacteria never before seen. Given the initial small sample size, this is an astounding discovery. How many more unique bacteria are in the worlds human population.