A Matter of Scale: Well Proximity Effect
In my post a couple of weeks back on A Matter of Scale: Electromigration, I mentioned that once silicon features shrunk below 100nm into the world of nanotechnology, previously negligible physical phenomena now play a big role. One of those annoying phenomena is the well proximity effect (WPE). To explain how WPE affects integrated circuit designers, we have to first talk just a little bit on how PMOS transistors are created. The figure above shows the standard textbook cross-section of a silicon wafer with an NMOS and PMOS transistor side-by-side. The silicon wafer, also called the substrate, is a crystalline structure where each silicon atom shares four covalent bonds with neighbouring silicon atoms. However, it is standard in the IC industry to lightly dope the silicon wafer substrate with boron. If you remember your high school chemistry, silicon has four valence electrons and boron has only three. When boron is…
Bad Reflections
Two weeks ago, the authors at Engineer Blogs opined about their favourite engineering classes. This week, it’s all about their worst. For me, there are many classes that come to mind where the professor would have been well-advised to attend a remedial teaching course. There was that 2nd year circuits course, where the frequency response of a circuit network was represented using the Laplace s-domain. The problem was that nobody in the class knew had ever seen the s-domain and the professor insisted on not teaching the math to us. A fifth of our class got weeded out by this course. Then there was the 3rd year statistics class, where I’m pretty sure I failed the final exam, but still ended up with 99% on my transcript due to the bell curve. Asking students to write the proof to an obscure, never-taught theorem on the final and making it worth…
A Matter of Scale: Electromigration
When I first arrived at FluxCorp, we were designing integrated circuits at the 130 nm node. The ‘130 nm’ refers to the smallest feature on the chip, typically the gate terminal of a MOS transistor, which is just above the 100 nm cusp of what is typically considered nanotechnology. Since then, we’ve moved on to designs in 90 nm, 65 nm, 45 nm, and now 28 nm as the struggle to keep pace with Moore’s prediction soldiers on. The challenges in scaling transistors isn’t just in fabrication and methods of lithography used to draw such tiny wires. Now firmly planted in the nano-world, circuit effects that used to be considered negligible are starting to rear their ugly head. One of those effects is electromigration, or EM. The concept behind EM is quite simple. Too much electrical current through a wire causes high speed electrons to bump into atoms, which either…
It’s All About The Flux
My favourite engineering class in university literally brings me back decades, to the second semester of my freshman year. The class — Electricity and Magnetism (E&M) — brought fear into the hearts of students. We knew this was the one class in Year 1 that would separate the would-be engineers from the pretenders. At least it would until Year 2 filtered out some more. The class was offered under the Department of Electrical and Computer Engineering, which meant not only did EEs have to take this class, those in computer engineering had to take it as well. We were taught by an accented old Dutch professor, whom our class would be his last before retirement. The CE class was taught by an accented young Chinese professor, an expert in photonics. In the hallways and school libraries, we’d often hear complaints of E&M from the CE class. In contrast, rarely anyone…
Women, Engineering, and Perception
Professional Engineers Ontario (PEO), of which I’m a license-holding member, publishes a bi-monthly magazine called Engineering Dimensions. In the September/October 2010 issue, a letter to the magazine caught my attention. Since online access to the magazine is restricted to members, I’ll quote the reader’s feedback in its entirety below: -President Seems to Support Discrimination- I read with surprise and disappointment our newly elected president’s avowed intention of supporting the concept of sexual discrimination (“Women in leadership,” Engineering Dimensions, July/August 2010, p. 3). However, her suggestion that our profession should support sexual or any other type of discrimination greatly concerned me. This is antithetical to our long and proud history of objectivity, neutrality and fairness. In fact, it calls into question our claim to professional status. Her first sentence–”At a time when women represent only 10 per cent of all professional engineers in Canada, there is a ray of light in…
PowerPoint Engineer
During the course of selling your soul for pieces of silver, there may come a time when the powers that be request that you sell out just a little more of yourself. Yes, they give you underlings. Soon, you will discover that all the skill and pride that you’ve carefully nurtured over the past many years will vanish in mere months. Where once you took pride in your ingenious cleverness, now you take care of babysitting disgruntled ex-peers who look upon you as an obstacle to their inventive genius. The complex computer modeling of the nano-world is replaced by Gantt charts and bar graphs. You start attending meetings, lots of them. Meetings with the boss. Meetings with your peers. Meetings with underlings. Food starts to taste funny; the flatulent co-worker seems to smell less; staring at the sun directly is no longer a problem; underling complaints seem to sound like…
Prototype vs. Simulation
In my own personal blog, I’ve complained more than once about the zero-bug prototype policy at FluxCorp and the ridiculous design processes that fall out from that. The whole premise was based on an internal study by the managers that showed we engineers spend 25% of our man-hours debugging problems on prototypes. Lots of bar charts, pie charts, tables, and scatter plots, all to convince us stupid engineers that if we could save that 25% in the lab, we’ll have time to design a whole new Flying Flux a year. They try to sell this to us by telling us we won’t be as stressed out if our designs are perfect. If engineers were to simulate more, simulate better, do more dog-and-pony show presentations, all these bugs would just melt away. I guess if I became the dictator of the world, I won’t have to work anymore. Both are fantasy…
The $150,000 Wire, Part 2/2
Yesterday, I presented a diagram of a problem circuit and asked if EB readers can spot the problem. Here’s that diagram again: Bill was the first to respond and came up with the correct answer; Chris Zeh of Idle-Logic.com feels my pain; while Paul Clarke, our contributing author, is still giggling like a little girl. Yes, this is a circular dependency problem. The digital buffer (triangle shape) depends on the voltage supply to be up and running to work. But the voltage supply can only be up and running if the digital buffer is working and passing through the power-on signal. So if you want to power on the chip by asserting the power-on signal, that signal can never get through to the rest of the chip because the digital buffer’s voltage supply is not up and running yet. So the chip is dead. The correct wiring diagram should have…
The $150,000 Wire, Part 1/2
At FluxCorp, I’m on a team of chip designers responsible for creating the Flying Flux. As with any piece of circuitry, it requires a voltage supply. In the case of the Flying Flux, a lot of its circuits run off a voltage supply that comes from an on-chip voltage regulator. Both this on-chip regulator and the Flying Flux can be turned on or off via a single power-on wire. This wire is a digital signal and comes from outside our design. When it comes on-chip, it is first buffered before appearing at both the Flying Flux and the regulator. A diagram of this setup is shown below. Take a look. What’s wrong with this picture? Answers tomorrow.
Uh…What’s Engineering?
That’s the question I found myself asking my father during my last year of high school. I was good in math and physics and it seemed that would be my fate in university — a pure math or physics degree. But when my dad suggested that I go into engineering, I had had only the vaguest notions of what it was. Engineers build things, he tells me. That’s great! I wanted to build a spaceship! I also found out something new about my father — he’s an engineer! Heck, I just thought he oversaw the building of container ships. I didn’t know they had a name for such people! Later on, I would see my dad work as a contractor for the U.S. Navy in Norfolk, Vriginia, setting foot on the most advanced naval warships and aircraft carriers in the world. Cool stuff, I thought. You see, that’s what I…