JC Feb 19 11:00 PM

EA Feb 19 11:00 PM

SW Feb 21 8:19 PM

Sustainability Issues

Environment

In terms of the environment, manufacturing integrated circuits has a huge impact. From Kuehr and Williams, the world uses millions of tons of chemicals and billions of gallons of water each year to manufacturer microchips. Many of these chemicals are extremely toxic. If any of these chemicals are accidentally released into the environment, the results could kill animals, plants or even people. Although many good steps have been made, by finding less harmful alternative chemicals, and by developing better containment processes, the technology is still unsustainable in the long run.[1]

Economics

IBM has recently developed a process for reusing silicon wafers from unused microchips. The boards are unsuited for their original use, due to problems in the manufacturing stage. Since these boards have private designs on them, the old method for disposing of them was to crush them and send them to landfills. By grinding the designs off of the wafers, IBM can reuse the silicon to make other electronics, such as solar panels. This is excellent, because this silicon had already gone through the refinement and processing needed to get it to the required purity levels for microchip production. By reusing the silicon, instead of throwing it away, we can lower the production cost of solar panels, and other electric devices that use this recycled silicon. This lets companies use this saved money to work on other projects for lowering waste and reducing environmental impact. [2]

Equity

In the Congo, there is a large tantalum mining operation. Tantalum is a metal that is extremely important in the production of small efficient capacitors. These capacitors are used in many different electronic devices, like cell phones and cameras. Unfortunately, the poor miners in the Congo are often times exploited and robbed. This exploitation of third world countries makes the production of these electronic devices unsustainable in a global community. In order to keep the world in a harmonious state, we need to stop the exploitation of those who are less fortunate than us. [3]

With memory, one of the important things is speed. When you have a high speed system, you have to pay for it with power. Generating this power is costly for the environment, if fossil fuels are used. In order to try to reduce this power, you can lower voltages and reduce size. Lowering the size lowers the parasitic capacitance in the FETS, which means they can switch faster with less current. Lowering the voltages reduces the I*V power product for the circuit. Intel does these by making 45nm chips, and they also are trying to help the environment even more by attempting to make their manufacturing plant green. By reusing and recycling things like water, they are able to save money and reduce the impact that their products have on the environment.[4]

The next most important thing in memory is size: the number of memory cells available for use. A large bank of memory will necessarily cost more and use more natural resources to produce; It follows that our memory cells should use the smallest footprint possible. Our Shift register takes at least 8 MOS transistors to implement, and would additionally require a 2-1 multiplexor to function as a data-storage register. Comparing this to 4-6 transistors for a SRAM cell [5] or one transistor and one capacitor [6] for a DRAM cell, we can see that the size discrepancy is nontrivial. While interfacing with a dynamic CMOS digital system may be easier with the shift register, it proves to be too unwieldy for large scale storage, and that is the reason there are few, if any, memory chips available that use dynamic shift register technology.

In experiment 6 we looked at the power dissipation of multiple logic families. For CMOS technology, they power dissipation is directly proportional to the operating frequency of the circuit. This makes it consume much less power than TTL logic families for low frequency operations. However, the TTL based families increase power dissipation much less as the frequencies increase. Based on the results of this lab, there should exist a frequency where they CMOS logic gate dissipates more power than the TTL based logic gate. This would indicate that once computing reaches a certain level, it will be more efficient to use a TTL based logic family like LS-TTL or ALS-TTL instead of CMOS. However, this still leaves the question of what the cost of generating this power is. Using current methods of burning fossil fuels, we don't have a sustainable method of generating power. Not only is the fuel supply limited, carbon is released into the atmosphere, throwing of the balance of the carbon cycle. Using renewable energy, like solar, will give us a clean and infinite, at least until the sun dies, supply of electricity. Solar energy has it's down sides though. Conventional solar cells are made of silicon and glass, making them hard, heavy and fragile. This makes them costly to maintain, because they are prone to breaking, and have to be replaced. It is possible to create a solar cell using a conductive polymer, but the efficiency of these solar cells was too low to make them commercially viable. A new breakthrough in conversion efficiency from New Mexico State University and Wake Forrest University has made these flexible solar cells closer to production, getting 5.2% efficiency. While still a ways from the 10% required for commercially viable production, and the 12% of modern silicon products, this breakthrough happened a decade before people thought it was going to happen. This is a good step in making more efficient solar cells that are a cost effective way of producing energy. [7]

In Lab 7 we looked at emitter coupled logic. The power dissapated by an ECL system is hyge comapred to the power dissapated by other logic families. the particular ECL gate that we built used 44mW of power. This was a one bit logic gate. One bit is not enough to do anything. According to a press release from Intel, the latest 45nm design Xeon processors have aproximately 820 million transistors, while the slightly older 90nm design Itanium processors have 1.72 Billion transistors.[8] 820 milion transistors, with each logic gate having an estimated of 6 transistors, at 44mW per gate would draw 6 GigaWatts of power. Running a computer in a household that drew that much current would be impossible. At 120V, you would need to 50KA to supply that much power. Again, generating this power is unsustainable based on the way power is produced today. Without focus on clean energy sources, the speed available to us using ECL will not be worth the cost to the environment.

Braun's comments:

• Good analysis specific to the experiment, and your analysis connects to later lecture course topics not covered in the lab.
• Rather than in high capacity memories, you would more likely find shift registers in systems such as serial to parallel conversion systems, FIFO buffers, and ALU registers.
• Also, connect your analysis directly to the four "E"s of sustainability and the laws of ecology.

1. E. Williams, “Environmental impacts in the production of personal computers,” in Computers and the Environment: Understanding and Managing Their Impacts, R. Kuehr and E. Williams, Eds. Dordrecht: Kluwer, 2003, pp. 41-72

2. DAVID HO, The Atlanta Journal-Constitution, October 30, 2007 http://www.semiconductor.net/articleXml/LN692909227.html?industryid=47534&nid=3572

3. Mark Michalovic, "Tantalum, Congo, and Your Cell Phone," ChemMatters, October 2007, pp. 16-18

4. Jon Stokes, Ars Technica, July 2000 http://arstechnica.com/paedia/r/ram_guide/ram_guide.part1-1.html

5. Bruce Jacob, David Wang, University of Maryland, Spring 2003 www.cs.berkeley.edu/~vwen/research/lowpower/papers/low_power_sram_circuit_design.pdf

6. [6]Sharon Gaudin, Computerworld, Tuesday, October 30, 2007

   http://www.pcworld.com/article/id,139089-c,intel/article.html

7. New Mexico State University. "Solar Breakthrough Will Help Spur Viability Of Alternative Energy." ScienceDaily 9 October 2005. 21 February 2008 http://www.sciencedaily.com/releases/2005/10/051009202947.htm

8. Intel. "Intel Processor History" ftp://download.intel.com/pressroom/kits/IntelProcessorHistory.pdf