Topic 5_Electrical Behavior and Diffusion_s

Topic 5_Electrical Behavior and Diffusion_s - Topic 5:...

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1 1 Topic 5: Electrical Behavior and Diffusion MATE 210 Introduction to Materials Engineering 2 Topic 5 Outline Topic 5 Outline Composition Structure Performance Processing
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2 3 Application: Photovoltaic Cells Most solar cells are made from a silcon-based semiconductor, but new technology arrives everyday, like this organic solar cell made from Pentacene. The opportunity: On a bright day, the sun shines ~1,000 watts of energy per square meter onto the Earth’s surface. The advantages – Solar energy is: Cheap Clean Secure 4 How do Solar Cells Work? Solar cells convert the energy of solar radiation into electricity by exciting electrons and “holes” in sandwich of two slightly different semiconductors (called a p-n junction) When these electrons and “holes” are excited they move through the semiconductor sandwich and produce a current, which then powers a load such as a light bulb.
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3 5 Anatomy of a Solar Cell 6 Solar in SLO SLO Prof. Harding’s old haunts. Brrr! Some places in the U.S. could benefit more than others based on the amount of sunlight.
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4 7 What’s taking so long? Solar energy suffers from two problems: The up-front cost of installing the cells and auxillary equipment (~$32,000 for a typical house!) Low efficiencies (14- 17%) in practice. 8 Why are they inefficient? Solar light is composed of many different wavelenghts of radiation, all with different energy levels. Solar cells only convert some of this energy into electricity. The rest either passes completely through the cell (low energy), is reflected, or given off as excess heat (high energy).
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5 9 Improving Efficiency Materials scientists and others continue to work on developing low cost, efficient solar cells. Laboratory efficiency of a variety of solar cell technologies 10 Microfabrication of Semiconductor Devices
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6 11 Silicon Wafer 10 Billion Components 8 Inch Diameter Earth 6 Billion People 8000 Mile Diameter Source: www.nsf.gov How Small is Small ? 12 How Do We Get There? - silicon boule sliced into the wafers that circuits are built on - grow silicon boule from melt - slowly pull single crystal Si (100) plane
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7 13 Single crystal Si Ingots 8-12” Silicon Ingot Typical Ingot 1-2 meters Sliced & Polished = 2000- 4000 Wafers 280-650 die (chips) per Wafer 26,000,000,000,000,000 transistors per ingot!!!!!!! 14 Over 100 different processing steps to get to the final circuits! Cut and Polished Wafers Finished Circuits on Wafer Wafer Processing
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8 15 Why do we care about atomic planes & directions? - convenient way to describe atomic arrangements - different property values result from different atomic arrangements Single Crystal Si (100) 16 Materials in Microelectronics W-silicide Ti/Al/Cu/TiN W-Ti W (tungsten) www.ibm.com/chips/technology SiOSiON/HfO Poly-Si CoSi SiO 2 BPSG
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9 17 Electrical Behavior
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Topic 5_Electrical Behavior and Diffusion_s - Topic 5:...

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