Working in Sweden Living and working in Sweden means being part of an open society in a truly dynamic and international environment. Quality of life is an important feature of life in Sweden and is found in areas ranging from education, healthcare and housing to culture, the environment and opportunities for personal fulfillment. Starting a new business in Sweden is easy and business procedures are simple and transparent. Invest in Sweden Agency, ISA, is ready to provide you with professional and business oriented assistance, free of charge. Magnet for talent of Public Policy at George Mason University. The report ranked European countries according to the 3Ts of economic growth – talent, technology and tolerance – regarded as indicators of a country’s creative potential. The report identified Sweden, Finland, Denmark and the Netherlands as the “creative crescent” of Northern Europe: countries that are challenging the economic power of the United States and “old Europe”. In forming their conclusions the researchers looked at a range of indicators, including investment in R&D, patents and the proportion of university-educated people, as well as attitudes to immigrants and freedom of expression.
Sweden is the most creative country in Europe, able to attract the world’s most talented workers and gain a competitive economic edge, according to a report by Professor Richard Florida of School
Monday, 20 August 2007
Investment in sweden
Saturday, 18 August 2007
Energy usage with chemical enginnering knowledge
home made experiments for school students as well as for small scale industry's (for unemployed youth)
some of the useful links
solar basics
basics1
Basics of Solar Power
What is a solar cell and how does solar power work? Here you will find a simple introduction to the technology for the uninitiated.
What is a Solar Cell?
A solar cell or photovoltaic cell is a device which generates electricity directly from visible light by means of the photovoltaic effect. In order to generate useful power, it is necessary to connect a number of cells together to form a solar panel, also known as a photovoltaic module. There is more about the the different types of solar cell here. The nominal output voltage of a solar panel is usually 12 Volts, and they may be used singly or wired together into an array. The number and size required is determined by the available light and the amount of energy required.
Can the power be stored?
The amount of power generated by solar cells is determined by the amount of light falling on them, which is in turn determined by the weather and time of day. In the majority of cases some form of energy storage will be necessary.It is possible to connect an array of solar panels to the mains to assist when the power required is greater than that being generated. The cost of this is offset by selling surplus power back to the electricity company when it is available.
This site, however, is concerned with self-contained systems where this is not possible. In this type of system the usual choice for energy storage is the lead-acid battery. Find out more about batteries here. The number and type of batteries is dependent on the amount of energy storage needed.
Power Control
No matter what, sometimes there will be too much power. Other times there won't be enough. The battery will be damaged if it is allowed to be overcharged or over discharged, so a controller is needed to protect it. Read more about controllers here.The smallest systems may have only a few 12 Volt lights, but in bigger systems 230 Volts will probably be needed. An inverter is used to transform the low voltage DC generated by the solar panels into mains voltage AC.
Rationalising your energy usage is the next step to building a successful solar powered system.
Energy Efficiency
Energy efficiency saves you money. Where solar energy is concerned it saves even more money. This page will get you to think about how much energy you use. Whether it's solar energy or not, you can reduce what you pay for electricity.
Energy Optimisation
What do you think of when you hear about energy efficiency? Saving electricity of course. That's an important thing, but its just as important to use the best energy source for each purpose. This is especially important if your electricity is generated by solar energy.What's the right energy source? Well it depends on two things; what is needed and what's available. For example, if you have a source of logs then that might be the best energy source for heating your living room.
Appropriate Energy
The biggest gains are usually to be found in lighting. Using the right sort of lamps in the right places can pay dividends for anybody, but especially for solar energy users. Click here to select the right sort of lights for you.Think about what you use for heating. Not just for space heating, but cooking and water heating as well. Solar power may be no use for heating, but you may find that solar energy could help. Find out more about heating here.
Refrigeration and other appliances need to be carefully considered to reduce energy use. It stands to reason that the fewer appliances you have the less energy you will use, but if there's something you have to have, then a little thought can make all the difference.
Now you understand all about energy efficiency, you can start to design your solar power system.
System Design
Getting the design of the system right is key to ensuring both reliability of supply and minimum cost. A little time spent in accurate estimation of energy consumption and planning the installation wil pay dividends in the future. The calculators on this page will help in the process of builing the optimum solar power system for your needs.
Solar Panel Sizing
If you followed the advice in the energy section, you will have reduced your electrical energy requirements to a bare minimum. The next stage is to use these to calculate the daily energy requirement. Start the loads calculator and follow the instructions to calculate your daily energy requirement. 
To size the battery, use the battery calculator. You'll need to use the daily energy requirement calculated earlier.
Other Components
Now that the major system components are in place, all that remains is the simple matter of sizing the:
- Charge Controller
and - Inverter
It is possible to do without a charge controller only if the battery is very large relative to the solar panel array. An example is the "Battery Saver" panels designed to plug into a car cigarette lighter. Otherwise, add up the short-circuit current of the solar panel array and use the next largest controller.
Apart from a few wiring tips, you are now ready to buy the parts.
Wiring Tips
If you have electrical experience then wiring up your solar power system should be strightforward. Although the wiring is likely to be more complicated than normal mains wiring, all the principles involved are the same. This page gives an outline of the differences between this type of wiring and normal wiring.Caution:If you are at all unsure of your abilities please employ a qualified electrician, preferably one with experience of wiring renewable energy systems.
DC Wiring
The DC wiring may be the whole system or confined to the battery room. Every system is different, but I have provided example wiring diagrams for a typical 12 Volt lighting system and 230 Volt system to help with the wiring design. The cable sizes can be calculated using the calculator on the design page but be aware that the low-voltage DC cables will need to be larger than you are used to. Normal mains wiring accessories can usually be used at their rated current at up to 30 Volts DC. You will also need some specialised low-voltage parts such as battery clamps which can be obtained from automotive wiring suppliers.
AC Wiring
The AC wiring is just the same as in any mains installation. It is very important that the manufacturer's instructions are closely followed when installing the inverter, especially with regard to earthing requirements. Always ensure that the AC and DC circuits are kept entirely separate.Useful Links
Links to various solar power resources and suppliers, sorted by category. If there is something you would like to see here, if you are a supplier or information source then please submit a link to this page.If you would just like to link to this site then go right ahead.
Most Recent
Eco-friendly Garden Offices and Granny AnnexesArchitect-designed, sustainable, highly insulated garden offices and granny flats. Constructed with Uk sourced materials, highlt insulated. If you want a shower room, we can add solar panels for water heating.
solar water heater
Supplier of solar water heater in China. The products are including thermal solar water heater and split solar water heater.
Greenworks Renewable Energy Solutions
Specialize in green energy solutions such as solar heating panels, domestic wind turbines, etc
solar power home
Solar power is a clean, renewable energy source for the future.
biodiesel
Biodiesel is a realistic and environmentally friendly alternative to gasoline.
Total Solar Energy
Discover how solar energy can help save both money and the environment
Energy Saving Products Company - Save n Energy
Energy saving Products company in West Palm Beach, Florida, providing Energy Star quality energy efficient Home Appliances.Save n Energy offers CFLs, fans, water heaters, and other efficient home appliances, which helps save energy.
Solar power
Solar Power you can get solar power in your home by using solar panels to capture the power of the sun. Company information includes solar hot water heating, energy efficient boilers, geothermal power and more. Reduce your carbon emissions and your energy bills.
Solar Houses for Sale in Costa Rica
Green Building in Costa Rica - Solar powered, sustainable Real Estate. Green Real Estate. Green Architecture.
OY Not Solar
We promote the use of solar electric systems for use by homeowners and small business applications.
Solar Sky Spain S.L.
Design and supply of Solar energy Systems. Solar electrical systems for remote homes inland Spain Solar water heating systems distributor
LED Bulbs
LED Bulbs can last for over 50,000 hours and save you up to 90% of your energy lighting bills
Latin America Wind Energy Association
Latin America Wind Energy Association / Asociacion Latino Americana de Energia Eolica
Solar kent
Practical examples of solar water heating and solar electric installations
Solar Watts
Installers of Photo Voltaic (electrical) Solar Panels. Many frequently asked questions answered on our web site.
The Solar Lights Blog
An introduction to Solar Lights and what kind of lighting applications can be achieved with solar energy
Equipment Suppliers
Southern Solar LtdSouthern Solar offers a range of solar power solutions for your home or business. Solar hot water systems, grid connected solar electric and wind power. Grants available!
Navitron Renewable Energy
Navitron Ltd is based in the UK, and provides affordable renewable energy solutions. European importer for solar water heaters, wind turbines, water turbines, heat pumps, backup petrol and diesel power generators and autogas conversion equipment.
Screwfix Direct
Suppliers of low-cost wiring accessories, lighting and tools amongst a wide selection of trade and DIY items.
Select Solar
Suppliers of a very wide range of solar power equipment, with a comprehensive web site.
Roadpro
A huge selection of low voltage equipment for all applications.
Energy and Environment
Online merchant with a wide range of solar power products.
County Battery
Suppliers of a wide range of batteries including leisure and deep-cycle types.
Infinigi - Infinite Energy Solutions
A renewable energy company that provides exceptional customer service and offer aggressive prices on solar panels, wind turbines, charge controllers, inverters, and other renewable and energy efficient products.
Solar Panels - Based in Essex UK
We are UK suppliers of a huge range of solar panels and solar products, secure online shop
Bright Light Solar Ltd UK
Suppliers of solar panels, charge controllers, batteries, refrigerators, lighting. Design & supply with 20 years experience.
Energy Force Ltd
We provide solar and wind power. We offer parts, systems,and other services. From start to finish.
Midnight Sun Innovations LLC
Features a innovative solar powered LED flashlight which does not require batteries.
Solarthermie24.de
Solarthermie - Gro�e Qualit�t zum kleinen Preis!
California Solar Electric Company
Serving Northern California, California Solar Electric Company specializes in solar power systems design, sales, and installation for your home or business.
NATURAL LANDSCAPES LTD
Low cost Kyocera Solar Modules. Luxeon LEDs, AirX & Forgen Wind turbines, environmental services
Energy Development Co-op Limited
UK based solar & wind power specialists, supplying mainly small commercial stand-alone power systems, typically for remote lighting, data collection & telecoms.
Cirkits
CirKits sells kits for solar charge controllers and lighting systems.
NJ Solar Solutions
Solar Power & Energy - NJ Solar Solutions Inc. specializes in solar powered electric installations with a partnership with BP Solar Energy and Home Depot.
Solar Battery Distributor
Advanced Power Products, a full stocking supplier of solar batteries, aircraft batteries, marine batteries, and rv batteries.
Midsummer Energy
We sell solar panels, regulators and other components of renewable energy systems.
Bright Green Energy
Based in Beckenham, Kent, we sell a wide range of solar panels, wind turbines and renewable energy products.
SkyLineSolar
SkyLineSolar is the Uk's first online energy warehouse that covers all sources of renewable energy. Including Solar power, Geothermal power, wind power and hydroelectric
4 Elements Renewable Energy Products
4 Elements provide a wide range of solar and wind powered products. All our branded quality products such as Sharp, Schüco, Rolls Batteries, BP Solar, Exide, Victron, Marlec, Studer etc… come with extensive manufacturers guarantees giving you peace of mind and protecting your investment. The renewable energy industry in the UK is now beginning to grow and as new renewable power technology comes on stream we will continue to add to our portfolio. So bookmark www.4elements-uk.com in your favourite browser or call us on 01844 210960.
Alpha Solar The renewable energy resource
We provide cost effective , state of the art , efficient renewable energy products, accessories and complete electric systems for homes, cabins, boats, remote site and back-up power at very competitive prices.
Wavemaker Energy Saving
Solar Panels, energy efficiency products, all available for worldwide distribution. Suitable for anything from home to business use - we have a wide range
Solar Energy - Soul-er for Solar
Designs and installs solar systems for residential and commercial applications.
Renewable Energy
Ener.G Group offerings, Cogeneration, Renewable Energy, Energy Management and Energy From Waste provide an energy solution for all businesses and industry types
solar energy
solar photovoltaic modules,micro solar panels solar torches solar lights solar educational kits solar caps
Solar Fusion Ltd
Government accredited supplier of the most advanced solar power systems, including solar PV. Based in Dorset and providing services nationwide.
BeaconTron
An alternative energy solutions company providing a wide range of equipment and kits from top renewable energy manufacturers. Offerings include solar power equipment, wind power and microhydro.
Turbine Technologies
Supply And Installation Of Renewable Energy Products To The Domestic And Commercial Market,
Lake Renewable Energy
Provider of renewable energy products including solar , wind and energy saving devices to the homeowner and small / medium business
Evacuated Tube Solar Panels
Distributors of evacuated tube & flat panel solar thermal collectors to trade & DIY.
Resources
Solar PlazaWorldwide directory of PV resources.
Earthtoys
Alternative And Renewable Energy News, Emagazine And Library
Centre for Alternative Technology
An essential for anybody interested in alternative technologies, CAT has a wide range of resources and an excellent visitor centre.
UK Solar Energy Society
The UK arm of the International Solar Energy Society, this is the organisation dedicated to advancing solar energy technology.
Positive Power
Renewable energy information service. Links to resources and news articles.
Gordon Clarke Architects
Eco architects specialising in organic design, and high quality sustainable architecture.
Odysen Renewable Energy
Renewable energy calculators, news archive, events, games, and location specific information.
Energy Concepts
Energy Concepts is an Energy Services and Consulting Organisation, providing technical knowledge relating to existing modes of power and the needs of development in the field of Alternative Energy
FreeSunPower
FreeSunPower provides Free tutorials, both beginner & advanced with interactive online design tools for Solar Energy Systems.
Renewable Energy Resources
Best education Websites on renewable and alternative energy resources, green power, fuel cells, alternative fuel vehicles, solar energy, water power or hydropower, wave, tidal, or ocean energy, and wind power.
Consumer Utility Services
Impartial information and advice on saving money on your energy bills and how to be more energy efficient in the home.
Natural Matters
Natural living directory with a dedicated sustainable power section including solar, products, services, news, articles
ENF - PV Industry Information
Solar power industry database (cells/module/panels, equipment, components, products, installers). Solar business & technical news, solar magazine, government tenders for solar projects
Solar Garage
My Solar garage, A beginners blog on starting and getting deep into solar power.
Solar Review
Provides News, Reviews, and Information about Solar and Photovoltaic Products
YourGreenDream
YourGreenDream - Hobby alternative energy production education and resources
Home Power Magazine
Home Power magazine is the Hands-on Journal of Home-Made Power. If you are interested in: making your own electricity from renewable energy, alternative vehicles, or finding out the latest in related technologies and life-styles, then this publication can keep you up to date.
This is their suggested link text, but I'd go further. Home Power is the best magazine about renewable energy, bar none.
Uk Energy Saving
The website gives information and tips on ways to save energy and also how to save money on household bills.
Solar Future
SOLARFUTURE is a NGO based in the European Union and South East Asia dedicated to promoting sustainable solutions for the future of mankind.
Sustainability Store
Directory of socially and environmentally responsible products and services.
Solar Times
The latest news going on in the solar industry.
New Energy Congress
The best news and directory service on the net regarding cutting edge energy technologies.
Solar Facts
Information on what is required and how it works for a domestic solar power system, all in easy to understand language.
Renewable Energy Stocks
RenewableEnergyStocks.com® is a global investor and industry research portal for the renewable energy sector. The website does not make stock recommendations but features industry and stock news, exclusive articles and financial columnists, audio interviews, investor conferences, Blogs, and a directory of stocks in the sector including solar, wind and ethanol
Solarist
New solar technologys. Renewable Energy
Solarism
Solarism promotes the use of all forms of renewable energy, in particular solar thermal water heating, enabling up to 70% reduction in annual water heating costs.
mrsolarenergy
a collection of energy and money saving tips, ideas, information and products from around the world
Solar power
Solar power, but what is solar power? and how will you make the best use of it? well, the answer to this is very.
Solar Panels
Information on how home solar panels can provide power for electricity or to heat your home. Also contains an environment articles database with an ever increasing number of related articles and press releases.
Home Solar Power
An expanding site providing information pertaining to all aspects of domestic solar power. Solar heating, photovoltaic power, active and passive solar heating etc.
Good to be Green
Our green building directory gives consumers free access to the most comprehensive list of green building products, eco-friendly materials and sustainable service professionals in residential and commercial markets.
Outdoor Solar Lights
Solar lights for every situation. Tips & Resources about outdoor solar lights.
SavingCivilization.org
Learn what you can do to conserve energy, fuel, water, and more. Help lower your bills as we move from today's throw-away lifestyle to a sustainable reduce-reuse-recycle economy!
House Energy Savings
How to get home energy savings through solar energy, advanced windows and other practises and renewable technologies.
Solar Exhibition
We are organizer for Malaysia International Solar Expo and Conference, we will develop a good market and joint co operate with solar world
Solar Heating
Thermomax LtdManufacturers of evacuated tube solar collectors, the best for water heating in the UK.
AES Solar Systems
AES Solar manufacture cost-effective flat-plate solar collectors. They offer a DIY kit with telephone backup.
Green Earth Energy
Suppliers and installers of Solar Hot Water and Solar PV Systems. Clear Skies fully accredited.
SolarVenti UK Ltd
Sole UK distributor for scandinavian manufactured SolarVenti units which are self contained solar powered dehumidification, ventilation and heating systems.
ECO-NEX SATELLITE SOLAR DISH
Sustainable Resources for the 21st Century, purchase eco chemical free vortex & silver water treatment to control legionella, plus eco energy, gshp, micro wind energy, stirling engine, solar energy
China Solar Power ,Solar Water Heating, Wind energy -Heat Pipe Solar Collector for Eu market.
We are a supplier of evacuated solar water heaters, heat pipe and u pipe solar collectors,separated water tanks, evacuated glass solar tubes, solar pv panels, wind generator, and wind energy products. We are the manufacturer and exporter of high quality solar water heating collectors for Europe.
Honeywell thermostat, Wirsbo Radiant Heat ,Wirsbo pex plumbing - Pexsupply.com
Wirsbo Radiant Heat Supplies, Taco Pumps and Valves and Wirsbo PEX Plumbing Supplies are available at PexSupply.com PEX Supply takes great pride in offering our customers a large selection of products at the lowest prices.Honeywell thermostats wirsbo Radiant Heat Supplies, Taco Pumps and Valves and Wirsbo PEX Plumbing Supplies are available at PexSupply.com.
Solar Panels Plus LLC
Importer and distributor of solar water heating, space heating & cooling products.
Grid Connect Solar
TranswesT SolarSolar Products - Entry level Inverters, meters etc,,, more to come
PV Systems
Suppliers and installers of grid-connected solar power systems.
Non Solar Power
Wisdom ebooksA comprehensive directory of ebooks
Human Ranked Directory Project
Human Ranked Directory Project
!tzalist Science Directory
!tzalist Science Directory
King of the Web
King of the web
LinkPartners.com
Free directory of websites who swap links with other websites.
Arakne-Links Directory
Arakne-Links Directory
Search Engine Web Directory
Search Engine Web Directory categorized by subject. eSearchLogic is a directory focused on family friendly results in our directory listings.
Sootle Directory
Add URL
Submit URL to our human-edited web directory. Submit your website today.
Richard Stubbs Web Creation
Value for money web design, located in northern Dordogne.
Free Add URL
Free directory related to web hosting and related industries.
Web Hot Link
Web Hot Link General Web Directory
SoMuch.com
Popular Internet Links directory focused mainly on Computers and Programming but also covers humor, entertainment, news, Medical, Real Estate and Property, Travel, Timeshare and Cruises, Fitness and Bodybuilding, Music and Graphics. Links are updated daily.
UU directory .
A searchable directory organized by topic, offering free submission.
RealEstateContacts.com
View real estate listings and homes for sale anywhere in the United States. We are your online resource for buying or selling your current home and getting the best possible financing.
Thursday, 9 August 2007
BASIC INTERNET tutorials
BASIC INTERNET
- A Basic Guide to the Internet
- A brief discussion of the Internet and its components
- Understanding the World Wide Web
- A discussion of the major protocols that make up the Web, the makeup of URLs, browsers and plug-ins, multimedia, Web programming languages and more
RESEARCH GUIDES
- Checklist of Internet Research Tips
- A collection of tips in a cogent format, with an emphasis on the use of subject directories and search engines
- Conducting Research on the Internet
- Advice on using e-mail discussion groups, Usenet news, and basic recommendations on the use of subject directories and search engines with tips on conducting searches
SEARCH ENGINES, SUBJECT DIRECTORIES & THE DEEP WEB
Alphabetical list of Search Engines
Alphabetical list of Subject Directories
- Getting Started: Selecting a Tool for Your Search
- A chart listing general query types and the kinds of search tools that support them
- Boolean Searching on the Internet
- The principles of search logic and the different manifestations of this logic on Web search engines
- The Deep Web
- A tutorial describing this newsworthy phenomenon: what it is, what to call it, tips for dealing with it, and how to locate its content
- How to Choose a Search Engine or Directory
- A chart listing numerous features and the search engines & directories that support them
- Searching the Internet: Recommended Sites and Search Techniques
- An extensive tutorial on the use of subject directories, search engine services, and the "deep Web." This tutorial covers the Yahoo Directory, BUBL Link, Brainboost, Don Busca and Google
- Second Generation Searching on the Web
- Tips on precision searching using features available on second generation search services. This tutorial covers Ask.com, Clusty, Ixquick, SurfWax and URL.com
Tuesday, 7 August 2007
P-MOS tutorial on ON-OFF ratio
on-off ratio of MOS transistor analysis
MOS Transistor Definitions
- Positive/negative voltage applied to the gate (with respect to substrate) enhances the number of electrons/holes in the channel and increases conductivity between source and drain.
- V t defines the voltage at which a MOS transistor begins to conduct. For voltages less than V t (threshold voltage), the channel is cut off.
MOS Transistor Definitions
- In normal operation, a positive voltage applied between source and drain (V ds ).
- No current flows between source and drain (I ds = 0) with V gs = 0 because of back to back pn junctions.
- For n-MOS, with V gs > V tn , electric field attracts electrons creating channel.
- Channel is p-type silicon which is inverted to n-type by the electrons attracted by the electric field.
n-MOS Enhancement Transistor
- When V ds <= V gs - V t (e.g. V ds = 3V, V gs = 5V and V t = 1V), the channel reaches the drain (since V gd > V t ).
- This is termed linear , resistive or nonsaturated region. I ds is a function of both V gs and V ds .
n-MOS Enhancement Transistor
- When V ds > V gs - V t (e.g. V ds = 5V, V gs = 5V and V t = 1V), the channel is pinched off close to the drain (since V gd <> t ).
MOS Enhancement Transistor
- MOS transistors can be modeled as a voltage controlled switch. I ds is an important parameter that determines the behavior, e.g., the speed of the switch.
- What are the parameters that effect the magnitude of I ds ? (Assume V gs and V ds are fixed, e.g. 5V).
- The distance between source and drain (channel length).
- The channel width.
- The threshold voltage.
- The thickness of the gate oxide layer.
- The dielectric constant of the gate insulator.
- The carrier (electron or hole) mobility.
Threshold Voltage
- Most are related to the material properties. In other words, V t is largely determined at the time of fabrication, rather than by circuit conditions, like I ds .
Threshold Voltage
- From equations, threshold voltage may be varied by changing:
- The doping concentration (N A ).
- The oxide capacitance (C ox ).
- Surface state charge (Q fc ).
- As you can see, it is often necessary to adjust V t .
- Two methods are common:
- Change Q fc by introducing a small doped region at the oxide/substrate interface via ion implantation.
Body Effect
- The source-to-substrate (V sb ) may increase at this connections, e.g. V sbN1 = 0 but V sbN2 /= 0.
- V sb adds to the channel-substrate potential:
.
Beta Ratios
- Region C is the most important region. A small change in the input voltage, V in , results in a LARGE change in the output voltage, V out .
- This behavior describes an amplifier, the input is amplified at the output. The amplification is termed transistor gain, which is given by beta.
- Both the n and p-channel transistors have a beta. Varying their ratio will change the characteristics of the output curve.
?
.Noise Margins
- A parameter that determines the maximum noise voltage on the input of a gate that allows the output to remain stable.
- NM L = difference in magnitude between the max LOW output voltage of the driving gate and max LOW input voltage recognized by the driven gate.
Noise Margins
- This implies that the transfer characteristic should switch abruptly (high gain in the transition region).
Pseudo-nMOS Inverter
.
Basics on NMOS transistor part1
MOS transistors are quite different from bipolar transistors - not only in their basic function, but also in the way they are integrated into a Si substrate. Lets first look at the basic structure
- We have a source and drain region in the Si (doped differently with respect to the substrate) with some connections to the outside world symbolically shown with the blue rectangles. Between source and drain is a thin gate dielectric - often called gate oxide - on top of which we have the gate electrode made from some conducting material that is also connected to the outside world.
- To give you some idea of the real numbers: The thickness of the gate dielectric is below 10 nm, the lateral dimensioon of the source, gate and drain region is well below 1 µm.
- You know, of course, what a MOS transistor is and how it works - at least in principle. If not: Use the link Basic MOS transistor.
- There seems to be no problem. The transistors are insulated from each other because one of the pn-junctions between them will always be blocking. However: We must also consider "parasitic transistors" not intentionally included in our design!
- If in the space between transistors a wire is crossing on top of the insulating layer as shown in the illustration, it will, on occasion be at high potential. The drain of the left
transistor together with the source of the right transistor will now form a parasitic transistor with the insulating layer as the gate dielectric, and the overhead wire as the gate electrode.
- Everything being small, the threshold voltage may be reached and we have a current path where there should be none.
- This is not an academic problem, but a typical effect in integrated circuit technology, which is not found in discrete circuits: Besides the element you want to make, you may produce all kinds of unwanted elements, too: parasitic transistors, capacitors, diodes, and even thyristors.
- ***********************///////********************************
- This gives us the structure in the next illustration
How we produce the additional insulator called field oxide between the transistors will concern us later; here it serves to illustrate two points:- Insulation is not just tricky for bipolar transistors, it is a complicated business with MOS technology, too
- There is now some "topology" - the interfaces and surfaces are no longer flat. Looks trivial, but constitutes one of the major problems of large-scale integration!
- However, if we need a large capacitance - say some 50 fF (femto Farad) - we need a large area (several µm2) because we cannot make the dielectric arbitrarily thin - we would encounter tunneling effects, early breakdown, or other problems. So we have to have at least a thickness of around 5 nm of SiO2. If the capacitor area than gets too large, the escape road is the third dimension: You fold the capacitor! Either into the substrate, or up into the layers on top of the Si.
- The "simple" way of folding integrated capacitors into the substrate is shown in the right hand side of the next illustration
