Beginner's guide to electronic components - Part I

The basic electronic components are the resistor, capacitor, inductor and memristor. Here is how the technologists draw them.

 

 

The most important electronic component that is more sophisticated is the transistor. Connect electronic components together and you have a product such as a radio, provided you supply electricity to this circuit (the watermill needs a river). The battery is a common source of power because an increasing percentage of electronic devices are portable. Sometimes batteries are kept charged by energy harvesting in the electronic circuit, such as vibration harvesting, heat harvesting or solar cells each producing the desired electricity. About 130 years ago, Edison was right when he said that, "Electricity should be made where it is to be used." To learn more about energy harvesting read Energy Harvesting Journal which is free daily.

 

An easy way to grasp how electronic components work is to look at the mechanical analogies of containers of liquid, springs and shock absorbers. Once, only large ones were available, they were used in power generation and vehicles but then small ones were developed and economically produced in huge numbers when they appeared in wristwatches and the like. So it was with electronic components.

 

 

Electronic devices are increasingly not just portable: they are disposable. Printing of electronics leads to this with the lowest price, highest volumes and most safely disposable components. Increasingly, electronic components are printed together on plastic film or paper and this can even improve performance and reliability over the clumsy old methods of connecting together separate components such as silicon chips, batteries and capacitors.

Consider a pipe that carries water current. The flow of water through the pipe is faster if the pipe is shorter and/or it has a larger diameter. So it is with electrical current, the force moving it being called voltage instead of pressure. A resistor impedes the flow of electricity by a given amount, . You can choose your shape of "pipe". As you see in the picture above, a resistor controls the amount of current "i" passed as a result of applying a certain voltage "v", this resistance being measured in ohms. Power handling capability in watts and other aspects are also measured. Resistors are easy to print.

An inductor is the electrical equivalent of a shock absorber. It can delay and moderate electrical impact just as a shock absorber delays and moderates mechanical impact. One useful example is a capacitor and an inductor connected side by side to filter varied electrical impulses received just as the suspension in a car works better when a shock absorber and a spring are used together. As you can see from the picture above, an inductor controls the amount of magnetic flux generated by certain current "i". When used as an aerial it works the other way round controlling the amount of current generated by a certain flux of electromagnetic signal coming in. The extent of this "inductance" is measured in henrys. Inductors are easy to print but not with high inductance. We need a better range of printed inductors.

A capacitor is the electrical version of a spring. Consider the analogies below.

 

 

 

 

A capacitor controls the amount of electricity ie charge "q" stored by applying a given voltage "v", this capacitance being measured in farads. Other aspects such as voltage tolerated are also measured. Capacitors of low capacity are easy to print. Flexible so-called supercapacitors thinner than one millimeter but not printed are already in use. We need a much better range of printed capacitors and it is difficult to find anyone working on this. Researchers tend to work on what interests them and what their funding bodies find near impossible and sexy, not what the market needs. Capacitors, having been invented in 1746, do not qualify. The shortage of options for printed memory is another example of this disconnect.

An analogy for a memristor is a pipe that expands or shrinks when water flows through it. If water flows through the pipe in one direction, the diameter of the pipe increases, thus enabling the water to flow faster. If water flows through the pipe in the opposite direction, the diameter of the pipe decreases, thus slowing down the flow of water. If the water pressure is turned off, the pipe will retain its most recent diameter until the water is turned back on. Thus, the pipe does not store water like a bucket (or electricity like a capacitor) - it remembers how much water flowed through it. Referring to the picture above, a memristor controls the relationship between an amount of electricity "q" and magnetic flux. There is no agreed unit for measurement of the strength of a memristor because they are so new.

 

 

The reason that the memristor is radically different from the other fundamental circuit elements is that, unlike them, it carries a memory of its past. When you turn off the voltage to the circuit, the memristor still remembers how much was applied before and for how long. That effect cannot be duplicated by any circuit combination of resistors, capacitors, and inductors, which is why the memristor qualifies as a fundamental circuit element. A lot of transistors (more complex devices) and capacitors in circuit can mimic the action of a tiny memristor but it is uneconomical for them to be used in this way.

 

Memristors were first made as recently as 2008. They only work near atomic dimensions because they rely on so-called quantum effects. They are not yet available in the shops but experimental versions that are very thin and potentially flexible have been demonstrated recently. They may help ease the chronic shortage of options for printing memory. They will also perform other functions in electronic circuits, reducing the number of components needed and therefore cost and probably permitting new types of performance such as progressing towards the stellar performance of the human brain. Memristors can only be made by printing or print-like thin film processes but they are little understood.

A battery is the electrical equivalent of a container of water. This may be single use or rechargeable - constructed differently for multiple use as with a cistern in a house. Multiple use ("rechargeable") is not unlimited - it wears out. So it is with batteries. Water eventually evaporates from a container or leaks out and electricity eventually leaks out of a battery. Batteries store a relatively large amount of electricity but it cannot usually be used or replaced very rapidly. Capacitors tend to be the opposite.

 

 

Pushing the limits of batteries presents danger, as with water in dammed reservoirs. Certain types of batteries have exploded or burst into flame in electric vehicles and laptops. However, this lithium cobalt based chemistry is now the favoured one for high performance electric vehicles, laptops, mobile phones and many other devices and, with advances in the technology, it is becoming safer all the time. Small containers of liquid and ones built sturdily rather than cheaply tend to be safer. Small batteries and those with poorer performance tend to be safer. In particular, printed and other thin film batteries are much safer, lower cost and can fit in more places where they are needed. There is an excellent choice of printed and thin film flexible batteries that can be used in totally new product concepts if only we could find more creative designers rather than just market researchers. As Henry Ford said, "If I had asked my customers what they wanted, they would have said faster horses." The capability of a battery is usually measured in deliverable energy in kilowatt hours, deliverable charge in ampere hours and deliverable power in watts.

A transistor is like a tap. A source of water enters at one end and drains out the other and a valve in between lets us control how much gets through without using much effort. A transistor has so-called source and drain electrodes controlling electricity instead of water but instead of calling the third, controlling electrode - that is in between - a valve, it is called a gate, just to confuse you. Thousands to tens of millions of transistors are typically made in one go in an integrated circuit. This uses less material, making them cheaper and the lack of separate connections makes them more reliable. Making the electricity go shorter distances in these "microchips" can improve performance. Other components can be made and connected reliably and cheaply in the same microchip. Indeed, Hewlett Packard is depositing memristors on chips for trials. However, silicon chips must be made ever smaller (more transistors per unit area) to be ever cheaper and there are not only physical limits to this - you find you can integrate fewer and fewer other components. For example, including a battery, solar cells, a wide area sensor or display is usually impossible. In that sense the silicon chip is on what Shakespeare called "The primrose path to eternal doom". Enter printed electronics which, of its nature, is thinner but with a bigger area. Now you can potentially print almost everything in one device, improving cost and reliability. Sorry silicon. Biter bit. Mind you, the silicon chip people can quote Mark Twain, "Rumors of my death are grossly exaggerated." In the next article we shall look at how all these electrical/ electronic devices are made.

 

 

For more read Introduction to Printed Electronics, Thin Film Photovoltaics and Batteries 2009-2029, Printed and Thin Film Transistors and Memory 2009-2029, Batteries, Supercapacitors, Alternative Storage for Portable Devices 2009-2019

and Displays and Lighting: OLED, e-paper, electroluminescent and beyond.

 

Also attend Printed Electronics Asia 2009 or Printed Electronics USA 2009.