Conductors, insulators and semiconductors

Hey! So you want to learn electronics? I hope you know where you're getting into. You probably have an invention in mind that you want to make, but wait, you need to have some basic foundations before getting to the interesting stuff. In this series of articles, we'll cover the key concepts so you can design and interpret circuits. You'll see that all the topics we'll cover are very simple, covered one by one, but don't be fooled; when they're interrelated, it's not that simple, so make sure you understand them all. By the way, a warning: everything I'm about to tell you is a lie in the strictest sense. Now, it's a reasonable approximation of the truth. Let's get to it.

Conductors, insulators, and semiconductors.

Even if you're not interested in electronics, these terms are familiar to you. For the first two, conductor and insulator, you probably have a good idea of what they mean. For the third, semiconductor, you might be more unsure. It's a word used in different contexts and can lead to confusion. For example, you've probably heard on the news that the semiconductor industry is key to the Western world. In that context, the word is likely being used by someone who doesn't know what a semiconductor is, and the message is being directed at an audience that isn't interested (not everyone is as geeky as we are). So, if you're not clear on what it means, reset your intuition. Don't worry, if you keep learning, you'll get to know them well. That said, let's look at each concept.

The conductor

A conductor is a material through which current can flow. Okay, I know we haven't talked about what current is yet, but it doesn't matter, I'm sure you got it. If you think of a conductor, what comes to mind? Probably a wire or a metal plate. Cool, you guessed it. In general, metals are conductors. Maybe you also thought of water. It's very typical in B-series action movies where many bad guys are electrocuted at the same time for being in water. Well, that could happen, although it depends on the purity of the water. Pure water doesn't conduct, but real water has impurities (salts, sediments, various particles) that can make it conductive. A better or worse conductor, but a conductor, nonetheless. If you ever decide to take action and make hardware, the typical conductors you'll come across will be copper or tin wires or tracks. Tracks are those little lines you see on electronics boards. In the following image, you have some examples.

We've said that if current can flow through a material, it's a conductor. Perfect up to that point. However, there are good and bad conductors. They are better or worse depending on their resistivity (note: a concept similar to resistance, but different). Resistivity is a property of a material that defines how well it conducts current, regardless of its geometry. Resistance takes into account the geometry of an object. For example: copper, as an element, has a certain resistivity. A piece of copper with specific dimensions, on the other hand, has resistance. Let's make an analogy with chicken breasts. Chicken breasts cost €7 per kilo. That's the intrinsic cost of chicken breasts, regardless of the shape of the chicken you buy. When you go to the checkout and pay them, they weigh the chicken, and you pay a specific amount. For example, if you buy half a kilo, you pay €3.50.

Resistance increases with the length of an object and decreases with its cross-section. Conclusion: thick, short conductors have low resistance. Long, narrow conductors have high resistance. Less current will flow through materials with high resistivity than through those with low resistivity, for a set of equal conditions. If we want to flow the same current through a high- and low-resistivity material, we'll have to use much more energy in the high-resistivity material, and that's not good. In general, in electronics, we use low-resistivity materials when we want to transmit energy without loss. High-resistivity materials are also used, in a controlled manner, in a component called a resistor, which has a ton of applications (basically, it's found in 99% of circuits) and which we'll look at soon. Resistivity is measured in units of Ohm-meters [Ω m]. You can understand this unit as "how much it takes for current to flow per unit of distance." By the way, the inverse of the physical property of resistivity is sometimes used. This property is called conductivity, and the unit is Siemens per meter [S/m], also known as Mho [ ℧ ] (yes, it's an Ohm upside down...). The resistivity of conductive materials is more or less constant at "human" temperatures. There are some materials that are exceptions to this and are used, specifically, to measure temperature indirectly after measuring their resistivity.

The quintessential conductor in electronics is copper. The reason is that it has a very low resistivity and is also inexpensive. However, it is not the only one. Other common materials are silver, gold, or aluminum (and derivatives). The main advantage of silver is that it conducts a little better than copper, although because the difference is so small, it is not often used. Gold conducts significantly worse than copper, but it is a material that reacts very little to its environment, preventing it from deteriorating over time or due to its environment. Aluminum has the advantage of being lightweight, so it can be advantageous in very large circuits. For example, in electrical distribution networks, cables must be run between towers. If these cables are heavy, the number of towers must be increased, which affects the cost of the network and the environmental impact. In addition to those mentioned, there are many other materials, as well as various alloys. It is a very broad topic. However, as users of the materials (electronics designers), we don't need to go into too much detail.

Let's move on to the next thing.

The insulator

What isn't a conductor is an insulator. Easy. Let's move on to the next topic.

Okay, there's one thing that might be interesting to mention. Insulators don't allow current to pass through them. For example, we know a piece of wood doesn't conduct electricity. Neither do most plastics. What's the main use of insulators in electronics? To act as safety elements. I'm not telling you anything new when I say electricity can kill you, so it's logical that materials are used to ensure that users of electrical products don't fry themselves when handling them. Putting insulators on accessible parts is a fairly natural way to do it. In some cases, we choose one insulator or another not for its primary characteristic, which is not conducting current, but for its secondary characteristics. For example, we might be interested in whether it transfers temperature well or poorly, whether it's hard or soft, whether it's durable... It's a whole different world.

There's an insulator you've seen many times, though probably without realizing it. It's the PCB mask. A PCB, or printed circuit board , is a base on which electronic components are mounted. I've summarized the concept a bit; we'll look at it in detail later. PCBs are coated with an insulator used to cover the conductive tracks and prevent short circuits if conductive particles fall on them. This insulator gives PCBs the characteristic green color so associated with electronic products. In reality, there are masks in many colors, but the industry has de facto standardized green.

In the image above, a green layer covers the PCB. Beneath this is copper, which has a shiny brown color, but has been hidden by the mask. If you look closely, in the holes (called vias ), you can see how some areas in the inner radius have been left uncovered by the mask.

The semiconductor

Wow, that's a difficult subject to explain. Knowing how to "control" semiconductors is what has enabled virtually all technological development since the beginning of the 20th century, so you can imagine it's a tremendously broad topic. Let's start with the easy stuff; you'll learn the rest in your lifetime.

To summarize: a semiconductor is a material that can behave as a conductor or an insulator. The key is that we can control how it behaves through electrical stimuli. We are interested in semiconductors' extreme states, that is, whether they conduct or insulate, as well as their intermediate states, that is, whether they conduct better or worse depending on the intended application. Extreme states give rise to a branch of electronics known as digital electronics, which includes microprocessors, memory, logic gates, FPGAs, etc. Their use in extreme states is not limited to this branch of electronics. Semiconductors are found in extreme states in virtually all applications. We find them in "controlled resistivity" mode in communications and audio systems. The most common semiconductor components are diodes and transistors, which, in turn, have many variants. Diodes are semiconductors that allow current to flow in only one direction. The most famous diodes are LEDs ( Light Emitting Diodes) , which function like normal diodes, but emit light of a certain color when in conducting mode. Transistors allow current to flow only when the transistor is activated by certain electrical conditions. In future posts, we will see, in abundance, different applications of semiconductors, as well as the electrical components that can be used in a circuit. Semiconductor components are used in association with each other in different ways. The famous "chips," or integrated circuits, are nothing more than a bunch of semiconductor components associated in certain ways to perform a specific function and packaged within a "package."

In the image above, you can see a close-up of a chip. What you're actually seeing is the package, since the semiconductors are inside.

The most widely used semiconductor material is silicon because it is abundant (it can be obtained from sand). Natural silicon is an insulator. However, impurities can be added that convert it into a conductor. The correct addition of impurities allows it to alternate between being a conductor and an insulator depending on the electrical conditions to which the material is subjected. The process of adding impurities is called doping the material. The physics involved in semiconductors is very complex, and we won't go into it for now.

Semiconductor manufacturing processes have evolved over the years at an incredible pace. As of this article's publication, semiconductors are manufactured between 2 and 10 nanometers. This is a million times smaller than a millimeter. The semiconductor industry is truly sophisticated, to the point that its control has become a geostrategic issue, but let's not stray from the topic. For several decades, efforts have been made to reduce the size of transistors in order to pack more of them into a specific space and, thus, increase computing power. The rate at which transistor size decreases over time is known as Moore's Law. This law (which is empirical) states that the number of transistors that fit on a chip doubles approximately every two years. This progression is quite dramatic if you look at it over a long period of time. Whether or not this progression is sustainable over time, only the future will know. It has been predicted many times that it would not be the case and (although a little more slowly) it is still there.

Where are we going?

In this post, we've covered the most fundamental aspects of electronics. It consists of properly combining conductive, semiconductor, and insulating materials to achieve the things we're interested in. Okay, that's a bit of a vague description. It's like telling you that building a house consists of moving different types of materials and placing them in a precise order. Technically, that's true, but without a lot of knowledge and planning, you won't build anything. Well, the same thing happens here, and that's what we're going to address in the following parts of this series, starting with the basics: What is a circuit?