{"id":1798,"date":"2022-01-16T21:10:08","date_gmt":"2022-01-16T20:10:08","guid":{"rendered":"https:\/\/lms.nanoproject.eu\/lms\/?post_type=unit&p=1798"},"modified":"2022-01-16T21:10:38","modified_gmt":"2022-01-16T20:10:38","slug":"transistor-the-magic-device","status":"publish","type":"unit","link":"https:\/\/lms.nanoproject.eu\/lms\/unit\/transistor-the-magic-device\/","title":{"rendered":"Transistor, the magic device"},"content":{"rendered":"

In the very beginning, we briefly mentioned how a computer works. Let us examine that concept step by step, starting from the whole ensemble down to the transistor.<\/p>\n

Obviously, you can write documents, email your friends or browse the world wide web with your computer. But what is actually happening in this machine to make those things work? Expressed in a very simple way, a computer only manipulates data. In this context the information is stored, retrieved and processed. Nonetheless what kind of data or information we are talking about? Back in the days the input as well as the output was limited to digits, which also is the reason why the name of the device is derived from the verb \u201ccompute\u201d. Even though modern PCs can also handle letters or sounds, those in turn are coded with digits. Consequently, the computer is a \u201csimple\u201d calculating machine up to this day. At this point we should remember that we use the binary system for that coding, which only uses 1s and 0s. For instance, every single letter is coded with a defined number and series of those binary digits. Thus, every movie, picture or song becomes a series of 0s and 1s for your PC.<\/p>\n

Now that we know about the basic operating-principle of a computer, a remaining question is: How do we generate those 0s and 1s? This can be imagined by thinking of the computer as a number of switches. Each and every one of those can be turned on or off, which is defined as 0 or 1. Increasing the number of switches means you increase the number of 0 and 1.<\/p>\n\n\n\n\n
\n

Definition<\/strong><\/p>\n<\/td>\n<\/tr>\n

What is a computer<\/strong><\/p>\n

A computer is a calculating machine. The device only operates with 0s and 1s. Latter are created with miniaturized switches.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

To get a step closer to the understanding of how a computer works, we should ask the question: How do those circuits, containing the switches, look like? What is the difference to the ones we are familiar with from the physics lessons in school or the fuse box at home? Latter are made of discrete building blocks such as transistors, diodes, capacitors, and resistors. The circuit in your PC on the other hand takes all of the discrete simple functions of all of the devices and integrates them on one single chip. This is the reason why they are called integrated circuits. If you ever opened such an electric device, you could have seen them as the little black squares or rectangles as in the picture below.<\/p>\n

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One of those black boxes, basically contains a single silicon chip on the inside, on which all of the building blocks mentioned before are printed on. The fact that nowadays it\u00b4s possible to bring billions of electronic components on those semiconductors, paved the way for microprocessors not being bigger than a bunch of square millimetres. You can imagine that with the miniaturization of ICs also the development of innovative physical and chemical processing technologies became more and more interesting. Just to have that mentioned alongside: This is the point where nanotechnology meets the different disciplines of science again, to produce such great modern devices. And we already know that the efforts of many developers paid off, by recalling the graphic of Moore\u00b4s Law to our mind again. There we saw that the number of transistors on a single chip increased tremendously and is still rising until today. Right now, we should understand that with more of these structures on the chip, microprocessors can reach better performances, because they can handle more 0s and 1s at the same time. And to implement an increasing number of components on the same sized chip, all of those single building blocks have to shrink in their size. For this reason, it is a good point in time, to have a closer look at the transistor, which can be understood as our miniaturized switch.<\/p>\n\n\n\n\n
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Definition<\/strong><\/p>\n<\/td>\n<\/tr>\n

What is an IC<\/strong><\/p>\n

An integrated circuit consists of discrete electronic components of a single silicon chip.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

There are different kinds of transistors. We want to understand the structure and operating principle of the \u201cMOSFET\u201d. The name MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor and already tells us the structure of the device. The basis of the device is a flat silicon bulk material, which contains intended impurities. Latter is called \u201cdoping\u201d. This bulk material can be p-doped (NMOS) or n-doped (PMOS). Those types of material differ in their charge carriers, which are electrons for NMOSFETs and holes for PMOSFETs. Our discussion will be about NMOSFETs. In this case the p-doped silicon substrate (you can imagine this as a slightly positive charged region) is drawn in blue in the picture below. In this material are two red areas, which are doped with a different type of ion. This generates regions of a n-type (you can imagine this as a slightly negative charged region) material, the so called \u201csource\u201d and \u201cdrain\u201d. The region between those two is called the \u201cchannel\u201d and is covered with an insulating oxide layer. On top of this oxide layer is a conducting metal material, what is referred to as the \u201cgate\u201d.<\/p>\n

The very basic concept of a MOSFET is to control the electron flow between the source and the drain, which is driven by a voltage between source and drain. The electron flow is then controlled by applying a voltage to the gate, what induces an electric field and influences the charge carriers in our doped material. Latter effects how good or bad electrons can be moved from source to drain. Nevertheless, let us dive a little bit deeper into those processes step by step.<\/p>\n

First of all, we want to describe the \u201coff\u201d-state of our switch. When no voltage is applied at the gate, no free charge carriers (electrons in our case) are present in the channel. Hence no electrons are moving from source to drain and there is no current. With this simple case we already defined the 0 for the computer. But how do we get the 1s? What we have to do is to apply a voltage at the gate, the so-called gate-voltage. This voltage in the case of NMOSFETs is always positive. For modern processors a gate-voltage around 0.2 V can be enough, which is very little. To get a feeling: A normal household battery operates at 1,5\u00a0V, a doorbell at 8 V, and a car battery at 12 V. So, we really do not need much energy. But why do we need this gate-voltage? What comes along with this voltage is the electric field that effects the p-doped bulk material even through the oxide layer. This induces holes in the bulk p-type substrate near the insulating layer to be repelled. Hence, there are less and less holes at this surface with an increasing gate-voltage. It makes sense that we call that area the \u201cdepletion-zone\u201d. After that, electrons from the n-type areas (the source and the drain) are attracted in this former depletion-zone and we generated a channel with a magnitude of negative charge carriers. We call this one the \u201cinversion-layer\u201d. To not lose the insight, this situation is shown in the figure below.<\/p>\n

\"\"<\/p>\n

Now we end up with a n-type channel in-between the also n-type source and drain. This enables electrons to flow through the device, which is shown with the red arrows. Thus, we reached our target and can define the digit 1 for our computer. By the way: We can imagine that higher gate-voltages attract more charge-carriers, the inversion-layer gets wider, and we create a channel, which potentially can transport more electrons.<\/p>\n\n\n\n\n
\n

Definition<\/strong><\/p>\n<\/td>\n<\/tr>\n

What is a transistor<\/strong><\/p>\n

The most common type on ICs is the MOSFET (metal-oxide-semiconductor field effect transistor). One of the applications of these transistors is to produce 0s and 1s in computers, as we described earlier.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"author":1,"featured_media":0,"parent":0,"comment_status":"open","ping_status":"closed","template":"","format":"standard","meta":{"_vibebp_attr":"","_vibebp_dimensions":"","_vibebp_responsive_height":"","_vibebp_accordion_ie_support":"","footnotes":""},"module-tag":[],"class_list":["post-1798","unit","type-unit","status-publish","format-standard","hentry"],"_links":{"self":[{"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/unit\/1798","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/unit"}],"about":[{"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/types\/unit"}],"author":[{"embeddable":true,"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/comments?post=1798"}],"version-history":[{"count":2,"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/unit\/1798\/revisions"}],"predecessor-version":[{"id":1827,"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/unit\/1798\/revisions\/1827"}],"wp:attachment":[{"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/media?parent=1798"}],"wp:term":[{"taxonomy":"module-tag","embeddable":true,"href":"https:\/\/lms.nanoproject.eu\/lms\/wp-json\/wp\/v2\/module-tag?post=1798"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}