Silicon is the chief ingredient of both glass and semiconductor devices, yet the physical properties of glass?

Question

are different from those of semiconductor devices. Why?

Answer 1

Glass is made from silica, which is silicon dioxide. Semiconductors are made from pure silicon doped with small amounts of other elements. So they are chemically very different.

Answer 2

Both glass and pure silicone are good insulators.

The crystalline structure of pure silicone can be intentionally "doped" with impurities to give it specific electrical characteristics.

For instance, when the pure silicone is doped with phosphorus, the electron density of the crystal is increased - the phosphorus atoms becomes part of the lattice structure of the crystal and, due to the excess of electrons, the material now becomes an N type semiconductor.
On the other hand, if boron is added to the pure silicone, it creates areas of electron deficiencies - and the material becomes a P type semiconductor.

If the two materials are joined, a voltage potential of approximately 0.6 volts will be necessary to conduct current through the junction due to the doped potentials introduced into the materials - and this DC current will only flow in one direction due to the junction becoming wider (because the electrons and "holes" are pulled away from the junction) if the current is reversed, making this an excellent rectifier or diode.
The same principal is used in transistors, diodes, integrated circuits and many other solid state devices.

Answer 3

the two glass and organic silicone are good insulators. The crystalline shape of organic silicone could be intentionally "doped" with impurities to grant it particular electric powered features. case in point, whilst the organic silicone is doped with phosphorus, the electron density of the crystal is greater - the phosphorus atoms will become portion of the lattice shape of the crystal and, because of the surplus of electrons, the fabric now will become an N variety semiconductor. on the different hand, if boron is extra to the organic silicone, it creates areas of electron deficiencies - and the fabric will become a P variety semiconductor. If the two ingredients are joined, a voltage ability of roughly 0.6 volts would be necessary to habit present day interior the trail of the junction because of the doped potentials presented into the ingredients - and this DC present day will in simple terms flow in a single direction because of the junction transforming into wider (because of the fact the electrons and "holes" are pulled faraway from the junction) if the present is reversed, making this an dazzling rectifier or diode. a similar significant is utilized in transistors, diodes, built-in circuits and various different sturdy state instruments.

Answer 4

Semiconductors are made with almost pure silicon, right, and present of course semiconductor properties, for example pure silicon absorbs almost visible light, for this reason silicon is also used for example as photodiode or in CCD cameras. Glass is essentially made from silicon oxide SiO2 with aditives, their properties are far from silicon is a dielectric: for example SiO2 is an electrical insolator as everybody knows and also doesnt absorbs visible light of course!.

Answer 5

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Answer 6

Okay, glass is a mixture of different things, silicon dioxide (quartz) lime (calcium oxide) and alkali (potassium salts), for one of the most common varieties of glass. Note that these are all compounds, which are further compounded together. And the different elements are mixed through the entire mass of the material.

The silicon used in semiconductors is highly purified. Through various industrial processes, which I won't get into here, it is purified over 99.9999 percent pure. (If you are really interested, search a description of the Czochralski zone-refining process. It is complex and time consuming, but you will understand better how difficult it is to make semiconductors. This is why we can't just make them at home on our kitchen ovens.)

The purified silicon (called, intrinisic silicon, silicon alone) is non-conductive. Tiny amounts of impurities must be carefully introduced to make it very slightly conductive (that's the 'semi' part of semiconductors.)

And they must be introduced in the right places. Perhaps the best way to imagine a semiconductor, like a microprocessor, is to liken it to a city. It has buried electrical power cables, sewerage, subways, steam pipes, oil pipelines, gas pipelines, etc. We have a map of each below-ground system. And, we must be careful when installing one basic service, not to interfere with any of the others!

With a city, we could dig the street up with backhoes and bulldozers, but we can't do that with silicon. What we have to do is somehow get the right kind of impurities into the crystal structure of the silicon in the right places.

The most common way of doing that is either to implant the atoms into the silicon crystal in a high speed beam of ions, or to diffuse them in as a gas under very high temperatures and pressures.

The map, the patterns that you want to lay down, must be reduced millions of times and copied onto the surface of the silicon as a pattern of what is called 'resist'. This is done by photographic means. Then the ion implantation or gas diffusion process can take place.The ions or gas cannot penetrate the resist, only the spaces in the resist pattern where the impurities are intended to go.

After each such step in the process, the wafer (a big slice of silicon, like a slice from a loaf of bread, before it is cut up into chips) must be cleaned, inspected, the resist cleaned off, and a new layer of resist put on for the next photographic step. Then the next layer of impurities is put in.

You can see from this that the whole thing takes many, many steps. Some complicated microprocessors may take 10,000 process steps...! Probably a quarter of them are cleaning and or inspection, but they are essential.

And to put the the whole thing in scale, think of icing a white cake in a pattern. Into the spaces between the icing design, you drip drops of red and blue and yellow food coloring. Wherever the drops overlap, red and blue make purple, or red and yellow make orange, or blue and yellow make green. But, the design is only in the top very thin layer of the cake!

So it is with a silicon wafer. The semiconducting part is just a very thin top surface layer; the ions or gasses have penetrated maybe 0.001 milimeter, while the wafer thickness might be 0.2 milimeter.

Okay, so now what? What do those impurities do...? There are two kinds, the N's and the P's. The N's are those kind of atoms that have a SINGLE electron in their outer shells. The P's are those that have their outer shells filled EXCEPT FOR a single electron. (Think of the different color food colorings.)

We put down a pattern of one color, first. Since this is the first layer, it will affect every layer that is put down after it. So, the base layer, which is called the substrate, is either N type or P type. This covers the entire surface of the water.

The entire design of the microprocessor started with this, way back on the drawing board. (today, we would say the CAD. CAM drafting program.) Each step of the process had to be calculated and the effects predicted, in order to make sure that the finished product does what it is intended to do.

Then we keep going: put down a layer of resist, inspect, clean, photographically project the pattern onto the resist, inspect, clean, wash away the unexposed resist, inspect, clean, diffuse the gas or implant the ions, inspect, clean, remove the resist from the previous step, inspect, clean.

When all the N and P layers have been put in, we have to make connections between the different devices of the microprocessor.That goes on the surface. Then, there is a 'passivation' layer, and that is silicon dioxide, quartz. It is done by introducing hot oxygen to the surface of the wafer, and it oxidizes, so that nothing else can get into the N and P layers. Certain spaces are left open, (masked off with resist, which is removed later) so that connections can be made to the finished microprocessor.

Then, the wafer is tested, with extremely fine probes that make contact (at the bare spots) to each microprocessor in turn. They run a sample program to test it. If it fails to operate properly, it is marked with a dot of ink. The wafer is then cut into 'chips', and the marked ones are discarded. They cannot be repaired-- they are waste material, and this is part of what contributes to the high cost of semiconductor devices.

(By the way, I forgot to mention, but I hope you can see-- the wafers are never touched by hand. Everything must be done under the most clean conditions. A speck of dirt smaller than the diameter of the finiest baby hair can ruin a semiconductor in process, stopping the N or P material from reaching the right place, or causing short circuits between adjacent area. On the scale of our city, it would be like digging for a new subway and cutting through the gas mains and the water mains! So everything is prepared in specially-designed 'clean rooms' and handled by robotic machines. Again, the amazing thing is not why computers are so expensive, but that they are so cheap! It is a good thing the manufacturers make millions of them and that they take very close precautions to keep their quality up there.)

So we have our finished microprocessor. What happens inside...? Let's look at two layers. We have an N layer and a P layer, one on the other. There is no space between them-- they are in contact. Say we apply a voltage (electrical pressure) to either side of the junction, where the two layers meet. Think of row upon row of N-type impurity atoms and P-type impurity atoms facing each other. (The whole junction, where the N's and the P's meet, might only be a few hundred atoms thick!)

Remember the basic laws of the universe: like charges repel and unlike charges attract (no such thing as gay electrons!) Suppose we put a negative charge on the P side and a positive charge on the N side. (Remember the N atoms are the ones with the single electron in the outermost orbital shell, and the P type atoms are the ones with only space for one more electron in the outermost orbital shell.)

The atoms themselves can't move. They are fixed, held in place by the crystal structure of the silicon. The single electrons in the N type impurity atoms are attracted to the positive voltage that is being applied. Those electrons move (rotating to the opposite side of the atom) as far as they can toward the positive voltage.

(I wish I had some graphics to show you, because this is a little difficult to imagine. But bear with me.)

The electrons in the P type impurity atoms are also attracted to the positive voltage, and the space they have in their outermost orbital shell (the place where an extra electron could fit) behaves as if it were a positive charge itself, and it moves as far away as possible from the positive voltage that is being applied, rotating to the far side of the atom.

What has happened, is that the single electrons and the single spaces for electrons (called 'holes') have moved as far away as possible from each other, facing away from the junction region.

Now, the junction region has become a 'no-man's land', like the demilitarized zone at the 38th parallel between North and South Korea. There are no charge carriers (electrons or holes) available to carry a current, and the junction is said to be 'depleted'.

What good does this do us...? Well, half of being able to control electrical currents and get them to do what you want is to be able to stop them when you don't want them to flow. So now, let's suppose that we reverse the polarity of the voltage that is being applied to the junction.

We now put the negative voltage to the N side of the junction, and the positive voltage toward the P side of the junction. The charge carriers (electrons and holes) rotate around the atoms so that they are facing each other. Remember, the junction region may be only a couple hundred atoms thick...? Once the applied voltage gets over 0.7 volt (for silicon) the depletion region collapses!

Now, it is like the Berlin Wall has come down! the electrons go streaming across, temporarily fall into the holes and get passed on to the next atom in line. We have a current flow!

What this means is that in this single junction, we have a device that can act as a one-way gate for electrons. This is a very useful and basic property that we can use to build more complicated electronic devices; it is called a diode. Diodes are used for processes called detection and rectification (you can look those up on your own.)

To make a transistor, we have three layers, with two junctions between them. It can act as a controlled switch, allowing a very small current to control a much larger one. We can even make a transistor act like a clamp on a garden hose, to control the amount of current, turning it on or off without interfering with the current.

Binary math is used (on/off values, ones and zeroes) to do everything in your computer. Your microprocessor has rows and columns of transistors in it; each row standing for a single pixel on your screen. The row takes the binary values from a similar row of transistors (on a memory chip) or from the magnetic patterns (on your disk drive) and transfers the pattern to the video controller, which then lights up each pixel to the proper brightness level, activating the correct LCD element in your screen to produce the right colors. Then letters and numbers can be built up from that, and you can see my Answer!

I figured that you would have a couple more questions, so I tried to answer them, too. Hope this helps you to understand better!

28 OCT 06, 1356 hrs.