How do ics work i am really confused!!!!!!!!!!!?

Question

im one of those people who want to know every exact detail like where the electrons are going and how this happens and why this works so can u try to explain ics to me plz?

Answer 1

IC are basically an entire circuit that has been built into a single unit. If you look at something like the 741 op-amp they give you an equivalent circuit.

As far as I remember from my friend that worked for Intel is that they etch out the circuit from a semiconductor substrate.

Answer 2

An IC is a piece of semiconducting material (usually silicon) where metallurgical processes are used to build circuitry directly on the die (the name for the piece of base material).

There are different processes and each makes different parts of the components. You can't easily make certain kinds of components using common processes. So, for example, a CMOS process can make n-mos and p-mos transistors as well as poor quality resistors and high quality capacitors. But you can't make, for example, significant values of inductance or a bipolar transistor using these processes.

The reason these processes result in inexpensive and tiny devices it that the processes are photographic in nature, so it is almost like printing, for example. If you want business cards made up, all the cost is in the first business card. So 100 cards might be $10, but 1000 cards are $15. The cost is setting up, not in the actual printing.

So consider a typical CMOS chip. It will have n-mos and p-mos FET transistors, resistors, and wires. They start with a silicon wafer which will be cut into many die at the end (they duplicate the same IC over and over again).

The silicon will probably be lightly "doped" let's say as n-type. To make the n-mos transistor channel, they will put the wafer in an oven. This will cause a thin layer of oxidation to grow (SiO2). Then they will put photoresist on top of the wafer and use a large "negative" to image a pattern on the photoresist. The "negative" (called a mask) is large but the projector shoots it down to the tiny sizes required on the wafer. A chemical bath will wash away the photoresist where light hit it (or sometimes, where light didn't hit it, which requires a reverse mask).

Now the wafer is exposed where we need n channels and "covered" where we don't want any change. The wafer is bombarded with ions which creates the "n" material where the wafer is exposed.

Another bath strips the resist and then they do it all over again to make the P channels. This photo process is call photolithography.

Another process will put a thin layer of glass (SiO2 but thicker than the last one) to insulate the transistors. Another photoresist step will cut holes in the glass (using acid, probably HF) where connections are required.

The wafer will then be put in an oven with silane (SiH4) which deposits a polysilicon layer. This will form the transistor gates and most resistors. Some poly will be one plate of a capacitor. Another photo step leaves photoresist on the polysilicon that you want to keep. An acid bath will wash away the uncovered poly. Next comes another layer of glass, and cuts in the glass.

The next thing to do is deposit a thin film of aluminum on top of the chip (usually using a sputtering technique). Another photoresist/acid step cuts away the aluminum you don't want. The aluminum that is left will form conductors (wires connecting everything together), very small resistors, and top plates of capacitors.

Finally, another layer of glass is placed down (called passivation) just to make everything stable. The only cuts made in this layer are around the bond pads that will connect the IC to the outside world.

That's how one type of IC is made and even then there is variations in the process possible. This is just one way to do it. There are also ICs that have multiple metal layers, use copper instead of aluminum, or don't use silicon as a base.

As for "where the electrons are going" it is important to realize that an IC circuit is -- more or less -- just like a regular circuit and so to answer that question we'd need to know what IC you wanted to know about. There are a few differences. For example, resistor tolerances are poor on an IC but can be very good in real world circuits. On the other hand, by controlling the size of the capacitor plates and the thickness of the glass between it is very easy to create two capacitors that have a very exact ratio of capacitance -- something hard to do in the real world. It is also easy to depend on transistors on an IC having very similar characteristics and operating at nearly the same temperature, unlike a "real" circuit. But in any event, there is no way to generically answer how an IC operates at the electrical level.

Good overview on the manufacturing process: http://en.wikipedia.org/wiki/Semiconduct...

Answer 3

It would take a book to describe in detail how ICs work.

Concentrate on understanding transistors and resistors and capacitors.

An IC is just a collection of these components formed into circuits. In some cases millions of transistors make up one IC.