lunes, 28 de junio de 2010

The History of the Integrated Circuit

Our world is full of integrated circuits. You find several of them in computers. For example, most people have probably heard about the microprocessor. The microprocessor is an integrated circuit that processes all information in the computer. It keeps track of what keys are pressed and if the mouse has been moved. It counts numbers and runs programs, games and the operating system. Integrated circuits are also found in almost every modern electrical device such as cars, television sets, CD players, cellular phones, etc. But what is an integrated circuit and what is the history behind it?

Electric Circuits

The integrated circuit is nothing more than a very advanced electric circuit. An electric circuit is made from different electrical components such as transistors, resistors, capacitors and diodes, that are connected to each other in different ways. These components have different behaviors.

The transistor acts like a switch. It can turn electricity on or off, or it can amplify current. It is used for example in computers to store information, or in stereo amplifiers to make the sound signal stronger.

The resistor limits the flow of electricity and gives us the possibility to control the amount of current that is allowed to pass. Resistors are used, among other things, to control the volume in television sets or radios.

The capacitor collects electricity and releases it all in one quick burst; like for instance in cameras where a tiny battery can provide enough energy to fire the flashbulb.

The diode stops electricity under some conditions and allows it to pass only when these conditions change. This is used in, for example, photocells where a light beam that is broken triggers the diode to stop electricity from flowing through it.

These components are like the building blocks in an electrical construction kit. Depending on how the components are put together when building the circuit, everything from a burglar alarm to a computer microprocessor can be constructed.

The Transistor vs. the Vacuum Tube

Of the components mentioned above, the transistor is the most important one for the development of modern computers. Before the transistor, engineers had to use vacuum tubes. Just as the transistor, the vacuum tube can switch electricity on or off, or amplify a current. So why was the vacuum tube replaced by the transistor? There are several reasons.

The vacuum tube looks and behaves very much like a light bulb; it generates a lot of heat and has a tendency to burn out. Also, compared to the transistor it is slow, big and bulky

When engineers tried to build complex circuits using the vacuum tube, they quickly became aware of its limitations. The first digital computer ENIAC, for example, was a huge monster that weighed over thirty tons, and consumed 200 kilowatts of electrical power. It had around 18,000 vacuum tubes that constantly burned out, making it very unreliable.

When the transistor was invented in 1947 it was considered a revolution. Small, fast, reliable and effective, it quickly replaced the vacuum tube. Freed from the limitations of the vacuum tube, engineers finally could begin to realize the electrical constructions of their dreams, or could they?

The Tyranny of Numbers

With the small and effective transistor at their hands, electrical engineers of the 50s saw the possibilities of constructing far more advanced circuits than before. However, as the complexity of the circuits grew, problems started arising.

When building a circuit, it is very important that all connections are intact. If not, the electrical current will be stopped on its way through the circuit, making the circuit fail. Before the integrated circuit, assembly workers had to construct circuits by hand, soldering each component in place and connecting them with metal wires. Engineers soon realized that manually assembling the vast number of tiny components needed in, for example, a computer would be impossible, especially without generating a single faulty connection.

Another problem was the size of the circuits. A complex circuit, like a computer, was dependent on speed. If the components of the computer were too large or the wires interconnecting them too long, the electric signals couldn't travel fast enough through the circuit, thus making the computer too slow to be effective.

So there was a problem of numbers. Advanced circuits contained so many components and connections that they were virtually impossible to build. This problem was known as the tyranny of numbers.

Jack Kilby's Chip - the Monolithic Idea

In the summer of 1958 Jack Kilby at Texas Instruments found a solution to this problem. He was newly employed and had been set to work on a project to build smaller electrical circuits. However, the path that Texas Instruments had chosen for its miniaturization project didn't seem to be the right one to Kilby.

Because he was newly employed, Kilby had no vacation like the rest of the staff. Working alone in the lab, he saw an opportunity to find a solution of his own to the miniaturization problem. Kilby's idea was to make all the components and the chip out of the same block (monolith) of semiconductor material. When the rest of the workers returned from vacation, Kilby presented his new idea to his superiors. He was allowed to build a test version of his circuit. In September 1958, he had his first integrated circuit ready. It was tested and it worked perfectly!

Although the first integrated circuit was pretty crude and had some problems, the idea was groundbreaking. By making all the parts out of the same block of material and adding the metal needed to connect them as a layer on top of it, there was no more need for individual discrete components. No more wires and components had to be assembled manually. The circuits could be made smaller and the manufacturing process could be automated.

Jack Kilby is probably most famous for his invention of the integrated circuit, for which he received the Nobel Prize in Physics in the year 2000. After his success with the integrated circuit Kilby stayed with Texas Instruments and, among other things, he led the team that invented the hand-held calculator.

Robert Noyce

Robert Noyce came up with his own idea for the integrated circuit. He did it half a year later than Jack Kilby. Noyce's circuit solved several practical problems that Kilby's circuit had, mainly the problem of interconnecting all the components on the chip. This was done by adding the metal as a final layer and then removing some of it so that the wires needed to connect the components were formed. This made the integrated circuit more suitable for mass production. Besides being one of the early pioneers of the integrated circuit, Robert Noyce also was one of the co-founders of Intel. Intel is one of the largest manufacturers of integrated circuits in the world.

Chip Production Today - in Short

Chip production today is based on photolithography. In photolithography a high energy UV-light is shone through a mask onto a slice of silicon covered with a photosensitive film. The mask describes the parts of the chip and the UV-light will only hit the areas not covered by the mask. When the film is developed, the areas hit by light are removed. Now the chip has unprotected and protected areas forming a pattern that is the first step to the final components of the chip.

Next, the unprotected areas are processed so their electrical properties change. A new layer of material is added, and the entire process is then repeated to build the circuit, layer by layer. When all the components have been made and the circuit is complete a layer of metal is added. Just as before, a layer of photosensitive film is applied and exposed through a mask. However, this time the mask used describes the layout of the wires connecting all the parts of the chip. The film is developed and the unexposed parts are removed. Next, the metal not protected with film is removed to form the wires. Finally, the chip is tested and packaged.

When making chips today, a process called "stepping" is often used. On a big wafer of silicon the chips are made one next to the other. The silicon wafer is moved in steps under the mask and the UV-light to expose the wafer. In this way, chip after chip can be made using the same mask each time.

Below is a more sequential description of the process of making a modern integrated circuit. But let us first take a look at the special place where integrated circuits are produced - the clean room.

The Clean Room

The sizes of the components on chips produced in a modern chip fabrication plant are extremely small. For a better understanding of how small they are, pick a hair from your head and cut it in half. Now look at the cross section. On this tiny area, hard to see with the bare eye, you can fit thousands of modern transistors.

With sizes this small, the production of a chip demands precision at an atomic level. Tiny particles like a hair, a speck of dust, a dead skin cell, bacteria or even the single particles in tobacco smoke become huge objects that are big enough to ruin a chip.

Therefore, chip production takes place in a clean room. This is a specially designed room, where furniture is built from special materials that don't give off particles, and where extremely effective air filters and air circulation systems change the air completely up to ten times a minute.

To further prevent contamination, workers wear special suits called "bunny suits." These protective outfits are made of ultra clean material and sometimes have their own air filtering systems.

Chip Production Today - in Detail

Building an integrated circuit like a computer chip is a very complex process. It is divided into two major parts, front end and back end. In the front end, you make the components of the circuit. In the back end, you add metal to connect the components and then you test and package the chip. Below is a simplified description of the steps.

Lenny Z Perez M

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