Microprocessor

Microprocessor

At the core of every computer is a microprocessor, a device that has been called the greatest invention of the century. The dictionary defines the microprocessor as "a semiconductor central processing unit usually contained on a single integrated circuit chip." More important than what a microprocessor is, is what a microprocessor can do.

The microprocessor is also known as a central processing unit, or CPU. The CPU actually runs the programs in a device, be it a computer, personal digital assistant (PDA), or cell phone; but the CPU depends on instructions from other microcomponents to tell it what to do. These instructions usually come from a software program that is stored in memory.

The CPU directs computer operations by sending control signals, memory addresses, and data from one area of the computer to another by using interconnected pathways called a bus. At locations along the bus are input and output ports that other components, such as memory and support chips, or co-processors, are attached. Data traveling to and from the CPU to other parts of the computer passes through these input/output (I/O) ports.

The manufacture of microprocessors begins with creation of a nearly pure (99.999999 percent pure) silicon nugget that serves as a nucleus for the growth of a cylinder of silicon called an ingot. The silicon ingot is grown in such a way that electricity flows through it in a predictable way. The ingot is cut into 8-inch or 12-inch diameter wafers, where each wafer is polished to a mirror-like finish and coated with an insulating material in preparation for building microprocessors.

Each 8-inch silicon wafer can yield hundreds of individual microprocessors. Many manufacturers, such as Intel, are retooling their microprocessor labs for 12-inch wafers. The microprocessor yield is much higher on a 12-inch wafer, meaning there is less scrap, or unused area of the wafer. Such a retooling effort is very expensive, costing hundreds of millions or even billions of dollars.

The millions of tiny transistors on these microprocessors are created using layers of conductive and insulating materials through a photolithography process that uses light and light-sensitive materials to yield layers of etched and printed lines of insulating and conducting material. Current technology is fast approaching line widths of 0.13 microns; one micron is one-millionth of a meter, or about 1/300th the thickness of a human hair. The vertical thickness of layers is measured in angstroms, where one angstrom is the average width of an atom. Some layers today measure just a few angstroms thick.

Once the individual microprocessors have been cut from the wafer, they undergo a wafer sort to separate the functioning microprocessors from those that are defective. The next major step is to package the microprocessor in way that allows it work in a PC or other device. Microprocessor packaging protects the microprocessor from moisture, scratches, and contamination, and provides the electrical contacts so the microprocessor can communicate with other components of the device. An automated wire-bonding process establishes electrical connections between the microprocessor and the package pins that connect the chip to the computer or other device.

Microprocessor packaging can come in several configurations in plastic and ceramic. "Plastic quad flat packaging," also known as PQFP, is a type of packaging used with many types of microprocessors, is soldered directly to a PC or device printed circuit board (direct solder is also known as "surface mount technology"). "Ceramic pin grid array" (PGA) technology is better suited to higher speed microprocessors because of ceramic's excellent thermal and electrical properties. This packaging technology is very expensive as it uses gold pins to enhance the electrical connections between the microprocessor and the PC or other device. The pins plug into a printed circuit board-mounted socket, making it easy to upgrade to faster microprocessors within the same family.

Gordon Moore, one of the founders of Intel, discovered that every new process technology doubles the number of available transistors for a given wafer size (Moore's Law). Today, 0.13 micron process technology is available, and microprocessors can reach speeds of 2 gigahertz (GHz). Microprocessor process technology of the future must be able to find a way to overcome the limitations submicroscopic wires impose on electron speed, clock frequencies, heat dissipation, and power consumption. Experiments have been carried out with surface-emitting microlasers, which can transfer encoded data at the speed of light. Such technology is not only ultrafast and energy efficient, it consumes far less power than silicon-based chips. Some experts predict that the next microprocessor process technology will be a revolution, and require a leap in physics, perhaps to nanotechnology and molecular computing. Should that occur, then perhaps Moore's Law will have to be restated.