Integrated Circuits(集成电路)
英文原稿:
The Integrated Circuit
Digital logic and electronic circuits derive their functionality from electronic switches called transistor. Roughly speaking, the transistor can be likened to an electronically controlled valve whereby energy applied to one connection of the valve enables energy to flow between two other connections.By combining multiple transistors, digital logic building blocks such as AND gates and flip-flops are formed. Transistors, in turn, are made from semiconductors. Consult a periodic table of elements in a college chemistry textbook, and you will locate semiconductors as a group of elements separating the metals and nonmetals.They are called semiconductors because of their ability to behave as both metals and nonmetals. A semiconductor can be made to conduct electricity like a metal or to insulate as a nonmetal does. These differing electrical properties can be accurately controlled by mixing the semiconductor with small amounts of other elements. This mixing is called doping. A semiconductor can be doped to contain more electrons (N-type) or fewer electrons (P-type). Examples of commonly used semiconductors are silicon and germanium. Phosphorous and boron are two elements that are used to dope N-type and P-type silicon, respectively.
A transistor is constructed by creating a sandwich of differently doped semiconductor layers. The two most common types of transistors, the bipolar-junction transistor (BJT) and the field-effect transistor (FET) are schematically illustrated in Figure 2.1.This figure shows both the silicon structures of these elements and their graphical symbolic representation as would be seen in a circuit diagram. The BJT shown is an NPN transistor, because it is composed of a sandwich of N-P-N doped silicon. When a small current is injected into the base terminal, a larger current is enabled to flow from the collector to the emitter.The FET shown is an N-channel FET, which is composed of two N-type regions separated by a P-type substrate. When a voltage is applied to the insulated gate terminal, a current is enabled to flow from the drain to the source. It is called N-channel, because the gate voltage induces an N-channel within the substrate, enabling current to flow between the N-regions.
Another basic semiconductor structure is a diode, which is formed simply by a junction of N-type and P-type silicon. Diodes act like one-way valves by conducting current only from P to N. Special diodes can be created that emit light when a voltage is applied. Appropriately enough, these components are called light emitting diodes, or LEDs. These small lights are manufactured by the millions and are found in diverse applications from telephones to traffic lights.
The resulting small chip of semiconductor material on which a transistor or diode is fabricated can be encased in a small plastic package for protection against damage and contamination from the out-side world.Small wires are connected within this package between the semiconductor sandwich and pins that protrude from the package to make electrical contact with other parts of the intended circuit. Once you have several discrete transistors, digital logic can be built by directly wiring these components together. The circuit will function, but any substantial amount of digital logic will be very bulky, because several transistors are required to implement each of the various types of logic gates. At the time of the invention of the transistor in 1947 by John Bardeen, Walter Brattain, and William Shockley, the only way to assemble multiple transistors into a single circuit was to buy separate discrete transistors and wire them together. In 1959, Jack Kilby and Robert Noyce independently invented a means of fabricating multiple transistors on a single slab of semiconductor material. Their invention would come to be known as the integrated circuit, or IC, which is the foundation of our modern computerized world. An IC is so called because it integrates multiple transistors and diodes onto the same small semiconductor chip. Instead of having to solder individual wires between discrete components, an IC contains many small components that are already wired together in the desired topology to form a circuit.
A typical IC, without its plastic or ceramic package, is a square or rectangular silicon die measuring from 2 to 15 mm on an edge. Depending on the level of technology used to manufacture the IC, there may be anywhere from a dozen to tens of millions of individual transistors on this small chip. This amazing density of electronic components indicates that the transistors and the wires that connect them are extremely small in size. Dimensions on an IC are measured in units of micrometers, with one micrometer (1mm) being one millionth of a meter. To serve as a reference point, a human hair is roughly 100mm in diameter. Some modern ICs contain components and wires that are measured in increments as small as 0.1mm! Each year, researchers and engineers have been finding new ways to steadily reduce these feature sizes to pack more transistors into the same silicon area, as indicated in Figure 2.2.
When an IC is designed and fabricated, it generally follows one of two main transistor technologies: bipolar or metal-oxide semiconductor (MOS). Bipolar processes create BJTs, whereas MOS processes create FETs. Bipolar logic was more common before the 1980s, but MOS technologies have since accounted the great majority of digital logic ICs. N-channel FETs are fabricated in an NMOS process, and P-channel FETs are fabricated in a PMOS process. In the 1980s, complementary-MOS, or CMOS, became the dominant process technology and remains so to this day. CMOS ICs
incorporate both NMOS and PMOS transistors.
IntegratedCircuits集成电路电子信息类专业英语计算机类专业英语文
