Микроэлектроника / Текст 2

Electronic Devices

The invention of the transistor triggered the rapid growth of the electronics industry. Before transistors, electronic circuits were large, bulky and unreliable; they consumed considerable power ergy) and therefore generated too much heat, which contributed to the deterioration of other circuit parts and materials, such as resis­tors, capacitors and insulation. With transistors, circuits became much smaller, more efficient in the use of energy, and far more reliable. The higher reliability of the transistor circuits compared to vacuum tube equivalents is an extremely important advantage.

The techniques used to manufacture transistors led to the development that made it possible to mass-produce very small and highly reliable electronics circuits commonly known as integrated circuits (ICs). ICs have diodes, transistors, resistors and all inter-connecting leads formed on a single piece of semiconductor material.

Microelectronics

It should first be made clear what the term "microelectronics" implies. Microelectronics embraces the entire body of the electronic art which is connected with, or applied to, the realization of electronic circuits, subsystems, or the entire systems from extremely small electronic devices. The terms "microelectronics" and "integrated circuits" are sometimes used interchangeably, but this is not correct.

Microelectronics is a name for extremely small electronic components and circuit assemblies, made by thin-film, thick-film or semiconductor techniques.

An integrated circuit (IС) is a special kind of microelectronics. It is a circuit that has been fabricated as an inseparable assembly of electronic elements in a single structure. It cannot be divided without destroying its intended electronic function. Thus, ICs come under the general category of microelectronics, but all microelectronic units are not necessarily ICs.

The Future of ICs

When assessing the future course of ICs, it is customary to project another order of magnitude in circuit performance through a continuing reduction in the feature size of the devices on chip.

However, at our current level of IС development we must face several pragmatic barriers that will require some degree of research creativity to overcome. For example, the chip complexity is extrapolated to 100,000,000 transistors per chip and beyond.

However, the latest models indicate that the power level of next-generation devices will be on the order of l0mW. Thus, a chip of this extrapolated complexity with these devices would require 1000 watts of input power and a packaging system capable of dissipating such power. Since these small devices would operate at reduced supply voltages, the 1000 watts of input power would require currents on the order of 200 amperes and perhaps greater on a chip that should be less than one square inch in area. This set of conditions would apply only to a high-duty cycle and high-performance design and points out that important complexity/performance trade-offs must occur.

Integrated Circuits

The potential of integrated circuits is so wide that in addition to replacing similar discrete component circuits they are responsible for creating a completely new technology of circuit design.

There are two basic approaches to modern microelectronics - monolithic integrated circuits and film circuits.

In monolithic ICs all circuit elements, active and passive, are simultaneously formed in a single small wafer of silicon. The elements are interconnected by metallic stripes deposited onto the oxidized surface of the silicon wafer.

Monolithic IС technology is an extension of the diffused planar process. Active elements (transistors and diodes) and passive elements (resistors and capacitors) are formed in the silicon slice by diffusing impurities into selected regions to modify electrical characteristics, and where necessary to form p-n junctions. The various elements are designed so that all can be formed simultaneously by the same sequence of diffusions.

Film circuits are made by forming the passive electronic component and metallic interconnections on the surface of an insulation substrate. Then the active semiconductor devices are added, usually in discrete wafer form. There are two types of film circuits, thin film and thick film.

In thin film circuits the passive components and interconnection wiring are formed on glass or ceramic substrates, using evaporation techniques. The active components (transistors and diodes) are fabricated as separate semiconductor wafers and assembled into the circuit.

Thick film circuits are prepared in a similar manner except that the passive components and wiring are formed by silk-screen techniques on ceramic substrates.

There can be many instances where the microelectronic circuit may combine more than one of these approaches in a single structure, using a combination of techniques.

In multichip circuits the electronic components for a circuit are formed in two or more silicon wafers (chips). The chips are mounted side by side on a common header. Some interconnections are included on each chip, and the circuit is completed by wiring the chips together with small diameter gold wire.

Hybrid IC's are combinations of monolithic and film techniques.

Active components are formed in a wafer of silicon using the planar process, and the passive components and interconnection wiring pattern formed on the surface of silicon oxide which covers the wafer, using evaporation techniques.