Semiconductors: Products & System Solutions
Introduction to semiconductor industry
The term semiconductor is applied to solid materials which, due to their structure – their lattice structure –and depending on the temperature, have a larger or smaller number of electrons (holes) which are free to move. Due to these mobile charge carriers, the material has a conductivity of a greater or smaller magnitude or, if we consider the reciprocal of this, the specific electric resistance of semiconductors at room temperature is in a range between 10 -2 and 106 Ωcm. Materials which have no mobile charge carriers, and thus have even higher specific resistances, are referred to as ”insulators” (glass, mica, amber). Materials which retain their conductivity even at the lowest temperatures, and which in normal circumstances have significantly lower specific resistances, are called conductors (copper, aluminum, silver, gold). In contrast to solid metallic objects, the conductivity of gases or liquid is due to the mobility of their ions, and hence depends on the mobility of the material itself.
1939 the physicists Walter Schottky and Eberhard Spenke, both pioneers in the semiconductor industry, published a scientific work about how crystal diodes with a metal/ semiconductor junction work. Their worked was based on intensive fundamental research which showed that the junctions described, exhibit a rectifying property, i.e. they offer different electrical resistance to an electrical current depending on its direction of flow.
The first rectifiers were manufactured using selenium and germanium.
A notable milestone in the history of semiconductors was the development of the transistor. William Shockley and his team constructed 1947 a so called diode out of polycrystalline germanium. The Team observed, by chance, that a change in the forward voltage across the first diode resulted in a change in the reverse current through the second diode. They gave this effect the name “transitor effect”, derived from “transit” and “resistor”.
Silicon’s victory parade in semiconductors history
Germanium has the advantage of a high conductivity so that it is particularly suitable for use at high frequencies. The disadvantages of germanium as a semiconductor, on the other hand, are that the crystal structure cannot withstand temperatures above about 75 oC without incurring damage. In addition, the reverse current causes interference, even at room temperatures. By contrast, silicon crystals will stand temperatures up to 150 oC, and its higher band gap together with the higher specific resistance result in a far lower reverse current. Apart from this, silicon occurs naturally to a practical unlimited extent. Therefore silicon is a widely-used semiconductor material.
Other semiconducting materials and components
In 1953 Heinrich Welker discovered that certain junctions between three- and five-valent materials, for example gallium and arsenic, possess semiconducting properties and could be used perfectly in semiconductor applications. These semiconducting materials have since then become of great importance in opto-electronics. (e.g. light emitting diodes, LED).
Field effect transitors: N-type and p-type semiconductors
In 1959 the first junction field effect transistor (JFET) was constructed and the first capacitively-controlled field effect transistor made in metal oxide form (the so called MOSFET) was presented. For a long time, MOS types with N-channels (n-type semiconductors) and p-channels (p-type semiconductors) existed alongside each other. With time however, the N-MOS technology proved to be more advantageous, so that the P-MOS technology was gradually pushed into the background.
In 1964 a complementary circuit design technology (Complementary MOS = CMOS) was introduced, in which both types were integrated on a single die. With this circuit variant, one transistor out of a number in series is always blocked, and for this reason the CMOS technology is to this day always used when power saving technology is required.
Categorization of semiconductor components
Semiconductor components can be distinguished from various points of view, including by:
- The semiconductor technology used (bipolar, MOS, CMOS, BICMOS, Schottky, ternary)
- their internal design i.e. individual semiconductors or integrated circuits (IC’s)
- their application area (analog, digital, power semiconductors, signal processing, optoelectronics)
From the user’s point of view it is the last distinction which is most meaningful.
Integrated semiconductors circuits
The essential driving forces of the semiconductor industry are:
- Cost reductions of about 25% p.a.
- Packing density doubling approximately every 18 months
- Increasing complexity from the integration of peripheral functions on-chip
- Power consumption especially for battery-powered devices
- Integration of additional functionality, e.g. in form of memories, and interfaces in the forms of sensors and actuators
Over the last 30 years power semiconductors have mostly replaced electromechanical solutions in the areas of drive technology as well as power management and supply, due to their ability to form high energy flows almost at will. The advantages of these components is their ability to switch extremly rapid (typically within a fraction of a second) between the "open" and the "closed" state. With the fast sequencesof on/off pulses, almost any form og energy flow can be created, e.g. a sinus wave.
Infineon Technologies AG
Infineon technologies AG located in Munich, Germany is a manufacturer of semiconductor devices s and semiconductor system solutions.