lunes, 28 de junio de 2010

The Junction Transistor

A bipolar junction transistor consists of three regions of doped semiconductors. A small current in the center or base region can be used to control a larger current flowing between the end regions (emitter and collector). The device can be characterized as a current amplifier, having many applications for amplification and switching.

Transistor as Current Amplifier

The larger collector current IC is proportional to the base current IB according to the relationship IC =βIB , or more precisely it is proportional to the base-emitter voltage VBE . The smaller base current controls the larger collector current, achieving current amplification.

The analogy to a valve is sometimes helpful. The smaller current in the base acts as a "valve", controlling the larger current from collector to emitter. A "signal" in the form of a variation in the base current is reproduced as a larger variation in the collector-to-emitter current, achieving an amplification of that signal.

Transistor Structure

Transistor as Current Amplifier

The larger collector current IC is proportional to the base current IB according to the relationship IC =βIB , or more precisely it is proportional to the base-emitter voltage VBE . The smaller base current controls the larger collector current, achieving current amplification.

Constraints on Transistor Operation

Transistor Maximum Values

Part of the manufacturer's data for transistors is a set of maximum values which must not be exceeded in its operation. These form some of the constraints on transistor operation which are a part of the design of any circuit. A typical set, for the silicon transistor 2N2222:

Collector-Base Voltage = 60 v
Collector-Emitter Voltage = 30 v
Base-Emitter Voltage = 5 v
Power dissipation = 500 mW
Temperature 125 C

Articules about transistor

Logic Circuits with Carbon Nanotube Transistors

We demonstrate logic circuits with field-effect transistors based on single carbon nanotubes. Our device layout features local gates that provide excellent capacitive coupling between the gate and nanotube, enabling strong electrostatic doping of the nanotube from p-doping to n-doping and the study of the nonconventional long-range screening of charge along the one-dimensional nanotubes. The transistors show favorable device characteristics such as high gain (>10), a large on-off ratio (>105), and room-temperature operation. Importantly, the local-gate layout allows for integration of multiple devices on a single chip. Indeed, we demonstrate one-, two-, and three-transistorcircuits that exhibit a range of digital logic operations, such as an inverter, a logic NOR, a static random-access memory cell, and an ac ring oscillator

Room-temperature transistor based on a single carbon nanotube

The use of individual molecules as functional electronic devices was first proposed in the 1970s. Since then, molecular electronics2,3 has attracted much interest, particularly because it could lead to conceptually new miniaturization strategies in the electronics and computer industry. The realization of single-molecule devices has remained challenging, largely owing to difficulties in achieving electrical contact to individual molecules. Recent advances in nanotechnology, however, have resulted in electrical measurements on single molecules. Here we report the fabrication of a field-effect transistor—a three-terminal switching device—that consists of one semiconducting single-wall carbon nanotube, connected to two metal electrodes. By applying a voltage to a gate electrode, the nanotube can be switched from a conducting to an insulating state. We have previously reported5similar behavior for a metallic single-wall carbon nanotube operated at extremely low temperatures. The present device, in contrast, operates at room temperature, thereby meeting an important requirement for potential practical applications. Electrical measurements on the nanotube transistor indicate that its operation characteristics can be qualitatively described by the semiclassical band-bending models currently used for traditional semiconductor devices. The fabrication of the three-terminal switching device at the level of a single molecule represents an important step towards molecular electronics.

Single- and multi-wall carbon nanotube field-effect transistors

We fabricated field-effect transistors based on individual single- and multi-wall carbon nanotubes and analyzed their performance. Transport through the nanotubes is dominated by holes and, at room temperature, it appears to be diffusive rather than ballistic. By varying the gate voltage, we successfully modulated the conductance of a single-wall device by more than 5 orders of magnitude. Multi-wall nanotubes show typically no gate effect, but structural deformations—in our case a collapsed tube—can make them operate as field-effect transistors. © 1998 American Institute of Physics.

High-Resolution Inkjet Printing of All-Polymer Transistor Circuits

Direct printing of functional electronic materials may provide a new route to low-cost fabrication of integrated circuits.However, to be useful it must allow continuous manufacturing of all circuit components by successive solution deposition and printing steps in the same environment. We demonstrate direct inkjet printing of complete transistorcircuits, including via-hole interconnections based on solution-processed polymer conductors, insulators, and self-organizing semiconductors. We show that the use of substrate surface energy patterning to direct the flow of water-based conducting polymer inkjet droplets enables high-resolution definition of practical channel lengths of 5 micrometers. High mobilities of 0.02 square centimeters per volt second and on-off current switching ratios of 105were achieved.

Coulomb blockade and the Kondo effect in single-atom transistors

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C60 molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.

Organic field‐effect transistors with high mobility based on copper phthalocyanine

Organic field‐effect transistors that employ copper phthalocyanine (Cu–Pc) as the semiconducting layer can function as p‐channel accumulation‐mode devices. The charge carrier mobility of such devices is strongly dependent on the morphology of the semiconducting thin film. When the substrate temperature for deposition of Cu–Pc is 125 °C, a mobility of 0.02 cm2/V s and on/off ratio of 4×105 can be obtained. These features along with the highly stable chemical nature of Cu–Pc make it an attractive candidate for device applications. © 1996 American Institute of Physics.

Lenny Z Perez M

1 comentario:

  1. The Theme of this Blog is not readable. White letters in Black background is making much strain to the eyes, Please try to redesign the Page.
    Thank you!