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6.  How can SOEs reduce the number of required packages in a system?

Write some final concluding comments on the article.

UNIT 6

GERMAN  TEAM  CREATES  NEW  TYPE

OF  TRANSISTOR-LIKE  DEVICE

Vocabbox

noun collocations

§  quantum effects

§  the tunneling of electrons

§  a nanoconductor bifurcated strip

§  a lateral field

§  a cardinal; transistor trait

§  the Y-shaped nanostructure

§  a transverse field

§  a 0.01-V sweep

§  Y- branch switches

§  high output  impedance

verb collocations

§  coerce the electrons to travel down

§  flow in the contact area

§  travel up the stem

§  steer the electrons into one branch

§  impede the flow of the electrons

§  prompt a change

§  ramp up the bias voltage

§  enhance switching

§  shield the external electric field

§  take on a role

§  fine-tune the geometry

Pre-reading task

What do you already know about the transistors?

Scan the article and say how the team refers to its experimental device.

Reading for gist

A surprise discovery of a new effect has opened the (admittedly long-term) possibility of creating active electronic components smaller than present-day conventional transistors. Downsizing transistors reaches a limit because quantum effects, such as the tunneling of electrons from the source to the drain or through the layer insulating the gate from the channel, start interfering with their operation. A team at the University of Wuerzburg in Germany has devised a device that has some transistor-like characteristics and could eventually replace transistors in some situations.

The Wuerzburg team calls its device a Y-branch. It consists of a nanoconductor bifurcated strip with channels about 50 nm wide. In the absence of an external field, equal amounts of electrons injected in the stem of the Y enter each branch, but applying a lateral field can coerce these electrons to travel down a single branch.

The team, led by Alfred Forchel, reported in the 25 November issue of Physical Review Letters that its Y- branch can amplify tiny changes in voltage by a factor of 30. Amplification of current, a cardinal transistor trait, has not been shown, however. So the team refers to its experimental device as a switch.

The researchers created a Y- branch by etching three channels into a 50-nm layer of gallium arsenide deposited on a second layer of GaAs. The GaAs regions between the channels form the Y- shaped nanostructure and also two side gates along each branch. Electrons flow in the contact area between the two GaAs layers. If a bias voltage is applied over the Y-stem and the extremities of its two branches, electrons travel up the stem and enter both branches. But if a voltage is applied over the two terminals leading to the two gates, a transverse field is created that steers the electrons into one branch and impedes the flow in the other branch.

In the circuit, which operated at 4.2 K, with the Y-branch structure biased at 1.75 V, the team observed that a 0.01-V sweep over the left and right gate terminals prompted a change of 0.3V over the output terminals directly connected to the two branches. This corresponds to a gain factor of 30.

Usually, downsizing field- effect transistors eventually runs into a problem: if the gate and channel become too small, the gate cannot store enough charge, resulting in a low gain and in the saturation of gain when the bias voltage is increased.

Forchel and his colleagues observed the contrary in their Y-branch: instead of reaching saturation, they found that the gain increased in an unexpected way when they ramped up the bias voltage. And the increase was even faster than linear, reports team member Lukas Worschech. “What we observe is an additional capacitance between the branches, and it is possible to use this capacitance to enhance switching.”