Plasma is a partially ionised gas in which a certain proportion of electrons are free rather than being bound to an atom or molecule.
Usually the plasma is confined in micro cavity sections such as cylinders or holes.
The remarkable properties of plasma make it suitable for application in electronics, although the resulting devices are expensive. The voltage required to ignite plasma or to modulate light is about 100 to 200 V, whereas the transistor-transistor logic (TTL) voltage in conventional integrated circuits (ICs) is just 5 V. This obstacle contributes to the high cost of plasma devices. Methods that can control the micro plasma at low voltages, in the range of 5 V to 10 V, are required to overcome these challenges.
A team of researchers from University of Illinois has now developed a novel device that can control the plasma conduction current and the light emission with an emitter of 5 V or less. The team combined a solid-state electron emitter and a micro cavity plasma device to manufacture lighter, less expensive and higher resolution flat panel displays.
A plasma transistor consists of a micro cavity, an electronic-photonic device in which an electrically charged gas plasma is contained within a microscopic cavity. The micro cavity is filled with gas and its diameter is very small (roughly that of a human hair) and two electrodes at voltages up to 200 V are used to supply power. The plasma is surrounded by a thin boundary-like layer called a sheath.
Electric current is carried within the sheath, and electrons carry the current, instead of the positively charged ions. Much heavier than electrons and therefore harder to accelerate, the ions require a large electric field generated by a large voltage drop across the sheath. The flow of electrons in the plasma can be increased by injecting electrons into the sheath from the emitter, which thereby increases the plasma’s conductivity and light emission.
The current that is sent through the sheath to the bulk plasma determines how much current is carried by the two electrodes driving the micro plasma. The injected electrons are excited and, as a result, the atoms in the plasma begin to radiate light. The colour of the emitted light depends on the gas filled in the micro cavity; for example, neon emits red light and argon emits blue light.
Designing an emitter and bringing the emitter close to the micro plasma were some of the hurdles faced by the team.
The plasma transistor developed by the team will find its application in manufacturing sharper flat panel displays. The researchers are working on methods to employ this transistor as a source of emission in flat lamps. This technology could potentially also find application in sectors like water purification, air purification and sterilisation, since plasma has the tendency to kill viruses and bacteria.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, [email protected], www.frost.com
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