Tropes

R_www.theregister.co.uk_science 2015 00384.txt.txt

#Boffins have made optical transistors that can reach 4 TERAHERTZ Aluminum-doped zinc oxide is the key to building faster, optical chips, according to researchers at Purdue University, Indiana. They've modelled an all-optical, CMOS-compatible transistor capable of 4thz speeds, potentially more than 1, 000 times faster than silicon transistors. The all-optical bit means that the data stream and the control of the switching is optical; previous optical transistors have used electrical control and optics for data. This has inhibited the switching speed. The use of aluminum-doped zinc oxide (AZO) opens up the opportunity for both. It is aimed very much at optical switching rather than building processors, and according to the researchers, the optical transistors have a tunable dielectric permittivity compatible with all telecoms infrared (IR) standards. e are pretty far away from building anything resembling an processor. In fact our transistor is only simulation at the current time, "said doctoral candidate Nate Kinsey, in conversation with El Reg.""However, we have taken care to use realistic parameters so that the performance should be very similar to our simulations, he added. He explained that one issue is that the transistor is controlled with UV light, and this is really not that practical for a highly integrated device. We envisioned our switch being more of use for ultra-small signal encoding, say in like a data centre"."Even the stages of developing something simpler, such as an adder, multiplier, or a gate poses problems, Kinsey explained, as the"things you're discussing you need light of the same wavelength in the signal and the control, so that the output of one transistor can control another"."""This is how you would build logical circuits. With our current system that uses a carrier of 1300nm and a control of 350nm, this would be extremely difficult to achieve, "he added.""However, in principle our device could be thought of as a stepping stone to such a system, as controlling light with light is somewhat difficult as photons do not interact with other photons like electrons do said, "Kinsey. Resistance is useless One of the reasons optics has the potential to be faster is that it doesn have the limitation of the RC time constant, also known as tau, where the capacitance of the resistor takes time to charge. Electrical transistors are limited by the RC delay time while the limiting mechanism for optical system is recombination time. By eliminating RC delay there is scope for massive increases in clock speeds. The manufacturing process is used similar to that for traditional CMOS (Complementary metal-oxide semiconductor chips. The transparent conducting oxides Perdue is working with are CMOS-compatible materials with low optical loss. ur materials are deposited using standard techniques, although there would need to be modification/optimisation for mass production, "Kinsey informed The Register.""Our oxide is deposited through pulsed laser ablation (i e. a strong laser pulse literally blows off some of the material which travels across a chamber and sticks onto a substrate, not unlike how you would get splashed if you throw a ball hard enough into water), while our other materials for the switch are deposited through sputtering or chemical vapor deposition, "he added.""The last two are friendly to semiconductor fabrication facilities but the former is not. We would likely need to modify this to another process for mass production, "he added. By using AZO plasmonic oxide, the boffins reckon they could speed up switching in optical applications ten fold, and claim such an application is around five years away. Kinsey cautions that something as advanced as a processor is at least two decades away, so while a 1, 000-fold increase in processor power sounds a lot, it not when considered over the kind of timescales we are talking e

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