Monday, May 07, 2007

Review of “Superconducting nanotransistor based digital logic gates”

By Bat-Otgon

Introduction

Currently Superconducting materials are being strongly studied for the future computational hardware designs, mainly for fabricating high speed switching devices. When the switching device’s size is reduced into the nanometric scale, conventional semiconductor devices will not function at all due to the quantum mechanical effects. This critical review examines the article about how the publishers successfully demonstrated the function and fabrication of logic gates based on a superconducting nanotransistor. Seung-Beck et al. have demonstrated and tested a NOT logic gate successfully and claim that other gates will be fabricated in this way, allowing low power consumption and improved levels of integration (Seung-Beck et al. p188).

Summary

In the introduction section of the article, the publishers propose that logic circuits based on a conventional Josephson junction is very difficult to produce. According to Seung-Beck Lee at al. the complex structure of a Josephson field effect transistor (JOFET) makes the circuit integration limited. Therefore they demonstrated a different type of superconducting nanotransistor (SNT) which uses an active load as a heater to insert “hot” phonons into the superconducting weak-link to switch the SNT on/off. In other words, the superconducting channel becomes non-superconducting when it is heated up. In this article they have explained briefly the function of an SNT and its fabrication method. The publishers used many reference materials for their research. The main point is this article was written based on their experimental data. Their proposed SNT has a layer structure. The layers are named from top down: the heater layer, the insulating layer and superconducting layer. The structure of a device and the fabrication process are illustrated in figure 2 of the article. In this figure we can see very narrow bridge between two big squares. In the superconducting layer (Nb) this narrow bridge makes the weak-link area; in top layer (NiCr) this narrow bridge will become a heater to produce “hot” phonons. When the bias voltage is applied to the heater, “hot” phonons will be produced and travel trough the insulating layer to the weak-link. When it reaches the link that superconducting current will stop to flow. In this article publishers described the circuit diagram of a NOT logic gate based on a single SNT (p190). The test result of a NOT gate is shown in figure 6 (p190). This result says that the circuit has voltage gain of 2. They claim that the power consumption of the NOT gate mentioned in this article was about ~50 nW which is much lower than the conventional Josephson junction.

Evaluation

In this detailed research work it has been achieved a very successful result. The publishers have proved by experimentation that their idea will work. Another important issue is that the fabrication of the device is much simpler than previously reported controllable superconducting transistors. Although they have mentioned the switching speed of the device and the factors that will affect the speed, they did not provide any experimental data on this issue. The importance of an SNT would have been clearly identified if they had run a test on the switching speed of an SNT and provide the result. Most important was their proof that device is a NOT logic gate which was mentioned in the results and discussion section. In figure 5, they showed how the logic gate became a member of the bigger integrated system (p190).
Publishers also described how to change the device in to a NOR logic gate by adding an additional heater section. This idea gives the sense that an SNT can be used for high speed digital computational hardware devices (p191).

Conclusion

Seung-Beck Lee et al. described the successful fabrication and digital logic operation of superconducting nanotransistors (Abstract, p188). Their demonstration proves that superconductor will be a key material for future computational devices. Beside the feature size of the switching device, low power consumption and higher switching speed are the most important issues in this field. Since they proved that an SNT can make either NOT or NOR logic gates, all other digital logic circuits can be implemented by using SNT’s.

The original article can be downloaded from:
http://ej.iop.org/links/rITI13MNv/Hi9NWJf82xGoVD2Uav5vpA/t30217.pdf

Labels:

6 Comments:

At 5:13 AM , Blogger munkhuu said...

Hi Merry christmas,

Buteeliig chini tataj boldoggui ee. yabal deer uu?

 
At 11:59 PM , Blogger altanbileg said...

Mash sonirholtoi sudalgaa hiideg yum bna. Ene transistoriin chini ajilladag temperatur ni yamarhuu ve?
IC bolgoh technology bdguu?

 
At 12:01 AM , Blogger altanbileg said...

SQUID ene ter sudaldaguu?

 
At 11:58 AM , Blogger Otgoo said...

Дээрх Ниобиум нь 9.25K темпарутурт хэт дамжуулагч болдог металл. Хэт дамжуулагчуудын температурын талаар http://superconductors.org/Type2.htm сайтаас харж болно.
Тэгэхээр одоохондоо IC хийх асуудал хүндрэлтэй л болов уу хэхэ.

 
At 12:07 PM , Blogger Otgoo said...

Superconducting Quantum Interface Device-ийн талаар бол судалж барьсан юм байхгүй. Энэ төхөөрөмжийн тусламжтай хүний оюун бодлыг бараг уншчих гээд байгаа юм гэж ойлгосон. Хүний тархин дотор болж буй процессын нөлөөгөөр мэдрэлийн нэг эс дотор өчүүхэн цахилгаан соронзон орон үүсдэг болохыг энэ төхөөрөмжөөр хэмжиж чадсан. Тэгэхээр бүх бодлыг уншихад ойрхон байгаа гэж Нобелийн шагналын Физикийн хорооны нарийн бичгийн дарга Проф. Tord Claeson-ий лекцэнд сууж байхдаа сонссон.Хэрэв чи сонирхож байвал энэ хүний лекцэндээ хэрэглэсэн РРТ файль надад байгаа, мэйлээр явуулж болох юм.

 
At 12:20 PM , Blogger altanbileg said...

ok. please send it to altanbileg1@yahoo.com

 

Post a Comment

Subscribe to Post Comments [Atom]

<< Home