Acquisition of Instrument for the Study of Artificial Atoms

购置用于研究人造原子的仪器

• 批准号: 9700818
• 负责人: Marc Kastner
• 金额: $ 16.11万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-06-15 至 2001-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9700818&HistoricalAwards=false
• 关键词: Acquisition; Instrument; Study; Artificial; Atoms

9700818 Kastner The power of computers has increased exponentially with time in large part because the size of devices has decreased exponentially with time, resulting in a higher density of transistors on a chip. Unfortunately, the cost of facilities for producing these devices has also increased exponentially, and although the market for devices has grown rapidly, it has not grown exponentially. Thus we are rapidly approaching the time when facilities for new generations of conventional devices may be too expensive to build. In the past it seemed that novel devices could not compete with conventional ones. However, the economic limitation to future fabrication facilities provides a new motivation for research into classes of devices that may have cost advantages. Single- electron devices may be one of these classes. Whereas single- electron devices have, in the past, operated only at very low temperatures, recent reports of operation near room temperature bring useful applications much closer to reality. This project builds upon past work at MIT in which it was discovered that when a transistor is made very small it behaves in an unusual way. Whereas a conventional transistor turns on only once as electrons are added to it, and whereas such a transistor requires the addition of about 103 electrons to change from the off-state to the on-state, the new transistor turns on and off again every time an electron is added to it. The single electron transistor is made by isolating a very small droplet of electrons in such a way that electrons can move into and out of the droplet only by quantum mechanical tunneling. The MIT work has shown that such a transistor behaves like an artificial atom, in that the number of electrons in the droplet and the energy are both quantized. The transistors made so far have used the semiconductor GaAs with metal electrodes on the surface, patterned using electron-beam lithography, to confine the droplet of electrons. Beca use the electrons in such GaAs structures are typically 100nm below the surface, the droplet of electrons has typically been ~100nm in radius r. The energy for adding an extra electron to the droplet scales like r-1, and this limits single electron operation to temperatures below ~1K for r=100nm. The goal of this project is to explore ways of increasing the operating temperature of single electron transistors and to better understand their physics. In particular, the MIT group has recently discovered a series of phase transitions in the droplet of electrons confined in the artificial atom at high magnetic fields. The acquisition of a higher-field magnet and dedicated refrigerator are proposed here to study these phase transitions further. %%% New artificial atoms will be fabricated using Si instead of GaAs. Since the electrons in these devices can be as close as 5nm from the surface, much smaller droplets and, consequently, much higher energy and temperature scales are expected. The devices will be fabricated in collaboration with MIT Lincoln Laboratory using the outstanding electron- beam and optical lithography capability developed there under Air Force sponsorship. In this way, the effect of the NSF funds will be strongly amplified. In addition to higher operating temperatures, Si offers the advantage that single electron devices can be easily integrated with conventional ones. It is expected that single electron devices in Si can be made to operate well above liquid nitrogen temperature. Higher magnetic fields are required for the study of the state of electrons in these smaller structures. It is also proposed to fabricate devices in GaAs in which the droplets of electrons will be smaller. This will be accomplished by growing structures in which the electrons are closer to the surface. A collaboration has been established with the Weizmann Institute in Israel where the expertise in making such structures has already been developed. Like the col laboration with Lincoln Laboratory, this amplifies the impact of NSF funding. Single electron devices have the advantage that they can be capacitively coupled. It has been proposed that, because of this, an array of such devices may function as an associative memory. That is, any set of input voltages close to, but not exactly equal to, a special set will give the same output. It is proposed that such an array be fabricated and studied. Although the first such memories will be read-only, understanding their physics may lead to ways of writing as well. ***

9700818卡斯特纳计算机的能力随着时间呈指数级增长，很大程度上是因为设备的尺寸随着时间呈指数级减小，导致芯片上的晶体管密度更高。不幸的是，生产这些设备的设备成本也呈指数级增长，尽管设备市场增长迅速，但并没有呈指数级增长。因此，我们正在迅速接近建造新一代常规设备的设施可能过于昂贵的时候。在过去，新设备似乎无法与传统设备竞争。然而，对未来制造设施的经济限制为研究可能具有成本优势的设备类别提供了新的动力。单电子器件可能就是其中的一类。虽然单电子设备过去只能在非常低的温度下运行，但最近关于在室温附近运行的报告使有用的应用变得更加接近现实。这个项目建立在麻省理工学院过去的工作基础上，在那里发现，当晶体管被制造得非常小时，它的行为方式是不寻常的。传统的晶体管在添加电子时只导通一次，而且这种晶体管需要增加大约103个电子才能从关断状态变为导通状态，而新晶体管每次添加电子时都会再次导通和关闭。单电子晶体管是通过隔离一个非常小的电子液滴来制造的，这样电子就可以通过量子力学隧道效应进入和流出液滴。麻省理工学院的研究表明，这种晶体管的行为类似于人造原子，因为液滴中的电子数量和能量都是量子化的。到目前为止制造的晶体管使用了表面有金属电极的半导体砷化镓，利用电子束光刻技术进行图案制作，以限制电子液滴。由于这种结构中的电子通常在表面以下100 nm处，电子液滴的半径通常为~100 nm。向液滴中添加额外电子的能量约为r-1，这将单电子的工作温度限制在~1K以下(r=100 nm)。该项目的目标是探索提高单电子晶体管工作温度的方法，并更好地了解它们的物理特性。特别是，麻省理工学院的研究小组最近发现，在强磁场下，限制在人造原子中的电子液滴发生了一系列相变。为了进一步研究这些相变，本文提出了获取高场磁体和专用制冷机的建议。%新的人造原子将用硅代替砷化镓来制造。由于这些器件中的电子距离表面可以接近5纳米，因此液滴要小得多，因此需要更高的能量和温度标度。这些设备将与麻省理工学院林肯实验室合作，利用那里在空军赞助下开发的出色的电子束和光学光刻能力来制造。如此一来，NSF基金的效应将被有力放大。除了更高的工作温度外，硅还具有单电子器件可以很容易地与传统电子器件集成的优势。预计硅中的单电子器件可以在远高于液氮温度的情况下工作。为了研究这些较小结构中的电子状态，需要更高的磁场。还提出了在GaAs中制作电子液滴更小的器件的建议。这将通过生长电子更接近表面的结构来实现。已经与以色列魏兹曼研究所建立了合作关系，在那里已经发展了制造这种结构的专门知识。就像与林肯实验室的合作一样，这放大了NSF资金的影响。单电子器件的优点是它们可以进行电容耦合。已经提出，正因为如此，这种设备的阵列可以用作关联存储器。也就是说，任何一组接近但不完全等于一组特殊电压的输入电压都会产生相同的输出。建议对这种阵列进行制作和研究。虽然第一批这样的记忆将是只读的，但了解它们的物理原理也可能导致书写方式。***