Acquisition of Instrument for the Study of Artificial Atoms

9700818 Kastner计算机的能力随着时间的推移呈指数级增长，这在很大程度上是因为设备的尺寸随着时间的推移呈指数级下降，导致芯片上晶体管的密度更高。不幸的是，生产这些设备的设施成本也呈指数级增长，尽管设备市场增长迅速，但并未呈指数级增长。 因此，我们正在迅速接近新一代传统设备的设施可能过于昂贵而无法建造的时候。 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。 单电子器件可以是这些类别中的一种。 过去，单电子器件只能在非常低的温度下工作，而最近关于在室温附近工作的报道使有用的应用更接近现实。 这个项目建立在麻省理工学院过去的工作基础上，在过去的工作中，人们发现，当晶体管做得很小时，它会以一种不寻常的方式工作。 传统的晶体管在电子加入时仅导通一次，并且这种晶体管需要加入约103个电子才能从截止状态变为导通状态，这种新的晶体管在每次加入一个电子时就会再次打开和关闭。单电子晶体管是通过隔离一个非常小的电子液滴而制成的，只能通过量子力学隧穿进出液滴。 麻省理工学院的工作表明，这种晶体管的行为就像一个人造原子，因为液滴中的电子数量和能量都是量子化的。 到目前为止，制造的晶体管都是使用半导体GaAs，表面有金属电极，用电子束光刻法形成图案，以限制电子液滴。 因为在这种GaAs结构中的电子通常在表面以下100 nm，所以电子滴的半径r通常为~ 100 nm。 向液滴中添加额外电子的能量与r-1相似，这将单电子操作限制在r= 100 nm时低于~ 1 K的温度。 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了一系列相变的电子液滴限制在人造原子在高磁场。 在这里，提出了一个更高的磁场磁铁和专用冰箱的收购，以进一步研究这些相变。 %新的人造原子将使用Si而不是GaAs制造。 由于这些设备中的电子距离表面可以接近5纳米，因此预计液滴会小得多，因此能量和温标会高得多。 这些设备将与麻省理工学院林肯实验室合作制造，使用在空军赞助下开发的出色的电子束和光学光刻技术。 这样，NSF基金的效果将被大大放大。 除了更高的工作温度外，Si还提供了单电子器件可以容易地与传统器件集成的优点。 可以预期的是，可以使Si中的单电子器件在液氮温度以上良好地工作。 研究这些较小结构中的电子状态需要更高的磁场。 也有人建议在GaAs中制造电子液滴较小的器件。 这将通过生长电子更接近表面的结构来实现。 与以色列魏茨曼研究所建立了合作关系，该研究所已经开发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资助的影响。 单电子器件的优点是它们可以电容耦合。 已经提出，由于这一点，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特定组的输入电压都将给出相同的输出。 有人建议，这样的阵列制造和研究。 虽然第一批这样的存储器将是只读的，但理解它们的物理特性也可能会导致写入的方法。 ***

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. ***