New approach to size selection and thin film growth of silicon quantum dots and applications

硅量子点尺寸选择和薄膜生长的新方法及应用

• 批准号: EP/G01664X/1
• 负责人: Yimin Chao
• 金额: $ 39.67万
• 依托单位: University of East Anglia
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FG01664X%2F1
• 关键词: New; approach; size; selection; thin

The intact sublimation of silicon nanocrystals is an extremely novel and unexpected observation. I have used this method to deposit silicon nanocrystals on a variety of substrates placed in the resulted vapour (sapphire plates, graphite sheet, silicon wafer and gold nitride films). The ability to evaporate and deposit nanocrystals in high vacuum may be useful for the size-controlled preparation of new nanoscale quantum-confined structures. Many of the potential uses of nanoparticles demand that the particles have well defined sizes. But this is not easy to achieve at such small scales, and it has previously been largely a matter of trial and error. This novel intact sublimation of silicon nanocrystals could provide a novel method for size selection and thin film preparation. One example of applications is replacing the conventional oxide layer in floating gate memory devices with a layer of nanocrystals. Currently, nonvolatile memory devices utilize floating gate field-effect transistor technology to store information, and these have many applications e.g. mobile phones, digital cameras, camcorders, MP3 players, digital games, iPods, flash cards and removable storage devices, which is in a rapidly growing market ($40 billion in 2007, up 12.9% from 2006). In such memory devices, charge is stored on a silicon floating gate that is separated from the substrate by a dielectric tunneling barrier. Typically, the tunneling barrier consists of a thin thermally-grown SiO2 layer. This tunneling barrier controls the retention time and the program/erase speed of the device. When a ''program'' bias is applied to the device, charge tunnels through the barrier and remains stored on the floating gate after the program voltage is removed. Firstly, since the tunneling barrier must be able to inject a current during programming and to retain charge, a compromise must be made when designing memory devices that integrate a tunneling barrier. When the barrier is made relatively thick, long charge retention times are achieved, but a higher voltage (and a longer time) is required to program and erase the floating gate. When the barrier is thin, the programming and erase process will be more rapid, but increased charge leakage will reduce the retention time. If a monolayer comprised of silicon nanocrystals (aka quantum dots) was to replace the SiO2 layer, an effective lowering of the barrier would be observed. This barrier lowering effect will allow an increase in the tunnel current density and a subsequent increase in the floating gate program/erase speed. Secondly, for a normal flash memory, a major problem is caused by the non-uniformity of the oxide; if there is a weak spot where the leakage current density is larger, it acts as a sink and all stored charges in the floating gate would leak away through it. This problem increases with the thinning of the oxide layer. Again, if the floating gate is replaced with nanoparticles the weak spot will only affect a small number of nanoparticles and has no effect on the charge stored in other particles. Therefore, in this design, the thickness of both tunneling barrier oxide and inter-level oxide can be reduced without sacrificing the memory retention time. Thirdly, since the shift in the device's threshold depends on the particle size, a wide size distribution would wash out the operating threshold. Thus the size selection is a big issue for this application. This research project is the first such research in Europe and is an opportunity for UK to enter this major area of nanocrystals based memory devices.In the research program described here we will study the dynamics of the evaporation-deposition process of nanocrystals in vacuum, which will contribute to the development of the novel method for nanocrystals selection by size. This novel method will be developed further for forming size-controlled nanocrystal thin films, which could be used to replace the SiO2 layer in floating gate memory devices.

硅纳米晶体的完整升华是一个极其新颖且意想不到的观察结果。我使用这种方法将硅纳米晶体沉积在置于所得蒸气中的各种基材上（蓝宝石板、石墨片、硅晶片和氮化金薄膜）。在高真空中蒸发和沉积纳米晶体的能力可能有助于新型纳米级量子限制结构的尺寸控制制备。纳米颗粒的许多潜在用途要求颗粒具有明确的尺寸。但在如此小的规模下实现这一目标并不容易，之前这在很大程度上是一个反复试验的问题。这种新颖的硅纳米晶体完整升华可以为尺寸选择和薄膜制备提供一种新方法。一个应用示例是用纳米晶体层取代浮栅存储器件中的传统氧化层。目前，非易失性存储器件利用浮栅场效应晶体管技术来存储信息，并且这些器件具有许多应用，例如手机、数码相机、摄像机、MP3 播放器、数字游戏、iPod、闪存卡和可移动存储设备，这是一个快速增长的市场（2007 年为 400 亿美元，比 2006 年增长 12.9%）。在这种存储器件中，电荷存储在通过电介质隧道势垒与衬底分离的硅浮置栅极上。通常，隧道势垒由热生长的 SiO2 薄层组成。该隧道势垒控制器件的保留时间和编程/擦除速度。当“编程”偏压施加到器件时，电荷隧道穿过势垒并在编程电压移除后仍然存储在浮置栅极上。首先，由于隧道势垒必须能够在编程期间注入电流并保留电荷，因此在设计集成隧道势垒的存储器件时必须做出折衷。当势垒做得相对较厚时，可以实现较长的电荷保留时间，但需要较高的电压（和较长的时间）来编程和擦除浮动栅极。当势垒很薄时，编程和擦除过程会更快，但增加的电荷泄漏会减少保留时间。如果用由硅纳米晶体（又名量子点）组成的单层取代 SiO2 层，将会观察到势垒的有效降低。这种势垒降低效应将允许隧道电流密度的增加以及随后浮栅编程/擦除速度的增加。其次，对于普通的闪存来说，一个很大的问题就是氧化层的不均匀性。如果存在泄漏电流密度较大的弱点，则该弱点将充当接收器，浮置栅极中所有存储的电荷都会通过该弱点泄漏出去。这个问题随着氧化层变薄而加剧。同样，如果用纳米颗粒替换浮栅，则薄弱点将仅影响少量纳米颗粒，并且对其他颗粒中存储的电荷没有影响。因此，在该设计中，可以减小隧道阻挡氧化物和层间氧化物的厚度，而不牺牲存储器保持时间。第三，由于设备阈值的变化取决于颗粒尺寸，因此宽的尺寸分布会消除操作阈值。因此，尺寸选择对于该应用来说是一个大问题。该研究项目是欧洲第一个此类研究，也是英国进入基于纳米晶体的存储器件这一主要领域的机会。在此描述的研究计划中，我们将研究纳米晶体在真空中蒸发沉积过程的动力学，这将有助于开发按尺寸选择纳米晶体的新方法。这种新颖的方法将进一步开发用于形成尺寸受控的纳米晶体薄膜，该薄膜可用于替代浮栅存储器件中的SiO2层。

项目成果

An abrupt switch between the two photoluminescence bands within alkylated silicon nanocrystals

• DOI: 10.1088/0022-3727/44/49/495301
• 发表时间: 2011-12
• 期刊: Journal of Physics D: Applied Physics
• 作者: P. Coxon;Qi Wang;Y. Chao

Measurement of Thermoelectric Properties of Phenylacetylene-Capped Silicon Nanoparticles and Their Potential in Fabrication of Thermoelectric Materials

苯乙炔封端硅纳米颗粒热电性能的测量及其在热电材料制造中的潜力

• DOI: 10.1007/s11664-012-2297-x
• 发表时间: 2012
• 期刊: Journal of Electronic Materials
• 影响因子: 2.1
• 作者: Ashby S

Thermal evaporation and x-ray photostability of dodecyl-passivated silicon nanoparticles

十二烷基钝化硅纳米颗粒的热蒸发和 X 射线光稳定性

• DOI: 10.1088/0022-3727/45/35/355303
• 发表时间: 2012
• 期刊: Applied Physics
• 作者: Coxon P

Amine-terminated nanoparticle films: pattern deposition by a simple nanostencilling technique and stability studies under X-ray irradiation.

胺封端纳米粒子薄膜：通过简单的纳米模板技术进行图案沉积以及 X 射线照射下的稳定性研究。

• DOI: 10.1039/c3cp55344b
• 发表时间: 2014
• 期刊: PCCP
• 作者: Coxon PR

The effect of alkyl chain length on the level of capping of silicon nanoparticles produced by a one-pot synthesis route based on the chemical reduction of micelle

• DOI: 10.1007/s11051-013-1425-8
• 发表时间: 2013-02-01
• 期刊: JOURNAL OF NANOPARTICLE RESEARCH
• 影响因子: 2.5
• 作者: Ashby, Shane P.;Thomas, Jason A.;Chao, Yimin
• 通讯作者: Chao, Yimin