Reconfigurable Field-Effect-Transistors

可重构场效应晶体管

• 批准号: 397662129
• 负责人: Professor Dr. Joachim Knoch
• 金额: --
• 依托单位: Institut für Halbleitertechnik (IHT)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/397662129?language=en
• 关键词: Reconfigurable; Field; Effect; Transistors

During the last decades, a performance increase and thus increased functionality of highly integrated circuits (ICs) has been achieved by increasing the number of transistors of decreasing size onto the same chip area. The scalability of transistors, however, will soon come to an end. Therefore, an attractive alternative approach to further increase the functionality of ICs is to add functionality to the devices themselves. This can primarily be achieved with so-called reconfigurable contacts that allow changing the devices to work as a-type, p-type as well as band-to-band tunnel field-effect transistor (TFET) dynamically.Field effect transistors (FETs) with reconfigurable contacts consist of at least two gate electrodes, namely one that is the actual gate and the other gate electrode (the polarity gate) that allows to reconfigure the transistor. Based on such multiple-gate device architectures, a number of reconfigurable devices based on nanotubes, nanowires and two-dimensional materials have been demonstrated. In particular, switching between the operation as a conventional transistor and a TFET is very attractive since this would enable circuits that can operate either optimized to highest performance (conventional FET operation) or to lowest power consumption (TFET operation). The major drawback of all current reconfigurable FETs is the fact that the polarity gate does not change the work function of the contact metal and as a result, a Fermi level line-up at mid-gap is necessary in order to obtain similar injection of electrons and holes. Hence, carriers are always injected through a substantial Schottky-barrier which yields strongly deteriorated device characteristics. Within the present project, reconfigurable contacts with an injection probability similar to ohmic contacts for electrons and holes are realized. Furthermore, the contacts are made in a way that enables unipolar device operation which is important for proper TFET functionality. To this end, a gated sandwich consisting of a silicon channel layer, ultrathin SiNx and graphene will be employed. The graphene will be used as a metallic source electrode. While graphene-silicon diode/contact structures have been studied in literature the important addition here is the ultrathin SiNx layer in-between the graphene and the silicon. This layer is decisive in order to obtain a very low density of gap-states in the silicon which is necessary for unipolar device operation and, more importantly, for TFET operation with low off-state leakage. The low density of states in graphene around the Dirac point further decreases the density of silicon gap-states and, in addition, enables sufficient gating of the silicon through the graphene/ultrathin SiNx stack so that the conduction/valence bands can be shifted with an appropriate gate voltage. As a result, the current approach provides truly reconfigurable FETs that can operate as n-type, p-type and tunnel field-effect transistors.

在过去的几十年里，通过在相同的芯片区域上增加减小尺寸的晶体管的数量，已经实现了高集成度电路(IC)的性能提高，从而增强了功能。然而，晶体管的可伸缩性很快就会结束。因此，进一步增加IC功能的一个有吸引力的替代方法是为设备本身增加功能。这主要可以通过所谓的可重构触点来实现，其允许将器件动态地改变为a型、p型以及带间隧道场效应晶体管(TFET)。具有可重构触点的场效应晶体管(FET)由至少两个栅电极组成，即一个是实际栅极，另一个栅电极(极性栅极)允许重构晶体管。基于这种多栅器件结构，人们已经展示了许多基于纳米管、纳米线和二维材料的可重构器件。特别是，在作为传统晶体管的操作和TFET之间切换是非常有吸引力的，因为这将使电路能够优化到最高性能(传统FET操作)或最低功耗(TFET操作)。所有电流可重构FET的主要缺点是，极性门不改变接触金属的功函数，因此，为了获得类似的电子和空穴注入，需要在中间禁带处进行费米能级排列。因此，载流子总是通过实质性的肖特基势垒注入，这会导致器件特性严重恶化。在本项目中，实现了具有类似于电子和空穴的欧姆接触的注入概率的可重构接触。此外，触点的制造方式允许单极器件操作，这对于正确的TFET功能非常重要。为此，将采用由硅沟道层、超薄SiNx和石墨烯组成的栅极三明治。石墨烯将被用作金属源电极。虽然在文献中已经研究了石墨烯-硅二极管/接触结构，但重要的是在石墨烯和硅之间增加了超薄的SiNx层。这一层是决定性的，以便在硅中获得非常低密度的带隙状态，这是单极器件操作所必需的，更重要的是，对于具有低关态泄漏的TFET操作。Dirac点附近的石墨烯中态密度较低，进一步降低了硅的带隙密度，此外，通过石墨烯/超薄SiNx堆叠，能够对硅进行足够的栅极，从而可以用适当的栅极电压移动导带/价带。因此，目前的方法提供了真正可重新配置的FET，可以作为n型、p型和隧道场效应晶体管运行。