Flexible high-speed thin-film transistors and circuits based on large-area grown two-dimensional transition metal dichalcogenides

该提案的目的是开发基于柔性衬底上大面积生长的过渡金属二硫属化物（TMD）的高速器件和电路。由于TMD具有上级机械性能，基于TMD的薄膜晶体管（TFT）的重要器件参数（如迁移率、开/关比）在理想的范围内，并且可以实现亚GHz范围内的高频操作，因此TMD是柔性衬底上的理想候选物。大面积均匀生长的TMD是必不可少的可扩展的集成电路。因此，通过金属有机化学气相沉积（MOCVD）和原子层沉积（ALD）的TMD生长工艺将在该项目中开发，其中还包括相关的前体化学组合，以获得高质量和大面积生长，厚度可控。特别地，ALD生长的TMD膜的低处理温度将使得能够在柔性衬底上实现基于TMD的器件和电路的自下而上的方法，而无需时间和成本密集的TMD转移。将制备n型和p型TFT，并在低接触电阻、无针孔的高k电介质层、最佳晶体管设计和合适的ALD/PEALD处理的钝化层方面逐步改进，以增强可靠性和稳定性。特别是对于p型TFT，中心挑战是减少电极和TMD之间的肖特基势垒以有效注入空穴。对于一个完美的波段对齐，必须处理三个任务：1.选择合适的缓冲层以最小化费米能级钉扎，2. TMD的厚度工程和3.选择具有适当功函数的金属。通过将TFT纳米化，我们期望在低GHz范围内实现截止频率。高性能n型和p型TMD TFT的阈值电压将被调整到接近零，并且随后的反相器理想地基于一种TMD材料（例如MoS2或WSe2）来制备。 作为大面积生长的TMD膜上的可扩展集成的证明，多级环形振荡器将被实现和表征。这种环形振荡器是新兴技术中的关键部件，例如射频识别以及无线传感器网络和短距离通信设备。最后将评估器件和电路的弯曲行为。该研究项目预计将导致新的范例方面的大规模合成的TMD通过气相方法和它们的应用灵活的可弯曲的电子无线通信系统。

The aim of the proposal is to develop high-speed devices and circuits based on large-area grown transition metal dichalcogenides (TMDs) on flexible substrates. TMDs are ideal candidates on flexible substrates, since they have superior mechanical properties, the important device parameters of TMDs based thin-film transistors (TFTs) (e.g. mobility, on/off ratio) are in a desirable range and a high-frequency operation in the sub GHz range can be achieved. Large area uniform growth of the TMDs is imperative for scalable integration of circuits. Thus, growth processes of TMDs by metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) will be developed within this project which also includes the relevant precursor chemistry combinations to obtain high quality and large area growth with controlled thickness. Particularly the low processing temperatures for ALD grown TMDs films will enable a bottom-up approach of TMDs based devices and circuits on flexible substrates without time and cost intensive TMDs transfer. n- and p-type TFTs will be prepared and gradually improved in terms of a low contact resistance, a pinhole-free high-k dielectric layer, an optimum transistor design and a suitable ALD/PEALD processed passivation layer for an enhanced reliability and stability. Especially for p-type TFTs, a central challenge is the reduction of the Schottky barrier between the electrodes and TMDs for an effective injection of holes. For a perfect band alignment three tasks must be handled: 1. choice of a suitable buffer layer to minimize Fermi-level pinning, 2. thickness engineering of the TMDs and 3. choice of a metal with an appropriate work function. By nanoscaling the TFTs we expect to achieve cut off frequencies in the low GHz range. The threshold voltage of the high-performance n- and p-type TMD TFTs will be tuned close to zero and subsequent inverters are prepared ideally based on one TMD material e.g. MoS2 or WSe2. As a proof of scalable integration on large area grown TMDs films multistage ring oscillators will be realized and characterized. Such ring oscillators are the key components in emerging technologies such as radio frequency identification as well as wireless sensor networks and short-range communication devices. Finally the bending behavior of the devices and circuits will be evaluated. This research project is expected to lead to new paradigms in terms of large scale synthesis of TMDs via vapor phase approaches and their application for flexible bendable electronics for wireless communication systems.