Kim Woohyun, Yoo Sijung, Yoo Chanyoung, Park Eui-Sang, Jeon Jeongwoo, Kwon Young Jae, Woo Kyung Seok, Kim Han Joon, Lee Yoon Kyeung, Hwang Cheol Seong
Department of Materials Science and Engineering, and Inter-University Semiconductor Research Center, Seoul National University, Seoul 08826, Republic of Korea.
Nanotechnology. 2018 Sep 7;29(36):365202. doi: 10.1088/1361-6528/aacda0. Epub 2018 Jun 19.
The ovonic threshold switch (OTS) based on the voltage snapback of amorphous chalcogenides possesses several desirable characteristics: bidirectional switching, a controllable threshold voltage (V ) and processability for three-dimensional stackable devices. Among the materials that can be used as OTS, GeSe has a strong glass-forming ability (∼350 °C crystallization temperature), with a simple binary composition. Described herein is a new method of depositing GeSe films through atomic layer deposition (ALD), using HGeCl and [(CH)Si]Se as Ge and Se precursors, respectively. The stoichiometric GeSe thin films were formed through a ligand exchange reaction between the two precursor molecules, without the adoption of an additional reaction gas, at low substrate temperatures ranging from 70 °C-150 °C. The pseudo-saturation behavior required a long time of Ge precursor injection to achieve the saturation growth rate. This was due to the adverse influence of the physisorbed precursor and byproduct molecules on the efficient chemical adsorption reaction between the precursors and reaction sites. To overcome the slow saturation and excessive use of the Ge precursor, the discrete feeding method (DFM), where HGeCl is supplied multiple times consecutively with subdivided pulse times, was adopted. DFM led to the saturation of the GeSe growth rate at a much shorter total injection time of the Ge precursor, and improved the film density and oxidation resistance properties. The GeSe film grown via DFM exhibited a short OTS time of ∼40 ns, a ∼10 ON/OFF current ratio, and ∼10 selectivity. The OTS behavior was consistent with the modified Poole-Frenkel mechanism in the OFF state. In contrast, the similar GeSe film grown through the conventional ALD showed a low density and high vulnerability to oxidation, which prevented the OTS performance. The ALD method of GeSe films introduced here will contribute to the fabrication of a three-dimensionally integrated memory as a selector device for preventing sneak current.
基于非晶硫属化物电压骤回特性的双向阈值开关（OTS）具有几个理想特性：双向开关特性、可控阈值电压（V ）以及三维可堆叠器件的可加工性。在可用作OTS的材料中，GeSe具有很强的玻璃形成能力（结晶温度约为350°C），且成分简单为二元体系。本文介绍了一种通过原子层沉积（ALD）制备GeSe薄膜的新方法，分别使用HGeCl和[(CH)Si]Se作为Ge和Se前驱体。通过两个前驱体分子之间的配体交换反应，在70°C至150°C的低衬底温度下，无需额外的反应气体即可形成化学计量比的GeSe薄膜。伪饱和行为需要长时间注入Ge前驱体才能达到饱和生长速率。这是由于物理吸附的前驱体和副产物分子对前驱体与反应位点之间有效化学吸附反应的不利影响。为了克服饱和缓慢和Ge前驱体使用过多的问题，采用了离散进料法（DFM），即多次连续供应HGeCl，每次脉冲时间细分。DFM在Ge前驱体的总注入时间短得多的情况下使GeSe生长速率达到饱和，并改善了薄膜密度和抗氧化性能。通过DFM生长的GeSe薄膜表现出约40 ns的短OTS时间、约10的开/关电流比和约10的选择性。OTS行为在关断状态下与修正的普尔-弗伦克尔机制一致。相比之下，通过传统ALD生长的类似GeSe薄膜密度低且抗氧化性差，这阻碍了OTS性能。这里介绍的GeSe薄膜的ALD方法将有助于制造三维集成存储器，作为防止潜行电流的选择器器件。
