Under the mainstream trend of continuous miniaturization and flexibility of semiconductor devices, two-dimensional semiconductor materials represented by transition metal chalcogenides (TMDC) such as molybdenum disulfide (MoS2) have shown unique advantages. The International Technology Roadmap for Semiconductors (ITRS) in 2015 clearly pointed out that it is a key material for next-generation semiconductor devices. Two-dimensional semiconductor materials have ultra-thin thickness (monoatomic layer or few atomic layer), excellent electrical, optical, mechanical properties and multi-degree-of-freedom controllability, making it lighter, thinner, faster, and more sensitive in the future Has advantages in electronic devices.
However, the current research on single-layer molybdenum disulfide based on device applications still has the following two key scientific issues: (1) material preparation, how to obtain high-quality large-scale molybdenum disulfide wafers; (2) device technology , How to achieve high-density, high-performance, large-area uniform device processing. This is a common problem that new semiconductor materials have to experience from the laboratory to the market. If the key scientific obstacles to their high-quality large-scale preparation and performance control of integrated devices can be solved, it will forcefully promote the application and development of two-dimensional semiconductor materials and give flexibility The electronics industry has injected new development momentum.
The 2D materials team led by Deputy Director Zhang Guangyu of Songshan Lake Materials Laboratory has been committed to the research of high-quality 2D materials epitaxy, band control, complex structure lamination, functional electronic devices and optoelectronic devices for more than ten years. Recently, the team successfully epitaxially prepared a four-inch high-quality continuous single-layer molybdenum disulfide wafer on a sapphire substrate using a four-inch multi-source chemical vapor deposition equipment independently designed and built, and the epitaxial high-quality film It is spliced by high orientation (0° and 60°) large grains (average grain size greater than 100 μm). In this highly oriented film, high-resolution transmission electron microscopy observed nearly perfect 4|4E type grain boundaries. Thanks to the unique multi-source design, the prepared wafers have the highest electronic quality currently reported in the world. Related work was published in the recent Nano Letters 2020
On this basis, the team carried out a series of device processing technology optimizations, including: (1) Using compatible micromachining technology to fabricate devices layer by layer to ensure the cleanliness between device layers and realize device array processing (2) Adopting a unique atomic layer deposition method combining physical adsorption and chemical reaction to improve the quality of the device insulation layer; (3) Adopting a gold/titanium/gold multilayer structure as the contact electrode, effectively reducing The contact resistance of the device.
Through these optimization methods, the production of large-area molybdenum disulfide flexible transistors and logic devices (such as inverters, NOR gates, NAND gates, AND gates, static random access memories, and five-ring oscillators, etc.) has been successfully realized, and the device performance Outstanding functional characteristics. Among them, the density of flexible field effect transistor devices can reach 1,518 pieces/cm², and the output is as high as 97%, which is the highest index among the reported results. In addition, a single device also exhibits excellent electrical properties and flexibility, with an on-off ratio of 1010, an average mobility of 55 cm2 V-1s-1, and an average current density of 35 μA μm-1. The relevant results were published in the recent Nature Electronics 2020.
These two works broke through the epitaxial technology of wafer-level high-quality molybdenum disulfide thin films, realized high-density integration of molybdenum disulfide flexible transistor devices and logic devices, and provided new ideas and technologies for the development of large-area flexible electronic devices Basically, it is expected to effectively promote the application of two-dimensional semiconductor materials in flexible displays and smart wearable devices.