Focusing on the above problems, the research group of Professor Wang Xinran from School of Electronic Science and Engineering of Nanjing University has made a breakthrough in the key technologies of two-dimensional semiconductor single crystal preparation and heterogeneous integration, which provides a new idea for the development of integrated circuits in the post-Moore era. Related research results were recently published in Nature Nanotechnology.
Semiconductor single crystal material is the cornerstone of microelectronics industry. Compared with the mainstream 12 inch single crystal silicon wafer, the preparation of two-dimensional semiconductor is still in the stage of small size and polycrystalline. Developing large-area and high-quality single crystal thin films is the first step towards two-dimensional integrated circuits. However, in the growth process of two-dimensional materials, millions of microscopic grains are randomly generated. Only by controlling the strict and consistent arrangement direction of all grains can a complete single crystal material be obtained.
Sapphire is a kind of substrate widely used in semiconductor industry, which has outstanding advantages in mass production, low cost and process compatibility. The cooperative team proposed a scheme to artificially construct an atomic scale "step" by changing the direction of the atomic step on the sapphire surface.
The directional growth of TMDC is realized by using the directional induction nucleation mechanism of "atomic step" Based on this principle, the team realized the epitaxial growth of 2-inch MoS2 single crystal film for the first time in the world.
Due to the improvement of material quality, the mobility and current density of field effect transistors based on MoS2 single crystal are as high as 102.6 cm2/Vs and 450 μA/ micron, which is one of the highest comprehensive properties reported in the world. At the same time, this technology has good universality and is suitable for the preparation of single crystals of other materials such as MoSe2. This work has laid a material foundation for the application of TMDC in the field of integrated circuits.
The breakthrough of large-area single crystal materials makes the application of two-dimensional semiconductor trend possible. In the second work, based on the accumulation of the third generation semiconductor research for many years, combined with the latest two-dimensional semiconductor single crystal scheme, the cooperative team of Institute of Electronics proposed the ultra-high resolution micro LED display technology scheme based on MoS2 thin film transistor driving circuit and monolithic integration.
Micro-LED refers to the technology that micron-scale LED is used as light-emitting pixel unit and assembled with driving module to form high-density display array. Compared with the current mainstream display technologies such as LCD and organic light emitting diode, Micro-LED has a generational advantage in brightness, resolution, energy consumption, service life, response speed and thermal stability, and is internationally recognized as the next generation display technology. However, the industrialization of Micro-LED still faces many challenges.
First of all, it is difficult to match the driving requirements of high-density display units under small size. Secondly, the popular mass transfer technology in the industry is difficult to meet the development needs of high-resolution display technology in terms of cost and yield. Especially for ultra-high resolution applications such as AR/VR, not only the resolution exceeds 3000PPI, but also the display pixels are required to have faster response frequency.
Aiming at the field of high-resolution micro-display, the cooperative team proposed a technical scheme of 3D monolithic integration of MoS2 thin film transistor driving circuit and GaN-based micro-LED display chip. The team has developed a low-temperature monolithic heterogeneous integration technology that is not a "large-scale transfer", and realized a high-brightness and high-resolution microdisplay of 1270 PPI by using the almost lossless manufacturing process of large-size two-dimensional semiconductor TFT, which can meet the cross-domain applications such as microdisplay, vehicle display and visible light communication in the future.
Among them, compared with the traditional two-dimensional semiconductor device process, the new process developed by the team improves the performance of thin film transistors by more than 200%, reduces the difference by 67%, and the maximum driving current exceeds 200 μA/ μ m, which is superior to commercial materials such as IGZO and LTPS, showing the huge application potential of two-dimensional semiconductor materials in the display driving industry.
This work integrates high-performance two-dimensional semiconductor TFT and Micro-LED for the first time in the world, which provides a new technical route for the development of Micro-LED display technology in the future.
The above work was completed on the basis of "The Epidemiology of Wafer-level Molybdenum Semiconductor Single Crystal on Sapphire" (Correspondents are Professor Wang Xinran and Professor Wang Jinlan from Southeast University) and "Three Dimensions". Al Monolithic Micro led Display Driven by Atomic Thin Emitter Matrix (written by professors, Shi Yi and Zhang Rong) was recently published online in Nature Nanotechnology.