Fudan researchers’ innovation of third-class storage technology published on Nature Nanotechnology

Recently, the team of Professor Zhang Wei and Professor Zhou Peng of School of Microelectronics developed a revolutionary 2D quasi-nonvolatile storage prototype device, paving the way to the third-class storage technology and solving the tradeoff between ‘writing speed’ and ‘non-volatile’ in semiconductor charge storage technology. On April 9, this work was published on Nature Nanotechnology entitled “A semi-floating gate memory based on van der Waals heterostructures for quasi-nonvolatile applications”.

New method for data storage: 10-nanosecond writing speed and customized validity

There are currently two types of charge storage technology in semiconductors, volatile storage, e.g., memories in computers, which loses data after powered off, and non-volatile storage, e.g., USB drives, which can save input data for 10 years without extra energy. The former can write in data in a few nanoseconds, while the latter requires several microseconds to tens of microseconds to save the data.

 But the new charge storage technology developed at Fudan reaches the writing speed of 10 nanoseconds and in the meantime enables customizing-on-demand (10 seconds to 10 years) adjustable nonvolatile data storage. The innovative change not only significantly lowers the storage’s power consumption, but also makes the data naturally vanish after the expiration time. Thus, the contradiction between confidentiality and transmission is resolved

       New combination of 2D materials: bringing the rich characteristics of energy band into full play between ‘opening the door’ and ‘hitting the wall’

  ‘This research is pioneering in combining multiple 2D materials to form the Semi-Floating-Gate Transistor (SFGT), making full use of their different energy band characteristics’ Professor Zhou Peng remarked. “Some of them are like a door which can be readily turned on and off, making electrons easy to go in and hard to go out. Others are like an impenetrable wall where electrons are hard to go in and out. The tailoring property of ‘writing speed’ and ‘non-volatile’ lies in the proportion of these two types of materials.

  The writing speed of the new device is 10000 times faster than the current USB drives and the data refreshing speed is 156 times of that of current memory technology. It also has excellent adjustability, which can design the storage structure based on the requirement of data validity. After careful experimentation, researchers found that this kind of new heterojunction based on 2D materials makes the implementation of the third-class storage possible. In 2017, the team reported that using the rich energy band structure of 2D semiconductors to deal with the over-erasing phenomenon in charge storage technology on Small. In their follow-up researches of storage device, the team found that using 2D semiconductors to build the new storage structure would introduce more ‘strange new characteristics’.

  2D materials originated from the discovery of Graphene have strong chemical bonds in the planes and are stacked together by intermolecular force between layers. Hence, single-layer atomic level crystalline with perfect boundary characteristics can be obtained through 2D materials. Meanwhile such materials can form a system of conductors, semiconductors and insulators, which can contribute to the further development of scaling, integrity, stability and storage in integrated circuit devices. It is a brand-new way of lowering storage power consumption and improving integrity. Besides, high-density integration can be realized by using 2D semiconductor quasi-nonvolatile storage based on large-scale synthesis technology, which will play an important role in many fields such as extreme-low power consumption, high speed storage and utilization of storage validity freedom.

  The scientific breakthrough, including the whole process of technology definition, structural model and performance analysis, was completed independently by the research team of Fudan University, and the result was published  on Nature Nanotechnology as a full article. PhD student Liu Chunsen and his supervisor Professor Zhou Peng are the first co-authors. Professor Zhang Wei and Professor Zhou Peng are the corresponding authors. The state key lab of ASIC and system in Fudan University is the only affiliation of the authors.