Preparation And Properties Of A TiAl₂O₅ Nanocrystal Charge Trapping Memory Device

Nowadays, portable electronic devices, such as laptop computers, cell phones and digital cameras, have been used widely. Flash memories have played important role in these devices. The development demand for the future Flash memory technology can be concluded to larger storage capacity, faster read/write speed, lower power operation and longer time retention. Since the concept of Flash memory was proposed, it has dominated current non-volatile semiconductor memory market. Now more than 90% of the non-volatile semiconductor memory market has been accounted by it. While the Flash memory application in the commercial market has get great success, the traditional floating gate has to face serious technical problems for the tradeoffs between the high speed, low power operation and long time retention. And higher requirement was proposed at several characters such as speed, power and reliability. Generally there are mainly two ways in searching for a next-generation non-volatile memory device in industry and academe. One is the evolution way to push the current Flash memory technology to more advanced technology node.The other is the revolution way to utilize a different storage mechanisms when Flash technology has approached its physical limits. This work focus on studying the preparation and properties of a novel TiAl2O5 nanocrystal charge trapping memory.The main conclusions are summarized as follows:1. In order to investigate the crystallization behaviors of Ti0.2Al0.8Ox films, Ti0.2Al0.8Ox films were deposited by using the PLD method, then annealed at 800,900,1000℃for 3 minutes in N2 with a RTA process, respectively. Ti0.2Al0.8Ox films annealed at the temperature lower than 900℃remain amorphous, while those annealed at 900℃or above suffered a phase separation reaction. TiAl2O5 nanocrystals are precipitated from the phase separation of Ti0.2Al0.8Ox film2. The nanocrystal charge trapping memory device with a Pt/Al2O3/Ti0.2Al0.8Ox (TAO)/Al2O3/p-Si stack was fabricated by PLD and ALD method. A memory window of 2.3 V and a stored electron density of 1 X 1013/cm2 were obtained. The good data retention characteristics of the memory device were obtained in the programming/erasing condition at room temperature and 80℃.3. In order to well understand the working mechanism of our CTM device, the cross-sectional image of the high resolution transmission electron microscopic (HRTEM) image of a memory device was observed and the band diagram for the hetero structure was determined by investigating the valence band offsets (VBO) and O 1s electron energy loss spectra of p-Si substrate, the interface and the surface of the device. It can be got from the band diagram that he deep trap level between TiA12O5 and A12O3 can suppress the migration of trapped electrons.