Multi-deposition effect: from diode to memristor
Teng-Yu Su1*, Yu-Chuan Shih1, Henry Medina1, Jian-Shiou Huang1, Yu-Lun Chueh1
1material science and engineering, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:Teng-Yu Su,
Resistive switching random access memory (ReRAM) is one of the most promising candidates for next generation nonvolatile memory due to simple structure (metal/insulator/metal), fast operation speed, high endurance and so on. The most common method of depositing insulator film is by sputtering. However, the sputtering process may cause some defects, which will affect the electrical behavior. To investigate this phenomenon, we try to use reactive sputtering process to deposit TiON film as insulating layer with Ti target in the atmosphere of mixing oxygen, nitrogen, and argon gas. The TiON film is deposited on TiN as bottom electrode and we deposited Pt as top electrode with sputtering and patterned by hard mask. We fixed the same thickness of TiON about 50nm and changed the deposition times of each device. For example, we deposit TiON with only one time which means it is without breaking the plasma and the other is deposited with six times which means we broke the plasma for six times forming six layers. By electrical measurement, we find out the some difference between these two kinds of devices. First, the uniformity of initial resistive state is different, the six layer device show high resistance and high uniformity. We tried three different O and N concentration to check this phenomenon and it showed the same trend. Furthermore, we discovered diode behavior in the device with six layers and it can be operated steadily within the threshold voltage. The more interesting thing is the diode behavior can be transformed into memristor by a forming process. This memristor can also be well operated with on/off ratio 102 and endurance over 100 times. For further discussion, we collected statics comparison among these two type device such as forming voltage, device yield and diode property. In six layer device with higher initial resistance state, it need higher forming voltage for conducting filament formation and the yield can achieve almost 100%. Despite electrical measurement, we tried to use other measurements, such as PL and XPS, to discuss about this phenomenon. In PL spectrum, we find out the internal defect inside the six layer thin film and it may be the main reason for this behavior. This defect may trap the electron from transporting through the insulting layer and also change the band diagram. By this research, we can figure out what plasma will affect the film and furthermore, we may have chance to do 1D1R device homogeneously.

Keywords: resistive switching, sputter, memory