A Study of Novel Polyimide Macromolecular Material for Nonvolatile Memory Applications

• Main Authors: Yu-Ping Hsiao, 蕭郁蘋
• Other Authors: Wen-Lug Yang
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/v2nk79

博士 === 逢甲大學 === 電機與通訊工程博士學位學程 === 104 === To achieve the properties of lightweight as well as low-cost and high yield, the critical manufacturing technique of non-volatile memories (NVMs) is entering into nano-scale generation. Flash memories have faced rigorous challenges regarding to device shrinking in vertical and horizontal dimensions, and multi-stacked 3-D structure, causing the fully attention and investigation of next-generation NVMs. Among them, resistive random access memories (ReRAMs) have stood up from the crowd because of its shrinkability, simple structure, low operation voltage, fast operation speed, excellent endurance, low power consumption, and high compatibility to current CMOS manufacturing process. A lot of materials have been studied to be the candidates of the switching layer of ReRAM devices. Organic polymer-based ReRAMs, exhibiting high capacity and reliable performance, have been drawn dramatic attention to be the next-generation NVMs because of its good properties such as simple device structure, low fabrication costs, printability, and flexibility. To apply the macromolecular organic material to NVMs for the coming flexible electronics generation, a novel polyimide (PI) was studied in this dissertation. Here we focus on the selections of critical monomer unit and clarification of switching mechanisms to develop manufacturing techniques and to achieve excellent reliability. First, the effects of molecular chain density on PI/metal contact have been investigated by adjusting the dilution of polyamic acid. Then, the influences of PI/metal contact on the memory properties of PI ReRAM have been studied via Al/PI/Al and TaN/PI/TaN vertical ReRAM structures. Meanwhile, the PI ReRAM composed of 4-(4-phenylpiperazin-1-yl)benzene-1,3-diamine (AP) and 4,4’-oxydiphthalic anhydride (ODPA), exhibits high ION/IOFF ratio, low power consumption, narrow distribution of operation voltages and resistance state currents, and excellent reliability. Also, a Fourier transform infrared spectrum was used to confirm the imidization level of PI, and the relation between imidization level and memory properties have been discussed and analyzed. The dangling bonds and interface shallow trap density of PI thin film can be reduced after a higher level imidization process. Hence, an excellent data retention property for PI-based ReRAM can be achieved. Besides, a higher ION/IOFF ratio, better data retention and endurance can be obtained using a higher level imidization process. This is because the lower number of dangling bonds, higher mobility of charge transfer, and lager size of conduction path lead to an increase in conductivity in low resistance state. Furthermore, rubbing process (RP), which is used in liquid-crystal display (LCD), is also applied in fabricating NVMs. Through this process, the molecular chains of the PI surface can be re-organized form random to more regular and uniform direction, resulting in the improvement of PI/metal Schottky effect. Therefore, the uniformity and leakage of the memory in the HRS, the power consumption in the LRS, as well as the data retention at high temperature, have all been improved. Finally, the research achievements and contribution are summarized. To evo lve the PI ReRAM and RP more mature and complete, some future recommendations have been given.