저항 변화 메모리 소자의 동작 파라미터 제어에 관한 연구

Abstract

Recently, due to scaling increase of devices, we faced with a difficulty of manufacturing process and various physical challenges. resistive random access memory(ReRAM) which shows bi-stable resistance switching characteristics between high and low resistance state by external applied voltage is very extensively investigated as an attractive memory device among next generation non volatile memory(NVMs). Because ReRAM has many advantages such as low power consumption and high operation speed and compatibility with conventional complementary metal oxide semiconductor, it is expected to be applicated to mobile-phone, MP3, camcorder so on future. Neverthless, resistance switching and conduction mechanism are not clarified yet. In this study, the resistive switching behaviors of 4 binary metal oxides(HfO2, ZrO2, TiO2, SiO2) deposited by using RF sputter and ALD technique were firstly investigated. The operating parameters including resistance ratio(HRS/LRS) and operation voltages were measured and the possibility of application to ReRAM insulator materials were checked. Secondly, the resistive switching behaviors of top-electrode/HfO2/bottom-electrode resistors were investigated with symmetric and asymmetric electrode structures of Pt and Al. The asymmetric electrode resistors brought about apparent asymmetric current curves with voltage polarity in a high resistance state. When the electron ejection electrodes of symmetric and asymmetric resistors were the same, the high resistance states were similar. With the strong electron ejection electrode effect, the conduction mechanisms at three domains at cathode, in insulator, and near anode, were suggested to explain the current behaviors in high resistance state. Thirdly, the resistive switching characteristics in a Pt/Ti inserted HfO2/Pt sandwiched structure is investigated for ReRAM application. Here, a Ti-inserted location was changed to top interface between top electrode and insulator, a center of bulk insulator and bottom interface between bottom electrode and insulator. Especailly, the device that Ti was inserted at top interface showed excellent resistive switching performance including good endurance, low operation electric field and a large storage window (ROFF/RON > 107). The formation and rupture of conducting filaments by stable oxygen vacancies generation is believed to be the reason for improvement of the resistance switching characteristics. The integrated experiment and mechanism studies set up the foundation for the development of high-performance multilevel ReRAM.