Abstract
The motivation of this thesis is to study and to improve the switching reliability of the HfOX resistive memory. Although the forming-free device with a 3-nm-thick HfOX film exhibits large on/off resistance ratio and good memory performances, the RHIGH of the forming-free device is not high enough to guarantee lower the operation current. Current overshoot, which degrades the RHIGH and elevating the operation current, is a critical issue for the operation of resistive memory and can be solved by using the transistor to perfectly clamp the current. The high RHIGH over 1 Mohm, large on/off ratio of 100, and excellent endurance of 1010 cycles is demonstrated for the 10-nm-thick HfOX device with 1T1R architecture. Under the appropriate current of 100 μA, the 1kb memory array exhibits the endurance exceeding more than 106 cycles. The effective suppression of soft-errors by novel verification methods can tighten RHIGH and RLOW distributions and restore the on/off ratio of the 1kb array during the endurance test. A possible scenario for the novel high voltage SET-RESET-SET (SRS) verification of low resistance state is addressed. Two nanometer scale devices with the concave and pillar structure are fabricated and investigated for the resistive switching. The 30 nm 1T1R device with adequate resistive switching performances is demonstrated in the concave structure. By using a Si3N4 encapsulation layer which is inert to Ti capping layer, the 50 nm pillar device exhibits a high RHIGH closing to that of micrometer scale control device, robust thermal immunity at 200 °C, good cycling reliability, and no current overshoot problem. Owing to excellent switching endurance of 1010 cycles, high device yield and large on/off ratio in the 1kb array, and superior scalability to 30 nm, the HfOX resistive memory with low operation power and ultra-high switching speed has a strong potential for replacing DRAM and flash, and being the next generation non-volatile memory.