Novel Program Method of String Select Transistors for Layer Selection in Channel-Stacked NAND Flash Memory
In this paper, we propose new string select transistors (SSTs)/dummy SSTs (DSSTs) threshold voltage (Vth) setting methods in simplified channel-stacked array with layer selection by multilevel operation (SLSM). In these methods, SSTs/DSSTs on each layer are set to their targeted Vth values by incremental step pulse program/one erase with various erase voltages, respectively. In the fabricated pseudo-SLSM, the validity of the new methods is verified. As a result, it is confirmed that the Vth values of SSTs/DSSTs are set to the targeted Vth values by the new methods and SSTs with extremely narrow Vth distribution can be obtained in the consequence. Moreover, memory operations such as erase, program, and read are performed in the fabricated structure after setting the Vth values of all the SSTs/DSSTs by the new methods. Despite unique LSM operations, stable memory operations are obtained successfully without the interference between stacked layers.
Multi-Level Threshold Voltage Setting Method of String Select Transistors for Layer Selection in Channel Stacked NAND Flash Memory
In this letter, we propose a simplified channel stacked array with a layer selection by multi-level operation (SLSM) and a new string select transistors (SSTs) threshold voltage (Vth) setting method that all the SSTs on each layer are set to targeted the Vth values simultaneously by one erase operation. To verify the validity of the new method in SLSM, TCAD simulations are performed, and a fabricated pseudo SLSM is measured. It is verified that the Vth values of SSTs are set to the targeted Vth values by the new method. Moreover, memory operations are examined in the fabricated structure after setting the Vth values of all the SSTs by the new method. As a result, stable memory operations are obtained successfully without the interference between stacked layers.
Water Quality Aspects of Irrigation and Drainage: Past History and Future Challenges for Civil Engineers
This paper presents a brief history of irrigation and drainage related to ASCE activities on its Jubilee. This paper discusses legislation and policies that affect irrigation and drainage practices, water quality constituents of increasing concern in irrigation and drainage practices, and presents a prognosis on the future of declining freshwater resources available for irrigated agriculture and growing water quality problems in irrigation and drainage. Civil engineers in ASCE’s Irrigation and Drainage Division have compiled an 80-year history of highly meritorious service and accomplishments. In the next millennium, civil engineers will face a formidable challenge in managing and protecting the precious freshwater resources in the U.S.