True Nonvolatile High-speed DRAM Cells Using Tailored Ultrathin IGZO.

Severe power consumption in the continuous scaling of Si-based DRAM technology quests for a transistor technology with a much lower off-state leakage current. Wide bandgap amorphous oxide semiconductors, especially IGZO exhibit many orders of magnitude lower off-state leakage. However, they are typically heavily n-doped and require negative gate voltage to turnoff, which prevent them from true nonvolatile operation. The efforts on doping density reduction typically result in mobility degradation and high Schottky barriers at contacts, causing severe degradation of on-current and operation speed of the DRAM cells. Here, we successfully demonstrate high-speed true nonvolatile DRAM cells by deep suppression of doping density in the IGZO channel using in-situ oxygen ion beam treatment and ohmic contact engineering by inserting a thin In-rich ITO at contact regions. A record high on-current of 40 μA/μm with a large positive threshold voltage of 1.78 V enables the first true nonvolatile DRAM with a fastest write speed of 10 ns and data retention up to 25 hours under power interruption, five orders of magnitude higher than the previously projected values. This article is protected by copyright. All rights reserved.