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

Area of Science:

• Materials Science
• Semiconductor Physics
• Electrical Engineering

Background:

• Silicon-based dynamic random access memory (DRAM) faces power consumption challenges due to scaling limitations and off-state leakage.
• Amorphous oxide semiconductors like indium-gallium-zinc-oxide (IGZO) offer lower leakage but are typically n-doped, hindering nonvolatile operation.
• Reducing IGZO doping density often degrades mobility and contact properties, impacting performance.

Purpose of the Study:

• To develop high-speed, true nonvolatile DRAM cells using wide bandgap amorphous oxide semiconductors.
• To overcome the limitations of n-doped IGZO, specifically the need for negative gate voltage and performance degradation issues.
• To achieve significantly improved data retention and reduced power consumption compared to existing DRAM technologies.

Main Methods:

• Deep suppression of doping density in the IGZO channel via in situ oxygen ion beam treatment.
• Ohmic contact engineering using a thin indium-rich indium-tin-oxide (ITO) insertion layer.
• Fabrication and characterization of high-speed true nonvolatile DRAM cells.

Main Results:

• Demonstration of true nonvolatile DRAM cells with a record high on-current of 40 µA µm⁻¹ at a threshold voltage of 1.78 V.
• Achieved the fastest write speed of 10 ns for nonvolatile DRAM.
• Exhibited data retention up to 25 hours under power interruption, a five-order-of-magnitude improvement over projections.

Conclusions:

• The developed IGZO-based nonvolatile DRAM cells successfully address power consumption and nonvolatility challenges.
• In situ oxygen ion beam treatment and ITO contact engineering are critical for high performance and reliability.
• This technology represents a significant advancement towards next-generation low-power, high-performance memory solutions.