Charge-triggered switching mechanism in selenium selector enabling ultralow leakage current

Area of Science:

• Materials Science
• Electrical Engineering
• Computer Science

Background:

• Current AI models demand memory solutions exceeding dynamic random-access memory/flash storage capabilities in speed, density, and energy efficiency.
• Three-dimensional phase-change memory presents a scalable solution, but its cross-point integration is hindered by selector performance limitations.

Purpose of the Study:

• To identify a high-performance selector material for 3D phase-change memory.
• To elucidate the operating mechanism of ovonic threshold switch (OTS) selectors.

Main Methods:

• Reverse-tracing previously reported OTS materials to identify novel candidates.
• Characterizing amorphous elemental selenium as an OTS selector, evaluating its electrical properties, switching speed, and endurance.
• Utilizing photoexcitation spectroscopy and density functional theory (DFT) calculations to investigate the switching mechanism.
• Integrating selenium-based selectors into 3D phase-change memory arrays for performance validation.

Main Results:

• Amorphous selenium demonstrated exceptional OTS selector performance: ultralow leakage current (4 × 10^-12 A), on/off ratio > 10⁸, high drive current density (21.2 MA cm^-2), fast switching (~20 ns), and high endurance (> 2 × 10⁹ cycles).
• A charge-triggered mechanism involving dense trap pairs and avalanche multiplication was identified as responsible for the abrupt switching and high on-current.
• Integrated memory arrays exhibited reliable write/erase operations with a significant 0.75-V read margin.

Conclusions:

• Amorphous selenium is established as a leading selector material for 3D memory applications.
• The study clarifies the fundamental mechanism behind OTS switching.
• The findings pave the way for next-generation, high-performance memory devices essential for advancing AI.