Unipolar Switching Characteristics for Self-Aligned WOx Resistance RAM (R-RAM)

For the first time a unipolar resistance memory with good performance and reliability is demonstrated. A short (20-50 ns) positive pulse switches the WO_x film from low resistance state (LRS) to high resistance state (HRS), while a longer (200-500 ns) positive pulse switches the film from HRS to LRS. Negative pulses, on the other hand, do not produce reversible resistivity changes. Despite the low energy switching, both LRS and HRS are very stable, capable of withstanding 2,500 hours of baking at up to 150 degC- Furthermore, the WO_x R-RAM can withstand > 1,000 cycles of LRS/HRS switching, and the device is also highly immune to read disturb. This unipolar device is promising for future 3D high-density NVM storage.