1. Fabrication and Characterization of Ultra-narrow RRAM Cells Byoungil Lee and H.-S. Philip Wong Electrical Engineering, Stanford University

2. Motivations AlOx RRAM typical cell characteristics Fabrication of ultra-narrow RRAM cells Characterization of ultra-narrow cells Summary and discussion Outline

3. Motivations –Issues with RRAM Over-SET by over-shoot current. Poor LRS uniformity, large reset current, and device failure. Current-limiting devices are required. Implementation of ‘Within-A-Cell-Current-Limiter’. –Study of scaling Ultra-narrow RRAM Cells

4. –Bipolar switching. –Large variation in LRS and I RESET. AlOx RRAM Large Cell AlOx Pt TiN 10nm W w w

5. AlOx RRAM Large Cell –Filamentary conduction property. –Does not scale with the size.

6. AlOx RRAM Large Cell –Filamentary conduction property. –Does not scale with the size. –LRS and I RESET are determined by I limit

7. I RESET  I SET in RRAM

8. Scaling Trend of RRAM –Filamentary conduction property. –No scaling with the size in the previous works. –LRS of our RRAM cell does scale with the size!

9. Ultra-narrow RRAM Cell using ALD AlOx w w 100nm –Top-view SEM of the fabricated devices. –Smallest cell size: 50nm X 50nm

10. - Top Pt: 40nm, TiN: 40nm - Oxides thickness: 7.4 nm - Bottom Pt: 40nm - Metal width: 100nm - AlOx width: 10nm TiN Pt 10nm AlOx SiO 2 20nm Ultra-narrow RRAM Cell using ALD AlOx

11. Pt SiO2 Pt TiN Pt SiO2 Pt TiN Pt SiO2 Pt TiN Pt SiO2 Pt TiN d w t AlO x Process Flow

12. DC I-V Characteristics –SET current is limited without any external current-limiters. –Due to resistive TiN layer and small contact area.

13. Line Resistance – Current-limiting is not a result of the long electrode line. – New device features ‘Within-A-Cell-Current-Limiter.’

14. Programming Cycle Test –500nm standard cell shows a broad tail in LRS distribution. –Ultra-narrow cells truncate lower-end of LRS distribution.

15. Scaling Trend of Ultra-narrow Cells –Filamentary conduction property. –I RESET and LRS does scale with the size!

16. - SET/RESET: 30ns/1us - SET/RESET: 4ns/20ns Programming Speed

17. Programming Endurance – 10 4 programming cycles.

18. Summary Demonstrated fabrication and characterization of ultra-narrow RRAM cells. Established new aspect of scaling trend of filamentary conduction devices. Within-A-Cell-Current-Limiter improves LRS distribution without integrating TRs.