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Phase change memory technology Rob Wolters September 2008.

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Presentation on theme: "Phase change memory technology Rob Wolters September 2008."— Presentation transcript:

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2 Phase change memory technology Rob Wolters September 2008

3 Rob Wolters, 29 september 2008 2 Contents Introduction Phase change materials Memory cell concepts Switching Endurance Retention Perspective

4 Rob Wolters, 29 september 2008 3 Programming and erasing the floating gate Control gate Floating gate Control gate SiO 2 Si 3 N 4 Polysilicon High voltage “Thick” gate oxide Double poly

5 Rob Wolters, 29 september 2008 4 Introduction (present NVM) density is improving! for how long? performance is stagnating! forever!

6 Rob Wolters, 29 september 2008 5 Optical storage: CD, DVD and Blu-ray disc

7 Rob Wolters, 29 september 2008 6 Optical storage: Blu-Ray DVD-RW 300 nm

8 Rob Wolters, 29 september 2008 7 Phase change materials SEM picture of DVD-RW dots Sb-M SbTe-M ‘ 225’

9 Rob Wolters, 29 september 2008 8 What is the PC RAM challenge: How to integrateinto DVD-RW materials on chip

10 Rob Wolters, 29 september 2008 9 PC RAM principle A simple scalable device: An access transistor and a programmable element (PE) High switching speed (~ns) Read/write endurance: >10 12 (Flash: 10 6 ) Memory array with NMOS transistors: PE word-lines bit-lines PE based on a switching resistance Phase-change materialsamorphous phase: ‘high’-Ohmic crystalline phase: ‘low’-Ohmic Fast switching between amorphous and crystalline phase

11 Rob Wolters, 29 september 2008 10 Phase change technology: Ovonyx cell (Ovshinsky in 1966) Small amorphous volume ~20 nm 3 ! Sidewall spacer contact 1T – 1R cell Ovonyx cell

12 Rob Wolters, 29 september 2008 11 Cell concepts Megabit demonstrators by Intel, STM, Samsung  Ovonyx concept Small contact area between PC-layer and electrode Small volume undergoes phase change “Ovonyx concept” (cross section) “NXP novel line concept” (top view) Small area highest resistance NXP Approach: Novel cell concept & Material = Electrode material= Phase-change material

13 Rob Wolters, 29 september 2008 12 line of phase-change material Thickness: 15 nm Width: 50nm Length: 1000 nm Metal contacts (TiN) Line concept

14 Rob Wolters, 29 september 2008 13 Switching Electric pulses induce Joule heating RESET pulse: - T > T melt - Rapid cooling down  amorphization SET pulse: - T > T cryst - Longer pulse  crystallization

15 Rob Wolters, 29 september 2008 14 Single cell data for “fast-growth” material

16 Rob Wolters, 29 september 2008 15 Electric pulses induce Joule heating RESET pulse: - T > T melt - Rapid cooling down  amorphization Phase-change materials Cell switching RESET PE word-lines bit-lines P = I 2. R (Joule heating) I: determined by technology node For optimum energy transfer: R PE = R transistor (~2 k Ω) R PE = ρ. L/A

17 Rob Wolters, 29 september 2008 16 20 nm 5 nm Phase-change materials Cell switching RESET I reset as a function of line width for 20 and 5 nm thick PC, L=2W

18 Rob Wolters, 29 september 2008 17 Phase-change materials Cell switching SET Amorphous state shows a threshold voltage

19 Rob Wolters, 29 september 2008 18 Cell switching 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.500.511.522.5 Vdut [V] Idut [mA] Crystalline Amorphous Threshold voltage PE word-lines bit-lines V dut = V T. L V: determined by technology node V T : material characteristic V = 1-2 V, L < 100 nm

20 Rob Wolters, 29 september 2008 19 Process integration PC cells embedded in a standard CMOS process W-plugs Metal 2 Via & Trench TaN Electrode Passivation STI Phase change cell Metal1 Top view SEM Cross-section SEM

21 Rob Wolters, 29 september 2008 20 Sensing window in SET/RESET resistance 2 kb memory sub-sector SET RESET Integrated Test Cells

22 Rob Wolters, 29 september 2008 21 Imin+15% Endurance

23 Rob Wolters, 29 september 2008 22 Retention DVD: amorphous dots in a crystalline matrix Size: appr. 300 x 300 nm PC cell: amorphous dot and crystalline areas aside. Size: appr. 50 x 100 nm System tends to the lowest energy: crystallinity!

24 Rob Wolters, 29 september 2008 23 Retention DVD: amorphous dots in a crystalline matrix Ga 15 Sb 75 Increased doping

25 Rob Wolters, 29 september 2008 24 Positioning of amorphous spot. Thomson Effect IEDM 2007 Thermoelectric effect

26 Rob Wolters, 29 september 2008 25 PCM performance Fast (~50 ns) Low voltage (0.4-2 V) Scaling: good Medium endurance (10 9 -10 13 ) Medium current (50-300  A) Energy (pJ/switch) PCM costs Only 3 additional masks NVM/Flash performance Slow (  s-ms) High voltage (10-15 V) Scaling: bad Short endurance (10 5 -10 6 ) Low current (~ nA) Energy (nJ/switch) NVM/Flash costs 8-10 additional masks Perspective

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