Low Crosstalk Differential Transmission Line Interconnect on Si ULSI 1. Background Si ULSI: Global Interconnect Freq. > GHz, Length = cm-order 1, Signal wavelengths Global interconnect length 2, The inductance ( L): Cannot be neglected Interconnect must be designed as transmission line. (= RLC distribution constant circuit model) Using the inductance positively High-speed signal transmission can be achieved. 3. Differential Transmission Line Structure for Long Interconnects 2. Purpose Employment of Differential Transmission Line to Interconnect Structures on Si ULSI Differential Transmission Line vs. Single-ended Transmission Line Ground planes or ground lines are not required Superior common-mode noise robustness 1. Differential Transmission Line Structure for Long Interconnects 2. Robustness to Crosstalk Noise Required characteristic of differential transmission lines 1. Low losses (Large bandwidth) 2. Z diff =100 Ω 3. Low interconnect-resource 4. No GND-plane Si M3 Frequency [GHz] Imaginary part of Zdiff [W] -300 -200 -100 0 1 10 100 0 100 200 300 1 10 100 Real part of Zdiff [W] Frequency [GHz] Frequency [GHz] Attenuation [dB/cm] -40 -30 -20 -10 0 1 10 100 W=1 mm W=4 mm W=8 mm W=12 mm W=16 mm W=20 mm w 1 4 8 12 16 20 d 2.2 4.2 6.8 9.8 13.3 16.5 [μm] Co-planar Line Free Parameter: W, d W W d + - Si M3 ILD M2 Frequency [GHz] Attenuation [dB/cm] -40 -30 -20 -10 0 1 10 100 Real part of Zdiff [W] Frequency [GHz] 0 100 200 300 1 10 100 Frequency [GHz] Imaginary part of Zdiff [W] -300 -200 -100 0 1 10 100 w 1 4 8 12 16 20 d 1.3 3.9 7.2 10.5 14.5 18.0 [μm] Diagonal-pair Line W W d Free Parameter: W, d W=1 mm W=4 mm W=8 mm W=12 mm W=16 mm W=20 mm + - Stacked-pair Line Cross-section W = 0.29 mm R DC = 2.4 k Ω/cm Use: M3 & M2 Si M3 ILD M2 + - Film Thickness: Fixed Free Parameter: W Large DC-resistance It is not feasible to use such lossy line for long interconnect. Si M3 ILD M1 W = 1 mm R DC =670 Ω /cm + - Al SiO2 Use: M3 & M1 4. Robustness to Crosstalk Noise 5. Conclusion & Future Work + - + - 4 μm 4 μm 4.2 μm Line Pitch + - + - 4 μm 4 μm 3.9 μm Line Pitch + - + - ILD : 3 m m 4 μm 4 μm 2.6 μm Line Pitch + - + - 4 μm 4 μm 1.2 μm Line Pitch Co-planar Line Diagonal-pair Line Diagonal-pair Line with Thick ILD Diagonal-pair Line of Cu/Low-k ( ε r =2) Z diff =100 Ω (for Lossless Metal) Consideration of transmission line structures Line Parameter: AMS 0.35 μ m CMOS M3: 0.9 μ m, M2&M1: 0.6 μ m, ILD: 1 μ m EM Simulation Ansoft 2D Extractor Forward Crosstalk Coefficient @ Line Length l: 1cm Rise Time tr: 10psec Backward Crosstalk Coefficient Crosstalk Margin : | Crosstalk Coefficient | 0.05 · : Individual Inductance, Capacitance : Mutual Inductance, Capacitance Line Pitch [μm] Crosstalk Coefficient -0.4 -0.2 0 0.2 0.4 4 6 8 10 12 14 16 Line Pitch [μm] Crosstalk Coefficient 0 0.1 0.2 0.3 0.4 12 14 16 18 20 22 24 Line Pitch [μm] Crosstalk Coefficient -0.4 -0.2 0 0.2 0.4 4 6 8 10 12 14 16 Line Pitch [μm] Crosstalk Coefficient -0.4 -0.2 0 0.2 0.4 4 6 8 10 12 14 16 Kf12 Kb12 Kf13 Kb13 Co-planar Line Diagonal-pair Line Diagonal-pair Line with Thick ILD Diagonal-pair Line with Cu/Low-k 0 0.1 0.2 0.3 4 6 8 10 12 14 16 Line Pitch [μm] Diagonal-pair Line Capacitive = Inductive Coupling Coefficient: K f 12 = 0 Coupling Coefficient (pair1 - pair2) 8.1mm Line Pitch 8.6mm 12.6 mm Line Pitch 5.0m m Line Pitch 5.2mm 11.2 mm Line Pitch 15.7 mm Line Pitch 18.2 mm Line Pitch Line Pitch 18.2μm pair 1 pair 2 pair 3 8.1μm pair 1 pair 2 pair 3 5.0μm pair 1 pair 2 pair 3 15.7μm pair 1 pair 2 pair 3 Co-planar Line Diagonal-pair Line Thick ILD Cu/Low-k -14% -56% -73% -62% vs. Co-planar Line of Cu/Low-k 1. Co-planar and diagonal-pair lines have superior attenuation-characteristics as a long interconnect. 2. Diagonal-pair lines reduce the line pitch and crosstalk noise concurrently. Better design-flexibility for Si ULSI Comparison between the electromagnetic simulation and the mesurement Line Pitch vs. Crosstalk Noise (Differential-mode Noise) Common-mode Noise Cancel Differential-mode Noise + - + - + - H. Ito, K. Okada, K. Masu