The Fifth Workshop on Nanoelectronics for Tera-bit Information Processing, 1 st Century COE, Hiroshima University Optical Interconnection in Silicon LSI Shin Yokoyama, Yuichiro Tanushi, and Masato Suzuki Research Center for Integrated Systems Hiroshima University, Japan http://www.rcis.hiroshima-u.ac.jp/rcns/ Electro-Optic (EO) Material () I. Optical Switches using Magneto-Optic Material. Optical Switches using Si Ring Resonator I. Summary 1 Why Optical Interconnection? (Ultra High Frequency) Why Optical Interconnection? Frequency (Hz) Optical Interconnection ~ THz (1.55 m) Small Size Optical Waveguide Coaxial Transmission Line 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 1 1 11 1 1 1 13 1 14 1 15 1 16 1 17 1 18 1 19 1 1 1 1 1 3 1 5 1 4 1 3 1 1 1 1 1-1 1-1 -3 1-4 1 1-6 1-7 1-8 1-9 1-1 1-11 1-1 1-13 1-14 Cellular Phone Wavelength (m) Electro Magnetic Wave Radio Television Microwave Tera-Hz Wave Far IR Satellite Broadcast IR Optical Fiber U X-Ray -Ray isible (1.55m) ~1 times as High Frequency as Tera-Hz Wave m Clad 1m 4 m Si 3 N 4 Core.5 m thick.6 db/cm 3 m 1 m 3 m 3 m 3 m Extremely High Information Transmission Capacity>Tera bits/s Low Power Dissipation m.4 db/cm 3 No Need of Impedance Matching etc. 4 Present Status of Usage of Optical Communication Submarine Optical Cable FTTH (Fiber To The Home) Between Computers Wiring in Airplane Wiring in Car Optical Interconnection is introduced in Cellular Phone Metal interconnection Oct. 1, 5 Asahi Newspaper Metal Wiring Optical Fiber Near Future Optical interconnection Between Computer Boards On Board Optical Interconnection (Chip to Chip) On Chip Optical Interconnection 5 6
Si Ring Resonator Optical Switch SOI Carrier injection into pin junction causes modulation of refractive index. Shift of Resonance Wavelength 1 m Normalized optical output Operation at 1.5 Gbit/s Qianfan Xu et al. Cornell Univ. Nature ol. 435, p. 35 (5). 7 8 Change in Clock Frequency of CPU Jump by Optical Interconnection 1G 1G 1M 1M 1993 1995 1997 1999 1 3 5 Electro-Optic (EO) Material () I. Optical Switches using Magneto-Optic Material. Optical Switches using Si Ring Resonator I. Summary 9 1 Target: Optical Global Interconnection in Si LSI Optical Switches using Ring Resonator Optical Fiber Metal interconnects Driving transistor for optical switch Transistors Ring resonance type switch is used for miniaturization. Electro-optic (EO) material () is used for optical switches. Optical switches are integrated on the top layer (process temp.<45c) Waveguide Photodetector Ring Resonator EO Materail Metal Microlens Optical switch Using electro-optic (EO) material 11 Ring (EO Material) Resonance EO Effect Metal R R 1 R m Integer 3 r : EO Coeff., R : Ring Radius, : Ref. Index, E: Electric Field Power (db) Resonance Characteristics n=1.9995 n=. With E Without E -1 - Switching Gain: 17 db -3 851.4 851.8 85. Ring Radius 1 m Width of Waveguide m Gap.1 m Switching Gain of 17 db at =5x1-4 1
Operation Speed of Ring Resonator Switch Factors Polarization Time of EO Material RC Time Constant of Device Resonance Time of Ring (db) -1 5 rounds (.5ps) - -3 1 rounds (5 ps) 3 rounds (15 ps) -35 85 851 85 853 854 Resonance peak becomes sharp with increasing in round time of the light. Resonance Time of Ring Model Coupling Peak Power (db) -1 1 m R i sin cos db/round..5 1. - 1 3 4 5 Time (ps) 13 Operation Speed of Ring Switch (cont d) SLOW Operation speed (s) 1-11 1-1 1-13 1-14 Resonance time FAST RC delay (, LN) Polarization 1 1 3 1 4 1 5 Operation frequency (GHz) Structure used for Calculation Resonance time determines the switching speed. ~ 1 GHz at R=1 m Cross Section Radius R Core Resistance Capacitance C clad C core C clad 14 Electro-Optic(EO) Material () I. Optical Switches using Magneto-Optic Material. Optical Switches using Si Ring Resonator I. Summary Mach-Zehnder Optical Modulator Mach-Zehnder Interferometer (MZI) Electro-Optic Material () Ever Introduced in Si Process Easy Formation Sputter Low Temperature Good Crystallinity 15 16 Film Formation by Annealing Behavior Repeat, 8 nm/cycle Final Thickness 5 nm XRD Spectra Surface Roughness Drop Source Liquid Rotation 6 rpm, 1 s rpm, s Low Temp. Bake 18C, 1 min High Temp. Bake 45C, 3 min Intensity (a.u.) 7 o C, 3 min 6 o C, 3 min 55 o C, 3 min as-deposited RMS (nm) Measured by AFM Post Anneal for Crystallization 45~75C (deg) Poly-Crystallized at >55 C Temperature () Roughness increases with Temp. 55 Annealed Film is used. 17 18
Fabricated Mach-Zehnder Optical Modulator Plan iew Cross Section m. m.6mm 633 nm 5m m 1m.35m.7m.15m. m 1. m 15m 1m Plan iew Photograph 1 m Monolithic Integration on 19 First Demonstration of Monolithic Optical Modulator using EO Mateiral Measurement System DC oltage Source Sample Photodetector Powermeter Lens Optical Microscope Recorder He-Ne Laser (=633nm) Intensity () 14 1 1 98 96 94 =633 nm 9 1 3 4 5 Time (min) Optical Modulation by -3% at 9 (E=1.7x1 4 /cm) Problem: Process Temp. of 55C Too High Our Group: Zhimou Xu et al. Appl. Phys. Lett. ol. 88 No.16, 16117 (6). <45C oltage () Mach-Zehnder Optical Modulator Sputter Deposition of Film Mach-Zehnder Interferometer (MZI) Electro-Optic Material () Ever Introduced in Si Process Easy Fabrication Sputter Low Temperature Good Crystallinity O Ar Target IR Lamp Quartz Window Exhaust RF Power Source (13.56 MHz) RF Power 5 W Base Pressure 1. x1-6 Pa Sputtering Gas Ar : O = 4 : 1 Pressure. Pa Substrate Temperature 3-7C Deposition Rate 1. nm/min 1 Intensity (a.u.) Thickness3 nm (1) Crystallinity and Optical Property XRD Spectra for Sputtered 45C 4C 35C 3C (11) Si () (111) 7C (.1) () 3 4 5 (degree) Propagation Loss versus Crystallinity High Crystallinity causes Loss of Propagation Deposition at 45C 47 db/cm Propagation loss (db/cm) 1 1 Acceptable Temp. after Metallization (45C) 1 1 3 4 5 XRD () peak intensity (count) 3 Mach-Zehnder Modulator using Sputtered waveguide phase shifter A electrode m B B.5 45 Si 3 N 4 waveguide A 4 m (a) (c) dd electrode m.7 m (b) Si 3 N 4 waveguide electrode waveguide electrode 1. m 1. m 1 m waveguide (length = 4 m) (d) Si 3 N 4 Si 3 N 4 and series connection is used because of high propagation loss of. Loss of phase shifter (4 m) is ~19dB. 4
Optical Modulation of Mach-Zehnder Modulator using Sputtered arious Electro-Optic Materials oltage () Intensity (%) 1 1 98 96 94 9 9 Sputtered at 45C 4 6 8 1 1 14 Device Time (sec) Modulation by ~1% at Dep. Temp. = 45C Ref. Index of =.3 Length of WG = 4 m Width of WG = m Thickness of =.7 m Measurement Low temperature formation of 45C, acceptable for the process after metallization. He-Ne laser (633 nm) (E=1.x1 4 /cm) 5 Material LiNbO 3 KTa 1-x Nb x O 3 LiNbO 3 BaTiO 3 LiTaO 3 (Pb,La)(Zr,Ti) O 3 This Work Phase Bulk s-cryst. Bulk s-cryst Epi Film c Film Substrate Glass MgO s-cryst. Glass ITO Thermal Thermal EO Coeff.(pm/) 3.8 6 1.34.3 1 5. 5. CZ CZ RF Sputter (75C) MOCD (75C) RF Sputter Method Aerosol Dep. (3C) RF Sputter (45C) (55C annealed) 6 Device Structure Performance Index L (cm) Distance between Electrodes EO Coeff. (pm/) Sub-Summary and Improvement Plan 5m.7m 1m m.35m m.15m. m 15 m 6 15 m 5. Sputtered dd 1m.65m m 1m Si Sub. 36.7 m 5. Dep. Temp. 55 C 45 C Plan (Sputtered ) 1 m. m m Si Sub..7. m.1 m direct contact to Miniaturization Electro-Optic(EO) Material () I. Optical Switches using Magneto-Optic Material. Optical Switches using Si Ring Resonator I. Summary Magneto-Optic Materials Magnetic Field Ring Resonator Optical Switches using Magneto-Optic Material Current R, n kmh m Refractive index for right handed mode: Refractive index for left handed mode: E R : E of positive circular-polarization wave (right handed mode) E L : E of negative circular-polarization wave (left handed mode) Low oltage Operation <.1 Electric Field 1 ER ( E 1 EL ( E Power TE TE ie ie TM TM Not Polarized P E R E L Polarized P E R E L Polarizer is not necessary., ), ),. Power (db) Power (db) -1 - With Polarizer 13.8 db H= H=3 Oe 198 199 13 131 13-1 - Without Polarizer 1.7 db H= H=3 Oe 7 198 199 13 131 13 9 Faraday Effect of Magneto-Optic Material Sputtered () Sputtered Bi 3 Fe 5 O 1 (BIG) at Room Temp. (Amorphous) N S Magnet Photodetector Polarizer Si Waveguide BIG Waveguide Polarizer Focus lens Powermeter Faraday effect Plane of polarization is rotated. Magnetic field BIG Semiconductor laser (= 155 nm).5mm BIG 3m ~% modulation is achieved at an external magnetic field of ~.T. 8 3
Electro-Optic(EO) Material () I. Optical Switches using Magneto-Optic Material Resonance Wavelength 1 Intensity (db) Principle of Si Ring Optical Switch R m Switching Gain R : 13.8 m Carrier Injection : 3.85 Wavelength (m) Si Ring n + p + Refractive index is changed by carrier injection. Stack type optical switch is proposed. 1-1 1 - =1.55. Optical Switches using Si Ring Resonator n 1-3 Free Electrons I. Summary 31 1-4 1 17 1 18 1 19 1 N (cm -3 ) IEEE J. Quantum Electron., ol. 3. No. 1 (1987)13. 3 Comparison between Stack and Plane Switch Gap Satck Type Structure Layers of Ring and I/O Key Technology Gap Control Process I/O Line Ring Resonator Electrode Stack Different Planarization Easy and Precise Complicated Plane Type Gap Plane Same Etching Difficult Simple 1.m p + Si 5 m Fabricated Si Ring Resonator 15~5 m n + Si PIN Si nitride waveguide 5 m Gap :. m Si ring A SiN A SiN I/O Line B Si (SOI) Si Ring 1 m 3 m B 33 34 Measurement Results for Si Ring Switches Summary Measurement System Optical Microscope Pumping Source (He-Ne Sample Laser: 633 nm) Intensity (a.u.) 78 77 76 75 74 73 7 CCD Camera Lens Display Tunable Semiconductor Laser (=18-13 nm, FWHM~. nm) ON OFF OFFON ON ON OFF OFF OFF He-Ne Laser 71 =199 nm 7 4 8 1 16 4 Times) Intensity (a.u.) 1 9 He-Ne Laser ON Shift to short 199131134 Theoretical 8 7 6 5 4 19 195 13 135 131 (nm) He-Ne Laser 633nm (1.96 e) ~3% of modulation is achieved by Si ring resonator optical switch. E c 1.1 e Ev v 35 () Optical Switch Low temperature (45C ) monolithic fabrication technology was developed. Optical modulation of ~1% was achieved by Mach-Zehnder modulator. Bi 3 Fe 5 O 1 (BIG) Optical Switch Ring switch without polarizer was proposed and the characteristics were simulated. Modulation of ~% was achieved using amorphous BIG film. Si Optical Switch Stack type ring switch was proposed and ~3% modulation was demonstrated by optical pumping. Next Stage Realization of optically interconnected LSI by improving the device properties. 36