Aluminum Nitride (AlN) Waveguides for Potential Soliton Propagation. by Am´ılcar Santamar´ıa Hern´andez M.Sc. Uppsala Universitet, Sweden B.Sc. Universidad Nacional, Honduras Dissertation submitted to the Graduate School in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering University of Cincinnati November 2015 Committee Chairman: Dr. Peter B. Kosel, Ph.D. Abstract The primary objective of this work was to build optical waveguide structures based on amorphous Aluminum Nitride (AlN) to study the coupling of short optical pulses into optical waveguides and their subsequent propagation through the waveguides and interfaces. A thin film of amorphous Aluminum Nitride, (AlN), was used as waveguide core, which was deposited by reactive plasma sputtering on various substrates, such as silicon and soda-lime glass to characterize their performance. Structures on AlN deposited thin film were built, by photolithography with negative photoresist and chemical etching with Sodium Hydroxide, (NaOH). Material characterization of deposited AlN, was performed. Electrical and optical properties were established. An attenuation rate of 0.09 dB/cm was determined at a wavelength of 1550 nm, and 0.22 dB/cm at a wavelength of 650 nm. The soliton is a very short light pulse that can be generated in optical fiber. It was proposed to launch solitons in AlN. Analysis proved that its dispersion has a crossover point at around 1550 nm, which would allow bright solitons to exist. ii iii ... dedicated to the most wonderful, generous and loving person, my wife Raquel, whose love, patience and sacrifice knows no limit. To my adorable twin boys Alejandro and Sebastian, for their unconditional love and sacrifice, who have walked with me in this journey. To the loving memory of my beloved parents in law Do˜na Maria de los Angeles Mendoza, Don Roberto Flores Machado and my dear grandmother Victorina Escobar Matute. iv Table of Contents Abstract ii Table of Contents v List of Tables viii List of Figures x List of Symbols xiv Acknowledgements xv 1 Introduction 1 1.1 Prelude...................................... 1 1.2 OpticalSolitons................................. 1 1.3 SolitonLogic .................................. 4 1.4 AluminumNitride................................ 5 1.5 Optical & Electronic Properties of AlN ................... 6 1.6 Optical Waveguide with a Core of AlN ................... 11 2 Theory of Soliton formation and Propagation 13 2.1 Introduction ................................... 13 2.2 NonlinearOptics ................................ 14 2.2.1 KerrEffect ............................... 14 2.3 NonlinearSchr¨odingerEquation . 15 2.3.1 Nonlinear Schr¨odinger Equation solution . 16 2.4 DispersionAnalysis .............................. 17 2.4.1 MaterialDispersion. 17 2.4.2 SellmeierEquation . 18 2.4.3 Simulation ............................... 21 3 Design and Modeling of AlN Optical Waveguides 27 3.1 MethodofNormalModes........................... 27 3.2 SlabWaveguides................................ 30 v 3.2.1 EvenTEModes ............................ 34 3.2.2 OddTEModes............................. 36 3.2.3 EigenvaluesofTEModes . 37 3.3 AsymmetricalSlabWaveguide . 38 3.3.1 TEModes................................ 38 3.4 EffectiveIndexMethod. 42 3.5 SellmeierEquation............................... 48 3.6 AluminumNitrideDispersion . 49 3.6.1 EffectiveIndexDispersion . 53 3.7 PhotodetectorResponsivity . 54 3.8 Photodiodes................................... 55 3.9 AttenuationMeasurements . 56 4 Fabrication Methods of Novel Optical Waveguides and Material Properties for Optimal Performance 58 4.1 Introduction ................................... 58 4.2 SubstrateCleaning............................... 58 4.2.1 SiliconWafers ............................. 59 4.2.2 Glasssubstrates............................ 59 4.2.3 Cuttingofglasssubstrates . 60 4.2.4 Polishingofglasssubstrates. 62 4.3 Reactive Magnetron Sputtering Deposition . ...... 63 4.4 AluminumDepositionSystem. 68 4.4.1 AluminumGroundPlaneDeposition . 68 4.4.2 AluminumDotsDeposition. 70 4.5 Photolithography................................ 72 4.5.1 Photolithographic Artwork Design . 74 4.5.2 IlluminatedScreen. 75 4.5.3 ReductionCamera....... ....... ........ ..... 78 4.5.4 CameraDepthofFocus. 80 4.5.5 ExposureandDevelopmentofEmulsion . 81 4.5.6 PhotoresistSpinner. 85 4.5.7 Contact Printing with Wafer Stepper . 86 4.5.8 MercuryDischargeLamp. 86 4.5.9 PositivePhotoresist. 88 4.5.10 NegativePhotoresist . 90 4.6 AluminumNitrideEtching. 93 4.6.1 PotassiumHydroxide . 93 vi 4.6.2 SodiumHydroxide....... ....... ........ ..... 95 5 Characterization Methods of Waveguide and AlN testing 100 5.1 Introduction ...................................100 5.2 AluminumNitridethickness. 100 5.3 Capacitance...................................104 5.4 Refractive Index of AlN ............................107 5.5 Breakdown Voltage and Leakage Current . 109 5.6 Characterization of Optical Instrumentation . ........ 111 5.6.1 Modulated Laser, Fibertech-105 . 111 5.6.2 Optical Power Meters . 115 5.6.3 LaserDriver .............................. 119 5.6.4 LaserCharacteristicsCurve . 124 5.7 Waveguide Attenuation Measurement Setup . 128 5.8 PhotodiodeCircuit ............................... 133 5.9 Optical Attenuation Measurements . 135 5.9.1 SlabWaveguide ............................ 137 5.9.2 Straight Ridge Waveguides . 142 5.9.3 Meander Waveguides . 147 5.9.4 OpticalCouplingsLoss . 153 5.10Conclusions ................................... 156 Appendix 158 Bibliography 172 vii List of Tables 1.1 Physical Properties of Aluminum Nitride, 2001 . ...... 11 1.2 Physical Properties of Aluminum Nitride, 2013 . ...... 12 3.1 Effective Index (N) on ridge waveguide . 46 4.1 ChemicalCompositionofLimeGlass . 60 4.2 AbrasivesGritSizes .............................. 63 4.3 Photolithographic Mask Linewidths . 76 4.4 ScreenLightDistribution . 77 4.5 Emulsion Exposure and Development Procedure. ..... 82 4.6 Angularspeed- Motor CurrentCorrelation. ..... 86 4.7 Positive Photoresist Photolithography . ....... 89 4.8 Negative Tone Photoresist Photolithographic SOP . ....... 90 4.9 Negative Tone Photoresist Photolithographic SOP . ....... 95 4.10 AlNetchingin10%KOH ........................... 95 4.11 AlNetchingin5%NaOH ........................... 97 5.1 Dielectric Constant and Resistivity Evolution of AlN . ......... 106 5.2 RefractiveIndexofAlN ........ ....... ........ ..... 107 5.3 Optical power drop when modulation is enabled. 113 5.4 Optical Power from Fibertech 105 Laser for various optical fibers mea- sured with AM3500 and LP5000 power meters. 117 5.5 LP-5000 vs. AM-3500 under same conditions . 119 5.6 Modulated Laser 650 nm vs λ, optical meter AM-3500. 120 5.7 Optical meter LP-5000 on Laser Diode, 650 nm. 126 5.8 Optical meter AM-3500 on Red Laser Diode, 650 nm. 127 viii 5.9 1550 nm Laser Diode, Optical meter LP-5000 . 127 5.10 650 nm Laser Diode, Optical meter AM-3500 . 128 5.11 RutileRefractiveIndex. 133 5.12 Slab Waveguide Attenuation, 650 nm Laser . 139 5.13 Slab Waveguide Att., at 1550 nm Laser . 140 5.14 Pattern Etched Waveguide Attenuation A, 650 nm Laser . ....... 142 5.15 Pattern Etched Waveguide Attenuation, 1550 nm Laser . ....... 143 5.16 Modulated Ridge Pattern Waveguide Attenuation, 650 nm Laser . 143 5.17 Modulated Ridge Pattern Waveguide Attenuation, 1550 nm Laser . 146 5.18 Meander I Waveguide Attenuation, 650 nm Laser . 148 5.19 Meander I Waveguide Attenuation, 1550 nm Laser . 148 5.20 Meander II Waveguide Attenuation, 650 nm Laser . 150 5.21 Meander II Waveguide Attenuation, 1550 nm Laser . 150 5.22 Waveguide-Prism-PD Attenuation, 650 nm Laser . 155 ix List of Figures 1.1 Kerr Effect and Group Velocity Dispersion (GVD) . .... 3 1.2 AluminumNitrideRefractiveIndex . .... 6 1.3 AluminumNitrideExtinctionCoefficient. ..... 7 1.4 AluminumNitrideEnergyBand . 9 1.5 AluminumNitrideHexagonalStructure . 10 2.1 Optical Fiber Material Dispersion . 20 2.2 Silica Fiber Soliton, Electric Field, P =100 mW . ..... 23 2.3 Silica Fiber Soliton, Envelope, P =100 mW . 23 2.4 Silica Fiber Soliton, Electric Field, P =1 W . ..... 24 2.5 SilicaFiberSoliton,Envelope,P=1W . 24 2.6 Amorphous AlN Soliton, Electric Field, P =100 mW . 25 2.7 AmorphousAlNSoliton,Envelope,P=100mW . 25 2.8 AmorphousAlN Soliton,ElectricField, P=1W . 26 2.9 AmorphousAlNSoliton,Envelope,P=1W . 26 3.1 Slab Waveguide; refractive index nf >ns >nc ................ 31 3.2 Symmetrical Slab Waveguide; refractive index n1 >n2 .......... 34 3.3 Slab Waveguide; refractive index nf >ns >nc ................ 39 3.4 AluminumNitrideEffectiveIndex. 43 3.5 ω− β Asymmetricslabwaveguide. 45 3.6 AluminumNitrideEffectiveIndex. 47 3.7 AlNRefractiveIndex .............................. 50 3.8 SiO2 &AlNDispersion ............................ 51 3.9 AlNDispersion................................. 52 3.10 EffectiveIndexAlNDispersion . 53 x 3.11 SiliconPhotoDiode .. ........ ....... ........ ..... 55 3.12 GermaniumPhotoDiode ....... ....... ........ ..... 56 4.1 PlasmainSputteringChamber. 61 4.2 Detailed description of Magnetron Sputtering System . ........ 64 4.3 Forward and Reflected Power on RF Generator Output . 65 4.4 PlasmainSputteringChamber. 66 4.5 Detailed description of Aluminum Evaporation System . ........ 67 4.6 Upper view of substrate. Top: Aluminum ground plane on silicon/glass substrate. Bottom: Aluminum dots on Aluminum Nitride/substrate . 69 4.7 Front View of Structure Built to Characterize Aluminum Nitride Prop- erties......................................