1. IMEC - INTEC Department of Information Technology http://www.intec.ugent.be WAVEGUIDES IN BOARDS BASED ON ORMOCER  s geert.van.steenberge@intec.ugent.be

2. INTEC - Department of Information Technology Outline Introduction ORMOCER  s Laser ablation Waveguides Deflecting optics Coupling structure Conclusion

3. INTEC - Department of Information Technology Introduction Integration of optical interconnects on board level Approaches Fiber based Waveguide based  glass sheet  polymers http://www.circuitree.com Printed Optical Waveguides: The Next Interconnect (H.Holden)

4. INTEC - Department of Information Technology ORMOCER  s ORganic Modified CERamics Fraunhofer Institute - Germany Inorganic-Organic Hybrid Polymers Applications  microoptical elements (lenses, lens arrays, gratings, prisms)  vertical integration: stacked optical waveguides (wafer scale)  board level optical interconnects General properties Compatibility with PCB manufacturing  lamination 180°C 200 Pascals  assembly (solder reflow) up to 250°C Good planarisation properties RMS roughness 2 - 4 nm Long-term stability under variable environmental conditions (humidity, temperature) Low shrinkage

5. INTEC - Department of Information Technology ORMOCER  s Optical properties (www.microresist.de) Refractive index @ 830 nm (adjustable)  CORE 1.5475  CLADDING 1.5306 Attenuation Waveguides Photolithography Laser ablation

6. INTEC - Department of Information Technology ORMOCER  s Application scheme application spin-coating softbake 80-120 °C, <5 min flood exposure post exposure bake 80-120 °C, <5 min developmentcuring 120-240 °C, up to 3 hrs laser ablation exposure curing 120-240 °C, up to 3 hrs

7. INTEC - Department of Information Technology Laser ablation Set-up KrF Excimer Laser (can be tilted) 248 nm Frequency tripled Nd-YAG Laser 355 nm CO2 Laser 9.6  m

8. INTEC - Department of Information Technology Waveguides UV-Defined Cross section: 20 x 20 μm 2 waveguides (250 μm pitch) Laser-ablated Compatible with standard electrical PCB manufacturing (microvia’s) Adapt the pattern as a function of distortion in the substrate (FR4) Rapid prototyping Define microstructures and microoptics on a top surface of a heterogeneous optoelectronic module in a very late phase of the assembly process Entire optical interconnection using one technology OPTICAL LAYERS COPPER FR4

9. INTEC - Department of Information Technology Waveguides Laser-ablated Laser beam moves over surface Technology sequence  bottom cladding layer  core layer  laser ablation microstructuring  upper cladding layer Experimental results KrF Excimer laser (248 nm) 50 x 50 μ m 2 trapezoidal shape low ablation speed roughness to high

10. INTEC - Department of Information Technology Waveguides Frequency tripled Nd-YAG laser (355 nm) 50 x 50 μ m 2 clean surfaces ablation speed: 1 mm/s photo-dissociation photo-thermal ablation

11. INTEC - Department of Information Technology Deflecting optics 45  micromirrors micro machining techniques (90  V-shaped diamond blade)  excellent cut surface  difficult to cut individual waveguides on the same substrate (physical size of the machining tool)  remove waveguide film from substrate  cutting from back-side diamond blade cladding core cladding substrate

12. INTEC - Department of Information Technology Deflecting optics 45  micromirrors reactive ion etching RIE (45  oblique etching)  limited by directional freedom  different process steps temperature controlled RIE (90  RIE + heat treatment)  not limited by directional freedom  material dependent laser ablation  set-up: excimer laser beam can be tilted –Total Internal Reflection (TIR) negative facet –coated mirror (Al, Au) positive facet RIE Al mask cladding core cladding substrate TIR condition crucial glue (mounting lens plate) humidity

13. INTEC - Department of Information Technology Deflecting optics Total Internal Reflection Smooth surface Tapering compensated Flatness of the mirror at core layer

14. INTEC - Department of Information Technology Coupling structure Example: MT-compatible coupling Microlenses and 700  m holes ablated in a polycarbonate (PC) plate (Kris Naessens, Ph.D. thesis Ghent University) Alignment: ribbon - lenses: 700  m pins match holes in PC plate Alignment: micromirror - lenses: flip chip set-up (alignment marks) Lenses ablated in upper-cladding layer Visual alignment under ablation set-up with respect to 45  micromirror

15. INTEC - Department of Information Technology Conclusion Integration of optical interconnects on board level polymer waveguides Compatibility with the manufacturing and assembly processes of the conventional electrical board technology ORMOCER  s Laser ablation Entire optical interconnection using one technology Waveguides Micromirrors Microlenses Alignment features SEM pictures show very smooth surfaces