Metamaterials Zaven Kalfayan Lindsay Hunting Phyllis Xu Joy Perkinson

Presentation Outline Motivation of project Project goals Processing and materials Results Cost analysis TechWatch and future work

What is a Metamaterial? A periodic material that derives its properties from its structure rather than its components. *Taken From 3.042 handout & Physics Worlds 2005 “Sound Ideas”

Project Motivation Developing field of research Applications in wide range of sectors, such as communications, optics, energy Currently used for wave manipulation

Project Goals Design a process using lithography to fabricate a 3D structure Create macroscale models of 2D structure, phase mask, and 3D structure Create a 3D metamaterial and image using SEM

Process Design Phase mask 3-D pattern Titania structure 2-D Interference lithography 2-D photoresist pattern Phase mask 3-D pattern Titania structure Sol-gel infiltration

2D Structure Fabrication Coat plain Si wafer coat with HMDS to promote adhesion coat with SU-8 20xx photoresist using spin coater soft bake @95° to evaporate solvent and cut into pieces Exposure post bake at first 65° then 95° to promote crosslink formation UV exposure for xx seconds flip 90° and expose again submerge in PM acetate to dissolve unexposed photoresist (20 min） submerge in isopropanol to wash away all remnants—final structure Develop

Phase Mask Fabrication Vacuum sample with open bottle of fluorosilane so that it evaporates onto sample. Step 1 Step 2 Layer with PDMS and heat at 65°to 75°for at least three hours. Step 3 Gently peel off PDMS layer as phase mask.

3D Structure Fabrication Coat plain glass slide coat with HMDS to promote adhesion coat with SU-8 2005 photoresist using spin coater soft bake @95° to evaporate solvent and cut into pieces Exposure post bake at first 65° then 95° to promote crosslink formation Place phase mask on top of slide Expose for xx seconds and remove phase mask submerge in PM acetate to dissolve unexposed photoresist (5-10 min) submerge in isopropanol to wash away all remnants—final structure Develop

Process Tuning Exposure times (contact lithography): SU8-2002: 0.5-25 seconds SU8-2005: 5-40 seconds SU8-2015: 1-45 seconds Exposure times (interference lithography): 3-20 seconds for all samples

Prototype Functionality Problems for 2D & 3D patterns 15s SU-8 2015 Top Overexposure Unwashed monomer Adhesion problems Inconsistent results 15s SU-8 2015 Cross

Design Functionality 2-D Patterns Coated with HMDS 5s exposure of SU-8 2015 Coated with HMDS Broadband laser filtered at 365nm Top down Hole spacing - 3.38 um Hole length ~1.5um 5s SU-8 2015 Cross 5s SU-8 2015 Top

Design Functionality Phase mask PDMS on SU-8 2015 2D pattern Coated with flourosilane Baked overnight 65C Column Spacing ~ 4 um Height ~15 um PM of 10s SU-8 2015 PDMS on 10s SU-8 2015

Design Functionality 3-D Patterns 3s exposure of SU-8 2005 3s SU-8 2005Top 3s exposure of SU-8 2005 Coated with HMDS Thickness ~ 5um 355 YAG pulse laser Used in continues mode

2-D Pattern Phase Mask 3-D Pattern CAD Model 3-D Printing Model Actual Sample

Cost Analysis Fixed cost: Spin coater, lasers, SEM General lab equipment, facilities Variable cost: SU-8 20xx and HMDS ($300/1L $30/500mL ) Trifluoroacetic acid and TiO2 ($60/100mL, $117/50mL) Si wafers ($15/piece) Glass wafers ($240/2500 slides) Total costs/sample: $6/sample

Future Work Optimize process Explore new thicknesses and exposure times Adhesion promoters Create more complicated 3D structures Characterize 3D structure properties

TechWatch 2004: Miniaturized antennas based on negative permittivity materials—Lucent Technologies Metamaterial scanning lens antenna systems and methods—The Boeing Company 2003: Metamaterials employing photonic crystal—MIT Methods of fabricating electromagnetic metamaterials—The Boeing Company 2002: Resonant antennas—Lucent Technologies

Questions?

Design Functionality Thick Film Photoresist Calculation: Sin (70) = 58 / t Thickness (t) ~ 61 microns Success! 45s SU-8 2050

Design Functionality Problems in 2-D patterns Un-washed monomer Over exposure Non-uniform columns 15s SU-8 2015 Top Width of top ~ 1.81 um Width of bottom ~ 1.00 um 15s SU-8 2015 Cross

TiO2 Sol Gel Infiltration Dip sample in TiO2 solution (trifluoroacetic acid, titanium oxide, and deionized water) for about 30 seconds. Step 1 Step 2 Dry the sample for at least 2 hours. Step 3 Heat sample up to 600°C in 8 hours and cool down to room temperature in 6 hours to evaporate photoresist.