Conformal Electronics Wrapped Around Daily-life Objects. Using Original Method: Water Transfer Printing.

Transcription

1 Supporting Information Conformal Electronics Wrapped Around Daily-life Objects Using Original Method: Water Transfer Printing. Brice Le Borgne, Olivier De Sagazan, Samuel Crand, Emmanuel Jacques, Maxime Harnois * Institut d'électronique et des Télécommunications de Rennes, Université Rennes 1, UMR CNRS 6164, Campus de Beaulieu, Rennes Cedex, France AUTHOR INFORMATION Corresponding Author * maxime.harnois@univ-rennes1.fr Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. S-1

2 This section includes: 1) Experimental section 2) Figures S1, S2, S3, S4, S5, S6, S7 and S8. 3) Videos S1, S2 and S3. 1. Experimental section a. Characterization. Optical microscope images were obtained using a Leica microscope equipped with a digital camera. Scanning electron microscope images were obtained using a JEOL 7100 FEG microscope. Profilometry measurements were performed using TENCOR KLA P6 equipment. b. PVA processing. A solution of poly-vinyl alcohol (PVA; Mw , 80% hydrolyzed from Aldrich) was prepared by mixing DI water and PVA powder (5:1w/w water/pva). The 0.4µm filtered solution of PVA was spin-coated to obtain a 50µm layer thickness and then baked at 100 C during 2 hours to dry the film. PVA spin-coating was performed at low rotation velocity and acceleration (velocity = 20 rpm and acceleration = 10 rpm.s 1 ) until water is evaporated. These spin-coating parameters guarantee good thickness uniformity of PVA layer. Indeed, baking PVA before complete drying leads to obtain non-uniform layer mainly due to evaporative flow (coffee ring effect). As shown in figure S2a and c, when PVA film was obtained by spin coating, an under-layer of photoresist can be deposited in order to facilitate the release of PVA necessary at the end of the process (before the transfer step). 11 For large area applications that require inkjet printing technology, PVA laminated on PET (Aicello, solublon PET 75µm thick and PVA 30µm thick) films is more suitable. S-2

3 c. Thin film patterning. Lift-off method (see in figure S2): As shown in figure S2, the lift-off process can be performed using a bi-layer of Su and another photoresist (e.g. S1818 photoresist). 2µm thick S1818 was spin-coated on PVA and hard baked at 120 C during 15 minutes. Then, Su was spin-coated on S1818. During the photoresists development step, Su8 developer etches S1818 and consequently, a special attention must be paid to guarantee lithographical accuracy of the patterns. Thin films such as aluminum or gold have been deposited by thermal evaporation. Acetone or Su8 developer can be used to etch photoresist during the lift-off step. Reactive ion etching method: 150 nm thin film have been deposited by thermal evaporation. Chlorinated gas was used in a ICP/RIE (inductive coupled plasma/ reactive ion etching) equipment to etch aluminum (working pressure: 5 mt; plasma power: 100 W; flow rate: 30 sccm) after classical lithographical process using S1818 photoresist. Inkjet printing method (see in figure S3): All the printing experiments were performed using CERADROP X-series printer. Inks were used without filtering steps. Epoxy based ink (Su series; MicroChem, Westborough, MA, USA) surface tensions and viscosity are 35 mn.m -1 and 2.49 cp respectively. Silver-based ink (Silverjet DGP 40LT-15C from ANP ) surface tension and viscosity are 35 mn.m -1 and 15 cp respectively. Silver ribbons were printed using 256 nozzles Q-class printhead (Dimatix ) and baked in an oven at 130 C for 30 min. If necessary, epoxy-based ink (squared mesh geometry) can be printed using a 16 nozzles cartridge (Dimatix ) and baked at 95 C for 5 min in an oven followed by UV (λ = 365 nm) exposure and baked again in an oven at 95 C for 5 min. Dipping and transfer steps: PVA film is deposited at the surface of water and must be dissolved before dipping the object through the floating patterns. Gently shaking the object inside the dip tank allows a better dissolution of PVA. Finally, the object is withdrawn and dried. Van Der Waals allow patterns sticking on the 3D object. S-3

4 2 Figures Figure S1: Optical pictures showing aluminum ribbons patterned on PEN substrate (25µm thick) that are transferred to Teflon ring. 3 basics techniques are used to obtain conformal wrapping but obviously because of the flexible substrate, the inner diameter of the ring cannot be conformally wrapped: a) PEN substrate is stretched on top the ring, b) PEN substrate is fixed on the outer diameter of the ring inducing folds because of the substrate, c) PEN must be cut out in order to decrease number of folds. S-4

5 Thin film patterning Lift-off method Figure S2: Electrodes patterned using conventional photoresists and water-free chemical reagents. 3D illustation of: a) Sacrificial (S1818) or low adhesion films (Su ) and PVA films spin-coated on carrier substrate; b) bilayer of S1818 and Su after water freedevelopment (Su8 dev. Microchem) on PVA film; c) release of PVA substrate from carrier substrate promoted by low adhesion photoresist or sacrificial photoresist (not shown here). Optical pictures of: d) gold (50nm thick) deposited on structures shown in b), e) after 25 minutes and f) after 2 hours immersed in Acetone or Su8 developer; g) electrodes after S-5

6 Acetone and isopropilyque alcohol bath; h) SEM (scanning electron microscope) crosssection picture of bilayer photoresists profile after the step shown in b); i) 150µm width electrodes spaced from 30µm. Inkjet printing method Figure S3: Optical pictures showing silver ink printed on PVA substrate for large area applications. a) Identical electrodes are designed in columns varying inter-electrodes distances (from 40µm to 1mm). b) Zoom in top right corner of PVA substrate showing squares ( µm), horizontal lines, vertical lines and isolated droplets. c) Zoom in electrodes with distances are equal to 40µm, 80µm and 160µm (from top to bottom). Due to PVA roughness electrodes spaced from 40µm are connected. S-6

7 Figure S4: PVA dissolution behavior as function of process variants. Optical pictures recorded during the first minute. Aluminum patterns on PVA which are not linked are designed in star configuration. a) When the PVA is dissolved, each line composing the star can move and the pattern is deformed. b) An additional layer of SU8 is printed on aluminum and designed in squared mesh configuration. When PVA is dissolved, each line composing the star cannot move and the patterns are not deformed. c) Additional film guides are added in the periphery of the PVA substrate. In this case, radial forces are drastically reduced which helps to respect pattern geometry. S-7

8 Figure S5: Electrodes transferred to curved glass showing no distortion. 150µm width electrodes spaced from 50µm. Gold electrodes thickness equal 50nm and Aluminum electrode thickness equals 150nm. Transparent polymeric mesh (printed Su8 photoresist) was used to overcome radial forces in order to obtain desired accuracy. S-8

9 Figure S6: Aluminum conformal wrapping around 50 cents euro coin. a) 3D scan of a star at the surface of the coin showing a maximum height of 70µm. b) 3D scan of a flat surface of the coin. Average roughness equals 0.8µm. c) Colorized SEM picture. The grey area shows aluminum ribbon. d) Optical picture reconstituted from profilometric scan of the area presented in c). e) Profilometric scan of the area presented in c). f) Zoom (see in d)) showing aluminum sharp ridge without mechanical failure. g) 2D scan along the profiles P1 to P4 presented in f). Aluminum ribbon reaches extreme bending radii (approximately 15µm). S-9

10 Figure S7: Aluminum interconnects wrapped around human hair; a) optical pictures of interconnects wrapped over human hair fixed onto bent object. b) Zoom on interconnects crossing hair showing no mechanical failure. scale bar equals 200µm. c) Current versus voltage measurmement before and after transfer step. Blue inset shows a zoom between 0.5 and 1V. No electrical failure is observed and ohmics behaviors are shown. S-10

11 Figure S8: MIM capacitors wrapped around 3D object. a) Optical picture of MIM capacitors at the edge of a plastic part. Active layer is conformally wrapped, forming a 90 angle. b) Capacitance as function of frequency. Capacitance slightly decreases with frequency increase due to dielectric loss tangent. 1 c) Capacitance as a function of bias voltage at consistent 100 khz. S-11

12 3 Videos Video S1: 76s-movie at 25 frame/s showing Water Transfer Printing concept. Video S2: 205s-movie at 25 frame/s showing 3-axis machine assisted water transfer printing technology. A maximum distortion of 9% has been measured from the object of the video (a sphere). Distortion was measured between the center and a corner of the pattern. Distortions are due to Stokes flow that occurs during the transfer step. Video S3: 12s-movie at 25 frame/s showing bent touchpad as remote to play pong game. References (1) Li, Y.; Torah, R.; Beeby, S.; Tudor, J; An All-Inkjet Printed Flexible Capacitor on a Textile Using a New Poly (4-vinylphenol) Dielectric Ink for Wearable Applications. Sensors 2012, IEEE, Taipei, 1-4. S-12