Supporting Information
Advanced Approaches for Quantitative Characterization of Thermal Transport
Properties in Soft Materials Using Thin, Conformable Resistive Sensors
Kaitlyn E. Crawford†a,b,e, Yinji Mac, Siddharth Krishnan a,b, Chen Weid, Daniel Capuaf, Yeguang
Xued, Shuai Xug, Zhaoqian Xied, Sang Min Wona, Limei Tianh, Chad Webba, Yajing Li b, Xue
Fengc, Yonggang Huangd, and John A. Rogersi*
a Department of Materials Science and EngineeringFrederick Seitz Materials Research LaboratoryUniversity of Illinois at Urbana-ChampaignUrbana, IL 61801, USA
b Department of Materials Science and EngineeringNorthwestern University,Evanston, IL 60208, USA
c AML, Department of Engineering Mechanics; Interdisciplinary Research Center for Flexible Electronics Technology, Tsinghua University, Beijing, 100084, China
d Departments of Civil and Environmental Engineering; Mechanical Engineering; Center for Bio-Integrated ElectronicsNorthwestern UniversityEvanston, IL 60208, USA
e Department of Materials Science and EngineeringUniversity of Central FloridaOrlando, FL 32816, USA
f Department of Biomedical EngineeringUniversity of Illinois at Urbana-ChampaignUrbana, IL 61801, USA
g Department of DermatologyFeinberg School of MedicineNorthwestern UniversityChicago, IL 60611, USA
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h Beckman Institute for Advanced Science and TechnologyUniversity of Illinois at Urbana-ChampaignUrbana, IL 61801, USA
i Departments of Materials Science and Engineering, Biomedical Engineering, Chemistry, Mechanical Engineering, Electrical Engineering and Computer Science, and Neurological Surgery; Center for Bio-Integrated Electronics; Simpson Querrey Institute for Nano/biotechnologyNorthwestern UniversityEvanston, IL 60208, USAE-mail: [email protected]
*Corresponding author. E-mail: [email protected] (J.A.R.)†These authors contributed equally to this work
Microfabrication steps for device formation.
1. Spin coat with PMMA 495-A2 (poly(methyl methacrylate), spun at 4000 rpm for 45 s)
2. Anneal at 180 °C for 1 min
3. Spin coat with polyimide (PI, poly(pyromellitic dianhydrideco-4,4-oxydianiline), amic acid
solution, DuPont, spun at 6000 rpm for 45 s
4. Anneal at 55 °C for 30 s
5. Anneal at 150 °C for 5 min
6. Anneal at 250 °C under vacuum for 1 h.
7. Deposit first metallization: E-beam 10/100 nm Cr/Au Pattern photoresist (PR; Clariant
AZ5214, 3000 rpm, 30 s; Bake 110 °C, 1 min) with 365 nm optical lithography through iron
oxide or Cr Mask (Karl Suss MJB3 or MJB4) for 6 s. Cr is for Adhesion, Au is the main
sensor layer
8. Develop in aqueous base developer (MIF 917)
9. Etch Cr with Cr Etchant
10. Etch Au with Au TFA Etchant (KI- KOH solution)
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11. Remove PR w/ Acetone. Rinse thoroughly with water (2 cycles).
12. Deposit second metallization: E-beam 20/500/20/25 nm Ti/Cu/Ti/Au
13. Pattern photoresist (PR; Clariant AZ5214, 3000 rpm, 30 s; Bake 110 °C, 1 min) with 365 nm
optical lithography through iron oxide mask (Karl Suss MJB3 or MJB4). Expose for 6 s; 3.
Develop in aqueous base developer (MIF 917)
14. Etch Au with Au TFA etchant, Etch Ti w/ BOE, Etch Cu w/ CE-100, Etch Ti w/ BOE
15. Remove PR w/ Acetone, IPA.
16. Spin coat with polyimide (PI, poly(pyromellitic dianhydride-co4,4-oxydianiline), amic acid
solution, DuPont, spun at 4000 rpm for 45 s)
17. Anneal at 110 °C for 30 s
18. Anneal at 150 °C for 5 min
19. Spin second coat with polyimide (PI, poly(pyromellitic dianhydride-co-4,4-oxydianiline),
amic acid solution, DuPont, spun at 4000 rpm for 45 s)
20. Anneal at 110 °C for 30 s
21. Anneal at 150 °C for 5 min
22. Anneal at 250 °C under vacuum for 1 h, in designated PI oven
23. Pattern photoresist (PR; Clariant AZ4620, 3000 rpm, 30 s; Bake 110 °C, 3 min) with 365 nm
optical lithography through iron oxide mask (Karl Suss MJB3). Expose for 15 s
24. Develop in aqueous base developer (AZ 400 K, diluted 3:1)
25. Etch in March RIE (200 mTorr, 150 W, 20 sccm O2, ~ 1800 s).
26. Release, pick up and print onto Silicone Elastomer:
27. Release in Acetone at 50C for 1–5 min
28. Pick up with 3 M Water Soluble PVA Tape
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29. E-Beam Deposit 3/30 nm Ti/SiO2 on Device Side of Tape
30. UV-O treat PDMS (ecoflex) for 5 min
31. Stick Ti/SiO2 side of device onto UV-O treated side of PDMS
32. Dissolve PVA tape in DI Water on hot plate at 100 °C
Figure S1. Comparison between scaling law and FEA. (a) Normalized time versus temperature
curves obtained by the scaling law and FEA. (b) Schematic representation (left: top-view, right
side-view) of the scaling law and FEA model.
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Figure S2. Comparison of transient heating time and temperature decay. (a), (b) and (c) are
representative plots of the change in temperature as a function of transient heating time (s) with
FEA fit (red curve) of experimental data collection (black curve) at 2 s, 20 s and 40 s intervals,
respectively). The plots are accompanied by corresponding 2-dimensional (2D) error surfaces
spanning a range of thermal diffusivity (0.05 mm2/s – 0.20 mm2/s) and thermal conductivity
(0.10 W/mK – 0.30 W/mK), which encompass only the rise (from ΔTmin to ΔTmax) at a specified
transient heating time of 2 s, 20 s or 40 s ((d), (e), and (f), respectively) or the complete rise
(over 2 s, 20 s or 40 s) and temperature decay post transient heating (over 30 s, 90 s or 130 s),
((g), (h), and (i), respectively). Measurements were collected while laminated on a silicone
substrate (Ecoflex, 10 mm thick, 60 mm diameter, cured at 70 °C x 24 hours) at a power density
of 3 mW/mm2, using a heater with a radius of 1.5 mm.
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Figure S3. (a) Representative plot of the linear relationship between temperature and resistance
for a given device. (b) Representative plot of the linear relationship between the change in
temperature as a function of power density of four separate measurements after identical
transient heating times.
Figure S4. Experimental Reproducibility. Representative temperature vs. time plots show
repeated experimental measurements on S184 at 3 mW/mm2 using a resistive sensor with
R=0.5 mm and number of samples, n=3.
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Figure S5. Thermal profile (IR). (a) IR image of the top of a resistive sensor (R=0.5 mm) after 5
s of actuation at 2 mW/mm2 on LDPE. (b) Cross-section view of the image from (a) plotted as
temperature (ºC) vs. distance (mm). (c) IR image of the top of a resistive sensor (R=2.0 mm)
after 5 s of actuation at 2 mW/mm2 on LDPE. (d) Cross-section view of the image from (c)
plotted as temperature (ºC) vs. distance (mm).
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Table S1. Thermal conductivity values deduced from 2D error surfaces deduced from FEA
based on experimental data collection as a function of sample type: Sylgard 170 (S170), low
density polyethylene (LDPE), Ecoflex (EF), Sylgard 184 (S184), polyisobutylene (PIB), and
polyacrylic (PA), heater size: R = 0.5 mm, R = 1.5 mm, and R = 2.0 mm, and transient heating
time: 2 s, 20 s, and 40 s.
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Table S2. Thermal conductivity values obtained by single point FEA and Scaling Law of 8
separate skin locations from two separate volunteers (Subject 1: 33 year old female; Subject 2:
33 year old male).
References
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[2] a. https://www.professionalplastics.com/professionalplastics/ThermalPropertiesofPlasticMat- erials.pdf. accessed 022518. b. https://www.makeitfrom.com/material-properties/Low-Density-Polyethylene-LDPE. c. www.spring.com/978-3540-44376-6. Accessed 022518.
[3] a. http://research.engineering.ucdavis.edu/ncnc/wp-content/uploads/sites/11/2013/05/Sylgard _184_data_sheet.pdf. accessed 022518. b. https://krayden.com/sylgard-184/. accessed 022518. c. Erickson D, Sinton D, Li D. Joule heating and heat transfer in poly(dimethylsiloxane) microfluidic systems. Lab Chip 2003, 3, 141-149.
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mentum:eCommerce_sol_EU:09007bb28001eca2.pdf. accessed 022518. b. Andersson SP. Pressure and volume dependence of thermal conductivity and isothermal bulk modulus up to 1 GPa for poly(isobutylene). J. Polym. Sci. B Polym. Phys. 1998, 36, 1781-1792.
[5] a. Springer Handbook of Condensed Matter and Materials Data. Martienssen W, Warlimont H. Springer-Verlag Berlin Heidelberg. 2005, 488 pp. ISBN: 978-3-540-30437-1. https://www.makeitfrom.com/material-properties/Polymethylmethacrylate-PMMAAcrylic. Accessed 022518. b. Dow Corning Sylgard 170 Silicone Elastomer Product Information. Accessed 022518.
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