Light Absorbing Dye‐Doped Siloxane Based Optical Filter Film for Image

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P-69 / S.-M. Kang Light Absorbing Dye-Doped Siloxane Based Optical Filter Film for Image and IR Sensors Seung-Mo Kang*, Yong Ho Kim*, Young-Woo Lim*, and Byeong-Soo Bae* *Wearable Platform Materials Technology Center, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea Contact Author Email : [email protected]

Abstract the flexible absorptive optical filter for flexible IR cut off filter and As a demand for thin & flexible optical sensors has increased, IR long-pass filter was fabricated by using light absorbing dye conventional glass substrates based optical filters needs to be doped siloxane resins. IR dye-doped siloxane based coating films replaced by flexible film based optical filters. In this paper, light for flexible IR cut off optical filter film were fabricated by light absorbing dye-doped siloxane based optical film filters are absorbing dye doped siloxane resin on COP film. It shows a high introduced for replacing conventional glass based optical filters. transmittance in visible area, low transmittance in near-infrared Light absorbing dye-doped siloxane hybrid optical film filters area and low haze value. Vis dye-doped siloxane based optical have good light filtering ability in diverse wavelength ranges filter films for flexible IR long-pass filter film were fabricated in with high transmittance in desired wavelengths, showing high two way: coating film and glass-fabric reinforced siloxane hybrid thermal and optical stability. (GFRHybrimer) film by using light absorbing dye doped siloxane resin according to the purpose.[6][7][8] Coating film has low haze Author Keywords value compare to GFRHybrimer film which is suitable for sensors Dye-doped siloxane; Optical filter; Image & IR sensor; IR cut-off requiring precision. GFRHybimer film has good mechanical filter; IR long-pass filter; Coating film; Transparent FRP film reliability compare to coating film which is suitable for sensors used in harsh condition.[9] Both IR long pass filter shows a high 1. Introduction transmittance in infrared area and low transmittance in visible area. Since early 21st century, as a demand for smart devices such as smartphones, smart watches, smart cars, smart houses, wearable 2. Results and Discussion devices, and the like has increased, a demand for optical sensors As mentioned above, dye-doped siloxane based optical filter films mounted on smart devices also has increased.[1] In particular, there for flexible optical filter was fabricated by siloxane resins is an increasing demand for image sensors required for digital containing diverse light absorbing dyes inside. As light absorbing cameras and infrared sensors required for security sensors such as dyes, triazine type, cyanine type, azo type were used for absorbing fingerprint recognition, iris recognition and biometrics, and for undesired wavelengths of light.[10] The dyes were added in position sensors such as autonomous navigation sensors. Generally, siloxane matrix during sol-gel reaction of the siloxane resin.[11] the optical sensor detects light and converts it into a digital signal. In case of the IR dye-doped siloxane based coating films for IR However, it also detects the light of undesired wavelengths in cut off filter (IR-dye siloxane film), we used two different types addition to the wavelengths of light necessary for sensing. For this of IR absorbing dye from QCR Solution Corp. For coating reason, the optical filter that effectively removes light of undesired process, dye-doped siloxane resin was mixed with 2-butanone wavelengths is necessary for optical sensors in order to obtain an (MEK). The solutions were coated the COP film by bar coating. accurate signal. It also applies to image sensors and IR sensors that We evaporated MEK under 80℃ and cured them under 100℃. previously mentioned. In case of image sensors, IR cut-off filters With further deposition of interference layer, we finally fabricate are necessary to remove UV and IR range of light. Without IR cut- flexible IR cut off filter for image sensor. off filters in camera, UV and IR light will cause ghost and flare problems to image taken by camera which will reduce resolution. Vis dye-doped siloxane based optical filter films for IR long pass In case of IR sensors, IR long-pass filters are necessary to remove filter, we used siloxane resin with diverse visible light absorbing visible range of light. Without IR long-pass filters in IR sensors, dyes from QCR Solution Corp. same as optical filter films for IR visible lights will cause problems to IR sensors in detecting only cut off filter. As mentioned above, we fabricate two types of IR which will reduce its resolution.[2] visible dye-doped siloxane based optical filter films. Unlike image sensor, as usage of IR sensor is wide, it need to satisfy the right Until now, the glass is widely used as the substrate of IR cut-off properties for the certain usage.[9] Coating film which has low filter and IR long-pass filter. Most widely used IR cut-off filter is haze value is much suitable for precise IR sensing. GFRHybrimer consist of ‘blue glass’ which has absorption properties in IR range which has good mechanical reliability is much suitable for IR coated with interference layer to clearly decrease transmittance in sensors using in mechanically harsh condition. The fabrication undesired wavelength. This structure also applies to IR long-pass process for vis dye-doped siloxane coating film (Vis-dye siloxane filter.[3][4] However, as a demand for thin and flexible smart film) is same with IR-dye siloxane films. In case of devices has increased, a demand for thin and flexible IR cut-off GFRHybrimer (vis-dye GFRHybrimer), vis dye-doped siloxane filter and IR long-pass filter has increased. Therefore, the glass resin was impregnated in glass-fabric and cured under 150℃. substrate needs to be replaced with plastic film for flexibility and Figure 1. are images of fabricated dye-doped siloxane based thin thickness of the filters. And the plastic film used for substrate optical filter films of IR cut-off filter and IR long-pass filter must have high optical, mechanical and thermal properties to use in real device. However, Figure 2. shows total transmittance of dye-doped siloxane optical it is hard to find flexible materials with these properties.[5] filter films. Figure 2. (a) shows total transmittance of IR dye- doped siloxane based optical filter films for flexible IR cut-off Here, we fabricated dye-doped siloxane based optical filter films filter. Total transmittance of IR-dye siloxane film 1 in visible for flexible IR cut off filter and IR long-pass filter. More precisely, range is above 85% with 88% of maximum transmittance at

505nm Total transmittance of IR-dye siloxane film 2 in visible range is above 80% with 85% of maximum transmittance in visible range which quite lower than previous one. Both films show very low transmittance value in near 700nm which is very important property for IR cut off filter. Unlike IR-dye siloxane film 1, IR-dye siloxane film 2 has absorption property from 800nm to 1200nm. Figure 2(b) shows total transmittance of vis dye-doped siloxane based optical filters film for flexible IR long- pass filter. All of the films have very low transmittance in visible range under 1%. By giving variation to type of dyes, vis-dye GFRHybrimer 2 and vis-dye siloxane film shows low transmittance until 820nm. All of the films show 90% of transmittance in IR range

Figure 2. (a) Total transmittance of IR dye-doped siloxane based optical filter films (b) Total transmittance of vis dye- doped siloxane based optical filter films

Figure 1. (a) Image of fabricated IR dye-doped siloxane based optical filter film 1 (left) and 2 (right) for flexible IR cut off filter. (b) Image of fabricated vis dye-doped siloxane based optical filter coating film (left) and vis dye-doped GFRHybirmer (Right) for flexible IR long pass filter Table 1. Specification of dye-doped siloxane based optical filter coating films Stability test at heat and moisture condition was done for IR-dye IR-dye Vis-dye siloxane film 1, vis-dye siloxane film 1 and vis-dye siloxane film 1 siloxane film 1 GFRHybrimer 1. The films were aged in temperature/humidity Total transmittance test chamber with a constant condition of 85℃/85% RH for ≥85% ≤0.1% (@430~565nm) 30days. UV stability was also done by exposing dye-doped Total transmittance siloxane based optical filter films for 72hrs to UVB irradiation ≤0.5% ≤0.1% which power is 20W. The distance between the films and the (@350~390nm) lamp was 20cm. After the stability test, the films still maintain Total transmittance their optical properties which represent high reliability of dye- ≤0.1% ≤0.1% doped siloxane based optical filter films in heat, moisture and UV (@700nm) condition. More precise specification of dye-doped siloxane based Total transmittance ≥90% ≥90% optical filter films are shown in Table 1 and Table 2. (@800~1200nm) Finally we deposited interference layer on the IR-dye siloxane Haze ≤0.5% ≤0.5% film 1 to fabricate IR cut off filter film. The 30 layers of SiO₂ and Heat and moisture TiO₂ were alternately deposited on the dye-doped siloxane optical 85℃/85% RH for 30days filter film 1 in thickness of 3nm each. After deposition, rest of resistance undesired wavelengths in IR range for image sensors were UV resistance UV-B (20W, 20cm) for 72hrs removed which is suitable for replacing glass based IR cut off filter for image sensor. Total transmittance of the fabricated dye- doped siloxane based IR cut-off filter film is shown in Figure 3. It shows high transmittance (≥90%) in visible range and zero transmittance in IR and UV range with low haze and high stability in heat, moisture and UV condition.

SID 2019 DIGEST • 1493 P-69 / S.-M. Kang

Table 2. Specification of vis dye-doped GFRHybrimer film 4. Impact of Research Vis-dye GFRHybrimer 1 This research is about fabrication of flexible IR cut off filter and IR long pass filter by using siloxane matrix and diverse light Total transmittance ≥90% absorbing dyes with high reliability to replace glass based optical (@900~1200nm) filters which is not flexible. Total transmittance ≤0.5% (@350~700nm) 5. Acknowledgements This work was supported by the Wearable Platform Materials Glass transition No Technology Center (WMC) funded by the National Research Thermal decomposition 286℃ (1wt% loss) , Foundation of Korea (NRF) Grant of the Korean Government temperature 400℃ (5wt% loss) (MSIP) (NRF-2016R1A5A1009926). C.T.E ≤15ppm/℃ 6. Reference Elastic modulus ≥10Gpa [1] J.Harwood, J.J Dooley, A.J. Scott, R. Joiner “Constantly connected-The effects of smart devices on mental health” Tensile strength ≥150Mpa Computers in Human Behavior 34, 267-272 (2015) Heat and moisture resistance 85℃/85% RH for 30days [2] S.-H.Pyo, B.-K. Kang, “Hybrid IR cut-off filter for digital UV-B (20W, 20cm) for camera”, U.S Patent Application no.12/820,646, (2009) UV resistance 72hrs [3] K.Nagaya, “Optical filter, and solid-state image pickup device and camera module using the optical filter, US patent Publication no. US2017/0003425 A1 (2017)

[4] M. Dandin, P.Abshire, E.Smela, “Optical filtering technologies for integrated fluorescence sensors” Lap Chip 7, 955-977 (2007) [5] W.S Wong and A. Salleo, “ Flexible electronics: materials and applications, Springer US (2009) [6] Y.-W, Lim, H. Lee, H.Y. Kim J.G. Bae, B.-S. Bae “ Composition Optimization of Transparent Glass-fabric Reinforced Siloxane Hybrid (GFRHybrimer) Films for Thermally Stable Flexible Display Substrate Film” SID Symposium Digest of Technical papers 48, 150-152 (2017) [7] J. Jin, J. H. Ko, S. Yang, and B. S. Bae, "Rollable transparent glass‐fabric reinforced composite substrate for flexible devices," Advanced Materials, vol. 22, no. 40, pp. 4510-4515 (2010) [8] T. Sathishkumar, S. Satheeshkumar, J. Naveen “Glass fiber- reinforced Polymer composites – a review” Journal of Reinforced and Composites 33, 1258-1275 (2014) Figure 3. Total Transmittance of IR dye-doped siloxane [9] J. Jayamon “Optical Position Sensor Type (One- based optical filter film for flexible IR cut off filter Dimensional, Two-Dimensional and Multiaxial) and End User(Aerospace & Defense, Automotive, Consumer 3. Conclusion Electronics, Healthcare)” Global Opportunity Analysis and Light absorbing dye-doped siloxane based optical filter films for Industry Forecast , 2014-2022 (2017) flexible IR cut off filter and IR long pass filter were well [10] J.Fabian, H.Nakazumi, M.Matsuoka “ Near-infrared fabricated by using siloxane resin and diverse light absorbing absorbing dyes” Chem. Rev., 92 (6), 1197-1226 (1992) dyes. In case of flexible IR long pass filter, vis dye-doped siloxane based optical filter films were fabricated in two ways : [11] G.-M. Choi, J. Jin, D. Shin, Y. H. Kim, J.-H. Ko, H.-G. IM, coating film and GFRHybrimer considering usage. These films J. Jang, D. Jang, B.-S. Bae “Flexible Hard Coating: Glass- show good optical properties for certain usages like image sensors Like Wear Resistant, Yet Plastic-Like Compliant, or IR sensors. Also, the films shows high stability in heat, Transparent Protective Coating for Foldable Display” moisture and UV condition which represent high reliability. Advanced materials, 29 673-638 (2017) Finally, we has deposited interference layers consists of alternative layers of SiO₂ and TiO₂ on the IR dye-doped siloxane based optical filter film to make flexible IR cut off filter.

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