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The 4th International Symposium on Organic and

The 4th International Symposium on Organic and Inorganic Electronic Materials and Related Nanotechnologies (EM-NANO 2013) 2013/06/18 17:30~17:50 B3-2. Structural Control and X-ray 3-D Characterization of Hexagonal Boron Nitride Assembly in Polysiloxane.

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The 4th International Symposium on Organic and

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  1. The 4th International Symposium on Organic and Inorganic Electronic Materials and Related Nanotechnologies (EM-NANO 2013) 2013/06/18 17:30~17:50 B3-2 Structural Control and X-ray 3-D Characterization of Hexagonal Boron Nitride Assembly in Polysiloxane Takeshi Fujihara*, Hong-Baek Cho, Masanao Kanno, TadachikaNakayama, Tsuneo Suzuki, HisayukiSuematsu and Koichi Niihara Extreme Energy-Density Research Institute Nagaoka University of Technology t_fujihara@etigo.nagaokaut.ac.jp

  2. Background (Thermal Interface Materials) Heat source Heat sink Next generation EV Withstand voltage 1200 V or more • High heat dissipation • High electric insulation • Light weight For 1200V Class Devices Thermal interface material (TIM) Thermal conductivity (HIGH) Electrical Insulation(HIGH) Peripheral components

  3. Background (Hybid materials) ◎: very good, ○:good, △:normal, ⅹ: bad Polymer Matrix (Polysiloxane) Structure Control is very important For Good Properties. Ceramics Filler (BN) Schematic image of Hibrids

  4. Orientation Control by Electric Field Filler orientation technique Shear force, Centrifugal force, Magnetic field, Electric field Electric field Texture Control?? T: field induced torque E: electric field V: volume of filler ε0 : vacuum permittivity ε1 : dielectric constant of filler ε2 : dielectric constant of polymer Ceramics Filler • Able to increase torque by increasing the electric field • Able to increase torque by using fillers with a high dielectric constant • Able to relocate fillers horizontally by electrophoresis

  5. Structure Design for TIM Structure of the BN filler was controlled by Electric Field • Switching Field • micro electrode Electric Field No treatment + + + Pillar structure Little vol.% filler as possible. Inexpensive process as possible.

  6. Research objectives Localization control of densely-packed BN nanosheets assembly in polymer matrix 3D identification of BN nanosheets assembles in the polymer Realization of the denser BN nanosheets bundles by electric field concentration Thermal diffusivity enhancement into the plane direction of the composite

  7. Experimental Homogeneous dispersion and degassing pre-polymer + BN, 5 vol% BN Sonication (160 W, 40 kHz, 10 min) Hybrid mixer (1500 rpm, 10 min) ITO coated glass Spacer (acrylic plate) Casting on Spacer (200 µm) - + Applying DC electric field (1 kV, 1h) SWDC electric field (1kV, every 10, 15, 20 min / 1h) Suspension Micro-mold Curing and demolding (60℃, 2h) BN nanosheets Micro Si mold D90: 10.6 μm, Thick.: 10-100 nm Patten: Line, Dot Width: 50 µm Depth: 10 µm 1μm

  8. Experimental Setup Copper electrodes sample Vacuum bag ITO electrodes

  9. SEM micrographs after Orientation Can Control the Texture of BN a) before b) after BN/polysiloxane composite film plane Cross-sectional image of polysiloxane/BN composites containing 10 vol% BN. a) before and b) after application of nano pulse width electric fields. ☛Journal of the Ceramic Society of Japan, express letter 118(1) (2010) 66.

  10. Electrophoresis Effect (Electric Migration) Δ- NH2 ＋ NH2 ＋ The surface of the BN are negatively charged. 0 hr － ＋ 3 hr So long time × ＋ 16 hr

  11. Switching Field Trietment Schematic images Δ- NH2 The surface of the BN are negatively charged. NH2 ＋ ＋ － － 2nd 3rd 1st － － ?? ＋ ＋

  12. Swiching Effect (Microscope) Side view Top view [ :20 μm] Pillar structure ! x1000 x1000 By Spinodal decomposition x1000 x1000 Anisotropic alignment (switching DC 1.0 kV) Linear networks of LABNs : thickness (50~85 μm), length ( 250 μm)

  13. X-ray CT Scan image of Pillar Structure BN nano sheet Want to Design The Position and Diameter of the Pillar! Pillar structure Silicone Polymer 2013, Ceramics photography Award by CerSJ

  14. Control the PositionandDiameterof the Pillar Structure The Well Designed electrode in order to concentrate the electric field. Well Designed Electrode Electromagnetic field simulation Electromagnetic Simulated by MAGIC by FDTD-PIC methods 50 mm ? Can Control of the Position of Pillar? Can Control of the Diameter of Pillar?

  15. 3D analysis of Hybrids (X-ray CT) Tomographic image, DC 1 kV 50µm Line Dot Side view   Mold   Film In-plane view LABNs started to develop from the tip of electrode pattern and anchors to the opposite side of the film. Low X-ray absorption High

  16. 3D analysis of composite (X-ray CT) Calculation BN constant in LABNs structure Composite film Pillar structure (Random) BN content in Pillar structure (vol.%) 50µm 200µm 50µm 50µm Switching number of electric field (1/h) Tomographic image, SWDC, Dot 50µm Switching number 2 3 5 BN nanosheet The best localization condition of BN in polysiloxane with 3 times of electric field switching

  17. Switching Effect for fabricate the Pillar structure Schematic images 3 Times (GOOD!!) ＋ ＋ Good Thermal Conductivity!! － － － － Separate ＋ ＋ 5 times (Too Much)

  18. Thermal mapping image 0kV, Plane (Random orientation) 1kV, Dot (LABNs structure) AFM image 50µm Thermal mapping image 50µm Possible to excellent Thermal flow of microscopic area by LABNs

  19. Local-Thermal Analysis Pillar structured (Hybrid) Nano-TA (Anasys Instruments Coop.) Non Treatment (Hybrid) 100mm 100mm Thermal Property Measured by Heater Current 100mm 100mm Keep the temperature 80ﾟC Cold Stage Cold Stage

  20. Conclusion • The localization of BN nanosheets can control • by using the electric field concentration • By using SWDC electric field, BN nanosheets are packed in linearly aligned BN nanosheets (LABNs) with high density • LABNs shows excellent thermal flow of microscopic area • Thermal diffusivity of macro area is also improve by densely packed LABNs

  21. Background Thermal management An important strategy in various fields of semiconductor industry Thermal Interface material (TIM) ・High thermal conductivity ・High electric insulation ・High flexibility Solution: Well designed hybrid materials Thermal flow Anisotropic & localization control ・low volume function of filler ・Efficient thermal conductivity enhancement

  22. Behavior of BN nanosheets under electric field 1. Polarization and rotation 2. Connection and movement 3. Localization ×102 [V/m] -80.00 Si(εr=11) : Anisotropic orientation : Electrophoresis : Coulomb attraction : Electric field concentration Simulation of electric field(MAGIC) Polysiloxane+BN(εr=4.5) - - - 0.00 Occurring electric field concentration at the tip of micro-pattern on the anode ⇒Possible to control of localization of LABNs Electrode spacing: 200mm Applied voltage:1kV Anode pattern: Line&Space Pattern width: 50µm Pattern depth: 10µm + + + [3] H. B. Cho et. al., Journal of Nanomaterials (2011).

  23. Thermal diffusivity analysis (perpendicular direction to the film plane) Composite film LABNs structure Calculation BN constant in LABNs structure 50µm 200µm Thermal diffusivity (m2/s) 50µm 50µm BN nanosheet BN content in LABNs structure (vol. %) Increasing of the thermal diffusivity by densely packed LABNs

  24. Orientation Analysis (XRD) Intensity ratio (%) (Random) Degree of perpendicular orientation Switching number of electric field (1/h) The degree of perpendicular orientation is increased by applying electric field Intensity ratio [%] = c-axis(002): 2θ=26.76, a-axis(100): 2θ=41.60

  25. Futurework For fabrication of the pillar structure with the narrower filler-to-filler gaps are still required Modification of BN surfaces with surface functional groups Application of Nano-sec pulse electric field Increase of BN contents after surface modification

  26. Orientation Analysis (XRD) ●: h-BN (002) plane, non applied voltage ● Intensity ratio (%) Intensity (a.u.) dot, DC 20 30 40 50 2 theta (deg) BN content (vol.%) Degree of perpendicular orientation Intensity ratio [%] = c-axis(002): 2θ=26.76, a-axis(100): 2θ=41.60 (101) (100) ● ●

  27. Hexagonal Boron Nitride c a c axis: 3 (W/m·K)[2] Heat source aaxis: 600(W/m·K)[2] • One of the best thermal conductor among electric insulators • Graphite-like layered structure with high aspect ratio • Anisotropic thermal conductivity [2] Properties of Advanced Semiconductor Materials : B : N

  28. 3D analysis of composite (X-ray CT) Tomographic image, SWDC 1 kV, (every 15min / 1h) Line, 50 µm Dot, 50 µm 50µm   in-plane view   out-of-plane view Linearly aligned BN nanosheets (LABNs) started to develop from the tip of electrode pattern and anchors to the opposite side of the film. Low X-ray absorption High

  29. Our orientation technique New orientation technique: -by application of electric field & -by using micro-dimensional electrode patterns Preliminary experiment Using DC electric field - - Behavior of BN nanosheets ①Localize into micro-space by capillary force between patterns ②Orientation by electric field ③Localize to anode side by electrophoresis ×102 [V/m] -80.00 Si(εr=11) + 50μm + Localization to anode side by electrophoresis[3] Simulation of electric field(MAGIC) Using micro-mold Polysiloxane+BN(εr=4.5) - Electrode spacing: 250mm Applied voltage:1kV Anode pattern: Line&Space Pattern width: 50µm Pattern depth: 10µm 0.00 ② ①,③ 5 μm Possible to align according to pattern shape by capillary force[4] Occurring electric field concentration at the tip of micro-pattern on the anode ⇒Possible to induce higher electric field + [3] H. B. Cho et. al., Journal of Nanomaterials (2011). [4] T. Fujihara et. al., 34th ICACC (2010).

  30. Distribution of BN nanosheets in polysiloxane(digital micro scope) Cross-section view, Electric field 50kV/cm BN nanosheets are localized to anode side by electrophoresis By micro-mold: Localized BN nanosheets developed into pillar structure

  31. Orientation state of BN nanosheets in pillar structure (SEM)  Cross-section view, Electric field 50 kV/cm, ○ Dot  Almost BNnanosheets have oriented perpendicular direction to the film plane   5 μm 5 μm  

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