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SCIENCE CHINA Information Sciences, Volume 61, Issue 6: 060419(2018) https://doi.org/10.1007/s11432-018-9430-2

Parylene-MEMS technique-based flexible electronics

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  • ReceivedJan 10, 2018
  • AcceptedMar 27, 2018
  • PublishedMay 14, 2018

Abstract

This paper reports a novel fabrication strategy for flexible electronics based on the parylene-MEMS (micro-electromechanical system) technique. A set of parylene-filled trenches is used to mechanically connect silicon-based functional units and realize a flexible 4$\times$6 temperature controlling array as a preliminary demonstration. The trench-filling performance of the parylene deposition is carefully studied, and an optimized process is established to minimize the keyhole inside the parylene-filled trench. The effect of trench width on the flexibility and bendability of the prepared flexible electronics devices is analyzed by finite element modeling. Performances of the thermal/electrical isolation and the mechanical connection of the prepared parylene-filled trenches have been tested. The experimental results indicate that the highest thermal isolation efficiency is approximately 72.5% with the 10 paralleled, 7 $\mu$m wide and 50 $\mu$m deep parylene-filled trenches. The leakage current of the 10 paralleled, 5 $\mu$m wide and 100 $\mu$m deep parylene-filled trenches is less than 2 pA under a voltage of 100 V. Besides, these parylene-filled trenches acting as the flexible linkage of connected silicon-based functional units exhibit high connection performance without rupture when the loading pressure is under 200 kPa. Due to the powerful silicon microfabrication capability and excellent compatibility of the parylene-MEMS technique, the present flexible electronics strategy holds a promising potential for applications in various areas.


Acknowledgment

This work was financially supported by National Natural Science Foundation of China (Grant No. U1613215), Beijing Natural Science Foundation (Grant No. L172005), and National Basic Research Program of China (973) (Grant No. 2015CB352100).


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  • Figure 1

    (Color online) Schematic illustration of the work principle of the proposed parylene-MEMS based flexible electronics. (a) Top view of two units and the parylene-filled trenches around them; (b) cross-sectional view of a set of parallel parylene-filled trenches; (c) the bended structure upon applied forces.

  • Figure 2

    (Color online) Microfabrication process of the flexible temperature controlling array. (a) Metal pattering on the silicon oxide layer; (b) trench etching; (c) parylene deposition to fill the trenches; (d) parylene etching by the oxygen plasma; (e) Au wires electroplating; (f) parylene deposition and patterning; (g)removing the silicon beneath the trench;protect łinebreak (h) parylene deposition after removing all the remnant silicon.

  • Figure 3

    (Color online) Results of the parylene trench-filling experiments. (a) SEM photos of the conformal deposition and the keyhole in the parylene-filled trench; (b) definitions of $X_b$ and $X_t$; (c) definition of the slant angle; (d) conformal ratios for the cases with different width of the trench: 3.3, 6.5, 15, 30 $\mu$m, the depth was 40 $\mu$m; (e) conformal ratios for the cases with different depth of the trench: 4, 18, 38, 60, 92 $\mu$m, the width was 5.5 $\mu$m; (f) conformal ratios for the cases with different slant angle of the trench: $-$0.8$^\circ$, 0$^\circ$, 2.3$^\circ$; the depth was 18 $\mu$m and the width of the bottom was 3 $\mu$m.

  • Figure 4

    (Color online) SEM images. (a) Profile of one-step-filled trenches, the inserted one is a magnified view of the trench opening; (b) profile of the trenches after a filling-etching-refilling process, the inserted one is a magnified view of the trench opening; (c) surface of the parylene-filled trenches.

  • Figure 5

    (Color online) Performances of thermal isolation, electrical isolation and mechanical connection of the parylene-filled trenches. (a) Schematic of the thermal isolation test; (b) schematic of the electrical isolation test; (c) schematic of the mechanical connection test; (d) the temperature variation of units 1 and 2 when unit 1 was heated; (e) I-V relationship of air, parylene-filled trenches, PMMA and glass, inset showed the details of the former three samples; (f) displacement of the unit when force was applied.

  • Figure 6

    (Color online) Simulation results. (a) Strains and displacements of the deformation model before and after the removal of the remnant silicon; (b) the influence of trench width on the displacement of array; (c) the influence of trench width on the approximate radius of array.

  • Figure 7

    (Color online) Photos of the flexible temperature controlling array. (a) Bending to the front side; (b) bending to the back side; (c) rolling the flexible array on a cylinder with a diameter of 5 mm.

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