Fabrication of High Aspect Ratio SiO2 and Tempax Glass Pillar Structures and Its Application for Optical Modulator Device

This paper presents the fabrication of deep SiO₂ and Tempax glass pillar structures by using reactive ion etching system, which intends to realize optical modulator mounted on an image sensor. The optical modulator consists of high aspect ratio SiO₂ or Tempax glass pillars that can modulate the transmitted light intensity by moving a liquid in and out of the spaces between pillars based on the reversible electrowetting of liquid on top of micro-pillars surfaces. SiO₂ pillars having smooth surfaces, vertical shapes, and high aspect ratio of 12 with a depth of 12 μm, diameter of 1 μm, and the pitch of the two pillars of 2 μm has been achieved. In addition, Tempax glass pillar structures are also successfully fabricated under investigation of gas mixtures of SF₆ and O₂. Finally, a 7.2 mm × 9.6 mm optical window area integrated with an image sensor for an optical modulator has been demonstrated where high transmission modulation together with a large contrast has been observed of approximately 65% and 0.86 for cases with and without matching oil penetration, respectively.