Fabrication and characterization of a tungsten microneedle array based on deep reactive ion etching technology

Abstract

In this paper, the authors report on a novel tungsten microneedle array fabricated using deep reactive ion etching. The fabricated sample was 10 mm long, 10 mm wide, and 40 μm in pitch. Each microneedle had a top-end diameter of 7.7 μm, a bottom-end diameter of 30 μm, a length of 60 μm, and a sidewall tilt angle of approximately 14°. The mechanical strength, hydrophobicity and contact impedance of the tungsten microneedle array were characterized. For the mechanical strength, a rubbing test was conducted, which involved moving the tungsten microneedle array structure on a 800-grit abrasive paper with an equivalent slide friction force of 2 × 10−3 μN. Results indicated no obvious damage to the microneedles at the scanning electron microscopy level. Hydrophobicity test results showed that the surface of the tungsten microneedle array was uniform and hydrophobic, with an average contact angle of 137.9° and a maximum contact angle variation of 5.9° for the best sample. The contact impedance of the tungsten microneedle array sample to skin was found to be stable after 1 h of contact at a value of less than 2000 Ω in the range of 50–100 kHz.