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.

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In this paper, a through-glass-via (TGV) interposer for 2.5D radio frequency (RF) integration is presented. A coplanar waveguide (CPW) transmission line with grounded TGVs on one side interconnects with the mounted RF devices, and an electrical ground plane on the other side. Tapered TGVs are fabricated using a combined method of sandblasting and thinning/polishing process to achieve precise control of the profile of the vias and improve uniformity. The TGVs are metalized by conformal copper (Cu) electroplating to form a vertical interconnection between the upper and lower metal layers, which can maintain RF performance and avoid thermal stress issues. The CPW transmission lines with electrically grounded TGVs and test structures are designed, fabricated and tested to evaluate the TGV's RF performance and suitability for 2.5D RF integration. The RF measurements show that the insertion loss is about 0.13 dB mm −1 @10 GHz for the CPW line with grounded TGV which is less than 0.1 dB@10 GHz for a single TGV. We analyzed S parameter for the tests and simulations when taking into account various factors in the manufacturing process, such as the surface roughness and metal resistivity. The results provide a research direction for the optimization of the parameters in the follow-up study. In addition, a 2.5D RF receiver module based on the proposed TGV interposer in the L-band is assembled and validated. The gain value of the TGV interposer integrated RF module is about 14.4 dB, which is close to the theoretical value.