Sunghyun Yoo

Deep wet etching of borosilicate glass and fused silica with dehydrated AZ4330 and a Cr/Au mask

This research highlights a superior glass-wet-etch technique which enables a glass wafer to be etched for more than 20 h in 49 wt% hydrofluoric acid (HF) only with Cr/Au film and a common positive photoresist, AZ4330. We demonstrated that pits on the wet-etched glass wafer were generated not only due to HF diffusion through the Cr/Au film but also due to pinholes on the Cr/Au films created by the diffusion of the Cr/Au etchant through a photoresist etching-mask during the Cr/Au wet etching process. These two types of diffusion, HF diffusion and Cr/Au etchant diffusion, were eliminated by the thermal curing of a photoresist (PR), AZ4330, before the Cr/Au wet etching process. The curing process allowed the PR to dehydrate, increased the hydrophobicity, and prevented the diffusion of the hydrophilic HF and Cr/Au etchant. Optimization of the curing process was performed, showing that curing at 130 °C for 20 min was the proper condition. With the optimized process, a 525 µm thick borosilicate glass wafer was penetrated with 49%wt HF. A fused silica wafer 525 µm thick was also wet-etched and penetrated with 49 wt% HF at 10 h. Moreover, no pits were found in wet etching of the fused silica for 20 h in 49 wt% HF. These findings demonstrate that the proposed technique allows the wet etching of a glass wafer for more than 20 h in 49%wt HF, the best result thus far. We fabricated a glass substrate with a 217.0 µm deep cavity and a penetrating through-via using the proposed technique, proving the feasibility of the product as an optical component with a surface roughness of 45.5 A in the cavity.

Square-shaped glass microlens array for fiber-optic neurostimulation

We present a square glass microlens array for the improvement of light transfer efficiency of the fiber-optic neural probe. Optimal design has been derived using finite element analysis and fabricated microlens array has been analyzed.

Silicon-rim-reinforced silicon nitride microscanner with vertical comb actuator and wafer-level vacuum packaging

This research proposes a silicon rim for an optically flat mirror and a vertical comb actuator in a silicon nitride (SiN) microscanner. A wafer-level vacuum packaging was also successfully implemented for large angular deflections with low driving voltage. Radius of curvature (ROC) of a SiN mirror of 1 μm-thickness and 1 mm-diameter was measured to be 0.357 m. Optical experiment showed optical tilt angle of 22° at driving voltage of 53 Vrms and resonant frequency of 14.8 kHz, respectively.

2-D forward optical scanner with glass microlens and isolation blocks using thermal reflow

We present a novel fabrication method of a two-dimensional forward optical scanner with integrated microlens. Glass microlens and electrical isolation blocks were integrated with silicon XY-stage using thermal reflow process. Measured scan angles in X and Y directions at resonance were ±4.9° and ±5.0°, respectively, at atmospheric pressure.

In-situ fabrication of {111} mirror and optical bench using double-sided anisotropic wet etching of {100} silicon wafer

This work presents a novel fabrication method for {111} dual mirror and optical bench using double-sided anisotropic wet etching of <;100>; oriented silicon wafer. The roughness of the wet etched {111} plane is 8 nm.