Combined UV laser and wet etching method for fabricating high-temperature superconducting terahertz emitters based on Bi2Sr2CaCu2O8+ <i>δ</i> single crystals

To advance the field of terahertz (THz) devices, we propose a high-temperature superconducting THz emitter based on Bi2Sr2CaCu2O8+δ (Bi2212) crystal chips. To enhance the micro-fabrication capabilities of Bi2212 chips, typically sized 80 × 400 × 5 μm3, we introduced an ultraviolet engraver (wavelength: 355 nm, average power: 5 W) and used it to fabricate metallic masks for the potassium hydroxide (KOH) wet etching of Bi2212 crystals. Thin metallic films of Ag (∼5 nm) and Au (∼12 nm) deposited on the Bi2212 surface were patterned into chip shapes using the laser. Optimal laser parameters for thin-film patterning were identified as a scan speed of 5–10 mm/s, a power level of 5% of the maximum output, and a repetition rate of ∼110 kHz. A crystal chip fabricated using laser patterning and a 13 wt. % KOH solution, with dimensions of 75 × 175 × 3.2 μm3, exhibited distinct THz-wave emission within the 0.44–0.64 THz range. Unlike conventional photolithography, the proposed approach simplifies the mask fabrication process into a single laser-patterning step and enables crystal chip fabrication in facilities without photolithography capability, a distinctive feature of this technique. Although the fabrication accuracy is lower than that achieved by photolithography, this method facilitates rapid preparation of test samples and efficient evaluation of device characteristics. Further optimization of laser processing conditions to improve accuracy and enable direct machining of bulk crystals is expected to make a significant contribution to the development of superconducting THz devices.