Remover pg solution

Firstly, the 13 nm indium tin oxide (ITO) on glass substrate is ultrasonically cleaned. The 800 nm TiO2 film is deposited on the ITO coated glass substrate by using an electron beam (Ebeam) evaporator (SKE_A_75). The refractive index, extinction coefficient, and thickness are measured by ellipsometer. The 100 nm electron-beam resist (PMMA) is spin-coated at 4000 rpm on the film and baked at 180 °C for 1 h. The resist is patterned by electron-beam lithography (Raith E-line) at a dose of 90 μC/cm² at an accelerating voltage of 30 keV. After immersing in MIBK&IPA (1:3) solution for 30 s, a reverse pattern is generated on the surface. A layer of 23 nm chromium (Cr) is deposited on the sample using Ebeam evaporation. After the samples is soaked in remover PG solution (Micro Chem) for 12 h, the pattern was then transferred to the TiO2 film by reactive ion etching (Oxford Plasmalab System 100). Finally, the Cr hard mask was removed by soaking in a Cr etchant solution (Aldrich Chemistry) for 10 min.

The Si metasurfaces were fabricated by a combined process of electron-beam lithography and reactive ion etching. The 230 nm single-crystal silicon film on a sapphire wafer was cleaned with acetone and coated with 100 nm electron-beam resist polymethyl methacrylate. The sample was baked at 180 °C for 1 h and then patterned by electron-beam writer (Raith E-line) with a dose 90 µC/cm² under an acceleration voltage 30 kV. After developing with MIBK&IPA (1:3) solution, 15 nm Cr was deposited on the sample using E-beam evaporation (SKE_A_75), and Cr hard mask was realized via a liftoff process in remover PG solution (Micro Chem) for 24 h. The pattern was transferred to the Si through reactive ion etching with SF₆ and CHF₃ in Oxford Plasmalab System 100. The vacuum degree was 10⁻⁵ and the gas flow was 5 and 50 sccm for SF6 and CHF3, respectively. Finally, the Si metasurfaces were obtained by removing the Cr mask in Cr etchant solution (Aldrich Chemistry) for 30 min.

The fabrication steps of the soft liquid-metal neural probe are as follows: (1) a Si wafer (Dasom RMS, Republic of Korea) was spin-coated by a LOR 3 A lift-off resist (MicroChem) as a sacrificial layer. (2) A 1 µm-thick parylene-C layer was deposited as the bottom layer of a neural probe using a parylene coating system (NRPC-500, Nuritech Co. Ltd., Republic of Korea). (3) EGaIn was printed to 5-µm-wide lines on this parylene-C layer. (4) Another 2.5-µm-thick parylene-C layer was deposited as the top layer of a neural probe. (5) The photoresist S1818 (MicroChem) was spin-coated and then photolithographically patterned for defining the probe shape with opening the tip area of electrodes. (6) The areas of parylene-C where the S1818 layer did not cover was etched away by O₂ plasma using a reactive ion etching (RIE) system (LAT Co. Ltd., Republic of Korea), and then the S1818 photoresist was dissolved out using acetone. (7) The S1818 photoresist was spun again and then photolithographically patterned for opening the electrode pads, and procedure (6) was repeated. (8) The resulting probes were lifted off using a remover PG solution (MicroChem) by dissolving the sacrificial layer (the LOR 3A lift-off resist) and by releasing the neural probes from the Si wafer. (9) The released neural probes were rinsed with deionized (DI) water.