lithium niobate / 05 Making / 5.9
5.9 Electrodes
L1 Phenomenon
Gold electrodes a few micrometres from the waveguide carry the microwave signal. They are made by lift-off: resist is patterned, metal is evaporated over it, and the resist is dissolved so that only the pattern stays.
Process viewer stepsopen in the Process viewer
| # | STEP | ROUTE |
|---|---|---|
| 20 | Au traveling-wave electrodes by lift-off | ridge |
| 18 | Ti/Au electrodes by DUV lift-off and e-beam evaporation | strip |
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20/23Au traveling-wave electrodes by lift-off (ridge route)
L2 Model and data
| Electrode | Value | Source; status |
|---|---|---|
| Ti/Au, DUV lift-off, e-beam evaporation | 5 nm Ti + 400 nm Au | P |
| Au, lift-off, segmented TW electrodes | 800 nm Au; gap 5 µm; on 600 nm film, 350 nm etch, quartz handle; 1 µm SiO2 cladding | P |
| Au, two lift-offs | 200 nm T-segments, 1.1 µm unloaded electrodes; signal width 75 µm; gap 1.8 µm; Si undercut by isotropic ICP etch | P |
| DUV lift-off with a dielectric sacrificial layer (LiTaO3 analog) | PECVD SiO2 thicker than the metal, patterned, BHF undercut, evaporate, lift off | P |
| Cr/Au poling electrodes | 40 nm Cr + 30 nm Au, AZ-5214E lift-off | P |
| Nb (superconducting) | 200-300 nm, e-beam evaporated at 2 × 10−8 torr, about 10 Å/s, PMMA lift-off | P |
| Waveguide-electrode geometry (2018) | w = 900 nm, rib 400 nm, slab 300 nm, gap 3.5 µm; loss about 3 dB/cm; about 5 dB/facet | P |
L3 Details and open points
- Electrode-gap choice trades VπL against metal absorption; a 900 nm overcladding allowed a 1.8 µm gap without excess absorption P.
- Thick Au lowers RF loss; segmented electrodes break the voltage-bandwidth limit (chapter 06).
- The 2018 MZM at CMOS-compatible voltages used x-cut TFLN with Au electrodes beside etched ridges P(abs); its main-text Vπ and bandwidth were not read (abstract only).