Fabrication of nanogap metal electrode with sacrificial layer techniques

Two simple lithography-independent methods by underetching the metal and using SiO₂ sidewall as sacrificial spacer to fabricate nanogap electrodes are demonstrated in this work. In the first method, by wet etching the metal layer after lithography and using the undeveloped photoresist (PR) as the sacrificial layer of the subsequent second metal lift-off process, a metal electrode with nanogap was fabricated. The width of the metal gap is mainly defined by the overetch under the PR. For the sidewall method, first depositing a conformal SiO₂ layer on a polysilicon pattern and then etching back the SiO₂ layer on the polysilicon, a sacrificial spacer is obtained after selectively remove the polysilicon. At last, a metal nanogap was fabricated after the metal sputtering and lift-off process. The width of the metal gap is mainly determined by the thickness of conformal SiO₂ layer. With the conventional lithography methods, metal electrode with the gap width smaller than 100nm can be obtained.