Novel fabrication process for sub-micron interdigitated electrode arrays for highly sensitive electrochemical detection

Interdigitated electrode arrays (IDAs) are often used for electrochemical detection using redox cycling for signal amplification. Its geometry, especially the gap width, is an important factor defining its electrochemical performance (sensitivity and collection efficiency). Minimal defect density on a wafer is a must, as a single shortcut prevents the function of the sensor chip. Therefore, the fabrication of interdigitated electrode arrays is a fundamental step in the integration of electrochemical sensors. This paper presents a novel fabrication approach that allows electrode spacing in the sub-micrometer region by using standard equipment such as UV Mask Aligner, physical vapor deposition and diffusion furnace. The fabrication procedure is a combination of dry etching, thermal oxidation and wet etching. This approach has potential to realize electrode distances down to 140 nm or even less. The proposed method enables the fabrication of sub-micron IDAs with the use of a conventional Mask Aligner and standard silicon technology. Moreover, it allows the electrode spacing adjustment without changing the mask design. The presented results demonstrate high sensitivity electrochemical sensors with amplification factors more than 12 without the need of e-beam lithography. Hence, this fabrication method offers a low-cost alternative to sub-micron e-beam written IDAs.