Towards bottom-up fabrication of a BDD chip electrode

Abstract

Boron-doped diamond (BDD) is an attractive electrode material. When sufficiently boron-doped, diamond has metal-like conductivity and in comparison with other electrode materials has several advantages, such as lowand stable background current, reduced biofouling, broad potentialwindow, corrosion resistance and chemical stability. However, current fabrication processes rely on top-down techniques, that often require cleanrooms and expensive micro fabrication techniques. This research focuses on a low-cost bottom-up fabrication technique by using an inkjet printing process to locally increase the substrate seeding density. Thin-film BDD can then be selectively grown into electrode geometries. The BDD electrodes can be used as more robust and better performing electrodes for detectingmicropollutants in environmental monitoring or for detecting biomarkers in saliva, sweat or blood, in health monitoring. Inkjet manufacturing is an emerging production process in micro fabrication. Due to its accuracy, material efficiency, and given that it is a digital process, inkjet printing is a strong candidate for bottom-up fabrication of low-cost and customizable BDD (micro)-electronics. Two inkjet printers were used to investigate themicro fabrication technique for a BDD chip electrode. A hacked desktop Epson printer was used to demonstrate the capabilities of selective seeding using ’diamond’ ink on silicon substrates and to grow patterned thin-film intrinsic diamond. However, the printer lacks the required control to produce continuous structures with high accuracy. A second method for selective seeding was employed by using a PIXDRO LP-50 commercial research printer, which has a high resolution, motion controlled print bed. With the application of surface treatments, such as oxygen plasma, on the silicon substrate and the development of different inks, continuous films of nanocrystaline diamond with line resolution of approximately 60 μm are produced in a final chemical vapor deposition (CVD) growth step. In addition, by loading the printer with a silver ink part of the diamond film has been coated with silver, which demonstrates that a reference electrodes or electrode leads can be manufactured with the same production technique. This research demonstrates the potential for the bottom-up fabrication of chip electrodes using the inkjet printing process. Furthermore, as this process is not limited to the production of BDD electrodes, it opens the path towards bottom-up fabrication of other (boron-doped) diamond sensor devices, such as gas sensors or 2D heaters.