A.C. Peixoto

Fabrication and mechanical characterization of long and different penetrating length neural microelectrode arrays

This paper presents a detailed description of the design, fabrication and mechanical characterization of 3D microelectrode arrays (MEA) that comprise high aspect-ratio shafts and different penetrating lengths of electrodes (from 3 mm to 4 mm). The arrays design relies only on a bulk silicon substrate dicing saw technology. The encapsulation process is accomplished by a medical epoxy resin and platinum is used as the transduction layer between the probe and neural tissue. The probes mechanical behaviour can significantly affect the neural tissue during implantation time. Thus, we measured the MEA maximum insertion force in an agar gel phantom and a porcine cadaver brain. Successful 3D MEA were produced with shafts of 3 mm, 3.5 mm and 4 mm in length. At a speed of 180 mm min−1, the MEA show maximum penetrating forces per electrode of 2.65 mN and 12.5 mN for agar and brain tissue, respectively. A simple and reproducible fabrication method was demonstrated, capable of producing longer penetrating shafts than previously reported arrays using the same fabrication technology. Furthermore, shafts with sharp tips were achieved in the fabrication process simply by using a V-shaped blade.

A 45° saw-dicing process applied to a glass substrate for wafer-level optical splitter fabrication for optical coherence tomography

This paper reports on the development of a technology for the wafer-level fabrication of an optical Michelson interferometer, which is an essential component in a micro opto-electromechanical system (MOEMS) for a miniaturized optical coherence tomography (OCT) system. The MOEMS consists on a titanium dioxide/silicon dioxide dielectric beam splitter and chromium/gold micro-mirrors. These optical components are deposited on 45° tilted surfaces to allow the horizontal/vertical separation of the incident beam in the final micro-integrated system. The fabrication process consists of 45° saw dicing of a glass substrate and the subsequent deposition of dielectric multilayers and metal layers. The 45° saw dicing is fully characterized in this paper, which also includes an analysis of the roughness. The optimum process results in surfaces with a roughness of 19.76 nm (rms). The actual saw dicing process for a high-quality final surface results as a compromise between the dicing blades grit size (#1200) and the cutting speed (0.3 mm s−1). The proposed wafer-level fabrication allows rapid and low-cost processing, high compactness and the possibility of wafer-level alignment/assembly with other optical micro components for OCT integrated imaging.

Long neuroprobes based on silicon dicing and iridium oxide for electrical stimulation/recording

This paper synthesizes the development of a new 3D neuroprobe array, constituted by microelectrodes capable of electrical stimulation and recording. The arrays design relies on a bulk silicon substrate dicing technology and it comprises 6 × 6 neuroprobes with three different penetrating lengths (from 3 to 4 mm) and a 180 μm cross-section. A reproducible fabrication method was demonstrated, capable of producing longer shafts than in previously reported arrays. In addition, sputtered titanium/iridium oxide microelectrodes have shown the required performance, with a consistent reversible electrochemical behavior and an impedance value of 145 Ω in the same frequency range as the stimulation protocols.

3 mm Deep microelectrode needle array based on aluminum for neural applications

This paper presents a simple and cost-effective fabrication method of invasive neural microelectrode arrays based on aluminum, which is a viable alternative to other state-of-the-art technologies that rely primarily on silicon. A 10 × 10 array with 3.0 mm deep reaching pillars were fabricated, each having a pyramidal tip profile. Each aluminum pillar is insulated with a biocompatible layer of aluminum oxide. The electrode tip was covered by an iridium oxide thin-film layer via pulsed sputtering, providing a stable and a reversible behavior for recording/stimulation purposes, each with a 145 Ohm impedance in a wide frequency range of interest (10 Hz-100 kHz). Each pillar is electrically individualized from the adjacent ones by an insulating layer of epoxy resin. High-aspect-ratio pillars (20:1) are achieved through a combination of dicing, thin-film deposition, anodizing and wet-etching. The described approach allows an array of deeper penetrating electrodes and a simpler fabrication procedure when compared to previous works.