Microprobe electrode array with individual interconnects through substrate using silicon through-glass via

This paper presents the fabrication and measurements of a vertical out-of-plane microprobe electrode array with individual interconnects through the substrate using a silicon through-glass via (TGV) with transparent properties. The TGV was fabricated using a low-resistance silicon (LRS) via and the glass reflow process. The microprobe structure was formed by multiple deep reactive ion etching and reactive ion etching processes using one-step photolithography and a single etch mask. The height and pitch of the microprobe are designed to be 90 μm and 210 μm, respectively. Cr and Au conductive layers were deposited and patterned on the silicon microprobe structure. A parylene-C thin film was used as an insulating layer and it was etched only at the tip-end through the self-alignment fabrication process using a thick photoresist to expose the conductive part. Each microprobe electrode was independently connected to the backside of the substrate through the silicon TGV. The single via resistance was measured to be 1.26 ± 0.041 Ω. To verify the electrochemical characteristics of the microprobe electrodes with individual interconnects, the steady-state limiting current through the redox reaction was measured by the cyclic voltammetry method for each electrode. The measured steady-state peak current of the microprobe electrode was compared with the theoretical calculation. Further, the electrode impedance was measured and the equivalent circuit analysis was constructed using the Zview impedance modeling software. Experiments were conducted to measure the impedance of 16 microprobe electrodes, and it was confirmed that the impedance did not exceed 1 MΩ at 1 kHz. Then, primary rat cortical neuron cells (DIV 7) were cultured on the fabricated microprobe electrodes and neural spike signals were successfully measured. Also, the light transmittance experiment was conducted to measure the transparency of the TGV structure fabricated through the glass reflow process.