Development of double-sided Si neural probe with microfluidic channels using wafer direct bonding technique

We have proposed the intelligent Si neural probe system which can realize high density and multifunctional recording of neuronal behaviors. In this device, LSI chips such as amplifiers, A/D converters, and multiplexers are integrated on the intelligent Si neural probe. In this paper, we report the development of a novel Si neural probe with microfluidic channels which is the key part of the intelligent Si neural probe system. The Si neural probe has microfluidic channels fabricated using a wafer bonding technique to deliver drugs into the brain when neuronal action potentials are recorded. Furthermore, our Si neural probe has recording sites on both front- and back-side of Si to realize high density recording. We fabricated the carefully-designed Si neural probe, and evaluated characteristics of microfluidic channels. From the liquid ejection test, we confirmed that there was no void at bonding interfaces. We observed the liner relationship between the flow rate and the pressure drop, and the relationship was identical to that from the calculation, which indicated that the microfluidic channel was successfully formed. In addition, we fabricated the Si neural probe for in vivo neural recording. Both front- and back-side recording sites of the fabricated Si neural probe had impedance values of 1.5 MΩ and 1.2 MΩ at 1 kHz, respectively, which indicated that both recording sites had equivalent characteristics. The neuronal action potentials in motor area of Japanese macaque's brain were successfully recorded by using the fabricated Si neural probe.