**5. Conclusions**

The fabrication and initial electrical characterization of an all-SiC neural probe is presented. The SiC neural probe was fabricated from p− and n<sup>+</sup>-type 3C-SiC epilayers grown on SOI wafers. First, a moderately p-type 3C-SiC film was grown on a SOI wafer, followed by a layer of n<sup>+</sup>-type 3C-SiC. The surface morphology of the top n<sup>+</sup> epilayer was measured. Neural probes with sixteen traces, electrode sites, and other test structures were patterned on the 3C-SiC epilayers via MEMS microfabrication processes. Metallic traces were absent from the shank of the probe, and instead a semi-metallic n<sup>+</sup> layer was formed into traces and electrode sites. A thin layer of *a*-SiC film was deposited on top of the epilayers to serve as an insulator. The probes were harvested using dissolution of the buried oxide layer in the SOI handle wafer to provide ease of manufacture. The backside silicon layer remaining after release of the probes was removed via back-thinning in a DRIE. Adjacent traces were electrically isolated through a n-p-n junction. After completion of device fabrication, the performance of the n-p-n junctions was evaluated through current-voltage measurements and the turn-on voltage was determined to be ~1.4 V. Electrical measurements showed satisfactory p-n junction performance, but leakage current needs to be improved via higher quality 3C-SiC epitaxial films. In addition, initial electrochemical characterization work with 491 μm<sup>2</sup> surface area test microelectrodes demonstrated good impedance, charge storage capacity, and charge per phase values. These results support the feasibility of neural stimulation and recording with the fabricated all-SiC neural probe. However, further studies are necessary to demonstrate the acute recording and stimulation capability and chronic stability of the fabricated SiC neural probes, and, consequently, in vitro accelerated aging and in vivo studies in a rodent model are planned and will be reported in the future.

*Micromachines* **2019**, *10*, 430

**Author Contributions:** M.B. conducted all device fabrication steps except for *a*-SiC deposition. He also performed dry electrical testing of the p-n and n-p-n structures and co-wrote the manuscript. J.T.B. was responsible for electrochemical characterization, performed all EIS and CV measurements, and co-wrote the manuscript. C.A.K. carried out the *a*-SiC deposition and provided XPS analysis of the films on blank companion samples. C.L.F. and S.E.S. developed the all-SiC INI concept, device design, and provided technical consulting to the fabrication team. E.J.B. initiated the 3C-SiC INI device fabrication at USF prior to graduating with his doctorate in 2018 and provided technical consultation to the fabrication team on this work. F.L.V. is an expert on 3C-SiC epitaxial growth and provided the epitaxial wafers used in this work along with technical consultation on the device characterization performed. A.T. is an expert on electrochemistry and provided technical consultation on the EIS and CV measurements and analysis. All authors reviewed and edited the final draft of the manuscript.

**Funding:** Funding at the University of South Florida was provided via teaching assistantships (M. Beygi and J. Bentley) and from Dr. Saddow's overhead funds to purchase consumable items.

**Acknowledgments:** The *a*-SiC films were grown in the NIMET at the University of Florida under the supervision of Jack Judy and his support is gratefully acknowledged. The assistance of Chenyin Feng with SEM image acquisition and Richard Everly with microfabrication processes in the University of South Florida Nanotechnology Research and Education Center (NREC) is appreciated.

**Conflicts of Interest:** The authors declare no conflict of interest.
