Advanced CMOS process for floating gate field-effect transistors in bioelectronic applications

We present a complementary metal oxide semiconductor (CMOS) process with floating gate field-effect transistors (FG FETs) as sensor inputs for bioelectronic applications. In order to achieve a stable passivation of the devices against electrolyte solutions, we included additional fabrication steps and materials into our advanced process. Main changes to the standard CMOS process were the application of titanium silicide for all interconnects, a passivation layer formed by LPCVD deposition of silicon nitride and oxide, and an oxidation step for the sensing areas exposed to the electrolyte at the end of the fabrication process. Different arrays of FG FETs were fabricated. We present extracellular recordings from rat cardiac myocytes and from genetically modified human embryonic kidney (HEK) cells. The extracellular recordings showed a good signal-to-noise ratio. Due to the design, the chips were robust and showed an excellent long-term stability. They were able to withstand several cleaning procedures and subsequent cell cultures. The CMOS process allowed the implementation of simple integrated circuits. With two 5-bit decoders it was possible to address an array of 32 × 32 FG FETs. Our study paves the way for future fabrication of higher integrated chips with a stable and robust operation when used in bioelectronic applications.