Nitrogen ratio and RTA optimization on sputtered TiN/SiO2/Si electrolyte-insulator–semiconductor structure for pH sensing characteristics

• Titanium nitride (TiN) was studied with N2 ratio in sputtering for pH sensing characterization.
• TiN/SiO2 electrolyte-insulator–semiconductor (EIS) structure is used.
• With rapid thermal annealing (RTA), pH sensing performance can be much improved.
• TiNlayer with N2 ratio of 20% and RTA at 800 °C is the acceptable condition.
• This developed pH sensing membrane can be fully processed in current CMOS technology.

Sputtered titanium nitride (TiN) with a novel N2 ratio adjustment and rapid thermal annealing (RTA) treatment are proposed in order to optimize pH sensing performance of electrolyte-insulator-semiconductor (EIS) structure. Selection of this methodology, which can be easily applied into standard CMOS and DRAM technology, results from the fact that TiN is a well-verified material as a buffer or a barrier layer. It was concluded that pH sensitivity of the order of 60.5 mV/pH and linearity of 99.9% could be obtained for a TiN/SiO2 EIS structure treated with N2 ratio of 20% and RTA at 800 °C, which could be a good candidate in sensor applications. This performance is stable for more than two months. Higher surface roughness shown in atomic force microscope (AFM) analysis and high oxygen level in sputtering process shown in x-ray photo photoelectron spectroscopy (XPS) could be the reasons for the high sensitivity of the fabricated TiN sensing layer.