Miniaturized pH‐Sensitive Field‐Effect Capacitors with Ultrathin Ta<sub>2</sub>O<sub>5</sub>Films Prepared by Atomic Layer Deposition
Denise Molinnus, Heiko Iken, Anna Lynn Johnen, Benjamin Richstein, Lena Hellmich, Arshak Poghossian, Joachim Knoch, Michael J. Schöning
Abstract
Miniaturized electrolyte–insulator–semiconductor capacitors (EISCAPs) with ultrathin gate insulators have been studied in terms of their pH‐sensitive sensor characteristics: three different EISCAP systems consisting of Al–p‐Si–Ta 2 O 5 (5 nm), Al–p‐Si–Si 3 N 4 (1 or 2 nm)–Ta 2 O 5 (5 nm), and Al–p‐Si–SiO 2 (3.6 nm)–Ta 2 O 5 (5 nm) layer structures are characterized in buffer solution with different pH values by means of capacitance–voltage and constant capacitance method. The SiO 2 and Si 3 N 4 gate insulators are deposited by rapid thermal oxidation and rapid thermal nitridation, respectively, whereas the Ta 2 O 5 film is prepared by atomic layer deposition. All EISCAP systems have a clear pH response, favoring the stacked gate insulators SiO 2 –Ta 2 O 5 when considering the overall sensor characteristics, while the Si 3 N 4 (1 nm)–Ta 2 O 5 stack delivers the largest accumulation capacitance (due to the lower equivalent oxide thickness) and a higher steepness in the slope of the capacitance–voltage curve among the studied stacked gate insulator systems.