High Sensing Performance of Nanoimprinted HfO₂Sensing Membrane for Electrode-Insulator-Semiconductor pH Sensors

In this paper, HfO2 thin films as a sensing membrane deposited on nanoimprinted Si substrates by both atomic layer deposition (ALD) and sputtering methods were investigated for an electrolyte-insulator-semiconductor (EIS) pH sensor application. X-ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy were performed to examine the crystalline structures, chemical compositions and surface morphologies of the HfO2 sensing films, respectively. The structural properties of these HfO2 films were correlated to their sensing performances. Compared with the sputtering method, the unpatterned HfO2 sensing film by the ALD method showed a higher pH sensitivity of 55.06 mV pH-1, a lower drift rate of 0.31 mV h-1 and a smaller hysteresis voltage of 0.90 mV. The high pH sensitivity and good stability may be attributed to the increase in surface roughness and the reduction of a silicate layer caused by the ALD method. Additionally, the ALD-HfO2 EIS sensor deposited on the nanoimprinted Si substrate demonstrated a Nernstian pH response (61.36 mV pH-1) than that on an unpatterned Si substrate. For compatibility with advanced complementary metal-oxide-semiconductor technology, the ALD-HfO2 sensing film deposited on the nanoimprinted Si substrate is a promising candidate for pH sensing applications.