The pH-sensing properties of tantalum pentoxide films fabricated by metal organic low pressure chemical vapor deposition

The pH-sensing properties of tantalum pentoside deposited by metal organic CVD and the influence of annealing in dry oxygen between 500 and 900 degrees C on pH sensitivity, hysteresis, and light response has been studied. The samples were characterized by capacitance-voltage measurements of EIS structures. The results obtained showed an optimal annealing temperature of 600 degrees C for which the pH sensitivity reaches is mV pH(-1) with a hysteresis of less than 1 mV. Using this annealing temperature, the voltage shift of the sensor signal caused by light-induced drift of the tantalum pentoxide is significantly reduced compared to the as deposited sample. Light-induced drift of the sensor signal can be minimized by using polycrystalline layers obtained al an annealing temperature of 900 degrees C. The pH sensitivity of these polycrystalline layers however is reduced to 54 mV pH(-1) and hysteresis is increased compared to tantalum pentoxide annealed at 600 degrees C. (C) 1997 Elsevier Science S.A.