IGZO Thin-Film Light-Addressable Potentiometric Sensor

An In-Ga-Zn oxide (IGZO) layer is applied, for the first time, as the semiconductor layer of a light-addressable potentiometric sensor (LAPS). The IGZO layer sputtered on the commercial ITO/glass substrate could be used as the active layer of an LAPS illuminated by a ultraviolet light-emitting diode (UV LED). In the operation of LAPS, an IGZO/ITO glass substrate with a higher photocurrent and less interference of the ambient light compared with a conventional n-type silicon wafer is obtained. A sensing membrane of sputtered niobium oxide directly on the IGZO layer, with a substrate temperature of 250 degrees C, is verified to have a pH sensitivity of 61.8 mV/pH according to photocurrent versus gate bias curves measured in various pH buffer solutions. The ac signal applied to the UV LED can be increased to 30 kHz for IGZO LAPS pH sensing. This improvement is beneficial for the sensor's use in high-speed 2-D chemical image applications.