pH electrode based on ALD deposited iridium oxide

AbstractWe have made planar pH electrodes that use iridium oxide (IrOx) fabricated by atomic layer deposition (ALD) as the pH sensitive layer. As far as we know, ALD has not been reported earlier as the method of producing IrOx layer on pH electrodes. The structure built on glass substrate consists of 300 nm thick titanium electrodes coated with 110 nm IrOx layer. When measured against a commercial Ag/AgCl reference electrode, we were able to observe a linear and super-Nernstian pH response over the tested range from pH 4 to pH 10. The average sensitivity of three electrodes was −67 mV/pH at 22 °C. After 30 s stabilization time the total drift during the next 90 s remained mainly below 1 mV. The 90% response time was determined to be less than 3 s