MICROSTRUCTURED SOLID-STATE ION-SENSITIVE MEMBRANES BY THERMAL-OXIDATION OF TA

The origin of light sensitivity in Al2O3- and Ta2O5-based ion-sensitive field-effect transistors (ISFETs) due to carrier generation in the Si substrate was studied using corresponding layer structures and field effect transistors (FETs). From optical reflection measurements, we conclude wavelength-dependent extended transmission minima and maxima for optical radiation in the Ta2O5/gate-SiO2/Si structures. To reduce the light sensitivity, an electrically insulated, buried Pt layer covering the drain-source and gate area of a FET was developed. A strong decrease in the light sensitivity was thereby obtained. The influence of phosphate-, Tris-, and Hepes-buffered electrolytes on the sensitivity of Ta2O5- and Al2O3-ISFETs was studied in the pH range between 2 and 11. We found no significant influence of the buffers, but deviations from the Nernst linearity. © 1990.