REDUCED LIGHT SENSIBILITY IN OPTIMIZED TA2O5-ISFET STRUCTURES

To reduce light-induced long-term drifts of aTa2O5-based ISFETs (TOSFETs), corresponding gate structures have been investigated using surface and interface analysis techniques (SIMS, XPS, EELS) and luminescence measurements. At an oxidation temperature T(ox) = 1073 K for Ta, SIMS indicates a diffusion of Si into the bulk Ta2O5. By EELS the band gap of Ta2O5 was determined to be E(gap) = 4.4 +/- 0.2 eV. During a gate Al anneal (aluminium on Ta2O5) in an N2 atmosphere, an Al/Ta mixed oxide is formed at the surface. This treatment affects optically active states located in the band gap, thereby causing a reduced light sensibility of the TOSFETs.