Stack layer SiO₂/Gd₂O₃/SiO ₂/GaAs pH-sensitive electrolyte insulator semiconductor capacitors and their anneal temperature dependency

The pH sensing capacitors with stacked SiO₂ / Gd₂ O₃ / SiO₂ oxide layers prepared on compound semiconductor GaAs substrate were fabricated and until recently had been reported on seldom. In this work, the proposed GaAs-based stack layer capacitors with a so-called electrolyte insulator semiconductor (EIS) structure are demonstrated and are easily further integrated with other GaAs-based radio-frequency or light emitting devices to construct an integrated multifunction sensor in the future. Among this work, three different EIS capacitors are fabricated for verification, which are Gd₂ O₃ /GaAs, Gd₂ O₃ / SiO₂ /GaAs, and SiO₂/Gd₂ O₃ / SiO₂ /GaAs structures. Their correspondent linear sensing range and sensitivity are pH 6-10 and 29.9 mV/pH, pH 4-8 and 52.9 mV/pH, and pH 2-8 and 57.9 mV/pH, respectively. Different post oxide annealing (POA) treatments are also carried out. The correspondent trilayer EIS devices' sensing ranges are then modified effectively from a grown pH 2-8 to POA-treated pH 8-12 with a sensitivity of 57.4 mV/pH.