The Safe Operating Area of AlGaN/GaN-Based Sensor

The concept of SOA (Safe Operating Area) of the AlGaN/GaN based sensor is proposed in this article. The limiting factors which define the SOA for different sensor structures are different. Two widely used sensor structures, pH sensor designed for pH measurement and BioFET sensor designed for biological detection applications are considered for the SOA analysis in this paper. The SOA of the pH sensor is limited by the potential barrier at the AlGaN/solution interface in gate area and the reliability of the passivation. The SOA of the BioFET is limited by the oxidation and reduction potentials of the gate metal. Since the gate metal is exposed to the solution and is tend to be corroded in the electric field, the SOA of the BioFET is much smaller than the pH sensor. Moreover, a failure model of the sensor passivation is also proposed in this article. Finally, the SOA is taken into consideration in the design of sensors in both separate functional sensor and sensor integrated with the readout circuit. The method to identify the global optimal quiescent operating point considering the limit of the SOA which can achieve the highest sensitivity is also proposed in this paper.