Temperature dependence of sensing characteristics of a pH sensor fabricated on AlGaN/GaN heterostructure

Abstract

The miniaturization of the pH sensor has been improved with the development of the silicon ion-sensitive field-effect transistor (ISFET). Gallium nitride (GaN) is a possible candidate for developing a pH sensor owing to its superior resistance to environmental effects, superior conductivity, wide bandgap and chemical stability compared with silicon. In this study, a pH sensor fabricated on an AlGaN/GaN heterostructure was developed and its sensing characteristics were evaluated at temperature range from room temperature to 80 °C. The sensor shows good pinch-off and transfer characteristics at each temperature point in three standard buffered solutions. The drain current decreased and the threshold voltage showed a positive shift with pH increasing. Drain current decrease and positive threshold voltage shift were also noted with increasing temperature. The pH sensitivities (ΔV/pH) are 52.3, 57.2, 64.2, and 69.5 mV/pH at temperatures of 20, 40, 60, and 80 °C, respectively, which are close to the theoretical values at all the temperature points.

Microfabricated electrochemical pH and free chlorine sensors for water quality monitoring: recent advances and research challenges

“…This is because light can generate charge carriers in Ta 2 O 5 and result in dri of the output signals. Other materials such as zinc oxide (ZnO), 106 hafnium oxide (HfO 2 ), 107 gadolinium oxide (Gd 2 O 3 ), 108 titanium-based binary oxides, 109 aluminum-gallium-nitride/gallium nitride (AlGaN/GaN), 110 and semiconductor nanowires 111,112 were used and they demonstrated with a sub-Nernst or near-Nernst pH responses.…”

Simulation of the pH Sensing Capability of an Open-Gate GaN-Based Transistor

“…is 59 mV per pH unit (17). Most experimental results show a sensitivity that is slightly less (near 57 mV/pH) (2,16,18). Results from our HEMT model reporting interface potential change and adsorbed charge density as functions of pH are shown in Figure 2.…”

Temperature Compensation Circuit for ISFET Sensor

“…Equation (18) illustrates the effectiveness of the proposed circuit for temperature reduction, since the two terms KVT and V T (pH7) (T 0 ) are neglected. In addition, the thermal voltage U T = K T 1 /q will always be present, because it is related to the MOSFET structure and cannot be neglected.…”

“…In addition, we notice that there is concordance between the mathematical demonstration and the simulation results in terms of a temperature coefficient. Here, we can assume that presented the Equations (18) and (19) can predict the temperature coefficient of ISFET/ReFET topology. Hence, the variation of the output voltage cannot exploit it easily, so we added an inverter amplifier to amplify the output voltage V out1 .…”

“…As a result, the ease of combining the temperature compensation circuit, the efficiency of the compensation technique, the circuit sensitivity, as well as the circuit simplicity with respect to body effects became the key design considerations in an integrated circuit design. Respectively, it is particularly challenging for ISFETs to work in an environment where the required task is to measure different pH ranges alongside different temperature values [18,19]. Nevertheless, the conventional means used in the signal processing of ISFETs, in particular the elementary current-voltage conversion circuits, do not reach optimal performance since they are sensitive to light variations and temperature especially when we use a sensor array (spread of the error that is related to temperature).…”