Investigation of AlInN barrier ISFET structures with GaN capping for pH detection

Abstract

The pH response of GaN/AlInN/AlN/GaN ion-sensitive field effect transistor (ISFET) on Si substrates has been characterized. We analyzed the variation of the surface potential (AV sp /ApH) and current (A/ ds /ApH) with solution pH in devices with the same indium content (17%, in-plane lattice-matched to GaN) and different AlInN thickness (6 nm and 10 nm), and compared with the literature. The shrinkage of the barrier, that has the effect to increase the transconductance of the device, makes the 2-dimensional electron density (2DEG) at the interface very sensitive to changes in the surface.Although the surface potential sensitivity to pH is similar in the two devices, the current change with pH (A/ds/ApH), when biasing the ISFET by a Ag/AgCl reference electrode, is almost 50% higher in the device with 6nm AlInN barrier, compared to the device with lOnm barrier. When measuring the current response (A/ ds /ApH) without reference electrode, the device with thinner AlInN layer has a larger response than the thicker one, of a factor of 140%, and that current response without reference electrode is only 22% lower than its maximum response obtained using reference electrode.

On a GaN-based ion sensitive field-effect transistor (ISFET) with a hydrogen peroxide surface treatment

“…It could be observed that the influences of interfering N + and K + ions on the studied ISFET are negligible. Comparisons of pH sensing performance among Device A and previously reported works are listed in Table 2 [20][21][22][23][24][25][26]. Although the highest average sensitivity (54.88 mV/pH) of treated ISFET is not outstanding as compared to previous works, the pH sensing performance is remarkably enhanced (∼26% improvement) by a simple H 2 O 2 surface treatment.…”

Enhanced Performances of AlGaN/GaN Ion-Sensitive Field-Effect Transistors Using H₂O₂-Grown Al₂O₃ for Sensing Membrane and Surface Passivation Applications

“…The enhanced hydrogen and hydroxyl ions adsorption capability improves the variation of the surface potential. The relationship between ( I DS / pH) and ( ψ s / pH) is realized as [12]:…”

“…Sensing membrane plays an important role for the ISFET since the site-binding model reveals that the sensitivity of the ISFET is determined by the amount of hydroxyl adsorption on the sensing membrane which causes the surface potential variation in different pH buffer solution. Some research have used the AlGaN [11] and GaN cap layer [12] as the sensing membrane. Although the aforementioned fabrication processes of the ISFET are much easier, surface defects affect performances of AlGaN/GaN ISFET dramatically.…”

Method to Predict and Optimize Charge Sensitivity of Ungated AlGaN/GaN HEMT-Based Ion Sensor Without Use of Reference Electrode

“…The realisation of reference electrode free measurements permits the fabrication of small, robust and on-chip AlGaN/GaN FET-based sensors, providing a clear advantage over existing glass electrode based pH and ion sensors. Although referenceelectrode free pH sensing has been demonstrated [12], [13], the scope of the reported investigations has been limited in terms of reference electrode free sensor optimization. Ion sensitivity in reference electrode free sensors has been shown to depend on AlGaN/GaN composition [14], which is not surprising given that the heterostructure design determines sheet carrier density.…”

“…Referenceelectrode free devices require a different approach, and device sensitivity in terms of induced surface potential needs to be extracted from I DS or V DS often employing simplifying approximations [16], [17]. In terms of heterostructure design, Brazzini et al recently demonstrated AlInN/ GaN-based sensors with high sensitivity even when employed in reference electrode free measurement configuration [13].…”