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. 2020 Jun 23;21(1):371-378.
doi: 10.1080/14686996.2020.1775477.

High-performance extended-gate ion-sensitive field-effect transistors with multi-gate structure for transparent, flexible, and wearable biosensors

Jin-Hyeok Jeon  1 , Won-Ju Cho  1
Affiliations

High-performance extended-gate ion-sensitive field-effect transistors with multi-gate structure for transparent, flexible, and wearable biosensors

Jin-Hyeok Jeon et al. Sci Technol Adv Mater. .

Abstract

In this study, we developed a high-performance extended-gate ion-sensitive field-effect transistor (EG-ISFET) sensor on a flexible polyethylene naphthalate (PEN) substrate. The EG-ISFET sensor comprises a tin dioxide (SnO2) extended gate, which acts as a detector, and an amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) for a transducer. In order to self-amplify the sensitivity of the pH sensors, we designed a uniquely-structured a-IGZO TFT transducer with a high-k engineered top gate insulator consisting of a silicon dioxide/tantalum pentoxide (SiO2/Ta2O5) stack, a floating layer under the channel, and a control gate coplanar with the channel. The SiO2/Ta2O5 stacked top gate insulator and in-plane control gate significantly contribute to capacitive coupling, enabling the amplification of sensitivity to be enlarged compared to conventional dual-gate transducers. For a pH sensing method suitable for EG-ISFET sensors, we propose an in-plane control gate (IG) sensing mode, instead of conventional single-gate (SG) or dual-gate (DG) sensing modes. As a result, a pH sensitivity of 2364 mV/pH was achieved at room temperature - this is significantly superior to the Nernstian limit (59.15 mV/pH at room temperature). In addition, we found that non-ideal behavior was improved in hysteresis and drift measurements. Therefore, the proposed transparent EGISFFET sensor with an IG sensing mode is expected to become a promising platform for flexible and wearable biosensing applications.

Keywords: 102 Porous / Nanoporous / Nanostructured materials; 208 Sensors and actuators; 306 Thin film / Coatings; Extended-gate ion-sensitive field-effect transistor; capacitive coupling; flexible; high-k engineered gate oxide; in-plane control gate; polyethylene naphthalate.

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Conflict of interest statement

No potential conflict of interest was reported by the authors.

Figures

None
Graphical abstract
Figure 1.
Figure 1.
(a) Schematic 2D cross-sectional image of a fabricated EG-ISFET sensor, consisting of a high-k engineered top gate oxide (SiO2/Ta2O5), an in-plane control gate, and an EG with a SnO2 sensing membrane, (b) photograph and (c) optical microscope image of a fabricated in-plane control gate a-IGZO TFT transducer on a PEN substrate. (d) Photograph of an EG detector fabricated on a separate PEN substrate.
Figure 2.
Figure 2.
(a) capacitance-voltage (C-V) and (b) current-voltage (I–V) curves of the fabricated MIM capacitors, with either a 20-nm-thick single SiO2 layer or a 10/35-nm-thick SiO2/Ta2O5 stacked layer.
Figure 3.
Figure 3.
Operating modes of the EG-ISFET sensors with high-k engineering oxide and in-plane control gates: (a) SG, (b) DG, and (c) IG sensing modes.
Figure 4.
Figure 4.
Equivalent circuits for the sensing modes of the EG-ISFET sensor: (a) SG, (b) DG, and (c) IG. C1 is the top gate insulator capacitance, C2 is the bottom gate insulator capacitance, C3 is the in-plane gate insulator capacitance, CIGZO is the a-IGZO depletion capacitance, and CSens is the sensing membrane capacitance.
Figure 5.
Figure 5.
Typical transfer curves of EG-ISFET sensors with (a) Device A and (b) Device B transducers, according to pH concentration (IG mode sensing). Sensitivity of (c) Device A and (d) Device B, according to SG, DG, and IG sensing modes.
Figure 6.
Figure 6.
Hysteresis and drift rate of EG-ISFET sensors with (a) Device A and (b) Device B transducers for evaluation of stability and reliability, according to SG, DG, and IG sensing modes.
See this image and copyright information in PMC

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