Solution-Gated Ultrathin Channel Indium Tin Oxide-Based Field-Effect Transistor Fabricated by a One-Step Procedure that Enables High-Performance Ion Sensing and Biosensing

Abstract

In this paper, we propose a one-step procedure for fabricating a solution-gated ultrathin channel indium tin oxide (ITO)-based field-effect transistor (FET) biosensor, thus providing an ″all-by-ITO″ technology. A thin-film sheet was placed on both ends of a metal shadow mask, which were contacted with a glass substrate. That is, the bottom of the metal shadow mask corresponding to the channel was slightly raised from the substrate, resulting in the creeping of some particles into the gap during sputtering. Owing to this modified metal shadow mask, a thin ITO channel (<30−40 nm) and thick ITO source/drain electrodes (ca. 100 nm) were simultaneously fabricated during the one-step sputtering. The thickness of ITO films was critical for them to be semiconductive, depending on the maximum depletion width (∼30− 40 nm for the ITO channel), similarly to 2D materials. The ultrathin ITO channel worked as an ion-sensitive membrane as well owing to the intrinsic oxidated surface directly contacting with an electrolyte solution. The solution-gated 20-nm-thick channel ITO-based FET, with a steep subthreshold slope (SS) of 55 mV/dec (pH 7.41) attributable to the electric double-layer capacitance at the electrolyte solution/channel interface and the absence of interfacial traps among electrodes formed in one step, demonstrated an ideal pH responsivity (∼56 mV/pH), resulting in the realtime monitoring of cellular respiration and the long-term stability of electrical properties for 1 month. Moreover, the chemical modification of the ITO channel surface is expected to contribute to biomolecular recognition with ultrahigh sensitivity owing to the remarkably steep SS, which provided the exponential pH sensitivity in the subthreshold regime. Our new device produced in this one-step manner has a great future potential in bioelectronics. KEYWORDS: solution-gated field-effect transistor (FET), one-step procedure, ultrathin channel, indium tin oxide (ITO), 2D material

Recent Advances in Metal-Oxide Thin-Film Transistors: Flexible/Stretchable Devices, Integrated Circuits, Biosensors, and Neuromorphic Applications

“…Furthermore, a new type of electronic device using metal oxides has been developed recently [18,19]. Biosensors [20] and neuromorphic devices [21] based on metal oxides as the active layer have also been developed.…”

Technical Perspectives on Applications of Biologically Coupled Gate Field-Effect Transistors

“…On the other hand, ultrasensitive recognition of biomolecules is expected in the subthreshold regime of Bio-FETs (Figure 3). For instance, the solution-gated FET with a 20 nm thick indium tin oxide (ITO) channel exhibited a markedly steep SS, which was very close to the thermal limit (60 mV/dec at 300 K) and may result in a steep SS of less than 60 mV/dec in two-dimensional (2D)-FETs [14]. As a result, the electrical signals measured in the subthreshold regime were about 10 times larger than those measured in the linear regime, which could contribute to the ultrasensitive detection of biomolecules.…”

“…As a type of potentiometric biosensor, biologically coupled gate field-effect transistors (Bio-FETs), which are originally based on solution-gated FETs, are attracting attention worldwide [1][2][3][4][5][6]. This is probably because various types of biomolecules with charges can be directly detected as electrical signals with the Bio-FETs in a label-free and real-time manner, and various semiconductive materials can also be applied to biosensing [7][8][9][10][11][12][13][14]. Furthermore, the integrated Bio-FET chip based on a complementary metal oxide semiconductor (CMOS) technology enables the simultaneous detection of multiple samples [15].…”

“…In other words, their features can be effectively utilized for biosensing. For instance, the subthreshold slope (SS) near the thermal limit contributes to a large shift in drain current (I D ) at a constant gate voltage (V G ) in the SS region, indicating a high sensitivity with a low limit of detection (LOD) [14,42,43]. Alternatively, the capacitive components of functional polymer membranes on the gate electrode are electrically changed by the interaction with noncharged biomolecules [41,44,45].…”

Self-oscillating chemoelectrical interface of solution-gated ion-sensitive field-effect transistor based on Belousov–Zhabotinsky reaction

“…This is why the change in the surface charge is detected from the change in pH without being mostly affected by other cations in accordance with the principle of the field effect 23 , 24 . Such ISFET sensors mostly have a silicon substrate, but a variety of semiconducting materials have recently been applied to pH-sensitive ISFET sensors 25 , 26 . Moreover, a large-scale and high-density ISFET (arrayed-gate ISFET) sensor has recently been developed with the progress of complementary MOS (CMOS) integrated circuit technologies 27 – 34 .…”