Tae-Eon Bae

High performance of silicon nanowire-based biosensors using a high-k stacked sensing thin film.

High performance silicon nanowire (SiNW) sensors with SiO2/HfO2/Al2O3 (OHA) engineered sensing thin films were fabricated. A lower interface state density, a larger capacitance and a stronger chemical immunity, which are essential for enhancing the performance of devices, were accomplished by stacking thin SiO2, HfO2, and Al2O3 layers, respectively, in sequence on the SiNW channel. Compared with the conventional single SiO2 thin film, the staked OHA thin films demonstrated improved sensing performances; a higher sensitivity, a lower hysteresis voltage, and a smaller drift rate, as well as a higher output current. Therefore, the SiNW sensors with OHA stacked sensing thin films are very promising to biological and chemical sensor applications.

Improved sensing performance of polycrystalline-silicon based dual-gate ion-sensitive field-effect transistors using high-k stacking engineered sensing membrane

Improved sensing performance, larger pH sensitivity that breaches the Nernst response limit with excellent stability, was realized on polycrystalline silicon based dual-gate (DG) ion-sensitive field-effect transistors. The capacitive coupling between the top and bottom gate oxides for a DG operation amplified its sensitivity to as high as 325.8 mV/pH. In particular, the SiO2/HfO2/Al2O3 (OHA) layer, proposed as an engineered sensing membrane, significantly reinforced the sensing margin of devices as well as the chemical stability for long-term use. The sensing characteristics of the OHA and conventional SiO2 layer were evaluated for single gate and DG operation modes, respectively.

Fabrication of high-performance graphene field-effect transistor with solution-processed Al2O3 sensing membrane

High performance graphene field-effect transistors (FETs) with a solution-processed Al2O3 sensing membrane were fabricated. The solution-processed deposition technique offers a lot of advantages in terms of low cost, simplicity, high throughput, and large-area devices. Especially, the solution-deposition process is well-suited for membrane formation of graphene FETs, which is vulnerable to plasma or thermal processes for insulator growth on surface. The graphene FETs with a solution-deposited Al2O3 sensing membrane exhibited a higher pH sensitivity as well as good chemical stability. Therefore, the graphene FETs with solution-deposited Al2O3 sensing membrane are very promising to biological sensors application.

Enhanced Sensing Properties by Dual-Gate Ion-Sensitive Field-Effect Transistor Using the Solution-Processed Al2O3 Sensing Membranes

The sensitivity of conventional ion-sensitive field-effect transistors (ISFETs) is limited to 59 mV/pH, which is the maximum value in electrochemical potential according to the Nernst equation. Here, the silicon-on-insulator (SOI) based dual-gate (DG) ISFETs with SiO2/Al2O3 (OA) using solution based process was evaluated to obtain higher pH sensitivity. The device exhibited a significantly enhanced pH sensitivity of 407.3 mV/pH for the DG operation by capacitive coupling between top and bottom gate oxide. Therefore, the SOI-based ISFETs using solution process and the DG monitoring method are very promising to biological sensors application in terms of high performance and large process area.

Biomimetic Trehalose Biosensor Using Gustatory Receptor (Gr5a) Expressed in Drosophila Cells and Ion-Sensitive Field-Effect Transistor

The development of potential applications of biosensors using the sensory systems of vertebrates and invertebrates has progressed rapidly, especially in clinical diagnosis. The biosensor developed here involves the use of Drosophila cells expressing the gustatory receptor Gr5a and an ion-sensitive field-effect transistor (ISFET) sensor device. Gustatory receptor Gr5a is expressed abundantly in gustatory neurons and acts as a primary marker for tastants, especially sugar, in Drosophila. As a result, it could potentially serve as a good candidate for potential biomarkers of diseases in which the current knowledge of the cause and treatment is limited. The developed ISFET was based on the outstanding electrical characteristics of the metal–oxide–semiconductor field-effect transistor (MOSFET) with a subthreshold swing of 85 mV/dec, low leakage current of <10-12 and high on/off current ratio of 7.3×106. The SiO2 sensing membrane with a pH sensitivity of 34.9 mV/pH and drift rate 1.17 mV/h was sufficient for biosensing applications. In addition, the sensor device also showed significant compatibility with the Drosophila cells expressing Gr5a and their response to sugar, particularly trehalose. Moreover, the interactions between the transfected Drosophila cells and trehalose were consistent and reliable. This suggests that the developed ISFET sensor device could have potential use in the future as a screening device in diagnosis.

Enhanced Sensing Properties of Fully Depleted Silicon-on-Insulator-Based Extended-Gate Field-Effect Transistor with Dual-Gate Operation

Fully depleted (FD) silicon-on-insulator (SOI)-based SnO2 extended-gate field-effect transistors (EGFETs) beyond the Nernstian limit of 59 mV/pH were realized by using the dual-gate (DG) operation. The thickness of buried oxide (BOX) of SOI-MOSFETs was adjusted to magnify the capacitive coupling effect between top and bottom gate oxides in DG operation. As a result, the separate SOI-MOSFETs with 750-nm-thick and 200-nm-thick buried oxide (BOX) showed pH sensitivities of 2037.1 and 554.2 mV/pH, respectively, far beyond the Nernstian limit of 59 mV/pH. Also, better stability characteristics, such as the hysteresis phenomenon and drift effect, are achieved from DG operation.

Influence of impurity concentration in Ge sources on electrical properties of Ge/Si hetero-junction tunneling field-effect transistors

We have experimentally demonstrated that there is the optimum B doping concentration in the Ge source in terms of the electric performance of Ge/Si hetero-junction tunneling field-effect transistors (TFETs). The degradation in subthreshold swing (SS) is observed for TFETs with the source B concentration higher than 1 × 1020 cm−3, which can cause the degeneration in Ge. This source concentration dependence can be explained by the depression of the energy filtering effect due to the degeneracy of the Fermi level (EF). This interpretation is supported by the temperature dependence of SS in the Ge/Si TFETs with different source concentrations. Also, a low SS value of 60.6 mV/dec, an Ion value of 82.3 nA/μm, and a large Ion/Ioff ratio of 6.8 × 106 are obtained for the 1.1% tensile strain channel with the optimized B concentration in the Ge source. It is found that the influence of the source EF on the electrical characteristics of TFETs is more pronounced for the strained-Si channel TFETs with smaller Eg.eff.We have experimentally demonstrated that there is the optimum B doping concentration in the Ge source in terms of the electric performance of Ge/Si hetero-junction tunneling field-effect transistors (TFETs). The degradation in subthreshold swing (SS) is observed for TFETs with the source B concentration higher than 1 × 1020 cm−3, which can cause the degeneration in Ge. This source concentration dependence can be explained by the depression of the energy filtering effect due to the degeneracy of the Fermi level (EF). This interpretation is supported by the temperature dependence of SS in the Ge/Si TFETs with different source concentrations. Also, a low SS value of 60.6 mV/dec, an Ion value of 82.3 nA/μm, and a large Ion/Ioff ratio of 6.8 × 106 are obtained for the 1.1% tensile strain channel with the optimized B concentration in the Ge source. It is found that the influence of the source EF on the electrical characteristics of TFETs is more pronounced for the strained-Si channel TFETs with smaller Eg.eff.

Signal Enhancement of Human IL5 Immunoassay by Enzyme Catalyzed Ag Reduction Beyond Limit of Debye Screening Length on Ion-Sensitive Field Effect Transistors

Department of Electronic Materials Engineering, Kwangwoon University, Seoul 447-1, Wolgye-dong, Nowongu, Seoul Korea 139-701, Phone: +81-2-940-5163, E-mail address: chowj@kw.ac.kr Nanobiotechnology Major, School of Engineering, University of Science and Technology, Republic of Korea Immune Therapy Research Center, Korea Research Institute of Bioscience and Biotechnology, Republic of Korea, Department of Photonics and Applied Physics and Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Republic of Korea

Study of High-k Sensing Membranes for the High Quality Electrolyte Insulator Semiconductor pH Sensor

We fabricated the electrolyte-insulator-semiconductor (EIS) devices with various high-k sensing membranes to realize a high quality pH sensor. The sensing properties of each high-k dielectric material were compared with those of conventional (O) and (ON) membranes. As a result, the high-k sensing membranes demonstrated better sensitivity and stability than the O and ON membranes. Especially, the (OH) stacked layer showed a high sensitivity and the (OA) stacked layer exhibited an excellent chemical stability. In conclusion, the high-k sensing membranes are expected to have excellent operating characteristics in terms of sensitivity and chemical stability for the biosensor application.