Acute kidney injury (AKI) is a frequently occurring severe disease with high mortality. Cystatin C (Cys-C), as a biomarker of early kidney failure, can be used to detect and prevent acute renal injury. In this paper, a biosensor based on a silicon nanowire field-effect transistor (SiNW FET) was studied for the quantitative detection of Cys-C. Based on the spacer image transfer (SIT) processes and channel doping optimization for higher sensitivity, a wafer-scale, highly controllable SiNW FET was designed and fabricated with a 13.5 nm SiNW. In order to improve the specificity, Cys-C antibodies were modified on the oxide layer of the SiNW surface by oxygen plasma treatment and silanization. Furthermore, a polydimethylsiloxane (PDMS) microchannel was involved in improving the effectiveness and stability of detection. The experimental results show that the SiNW FET sensors realize the lower limit of detection (LOD) of 0.25 ag/mL and have a good linear correlation in the range of Cys-C concentration from 1 ag/mL to 1 pg/mL, exhibiting its great potential in the future real-time application.

By reactive DC magnetron sputtering from a pure Ta target onto silicon substrates, Ta(N) films were prepared with different N₂ flow rates of 0, 12, 17, 25, 38, and 58 sccm. The effects of N₂ flow rate on the electrical properties, crystal structure, elemental composition, and optical properties of Ta(N) were studied. These properties were characterized by the four-probe method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). Results show that the deposition rate decreases with an increase of N₂ flows. Furthermore, as resistivity increases, the crystal size decreases, the crystal structure transitions from β-Ta to TaN(111), and finally becomes the N-rich phase Ta₃N₅(130, 040). Studying the optical properties, it is found that there are differences in the refractive index (n) and extinction coefficient (k) of Ta(N) with different thicknesses and different N₂ flow rates, depending on the crystal size and crystal phase structure.

In this paper, the poly-Si nanowire (NW) field-effect transistor (FET) sensor arrays were fabricated by adopting low-temperature annealing (600 °C/30 s) and feasible spacer image transfer (SIT) processes for future monolithic three-dimensional integrated circuits (3D-ICs) applications. Compared with other fabrication methods of poly-Si NW sensors, the SIT process exhibits the characteristics of highly uniform poly-Si NW arrays with well-controlled morphology (about 25 nm in width and 35 nm in length). Conventional metal silicide and implantation techniques were introduced to reduce the parasitic resistance of source and drain (SD) and improve the conductivity. Therefore, the obtained sensors exhibit >10⁶ switching ratios and 965 mV/dec subthreshold swing (SS), which exhibits similar results compared with that of SOI Si NW sensors. However, the poly-Si NW FET sensors show the V_th shift as high as about 178 ± 1 mV/pH, which is five times larger than that of the SOI Si NW sensors. The fabricated poly-Si NW sensors with 600 °C/30 s processing temperature and good device performance provide feasibility for future monolithic three-dimensional integrated circuit (3D-IC) applications.

The interface passivation of the HfO₂/Si_0.7Ge_0.3 stack is systematically investigated based on low-temperature ozone oxidation and Si-cap methods. Compared with the Al₂O₃/Si_0.7Ge_0.3 stack, the dispersive feature and interface state density (D_it) of the HfO₂/Si_0.7Ge_0.3 stack MOS (Metal-Oxide-Semiconductor) capacitor under ozone direct oxidation (pre-O sample) increases obviously. This is because the tiny amounts of GeO_x in the formed interlayer (IL) oxide layer are more likely to diffuse into HfO₂ and cause the HfO₂/Si_0.7Ge_0.3 interface to deteriorate. Moreover, a post-HfO₂-deposition (post-O) ozone indirect oxidation is proposed for the HfO₂/Si_0.7Ge_0.3 stack; it is found that compared with pre-O sample, the D_it of the post-O sample decreases by about 50% due to less GeO_x available in the IL layer. This is because the amount of oxygen atoms reaching the interface of HfO₂/Si_0.7Ge_0.3 decreases and the thickness of IL in the post-O sample also decreases. To further reduce the D_it of the HfO₂/Si_0.7Ge_0.3 interface, a Si-cap passivation with the optimal thickness of 1 nm is developed and an excellent HfO₂/Si_0.7Ge_0.3 interface with D_it of 1.53 × 10¹¹ eV⁻¹cm⁻² @ E−E_v = 0.36 eV is attained. After detailed analysis of the chemical structure of the HfO₂/IL/Si-cap/Si_0.7Ge_0.3 using X-ray photoelectron spectroscopy (XPS), it is confirmed that the excellent HfO₂/Si_0.7Ge_0.3 interface is realized by preventing the formation of Hf-silicate/Hf-germanate and Si oxide originating from the reaction between HfO₂ and Si_0.7Ge_0.3 substrate.

Surface-enhanced Raman spectroscopy (SERS) substrates with high sensitivity and reproducibility are highly desirable for high precision and even molecular-level detection applications. Here, large-scale uniformly hybrid nanoparticle-enhanced Raman spectroscopy (NERS) substrates with high reproducibility and controllability were developed. Using oxygen plasma treatment, large-area and uniformly rough polystyrene sphere (URPS) arrays in conjunction with 20 nm Au films (AuURPS) were fabricated for SERS substrates. Au nanoparticles and clusters covered the surface of the URPS arrays, and this increased the Raman signal. In the detection of malachite green (MG), the fabricated NERS substrates have high reproducibility and sensitivity. The enhancement factor (EF) of Au nanoparticles and clusters was simulated by finite-difference time-domain (FDTD) simulations and the EF was more than 10⁴. The measured EF of our developed substrate was more than 10⁸ with a relative standard deviation as low as 6.64%–13.84% over 15 points on the substrate. The minimum limit for the MG molecules reached 50 ng/mL. Moreover, the Raman signal had a good linear relationship with the logarithmic concentration of MG, as it ranged from 50 ng/mL to 5 μg/mL. The NERS substrates proposed in this work may serve as a promising detection scheme in chemical and biological fields.

Silicon nanowire field effect (SiNW-FET) biosensors have been successfully used in the detection of nucleic acids, proteins and other molecules owing to their advantages of ultra-high sensitivity, high specificity, and label-free and immediate response. However, the presence of the Debye shielding effect in semiconductor devices severely reduces their detection sensitivity. In this paper, a three-dimensional stacked silicon nanosheet FET (3D-SiNS-FET) biosensor was studied for the high-sensitivity detection of nucleic acids. Based on the mainstream Gate-All-Around (GAA) fenestration process, a three-dimensional stacked structure with an 8 nm cavity spacing was designed and prepared, allowing modification of probe molecules within the stacked cavities. Furthermore, the advantage of the three-dimensional space can realize the upper and lower complementary detection, which can overcome the Debye shielding effect and realize high-sensitivity Point of Care Testing (POCT) at high ionic strength. The experimental results show that the minimum detection limit for 12-base DNA (4 nM) at 1 × PBS is less than 10 zM, and at a high concentration of 1 µM DNA, the sensitivity of the 3D-SiNS-FET is approximately 10 times higher than that of the planar devices. This indicates that our device provides distinct advantages for detection, showing promise for future biosensor applications in clinical settings.