Yu-Ren Li

Effect of oxygen plasma treatment on horizontally aligned carbon nanotube thin film as pH-sensing membrane of extended-gate field-effect transistor

The high-performance pH-sensing membrane of extended-gate field-effect transistors (EGFET) composed of high-conductivity horizontally aligned carbon nanotube thin films (HACNTFs) after oxygen plasma treatment is successfully demonstrated. The 10-µm-wide catalytic metal lines with 60 µm interspace produced CNT vertical plates, and the plates were mechanically pulled down and densified to form HACNTFs. A large amount of oxygen-containing functional groups are decorated on the CNTs after the oxygen plasma treatment. These functional groups act as the sensing sites and respond to the H+ or OH− ions in solutions with different pH values. Therefore, these functionalized HACNTFs as pH-EGFET-sensing membranes can achieve a high voltage sensitivity of 40 mV/pH and high current sensitivity of 0.78 µA1/2/pH. Moreover, large linearity of 0.998 is measured in a wide sensing range from pH 1 to 13. These results reveal that the oxygen plasma treatment is an effective way to improve the CNT-sensing characteristics in pH-EGFET sensors.

Sensitivity Enhancement of Ultraviolet Photodetectors With the Structure of p-NiO/Insulator-SiO 2 /n-ZnO Nanowires

A high-performance photodetector with the structure of NiO/SiO₂/ZnO nanowires has been proposed. The devices with 6-nm-thick SiO₂ exhibited a better rectification ratio (Jforward/Jreverse) of 246 at ±2 V, lower dark current density (Jdark) of 3.5 × 10^-7 A/cm² at a reverse bias of 2 V, and superior ultraviolet (UV) sensitivity (IUV/Idark) of 16.23 than those without the SiO₂ layer (J_forward/J_reverse = 44, Jdark = 4.7 × 10^-6 A/cm², and IUV/Idark = 5.5). The improved performance was mainly due to the ultrathin inserted SiO₂ layer that builds a barrier height to minimize the transmission probability of low-energy carriers, leading to the enhancement of the UV sensing characteristics.

Location-Controlled Single-Crystal-Like Silicon Thin-Film Transistors by Excimer Laser Crystallization on Recessed-Channel Silicon Strip With Under-Layered Nitride

High-performance Si thin-film transistors (TFTs) on the recessed-channel Si strips with the under-layered nitride film have been fabricated using excimer laser crystallization (ELC). A nitride film was added as a light absorption layer to suppress solidification along the edge of the Si strip. Thus, only one primary grain boundary perpendicular to the Si strip formed in the middle of the recessed region during ELC. The single-crystal-like Si TFTs fabricated on one-half of the recessed region are capable of excellent field-effect mobility of 640 cm2/V-s, with only minor deviation.

Densification effects of the carbon nanotube pillar array on field-emission properties

In this study, a simple densification method for carbon nanotube (CNT) pillars is proposed to achieve high-performance field emission characteristics and stable emission. Through capillary force during solution evaporation, the CNT density in each pillar can be increased by about six times without causing damage to the crystallinity of CNTs. The densified CNT pillars exhibit lower series resistance, sharper pillars, better contacts, higher thermal conductivity, and better mechanical stiffness than as-grown ones. Therefore, the threshold field of the field emitter with such CNT pillars of 50 µm height can be reduced to 1.98 V/µm, as compared with 2.2 V/µm for the undensified ones. Moreover, the fluctuation of field-emission current decreases from 15.5 to 9.4% after the stress tests at a field of 2 V/µm for 1800 s. These findings imply that the densified CNT pillars are promising for the field-emission applications.

High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads

A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5 mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1–13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9 mV/pH compared with 45.0 mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance.

Annealing effect on the photoluminescence characteristics of ZnO-nanowires and the improved optoelectronic characteristics of p-NiO/n-ZnO nanowire UV detectors

Transparent ultraviolet (UV) detectors with nanoheterojunctions (NHJs) of p-type NiO and n-type ZnO nanowires (ZnO-NWs) were successfully fabricated using a DC sputtering system and a hydrothermal process, respectively. After annealing in nitrogen ambient, the near-band-edge emission to deep level emission ratio (NBE/DLE) of ZnO-NWs gradually increased as the temperature increased and reached a maximum of 28.9 at a temperature setting of 500 °C. In contrast, after annealing in oxygen atmosphere, the NBE/DLE of ZnO-NWs initially increased from 1.2 to 5.9 and then decreased to 3.2. At a reverse bias of 2 V, the devices with the 500-°C-N2-annealed ZnO-NWs exhibited better sensitivity (JUV/JDark = 5.65; JVisible/JDark = 1.35) to UV light (365 nm, 0.3 mW/cm2) than those with the as-grown ZnO-NWs (JUV/JDark = 4.98; JVisible/JDark = 3.82) because the structural defects in ZnO-NWs were effectively eliminated after annealing in nitrogen ambient at 500 °C.

Highly Sensitive pH Sensors of Extended-Gate Field-Effect Transistor With the Oxygen-Functionalized Reduced Graphene Oxide Films on Reverse Pyramid Substrates

The oxygen-plasma-treated reduced graphene oxide films (OPT-RGOFs) as the pH sensing membranes for the extended-gate field-effect transistors were demonstrated to achieve the higher pH sensitivity of 52 mV/pH and better linearity of 0.996 in a wide sensing range of pH 1-13 than those without plasma treatment. It was attributed to the oxygen-containing functional groups on the RGOF induced from the plasma treatment. In addition, the OPT-RGOFs sprayed on the reverse pyramid substrates were also proposed to further enhance the sensing sites, leading to a superior pH sensitivity of 57 mV/pH with an excellent linearity of 0.996.

Highly Sensitive pH-EGFET Sensors with Oxygen-Plasma-Treated Reduced Graphene Oxide Films Sprayed on the Reverse Pyramid Substrate

The oxygen-plasma-treated reduced graphene oxide films (RGOFs) are firstly used as the sensing membranes in extended-gate field-effect transistors (EGFETs) for the pH sensors. A large amount of oxygen-containing functional groups are effectively decorated on the RGOFs, resulting in increasing the sensing sites. Furthermore, the reverse pyramid (RP) structure is used as the substrate to increase surface roughness with fixed sensing window. The pH-EGFET current sensitivity of the plasma-treated RGOF on the RP structure can achieve as high as 1.09 uA/pH with excellent linearity of 0.999, and a wide sensing range from pH 1 to 13.

Electrical Characteristic of AlGaN/GaN HEMTS with AlN Spacer Layer

Two-dimensional electron gas (2DEG) formed at AlGaN/GaN interface is a critical part to tune the characteristic of AlGaN/GaN HEMT devices. In this work, AlN spacer layer is used between AlGaN and GaN layer to improve 2DEG density, mobility, and drain current. Modeling and simulation of AlGaN/AlN/GaN is successfully performed to explore transport properties. The carrier’s mobility attains a maximum at the 0.5-nm-thick AlN spacer thickness. Current and transconductance increases with the thickness of AlN spacer and reaches a maximum at a critical thickness. Beyond the critical thickness, the current and transconductance decrease due to degradation of ohmic contact. The critical thicknesses for the drain current and transconductance are 1.5 nm and 1.2 nm respectively.

Random Interface-Traps-Induced Characteristic Fluctuation in 16-nm High-k/Metal Gate CMOS Device and Digital Circuit

Abstract In this work, we for the first time study the DC and dynamic characteristic variability in 16-nm-gate high-κ/metal gate (HKMG) complementary metal-oxide-semiconductor (CMOS) devices and circuit induced by random interface traps (ITs) at Si/high-κ interface. Totally random devices with 2D ITs at Si/HfO2 interface are incorporated into 3D device simulation. Random ITs’ number, position and density on fluctuations of threshold voltage (Vth), on-/off-state current, gate capacitance, cutoff frequency, intrinsic gate delay, and noise margin (NM) of timings are explored. The results of this study indicate the random ITs induced fluctuation of NM is 20 mV which is smaller than 30 mV resulting from the random dopants. Note that the random position of ITs induces rather different fluctuations in DC/AC and timing in spite of the same number of ITs.