Hui Ling Tai

The Investigation of a New NO2 OTFT Sensor Based on Heterojunction F16CuPc/CuPc Thin Films

The bottom contact heterojunction organic thin film transistors (OTFTs) based on n-type hexadecafluorophthalocyaninatocopper (F16CuPc) and p-type copper phthalocyanine (CuPc) bilayer were developed by the vacuum evaporation, which were applied to detect nitrogen dioxide (NO2). The sensors with different thickness (5nm, 10nm, 15nm and 20nm) of CuPc were prepared to investigate the influence of CuPc film thickness on the properties of devices. The results showed that four parameters including the source-drain current (IDS), grid current (IGS), threshold voltage (VT) and carrier mobility (μ) changed in a few seconds when the sensors were exposed to the atmosphere of NO2. Further more, IDS and IGS presented extremely similar variation trend. So the grid current would be taken as a new parameter to reveal the response characteristic of OTFT gas sensor. By comparison, the device with 15nm CuPc thin film exhibited the optimum electronic and gas sensing properties.

A PVP-Based Quartz Crystal Microbalance Sensor for H2S Detection

Hydrogen sulfide is a typical toxic, inflammable gas. The detection of H2S is crucial in the areas of oil, natural gas and so on. However, studies on H2S gas sensors at room temperature were seldom reported. In this study, Quartz crystal microbalance (QCM) sensors have been utilized, and PVP film were prepared on the QCM by airbrush method with different airbrush volume for H2S detection. The results showed that the PVP film with airbrush volume 0.2ml exhibited a better sensing response to H2S gas. Besides, sensitive characteristics parameters, i.e. selectivity, stability, linearity and sensitivity of prepared sensors were studied for comparison. The relative sensing mechanism associated with SEM pictures was studied as well.

Fabrication and Formaldehyde-Sensing Property of Quartz Crystal Microbalance (QCM) Coated with PVP-MWCNTs Composites

In this paper, the quartz crystal microbalance (QCM) sensors coated with polyvinyl pyrrolidone (PVP)-multiwalled carbon nanotubes (MCWNTs) nanocomposite thin films were developed by the spray process, which were used for the detection of low concentration formaldehyde at room temperature. The surface morphology and structure of films was analyzed by scanning electron microscope (SEM), UV-Vis absorption spectrometry, respectively, and the formaldehyde-sensing properties of sensors were investigated. The results showed that the prepared QCM gas sensor exhibited the linear characteristic, fast response, good reproducibility to low concentration formaldehyde within 6 ppm, and the poisoning of films was observed when the formaldehyde concentration exceeded 6ppm. Moreover, the sensitivity of the sensor could achieve up to 1Hz/ppm and had the good stability of response values.

The Investigation of a Novel Large-Strain Sensor Based on a Dual Capacitive Structure

In this paper, a novel large-strain sensor based on a dual planar capacitive structure has been developed. It has the capacity of large-strain measurement up to 200,000 με (0.2 ε). The change in strain causes a measurable transformation in the capacitance of the sensor by relative shift of the overlap area between two capacitive plates, one fixed (i.e. fixed plate) and the other one movable (i.e. movable plate), and is thus converted into a voltage signal by a read-out circuit module. The dual capacitor structure was designed for increasing the initial capacitance and improving the resolution of sensors compared with a single capacitor structure. The experimental results showed that the sensor had a linearity of 2.29% full scale (FS), a hysteresis error of 1.146%FS, repeatability of 0.226%FS and a resolution of 0.5%FS, suggesting excellent performance of the sensor.

Formaldehyde Detection Based on P3HT/InSnO Composite Thin Film Transistor

Formaldehyde, a colorless and pungent-smelling gas, had been confirmed be a huge threat to people health. The detection of formaldehyde was necessary and important at room temperature. Sprayed P3HT/InSnO composite film based on organic thin film transistors (OTFT) was fabricated to detect formaldehyde at room temperature in this paper. The results showed that P3HT/ InSnO-OTFT showed better response and recovery to HCHO compared with P3HT-OTFT at room temperature.

Preparation of Ethanol-Sensing Gas Sensor Based on PECH/Multi-Wall Carbon Nanotubes Sensitive Films

Abstract: In this paper, Polyepichlorohyron(PECH)/multi-wall carbon nanotubes(MWCNTs) composite films and PECH/multi-wall carbon nanotubes twolayer film were deposited on interdigitated electrodes by airbrush technology to detect ethanol vapor of various concentrations at room temperature. Thickness and structure of the film were taken into account, so films of different thicknesses and with different structures were prepared respectively. The responses of the sensors to ethanol showed that composite film had a higher response thantwolayer film, and the thick composite film performed better than its counterpart when they were exposed to ethanol vapor.

Study on Reactive Ion Etching of Vanadium Oxide Thin Film by Taguchi Method

A high selectivity patterning technology of vanadium oxide (VOx) thin film was suggested in this paper. VOx thin film was etched through a photoresist (PR) mask using Cl/N based gases in a reactive ion etching (RIE) system. Taguchi method was used for process design to identify factors that influence the patterning and find optimum process parameters. Experimental results suggested that RF power was the largest contribution factor for VOx etch rate, PR selectivity and uniformity on 6 inch diameter wafer. Uniformity and PR selectivity were improved by introducing a small amount of N2. High resolution and low roughness patterning transfer was achieved with a non uniformity of 2.4 %, an VOx etch rate of 74 nm/min, a PR selectivity of 0.96, a Si3N4 selectivity of 5 and a SiO2 selectivity of 10.

Reactive ion etching and OES endpoint detection of AlCu thin film

Patterning of AlCu alloy thin films is a key technology in MEMS fabrication. In this paper, reactive ion etching (RIE) process of Al-1%Cu films was described using BCl3 and Cl2 as etching gases and N2 and CH4 as neutral gases. A four-step process was presented to meet the etching requirements using BCl3, Cl2, N2 and CF4 as process gases. Optical emission spectroscopy (OES) was used to monitor the state of the plasma in real time. The etching endpoint was detected by detecting the spectral intensity change in the wavelength range of 395 ~ 400nm.

The Formaldehyde OTFT Sensor Based on the Airbrushed P3HT/ZnO Composite Thin Film

The pure conducting polymer P3HT film is less sensitive to the formaldehyde (HCHO), and the pure ZnO film needs a high temperature to militate the HCHO, as a result, the P3HT/ZnO composite was fabricated on the organic thin film transistor (OTFT) by spraying to detect the HCHO at room temperature, the electrical properties and sensing properties of all the prepared OTFT devices were measured by Keithley 4200-SCS source measurement unit. What is more, the effect of different P3HT/ZnO composite masses on the response of sensors were tested, all the sensors showed a remarkable response to HCHO, and the optimized composite mass of 1.0ml was obtained. Since most detecting methods for the HCHO vapor require an high temperature, the experiments and results in this paper showed the important significance for the field of HCHO detecting.

Preparation and Investigation of Toluene-Sensing Properties of Polymer/Inorganic Composite and Multi-Layer Films

In this paper, poly 4-vinylphenol (P4VP)/multi-wall carbon nanotubes (MWNTs) composite film, P4VP/ carbon black (CB) composite film and P4VP/MWNTs multi-layer sensitive films prepared using airbrush technology were deposited on interdigitated electrodes to detect tolunene vapor at room temperature. The surface of the composite film was observed under a scanning electron microscope (SEM). It was found that the resistance of the sensor increased after the exposure to toluene vapor and the increased magnitude of the changes had a good linearity with concentrations of toluene. Meanwhile, the P4VP/MWNTs composite film sensor also has a higher sensitivity than P4VP/CB composite film sensor. P4VP/MWNTs three-layer film sensor was fabricated as well. It was estimated that the response time and recovery time of P4VP/MWNTs three-layer films sensor were about 15 s and 20 s, respectively. The sensor responses of S=0.12% at 10mg/m3 toluene vapor for P4VP/MWNTs three-layer films. The results showed that the multi-layer films sensor exhibited a lower detection limit and better sensing properties compared with the sensors based composite film.