Guangji Li

Photo-, thermal and humidity sensitivity characteristics of Sr1−xLaxTiO3 film on SiO2/Si substrate

Abstract Strontium lanthanum titanate (Sr 1− x La x TiO 3 ) film deposited on a SiO 2 /Si substrate by the argon ion-beam sputtering technique has been used to fabricate a thin-film resistor and a metal-insulator-semiconductor (MIS) capacitor by standard integrated-circuit technology. Measurements show that the film resistor has superior sensitivity for visible light and a thermal sensitivity within the range 28–200°C, while the MIS capacitor is highly sensitive to relative humidity. The optical absorption spectrum of the film has been measured and the bandgap of the film determined. The effects of test frequency on the impedance of the film resistor at various temperatures and on the humidity-sensitive characteristics of the MIS capacitor have been investigated.

A new thin-film humidity and thermal micro-sensor with Al/SrNbxTi1-xO3/SiO2/Si structure

Abstract Strontium titanate–niobate (SrNb x Ti 1− x O 3 ) film deposited on a SiO 2 /Si substrate by the argon ion-beam sputtering technique is used to fabricate thin-film resistors and metal–insulator–semiconductor (MIS) capacitors by standard integrated-circuit technology. Results show that the film resistor has superior thermal-sensitivity characteristics within the temperature range of 27–200°C, and the MIS capacitor is highly sensitive to relative humidity. Besides investigating the effects of frequency on the impedance of the film resistor at various temperatures and on the current of the MIS capacitor at low and high relative humidities, the response times of the MIS capacitor to adsorption and desorption of water vapor are found to be reasonably short (15 s and 10 s) and its humidity hysteresis can be greatly suppressed at higher operating voltages.

Effects of chemical composition on humidity sensitivity of Al/BaTiO3/Si structure

Argon‐ion‐beam sputtering technique has been applied to deposit barium titanate (BaTiO3) films on silicon wafers at room temperature under vacuum, and then Al/BaTiO3/Si structures were fabricated. Results show that the current and capacitance of these devices are sensitive to the change of relative humidity at room temperature, and saturation absorption (response) time as well as humidity sensitivity of the devices depend on the chemical composition of the BaTiO3 films. For higher annealing temperature and longer annealing time, the oxygen composition increases while fixed charge density decreases. These changes result in lower humidity sensitivity and longer response time.

A humidity-sensing model for metal–insulator–semiconductor capacitors with porous ceramic film

A new physical model for a humidity-sensitive metal–insulator–semiconductor (MIS) capacitor with porous thin film is proposed. The model is used to determine water adsorption isotherm and calculate pore-size distribution of the film. The relative-humidity dependences of the capacitance and resistance of the film were measured. The effects of frequency on the dielectric constant of the film and the current of the MIS structure under various relative humidities were investigated.

A new multi-function thin-film microsensor based on Ba1-xLaxTiO3

A new multi-function microsensor with a barium lanthanum titanate (Ba1-xLaxTiO3) thin film is developed for the fabrication of a thin-film resistor and a metal-insulator-semiconductor (MIS) capacitor on a SiO2/Si substrate. The results reveal that the thin-film resistor has good sensitivity to visible light and good thermal sensitivity within the temperature range of 28-400 °C. The MIS capacitor is sensitive to changes in the relative humidity (RH), with a 130% change of the current for a humidity change from 12 to 92% RH at a test frequency of 500 Hz, and with short response times of 5 and 4.5 s for the adsorption and desorption of water vapor, respectively. The effects of the test frequency on the photo, thermal and humidity sensitivity performances are also investigated. Since the lifetime of charge carriers of Ba1-xLaxTiO3 thin films is only 16 ms, about half that of Sr1-xLaxTiO3 thin films, the device can detect light modulation at higher frequencies.

INFLUENCE OF BACKSURFACE ARGON BOMBARDMENT ON SIO2-SI INTERFACE CHARACTERISTICS

A low‐energy (550 eV) argon‐ion beam was used to directly bombard the backsurface of polysilicon‐gate metal‐oxide‐semiconductor (MOS) capacitors after the completion of all conventional processing steps. The interface characteristics of the MOS capacitors were investigated. The results show that, as the bombardment dose increases, the active dopant concentration near the oxide‐semiconductor interface gets higher; maximum midgap energy increases; and interface‐state density becomes lower. This simple technique is compatible with existing integrated‐circuit processing, and can easily improve the interface characteristics, and therefore the electrical characteristics of MOS devices.

Optical properties of synthesized organic nanowires

Organic nanowires have been synthesized by hydrothermal method. The functional groups in chemical structure of the organic nanowire have been characterized by Fourier-transform infrared spectrum. Optical properties of organic nanowires have been demonstrated by linear absorption, photoluminescence spectroscopy, and time-resolved photoluminescence spectroscopy. Two emission peaks at 3.91 and 3.3eV have been revealed by fluorescence spectrum at room temperature. For the emission peak at 3.3eV, a blueshift occurred when the temperature rises. Two time components have been observed in fluorescence dynamic process of the nanowire by time-resolved decay curve.

Encapsulation of Tandem Organic Luminescence Solar Concentrator With Optically Transparent Triple Layers of SiO 2 /Epoxy/SiO 2

Developing an organic luminescent solar concentrator (LSC), featuring ultralong lifetime and high transparency simultaneously, is crucial for building-integrated photovoltaic applications, such as solar energy harvesting clear windows. In this paper, a tandem organic LSC is encapsulated and connected with three optically transparent layers, namely an encapsulating epoxy layer and two insulating SiO2 layers that prevent dissolving the organic dyes into the epoxy layer. Experimental results demonstrate that the encapsulated organic LSC maintains the high average transmission of 60% in the visible range of 390-750 nm, and has an ultralong lifetime of ~ 6.7 × 104 h under illuminated test in laboratory environment, which is around five times longer than that of the organic LSC without any encapsulation. In addition, experiments confirm that most of the photoluminescence radiation generated in the organic dyes is trapped in the high-index SiO2/epoxy/SiO2 structure, and guided between the glass substrate before emerging from the four edges of the organic LSC sample for conversion to electricity. A 30% increase in short-circuit current is attained, in comparison with a similar unencapsulated organic LSC structure.

Photoelectrical properties of Ba1-xLaxTiO3 thin-film resistor

Abstract Thin Ba 1− x La x TiO 3 film is deposited on a SiO 2 /Si substrate by argon ion-beam sputtering technique. The optical and photoelectrical properties of the film are studied. The optical absorption spectrum of the film is measured and the bandgap of the film is then determined. Effects of applied voltage and illumination intensity on photocurrent of thin-film resistors with different spacing lengths are investigated, and results show that devices with shorter spacing have more linear I – V characteristics. Moreover, a study of heat treatment in O 2 on the dark current of the resistor is performed, revealing that a heat treatment at 400°C for an optimal time of 10 min can greatly improve the photosensitivity of the resistor by reducing its dark current.

A cost-effective, long-lifetime efficient organic luminescent solar concentrator

In this paper, we demonstrate the concept of a cost-effective, environment-friendly, highly stable, and efficient organic luminescent solar concentrator (OLSC) structure based on the use of an optically transparent lamination layer comprising a blend of an organic semiconductor host material and an organic red dye material, which is sandwiched between two glass panes. Experimental results demonstrate that the developed OLSC can achieve a power conversion efficiency of up to 5.3% and a lifetime of >1.0 × 105 h when operated in ambient environment. This is attributed to the enhanced solar light harvesting of the host materials, the ultra-low ultraviolet transmission, and negligible oxygen and water content permeability of the ultraviolet cured lamination layer. The high efficiency in conjunction with the cost-effective material selection contributes to the low cost per peak watt, making the reported OLSC structures attractive for building-integrated photovoltaic applications.