Zhang Wendong

Design, fabrication and characterization of pyroelectric thin film and its application for infrared gas sensors

Prepared by a sol–gel process, the lead zirconate titanate (PZT) (PbZr0.3Ti0.7O3) thin film, which is chosen as an infrared sensing film, uses lead acetate trihydrate, zirconium acetylacetone, acetylacetone, and titanium isopropoxide as starting materials. The pyroelectric infrared sensor with the PZT thin film has been successfully fabricated. The fabrication process of the device is discussed in detail. A new Au Pt–PZT–Pt infrared detecting structure on silicon substrate with a micro bridge is designed. Under the response and reference dual-element configuration, undesirable signals, caused by vibration, ambient temperature change, and sunlight, are cancelled out at the input of the preamplifier circuit. The dual-element structural design of the device is discussed and analyzed in detail. In order to realize our purpose to use this detector to monitor gas concentration, we designed a detection set-up in the light of a certain gas which absorbs infrared radiation at specific wavelengths. The gas concentration is obtained by designing a weak signal detect circuit and data arithmetic. The first measurement for methane is reported. Experimental result shows the ability of methane detection of the detector based on the infrared sensor element. & 2008 Elsevier Ltd. All rights reserved.

Temperature dependence of biaxial strain and its influence on phonon and band gap of GaN thin film

Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition (MOCVD) is studied using Raman scattering and photoluminescence in a temperature range from 100 K to 873 K. The model of strain (stress) induced by the different lattice parameters and thermal coefficients of epilayer and substrate as a function of temperature is set up. The frequency and the linewidth of E2high mode in a GaN layer are modelled by a theory with considering the thermal expansion of the lattice, a symmetric decay of the optical phonons, and the strain (stress) in the layer. The temperature-dependent energy shift of free exciton A is determined by using Varshni empirical relation, and the effect of strain (stress) is also investigated. We find that the strain in the film leads to a decreasing shift of the phonon frequency and an about 10meV-increasing shift of the energy in a temperature range from 100 K to 823 K.

Research on double T-shape MEMS bionic vector hydrophone and its application in obstacle avoidance sonar

Purpose – The purpose of this paper is to develop a novel MEMS vector hydrophone with the key features of smaller size, better consistency, higher sensitivity and directional reception, and to develop a highly effective and economical obstacle avoidance sonar system. Currently, the typical vector hydrophones are resonant vector hydrophones based on the accelerometer, which greatly increases the volume and constrains the detection sensitivity. Also, because the system is composed of a number of devices, its size is difficult to be reduced. Design/methodology/approach – A novel double T-shape MEMS vector hydrophone is proposed with a fish’s lateral line organs as prototypes. The structure size and layout location of the piezoresistors were determined by simulation analysis, and the double T-shape microstructure was fabricated integrally by MEMS manufacturing technology, after which, the acoustic package of the microstructure was completed and the prototype was produced. Finally, the packaged hydrophone was ...

Effect of temperature on phase transition behavior of antiferroelectric (Pb0.97La0.02)(Zr0.75Sn0.25?xTix)O3 ceramics

Pb0.97La0.02(Zr0.75Sn0.25−xTix) O3 (x = 0.10, 0.105, 0.11) (PLZST) antiferroelectric ceramics with highly preferred-(110) orientation were successfully fabricated via the conventional solid-state reaction method. The antiferroelectric nature of PLZST ceramics induced by electric field was demonstrated by the dielectric constant-temperature (D-T) and the polarization-electric field (P-E) measurement. Typical phase transition from ferroelectric (FE) to antiferroelectric (AFE), and then to paraelectric (PE) is obtained. The results indicate that the phase transition behavior is suppressed with increasing of x, and Tc is remarkably shifted to higher temperature of 168 °C, 170 °C and 174 °C, respectively. Besides, high phase transition current (1 × 10−6 A, 8 × 10−7 A and 6 × 10−7 A, respectively) is obtained with temperature induced. Consequently, the excellent electric properties and the restraint between temperature and electric field would provide basis on the application of PLZST antiferroelectric ceramics in microelectronic integrated systems and sophisticated weapons systems.

The resonance frequency shift in an SOI nano-waveguide microring resonator

To research the effect of a deposited SiO2 insulating layer on the resonance frequency modulation of an SOI nanowaveguide ring cavity during integration fabrication, a rib waveguide ring resonator was systematically designed and fabricated. SiO2 insulating layers with different thicknesses were deposited for analysis of the frequency shift characteristics. By testing the resonance transmission spectrum power of this structure, it is found that there are blue shifts after SiO2 deposition, and the frequency shift value of a structure with a 500 nm SiO2 insulating layer deposited is 0.8 nm, that is 0.24 THz at the resonance point where wavelength is around 1550 nm. Taking advantage of this conclusion, efficient optical modulation is available by choosing different frequency band resonance wavelengths to narrow the frequency modulation range.

Comparison between photoluminescence spectroscopy and photoreflectance spectroscopy in CuGaSe2 epilayer

Photoluminescence (PL) spectroscopy and photoreflectance (PR) spectroscopy are very useful techniques for studying the properties of materials. In this paper, the same material of Cu-rich metal-organic vapour phase epitaxy (MOVPE) grown CuGaSe2 layer is investigated in a temperature range from 20 to 300K to compare these two techniques. Both PL and PR spectra appear red shifted, less intense and broadened. The temperature dependence of interband transitions is studied by using the Manoogian-Leclerc equation. The values of the band gap energy at T = 0K and the effective phonon temperature are estimated. The temperature dependences of intensities and broadenings of PL and PR spectral lines are also analysed. Based on the results of the comparison, the features and applications of the PL and PR can be shown in detail.