Xue Zhong Wu

Performance-Enhancing Methods for Au Film over Nanosphere Surface-Enhanced Raman Scattering Substrate and Melamine Detection Application

A new high-performance surface-enhanced Raman scattering (SERS) substrate with extremely high SERS activity was produced. This SERS substrate combines the advantages of Au film over nanosphere (AuFON) substrate and Ag nanoparticles (AgNPs). A three order enhancement of SERS was observed when Rhodamine 6G (R6G) was used as a probe molecule to compare the SERS effects of the new substrate and commonly used AuFON substrate. These new SERS substrates can detect R6G down to 1 nM. The new substrate was also utilized to detect melamine, and the limit of detection (LOD) is 1 ppb. A linear relationship was also observed between the SERS intensity at Raman peak 682 cm−1 and the logarithm of melamine concentrations ranging from 10 ppm to 1 ppb. This ultrasensitive SERS substrate is a promising tool for detecting trace chemical molecules because of its simple and effective fabrication procedure, high sensitivity and high reproducibility of the SERS effect.

Vibration Frequency Analytical Formula and Parameter Sensitivity Analysis for Rocking Mass Gyroscope

Rocking-Mass Gyroscope (RMG) is a dual-axial symmetry vibrating mass gyroscope, whose operational modes are completely uniform, and values of frequency are equal. RMG has the potential to be the gyroscope with high sensitivity. Predicting the frequencies for the operational modes of RMG is critical. The natural frequency analytical formula of RMG is developed by using the assumed modal method and vector composition method. The FEM simulations and experiments validate the analytical formula. The sensitivities of natural frequency to different parameters are also analyzed. The presented results provide references for optimization design of RMG.

Design and Analysis of a Monolithic 3-Axis Micro-Accelerometer

Due to many inherently problems of accelerometers on market, such as complex fabrication process and low precision, a monolithic three-axis accelerometer is proposed and fabricated. The 3-axis accelerometer consists of four individual seismic mass, each has a wafer-thick of 240μm and is fabricated by anisotropic wet etching technology. In this paper, the design, fabrication, and characterization of the 3-axis accelerometer are presented. The performance is characterized and demonstrated.

A Novel Fabrication Process of Large Area Triangular Nanocavity Arrays by Bilayer Nanosphere Lithography

A simple and novel self-assembly based process is presented in this paper for the fabrication of gold triangular nanocavity arrays. This process combines nanosphere lithography (NSL) with some standard MEMS technologies. A carboxylated polystyrene (PS) nanosphere bilayer with a relatively large area is fabricated on silicon wafer as the starting template by spin-coating. Oxygen plasma etching, metal deposition and lifting-off of the PS upper layer are then orderly carried out for the formation of triangular space, which is made up of Cr film and the remaining PS nanoparticles. Then silicon etching is used to transfer the triangle pattern onto the silicon wafer. Finally, a 50 nm thick gold layer is deposited on the pattern to fabricate gold triangular nanocavity arrays. With this strategy, both the period and the cavity size can be adjusted independently. This will allow the tuning of the optical properties for desired application.

MEMS Assisted Fabrication of Cr Nanobowls

Various bowl-shape nanostructures have attracted widely attention for their potential applications in novel optical, electronic and biomedical fields. With the assistance of MEMS standard process, we present an inexpensive and fast approach in this paper for the fabrication of 2-D interconnected networks of Cr nanobowls. Spin-coated monolayer silica-polymer hexagonal ordered colloidal crystal was used as starting templates to create polymer nanowells. Then metal deposition and calcination process helped to develop Cr nanobowls with polymer nanowells as templates. The 2-D nanostructures were characterized by field emission scanning electron microscopy (SEM). Our fabrication approach of nanobowls can be extended to a wide range of metal materials and substrates with controlled size and wall thickness.

Measurement on the Mechanical Properties of SiC Thin Films Based on Square Thin Films Theory

SiC films made of different methods may have different mechanical properties, so their mechanical properties need to be determined by mechanical property measurement [1]. Since SiC films have stable chemical properties, it’s very difficult to be etched [2]. This paper introduce a method for SiC films mechanical property testing without processing SiC. Moreover, in view of the lack of square SiC films’ mechanical properties research, this paper also do simulation on it.

Modeling of Vibratory Microgyroscope with Manufacture Errors Based on Parameters Identification Theory

This paper presents a modeling method of vibratory microgyroscope with manufacture errors based on parameters identification theroy. owing to the manufacture errors, such as quadrature error and cross-axis perturbation, the resonant vibrations of the drive mode to the sense mode are coupled not only through the Coriolis force. In reality, also by elastic forces, damping and so on. Accurate modeling and identification of manufacture errors enhance significantly the ability to compensate for the consequent errors via feedback/feedforward control strategies. In this article, a really direct model with manufacture errors of the microgyroscope is proposed and the parameters of the model are identified with Frequency-Response Analysis (FRA) and State-Space-based system-identification approach.

Research on the Method of Laser Trimming to Reduce the Mode Coupling Error of Micro-Machined Vibratory Gyroscopes

Large mode coupling error would seriously restrict the improvement of gyroscope performance. In order to decrease the adverse influence from mode coupling error, this paper studied the formation mechanism of mode coupling error for a micro-machined vibratory gyroscope and certified the result studied by ANSYS analysis. Based on our analysis, it is found that removing material from both sides of the center lines of oscillation could arouse errors of anti-phase each other, which demonstrates that trimming could reduce mode coupling error on the other hand. Finally, experimental study was implemented on the micro-machined vibratory gyroscope by UV laser micromachining technology. Results indicated that laser trimming method on the basis of the phase relationship between mode coupling error signal and driving signal could effectively degrade the error. For certain prototype, the peak-peak voltage of the mode coupling error could be reduced from 6.6V to 0.2V after trimming when there is no angular velocity input.

A Silicon Micro-Accelerometer with Triangle Cross-Section Beam by Anisotropic Wet Etching in TMAH Solution

A capacitive accelerometer with triangle cross-section beam fabricated by anisotropic wet etching of (100) silicon is presented in this paper. The feature of this accelerometer is that eight suspension beams with triangle cross-section are formed by anisotropic wet etching of (100) silicon in TMAH solution, without heavy boron doping or Si-Si bonding. When the width of beam is decided, the beam’s geometry is determinate. The formation procedure of the triangle cross-section beam is analyzed in detail. Through this beam-fabrication approach, the beam’s thickness can be well controlled by beam’s width and intrinsic stress in the beams is minimized. Accelerometers with different sensitivities can be easily fabricated by varying the width of the beams. For a device with 23 μm width beams, the resonance frequency and the quality factor are 644 Hz and 32, respectively. The sensitivity of accelerometer is measured as 2 V•g-1.

Design and Empirical Study for Coner Compensation in 25% Wt TMAH Etching on (100) Silicon Wafers

Anisotropic wet etching is a key processing step for the fabrication of microstructures. In general, convex corner structures and non {111} crystal planes will be undercut during wet anisotropic etching. This characteristic of Si is an obstacle to the fabrication of structures in various applications. Among a number of silicon etchants, TMAH is becoming popular for low toxicity and CMOS compatibility. In this paper, a new design of compensation structure has been proposed to solve the undercutting problem with 25%wt TMAH solution. The new compensation structure is made up by squares which are connected to the convex corner. An empirical expression between the parameters of the new compensation structure and etching depth is derived. The changes of the compensation structure in different etching process are shown by photographs. Experimental results prove the high accuracy of this method. Compared to two widely used compensation structures, the new structure is more space efficient.