Dayu Tian

Aluminum-coated silicon wafer bonding with tin intermediate layer

Abstract. Metallic wafer bonding is becoming a key enabling technology in microelectromechanical systems packaging and heterogeneous integration. We realize the bonding of silicon (Si) wafers coated with aluminum (Al) film with thin tin (Sn) film as the intermediate layer. The bonding pressure is 0.25 MPa. The bonding is achieved at temperatures as low as 280°C after a short bonding time of 3 min. The average bonding strength is 9.9 MPa. The minimum variation of bonding layer thickness is about 0.2 μm within a large area. A fracture surface study and a cross-section analysis are conducted and the bond mechanism is investigated. It is found that the fracture mainly occurs at Al/Sn interface during the shear test. Two bonding conditions are compared and the results show that applying bonding pressure before heating is important to achieve a uniform bonding layer.

A method to evaluate the influence of different substrate on stress mismatch induced deformation in MEMS accelerometer

This paper presents a method to evaluate the influence of stress mismatch between sensor structure and different die-attachment on the thermal stability of accelerometers. The local deformation of MEMS accelerometers under different thermal load and differential die-attachment conditions are investigated. White light interferometer and a home-made heating stage are used to carry out the measurement. Capacitance variations of differential capacitors can be calculated based on the data of the local deformation of MEMS accelerometers. Both the visual evidences and calculated capacitance variations in this work can give clear guidance to optimize both the structural design and packaging conditions.

Research on the structure of ultrathin Si PIN detector

Ultrathin PIN Detectors have been applied in radiation detection for particle identification and etc. In this paper, we present simulation research on the structure of ultrathin Si PIN detector based on bonding technology by using Sentaurus TCAD tool. The normal structure and reverse structure of ultrathin Si PIN detector are simulated and compared. The reverse current of detector and electrical field distribution are analyzed. It is found that the reverse current of the reverse structure increases fast when the voltage exceeds a threshold value. It is explained by considering the parasitic MOS structure. This effect can be reduced by increasing the thickness of buried SiO2.

Simulation studies on PECVD SiO 2 process aiming at TSV application

A simulation for studying the process of plasma enhanced chemical vapor deposition (PECVD) technology, which is a key process in through-silicon-via (TSV) technology, is proposed in this paper. Elementary models (including ions and neutral particles direct incidence, re-emission and so on) corresponding to the mechanism of PECVD are included, which contributes to the morphology of Si02 film deposition. By selecting proper parameters of models such as flux of particles and sticking coefficient (Sc), the effect of different particles on deposition and the step-coverage effect of trenches with different aspect ratios are studied.

Fabrication of ultrathin silicon PIN detector

Ultra-thin silicon PIN detectors are applied widely in nuclear physics experiments and space exploration. It is used in ΔE-E telescope system as the ΔE detector to detect the energy loss of high energy particles so that to identify the charge and mass of the particle. The ΔE detector is required to be very thin(<50μm) in order to let low energy particles to go through the ΔE detector and enter the followed E detector. The fabrication of ultra-thin silicon detector is very difficult and challenging due to the fragility of the ultra-thin silicon membrane considering that the area of the detector is required to as large as 10~100 mm2. Several different technologies have been proposed to fabricate the ultra-thin silicon PIN detector, such as back side locally thinning of the high resistivity silicon wafer, application of the SOI technology or wafer thinning and bonding technology. The monolithic ΔE-E detector telescope technology has also been proposed. In this talk we review the development of ultra-thin silicon PIN detector technology including our research work.

A new type of silicon drift detector with curved surface

A new Silicon Drift Detector (SDD) with curved surface has been proposed and analyzed by simulation. The adjacent drift cathodes punch-through problem in traditional SDD has been eliminated in the novel SDD. The potential distribution and advantages of this new SDD in comparison with the normal one are presented and discussed in this paper.