We present a new single-chip diaphragm-type Fabry-Perot microcavity pressure sensor with a novel single deeply corrugated diaphragm. Both analytical and experimental results have shown that some common issues, such as signal-averaging effect and cross-sensitivity to temperature with diaphragm-type Fabry-Perot microcavity pressure sensors, can be substantially alleviated by the proposed technique.
In this study, an analytical model, taking into account the coupled photoelastic and thermal-optical effects, is established to evaluate the temperature dependence of a single-chip silicon micromachined Fabry-Perot pressure sensor. The results show that temperature variation has significant impact on the micromachined Fabry-Perot pressure sensor with conventional flat diaphragm. A new membrane-type silicon micromachined Fabry-Perot pressure sensor with a novel deeply corrugated diaphragm is then proposed. The sensor is fabricated on a single-chip using both surface- and bulk-micromachining techniques. Both analytical and experimental results show that the cross-sensitivity to temperature of Fabry-Perot pressure sensors, can be substantially alleviated by the proposed single deeply corrugated diaphragm/mirror.
The study of smart structures with active devices of sensors and actuators for self-monitoring and self-adaption has been of much recent research interest. Active vibration control is a major application focus and there has been tremendous amount of research work on active vibration control of flexible structures using piezoelectric materials. In this paper, the control mechanism for a flexible cantilever plate structure using surface bonded piezoelectric sensors and actuators has been studied through analytical simulations and experiments. The sensor outputs were used to determine the amount of input to the actuators for controlling the response of the structure in a closed loop. The responses under different control mechanisms were analysed by three dimensional finite element model. The effectiveness of different feedback control methods in altering system characteristics and system responses of the structure was investigated. Experimental investigations on active vibration control were also conducted on a cantilever plate with surface bonded piezoelectric sensors and actuators.
This paper presents results on optical cross-connect switches based on novel MEMS vertical mirrors. The switch consists of two mirror arrays to redirect optical beams from an input fiber array to an output fiber array. Each mirror is actuated by two electrostatic comb drive actuators, and can be rotated bi-directionally and perpendicularly to the chip surface. Finite element model (FEM) and Gaussian beam optics have been used to simulate and optimize the optical cross-connect switch architecture. Results have shown that the switch is much less constrained by the scaling distance of light propagation as the port count grows. However, the coupling efficiency is sensitive to angular alignment for large port-counts; thus mechanism for ensuring precise angular control of the micro-mirror is crucial for the proposed MEMS optical cross-connect switches.
In this paper, the vibration characteristics of 2-DOF mechanical vibration absorber system are adopted to improve the mechanical sensitivity of a micro-electro-mechanical (MEMS) vibratory gyroscope sensor. The proposed gyroscope is basically composed of two oscillating masses that are interconnected with flexures. It can be shown that, at their resonance, the secondary mass will absorb most of vibration energy from the primary mass, thus resulting in the vibration amplification that is directly related to the mass ratio between the masses. Therefore, when an angular velocity is applied to such a gyroscope, most of the energy gained due to Coriolis force is transmitted from the primary element to the secondary element. As the primary mass is normally designed to be much bigger than the secondary mass, the Coriolis displacement of the secondary element will be amplified depending on the mass ratio. With the use of the secondary oscillating mass as a capacitive sensing element, the mechanical sensitivity of the gyroscope can be increased significantly. Modelling and simulation of a practical gyroscope design were conducted using ANSYS54 finite element code. The results are presented and verified with the theory.
Influence of LPCVD deposition condition, substrate, film thickness, crystallized degree and pre-annealing on residual stress in LPCVD polysilicon films was studied. The polysilicon deposited on PSG substrate shows the lowest residual stress. The relationship between crystallized degree of polysilicon films and the film thickness was investigated with the aid of Raman Scattering Spectrum. The residual stress shows a significant dependence on the film thickness because crystallized degree raises with the film thickness increase. The test results show that (1) for a thinner film (0.20 micrometer), even if to use a higher deposition temperature (630 degrees Celsius), its crystallized degree is still quite low and a quite higher residual tensile stress is resulted in the film. (2) for a thick film (4 micrometer), even if to use a lower deposition temperature (580 degrees Celsius), a significant crystallization still will occur in as-deposited films and a residual tensile stress is resulted in the films. A pre-annealing step before polysilicon boron doping is brought into the fabrication process of multi-layer diaphragm structure. It can be used as a method to control stress in highly doped polysilicon films. The stress control test of highly boron doped polysilicon/oxide diaphragm structure was carried out. The result shows that the property and magnitude of the stresses in highly boron doped polysilicon-oxide diaphragm can be arbitrarily changed in certain range by varying the holding time of final annealing.
We present and compare the different design of micromachined silicon condenser microphones. The aim is to develop the microphones with high sensitivity and low fabrication cost. Slotted and corrugated diaphragms have been designed and fabricated in order to increase the mechanical sensitivity of microphones. At the same time we developed the fabrication process for the low stress so stress-free multilayers polysilicon used as the microphone diaphragms. To increase the microphone chip density on one wafer and avoid the sticking problem during the wet release process, a new process design using deep reactive ion etching is prosed, such process system is available in our laboratory.
To understand the high-cycle reliability of plastic ball grid array (PBGA) interconnections under external random vibration loading, a series of vibration test of PBGA assemblies were conducted. The test vehicle has four PBGA modules assembled on a printed circuit board. The assembly was clamped at two opposite sides on a fixture, which was bolted to a vibration excitation. Firstly, the dynamic properties of the assembly under external random vibration excitation were characterized. The resonant frequencies of the assembly were identified, and the maximum dynamic deflection was estimated. Then the reliability test were carried out. In the reliability tests, the electrical resistance of PBGA modules was continuously monitored, so that any failure could be detected. This paper describes the test procedures, and shows the typical vibration fatigue failures in the PBGA interconnections. Test results will be analyzed in detail.
Presented in this paper is the investigation on sensitivity of micromachined condenser microphone. The sound-sensitive diaphragm of the microphone is formed by surface micromachined thin-film that is normally initially stressed due to the deposition process of the thin-film. Three varieties of diaphragm constructions, conventional flat diaphragm (FD), corrugated diaphragm (CD) and deep cavity-shaped diaphragm (DCD), are involved into the study. Both analysis and finite element model (FEM) are used for comparison of the mechanical sensitivity of the different kinds of diaphragm. Reasonable initial stress range of poly crystalline silicon thin films is assumed for the microphones. The DCD shows a much higher mechanical sensitivity compared to the other two kinds of diaphragm for the assumed film-stress range. A fabrication technology of low tensile-stress poly-silicon film is also provided and proposed for the high sensitivity microphone with the DCD.
Anisotropic etching of silicon creates different convex- corner undercutting contours in different varieties of etchant. This difference in undercutting configuration is investigated by analyses of the undercutting formation in detail. Based on Wulff-Jaccodine rules and some experimental results, theoretical analyses are given to clarify the reasons of different undercutting configuration caused by different etchant and the rationality of a certain plane occupying the undercutting position for a certain etchant. Furthermore, the investigation is lead to the convex-corner undercutting under maskless etching, i.e., during the etching mask on the structure removed. Experimental results show that the convex-corner undercutting under maskless etching is far different from that of conventional masked etching. The geometrical evolution of the undercutting is studied both experimentally and analytically. The compensation criteria for maskless etching are discovered and the corresponding compensation schemes are provided.
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