An accelerometer with concise structure having a resonant microbeam to measure 2-D acceleration is proposed. This structure is configured with a central proof mass suspended by four symmetrical and orthogonal high-aspect-ratio (HAR) microbeams. This dual-axis design is able to decouple a two-axis signal from a 2-D acceleration. An analytical model relating the linear relationship between the acceleration and the associated resonant frequency shift of microbeam is derived, and a finite element analysis (FEA) is also performed to confirm this model. The FEA result also shows that there is little cross talk between x and y directions of measurement, meaning that this structure is able to decouple a planar 2-D acceleration into two independent acceleration components, and therefore the 1-D analytical model can be used to evaluate the 2-D acceleration on the x-y plane. In addition, the model is verified by testing results of one conventional dual-axis natural frequency shifted microaccelerometer (DFSM). The simulation result also shows that the sensitivity of the proposed HAR accelerometer is triple that of a conventional DFSM.
A new Kirkpatrick-Baez-type focusing mirror system for use in synchrotron radiation IR beamlines is designed and fabricated. This mirror system, which contains two fifth-order-polynomial-corrected cylindrical mirrors, can collect and focus the long arc shape IR source from the bending magnet into a nearly perfect point image. To fabricate these two uncommon mirrors, 17-4 PH type stainless steel substrates are chosen and mechanically bent from planar to the desired fifth-order-polynomial-corrected cylindrical shapes with central radii of 3.74 and 5.43 m. The root mean square (rms) roughness and the slope error of these two mirrors are measured to be 0.3 nm and less than 6.3 µrad, respectively. The method for calculating the polynomial coefficients of both mirrors as well as the mirror fabrication process, mechanical design, and the method for adjusting the mirror shape using a long trace profiler are presented.
In the current paper, the fabrication process of a novel proposed hemispherical polysilicon shell standing on a hemispherical silicon cavity is demonstrated. This micro-fabrication process combines both bulk and surface micromachining, which include the isotropic wet etching, a novel mask design, the thick photo resist coating and exposure, and high-aspect-ratio curved sacrificial technique. In isotropic wet etching of a hemispherical cavity, the optimal concentration of etchant is experimentally determined along with adequate ultrasonic vibration during wet etching to produce the circle-like of hemispherical cavity. The conventional alignment mark, which will be destroyed during the rather long isotropic wet etching process, is replaced by a novel mask design with the second alignment mark. Also, for a deep hemispherical cavity larger than 100úgm, the traditional photo resist can not be coated on the corner surface well. The thick photo resist, AZ4620, is found to be able to overcome this problem and be successfully exposed all through its bottom surface. Furthermore, the deposited sacrificial layer materials (PSG) on this cavity will usually result in thinner layer near the corner. In addition, the curved gap of PSG layer has the feature with high-aspect-ratio. These make the PSG etching difficult. Therefore, two steps etching process with two different hydrofluoric concentrations are used to release the PSG with 2micrometers thickness and 150micrometers arc length.
In the current study, a systematic recipe set was developed for processing SU8-5 photoresist in order to fabricate a microaccelerometer with high-aspect-ratio structure by UV-LIGA process. The disclosed recipe set comprises a series of relative recipes for processing SU8-5, including spin speed, soft bake, exposure dose, post exposure bake and developing time. The recipe set is capable of processing SU8-5 film with thickness from 5micrometers to 80micrometers . General hot plate, Karl Suess Gyrset spinner RC8 CT62 (spin coater) and MJB3 exposure aligner which all belongs to the frequently adopted equipments in the traditional IC fab, were used to explore these recipes. To verify these recipes, the SU8-5 micromold fabricated according to the presented recipe set is employed to electroplate the structure of the biaxial microaccelerometer with critical dimension of 4x20x500micrometers . The detail and most effective process parameters described in this systematic recipe set promote the beginner to process SU8-5 and fabricate the SU8-5 micromold. In addition, various failure reasons due to adopting the improper recipes are also discussed to provide the guide line for the reader to develop and approach their own proper recipe to process SU8-5.
By investigating microaccelerometers with various configurations including the amplitude type and the resonant type, we summarize that dynamic behavior, geometry, structure rigidity and dimension are important considerations to design a microaccelerometer. In which, a linear dynamic response is better for its easiness to be processed, and a significant variation tendency in responding to the detected acceleration is required. A good geometry is necessary to decouple a detected acceleration, such as a 2D or 3D acceleration into two or three measurable independent accelerations components. In addition, a strong rigidity and stiffness are necessary to avoid the influence, such as the associated crosstalk from other non-interested acceleration, e.g., gravitation. Moreover, the dimensions of the structural components dominate the mechanical and electrical sensitivity of the device. We utilize these considerations to design a biaxil frequency-shifted microaccelerometer. This accelerometer is configured with a central proof mass connected via four identical and symmetrical beams with high-aspect ratio, and operates using natural frequency shift of the microbeam. The good performance of the accelerometer is verified by using analytical simulation and FEA (Finite Element Analysis). Moreover, to achieve a most sensitive structure, the best dimension arrangement of 1:2 for the ratio of the microbeam to the proof mass is also realized.
This study presents a Kirkpatrick-Baez mirror system which includes two high-order polynomial bendable mirrors in a Taiwan Light Source (TLS) infrared beamline to create and adjust more accurately collimating images on a focusing point. The source of infrared rays is synchrotron radiation from a TLS bending magnet, so the surface of a vertical focusing mirror (VFM) is designed on an elliptical shape. The Runge-Kutta numerical method is used to compute the optimal high-order polynomial shape of the horizontal focusing mirror (HFM), to focus the horizontal arc source on the point image. The HFM and VFM using 17-4 PH stainless steel substrate without an electroless nickel plate are mechanically bent from planar to the desired fifth-order polynomial shapes with central radii of 3.74 m and 5.43 m by the application of equal couples, respectively. The mirror fabrication process, mechanical design, and the method of adjusting the mirror shape using the Long Trace Profiler measurement system are described. Finally, the roughness of mirrors is 3 angstrom RMS. After the mirrors have been bent, the slope error over 2/3 of clear aperture length (170 mm) was reduced to less than 6.3 (mu) rad RMS.