Analysis and prevention of convex corner undercutting in bulk micromachined silicon microstructures

Convex corner undercutting in <100> silicon is an undesired phenomena during bulk micromachining of crystalline silicon substrate using anisotropic wet chemical etching process. The present investigation concentrates on the studies of convex corner undercutting at the free end of silicon cantilever beams released by anisotropic etching process. It also reports a simple, space efficient compensation design for complete prevention of corner deformation. Various compensation patterns such as square, rectangle and superposition of square and rectangular blocks of various dimensions have been employed at the free end corners of cantilever beam to protect corner deformation due to undercutting. The experiment was carried out in 44 wt.% KOH at 70 °C using <100> oriented silicon wafer. Both n-type and p-type silicon wafers were used to study the variations in the nature of corner deformation. A simple empirical relation has been obtained from the experimental data to calculate the lateral dimensions of the compensation layout from the total etch depth required to release the structure.     

硅的凸角补偿尺寸及腐蚀中避免削角的新方法

在硅的腐蚀过程中,如果不对台面凸角加以补偿,会产生严重的削角现象。本文采用在凸角上补偿正方形掩膜的方法,通过实验得出要在TMAH腐蚀液中将厚度约为300μm的硅片腐蚀出完整的台面凸角结构需要补偿多大尺寸的正方形掩膜。硅片与玻璃键合后,由于硅晶格的变化使得与玻璃键合的那一层硅很难腐蚀掉,本文也介绍了一种缩短腐蚀时间、避免削角的方法。     

Nonplanar oxidation and reduction of oxide leakage currents at silicon corners by rounding-off oxidation

We report that, based on the curvature radius at the convex corner of a trenched Si surface and electric field intensification, sacrificial thermal oxidation before gate oxide formation is very effective to round off the convex corner. We call it a rounding-off oxidation. From a simple one-dimensional model that considers both stress generation during Si oxidation and Stress relaxation by oxide viscous flow, it is foreseen that oxidation in a diluted oxidizing ambient and/or at a higher oxidation temperature reduces the stress in the oxide films. Experimentally, we report that the rounding-off oxidation with the above condition effectively rounds off the convex Si corner and decreases the thin gate oxide leakage currents and that the addition of a few percent of H2O to the dry oxygen rounding,off oxidation ambient is also effective. The relation between the sacrificial rounding-off oxidation and the time-dependent dielectric breakdown of thin gate oxides formed at the convex corner is also shown.     

A study of the corner effect in trench-like isolated structures

In trenchlike isolated devices, several parasitic effects exist. In a real-case test simulation, two such effects are shown. The most difficult to handle is the corner effect at the convex and concave corners in the structure. The corner effect is studied for two simple structures where no other parasitic effect exists. This makes it possible to look at the controlling factors of the effect and to formulate possible solutions of the corner effect. Results show that the corner effect is very strong, even with low gate bias and oxide charge density (Q_f) values. To eliminate the inversion of the convex corner, doping levels higher than 1E17/cm³ are necessary when Q_f⩾1E11/cm². It is shown that rounding the convex corner is a very effective way to eliminate the effect. However, to minimize the area loss, a compromise must be chosen between the substrate doping concentration (N _sub), oxide thickness, and rounding radius. Furthermore, the carrier concentration in the corner is controlled by the neighborhood of a biased drain (well). This can have an important influence on the leakage currents along a trench. The corner effect in a concave structure seems to have a very strong pinning function on the potential. Sharp corners prevent leakage currents around a trench, even with a relatively low N_sub     

硅基微结构制作及其在微分析芯片上的应用

基于一种新的湿法刻蚀条件和新型的凸角补偿结构,以KOH溶液为腐蚀液,对单晶(100)Si材料进行了湿法刻蚀,获得了表面平整和凸角完整的刻蚀结果,制作了用于微模塑工艺的硅基阳模,并成功地用于聚甲基乙烯基硅氧烷微分析芯片的制作上.     

硅各向异性腐蚀中生成直角补偿结构的新方法

Detailed characteristics of three classical rectangular convex corner compensation structures on（100） silicon substrates have been investigated, and their common design steps are summarized.By combining the basic method of a silicon wet anisotropic etching process, a general method of generating compensation structures for a rectangular convex corner is put forward.This calls for the following two steps：define the topological field and fit some borderlines together into practical compensation patterns.The rules, which must be obeyed during this process, are summarized.By introducing this method, some novel compensation patterns for rectangular convex corner structures are created on both（100） and（110） substrates, and finally simulation results are given to prove this new method＇s validity and applicability.     

Experimental study and analysis of corner compensation structures for CMOS compatible bulk micromachining using 25 wt% TMAH

In the present work, most common compensation structures (〈1 1 0〉 squares and 〈1 0 0〉 bars) have been used for convex corner compensation with 25 wt% TMAH-water solution at 90±1 °C temperature. Etch flow morphology and self-align properties of the compensating structures have been investigated. For 25 wt% TMAH water solution {3 1 1} plane is found to be responsible for corner undercutting, which is the fast etch plane. Etch-front-attack angle is measured to be 24°. Generalized empirical formulas are also discussed for these compensation structures for TMAH-water solution. 〈1 1 0〉 square structure protects mesa and convex corner and is the most space efficient compared to other compensation structures, but unable to produce perfect convex corner as 〈1 0 0〉 bar type structures. Both the 〈1 0 0〉 bar structures provide perfect convex corners, but 〈1 0 0〉 wide bar structure is more space efficient than the 〈1 0 0〉 thin bar structure. Implications of these compensation structures with realization of accelerometer structure have also been discussed. A modified quad beam accelerometer structure has been realized with these compensation structures using 25 wt% TMAH.     

新型风力压电发电装置设计及发电性能

为了利用压电发电装置采集自然界中的风能,并解决传统压电发电装置受外界振源限制的缺陷,设计了一种新型的风力压电发电装置。对装置中的悬臂梁压电振子进行了发电电压的理论分析及有限元验证,结果表明,压电振子发电电压的理论计算结果与ANSYS仿真结果基本吻合,两者之间的误差仅为0.54%。在此基础上,运用ANSYS有限元软件来计算该新型风力压电发电装置的发电能力,计算得到装置在振幅为1 mm、频率为20Hz的简谐力作用下,一个悬臂梁压电振子所产生的电压为30.1V。为了获得最佳的发电性能,对发电装置的结构参数进行了优化设计,研究结果表明,当悬臂梁压电振子的上表面比风车轴凸轮上凸点的最低点位置高2mm时,该装置具有最佳的发电性能,一个悬臂梁压电振子可产生约60.3V的发电电压。     

The effect of trench corner shapes on local stress fields: athree-dimensional finite-element modeling study

Local stress fields associated with deep trench structures are modeled in three dimensions utilizing a finite-element method. A model consisting of a SiO₂-filled deep trench residing in a silicon substrate is utilized, and stress is generated by differential thermal contraction. It is shown that corner regions, especially convex, `outside' corners, dramatically enhance the elastic energy density and shear stresses locally compared to noncorner regions. The effects of the specific corner geometry on these local stress fields is then investigated and it is shown that subtle geometric changes can yield substantial decreases in the magnitude and lateral extent of the fields     

硅(100)晶面的凸角腐蚀及其补偿

在进行Si(100)台面腐蚀时,由于硅的各向异性腐蚀特性,凸角处呈现严重切削现象。凸角侧向腐蚀程度与腐蚀深度、腐蚀温度、腐蚀剂配比等诸多因素有关。针对方形补偿结构探讨了凸角腐蚀的补偿原理,设计了补偿版图,并在KOH腐蚀液中进行实验验证,获得了与理论分析结果相一致的直角凸面补偿效果。     

Convex corners undercutting and rhombus compensation in KOH with and without IPA solution on (1 1 0) silicon

The present investigation introduces convex corners undercutting and results of rhombus compensation patterns in 40% aqueous KOH solution and in KOH saturated with isopropanol (IPA) solution. All experiments are carried out on (1 1 0) silicon at 70 °C. Undercuts take place on convex corners in both solutions. Moreover, the front etch planes governing undercut vary with solutions. Rhombus compensations are used to correct the undercut. Perfect acute corner without residue is obtained, and there are only some residue structures on both sides of obtuse convex corners in KOH with IPA solution, which are better results than those in pure aqueous KOH solution.     

基于ANSYS的工形压电发电装置有限元分析

针对目前悬臂梁压电发电装置的局限性,设计了一种工形的压电发电装置。运用ANSYS有限元软件建立了工形压电发电装置的有限元模型,并进行了静力分析及模态分析。分析结果表明,该工形压电发电装置的最大应变出现在每个转角折弯处,且每个转角折弯处的应变基本一致。根据压电方程可知,该处将产生最大的发电电压,所以在此粘贴压电片将具有最佳的发电能力。通过建立发电装置的压电耦合分析模型,计算得到在0.1mm的位移载荷作用下,每片压电片上将产生约15.1V的电压。最后,对该工形压电发电装置进行了参数化研究,结果表明,当选择长80 mm、宽15 mm、厚0.4 mm的压电工形板时,发电效果最佳,最大发电电压可达16.5V。     

Image registration and object recognition using affine invariantsand convex hulls

This paper is concerned with the problem of feature point registration and scene recognition from images under weak perspective transformations which are well approximated by affine transformations and under possible occlusion and/or appearance of new objects. It presents a set of local absolute affine invariants derived from the convex hull of scattered feature points (e.g., fiducial or marking points, corner points, inflection points, etc.) extracted from the image. The affine invariants are constructed from the areas of the triangles formed by connecting three vertices among a set of four consecutive vertices (quadruplets) of the convex hull, and hence do make direct use of the area invariance property associated with the affine transformation. Because they are locally constructed, they are very well suited to handle the occlusion and/or appearance of new objects. These invariants are used to establish the correspondences between the convex hull vertices of a test image with a reference image in order to undo the affine transformation between them. A point matching approach for recognition follows this. The time complexity for registering L feature points on the test image with N feature points of the reference image is of order O(NxL). The method has been tested on real indoor and outdoor images and performs well.     

Eigenvalue localization ofG-stable matrix polytopes

A simple geometric test can be applied to evaluateG-stability of a polytope of matrices. In case of a regionG being a convex subset of the complex plane, it suffices to assume that four (for some regions even less) corner points of a certain rectangle are contained inG.     

基于MATLAB的硅各向异性腐蚀过程模拟

根据硅各向异性腐蚀特点,在硅各向异性腐蚀速率图基础上,提出算法,利用数学软件MATLAB模拟了几种简单掩膜图形的腐蚀过程.程序从二维掩膜描述出发,找到相关晶面,产生动态的三维几何结构的输出.并推导出凸角补偿时补偿条的相关尺寸.其结果对MEMS加工有一定参考价值.     

Salient object detection via images frequency domain analyzing

Salient object detection has become an important direction in image processing and computer vision. The traditional center-priori theory believes that salient target should be closer to the central area of the image. However, false detection will often occur when the salient object is closer to the image boundary. So, this paper obtains center coordinates of the salient object by using Harris corner detection algorithm and convex hull. Accordingly, an improved center-priori saliency detection model is obtained by applying the frequency-tuned method. And then, the local saliency is set up by wavelet transforming which has the local characteristic information representation ability in the time domain and frequency domain. In addition, we obtain the global saliency by spectral residual analyzing. Finally, an advanced center-priori saliency model is established. The experimental results show that the model in this paper has better detection effects and higher target detection rates.     

梯形梁压电俘能器的特性研究

传统悬臂梁压电俘能器通常采用矩形梁结构,其压电片宽度为定值,对于压电片的利用效率有限。该文设计了一种梯形梁结构,将悬臂梁及其上附着的压电层设计为梯形,压电片宽度沿梁长方向逐渐变窄,并针对梯形梁结构的压电俘能器进行理论研究、仿真计算与实验分析,同时与传统矩形梁俘能器进行了对比。结果表明,同样的谐振状态下,梯形压电片中应力分布比矩形压电片中更均匀,且梯形梁压电俘能器具有更高的电压输出。     

可调谐微腔发光二极管微光机电系统悬臂梁的特性

采用微机械表面加工技术,成功设计并研制出具有GaAs基微光机电系统(MOEMS)悬臂梁结构的可调谐微腔发光二极管。对其工作特性进行了分析,测量得到悬臂梁载荷-位移关系曲线,并对微光机电系统悬臂梁可调谐微腔发光二极管进行调谐光谱测量。实验结果表明,在直流电流40mA,调谐电压范围4～22V时,波长从974.5nm蓝移至956.9nm,室温下波长调谐最大达到17.6nm。在实验基础上,采用有限元方法对具有分布布拉格反射镜(DBR)结构的悬臂梁动力学特性进行了研究,模拟结果与实验结果吻合较好。当悬臂梁长度为400μm时,最大位移达到411nm,最大调谐电压达到24V。     

Corner diffraction coefficients for the quarter plane

The current near a right-angled corner on a perfectly conducting flat scatterer illuminated by a plane wave is expressed as a sum of three currents. The first is the physical optics current, which describes the surface effect. The second is the fringe wave current, which is found from the half-plane solution and accounts for the distortion of the current caused by the edges. The third is the corner current, which is found from the numerical solution to the electric-field integral equation applied to the square plate, and accounts for the distortion of the current caused by the corner. It is found that the corner current for the right-angled corner, illuminated from a forward direction, consists mainly of two edge waves propagating along the edges forming the corner. Analytical expressions for these edge wave currents are constructed from the numerical results. A corner diffracted field is calculated by evaluating the asymptotic corner contributions to the radiation integral over the sum of the three currents. It is found that the corner contribution from the edge wave currents in some cases is of the same size as the corner contributions from the physical optics current and the fringe wave current     

Fabrication of low-stress low-stiffness leveraged cantilever beam for bistable mechanism

This paper presents the fabrication and application of a leveraged cantilever beam with low-stress and low-stiffness. This cantilever beam is overhanged with two free ends and suspended in air by the supporting torsion flexures fixed at its middle. The teeterboard-typed cantilever features a low-stiffness with 1.63 N/m, and a low-stress with ±6.27 MPa. The cantilever beam was prepared by a laminated photoresist sacrificial layer process (LPSLP), that is, a multilayered photoresist film for supporting the suspended cantilever beams. In this work, two main problems related to microfabrication process were discussed. One is the control of residual stress in permalloy cantilever with varying the contents of additive saccharin to minimize the deformation of the free end of the beams. The other is an improved wet release method to avoid the adhesion or stiction of the all metal microstructures. The proposed leveraged cantilever beam has a potential application on the bistable switching mechanism in single-pole-double-through (SPDT) latching relay fields. Switching between two stable states of the microbeam mechanism was successfully validated with WYKO NT1100 optical profiling system.