基于硅塑性变形的蛇形梁垂直梳齿驱动器

设计了基于硅塑性变形的垂直梳齿驱动器,中央可动微镜由四组蛇形曲折梁支撑。驱动器的制作采用硅—硅键合技术,首先利用DRIE干法刻蚀技术释放可动梳齿与固定梳齿,然后通过各向异性湿法腐蚀制作的施压凸台实现可动梳齿和固定梳齿的精确自对准,最后利用硅塑性变形使可动梳齿和固定梳齿在垂直方向上产生位错,成功制作出在Z方向依靠位错梳齿实现垂直驱动的蛇形梁静电梳齿驱动器。     

硅微陀螺仪的误差分析

以z轴硅微陀螺仪为研究对象,对加工误差产生的误差信号进行了分析.由于加工误差,使得陀螺仪结构不对称,主要表现为支承梁不对称、梳齿间距不等,产生了不等弹性、阻尼不对称以及力不平衡这三种现象.以动力学方程为基础,分析了不等弹性和阻尼不对称产生的误差信号;以静电理论为基础,分析了驱动梳齿和敏感梳齿间距不等时产生的误差信号.分析结果表明,这些误差信号包含了正交耦合误差和与有用信号同相位的误差信号.最后,介绍了一种减小正交误差的方法,并进行了仿真.     

Fabrication of a rotary micromirror for fiber-optic switching

The implementation of all-optical telecommunication networks requires more efficient optical-to-optical wavelength routing devices to replace the conventional optical-to-electrical cross connects. In this paper, we demonstrate a novel rotary micromirror for directly fiber-optic switching. To fabricate this electrostatically actuated rotary micromirror, a very simple micromachining process has been developed using SOI wafer and DRIE technology. Based on this one-mask process, all the components for an NxN cross-connect with 2N-switch-architecture can be fabricated on a monolithic silicon substrate, including the optic fiber couplers, electrostatic comb drives and reflective vertical mirror arrays.     

Surface/bulk micromachined single-crystalline-siliconmicro-gyroscope

A single-crystalline-silicon micro-gyroscope is fabricated in a single wafer using the recently developed surface/bulk micromachining (SBM) process. The SBM technology combined with deep silicon reactive ion etching allows fabricating accurately defined single-crystalline-silicon high-aspect-ratio structures with large sacrificial gaps, in a single wafer. The structural thickness of the fabricated micro-gyroscope is 40 μm, and the sacrificial gap is 50 μm. For electrostatic actuation and capacitive sensing of the developed gyroscope, a new isolation method which uses sandwiched oxide, polysilicon, and metal films, is developed in this paper. This triple-layer isolation method utilizes the excellent step coverage of low-pressure chemical vapor deposition polysilicon films, and thus, this new isolation method is well suited for high-aspect-ratio structures. The thickness of the additional films allows controlling and fine tuning the stiffness properties of underetched beams, as well as the capacitance between electrodes. The noise-equivalent angular-rate resolution of the SBM-fabricated gyroscope is 0.01°/s, and the bandwidth is 16.2 Hz. The output is linear to within 8% for a ±20°/s range. Work is currently underway to improve these performance specifications     

The surface/bulk micromachining (SBM) process: a new method forfabricating released MEMS in single crystal silicon

This paper presents the surface/bulk micromachining (SBM) process to allow fabricating released microelectromechanical systems using bulk silicon. The process starts with a (111)-oriented silicon wafer. The structural patterns are defined using the reactive ion etching technique used in surface micromachining. Then the patterns, as well as sidewalls, are passivated with an oxide film, and bare silicon is exposed at desired areas. The exposed bare silicon is further reactive ion etched, which defines sacrificial gap dimensions. The final release is accomplished by undercutting the exposed bulk silicon sidewalls in aqueous alkaline etchants. Because {111} planes are used as etch stops, very clean structural surfaces can be obtained. Using the SBM process, 5-, 10-, and 100-μm-thick arbitrarily-shaped single crystal silicon structures, including comb-drive resonators, at 5-, 30-, and 100-μm sacrificial gaps, respectively, are fabricated. An electrostatic actuation method using p-n junction isolation is also developed in this paper, and it is applied to actuate comb-drive resonators. The leakage current and junction capacitance of the reversed-biased p-n junction diodes are also found to be sufficiently small for sensor applications. The developed SBM process is a plausible alternative to the existing micromachining methods in fabricating microsensors and microactuators, with the advantage of using single crystal silicon     

A self-aligned fabrication method of dual comb drive using multilayers SOI process for optical MEMS applications

A novel method for fabricating a self-aligned electrostatic dual comb drive using a multi-layer SOI process is developed. The present method utilizes four aligned masks, greatly simplify the existing SOI-MEMS fabrication methods in manufacturing optical MEMS devices. Here, the actuating structure consists of fixed combs and moving combs that are composed of single crystal silicon, nitride and polysilicon. One mask is used to provide a deep etching to etch polysilicon, nitride and single crystal silicon respectively. The nitride separates polysilicon and single crystal silicon and provides an additional dielectric for the purpose of producing bi- directional motion upon applying electrostatic forces. A dual comb drive actuator with optical structures was fabricated with the developed process. The actuator is capable of motion 250 nm downward and 480 nm upward with 30 V applied voltage at 4 kHz frequency. The dynamic characteristics of the first and the second resonant frequency of the dual comb-drive actuator are 10.5 kHz and 23 kHz respectively. Experimental results indicated that the measured data agreed well with simulation results using the ANSOFT Maxwell^® 2D field simulator, ANSYS^® and Coventor Ware^®.     

Silicon micro-cantilever chemical sensors fabricated in double-layer silicon-on-insulator (SOI) wafer

Micro-cantilever piezoresistive sensors are optimally designed and fabricated in a double-layer silicon-on-insulator (SOI) wafer. The sensor geometry is optimized by placing the sensing piezoresistor at the cantilever root region to increase effective piezoreisistive sensing area. According to finite-element simulation results, high sensitivity can be obtained by design the cantilever into a wide and short shape. In order to use single-crystalling silicon to fabricate both the cantilever and the piezoresistor for high sensitivity, double-layer SOI wafer, which has two active layers and two insulating layers, is proposed to fabricate the self-sensing micro-cantilever sensor. The piezoresistor is made of the top active-layer single-crystalline silicon. Without p–n junction isolation, such a piezoresistor can be free from leakage-current relative noise that helps to achieve fine sensing resolution. The bottom active-layer is used to form the cantilever, with well controlled cantilever thickness and high fabrication yield. With the top surface of the micro-cantilever is modified with the functionalized self-assembled monolayer, detection of trace-concentration Trinitrotoluene (TNT) vapor is experimentally carried out, with reproducible sensing response to 7.6 ppb TNT.     

Fabrication and characterization of DRIE-micromachined electrostatic microactuators for hard disk drives

In this paper, deep micromachined three-dimensional (3-D) electrostatic microactuators used for dual-stage positioning system of hard disk drives are reported. Actuators with parallel-arranged comb drives enhance the electrostatic driving force. By using proper flexures, secondary stage actuators will drive the magnetic head with fast response and high accuracy. Fabrication of the actuators starts with a 200-μm-thick n-type silicon wafer, and it is subsequently bonded to a Pyrex glass substrate, which can be called silicon-on-glass process. This process is more cost-effective than the SOI wafer process, and the high aspect ratio structures with large thickness also provide good strength and reliability for the microactuators. Deep RIE and wafer bonding techniques were utilized to fabricate the electrostatic actuators. The fabricated actuators were statically and dynamically characterized for three different designs of straight-flexures, folded-flexures and quad-flexures with bandwidth of 7.15, 5.85 and 15.85 kHz, respectively. With proper designed flexures, the proposed microactuators would fulfill the requirements of the dual-stage servo of hard disk drives.     

几种基于MEMS的纳米梁制作方法研究

特征尺度在纳米量级的梁结构是多种纳机电器件的基本结构.提出了几种基于MEMS技术的纳米梁制作方法,通过利用MEMS技术中材料与工艺的特性实现单晶硅纳米梁的制作.在普通(111)硅片上,利用各向异性湿法腐蚀对(111)面腐蚀速率极低的特性,通过干法与湿法腐蚀相结合制成厚度在100 nm以下的纳米梁.该方法不使用SOI硅片,有效控制了成本.在(100)SOI硅片上,通过氧化减薄的方法得到厚度在100 nm以下的多种纳米梁,由于热氧化的精度高,一致性好,该方法重复性与一致性均较好.在(110)SOI硅片上,利用硅的各向异性腐蚀特性以及(110)硅片的晶向特点,制作宽度在100 nm以下的纳米梁,梁的两个侧面是(111)面.     

Two-Dimensional MEMS Scanner for Dual-Axes Confocal Microscopy

In this paper, we present a novel 2-D microelectromechanical systems (MEMS) scanner that enables dual-axes confocal microscopy. Dual-axes confocal microscopy provides high resolution and long working distance, while also being well suited for miniaturization and integration into endoscopes for in vivo imaging. The gimbaled MEMS scanner is fabricated on a double silicon-on-insulator (SOI) wafer (a silicon wafer bonded on a SOI wafer) and is actuated by self-aligned vertical electrostatic combdrives. Maximum optical deflections of plusmn4.8deg and plusmn5.5deg are achieved in static mode for the outer and inner axes, respectively. Torsional resonant frequencies are at 500 Hz and 2.9 kHz for the outer and inner axes, respectively. The imaging capability of the MEMS scanner is successfully demonstrated in a breadboard setup. Reflectance images with a field of view of are achieved at 8 frames/s. The transverse resolutions are 3.94 mum and 6.68 mum for the horizontal and vertical dimensions, respectively.     

基于BOE硅腐蚀现象的硅纳米线制作

介绍一种硅纳米线制作方法.在SOI顶层硅上制作硅纳米梁,通过离子注入形成pnp结构,利用新发现的没有特殊光照时BOE溶液腐蚀pn结n型区域现象,结合BOE溶液氧化硅腐蚀,实现硅纳米线制作.制作完全采用传统MEMS工艺,具有工艺简单,成本低,可控,可靠性好,可批量制作等优点.利用该方法制作出了厚50 nm,宽100 nm的单晶硅纳米线,制作的纳米线可用于一维纳米结构电学性能研究、谐振器研究等.     

The SOI DAWN process for three-dimensional silicon micromachining and its applications

A DRIE assisted wet anisotropic bulk micromachining (DAWN) process is demonstrated to fabricate various three-dimensional MEMS devices on a silicon-on-insulator (SOI) wafer. This SOI DAWN process can realize thin film structures, reinforced (thin film) structures, and thick structures with totally different mechanical characteristics. Various passive and active mechanical components, including flexible springs, rigid structures, and actuators, have been fabricated using the SOI DAWN process and have been further integrated to create MEMS devices which are flexible as well as movable in both in-plane and out-of-plane directions. This SOI DAWN process has been successfully applied to produce various multi-DOF devices made of single crystal silicon (SCS).     

Porous silicon bulk micromachining for thermally isolated membrane formation

A novel low thermal budget technique is proposed for the preparation of thermally isolated silicon membranes. The selective formation of porous silicon in a p-type silicon wafer results in an undercut profile below the implanted n-type silicon regions. The sacrificial porous layer is subsequently removed in a dilute KOH solution. A non-stoichiometric LPCVD nitride layer combination forms the suspension of the single-crystalline silicon membranes. This technique eliminates the need for epitaxial substrates and backside alignment, and proves to be very efficient in the realization of a high-temperature micro-hotplate operating with minimum power consumption for the purpose of integrated gas sensors.     

Simple Fabrication Process for Self-Aligned, High-Performance Microscanners— Demonstrated Use to Generate a 2-D Ablation Pattern

A new, straightforward, complementary metal-oxide-semiconductor (CMOS)-compatible, three-mask process is used to fabricate high-performance torsional microscanners driven by self-aligned, vertically offset comb drives. Both the moving and fixed combs are defined using the same photolithography mask and fabricated in the same device layer, a process allowing the minimum gap between comb fingers to be as small as twice the alignment accuracy of the photolithography process. Our fabricated microscanners have torsional resonant frequencies between 58 Hz and 24 kHz and maximum optical-scanning angles between 8deg and 48deg with actuation voltages ranging from 14.1 to 67.2 V_ac-rms. The yields on two separate fabrication runs have been better than 70%. To demonstrate an application for these scanners, we used them to generate laser-ablation patterns suitable for ocular cornea surgery. We assembled a 2-D scanning system by orienting two identical microscanners at right angles to one another. When driven by two 90deg out-of-phase 6.01-kHz sine waves, the cross-coupled scanners produce circular patterns having radii fixed by the amplitude of the driving voltage. Then, we emulated a small pattern from the surface topography found on a U.S. Roosevelt dime and built up an ablation pattern that compares favorably with similar emulations reported by earlier researchers who used larger, more complicated ablation systems     

Fabrication of a freestanding micro mechanical structure using electroplated thick metal with a HAR SU-8 mold

In this thesis, fabrication technology of a freestanding micro mechanical structure using electroplated thick metal with a high-aspect-ratio SU-8 mold was studied. A cost-effective fabrication process using electroplating with the SU-8 mold was developed without expensive equipment and materials such as deep reactive-ion etching (DRIE) or a silicon-on-insulator (SOI) wafer. The process factors and methods for the removal of SU-8 were studied as a key technique of the thick metal micro mechanical structure. A novel method that removes cross-linked SU-8 completely without leaving remnants of the resist or altering the electroplated microstructure was utilized. The experimental data pertaining to the relationship between the geometric features and the parameters of the removal process are summarized. Based on the established SU-8 removal process, an electroplated nickel comb structure with high-aspect-ratio SU-8 mold was fabricated in a cost-effective manner. In addition, a freestanding micro mechanical structure without a sacrificial layer was successfully realized. The in-plane free movements of the released freestanding structure are demonstrated by electromagnetic actuation. This research implies that various types of MEMS devices can be developed at a low-cost with design flexibility.     

微陀螺静电力调频的快速收敛算法研究

针对电容式微陀螺谐振结构,研究了静电力对谐振频率的影响规律,提出了一种快速收敛的静电力调频算法,建立了微陀螺调频实验系统,该系统采用扫频方法测量谐振频率,利用计算机控制调频收敛过程,并对微陀螺进行了调频实验,调频过程用时少于5分钟,实验结果表明该调频算法具有较快的收敛速度。     

Polymer microstructure generated by laser stereo-lithography and its transfer to silicon substrate using reactive ion etching

Micro-fabrication combining stereo-lithography with reactive ion etching is proposed. Three-dimensional polymer structures smaller than 1 mm are fabricated on silicon wafer by He-Cd (325.0 nm) laser stereo-lithography. Using the polymer structure having a high-aspect ratio as resist for deep reactive ion etching, the microstructure is transferred to the silicon substrate with an etching ratio of 0.5. The proposed technique has been demonstrated by the fabrication of lens-like structures.     

A single-layer PDMS-on-silicon hybrid microactuator with multi-axis out-of-plane motion capabilities-Part i: design and analysis

This paper proposes a new single-layer electrostatic microactuator design that generates three-axis motion resulting in vertical translation and out-of-plane tilting. The new actuator design combines a micrometer-scale three-dimensional (3-D) polydimethylsiloxime (PDMS) structure fabricated using soft lithography with comb drives processed using a single mask on a silicon-on-insulator (SOI) wafer. The multi-axis actuation capability of the proposed actuator is enabled by coupling the in-plane actuation motion of the comb drives with the elastic bending of PDMS flexural microjoints. To predict the static and dynamic performance of the actuator, this paper develops a four-bar-linkage model and applies Lagrangian dynamics theory. The developed analytical model is validated using finite element analysis (FEA) and allows us to perform parametric design of the actuator. The analysis indicates that the proposed PDMS-on-silicon hybrid actuator can yield the desired multi-axis actuation capability with a dynamic bandwidth as large as 5 kHz.     

A study of an autonomous mobile robot in an outdoor environment

This paper describes an experimental study of the fabrication of micro-mechanisms on a silicon wafer. Planar process technology developed in the industry of CMOS LSI was employed. The structural material is CVD-polycrystalline silicon with a thickness of 2.5 μm and the sacrificial material is CVD-SiO₂ with a thickness of 1.0 μm. In the experimental study, micro-rotors with a shaft and a cap in an assembled form were fabricated on a silicon wafer. The self-alignment process gave a tolerance of 1.0 μm between the rotor and the shaft. The maximum rotation speed observed was 9 x 10⁴ rpm by blowing nitrogen gas.