Copper-encapsulated silicon micromachined structures

Selective copper encapsulation on silicon has been used to fabricate micromachined devices such as inductors with quality factors over 30 at frequencies above 5 GHz. The devices are fabricated using either polysilicon surface micromachining, or integrated polysilicon and deep reactive ion etching bulk silicon micromachining. Their exposed silicon surfaces are selectively activated by palladium activation, which allows the subsequent copper deposition on the activated silicon surfaces only. This silicon encapsulated-with-copper technique takes advantage of both the excellent mechanical properties of silicon (to maintain structural integrity), and the high conductivity of copper (for electrical signal transmission). Furthermore, the process not only minimizes interfacial forces typical of physical metal deposition on silicon, but also balances the forces by metal encapsulation on all sides of the silicon structures     

Multi-range silicon micromachined flow sensor

A new approach of enlarging the measurement range of a thermal calorimetric flow sensor is presented. It is based on the fact that the response of these kind of sensors tends to saturate at a certain flow ratio, so the widening of the flow range can be achieved by increasing the number of sensing elements of the sensor. This implies only a redesign of the flow sensor device, which is fabricated with an existing standard low cost technology. This approach has been implemented achieving measurement ranges from 0.1 up to 8 SLM by placing three different pairs of sensing resistors on the same membrane. Characterisation results and a simulation-based procedure to design flow sensors according to specific applications are included.     

一种扭摆式硅微机械加速度传感器

介绍了一种基于体硅微机电系统(MEMS)工艺制作的扭摆式硅微机械加速度传感器,对制作过程的一些工艺问题进行探讨,并提出相应的解决办法,主要涉及到硅-玻璃阳极键合、结构释放等关键工艺。对测试结果进行了初步分析,分辨力可以达到1mgn,测试±1gn范围内线性度可以达到99.99%。     

A monolithic three-axis micro-g micromachined silicon capacitive accelerometer

A monolithic three-axis micro-g resolution silicon capacitive accelerometer system utilizing a combined surface and bulk micromachining technology is demonstrated. The accelerometer system consists of three individual single-axis accelerometers fabricated in a single substrate using a common fabrication process. All three devices have 475-/spl mu/m-thick silicon proof-mass, large area polysilicon sense/drive electrodes, and small sensing gap (<1.5 /spl mu/m) formed by a2004 sacrificial oxide layer. The fabricated accelerometer is 7/spl times/9 mm/sup 2/ in size, has 100 Hz bandwidth, >/spl sim/5 pF/g measured sensitivity and calculated sub-/spl mu/g//spl radic/Hz mechanical noise floor for all three axes. The total measured noise floor of the hybrid accelerometer assembled with a CMOS interface circuit is 1.60 /spl mu/g//spl radic/Hz (>1.5 kHz) and 1.08 /spl mu/g//spl radic/Hz (>600 Hz) for in-plane and out-of-plane devices, respectively.     

一种高灵敏度硅微机械陀螺的设计与制造

设计与制造了一种高灵敏度的硅微机械陀螺。陀螺用静电来驱动,用连接成惠斯顿电桥的压阻式力敏电阻应变计来检测。主梁、微梁 质量块结构实现了高灵敏度。比较硬的主梁提供了一定的机械强度,并且提供了高共振频率。微梁很细,检测时微梁沿轴向直拉直压。力敏电阻应变计就扩散在微梁上,质量块很小的挠动就能在微梁上产生很大的应力,输出很大的信号。5V条件下,陀螺检测部分的理论灵敏度达到27.45mV/gn。压阻式四端器件用来监测驱动振幅,可以反馈补偿压阻的温度系数。检测模态的Q值达260使陀螺能在大气下工作。陀螺利用普通的n型硅片制造,为了刻蚀高深宽比的结构,使用了深反应离子刻蚀(DRIE)工艺。     

Experimental characterization of piezoelectrically actuated micromachined silicon valveless micropump

In this paper, performance of piezoelectrically actuated pyramidal valveless micropumps is studied experimentally in detail. Valveless micropumps based on silicon and glass substrate are fabricated using MEMS technology. Two different sizes of micropumps having overall dimensions of 5 mm × 5 mm × 1 mm and 10 mm × 10 mm × 1 mm are fabricated and characterized. In the fabricated micropumps, the thickness of silicon diaphragm is <20 µm which gives the advantage of operating pump at low voltage with excellent stability and consistency. The performance of micropumps in terms of flowrate and backpressure is evaluated for a wide range of driving frequency and actuating voltages. The maximum flowrate of water in the 10-mm micropump is 355 µl/min and backpressure of 3.1 kPa at zero flowrate for an applied voltage of 80 V at frequency 1.05 kHz. The reported micropumps have low footprint, high flowrate and backpressure. Thus, these micropumps are especially suited for biological applications as these can withstand adequate amount of backpressure. Comparative study of the performance of these micropumps with those available in the literature brings out the efficacy of these micropumps.     

静电激励硅微机械谐振压力传感器设计

设计了一种静电激励/电容检测的硅微机械谐振压力传感器,采用改进的侧向动平衡双端固支音叉谐振器,利用基于绝缘体上硅的加工工艺制作。为了抑制压力敏感膜片受压变形时谐振器的高度变化,在谐振器固定端设计了全新的桁架结构。针对传感器检测信号微弱和同频干扰严重的特点,在芯体和接口电路设计中采取添加屏蔽电极、降低交流驱动电压幅值、差动电容检测和高频载波调制解调方案等多项措施。同时基于该接口电路设计了开环测试系统,并在常压封装条件下对传感器进行了初步性能测试。实验结果表明:其基础谐振频率为33.886 kHz,振动品质因数为1222;测量范围为表压0~280 kPa,非线性为0.018%FS,迟滞为0.176%FS,重复性为0.213%FS;在-20~60℃的温度范围内,谐振器的平均温度漂移为-0.037%/℃。     

Laser bending of etched silicon microstructures

 The process of contactless laser bending using the laser induced thermal stresses that up to this moment is performed with steels and other metal alloys is firstly applied to silicon microstructural elements. One-side-fastened Si beams prepared by anisotropic wet etching were locally heated by a Nd:YAG laser. The beams were bent without additional tools towards the incident laser beam. Bending angles up to 90° are realizable. The degree of bending is strongly dependent on the used laser parameters, the position of heating and the number and distance of the laser scans. Received: 8 February 2000/Accepted: 12 April 2000     

On control of stresses in silicon web growth

It has been observed that the residual stresses and dislocations during the silicon crystal growth for photovoltaic applications are caused by thermal stresses. The temperatures along the boundaries of the silicon crystal ribbon are prescribed to meet the requirements of the crystal growth. It is shown that by allowing the temperatures to satisfy a second-order partial differential equation in the ribbon, all thermal stresses, and others induced by them, may be eliminated for the stress-free growth of the silicon crystal.     

Temperature compensation of micromachined silicon hot wire sensor using ANN technique

Temperature is one of the most important factors influencing accurate silicon sensor devices and is one of the largest sources of error in measurement. In this paper, a model based on Neural Networks (NN), has been implemented to generate fluid velocity data, knowing fluid temperature measurements. The proposed model based on neural networks can provide the calibrated response characteristics irrespective of change in the sensor characteristics due to change in ambient temperature. The NN-based sensor model automatically calibrates and compensates with high accuracy for the nonlinear response characteristics and nonlinear dependency of the sensor characteristics on the environmental parameters. Through extensive simulated experiments, we have shown that the NN-based silicon hot wire sensor model can provide flow speed readout with a maximum full-scale error of only 1.5% over a temperature range from 0 to 40°C for nonlinear dependencies.     

Optical detection of the Coriolis force on a silicon micromachined gyroscope

In this paper, we report on the optical characterization of a micromachined gyroscope prototype for automotive applications, by means of feedback interferometry. In order to directly detect the rotation-induced Coriolis force, we have developed a compact and stable interferometric setup, which has been positioned inside a small vacuum bell, mounted on a rotating table. By this setup, which has a noise limit of the order of 10/sup -11/ m/(Hz)/sup 1/2/, we have measured the gyro responsivity curve, demonstrating the feasibility of the optical interferometric detection of the in-plane response of a MEMS sensor. In addition, we have carried out the full mechanical characterization of the device at different pressures, and we have performed the matching of the gyro resonance frequencies by the interferometric monitoring. Our gyro had a resonance frequency of 3986 Hz for both axes after tuning; at a pressure of 7 10/sup -2/ torr, the quality factor were Q=18000 for the driving axis and Q=1800 for the sensing axis, while the measured responsivity was 7 10/sup -10/ m/(/spl deg//s). The optical characterization represents an important feedback to the designer and is especially powerful in the case of prototypes for which the on-board electronics is not yet available.     

ADINA analysis of large deflections and stresses in bending fatigue specimens

Laboratory tests of flapper valve steel bending fatigue specimens are compared to large deflection ADINA analyses based on the nine-node shell element. Three standard thicknesses, 1/100 in. (0.254 mm), 3/200 in. (0.381 mm) and 1/50 in. (0.508 mm), are investigated. Both the longitudinal and the anticlastic curvatures could be brought into good agreement with experiment through proper modelling of the grip section by bakelite brick elements in sandwich form. The calculated stress maxima are observed in the specimen edge region. This result is consistent with observations that fracture initiation usually occurs in that region.     

A static turbine flow meter with a micromachined silicon torque sensor

A new class of flow sensors is introduced where a static turbine converts the volume flow into a torque. The structure consists of a turbine fixed to a torque sensor, which in turn is connected to the pipe wall giving a perfectly symmetric, bidirectional flowmeter. In contrast to conventional turbine flowmeters, the wheel does not rotate and consequently it is insensitive to bearing friction and wear that conventional, rotating turbines experience. Furthermore, the flow passing the wheel is distributed over the circumference of the wheel and levels out nonuniform flow profiles leading to profile independent volumetric flow measurement. The torque-sensing element is a 300-/spl mu/m-thick silicon cantilever, 2 mm wide and 16 mm long. The stiffness of the torque sensor, and thereby the sensitivity, is mainly determined by lateral dimensions of specially designed stiffness reduction parts defined by photolithography, thus giving good control of the sensitivity. Two polysilicon strain gauges are placed on each side of the cantilever, measuring the bending moment from the turbine wheel. The torque sensor has been evaluated for different geometries and together with the turbine to evaluate the flow sensing performance. A turbine with a blade length of 2.7 mm and a blade angle of 30/spl deg/ has a sensitivity of 4.0 /spl mu/V/V/(1/min)/sup 2/ when measured using the silicon torque sensor. The output signal shows good symmetry between different flow directions.     

Novel fabrication method for surface micromachined thin single-crystal silicon cantilever beams

This paper describes a novel technique for the fabrication of surface micromachined thin silicon cantilever beams using merged epitaxial lateral overgrowth (MELO) of silicon and chemical-mechanical polishing (CMP). The objective is to demonstrate the feasibility of using this novel technique for the fabrication of arrays of ultrathin, low-stress, single-crystal silicon cantilever beams for use in ultrahigh sensitivity surface-stress or resonant-frequency-based chemical or biological detection schemes. The process flow used in this work is described in detail and the issues that were faced during the fabrication are discussed. Cantilever beams with thickness of 0.3-0.5 /spl mu/m that were 10-25-/spl mu/m wide and 75-130-/spl mu/m long were fabricated. Mechanical characterization of the cantilever beams were performed by measuring their spring constant using the "added mass" method, which also demonstrated the use of these initial structures to detect masses as low as 10-100 pg. Further work is underway to scale the thickness of these beams down to the sub-100-nm regime.     

Electrochemically driven polypyrrole bilayers for moving andpositioning bulk micromachined silicon plates

The conjugated polymer polypyrrole undergoes a volume change of several percent when its oxidation state is changed electrochemically by the application of voltages between 0 and -1 V (versus Ag/AgCl). This volume change is due to ion movements in or out of the polymer film. Bilayers of polypyrrole and gold undergo a large bending and can deliver high force. They can thus function as hinges to lift rigid components. In this work, we demonstrate that silicon plates produced by reactive ion etching can be lifted by such PPy/Au hinges. The strength and efficiency of these bilayers are also determined     

Improved design of a silicon micromachined gyroscope withpiezoresistive detection and electromagnetic excitation

In this paper, an improved design of a silicon micromachined gyroscope (angular rate sensor) is presented. It is based on the tuning fork principle and realized by combining two proof masses. The gyroscope is driven by electromagnetic forces and detects the Coriolis force by means of four piezoresistors connected in a Wheatstone bridge. The main fabrication steps including advanced deep reactive ion etching (ADRIE) and a wafer scale packaging are reported. The major novelty consists in a new design to reduce output drift. Both a higher symmetric mechanical structure and a separation of the first and the second mechanical resonant frequencies have been successfully investigated. This allows both driving and sensing of the device at its first resonant frequency while not exciting the second one. Thus, better uncoupling between the sensor modes has been obtained. As main results, a bandwidth of 10 Hz has been achieved and long-term measurements have been performed which were not possible with the previous design due to the low stability of the zero rate signal. For the current design, the dynamic behavior, the temperature dependence, rotation measurement, and the sensor stability have been characterized     

Pressure nonlinearity of micromachined piezoresistive pressure sensors with thin diaphragms under high residual stresses

Thermal residual stress plays a significant role in the performance of microelectromechanical system (MEMS) pressure sensor devices. For example, the voltage span and pressure nonlinearity (PNL) on the voltage output of a pressure sensing element can be significantly affected by the residual stresses of passivation films on the silicon diaphragm. The objective of this study is to resolve a pressure nonlinearity problem in terms of silicon nitride residual stress and diaphragm thickness in order to meet the PNL design criteria within ±3% at 25 °C. The curvatures of wafers were measured and the film residual stresses were calculated. Finite element analyses (FEA) were conducted and correlated with the PNL experimental tests. To build a design window for optimization, a central composite design (CCD) method was utilized to significantly reduce the number of FEA runs. It is concluded that the residual stress of PECVD silicon nitride needs to be optimized and controlled in order to reduce the pressure nonlinearity.     

BICEPS: a modular environment for the design of micromachined silicon devices

An environment for the design of micromachined silicon devices (BICEPS) is presented, which is based on a 3D simulation module for silicon anisotropic etching. The simulation data are transformed into a volume model used in finite element analysis. The environment employs an object-oriented geometric modelling interface serving as the basis of a product model which centrally stores the data of the whole design process. The design process is controlled by the workflow management of the Lean Integration Platform (LIP), which allows the easy definition of domain-specific design processes. With the help of an example, the design process using BICEPS is demonstrated.     

电容式微机械加速度计测量范围上限设计

测量范围上限设计一直是高gn值微惯性引信研制的一个难题,对差动电容式微加速度计各参数对量程的本质影响及其相互关系进行了研究,理论分析和计算机仿真结果表明:按同一比例尽量减小封装间隙和电极面积,使得受限于临界偏压的外加偏压取值刚好能提供需要的量程,同时使用质量块减薄和打孔并用的方法来提高最大量程,所设计出的加速度计可具有70gn以上量程。     

Two-dimensional stress measurement of a micromachined piezoresistive structure with micro-Raman spectroscopy

This paper describes the stress characterization of a cantilever structure of a piezoresistive microflowmeter using micro-Raman spectroscopy. In order to obtain the relationship between the stress and the shift of Raman frequency, the mechanical stress in the structure was assumed to be uniaxial according to the applied loading and the boundary conditions. Also, the two-dimensional stress distribution of the structure was simulated using a finite element tool (ABAQUS v6.2). The experimental results agree well to those predicted by the finite element simulation. It is concluded that micro-Raman spectroscopy is an accurate, non-destructive technique for measuring Microelectromechanical systems (MEMS) local stress with micrometer spatial resolution.The supports from the Key Project from the Chinese Academy of Sciences (No. KJCX2-SW-L2), projects from the National Natural Science Foundation of China (Nos. 10225209, 50131160739 and 90305020), the National 973 project (No. G1999033103), and the Joint Laboratory of Microsystems between the Institute of Mechanics (CAS) and HKUST are gratefully acknowledged.