方膜上横向压阻压力传感器的非线性研究

本文对方膜的硅压力传感器结构进行了应力非线性的计算分析,得出了应力-压力关系非线性与压力量程、膜的几何参数以及器件位置的关系,并给出了实现线性最佳化设计的结果.实验与理论结果的比较表明:(1)压阻效应非线性很小,压力传感器的非线性主要决定于应力非线性;(2)方膜边缘的四端力敏电阻设计不仅灵敏度高,而且有较好的线性;(3)进一步改进压力传感器精度的方法是选用应力线性优良的结构.     

Slotted capacitive microphone with sputtered aluminum diaphragm and photoresist sacrificial layer

In this paper, we have fabricated a new microphone using aluminum (Al) slotted perforated diaphragm and back plate electrode, and photoresist (AZ1500) sacrificial layer on silicon wafer. The novelty of this method relies on aluminum diaphragm includes some slots to reduce the effect of residual stress and stiffness of diaphragm for increasing the microphone sensitivity. The acoustic holes are made on diaphragm to reduce the air damping, and avoid the disadvantages of non standard silicon processing for making back chamber and holes in back plate, which are more complex and expensive. Photoresist sacrificial layer is easy to deposition by spin coater and also easy to release by acetone. Moreover, acetone has a high selectivity to resist compared to silicon oxide and Al, thus it completely removes sacrificial resist without incurring significant damage silicon oxide and Al. The measured zero bias capacitance is 17.5 pF, and its pull-in voltage is 25 V. The microphone has been tested with external amplifier and speaker, the external amplifier was able to detect the sound waves from microphone on speaker and oscilloscope. The maximum amplitude of output speech signal of amplifier is 45 mV, and the maximum output of MEMS microphone is 1.125 μV.     

Enhancing displacement of lead-zirconate-titanate (PZT) thin-film membrane microactuators via a dual electrode design

A common design of piezoelectric microactuators adopts a membrane structure that consists of a base silicon diaphragm, a layer of bottom electrode, a layer of piezoelectric thin film, and a layer of top electrode. In particular, the piezoelectric thin film is often made of lead-zirconate-titanate (PZT) for its high piezoelectric constants. When driven electrically, the PZT thin film extends or contracts flexing the membrane and generating an out-of-plane displacement. Many manufacturing defects, however, could significantly reduce the designed actuator displacement. Examples include residual stresses, warping, non-uniform etching of the silicon diaphragm, and misalignment between the top electrode and the silicon diaphragm. The purpose of this paper is to develop a dual top-electrode design to enhance the actuator displacement. In this design, the top electrode consists of two disconnected (thus independent) electrode areas, while a continuous bottom electrode serves as the ground. The two top electrodes are located in two regions with opposite curvature when the diaphragm deflects. When the two top electrodes are driven in an out-of-phase manner, the actuator displacement is enhanced. Finite element analyses and experimental measurements both confirm the feasibility of this design. When manufacturing defects are present, experimental results indicate that the actuator displacement can be optimized by adjusting the phase difference between the dual top electrodes.     

Calibration of residual stress difference of MetalMUMPs silicon nitride films

The metal multi-user MEMS processes (MetalMUMPs) provide one nickel film, two silicon nitride films and one polysilicon film for constructing various nickel MEMS devices. The two silicon nitride films are either bonded together as a bi-layered structure or they sandwich the polysilicon film to form a tri-layered structure to support nickel structures. The residual stress difference of the two silicon nitride films causes undesired deformations of suspended MetalMUMPs devices. In this paper, the residual stress difference of the two MetalMUMPs silicon nitride thin films is calibrated and the result is 169 MPa. The Young’s modulus of the MetalMUMPs nitride films is also measured, which is 209 GPa.     

一种大量程SOI压阻式压力传感器

对传统的SOI压阻式压力传感器进行了结构优化。目的是提高灵敏度,以满足在高温环境下大量程压力测量的实际需求。通过力学性能模拟,采用浅凸台结构来提高灵敏度和测量范围。分析并模拟了凸台厚度和形状对灵敏度的影响。得到了适合高温工作的掺杂浓度,压敏电阻的尺寸,金属引线的材料和布局。电阻放置在(σl-σt)最大的区域以保持灵敏度和线性度。采用U形电阻补偿在浅凸台制作过程中的工艺偏差对灵敏度的影响。有限元分析(FEA)表明,优化后的芯片结构可以测量10 MPa范围内的压力,灵敏度高达86.6 mV/(V·MPa),非线性误差在0.1％以下。和其他文献报道的大量程压力传感器相比,浅凸台芯片结构灵敏度和过载能力优异。     

A silicon test chip for the thermomechanical analysis of MEMS packagings

This paper reports on a method for the investigation of mechanical stress on MEMS sensor and actuator structures due to packaging processes. A silicon test chip is developed and manufactured to validate the simulation results. Finite element analysis (FEA) is used to optimize the geometric parameters and to find a stress sensitive sensor geometry. A diaphragm structure is used as mechanical amplifier for bulk induced stresses during the packaging process. Piezo resistive solid state resistors are doped into the surface of the chip to measure the stress in the diaphragms and at the contact pads being most significant locations for analysis. A high precision ohmmeter was used to measure the resistance prior and past the packaging process. The captured data allows for computation of the resulting stress loads in magnitude. Therefore, a stress evaluation of different packaging technologies is conducted and the impact of the packaging process on reliability can be estimated immediately.     

Identification of material and geometrical parameters for microstructures by dynamic finite element model updating

This paper describes a procedure to identify material and geometrical parameters for microstructures using the concept of finite element model updating. This scheme utilizes measured and finite element analysis (FEA) natural frequencies that are paired together according to their mode shapes, and it incorporates an optimization sequence that formulates the frequency differences as an error vector to be minimized. To demonstrate the effectiveness of the proposed procedure, two examples are shown in this paper. One example involves a microcantilever fabricated from a single-crystalline silicon wafer, and the updating process is applied on the cantilever to identify its Young’s modulus. The identified Young’s modulus (along <100> direction) of 130.29 GPa is very comparable to those in the literature. The other example concerns a commercial, V-shaped silicon nitride probe used in an atomic force microscope. The natural frequencies and mode shapes of the probe are measured, the FEA performed, and the probe thickness and the Young’s modulus of the silicon nitride substrate determined. The identified thickness is also verified by SEM images of the probe. Both examples show that the updating procedure converged in just a few iterations.     

Parametric study of flip-chip packaging for an MEMS device with diaphragm

A backside-etched silicon chip with a polysilicon diaphragm flip-chip attached on a printed wiring board and globally bumped on a FR4 printed circuit board was investigated through a finite element analysis for determining three key parameters of flip-chip chip size packaging, namely, the size of solder bump, and the thickness of the printed wiring board with/without U8437-3 underfill. Four kinds of thermal-induced stresses and deformations in the diaphragm, solder bump, and printed wiring board were evaluated for the parametric study. As the simulation results show, the thermal-induced stresses in the diaphragm and solder bump can be reduced effectively if the printed wiring board is thinner. However, the printed wiring board is still required to be sufficiently thick to prevent warping. In addition, the underfill material also can reduce the induced stress occurring at the interface between the solder joint and the chip and improve reliability. In general, the parametric study can provide a basis for the flip chip package of a MEMS device with a diaphragm, such as a MEMS microphone, MEMS pressure sensor, etc.     

一种基于MEMS技术的压电微泵的研究

介绍了一种基于MEMS技术的压电微泵。该微泵利用聚二甲基硅氧烷(PDMS)作为泵膜,使用了一个主动阀和一个被动阀,并利用压电双晶片作为驱动部件。压电双晶片和PDMS泵膜的组合可以产生较大的泵腔体积改变和压缩比,显著降低了加工成本,并提高了成品率。对压电微泵的输出流量进行了测试,结果显示:电压、频率以及背压对流量均有显著影响。在100 V,25Hz的方波驱动下,该压电微泵的最大输出流量为458μL/m in,最大输出压力为6 kPa。     

A novel high sensitive MEMS intraocular capacitive pressure sensor

This paper presents a novel high sensitive MEMS capacitive pressure sensor that can be used as a part of LC tank implant circuit for biomedical applications. The pressure sensor has been designed to measure pressures in the range of 0–60 mmHg that is in the range of intraocular pressure sensors. Intraocular pressure sensors are important in detection and treatment of an incurable disease called glaucoma. In this paper two methods are presented to improve the sensitivity of the capacitive pressure sensor. First low stress doped polysilicon material is used as a biocompatible material instead of p++silicon in previous work (Gu in Microfabrication of an intraocular pressure sensor, M.Sc Thesis, Michigan State University, Department of Electrical and Computer Engineering, 2005) and then some slots are added to the poly Si diaphragm. The novelty of this research relies on adding some slots on the sensor diaphragm to reduce the effect of residual stress and stiffness of diaphragm. The slotted diaphragm makes capacitive pressure sensor more sensitive that is more suitable for measuring intraocular pressure. The results yield a sensor sensitivity of 1.811 × 10^?5 for p++silicon clamped, 2.464 × 10^?5 1/Pa for polysilicon clamped and 1.13 × 10^?4 1/Pa for polysilicon slotted diaphragm. It can be seen that the sensitivity of the sensor with slotted poly Si diaphragm increased 6.2 times compared with previous work (clamped p++silicon diaphragm).     

Study of symmetric microstructures for CMOS multilayer residual stress

This study presents a fabrication-based approach to improve the curl-up effect in complementary metal oxide semiconductor (CMOS) multilayer large-area planar structures. Control of the residual stress of CMOS multilayer microstructures is necessary for development of microelectromechanical systems (MEMS) sensors such as accelerometers and micromirrors. In this work, 3D symmetric geometry can be used to overcome effectively the residual stresses in CMOS multilayer microstructures. To demonstrate this concept, a symmetric multilayer flat-plane is fabricated and release-etched using an isotropic plasma etching process. The isotropic etch characteristics and lateral undercut can be controlled using a chamber pressure of 0.47 ± 0.2 Torr. A flat-plane structure with an area of 500 μm × 500 μm is fabricated using multilayer materials, including four metal and three silicon dioxide layers. Based on this approach, the measured results show the residual stress effect can be minimized in CMOS multilayer microstructures, and furthermore the curl-up effect of flat-plane is less than 2 μm across the 500 μm × 500 μm area.     

微型应变传感器的设计与制造

把压敏电阻敏感元件、温度补偿电路和高电平放大器,在硅片上采用集成技术制成微型应变传感器,它有电压及频率两种形式的输出。给出了该传感器的设计、制造和测试结果。这种传感器也可以做压力传感器使用,不过在设计几何布局和制造处理上略有不同。     

Thermal stresses on membrane based microdevices

We developed a closed form analytical solution for thermal stresses on membrane based “released” MEMS devices. As all the layers forming the membrane has thicknesses close to one another, the assumption of having thick substrate fails. We employed stress superposition principles to obtain the intrinsic stresses caused by coefficient of thermal expansion (CTE) mismatch of the membrane layers. We also accounted for the membrane release. We illustrated that for a bilayer strip consisting of a thin film on a thick substrate, our formulation simplifies to the well-known Stoney equation. The results indicate that the thermal stress can be minimized by the appropriate choice of dielectric materials, metal electrode selections and deposition tools. Replacing the silicon nitride (Si₃N₄) layer deposited by low pressure chemical vapor deposition (LPCVD) with a silicon oxide (SiO₂) layer deposited by plasma enhanced chemical vapor deposition (PEVCD) reduces the average thermal stress by 93%.     

Smart ultrasonic sensors systems: potential of aluminum nitride thin films for the excitation of the ultrasound at high frequencies

We investigated the potential of the aluminum nitride films to excite ultrasonic waves at frequencies >50?MHz. The deposition process of the aluminum nitride thin film layers on silicon substrates was investigated and optimized regarding their piezoelectric behavior. Large single element transducers were deposited on silicon substrates with aluminum electrodes, under different parameters for the magnetron sputter process, like pressure and bias voltage. Special test setup and a measuring station were created to characterize the sensors. Acoustical measurements were carried out in pulse echo mode up to 500?MHz and the values of piezoelectric charge constant (d₃₃) were determined. As a result, two parameter sets were found for the sputtering process to obtain an excellent piezoelectric charge constant of about 7.2?pC/N maximum. Then the sputtering process with these parameters was used to deposit sensors on various substrate materials and with different electrode sizes.     

A new transparent Bio-MEMS for uni-axial single cell stretching

A novel, completely transparent bio-MEMS (bio-Micro Electro Mechanical System) device has been devised and manufactured using finite element analysis (FEA) and micro-fabrication techniques. The device has been designed to be used for testing the mechanical properties of single living cells, it is versatile and suitable for coupling with other analysis techniques. Furthermore, being completely transparent, it can be used with either transmission or reflection microscopes. The transparent bio-MEMS is based on a silicon dioxide–silicon nitride structure and, since the main goal is to test living cells, it is meant to work in a liquid environment and allow for cell stretching. Sensors for cell deformation and for platform displacement are also present and the required sensitivity for single cell analyses is granted. The device will moreover allow the recording of the stress–strain curve for single living cells.

     

工业化硅微机械电容式麦克风的设计与性能计算

给出了一种单芯片硅微机械电容式麦克风的结构设计,并针对此结构对其进行了动态特性分析计算。硅微机械电容式麦克风的两个电极由一个复合敏感膜和一个金属铜底板构成。复合敏感膜包括三层,中间一层是掺杂硼的多晶硅,上下两层是氮化硅,三层复合膜的厚度设计和制作工艺使复合膜处于轻微的拉应力状态。底板采用低温电镀铜技术制作,底板上分布有许多圆形通气孔来调节敏感膜与底板间的空气压膜阻尼。在复合敏感膜和金属铜底板之间采用牺牲层技术制作了一空气间隙,使复合敏感膜和一个金属铜底板之间构成一工作电容。在硅基体的背面采用湿法腐蚀出声音进口腔。针对这一结构我们对其动态特性进行了分析计算,计算出麦克风在9V偏置电压下开环灵敏度为4.99mV/Pa,麦克风最大偏置电压为32.83V,麦克风工作时的频率带宽为0~134kHz。分析结果表明该硅微机械电容式麦克风能满足工业界的使用要求。     

微型高温压力传感器芯片设计分析与优化

基于弹性力学和板壳力学理论,分析了微型高温压力传感器圆形膜片的受力分布,为力敏电阻在应变膜上的布置提供依据;利用有限元分析方法,借助ANSYS仿真软件,对微型高温压力传感器应变膜进行了一系列的分析和计算机模拟,探讨了传感器圆形应变膜简化应力模型的合理性以及温度对应力差分布的影响,得到了直观可靠的结果,为微型高温压力传感器芯片设计和研发新颖的微型高温压力传感器芯片提供有力的依据.     

Design and fabrication of a new MEMS capacitive microphone using a perforated aluminum diaphragm

In this paper, a novel single-chip MEMS capacitive microphone is presented. The novelties of the method relies on the moveable aluminum (Al) diaphragm positioned over the backplate electrode, where the diaphragm includes a plurality of holes to allow the air in the gap between the electrode and the diaphragm to escape and thus reducing acoustical damping in the microphone. Spin-on-glass (SOG) was used as a sacrificial and isolating layer. Backplate is monocrystalline silicon wafer, that it is more stiff. This work will focus on design, simulation, fabrication and characterization of the microphone. The structure has a diaphragm thickness of 3 μm, a diaphragm size of 0.5 mm × 0.5 mm, and an air gap of 1.0 μm. The results show that the pull-in voltage is 105 V, the initial stress of evaporated aluminum diaphragm is around 1500 MPa and the zero bias capacitance of microphone is 2.12 pF. Comparing with the previous works, this microphone has several advantages: the holes have been made on diaphragm, therefore no need of KOH etching to make back chamber, in this way the chip size of each microphone is reduced. The fabrication process uses minimal number of layers and masks to reduce the fabrication cost.     

Microelectromechanical systems vibration powered electromagnetic generator for wireless sensor applications

This paper presents a silicon microgenerator, fabricated using standard silicon micromachining techniques, which converts external ambient vibrations into electrical energy. Power is generated by an electromagnetic transduction mechanism with static magnets positioned on either side of a moving coil, which is located on a silicon structure designed to resonate laterally in the plane of the chip. The volume of this device is approximately 100 mm³. ANSYS finite element analysis (FEA) has been used to determine the optimum geometry for the microgenerator. Electromagnetic FEA simulations using Ansoft’s Maxwell 3D software have been performed to determine the voltage generated from a single beam generator design. The predicted voltage levels of 0.7–4.15 V can be generated for a two-pole arrangement by tuning the damping factor to achieve maximum displacement for a given input excitation. Experimental results from the microgenerator demonstrate a maximum power output of 104 nW for 0.4g (g=9.81 m s^?1) input acceleration at 1.615 kHz. Other frequencies can be achieved by employing different geometries or materials.     

Out-of-plane deformation and pull-in voltage of cantilevers with residual stress gradient: experiment and modelling

The out-of-plane deformation and the pull-in voltage of electrostatically actuated cantilevers with a residual stress gradient, is investigated in the length range 100–300 µm. Measured pull-in voltages are compared with calculations, which are obtained using previously proposed analytical expressions and a finite element method (FEM) modelling. In particular, a simplified model of the residual stress distribution inside cantilevers is formulated that enables FEM simulation of measured out-of-plane deformations and pull-in voltages for all lengths of fabricated cantilevers. The presented experimental results and FEM model are exploitable in the design of cantilever-based microelectromechanical systems, in order to provide a reliable prediction of the influence of residual stress gradient on device shape and pull-in voltage.