Design and fabrication of silicon condenser microphone usingcorrugated diaphragm technique

A novel silicon condenser microphone with a corrugated diaphragm has been proposed, designed, fabricated and tested. The microphone is fabricated on a single wafer by use of silicon anisotropic etching and sacrificial layer etching techniques, so that no bonding techniques are required. The introduction of corrugations has greatly increased the mechanical sensitivities of the microphone diaphragms due to the reduction of the initial stress in the thin films, For the purpose of further decreasing the thin film stress, composite diaphragms consisting of multilayer (polySi/Si_xN_y/polySi) materials have been fabricated, reducing the initial stress to a much lower level of about 70 MPa in tension. Three types of corrugation placements and several corrugation depths in a diaphragm area of 1 mm² have been designed and fabricated. Microphones with flat frequency response between 100 Hz and 8~16 kHz and open-circuit sensitivities as high as 8.1~14.2 mV/Pa under the bias voltages of 10~25 V have been fabricated in a reproducible way. The experimental results proved that the corrugation technique is promising for silicon condenser microphone     

The design, fabrication, and testing of corrugated silicon nitridediaphragms

Silicon nitride corrugated diaphragms of 2 mm×2 mm×1 μm have been fabricated with 8 circular corrugations, having depths of 4, 10, or 14 μm. The diaphragms with 4-μm-deep corrugations show a measured mechanical sensitivity (increase in the deflection over the increase in the applied pressure) which is 25 times larger than the mechanical sensitivity of flat diaphragms of equal size and thickness. Since this gain in sensitivity is due to reduction of the initial stress, the sensitivity can only increase in the case of diaphragms with initial stress. A simple analytical model has been proposed that takes the influence of initial tensile stress into account. The model predicts that the presence of corrugations increases the sensitivity of the diaphragms, because the initial diaphragm stress is reduced. The model also predicts that for corrugations with a larger depth the sensitivity decreases, because the bending stiffness of the corrugations then becomes dominant. These predictions have been confirmed by experiments. The application of corrugated diaphragms offers the possibility to control the sensitivity of thin diaphragms by geometrical parameters, thus eliminating the effect of variations in the initial stress, due to variations in the diaphragm deposition process and/or the influence of temperature changes and packaging stress     

Fabrication, experiment of a microactuator using magnetic fluid for micropump application

This paper presents the characteristics of the first microactuator using magnetic fluid (MF). MF actuators with flat and corrugated diaphragms are fabricated by the micromachining technique and their deflections are measured. The MF actuator consists of an inductor, a fluid chamber filled with magnetic fluid, and a parylene diaphragm. In the presence of the magnetic field, magnetic fluid easily deforms its shape and generates some pressure. The relation between the MF pressure and magnetic flux density is obtained by the comparison of the deflection for the applied air pressure with that for the MF pressure. At 110 Gauss, the deflection of MF actuator with corrugated parylene diaphragm is more than 200 μm and the generated MF pressure is 2.8 kPa. The successful operation of the first MF actuator shows the high potential for the application to the micromachined devices.     

Performance of nonplanar silicon diaphragms under large deflections

The successful realization of many high-performance microactuators, including many microvalves and micropumps, depends critically on the development of diaphragms which are capable of large displacements and free from fatigue. Thin nonplanar silicon diaphragms are promising candidates for such applications since they can be batch fabricated using techniques and materials that are compatible with the other portions of these devices. This paper reports the detailed simulation, fabrication, and characterization of such diaphragms, which are corrugated-bossed structures that unfold, accordion-like, to produce high boss deflections. Boron-doped diaphragms 1 mm on a side, 3 μm in thickness, and containing five 10-μm-deep corrugations produce boss deflections of more than 30 μm at 760 mmHg, in close agreement with simulations. The maximum deflection measured at diaphragm fracture is 38 μm under a 1050 mmHg differential pressure. The effects on load-deflection performance due to changes in diaphragm internal stress (residual stress), corrugation profile, and diaphragm thickness are also explored     

Kinematically Stabilized Microbubble Actuator Arrays

In this paper, the concept, fabrication, and characterization of a kinematically stabilized polymeric microbubble actuator (endoskeletal microbubble actuator) for a pneumatic tactile display application are presented. The kinematic stabilization is achieved by the combination of two polymeric layers with complementary functions: a microcorrugated parylene diaphragm layer as a ldquoskeletonrdquo to provide a directional deflection in a desired axial direction while suppressing undesired lateral deflections and an overcoated elastomer diaphragm layer as a ldquoskinrdquo to help the extended membrane recoil to its original shape, ensuring diaphragm stability. Arrays of microcorrugated diaphragms are implemented in a mass producible fashion using inclined rotational UV lithography, micromolding, and pattern transfer techniques. Both the number of corrugations and the corrugation profile of the endoskeletal actuator are determined through numerical analysis, taking into account the constraints of the microfabrication processes utilized. A prototype of a single endoskeletal bubble actuator with a diameter of 2.6 mm has been fabricated and characterized. For comparison purposes, elastomer microcorrugated diaphragm (skin only) actuators and parylene microcorrugated diaphragm (skeleton only) actuators of the same materials and dimensions have also been fabricated and tested. While the skin-only diaphragm actuators demonstrated undesired omnidirectional inflation and the skeleton-only diaphragm actuators have shown unstable and irreversible deformation during extension, the proposed endoskeletal microbubble actuators have shown stable reversible axial extensions with a deflection of approximately 0.9 mm. A 6 6 array of endoskeletal polymer microbubble actuators integrated with a microfluidic manifold has been successfully fabricated, demonstrating its mass manufacturability.     

Design and fabrication of high sensitive microphone diaphragm using deep corrugation technique

In this paper, single deeply corrugated diaphragm (SDCD) with various corrugation depths and initial stresses are studied extensively for applications to micromachinined high-sensitivity devices. Both theoretical analysis and finite-element-model (FEM) simulation results show that significant improvement in sensitivity can be achieved using the diaphragm with larger corrugation depth. The measured mechanical sensitivity of the SDCD structure shows reasonable agreement with the theoretical prediction. The SDCD structures with various corrugation depths have been applied to the realization of high-sensitivity microphones. The measurements show that deep corrugation technique is promising in its applications to high-sensitivity devices.     

Analysis of partly corrugated rectangular diaphragms using theRayleigh-Ritz method

In this paper, the Rayleigh Ritz method is applied to static analyses of partly corrugated four-edges-clamped rectangular diaphragms. We use coupled variational equations (derived from the principle of virtual displacement), and describe some practical considerations needed to analyze multiregional diaphragms by the method. We approximate a sinusoidal corrugation by an equivalent flat single layer, and derive equivalent in-plane and bending stiffnesses using the theory of engineering mechanics. We demonstrate the effectiveness and usefulness of the present method through examples (in one example, we compare the calculated deflection with that obtained by a finite-element program). We examine a partly corrugated rectangular plate with residual stress, and investigate the effects of corrugation parameter variations. The analysis technique presented in this paper is very convenient, efficient, and reliable for analyzing seemingly difficult microelectromechanical system devices built on partly corrugated thin diaphragms with various residual stresses     

Design and optimization of parylene nanomechanical cantilevers with integrated piezoresistors for surface-stress based biochemical sensing

The sensitivity of surface-stress based cantilever sensor can be significantly increased by using polymer as the cantilever material. In our previous research, parylene nanomechanical cantilevers with integrated poly-crystal silicon piezoresistors have already been developed for biochemical applications. However, parylene cantilevers exhibit different behaviors compared with their more rigid counterparts. In this paper, a new analytical model has been developed and verified using finite element simulations. The design optimization has also been discussed based on the new analytical model, resulting in several useful design guidelines that are unique to parylene or more generally to polymer cantilevers with integrated poly-crystal or single-crystal silicon piezoresistors for surface stress sensing.     

压力传感器封装中波纹膜片的结构优化

对压力传感器隔离封装中的关键部件——波纹膜片,采用有限元分析的方法,分别得到了2,4,6个波纹的膜片的弹性特性,并根据封装要求选择了6波纹的膜片。通过比较不同波数的膜片对压力传感器输出信号的影响,验证了膜片结构优化的正确性。最后,使用6波纹的膜片进行封装,得到了性能稳定的压力传感器,并测试得到了其主要的静态参数。     

Silicon condenser microphones with corrugated silicon oxide/nitride electret membranes

Corrugated electret membranes are used in a micromachined silicon microphone. The membranes consist of a permanently corona-charged double layer of silicon dioxide and silicon nitride, known to have excellent charge-storing properties. This electret can replace the external bias needed for condenser microphones. The well-known LOCOS technique—also combined with dry etching—is used for the first time to fabricate membranes with corrugation depths of several microns. The membrane thickness amounts to 600 nm.

The interferometrically measured center deflection is up to 40 nm/Pa for diaphragms with four corrugations of up to 3.3 μm depth and a size of A_M=1 mm². This high mechanical sensitivity limits the dynamic range to sound pressures below 50 Pa. The obtained mechanical sensitivities are in excellent agreement with the theory.

The most compliant corrugated diaphragms result in a microphone sensitivity of 2.9 mV/Pa, an equivalent noise level of 39 dB(A) and a total harmonic distortion below 1.7% at 28 Pa (123 dB SPL). The corrugation depth in the sensors has been only 1.3 μm. All sensors cover the whole audio and low ultrasonic range. The temperature coefficient is between 0.05 and 0.1 dB/K.     

Dynamical modeling and experimental validation of a micro-speaker with corrugated diaphragm for mobile phones

As the design trend of modern cellular phones evolves to be miniaturization and versatile sound in quality, the electro-mechanical components including the micro-speaker are essential toward size reduction and broad frequency range of sound. To reduce size, a diaphragm type micro-speaker is commonly employed in industry, while to broaden the sound frequency range corrugations on the diaphragm are adopted. The corrugations are generally capable of leading to fairly flat response over a broad range since diaphragm stiffness is decreased in axial direction. To confirm the aforementioned capability, the modeling on a corrugated diaphragm is performed first using finite element method (FEM) to obtain the associated dynamic equations in terms of modal coordinates; then the equations are next combined with the magneto-electrical model of the voice coil motor (VCM) that is attached to the bottom side of the diaphragm. Finally, the acoustic effects of the air inertia on the diaphragm and vents of the outer case are modeled using basic acoustic theories. Assembling all derived system equations and solving them, the frequency response of the micro-speaker in sound pressure level (SPL) can be simulated. It shows that the diaphragm corrugation in fact helps flatten the SPL response of the micro-speaker (especially in high frequency range) to lessen sound distortion. Furthermore, the corrugation angle approximately below 45° is favored over other angles or flatter SPL response. Experiments are also conducted to verify the theoretical findings.     

Piezoelectrically actuated dome-shaped diaphragm micropump

This paper describes a piezoelectric micropump built on a dome-shaped diaphragm with one-way parylene valves. The micropump uses piezoelectric ZnO film (less than 10 /spl mu/m thick) to actuate a parylene dome diaphragm, which is fabricated with an innovative, IC-compatible process on a silicon substrate. Piezoelectric ZnO film is sputter-deposited on a parylene dome diaphragm with its C-axis oriented perpendicular to the dome surface. Two one-way check valves (made of parylene) are integrated with a piezoelectrically actuated dome diaphragm to form a multi-chip micropump. The fabricated micropump (10/spl times/10/spl times/1.6 mm/sup 3/) consumes extremely low power (i.e., 3 mW to pump 3.2 /spl mu/L/min) and shows negligible leak up to 700 Pa static differential pressure.     

方形重掺杂硅薄膜的极限载荷分析*

考虑残余应力的情况下,薄膜在大挠度时总应力的解析表达式.通过实验观察,深腐蚀得到的浓硼重掺杂硅薄膜表面存在微蚀坑.考虑微蚀坑和残余应力的影响,运用总应力表达式和Griffith裂口强度理论,定量的得到方形浓硼重掺杂硅薄膜的最大挠度和极限载荷Pmax,与已报道的实验值相符.从而解释了浓硼重掺杂硅薄膜的实际断裂强度值远小于晶体理论断裂强度值的矛盾.可以得出,极限载荷Pmax不仅与薄膜的尺寸与形状有关,而且也与材料特性,特别是与制备工艺有关.     

Simulation of Thin-Film Damping and Thermal Mechanical Noise Spectra for Advanced Micromachined Microphone Structures

In many micromachined sensors the thin (2-10 thick) air film between a compliant diaphragm and backplate electrode plays a dominant role in shaping both the dynamic and thermal noise characteristics of the device. Silicon microphone structures used in grating-based optical-interference microphones have recently been introduced that employ backplates with minimal area to achieve low damping and low thermal noise levels. Finite-element based modeling procedures based on 2-D discretization of the governing Reynolds equation are ideally suited for studying thin-film dynamics in such structures which utilize relatively complex backplate geometries. In this paper, the dynamic properties of both the diaphragm and thin air film are studied using a modal projection procedure in a commonly used finite element software and the results are used to simulate the dynamic frequency response of the coupled structure to internally generated electrostatic actuation pressure. The model is also extended to simulate thermal mechanical noise spectra of these advanced sensing structures. In all cases simulations are compared with measured data and show excellent agreement - demonstrating 0.8 and 1.8 thermal force and thermal pressure noise levels, respectively, for the 1.5 mm diameter structures under study which have a fundamental diaphragm resonance-limited bandwidth near 20 kHz.     

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.     

Front-to-backside alignment using resist-patterned etch control andone etching step

A processing technique that aligns features on the front side of a wafer to those on its backside has been developed for bulk micromachining. A 30 μm-square and 1.6 μm-thick diaphragm serves as an alignment pattern. At the same time that the alignment diaphragm is made, much thicker, large-area diaphragms can be partially etched using `mesh' masking patterns in these areas. The mesh-masking technique exploits the etch-rate differences between (100) and (111) planes to control the depths reached by etch pits in selected areas. The large partially etched diaphragms (2 to 3 mm², roughly 100 μm thick) are sufficiently robust to survive subsequent IC-processing steps in a silicon-foundry environment. The thin alignment diaphragm can be processed through these steps because of its very small area. The partially etched diaphragms can be reduced to useful thicknesses in a final etch step after the circuits have been fabricated     

Investigations on fractal frequency selective diaphragms in rectangular waveguide

In this article, self‐similarity and space‐filling properties of fractal structures are explored as frequency selective diaphragms in rectangular waveguide, which can find applications in the design of compact, lightweight, and multiband waveguide filters with better out‐of‐band rejection ratio. Some self‐affine fractal structures, based on Sierpinski gasket and plus shape fractals, are proposed, and the effect of scaling factor on the location of transmission bands is investigated. Self‐similar structures like Hilbert curve, Koch curve, and Minkowski fractals are shown to be efficient in reducing resonant frequency of the diaphragm. Numerical results are presented along with the results obtained from HFSS, which show a good agreement. A typical application of the fractal diaphragm in the design of waveguide bandstop filter has also been demonstrated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Non-linear vibration behavior of thin multilayer diaphragms

The vibration spectrum of piezoelectrically driven (ZnO) thin silicon diaphragms in the driving frequency range up to 200 kHz has been studied. The response of the structure on the driving conditions (a.c. voltage amplitude and frequency) is presented. The limits of the linear plate theory and specific non-linear effects are discussed. Non-linear effects in the vibration behavior occur for vibration amplitudes even smaller than 4% of the diaphragm thickness. Superharmonic, harmonic and subharmonic vibration modes are observed. The vibration amplitudes of the subharmonic modes are of the same order as the diaphragm thickness. The characteristic non-symmetric resonance peaks of the subharmonic vibration modes indicate the existence of a hard-spring effect in the system. In the case of a system with a hard-spring effect, the concept of vibration modes with fixed resonance frequencies fails.     

Piezoelectric bimorph microphone built on micromachined parylene diaphragm

This paper describes a novel bimorph piezoelectric microphone built on a micromachined parylene diaphragm with two ZnO films of opposite c-axis orientations. Both the sensitivity and signal-to-noise ratio (SNR) of the bimorph parylene-diaphragm microphone have been demonstrated to be much higher than those of a conventional unimorph silicon-nitride-diaphragm microphone.     

应力对硅悬空薄膜的机械灵敏度的影响

运用四周固支薄板小挠度理论,分析了存在较大残余应力的浓硼重掺杂硅悬空薄膜的力学特性.给出了小挠度下,在外界载荷作用下总应力表达式和薄膜机械灵敏度表达式,并分析了残余应力对二者的影响.研究表明,对存在较大残余应力的硅薄膜,总应力和机械灵敏度主要由残余应力决定,其中机械灵敏度较忽略残余应力时的值减小三个数量级.