Using Micro-Raman Spectroscopy to Assess MEMS Si/SiO2 Membranes Exhibiting Negative Spring Constant Behavior

We introduce a novel micro-mechanical structure that exhibits two regions of stable linear positive and negative stiffness. Springs, cantilevers, beams and any other geometry that display an increasing return force that is proportional to the displacement can be considered to have a “Hookean” positive spring constant, or stiffness. Less well known is the opposite characteristic of a reducing return force for a given deflection, or negative stiffness. Unfortunately many simple negative stiffness structures exhibit unstable buckling and require additional moving components during deflection to avoid deforming out of its useful shape. In Micro-Electro-Mechanical Systems (MEMS) devices, buckling caused by stress at the interface of silicon and thermally grown SiO2 causes tensile and compressive forces that will warp structures if the silicon layer is thin enough. The 1 mm2 membrane structures presented here utilizes this effect but overcome this limitation and empirically demonstrates linearity in both regions. The Si/SiO2 membranes presented deflect ~17 μm from their pre-released position. The load deflection curves produced exhibit positive linear stiffness with an inflection point holding nearly constant with a slight negative stiffness. Depositing a 0.05 μm titanium and 0.3 μm layer of gold on top of the Si/SiO2 membrane reduces the initial deflection to ~13.5 μm. However, the load deflection curve produced illustrates both a linear positive and negative spring constant with a fairly sharp inflection point. These results are potentially useful to selectively tune the spring constant of mechanical structures used in MEMS. The structures presented are manufactured using typical micromachining techniques and can be fabricated in-situ with other MEMS devices

A 2 degree-of-freedom SOI-MEMS translation stage with closed loop positioning

This research contains the design, analysis, fabrication, and characterization of a closed loop XY micro positioning stage. The XY micro positioning stage is developed by adapting parallel-kinematic mechanisms, which have been widely used for macro and meso scale positioning systems, to silicon-based micropositioner. Two orthogonal electrostatic comb drives are connected to moving table through 4-bar mechanism and independent hinges which restrict unwanted rotation in 2-degree-of-freedom translational stage. The XY micro positioning stage is fabricated on SOI wafer with three photolithography patterning processes followed by series of DRIE etching and HF etching to remove buried oxide layer to release the end-effector of the device. The fabricated XY micro positioning stage is shown in Fig1 with SEM images. The device provides a motion range of 20 microns in each direction at the driving voltage of 100V. The resonant frequency of the XY stage under ambient conditions is 811 Hz with a high quality factor of 40 achieved from parallel kinematics. The positioning loop is closed using a COTS capacitance-to-voltage conversion IC and a PID controller built in D-space is used to control position with an uncertainty characterized by a standard distribution of 5.24nm and a approximate closed-loop bandwidth of 27Hz. With the positioning loop, the rise time and settling time for closed-loop system are 50ms and 100ms. With sinusoidal input of ω=1Hz, the maximum phase difference of 108nm from reference input is obtained with total motion range of 8μm

Analysis Of The Suspension Beam In Accelerometer For Stiffness Constant And Resonant Frequency By Using Analytical And Numerical Investigation

Mikro-meterpecut yang digunakan dalam pelbagai penerapan hanya akan tercapai dengan jayanya sekiranya keperluan frekuensi resonans dan kepekaan dapat dipenuhi dan konsisten. A successful and consistent performance of micro-accelerometer which has been applied in various applications can only be achieved when the resonant frequency and the sensitivity requirement are fulfilled

Analysis Of The Suspension Beam In Accelerometer For Stiffness Constant And Resonant Frequency By Using Analytical And Numerical Investigation [TL589.2.A3 W872 2007 f rb].

Mikro-meterpecut yang digunakan dalam pelbagai penerapan hanya akan tercapai dengan jayanya sekiranya keperluan frekuensi resonans dan kepekaan dapat dipenuhi dan konsisten. Berdasarkan syarat-syarat tersebut, analisis struktur pada pekali kekukuhan and frekuensi resonans bagi rasuk ampaian dalam meter pecut dan seterusnya pengoptimuman kepada kepekaan haruslah dilakukan. A successful and consistent performance of micro-accelerometer which has been applied in various applications can only be achieved when the resonant frequency and the sensitivity requirement are fulfilled. In view of this, structural analysis on stiffness constant and resonant frequency for the suspension beam in accelerometer, and subsequently optimization design of accelerometer with respect to sensitivity in term of displacement against acceleration must be performed

Electrostatic micro actuators for mirror and other applications

Micro-electro-mechanical systems (MEMS) based electrostatic micro actuators are becoming important building blocks for innovations in optical signal processing and computing systems due to their inherently small size, high density, high speed and low power consumption. Generally, the principle of operation in these systems can be described as: an electrostatic attractive force causes a mechanical rotation, translation or deformation of a mirror plate, controlling the power, phase or direction of a light beam while it propagates through some medium or through free space. The fast paced, competitive research and development efforts widely being undertaken, both in academia and industry, are demanding simple, fast methods for the design of quasi-static Mirror systems, with a large, stable, analog range of operation. In addition fast prototyping methods are in demand for the proof of concept fabrication of these mirror designs. This dissertation addresses these research topics by presenting 1) a general capacitance-based quasi-static design theory and methodology for electrostatic micro actuators, 2) a study of electrostatic travel range extension methods to minimize the pull in effect, and 3) a fast prototyping approach for electrostatic mirror devices using ultra thin silicon wafer bonding and deep reactive etching technologies. In the first topic, two fundamental capacitance-based differential equations are developed for the quasi-static description of electrostatic micro actuator systems. A structural equation is developed to represent the coupled electromechanical response of the system under applied voltage bias, and a pull in equation is determined to identify the intrinsic collapse point beyond which an actuator system no longer has a stable equilibrium, the so-called pull in point. These equations are applied to various complex electrostatic micro actuator systems to predict specific quasi-static behavior. A unitless equation is introduced for each actuator category, and based on it, a design method is proposed to quickly provide specifications for a particular desired performance of an electrostatically actuated micro-mirror system. In the second topic, and as an application of the proposed design methodology, the travel range extension issue is addressed leading to two new methods to increase travel range by sacrificing driving voltage. Both methods are applied directly in the electrostatic domain. The first method utilizes a series capacitor to modulate the effective actuation voltage across the variable capacitor micro mirror. The second method utilizes negative feedback due to the coulombic repulsive interaction between charge layers inserted between the micro mirror electrodes. An analytical study of representative mirror devices is presented, and verification of the travel range extension models is provided via finite element analysis (FEA) simulation. As a further application of the design methodology developed as part of the first research topic, three state-of-the-art micro actuator systems are designed and studied: 1) a variable optical attenuator (VOA), 2) an optical cross connect device (OXC) and 3) an electrostatically tunable, wavelength selecting device. FEA simulations are used to confirm design specifications. In the third research topic, VOA and electrostatically tunable, wavelength selecting devices are fabricated using fast prototyping via ultra thin wafer bonding and deep reactive etching (DRIIE) technologies. Both silicon wet-etching and SU-8 patterning are investigated for the formation of mirror gaps. Testing in the mechanical domain and partial device characterization in the optical domain is provided for these devices. Finally, as a demonstration that the actuator design approach developed in this thesis can be applied to systems other than micro mirrors, we use the approach to design an innovative true mass flow sensor using an electrostatic resonant beam as the sensing element

Curvature of BEOL cantilevers in CMOS-MEMS processes

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents the curvature characterization results of released back-end-of-line 5 µm-wide cantilevers for two different 0.18-µm 1P6M complementary metal-oxide semiconductor microelectromechanical systems processes. Results from different runs and lots from each foundry are presented. The methodology and accuracy of the characterization approach, based on optical measurements of test cantilever curvature, are also discussed. Special emphasis is given to the curvature average and variability as a function of the number of stacked layers. Analythical equations for modeling the bending behavior of stacked cantilevers as a function of the tungsten (W) vias that join the metal layers are presented. In addition, the effect of various post-processing conditions and design techniques on the curvature of both single and stacked cantilevers is analyzed. In particular, surpassing certain time-dependent temperature stress conditions after release lead to curvature shifts larger than one order of magnitude. Also, the W via design was found to strongly affect the curvature of the test cantilevers.Peer ReviewedPostprint (author's final draft