Payal Verma

Ultraviolet-LIGA-based fabrication and characterization of a nonresonant drive-mode vibratory gyro/accelerometer

Abstract. A dual-purpose nonresonant 2-degrees of freedom (DOF) drive-mode and 1-DOF sense-mode vibratory gyro/accelerometer fabricated using the economical ultraviolet-lithographie-galvanoformung-abformung (UV-LIGA) fabrication process using SU-8 photoresist is reported. The dual-purpose device presented is capable of detecting acceleration at the lower-frequency band and angular rate at the operating frequency band thereby functioning as both accelerometer and gyroscope. This is achieved by designing the structure such that the frequency response of the drive oscillator has two drive resonances with a flat zone between them, while the sense oscillator has one resonance, which is deliberately placed in the flat region between the two drive resonances. For angular rate detection, the device is operated in the flat zone at the sense resonance frequency at which the device is less susceptible to frequency variations due to both environmental variation and fabrication imperfections and hence is said to be operating in robust mode. The steady-state response and discrimination for angular rate and acceleration sensing have been devised using analytical modeling. The fabrication process is optimized to realize a gyro/accelerometer that has a 9-μm-thick nickel structural layer and 4-μm capacitive gaps. The overall miniature device size is 2.0  mm×1.9  mm. The experimental frequency response of the fabricated devices shows drive-mode resonances at 2.85 and 4.96 kHz and sense resonance at 3.85 kHz compared to the respective design values of drive-mode resonance frequencies 2.97 and 4.81 kHz and sense resonance frequency of 4 kHz. To demonstrate the dual-purpose capability of the device, acceleration characterization has been carried out and presented. The fabricated sensor is packaged in a ceramic package and interfaced with a MS3110 differential capacitive read out IC to characterize the acceleration response of the sensor, using an out-of-plane shaker. The bandwidth for acceleration detection is found to be 10 to 100 Hz and the sensitivity of the sensor at 30 Hz is found to be 57  mV/g.

Dynamic characteristics of vibratory Gyro-accelerometer

Thispaper presents a systematic approach inreaching governing equation for microgyroaccelerometer. The study is focused on to analyze the dynamic characteristics of vibratory microgyroaccelerometer. In this device, the mechanical structure is excited into oscillatory motion. The angular velocity input to the sensor is then multiplied by the periodic driven motion. A demodulation is required to recover the angular velocity input and linear acceleration from the sense responses, as the governing differential equations for the Gyro-accelerometer input and output are time variant. The frequency responses for the time variant linear system is obtained through the demodulation and low pass filtered steady-state output to sinusoidal excitation. The frequency response, thus, obtained are validated with MATLAB Simulink data.

Effect of power on growth of nanocrystalline silicon films deposited by VHF PECVD technique for solar cell applications

An investigation of the effect of power on the deposition of nanocrystalline silicon thin films were carried out using a gaseous mixture of silane and hydrogen in the 60MHz assisted VHF plasma enhanced chemical vapor deposition (PECVD) technique. The power was varied from 10 to 50 watt maintaining all other parameters constant. Corresponding layer properties w.r.t. material microstructure, optical, hydrogen content and electrical transport are studied in detail. The structural properties have been studied by Raman spectroscopy and x-ray diffraction (XRD). The presence of nano-sized crystals and their morphology have been investigated using atomic force microscopy (AFM). The role of bonded hydrogen content in the films have been studied from the results of Fourier transform infrared spectroscopy. It was observed from the results that with increase in power, crystalline volume fraction increases and crystallite size changes from 4 to 9 nm. The optical band gap varies from 1.7 to 2.1eV due to quantum confine...

Design and fabrication of a 1-DOF drive mode and 2-DOF sense mode micro-gyroscope using SU-8 based UV-LIGA process

This paper presents design and fabrication of a 1-DOF (degree-of-freedom) drive mode and 2-DOF sense mode micro-gyroscope. It is an inherently robust structure and offers a high sense frequency bandwidth. The proposed design utilizes resonance of the1-DOF drive mode oscillator and employs dynamic amplification concept in sense modes to increase the sensitivity while maintaining robustness. The 2-DOF in the sense direction renders the device immune to process imperfections and environmental effects. The design is simulated using FEA software (CoventorWare®). The device is designed considering process compatibility with SU-8 based UV-LIGA process, which is an economical fabrication technique. The complete fabrication process is presented along with SEM images of the fabricated device. The device has 9 µm thick Nickel as the key structural layer with an overall reduced key structure size of 2.2 mm by 2.1 mm.

Far-field light imaging in the presence of atmospheric turbulence with rotating anti-phase apertures: Theoretical investigation

We investigated the diffraction of far-field light objects in the presence of turbulence formed by an optical system with a rotating anti-phase mask. This mask facilitates to detect the position of faint companion in every direction around the bright companion. In the presence of atmospheric turbulence, diffraction images of distant objects are beyond the diffraction limits, the proposed phase shift mask has a merit to compensate the turbulence results high contrast astronomical imaging under partially coherent light illumination and it is proficient to increase the resolution limits in a Sparrow criterion sense. In this approach, we demonstrated the mask fabrication in laboratory conditions for future prospects and analyse the performance by computing the point spread function of the composite image under various considerations analytically.

SU-8 BASED UV-LIGA FABRICATION PROCESS FOR REALIZATION OF NICKEL BASED MEMS INERTIAL SENSOR

This paper reports the complete fabrication process flow based on UV-LIGA technology for realization of metal based MEMS inertial sensor. In this process, nickel is used as the structural layer and copper as the sacrificial layer. The economical three mask process has been optimized and the detailed step by step procedure for carrying out the fabrication is presented. The opti- mized process parameters to achieve void free copper and nickel electroplated layers with extremely low roughness have been reported. Footing problem asso- ciated with lithography process has been analysed and its solution discussed. The fabrication results after each process step have been presented and dis- cussed. Scanning electron micrograph images of the released prototype inertial sensor devices have been presented to demonstrate the successful fabrication of the prototypes using the economical UV-LIGA process.

Analytical modeling of discrimination scheme for detection of angular rate and acceleration for a 4-dof mems gyro-accelerometer

The paper reports an analytical model of a 4-DOF gyroaccelerometer consisting of 2-DOF drive and 2-DOF sense oscillators configured orthogonally. A detection scheme for time varying angular rate and linear acceleration, by combining the structural-model of gyro-accelerometer with the processes of synchronous demodulation and filtration, which leads to the inphase and quadrature components of the system’s output signal. These two components can be utilized in the detection of angular motion and linear acceleration. The in-phase signal can be used for angular rate detection and the quadrature signal can be utilized for linear acceleration. Finally, the results of the model have been validated by comparing with MATLAB/Simulink data which shows excellent matching with each other.

FABRICATION AND CHARACTERIZATION OF PASSIVE MICROPUMP FOR MICROFLUIDICS BASED DEVICES

Point-of-care and low cost microfluidics platforms has found an ac- celerated research focus. One of the essential elements of microfluidics is driv- ing liquid flow in microchannels. Device discussed gives a way to pump liquid passively through a microchannel. The present work represents fiber and paper based passive micro-pumping of liquids through microfluidic devices. The po- rous structure and network of capillaries inside the paper and fiber materials support spontaneous liquid movement. Agarose gel coating is used with paper in order to achieve variations flow rates. The effect of gel concentration on liq- uid flow is studied. The concept can be used ubiquitously for microfluidics de- vice application for its low-cost and is feasible to integrate with devices for low resource settings.

Anchored multi-DOF MEMS gyroscope having robust drive mode

This paper presents the new architecture of 2-DOF (degree-of-freedom) drive mode and 1-DOF sense mode gyroscope with the concept of additional anchoring that retains all the advantages of the Dynamic Vibration Absorber (DVA) concept while being operated at high frequencies. These concepts allow reduction of the bandwidth by varying the coupling parameter during the design, thereby increasing the mechanical sensitivity. In the present design, the anchoring concept has been implemented by adding a central anchor for the sense mass. The steady state response and design concept have been devised using analytical modeling.