Ram Gopal

Architecture of torsional gyroscope having robust sense mode

Abstract. An architecture of a torsional gyroscope having robust sense mode is reported. The robustness is achieved by utilizing dynamic amplification of torsional oscillations in the sense oscillator. The frequency response of the sense oscillator, which essentially is a 2-degree-of-freedom (DOF) one, has two resonance peaks and a flat region between the peaks, where the amplitude is less sensitive to ambient damping resulting in the robust sense mode. The frequency response of the 1-DOF drive oscillator has one resonance peak, which is designed to fall within the flat region of the sense amplitude. This helps in reducing the effects of change in the geometry and material properties of the device, induced by inevitable fabrication imperfections, on the device performance. The device is modeled by deriving the equations for electrostatic moment, moments of inertia, and spring constants. The design concepts of antiresonance and zero-phase frequency, along with analytical expressions for resonance frequencies and 3-dB bandwidth are also presented. The design is then realized using an SU-8 based ultraviolet-lithographie, galvanoformung, abformung (UV-LIGA) process having 8-μm thick Ni–Fe as the key structural layer. A characterization technique is developed to extract the frequency response of the fabricated device.

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.

Glass to silicon anodic bonding

Glass-to-silicon anodic bonding is a well known process for fabricating number of microelectromechanical components and subassemblies. Experiments have been carried out by varying bonding parameters, i.e. temperature and bias voltage, to get strong bond between silicon and 7740 pyrex glass pieces. Bias voltage in the range of 400 - 450 V at 420 degree(s)C appears to be appropriate for quality bonds between silicon and glass.

Batch Fabrication of Millimeter-Wave Silicon Impatts

Large number of millimeter wave Impatt diodes have been fabricated out of reasonably large size silicon wafer with very good uniformity in electrical characteristics using the technique reported here. Modification in processing adopted in the present work led to very high yield and improved thermal impedance during packaging of Impatts. These improvements are due to better surface finish in integral heatsink pads and controlled thinning. The present process has been tried on silicon SDR and DDR Impatts over a frequency range of 10 to 100 GHz. Other devices like silicon Baritts and GaAs transferred electron devices have also been batch fabricated successfully using the same technique.

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.

Design and simulation of MEMS capacitive magnetometer

This paper presents the design and simulation of a MEMS Capacitive Magnetometer using FEM (Finite Element Method) tool COMSOL Multiphysics 4.3b and results from this simulation are closely matched with analytically calculated results. A comb drive structure is used for actuation purpose which operates at resonant frequency of device is 11.791 kHz to achieve maximum displacement. A magnetic field in z-axis can be detected by this comb drive structure. Quality factor of MEMS capacitive magnetometer obtained is 18 and it has good linear response in the magnetic field range of 100 µT.

Electrostatic tuning of drive and sense modes in two-gimbal torsional gyroscope

This paper demonstrates electrostatic tuning of drive and sense modes in two-gimbal torsional gyroscope. The gyroscope is fabricated by SU-8 based UV-LIGA process and is then packaged in vacuum. The device is first characterized for frequency responses of drive and sense modes using laser Doppler vibrometer (LDV). Finally, electrostatic tuning of drive and sense modes is carried out by varying DC bias voltage applied to the proof-mass.

Design and simulation of non-resonant 1-DOF drive mode and anchored 2-DOF sense mode gyroscope for implementation using UV-LIGA process

This paper presents the design and simulation of a 3-DOF (degree-of-freedom) MEMS gyroscope structure with 1-DOF drive mode and anchored 2-DOF sense mode, based on UV-LIGA technology. The 3-DOF system has the drive resonance located in the flat zone between the two sense resonances. It is an inherently robust structure and offers a high sense frequency band width and high gain without much scaling down the mass on which the sensing comb fingers are attached and it is also immune to process imperfections and environmental conditions. The design is optimized to be compatible with the UV-LIGA process, having 9 μm thick nickel as structural layer. The electrostatic gap between the drive comb fingers is 4 μm and sense comb fingers gap are 4 μm/12 μm. The damping effect is considered by assuming the flexures and the proof mass suspended about 6 μm over the substrate. Accordingly, mask is designed in L-Edit software.

FEM simulation of CMUT cell for NDT application

This paper presents the simulation of various electromechanical performance parameters for an efficient and broadband air coupled Capacitive Micromachined Ultrasonic Transducer (CMUT) for Non Destructive Testing and Evaluation (NDT/NDE) using FEM simulation tool, Coventor Ware. The non contact ultrasonic inspection performed in ambient air reduces the complexity and cost. Various critical parameters like collapse voltage, resonant frequency, coupling coefficient, squeeze film damping, bandwidth, quality factor and transient response of the single cell of CMUT are discussed. We employ a hexagonal CMUT cell for the modeling to improve the CMUT’s transmission/reception efficiency as the average membrane displacement is high.