Karl Yee

Effect of Temperature on MEMS Vibratory Rate Gyroscope

We report the temperature dependence of the JPL/Boeing MEMS second generation post resonator gyroscopes and determine the effect of hysteresis over the range 35degC to 65degC. The results indicate a strong linear dependence of the drive frequency and sense frequency with temperature of 0.093Hz/degC and AGC bias voltage with temperature of 13mV/degC. The results also indicate a significant time lag of the gyroscope of these quantities when responding to external temperature variations but determined no hysteresis exists in the drive frequency, sense frequency, and AGC bias. Both the time-frequency and time-bias voltage relationships are of the form y = A+B*exp(-t/T) where A is an offset parameter in Hertz and Volts respectively and B depends on the magnitude of the temperature variation

High performance MEMS micro-gyroscope

This paper reports on JPLs on-going research into MEMS gyroscopes. [1-4] This paper will describe the gyroscopes fabrication- methods, a new 8-electrode layout developed to improve performance and performance statistics of a batch of six gyroscopes (of the 8- electrode design) recently rate tested. Previously in our group, T. Tang and R. Gutierrez presented the results of their extensive use of ethylene diamine pyrocatechol (EDP) to deep-etch the inertial- sensitive r4esonators and post-supporting structures in a 4- electrode gyroscope design. Today, JPL is utilizing an in-house STS DRIE, replacing the old wet-etching steps. This has demonstrated superior precision in machining symmetry of the resonators, thus significantly reducing native rocking mode frequency splits. A performance test of six gyros has shown an average, un-tuned, frequency split of 0.4% (11Hz split for rocking modes at 2.7KHz). The new JPL MEMS gyroscope has a unique 8-electrode layout, whose large electrodes can provide significant electrostatic softening of the resonators springs. This allows matching of the Coriolis sensitive rocking modal frequencies to be improved from the native 0.4% to an average tuned frequency split of 0.02%. In separate tests, electrostatic tuning in the 8-electrode design has demonstrated the ability to match frequency-splits to within 10mHz, thus ensuring full degeneracy in even a very high Q device. In addition, a newly selected ceramic package-substrate has improved the devices dampening loses such that a mean Q of 28,000 was achieved in the six gyroscope tested. These Qs ere measured via the ring-down time method. The improved fabrication development and other modifications described have led to the JPLs MEMS gyroscope achieving an average bias instability (Allan variance 1/f floor estimate) of 11degree/hr with best in the group being 2degree/hr. In an independent test, Honeywell Inc. reported one of our MEMS gyroscopes as achieving 1degree/hr bias instability flicker floor estimate measured at constant temperature.

Control of MEMS Disc Resonance Gyroscope (DRG) using a FPGA Platform

Inertial navigation systems based upon optical gyroscopes tend to be not long lived. Micro-electromechanical systems (MEMS) based gyros do not have these shortcomings; however, until recently, the performance of MEMS based gyros had been below navigation grade. Boeing and JPL have been cooperating since 1997 to develop high performance MEMS gyroscopes for miniature, low power space inertial reference unit applications. The efforts resulted in demonstration of a post resonator gyroscope (PRG). This experience led to the more compact disc resonator gyroscope (DRG) for further reduced size and power with potentially increased performance. Currently, the mass, volume and power of the DRG are dominated by the size of the electronics. This paper will detail the FPGA based digital electronics architecture and its implementation for the DRG which will allow reduction of size and power and will increase performance through a reduction in electronics noise. Using the digital control based on FPGA, we can program and modify in real-time the control loop to adapt to the specificity of each particular gyro and the change of the mechanical characteristic of the gyro during its life time.

Technology development towards WFIRST-AFTA coronagraph

NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.

High contrast internal and external coronagraph masks produced by various techniques

High contrast internal and external coronagraphic imaging requires a variety of masks depending on different architectures to suppress star light. Various fabrication technologies are required to address a wide range of needs including gradient amplitude transmission, tunable phase profiles, ultra-low reflectivity, precise small scale features, and low-chromaticity. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks, and lab-scale external occulter type masks by various techniques including electron beam, ion beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each. Further development is in progress to produce circular masks of various kinds for obscured aperture telescopes.

FPGA platform for MEMS Disc Resonance Gyroscope (DRG) control

Inertial navigation systems based upon optical gyroscopes tend to be expensive, large, power consumptive, and are not long lived. Micro-Electromechanical Systems (MEMS) based gyros do not have these shortcomings; however, until recently, the performance of MEMS based gyros had been below navigation grade. Boeing and JPL have been cooperating since 1997 to develop high performance MEMS gyroscopes for miniature, low power space Inertial Reference Unit applications. The efforts resulted in demonstration of a Post Resonator Gyroscope (PRG). This experience led to the more compact Disc Resonator Gyroscope (DRG) for further reduced size and power with potentially increased performance. Currently, the mass, volume and power of the DRG are dominated by the size of the electronics. This paper will detail the FPGA based digital electronics architecture and its implementation for the DRG which will allow reduction of size and power and will increase performance through a reduction in electronics noise. Using the digital control based on FPGA, we can program and modify in real-time the control loop to adapt to the specificity of each particular gyro and the change of the mechanical characteristic of the gyro during its life time.

Measurement approach and design of the CubeSat Infrared Atmospheric Sounder (CIRAS)

The CubeSat Infrared Atmospheric Sounder (CIRAS) will measure upwelling infrared radiation of the Earth in the MWIR region of the spectrum from space on a CubeSat. The observed radiances have information of potential value to weather forecasting agencies and can be used to retrieve lower tropospheric temperature and water vapor globally for weather and climate science investigations. Multiple units can be flown to improve temporal coverage or in formation to provide new data products including 3D atmospheric motion vector winds. CIRAS incorporates key new instrument technologies including a 2D array of High Operating Temperature Barrier Infrared Detector (HOT-BIRD) material, selected for its high uniformity, low cost, low noise and higher operating temperatures than traditional materials. The detectors are hybridized to a commercial ROIC and commercial camera electronics. The second key technology is an MWIR Grating Spectrometer (MGS) designed to provide imaging spectroscopy for atmospheric sounding in a CubeSat volume. The MGS has no moving parts and includes an immersion grating to reduce the volume and reduce distortion. The third key technology is an infrared blackbody fabricated with black silicon to have very high emissivity in a flat plate construction. JPL will also develop the mechanical, electronic and thermal subsystems for CIRAS, while the spacecraft will be a commercially available CubeSat. The integrated system will be a complete 6U CubeSat capable of measuring temperature and water vapor profiles with good lower tropospheric sensitivity. The CIRAS is the first step towards the development of an Earth Observation Nanosatellite Infrared (EON-IR) capable of operational readiness to mitigate a potential loss of CrIS on JPSS or complement the current observing system with different orbit crossing times.

Application specific electrode-integrated nanotube cathodes (ASINCs) for miniature analytical instruments for space exploration

JPL has developed high performance cold cathodes using arrays of carbon nanotube bundles that routinely produce > 15 A/cm2 at applied fields of 5 to 8 V/μm without any beam focusing. They have exhibited robust operation in poor vacuums of 10-6 to 10-4 Torr- a typically achievable range inside hermetically sealed microcavities. A new double-SOI process to monolithically integrate gate and additional beam tailoring electrodes has been developed. These electrodes are designed according to application requirements making carbon nanotube field emission sources application specific (Application Specific electrode-Integrated Nanotube Cathodes or ASINCs). ASINCs, vacuum packaged using COTS parts and a reflow bonding process, when tested after 6-month shelf life have shown little emission degradation. Lifetime of ASINCs is found to be affected by two effects- a gradual decay of emission due to anode sputtering, and dislodging of CNT bundles at high fields (> 10 V/μm). Using ASINCs miniature X-ray tubes and mass ionizers have been developed for future XRD/XRF and miniature mass spectrometer instruments for lander missions to Venus, Mars, Titan, and other planetary bodies.

Exoplanet coronagraph shaped pupil masks and laboratory scale star shade masks: design, fabrication and characterization

Star light suppression technologies to find and characterize faint exoplanets include internal coronagraph instruments as well as external star shade occulters. Currently, the NASA WFIRST-AFTA mission study includes an internal coronagraph instrument to find and characterize exoplanets. Various types of masks could be employed to suppress the host star light to about 10-9 level contrast over a broad spectrum to enable the coronagraph mission objectives. Such masks for high contrast internal coronagraphic imaging require various fabrication technologies to meet a wide range of specifications, including precise shapes, micron scale island features, ultra-low reflectivity regions, uniformity, wave front quality, achromaticity, etc. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks by combining electron beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each, highlighting milestone accomplishments from the High Contrast Imaging Testbed (HCIT) at JPL and from the High Contrast Imaging Lab (HCIL) at Princeton University. We also present briefly the technologies applied to fabricate laboratory scale star shade masks.

Finite element modelling and simulation of thermo-elastical damping of MEMS vibrations

The contribution is directed to providing accurate simulation and approximation of the Q-factor determined by thermalelastic damping in complex micro-electromechanical (MEM) resonators. The base model created is presented as a system of partial differential equations, which describe the elastic and thermal phenomena in the MEM structure. The FEM calculations were performed by using COMSOL Multiphysics software. The model was verified by comparing numerically and analytically obtained damped modal properties of a MEM cantilever resonator. The comparison of calculated and experimentally obtained resonant frequencies and Q-factor values indicated a good agreement of tendencies of change of the quantities against temperature. Investigation of longitudinal and bending vibration modes in 3D of a beam resonators was accomplished by taking into account the layered structure of the resonator and the influence of the geometry of the clamping zone. Modal properties of rectangle- and ring-shaped bulk-mode MEM resonators were examined, too.