Kirill Shcheglov

Temperature dependent characteristics of the JPL silicon MEMS gyroscope

Advances in aeronautics and space technology have created a need for miniaturized navigation instruments such as gyroscopes, a need which is currently being addressed by a number of micromachined designs. While micromachined devices have already proven their advantages being light-weight and low-power, the performance limitations of these devices have not been thoroughly investigated. In particular the effects of the temperature environment on the performance is of great interest since they can be a dominant source of error in micromachined devices. We have investigated the temperature-dependent drift and noise characteristics of a packaged silicon MEMS gyroscopes. Packaged devices were subjected to various temperatures environments between -60 and +60/spl deg/C, and their resonant frequencies, signal drifts and quadrature drifts were monitored. The results obtained from these tests point out the mechanisms of temperature-dependent and temperature-independent drift and suggest a scheme for temperature compensation.

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.

LIGA-fabricated two-dimensional quadrupole array and scroll pump for miniature gas chromatograph/mass spectrometer

A 3X3 array of hyperboloid quadrupole mass filters with a 3 mm pole length was fabricated using the LIGA (LIthographic Galvanoformung and Abformung) process. Electrical connectivity and spatial orientation are established by bonding the pole array to a low temperature co-fired ceramic (LTCC) substrate. A miniature scroll pump for vacuum pumping with a scroll height of 3 mm was also fabricated using the LIGA process. New LIGA fabrication steps (e.g. expose and developed freestanding PMMA, compression bonding of electroplating base and PMMA, low-stress electroplated films) have been developed to fabricate ultra thick PMMA molds with high aspect ratios (70:1) and high precision. Computational analysis was performed to estimate the miniature scroll pump performance characteristics.

Method of producing an inertial sensor

The present invention discloses an inertial sensor comprising a planar mechanical resonator with embedded sensing and actuation for substantially in-plane vibration and having a central rigid support for the resonator. At least one excitation or torquer electrode is disposed within an interior of the resonator to excite in-plane vibration of the resonator and at least one sensing or pickoff electrode is disposed within the interior of the resonator for sensing the motion of the excited resonator. In one embodiment, the planar resonator includes a plurality of slots in an annular pattern; in another embodiment, the planar mechanical resonator comprises four masses; each embodiment having a simple degenerate pair of in-plane vibration modes.

Error correcting sparse permutation channel codes for digital holographic data storage

We present a new class of modulation codes based on permutation coding which satisfy the channel coding constraint suitable for the digital holographic data storage, and which simultaneously provide strong error correction at high code rates. The channel decoding scheme is based on the true maximum likelihood detection realized using a newly developed efficient algorithm. The sparse permutation codes of large block sizes closely approach the information theoretic limits for the binary channel data capacity.

Analysis of a Two Wrap Meso Scale Scroll Pump

The scroll pump is an interesting positive displacement pump. One scroll in the form of an Archimedes spiral moves with respect to another, similarly shaped stationary scroll, forming a peristaltic pumping action. The moving scroll traces an orbital path but is maintained at a constant angular orientation. Pockets of gas are forced along the fixed scroll from its periphery, eventually reaching the center where the gas is discharged. A model of a multi‐wrap scroll pump was created and applied to predict pumping performance. Meso‐scale scroll pumps have been proposed for use as roughing pumps in mobile, sampling mass spectrometer systems. The main objective of the present analysis is to obtain estimates of a scroll pump’s performance, taking into account the effect of manufacturing tolerances, in order to determine if the meso scale scroll pump will meet the necessarily small power and volume requirements associated with mobile, sampling mass spectrometer systems. The analysis involves developing the govern...

Concept, modeling, and fabrication techniques for large-stroke piezoelectric unimorph deformable mirrors

Large-stroke micromachined deformable mirror technology can boost the imaging performance of an otherwise non-rigid, lower-quality telescope structure. The proposed deformable mirror concept in this paper combines a microfabricated large-stroke piezoelectric actuator with a reflective membrane “transferred” in its entirety from a separate wafer. This process allows the large-stroke actuation of the continuous membrane and can provide the necessary large wavefront correction. The micromachined deformable mirror approach allows mass-production of actuators as well as scalable structures with, high actuator densities. The piezoelectric unimorph actuator design approach delivers large actuator stroke with a highly localized influence function, while maintaining a surface figure of optical quality. Both of these component fabrication techniques are easily scaled to accommodate deformable mirrors with very large areas.

A Piezoelectric Unimorph Deformable Mirror Concept by Wafer Transfer for Ultra Large Space Telescopes

Future concepts of ultra large space telescopes include the telescopes with segmented silicon mirrors and inflatable polymer mirrors. Primary mirrors for these systems cannot meet optical surface figure requirements and are likely to generate over several microns of wavefront errors. In order to correct for these large wavefront errors, high stroke optical quality deformable mirrors are required. The deformable mirror in this paper consists of an optical quality membrane mirror backed by a piezoelectric unimorph actuator array. A fabrication technology has been recently developed for transferring an entire wafer-level mirror membrane from one substrate to another. A thin membrane, 100 mm in diameter, has been successfully transferred without using adhesives or polymers. The measured peak-to-valley surface figure error of a wafer-level transferred and patterned membrane (1 mm × 1 mm × 0.016 mm) is only 9 nm. The mirror element actuation principle is based on a piezoelectric unimorph. A voltage applied to the piezoelectric layer induces stress in the longitudinal direction causing the film to deform and pull on the mirror connected to it. The advantage of this approach is that the small longitudinal strains obtainable from a piezoelectric material at modest voltages are thus translated into large vertical displacements. Modeling is performed for unimorph membranes consisting of clamped rectangular membranes with piezoelectric layers with variable dimensions. The membrane transfer technology combined with the piezoelectric unimorph actuator concept constitutes the successful demonstration of high quality, compact, large stroke continuous deformable mirror devices, resulting in compact AO systems for use in ultra large space telescopes.

Testbed for extended-scene Shack-Hartmann and phase retrieval wavefront sensing

We have implemented a testbed to demonstrate wavefront sensing and control on an extended scene using Shack-Hartmann and MGS phase retrieval simultaneously. This dual approach allows for both high sensitivity and high dynamic range wavefront sensing. Aberrations are introduced by a silicon-membrane deformable mirror. The detailed characterization of this mirror and its sensitivity matrix are presented. The various Shack-Hartmann algorithms, including a maximum likelihood approach are discussed and compared to phase retrieval results using a point source. The next phase of the testbed will include results with extended scenes.

Beam splitting mirrors for miniature Fourier transform soft x-ray(FTXR) interferometer

The development of Fourier Transform (FT) spectral techniques in the soft X-ray spectral region has been advocated in the past as a possible route to constructing a bench-top size spectral imager with high spatial and spectral resolution. The crux of the imager is a soft X-ray interferometer. Auxiliary subsystems include a wide-band soft X-ray source, focusing optics and detection systems. When tuned over a sufficiently large range of path delays, the interferometer will sinusoidally modulate the source spectrum centered at the core wavelength of interest, the spectrum illuminates a target, the reflected signal is imaged onto a CCD, and data acquired for different frames is converted to spectra in software by using FT methods similar to those used in IR spectrometry producing spectral image per each pixel. The use of shorter wavelengths results in dramatic increase in imaging resolution, the modulation across the beam width results in highly efficient use of the beam spectral content, facilitating construction of a bench-top instrument. With the predicted <0.1eV spectral and <100 nm spatial resolution, the imager would be able to map core-level shift spectra for elements such as Carbon, which can be used as a chemical compound fingerprint and imaging intracellular structures. We report on our progress in the development of a Fourier Transform X-ray (FTXR) interferometer. The enabling technology is X-ray beam splitting mirrors. The mirrors are not available commercially; multi layers of quarter-wave films (used in IR and visible) are not suitable, and several efforts by other researchers who used parallel slits met only a very limited success. In contrast, our beam splitters use thin (about 200 nm) SiN membranes perforated with a large number of very small holes prepared in our micro-fabrication laboratory at JPL. Precise control of surface roughness and high planarity are needed to achieve the requisite wave coherency. The beam splitters prepared-to-date had surface RMS and planarity better that <0.3 nm over a 0.45 mm x 1.4 mm area, meeting requirements for spectral imaging at 100eV. Efforts to improve the mirror flatness to a level required for core-level shifts of Carbon are under way.