High Alignment Accuracy Research Articles

A Fast SINS Self-Alignment Method Under Geographic Latitude Uncertainty

To achieve high alignment accuracy of strapdown inertial navigation system (SINS) with the limited time and the unknown geographic latitude constraints, a novel fast self-alignment method with the real-time estimated latitude is proposed. In the stage of the coarse alignment, the latitude self-estimation and the coarse alignment are performed at the same time. The geometric relationship between the transition angle and the latitude is established, where the angle can be determined by the gravity acceleration vector at different times. Based on the reconstructed observation vector and the set dynamic window, a real-time latitude self-estimation algorithm is proposed for a swaying case, and the attitude determination procedure is accomplished by the improved filter quaternion estimator (filter-QUEST) algorithm, where the vectors are constructed based on a generalized integration regulation. With the deduced backtracking alignment error model, the forward fine alignment is performed with the statistical latitude estimate and the saved data during the process of the coarse alignment, thus will obviously speed up the overall alignment time. The results of the mathematical simulation and the turntable experiment are performed to validate the estimation and alignment performance of the proposed approach.

A New Alignment and Breakthrough Accuracy Optimization Strategy in Long Immersed Tunnel Surveys

For ultra-long tunnels, the effective means of alignment and breakthrough accuracy optimization is to measure the gyro azimuths or transfer the coordinates of surface known points or the directions to the inside of the tunnel through vertical shafts or inclined shafts. Compared with bored tunnels, immersed tunnels have different engineering characteristics and construction environments, and have higher alignment control accuracy requirements. However, the immersed tunnel has no vertical shafts or inclined shafts that can be used for coordinate transfer to improve the measurement accuracy. In order to provide high-accuracy alignment control and breakthrough for long immersed tunnels, we put forward a new strategy after network stability analysis, and consistency analysis between the results of the element positioning system and the results of the control network. The results of the element positioning system are taken as constraints to improve the accuracy of the control network. The analysis on 100,000 simulations of a 20 km-long immersed tunnel shows that the accuracy of the last point pair of the traverse network with angle and distance observations is 60.8 mm, while the accuracy of the same point pair after adopting the new strategy in this paper is 11.8 mm. The results of a 7 km-long experimental traverse network show that the lateral breakthrough accuracy is improved by 73%. All of these indicate that the new strategy can effectively improve the measurement accuracy and the lateral errors can be kept at a small level. Following the new strategy, the high-accuracy alignment and breakthrough can be achieved for long immersed tunnels.

Kalign 3: multiple sequence alignment of large data sets.

MotivationKalign is an efficient multiple sequence alignment (MSA) program capable of aligning thousands of protein or nucleotide sequences. However, current alignment problems involving large numbers of sequences are exceeding Kalign’s original design specifications. Here we present a completely re-written and updated version to meet current and future alignment challenges.ResultsKalign now uses a SIMD (single instruction, multiple data) accelerated version of the bit-parallel Gene Myers algorithm to estimate pairwise distances, adopts a sequence embedding strategy and the bi-secting K-means algorithm to rapidly construct guide trees for thousands of sequences. The new version maintains high alignment accuracy on both protein and nucleotide alignments and scales better than other MSA tools.Availability and implementationThe source code of Kalign and code to reproduce the results are found here: https://github.com/timolassmann/kalign.

Fast Self-Alignment Technology for Hybrid Inertial Navigation Systems Based on a New Two-Position Analytic Method

Initial alignment technology is a key technology for inertial navigation systems (INSs) because the speed and accuracy of the initial alignment determine the working accuracy and rapid response capability of the INS. Thus, the initial alignment technique of an INS must be investigated. In a swaying base environment, traditional alignment methods cannot meet the requirements of alignment accuracy due to the occurrence of interference acceleration and angular velocity, and filtering methods do not perform well in practical and universal applications. This paper studies the self-alignment problem for the swaying base of a rotary strapdown inertial navigation system and uses the latest hybrid inertial navigation system (HINS) as the research platform. Using the double-position rotation strategy, a navigation algorithm based on an updated attitude transformation matrix and a dynamic error compensation algorithm are established, and they effectively resolve the fast and high-precision self-alignment problem of the rotary inertial navigation system (RINS) under the oscillating state. The accuracy and feasibility of the method are demonstrated by mathematical simulations. Experiments show that compared with traditional single-position and continuous-rotation alignment methods, the proposed dynamic self-alignment technology of HINS has the advantages of short alignment time, high alignment accuracy, and dynamic environment adaptability.

Moiré-Based Alignment Using Centrosymmetric Grating Marks for High-Precision Wafer Bonding.

High-precision aligned wafer bonding is essential to heterogeneous integration, with the device dimension reduced continuously. To get the alignment more accurately and conveniently, we propose a moiré-based alignment method using centrosymmetric grating marks. This method enables both coarse and fine alignment steps without requiring additional conventional cross-and-box alignment marks. Combined with an aligned wafer bonding system, alignment accuracy better than 300 nm (3σ) was achieved after bonding. Furthermore, the working principle of the moiré-based alignment for the backside alignment system was proposed to overcome the difficulty in bonding of opaque wafers. We believe this higher alignment accuracy is feasible to satisfy more demanding requirements in wafer-level stacking technologies.

Performance verification of a precise vibrating-wire magnet alignment technique for next-generation light sources.

The high-accuracy alignment of magnets is a key issue in the development of next-generation light-source rings. To obtain adequate dynamic apertures, the magnets must be aligned to an accuracy of 10 µm or better. Recently, a new technique that utilizes a vibrating wire has attracted attention for this purpose as it can directly determine with high resolution the magnetic centers in a series of multipole magnets on a straight section between bending magnets. In conventional vibrating-wire alignment techniques, wire sag, which causes alignment errors, is determined from the theoretical catenary curve. By contrast, in the present study, we have measured the sag profiles of various wires in the longitudinal direction to micrometer-order accuracy. We concluded that we can reduce deviations of the actual wire sag from the theoretical curve by choosing a suitable wire. By setting up a test bench of a vibrating-wire alignment system for a series of multipole magnet on a straight section, we have achieved the total error of the magnetic-center measurements of micrometer-order in the standard deviation. Moreover, two systematic error factors, the drift of the magnetic centers due to thermal deformations of the magnets after they are excited and the change in the magnetic centers due to reassembly of the magnets after installing the vacuum chamber, are included in practical magnet alignments. We have experimentally investigated these error factors using the test bench.

Multistage Attitude Determination Alignment for Velocity-Aided In-Motion Strapdown Inertial Navigation System with Different Velocity Models.

A novel multistage attitude determination alignment algorithm with different velocity models is proposed to implement the alignment process of in-motion attitude determination alignment (IMADA) aided by the ground velocity expressed in body frame () in this paper. Normally, The -based IMADA is used to achieve the coarse alignment for strapdown inertial navigation system (SINS). The higher the coarse alignment accuracy, the better initial condition can be achieved to guarantee the performance of the subsequent fine alignment. Consider the influence of the principal model errors and the calculation errors on the alignment accuracy in traditional -based IMADA, this paper deals with a novel alignment algorithm by integrating two different velocity-based IMADAs and the multiple repeated alignment processes. The power of this novel alignment algorithm lies in eliminating the principal model errors and decreasing the calculation errors. Then, the higher alignment accuracy is achieved. Simulations and vehicle experiment are performed to demonstrate the validity of the proposed algorithm.

A Method for Gravitational Apparent Acceleration Identification and Accelerometer Bias Estimation

Accelerometer bias in an inertial navigation system (INS) is the key factor determining the navigation accuracy. Two methods, named separated calibration and system calibration are always used for acceleration bias calibration. The former one needs a high precision turntable to provide reference and the latter cannot estimate accelerometer bias along horizontal direction because of coupling effects between horizontal misalignment angles and horizontal accelerometer bias. In this paper, a new estimation method is designed to estimate accelerometer biases and acquire high horizontal alignment accuracy without a turntable. In the proposed method, different expressions about gravity and accelerometer biases in an inertial frame are analyzed and coupling models about gravity and biases are constructed. Then, measurements from gyroscopes and accelerometers are used to construct gravitational apparent acceleration and Kalman filter used to estimate parameters describing apparent acceleration and estimate accelerometer bias. The simulation and turntable tests show that when the carrier is without translational but with swinging motion, the proposed method can finish gravitational apparent acceleration identification and accelerometer bias estimation effectively at the same time, and when the reconstructed gravitational apparent acceleration used for alignment, horizontal alignment errors can nearly approach zeros.

Bioinspired transfer method for the patterning of multiple nanomaterials.

Patterned nanomaterials have promising applications in various fields, particularly for microfluidic analysis and functional surfaces. Studies on such materials have focused on developing effective methods for fabricating patterns with various nanomaterials. Here, inspired by pollen transfer by bees, we present a simple and effective method for patterning multiple functional materials onto flexible substrates by using adhesive tapes. With the advantages of high alignment accuracy, high pattern resolution and not requiring additional etching or harsh processes, the proposed method can easily be applied to diverse nanomaterials that would not be tolerant of physical, thermal, or chemical treatments, as such treatments could deform the thin film and alter its functionalities. Patterned devices were fabricated and showed excellent performance, demonstrating the applicability of this simple and practical transfer printing technique. The proposed patterning method possesses the distinct advantages of a short operating time and high patterning yield, which highlight the considerable potential for the application of this method for optical and biomedical devices.

Alignment mark optimization for improving signal-to-noise ratio of wafer alignment signal.

Phase diffraction gratings are widely used as alignment marks in wafer alignment systems. A higher alignment accuracy can be obtained by using higher diffraction orders of the alignment mark. Meanwhile, the alignment accuracy is also affected by the signal-to-noise ratio (SNR) of the alignment signal. The diffraction efficiency of the alignment mark is significantly reduced in the practical lithography process because of the strong absorption of the opaque film stacks on the mark surface, especially the metal layer. The reduction of the diffraction efficiency leads to a deterioration of the SNR of the alignment signal. An equal subsegmented phase grating is usually used to improve the diffraction efficiency of higher odd orders, so as to improve the SNR of the corresponding alignment signal. However, there is still a relatively high diffraction efficiency of the zeroth and even orders of such a grating. They will affect the SNR of the alignment signal of odd diffraction orders, which are usually used to measure mark position. In this paper, we propose a method to improve the diffraction efficiency of odd orders for a subsegmented phase grating through optimizing the structure of the alignment mark. Moreover, the diffraction efficiency of the zeroth and even orders, which are not used in the measurement process of mark position, are sufficiently reduced. Simulation results indicate that the SNR of the alignment signal was obviously improved by the proposed method, which is very helpful for improving alignment accuracy.

Cu/SiO2 hybrid bonding obtained by surface-activated bonding method at room temperature using Si ultrathin films

The hybrid bonding technique, used for the bonding of metal-electrode and insulator hybrid interfaces with a high alignment accuracy, is very important for the three-dimensional integration technology. Bonding of Cu and SiO2 hybrid interfaces was performed by surface activated bonding (SAB) method at room temperature using a Si ultrathin film, which we previously proposed. Transmission-electron-microscopy (TEM) observations reveal that no microvoids and gaps are present at the interfaces of bonded Cu/Cu electrodes and SiO2/SiO2. The intermediate layer with the thickness of approximately 5 nm was confirmed at both bonding interfaces. The contact resistance of a pair of bonded electrodes was approximately 4.1 Ω. The bonded specimen fractured at the bonded interface by tensile test, and the bonding strength was then approximately 2 MPa. An electron-energy-loss spectroscopy analysis combined with TEM confirmed that SiO2 was present in the intermediate layer with a two-layer structure including an amorphous Si and SiO2 layers. It seems that the two-layer structure resulted in high contact resistance and low bonding strength. Although the contact resistance was not sufficiently low, the electrical connection of the bonded Cu/Cu electrodes was achieved. These results suggested that hybrid bonding was achieved at room temperature using our novel bonding technique.

A New Bias Error Prediction Model for High-Precision Transfer Alignment.

The purpose of this work was to study bias error in acceleration-based transfer alignment, which is probably caused by cross-correlation between the dynamic lever-arm and the linear motion of a ship. A new prediction model for the cross-correlation-caused error is proposed in this paper. We adopt the Bernoulli-Euler Beam as a simplified ship hull-girder model to verify the existence of the cross-correlation. Then, the mathematical mechanism and the prediction model of the bias error are deduced via the ordinary least squares theory. Three factors influence the bias error in the prediction model: the amplitude of the dynamic lever arm acceleration, the amplitude of the ship motion acceleration, and the cross-correlation between them. Simulation experiments are then conducted to test the influence of the factors. The results show that the mechanism analysis is reasonable, and the bias error prediction model is in agreement with the experimental results. Thus, the proposed prediction model has the potential to deduce the bias error in high-accuracy transfer alignment.

Electroformed Fabrication of Extremely High Aspect Ratio Diffraction Gratings for X-Ray Phase Contrast Imaging

Sandia National Laboratories has developed extremely high aspect ratio, small feature diffraction gratings. Rising interest in non-destructive imaging using X-ray phase contrast imaging (XPCI), has created a need to produce large 100 cm2 area, small 2 µm dimension, high aspect ratio (> 50:1) x-ray absorbing, metal diffraction gratings. Lab based XPCI systems have been primarily the interest of the medical community but have excited other industries with the ability to detect defects in low density materials. Imaging higher density materials or thicker samples requires higher x-ray energies. Higher x-ray energies require thicker gratings, increasing the already challenging aspect ratio demands on the three gratings in an XPCI system. Our work investigates anisotropic aqueous etching of monocrystalline silicon, in conjunction with precision electroformed gold coatings to fabricate such gratings. We show methods for determining Si crystalline plane directions and techniques to achieve high alignment accuracy of an etch mask to these crystalline planes. This enables a deep potassium hydroxide etching, which we follow with a precision electroplating process over a ridged Si template to achieve small dimension, deep anisotropic 1D trenches. Several observations are made regarding the difficulty of accurate alignment to silicon crystalline planes for high accuracy, with subsequent electroformed gold coatings, to achieve optimal pitch and grating feature dimensions. Figure 1 shows the result of aspect ratios demonstrated at 80:1, with a precision electroformed gold coating. Improvements to alignment features and etch process are being studied and show promise to continue increasing accuracy for higher aspect ratio gratings to increase energy exposures in XPCI systems.

Pluggable photonic circuit platform for single-mode waveguide connections using novel passive alignment method

We describe a novel photonic circuit platform and a method for its passive alignment that will allow pluggable and large-scale multi-chip integration for highly functional single-mode waveguides based on planar lightwave circuit (PLC) chips. We achieve our proposed passive alignment method by employing precise mechanical interdigitation between optical fiber based spacers and dry etched rectangular grooves in silica-based PLCs. The method was applied to a PLC–PLC connection device in which two daughter PLC chips were mounted on a mother PLC chip. The assembled device successfully yielded a low connection loss of less than 0.4 dB for all 16 ports with an extremely simple assembly process. We also determined the alignment accuracy of our method by measuring and calculating the connection losses of an assembled Vernier pitch device. The estimated results show that our passive alignment method efficiently provides high alignment accuracy with submicron accuracy.

High aspect ratio anisotropic silicon etching for x-ray phase contrast imaging grating fabrication

Lab based x-ray phase contrast imaging (XPCI) systems have historically focused on medical applications, but there is growing interest in material science applications for non-destructive analysis of low density materials. Extending this imaging technique to higher density materials or larger samples requires higher aspect ratio gratings, to allow the use of a higher energy x-ray source. In this work, we demonstrate the use of anisotropic silicon (Si) etching in potassium hydroxide (KOH), to achieve extremely high aspect ratio gratings. This method has been shown to be effective in fabricating deep, uniform gratings by taking advantage of the etch selectivity of differing crystalline planes of silicon. Our work has demonstrated a method for determining Si crystalline plane directions, specific to (110) Si wafers, enabling high alignment accuracy of the etch mask to these crystalline planes.

Enhancing data acquisition for calibration of optical see-through head-mounted displays

Single point active alignment method is a widely used calibration method for optical-see-through head-mounted displays (OST-HMDs) since its appearance. It always requires high-accuracy alignment for data acquisition, and the collected data affect the calibration accuracy to a large extent. However, there are often many kinds of alignment errors occurring in the calibration process. These errors may contain random errors of manual alignment and system errors of the fixed eye-HMD model. To tackle these problems, we first leverage a random sample consensus approach to recurrently decrease the random error of the collected data sequence and use a region-induced data enhancement method to reduce the system error. We design a typical framework to enhance the data acquisition for calibration, sequentially reducing the random error and the system error. Experimental results show that the proposed method can significantly make the calibration more robust due to the elimination of sampling points with large errors. At the same time, the calibration accuracy can be increased by the proposed dynamic eye-HMD model that takes the eye movement into consideration. The improvement about calibration should be significant to promote the applications based on OST-HMDs.

Uneven-Topography-Chip Packing Approach Using Double-Self-Assembly Technology for 3-D Heterogeneous Integration

Although chip-level heterogeneous integration has high yield for production, low-throughput issue of chip-to-wafer bonding is necessary to be improved. Due to the uneven topography and small chip size, handling issue and alignment accuracy are important factors that impact the difficulty in heterogeneous integration. Self-assembly technology has a high potential to be applied in 3-D heterogeneous integration. By using hydrophobic film to define the stacking area, hydrophilic chips can be assembled to realize alignment process on these areas through wafer surface tension in a very short time. With this concept, double-self-assembly technology is accomplished to resolve both handling and alignment issues for uneven-topography-chip integration. In this paper, different chip sizes of $\mu $ -pillar are simulated to investigate the optimal water volume for double-self-assembly process. High alignment accuracy of misalignment measurement can be accomplished with the optimal water volume. Furthermore, microstructure of Cu/In bonded structures and corresponding electrical analyses are evaluated, while various reliability tests are investigated for bonding quality. Excellent results verify that the double-self-assembly technology could be applied to 3-D heterogeneous integration for uneven-topography-chip integration.

High-alignment-accuracy transfer printing of passive silicon waveguide structures.

We demonstrate the transfer printing of passive silicon devices on a silicon-on-insulator target waveguide wafer. Adiabatic taper structures and directional coupler structures were designed for 1310 nm and 1600 nm wavelength coupling tolerant for ± 1 µm misalignment. The release of silicon devices from the silicon substrate was realized by underetching the buried oxide layer while protecting the back-end stack. Devices were successfully picked by a PDMS stamp, by breaking the tethers that kept the silicon coupons in place on the source substrate, and printed with high alignment accuracy on a silicon photonic target wafer. Coupling losses of -1.5 +/- 0.5 dB for the adiabatic taper at 1310 nm wavelength and -0.5 +/- 0.5 dB for the directional coupler at 1600 nm wavelength are obtained.

Disease Sequences High-Accuracy Alignment Based on the Precision Medicine.

High-accuracy alignment of sequences with disease information contributes to disease treatment and prevention. The results of multiple sequence alignment depend on the parameters of the objective function, including gap open penalties (GOP), gap extension penalties (GEP), and substitution matrix (SM). Firstly, the theory parameter formulas relating to GOP, GAP, and SM are inferred, combining unaligned sequence length, number, and identity. Secondly, we tested the rationality of the theory parameter formulas, with experiment on the ClustalW and MAFFT program. In addition, we obtained a group of MAFFT program parameters according to the formulas proposed. The results of all experiments show that the SPS (sum-of-pair score) obtained from theory parameters is better than the SPS obtained from the default parameters of ClustalW and MAFFT. In both theory and practice, our method to determine the parameters is feasible and efficient. These can provide high-accuracy alignment results for precision medicine.

Enhancing the photon-extraction efficiency of site-controlled quantum dots by deterministically fabricated microlenses

We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 ± 2)% and a high suppression of multi-photon events with g(2)(τ = 0) < 0.06 without background subtraction. The demonstrated combination of site-controlled growth of QDs and in-situ electron-beam lithography is relevant for arrays of efficient SPSs which, can be applied in photonic quantum circuits and advanced quantum computation schemes.