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Design features of a folded MEMS pyramid IMU including interlocking latches, SOI sensors, flexible interconnect hinges, and packaging lids.
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This paper reports a new approach for design and fabrication of chip-level inertial measurement units (IMUs). The method utilizes a 3-D foldable silicon-on-insulator (SOI) backbone with in-situ fabricated high-aspect-ratio sensors. A planar multi-sensor unit was fabricated and subsequently folded in a pyramidal shape, forming a compact IMU. Inertia...
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... though the proposed approach has many advantages, several design challenges should be considered, including the structural rigidity of the folded microsystem, durability, sensor alignment, and packaging. Design of the IMU involves a number of elements, Fig. 2, including a rigid backbone, inertial sensors, mechanical latches, flexible hinges, electrical interconnects, and glass lids for ...
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... suitable interface, such as a DIP package. Sensor anchors are connected to the electrical traces on the polyimide substrate using glass encapsulation lids containing metal traces. Wafer- level fabrication of the lids is performed on a 500 D-263 glass substrate and metal is patterned using a liftoff process to define the electrical interconnects, Fig. 2. Deposition of metal is done utilizing the same procedure as for the IMU structure inter- connects to create a 5000 layer of gold atop a 500 adhesion layer of chrome. After fabrication, the wafer is diced to separate each individual encapsulation lid. Impedance of the traces man- ufactured with this procedure is measured to have a ...
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... silicon does not inherently allow for wetting of solder, a layer of gold is first deposited onto the bonding joints, Fig. 2. Metal deposition is conducted in post-fabrication pro- cessing by mounting the unfolded structure facedown, leaving the backside exposed. With the current process, the entire backside area is coated, however, a shadow mask or lithography can also be used to mask the sidewalls and selectively deposit metal only on the latches. Similar ...
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Citations
... A thin metal film (<5 µm) can be made via magnetron sputtering or electron beam evaporation technology, which is very smooth and compact, and the adhesion properties between a metal layer and the substrate are strong. For pyramid-type atom chips, some micro/nano-electro-mechanical system (M/NEMS) fabrication technologies have been applied [81,122,123] including anisotropic wet etch with a KOH solution, inductively coupled plasma (ICP) etches, and so on. Usually, the design and fabrication technologies of atom chips should be considered simultaneously. ...
As a powerful tool in scientific research and industrial technologies, the cold atom absolute gravity sensor (CAGS) based on cold atom interferometry has been proven to be the most promising new generation high-precision absolute gravity sensor. However, large size, heavy weight, and high–power consumption are still the main restriction factors of CAGS being applied for practical applications on mobile platforms. Combined with cold atom chips, it is possible to drastically reduce the complexity, weight, and size of CAGS. In this review, we started from the basic theory of atom chips to chart a clear development path to related technologies. Several related technologies including micro-magnetic traps, micro magneto–optical traps, material selection, fabrication, and packaging methods have been discussed. This review gives an overview of the current developments in a variety of cold atom chips, and some actual CAGS systems based on atom chips are also discussed. We summarize by listing some of the challenges and possible directions for further development in this area.
... By layering a flexible layer such as photosensitive polyimide on a pattern of a rigid material such as silicon or any metal, a planar compliant mechanism can be fabricated. For example, Zotov et al. fabricated a hinge made of photosensitive polyimide on a silicon-on-insulator wafer and assembled it similar to origami for realizing a three-dimensionally arranged inertial sensor unit [5] . Matei et al. and Asamura et al. also reported miniatured actuators with compliance mechanism using similar processes [ 6 , 7 ]. ...
We developed a process for fabricating a miniaturized hinged mechanism for microrobots by customizing our previously reported flapping-wing method to fabricate microscopic wing structures resembling insects. Flexible hinges were realized by removing the titanium layers of the structure, which were previously sandwiched between thin polyimide layers. A three-dimensional structure can also be realized via origami-like assembly owing to the hinge structure, where the hinge is made to work as a crease. Details of our method and a reference design are reported through a demonstration of a translation-to-rotation conversion mechanism for a piezoelectric actuator.
• Simple fabrication using a single hot lamination and origami-like assembly.
• Method based on FPC manufacturing technologies would be easy to implement in a variety of research.
• Transmission mechanism for piezoelectric actuators was demonstrated, verifying that the structures fabricated by this process function appropriately.
... Here, the standard deviation (SD) of the error accumulation from the rotation angle determination was caused by the presence of white noise in the gyroscope output signal. Moreover, it increases proportional to the square root of the time: [22,23]. ...
A problem of estimating the movement and orientation of a mobile robot is examined in this paper. The strapdown inertial navigation systems are often engaged to solve this common obstacle. The most important and critically sensitive component of such positioning approximation system is a gyroscope. Thus, we analyze here the random error components of the gyroscope, such as bias instability and random rate walk, as well as those that cause the presence of white and exponentially correlated (Markov) noise and perform an optimization of these parameters. The MEMS gyroscopes of InvenSense MPU-6050 type for each axis of the gyroscope with a sampling frequency of 70 Hz are investigated, as a result, Allan variance graphs and the values of bias instability coefficient and angle random walk for each axis are determined. It was found that in the output signals of the gyroscopes there is no Markov noise and random rate walk, and the X and Z axes are noisier than the Y axis. In the process of inertial measurement unit (IMU) calibration, the correction coefficients are calculated, which allow partial compensating the influence of destabilizing factors and determining the perpendicularity inaccuracy for sensitivity axes, and the conversion coefficients for each axis, which transform the sensor source codes into the measure unit and bias for each axis. The output signals of the calibrated gyroscope are noisy and offset from zero to all axes, so processing accelerometer and gyroscope data by the alpha-beta filter or Kalman filter is required to reduce noise influence.
... The matrix represented in Table III defines correspondence between axes of navigation reference frame xyz and measuring reference frame Taking into consideration [4], [7], [8] the blockscheme of the process of designing the smart measuring instruments based on autonomous vector sensors and nonorthogonal redundant configurations is represented in Fig. 4. ...
... MEMS technology is often used to fabricate IMUs [19]. Using this approach, 3D foldable silicon-on-insulator wafers are used for sensor microfabrication [18] with several steps including photolithography and other processes. ...
... Folded MEMS approach for implementation of a multiaxis IMU was first demonstrated by the research group at UC Irvine, [26]. The method utilized a 3D foldable SOI structure with in-situ fabricated inertial sensors. ...
... Along with all the advantages of the single-sided Folded IMU approach [26], including a relatively simple 4-mask fabrication process, a small size of IMU, structural rigidity, and compatibility with the wafer-level packaging process, several challenges emerged during the initial studies. First, the thick layer of polyimide on the device side of a wafer limited the accuracy of lithography resulting in reduced performance of inertial sensors. ...
... To maintain the original alignment of sensors (after the calibration) under different environmental conditions, the Folded IMU structures are reinforced by means of epoxy, eutectic soldering, or silicon welding of the interlocking latches located along the silicon panels. It was previously shown in [26] that solder reinforced IMU structures exhibit <0.2 mrad change in sidewall alignment angle during thermal testing in the range of temperatures from 25°C to 85°C. The misalignment error due to temperature can be further minimized using silicon welding for reinforcement of IMU structures, [27]. ...
... Theoretical basis and the questions of structurally redundant inertial measurement units (IMUs) realization have already been investigated in numerous publications [15 -17]. Initially, the aim of structural redundancy was not to improve accuracy but to detect and isolate faults of primary inertial information measurement units and as a result to increase navigation system's fault tolerance [18]. The specificity of structurally redundant IMUs development applied to the miniature pedestrian navigation systems is that reserving IMUs to increase reliability is impractical, since this would lead to unnecessary increase in the cost and complication of these systems, so instead of this the requirements for positioning accuracy are in the first place. ...
Employing the redundant number of inertial MEMS sensors is a promising line of pedestrian positioning technologies development offering a great potential in reliability, measurement accuracy and low level of noise. For this reason the article considers the design and realization features of a miniature pedestrian navigation system implementing this principle. Firstly, the model of a non-orthogonal redundant measurement unit measuring channels is presented in the article. Furthermore, details of algorithmic and hardware solutions used in the proposed pedestrian navigation system based on redundant inertial measurement unit are discussed. The results of the developed system’s field tests demonstrating higher navigation accuracy for redundant navigation system than for non-redundant are also presented.
... Recently, several research groups have made advances in the hybrid approach, such as the multi-layer stacked IMU, [3], and the tri-fold integrated IMU, [4]. Our solution to miniaturization of tactical-grade IMU is through the folded IMU approach, [5], which combines the advantage of high performance single-axis sensors, and the ability to have 6-DOF sensitivity in a miniaturized footprint IMU. This is accomplished by fabricating foldable MEMS structures on a wafer-level and assembling them into 3D cubic or pyramidal configurations. ...
... In this paper, we focus only on the survivability and stability of the folded MEMS backbone structure. An initial structural rigidity study under variations in temperature, vibration, and shock for a folded pyramid was conducted in [5]. We expanded the scope of our previous study beyond consideration of reinforcement materials, and investigated the effect of size and geometry in environmental tests. ...
... Prototype of 3D MEMS origami-like IMU has previously been demonstrated in [5]. The updated double-sided process has been shown in [7] with in-situ fabricated sensors, and integration with separately fabricated sensors, [8]. ...
... This, in general, requires simultaneous noise reduction, improved vibration rejection, and offset and sensitivity stabilization against environmental changes. A non-exhaustive list of examples includes (i) ultra-high-Q-factor capacitive devices [2,3], where the high Q allows reducing ARW and phase noise; (ii) frequency modulated (FM) devices [4,5], where the scale factor is ratiometric and independent on process tolerances; (iii) robust device design [6,7] or high frequency operation [8] to minimize effects of external vibrations generating spurious output signals. ...
... The high sensitivity guaranteed by these sensing elements enables lownoise operation at relatively large frequency mismatches between drive and sense mode, ensuring good stability. Unlike the devices proposed in [2][3][4][5], this approach is fully compatible with 3-axial devices. A planar 3-axis gyroscope based on nanogauges has been e.g. reported in details in [11]. ...
... The Z-axis gyroscope adopted for the measurements is shown in Fig. 1 [3]. It consists of a doubly-decoupled architecture including a comb-actuated drive frame, a Coriolis (decoupling) frame and a levered sense frame whose dual fulcrum is represented by two 5-μm-long, (250 nm) 2 crosssection, monocrystalline Silicon nano gauges (the NEMS part of the device) directly patterned from the original SOI wafer at the beginning of the surface micromachining process. ...
This work demonstrates high-performance in a low-footprint MEMS gyroscopes based on piezoresistive nano-gauge readout. Significant noise reduction can be obtained by increasing the current dissipation in differential nano gauges, each having a (250 nm)2 cross-section. Though the device is fabricated in a low-cost process and operates at relatively large pressures (about 4 mbar), the achievable angle random walk (ARW) approaches the theoretical thermomechanical limit of 0.9 mdps/√Hz. Within 800 µm × 450 µm only, and at biasing voltages for the sense electronic chain of 1.5 V only, the measurement of Earth rotation rate through gyroscope carouseling is clearly demonstrated with stability up to more than 1000 s.
... Characterization of the experimental setup is crucial for understanding the repeatability and accuracy of maytagging and carouseling measurements. An optical characterization method was developed to precisely measure the azimuth uncertainty of the setup [29], Fig. 2. The method relies on measuring a misalignment of the gyroscope fixture before and after each 360°full turn. The gyroscope fixture is rotated using a precision-controlled single-axis Ideal Aerosmith 1291BR rate table with an angular accuracy of ± 0.07 mrad and repeatability of ± 0.015 mrad. ...
North-finding based on micromachined gyroscopes is an attractive possibility. This paper analyzes north-finding methods and demonstrates a measured 4 mrad standard deviation azimuth uncertainty using an in-house developed vibratory silicon MEMS quadruple mass gyroscope (QMG). We instrumented a vacuum packaged QMG with isotropic Q-factor of 1.2 million and Allan deviation bias instability of 0.2 °/hr for azimuth detection by measuring the earth's rotation. Continuous rotation (“carouseling”) produced azimuth datapoints with uncertainty diminishing as the square root of the number of turns. Integration of 100 datapoints with normally distributed errors reduced uncertainty to 4 mrad, beyond the noise of current QMG instrumentation. We also implemented self-calibration methods, including in-situ temperature sensing and discrete ±180° turning (“maytagging” or two-point gyrocompassing) as potential alternatives to carouseling. While both mechanizations produced similar azimuth uncertainty, we conclude that carouseling is more advantageous as it is robust to bias, scale-factor, and temperature drifts, although it requires a rotary platform providing continuous rotation. Maytagging, on the other hand, can be implemented using a simple turn table, but requires calibration due to temperature-induced drifts.
