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This paper describes a novel high-precision, low-noise, high-stability, calibrated and compensated digital oscillatory gyroscope with SPI interface, housed in custom-made ceramic packages. The device is factory-calibrated and compensated for temperature effects to provide high-accuracy digital output over a broad temperature range. Optimized tuning...
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... factor that limits the stability and reliability of capacitive devices [13, 14]. To avoid the electrostatic charging caused by external sources, custom-made packages with metal lids are used. To avoid the internal generation of electrostatic charging in the sensing element, screening electrodes are designed to surround entirely the active electrodes. The inherent non-linearity associated with the asymmetry of the driving springs has raised additional stability concerns [15-17]. Consequently, great care has been taken to avoid any parametric, sub- or superharmonic resonances in the system. III. S ENSOR M ANUFACTURING The manufacturing of the sensing element involves an innovative double-side processing and bonding of two capping composite wafers and a single-silicon substrate [9]. Fig. 5 illustrates the fabrication sequence that structures the top and bottom composite wafers. First, the pattern of the future glass inserts is defined by deep reactive ion etching (DRIE) in a single-crystal silicon wafer. Borosilicate glass is then reflowed in the created deep recesses [10, 11]. All the excess materials, silicon and glass, are removed by grinding and chemical-mechanical polishing (CMP). A contiguous layer of glass is kept on the outer surface of the composite wafers in order to enable the subsequent anodic bonding steps. The process continues by locally etching the glass inserts in those particular areas that are not intended for bonding, to form shallow recesses. A metal layer is deposited and patterned to form one part of the electrical press-contacts. An additional, distinct patterned metal layer is applied to one of the composite wafers to serve as getter for the various gases that may affect in long term the damping of the oscillations. Note that, in order to achieve the required full symmetry, the corresponding elements of the top and bottom composite wafers have identical structure and geometry. In order to achieve reliable thickness control, the MEMS elements are manufactured within the single-crystal silicon device layer of an SOI wafer. Fig. 6 illustrates the fabrication sequence that structures the front surface of the SOI wafer. First, contact recesses are de- fined within the device layer to serve as requisite spacing for the top side electrical press-contacts. Then, electrode recesses are defined to serve as gaps for a number of subsequent top side capacitors. The combination of the contact and electrode recesses offers the possibility to create, at dedicated locations, silicon stoppers. An aluminium layer is deposited and patterned to form one part of the top side electrical press-contacts. Then, the upper-half profile of the beams is defined by DRIE. Anodic bonding is used to permanently attach the machined SOI wafer and the top composite wafer to form the double- stack bonded wafer shown in Fig. 7. Fig. 8 shows a detail of the formed double-stack bonded wafer, illustrating an example of top side capacitor, top side electrical press-contact and top side stopper. Fig. 9 illustrates the fabrication sequence that removes the excess materials from the double-stack wafer. Grinding, followed by chemical-mechanical polishing (CMP), is used to remove the contiguous layer of glass, thus exposing the silicon pattern of the top composite wafer. Grinding, followed by reactive ion etching with etch stop on the buried oxide layer, is used to remove the handle wafer. Wet etching is then used to remove the buried oxide, thus exposing the back surface of the device layer. Fig. 10 illustrates the fabrication sequence that structures the back surface of the double-stack bonded wafer. Identical processing sequence and layer geometry as on the front surface are used. The masses and the beams are formed and released in the process. Anodic bonding, performed in high-vacuum, is used to permanently attach the machined double-stack wafer and the bottom composite wafer to form the triple-stack bonded wafer shown in Fig. 11. Bottom side press-contacts and capacitors, similar to those illustrated in Fig. 8, are formed in the process. The anodic bonding between a silicon substrate and silicon- glass composite wafers allows the formation of a hermetic seal not only between the involved wafers, but between the internal silicon-glass interfaces of the composite wafers as well. Fig. 12 illustrates the fabrication sequence that completes the structuring of the triple-stack bonded wafer. First, grinding, followed by CMP, is used to remove the contiguous glass layer, thus exposing the silicon pattern of the bottom composite wafer. Metal layers are then deposited and patterned on both surfaces of the triple-stack wafer to form the top and bottom pads. Finally, sawing is used to separate the wafer into dice. Fig. 13 shows the top view of the sensing element, with the distinctive silicon-glass structure clearly visible. IV. S IGNAL PROCESSING The signal processing in the SAR500 is based upon two main feedback loops, as shown in Fig. 14. The excitation loop is a positive feedback loop with automatic gain control (AGC), which keeps the drive mode of the sensor oscillating at its natural frequency, at constant amplitude. The detection loop has a negative feedback that reduces the Q factor of the sense mode to provide the required bandwidth of the gyroscope. The capacitive sensor signal is read by a fully differential low-noise charge amplifier with correlated double sampling. A 5 th order sigma-delta (SD) ADC converts the signal to a bit- stream for processing in the digital part of the feedback loop. The digital signal processing provides a stable, high-reso- lution implementation of the loop filters and sigma-delta (SD) DACs for excitation and detection feedback. It also performs low-noise synchronous demodulation and compensates for temperature drift of bias and scale factor. The analog reconstruction filter is matched to the SD DAC, as illustrated in Fig. 15, to remove the quantization noise from the analog voltage that is fed back to the sensing element. Since the gyroscope operates in a narrow bandwidth close to 10 kHz, the 1/f noise is not a major issue in most of the circuits. Yet some of the circuits depend on the stability of the reference voltage and are therefore quite sensitive to the low frequency noise. Great care has been taken to reduce the impact of the 1/f noise in those particular circuits. Though the analog chip contains a voltage reference, in order to achieve the targeted long-term stability, an external voltage reference is used. The readout and force feedback in the two loops is time multiplexed at a frequency of about 300 kHz. Innovative algo- rithms are used to generate feedback signals for quadrature compensation and frequency matching. The electronics is realized on two chips, an analog and a digital ASIC. The read-out amplifiers, sigma-delta ADCs, reconstruction filters and voltage reference have been implemented in a 0.35 μm process with a 20V process option, as shown in Fig. 16. The digital circuits are currently implemented in an FPGA, but will be realized in a 90 nm structured ASIC at a later stage. A 32 bit microcontroller is included to perform temperature compensation and other auxiliary tasks. The gyroscope is configured as an SPI slave for efficient readout of angular rate and other data. V. A SSEMBLY AND P ACKAGING The packaging has a major influence on the performance of the device, especially with respect to factors such as long-term drift and stability. Since the analog ASIC is a major heat source, capable of inducing significant temperature gradients across the sensing element, the sensing element and the analog ASIC are mounted in distinct, separated packages, subsequently soldered together. The main design requirements for the SAR500 packages were: i) full symmetry around the sensing element (with respect to mechanical and thermal loads); ii) reduced levels of transmitted stress and strain to the sensing element; iii) high thermal efficiency (fast evacuation of heat from the analog ASIC and uniform temperature distribution inside the sensing element). The sensing element is mounted in a fully symmetrical, custom-made 16 pin, side-brazed ceramic package, shown in Fig. 17. The high thermal efficiency of the package is achieved by using internally a large number of dedicated thermal vias and metal layers. Two identical, metal lids are subsequently attached in high vacuum on either sides of the package by electron-beam welding, thus sealing hermetically the sensing element. The size of the 16 pin package, including the pins, is 14.8 mm x 14.8 mm x 3.8 mm. The ASIC is mounted in a custom-made 32 pin, side-brazed ceramic package, shown in Fig. 18. The high thermal efficien- cy of the package is achieved by using a CuW thermal slug that is in direct physical contact with the ASIC. The thermal slug is provided with four filleted metal studs for versatile mounting on 'heat sinks'. A metal lid is subsequently soldered in inert atmosphere. The size of the 32 pin package, including the pins, is 17.6 mm x 17.6 mm x 5.0 mm. Finally, the two ceramic packages are soldered on top of each other, as shown in Fig. 19. VI. C ONCLUSIONS SAR500, a novel high-precision, low-noise, high-stability, calibrated and compensated digital oscillatory gyroscope with north seeking capability, is reported. The SAR500 contains a ButterflyTM MEMS die and an analog ASIC, individually housed in rigid, thermally efficient, custom-made ceramic packages. An FPGA or a digital ASIC contains the needed control and functional algorithms to achieve the superior performance. The gyroscope is configured as an SPI slave for efficient readout of angular rate. The device is factory-calibrated and compensated for temperature effects to provide high-accuracy digital output over a broad temperature range. Optimized tuning of the excitation and detection frequencies, as well as optimized mechanical and electrical balancing of the dual ...
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Citations
... Therefore, the MEMS capacitor sensor, as an important sensor system, is widely used in aerospace, industrial control, military and medical fields [7][8][9]. In recent years, with the huge demand in the consumer electronics market, high performance gyro systems such as frame type [10], disk type [11][12][13] and butterfly type [14][15][16] have been researched and developed successively. Therefore, how to further improve the overall performance of the MEMS gyroscope and develop its potential performance has become a research hotspot in recent years. ...
... cos(ωt + ϕ s1 +ϕ s2 2 + ϕ d ) can be used as the demodulation signal of the angular velocity sensitive detection signal in Equation (15). After the double frequency signal is filtered by the low-pass filter, the final output of the gyroscope can be written: ...
This paper introduces a digital interface application-specific integrated circuit (ASIC) for a micro-electromechanical systems (MEMS) vibratory gyroscope. The driving circuit of the interface ASIC uses an automatic gain circuit (AGC) module instead of a phase-locked loop to realize a self-excited vibration, which gives the gyroscope system good robustness. In order to realize the co-simulation of the mechanically sensitive structure and interface circuit of the gyroscope, the equivalent electrical model analysis and modeling of the mechanically sensitive structure of the gyro are carried out by Verilog-A. According to the design scheme of the MEMS gyroscope interface circuit, a system-level simulation model including mechanically sensitive structure and measurement and control circuit is established by SIMULINK. A digital-to-analog converter (ADC) is designed for the digital processing and temperature compensation of the angular velocity in the MEMS gyroscope digital circuit system. Using the positive and negative diode temperature characteristics, the function of the on-chip temperature sensor is realized, and the temperature compensation and zero bias correction are carried out simultaneously. The MEMS interface ASIC is designed using a standard 0.18 μM CMOS BCD process. The experimental results show that the signal-to-noise ratio (SNR) of sigma-delta (ΣΔ) ADC is 111.56 dB. The nonlinearity of the MEMS gyroscope system is 0.03% over the full-scale range.
... The automotive industry, military equipment, consumer electronics and other application markets require MEMS gyroscopes for lower cost, easier integration, higher sensitivity, lower vibration sensitivity, higher Q factor and better reliability [1][2][3][4]. Numerous scientific research institutions have put a lot of efforts into structure design, micromachining technology and readout electronic circuits. G. Andersson, who worked at IMEGO Institute, first proposed the butterfly gyroscope in 1999 [5]. ...
... G. Andersson, who worked at IMEGO Institute, first proposed the butterfly gyroscope in 1999 [5]. After continuous development and progress, this structure shows the ability to achieve high performance [3,4,6,7]. ...
... The processing of combs is particularly complex and an uneven electrode gap will lead to excessive ZRO [1,9]. BFVG works based on plate electrodes, which avoids the manufacture of combs [3]. This simple structure design does not have many suspension beams, anchors and combs, and the sense vibration occurs outside the plane with higher sensitivity. ...
A novel three-dimensional (3D) wafer-level sandwich packaging technology is here applied in the dual mass MEMS butterfly vibratory gyroscope (BFVG) to achieve ultra-high Q factor. A GIS (glass in silicon) composite substrate with glass as the main body and low-resistance silicon column as the vertical lead is processed by glass reflow technology, which effectively avoids air leakage caused by thermal stress mismatch. Sputter getter material is used on the glass cap to further improve the vacuum degree. The Silicon-On-Insulator (SOI) gyroscope structure is sandwiched between the composite substrate and glass cap to realize vertical electrical interconnection by high-vacuum anodic bonding. The Q factors of drive and sense modes in BFVG measured by the self-developed double closed-loop circuit system are significantly improved to 8.628 times and 2.779 times higher than those of the traditional ceramic shell package. The experimental results of the processed gyroscope also demonstrate a high resolution of 0.1°/s, the scale factor of 1.302 mV/(°/s), and nonlinearity of 558 ppm in the full-scale range of ±1800°/s. By calculating the Allen variance, we obtained the angular random walk (ARW) of 1.281°/√h and low bias instability (BI) of 9.789°/h. The process error makes the actual drive and sense frequency of the gyroscope deviate by 8.989% and 5.367% compared with the simulation.
... The properties of the out-of-plane mode are strictly related to the shape of the cross section of the connecting beams. Another interesting tuning fork structure is the butterfly gyroscope [56], [57], whose out-of-plane mode is like a butterfly flapping its wings. Besides, a tuning fork structure that can detect both yaw and pitch rotations was proposed by [58], [59]. ...
... Using the bonding techniques is also an effective and feasible method. So far, glass frit bonding [112], Ge-Al bonding [113], glass-silicon bonding [56], [114] and Al-Al bonding [115], etc. have been used for wafer-level packaging. In addition, how to realize the electric connection between the transducers inside the package and the components outside is another important issue. ...
... Designs of conductive layers, vertical feedthrough (Fig.28), or through-wafer vias are generally used for the conducting purpose. [56], [112], [116]- [119]. ...
As a high-precision angular rate sensor, the Frequency-Modulated (FM) gyroscope based on MEMS craft has attracted more and more attention in recent years, owing to its advantages in low power consumption, low temperature sensitivity, very high bandwidth, and excellent scale factor stability. This review summaries the history and latest development of the FM gyroscope research. The theory of the frequency modulation effect of the Coriolis coupling is provided based on the method of rotating wave approximation in a systematic and explicit way. Typical FM gyroscope operation modes, such as QFM, IFM, LFM, and their working principles are introduced minutely. The error sources of FM gyroscopes, and the characters comparison between FM and AM gyroscopes are discussed in detail as well.
... As an important part of inertial measurement systems, gyroscopes have broad applications spanning from navigation and intelligent control to attitude measurement [1][2][3][4]. So far, a variety of gyroscopes, ranging from the original mechanical rotor type to laser and fiber-optic versions, have been developed [5][6][7][8]. Recent interest in developing an integrable and energyefficient inertial navigation system has created a compelling need for miniaturization of the gyroscope. ...
We demonstrate a novel, to the best of our knowledge, micro-opto-electro-mechanical system (MOEMS) gyroscope based on the Talbot effect of a single-layer near-field diffraction grating. The Talbot effect of an optical grating is studied both theoretically and experimentally. A structure of grating–mirror combination, fabricated by the micro–nano processing method, is used for out-of-plane structure detection. The detection of a weak Coriolis force is realized by using the highly sensitive displacement characteristic of Talbot imaging of near-field diffraction with a mirror mass block and single-layer grating. The experimental results show that, the micro-displacement detection sensitivity can reach up to 0.09%/nm, and the MOEMS gyroscope can be moved in the driven direction, with a resonant frequency of 7048 Hz and a quality factor of 700, which indicates great potential of the Talbot effect in developing novel high-performance micro-gyroscopes.
... To achieve large vibration amplitude, the silicon wafers prefabricated with sensing structures were anodically bonded under high vacuum pressure (about 0.8 mbar) at wafer level [24]. Photograph of the Wafer-Level-Package (WLP) capacitive vibration gyroscopes is shown in Fig. 6, the size of the gyroscopes is only 3 mm × 3 mm, custom-made packages with metal lids are used to avoid the electrostatic charging caused by external sources [25]. The designed real-time circuit phase delay correction system is tested on these Self-developed shock resistant vibration gyroscopes. ...
With the development of designing and manufacturing level for micro-electromechanical system (MEMS) gyroscopes, the control circuit system becomes a key point to determine their internal performances. Nevertheless, phase delay of electron components may result in some serious hazards. This paper describes a real-time circuit phase delay correction system for MEMS vibratory gyroscopes. A detailed theoretical analysis is provided to clarify the influences of circuit phase delay on the in-phase and quadrature (IQ) coupling characteristics and zero rate output (ZRO) utilizing force-to-rebalance (FTR) closed-loop detection and quadrature correction system. By deducing the relationship between amplitude-frequency, phase-frequency of MEMS gyroscope and the phase relationship of the whole control loop, a real-time correction system is proposed to automatically adjust the phase reference value of phase-locked loop (PLL) and thus compensate for the real-time circuit phase delay. The experimental results show that the correction system can accurately measure and compensate the circuit phase delay in real time. Furthermore, the unwanted IQ coupling can be eliminated and the ZRO is decreased by 755% to 0.095°/s. This correction system realizes a small angle random walk of 0.978°/√h, and a low bias instability of 9.458°/h together with a scale factor nonlinearity of 255 ppm at room temperature. Besides, the thermal drift of ZRO is reduced to 0.0034°/s/°C at a temperature range from -20°C to 70°C.
... To solve the above problems, a composite wafer was presented to complete vertical interconnection [12][13][14]. The composite wafer was first reported by VTI company in 2001, and is [12] used for packaging sandwich-type accelerometers and also used for packaging butterfly-type gyroscopes, as reported by the Sensonor company in 2010 [13]. ...
... Vertical interconnection techniques can reduce parasitic capacitance and power consumption due to shorter interconnection lengths [10] and improve the integrated level and space efficiency [11]. To solve the above problems, a composite wafer was presented to complete vertical interconnection [12][13][14]. The composite wafer was first reported by VTI company in 2001, and is [12] used for packaging sandwich-type accelerometers and also used for packaging butterfly-type gyroscopes, as reported by the Sensonor company in 2010 [13]. ...
... To solve the above problems, a composite wafer was presented to complete vertical interconnection [12][13][14]. The composite wafer was first reported by VTI company in 2001, and is [12] used for packaging sandwich-type accelerometers and also used for packaging butterfly-type gyroscopes, as reported by the Sensonor company in 2010 [13]. In 2018, Meng Zhang et al. proposed a 3D packaging technology based on a composite wafer [14]. ...
In this paper, we report a novel teeter-totter type accelerometer based on glass-silicon composite wafers. Unlike the ordinary micro-electro-mechanical systems (MEMS) accelerometers, the entire structure of the accelerometer, includes the mass, the springs, and the composite wafer. The composite wafer is expected to serve as the electrical feedthrough and the fixed capacitance plate at the same time, to simplify the fabrication process, and to save on chip area. It is manufactured by filling melted borosilicate glass into an etched silicon wafer and polishing the wafer flat. A sensitivity of 51.622 mV/g in the range of ±5 g (g = 9.8 m/s2), a zero-bias stability under 0.2 mg, and the noise floor with 11.28 µg/√Hz were obtained, which meet the needs of most acceleration detecting applications. The micromachining solution is beneficial for vertical interconnection and miniaturization of MEMS devices.
... With the continuous improvement of performance, it will excel in high-end applications such as navigation, defense, aviation and aerospace [1,2]. Recently, high performance gyros such as the frame type [3][4][5][6][7], the disc type [8][9][10][11][12], the butterfly [13][14][15][16][17][18][19], etc. have attracted a lot of attention from academia and industry. The vibratory MEMS gyro is based on the Coriolis effect to measure the input angular velocity [20]. ...
Traditional MEMS gyroscope readout eliminates quadrature error and relies on the phase relationship between the drive displacement and the Coriolis position to accomplish a coherent demodulation. This scheme shows some risk, especially for a mode-matching gyro. If only a slight resonant frequency deviation between the drive and sense mode occurs, a dramatic change in the phase relationship follows, which leads to a wrong demodulation. To solve this, this paper proposes a new readout based on the quadrature error and an auxiliary phase-locked loop (PLL). By tuning the phase shifter in the sense-mode circuit, letting the quadrature error and the carrier of the mixer be in 90° phase alignment, the Coriolis was simultaneously in phase with the carrier. Hence, the demodulation was accomplished. The carrier comes from the PLL output of the drive-mode circuit due to its low jitter and independence of the work mode of the gyro. Moreover, an auxiliary PLL is used to filter the quadrature error to enhance the phase alignment accuracy. Through an elaborate design, a printed circuit board was used to verify the proposed idea. The experimental results show the readout circuit functioned well. The scale factor of the gyro was 6.8 mV/°/s, and the bias instability was 204°/h.
... A resonating mass is the central sensing element in a MEMS vibratory gyroscope. Among various resonator structures, butterfly resonators attracted attention from both the industry and academia (Andersson et al. 1999;Su et al. 2013;Hedenstierna et al. 2001;Xu et al. 2017;Mochida et al. 2007;Lapadatu et al. 2010;Jeong et al. 2004;Xiao et al. 2013;Wu et al. 2015) due to its simple structure that does not require many suspension beams, anchors and comb drives. It has a unique geometry consisting of four proof-masses attached to a synchronizing beam as shown in Fig. 1. ...
... The diamond shaped coupling mechanism utilizes two folding springs that can adjust the stiffness of the gyroscope in different conditions. Apart from structural optimization, electrostatic tuning (Lapadatu et al. 2010;Jeong et al. 2004) showed that the drive and sense frequencies can enhance the performance and demonstrated north finding application. Recently, hexagonal oblique beam has been studied and was used for enhancing sensitivity . ...
This paper presents beam modeling techniques for maximizing mechanical sensitivity of a butterfly resonator for gyroscopic applications. We investigate the geometric aspects of synchronizing beam that connects the wings of a butterfly resonator. Our results show that geometric variation in the synchronizing beam can have a large effect on the frequency split and sensitivity of the device. The model simulation shows a sensitivity of \( 10^{ - 12} \)\( (m/^\circ /s) \) for a frequency split of 10 Hz resulting from the optimized synchronized beam. Out of plane actuation was developed to drive and sense the resonators displacement. Fabricated butterfly resonators were tested, and the experimental results show a frequency split of 305 Hz and 400 Hz while the model illustrated a split of 195 Hz and 330 Hz respectively. The design and analysis presented in this paper can further aid the development of MEMS butterfly resonators for inertial sensing applications.
... Maytagging has been widely applied in various methods of north finding angle detection, such as the two-point method, four-point method, and multiposition method. (6)(7)(8) It is simple to operate and is widely employed in practical applications. However, this method will increase the error caused by the rate random walk (RRW), which conflicts with the angular random walk (ARW). ...
... In this paper, we focus on reducing the bias warm-up time of the MEMS gyroscope for tactical applications that are cost sensitive. Although the mode-matched gyroscope is normally considered a very effective technical solution to obtain high performance [17][18][19][20] , the complexity of the readout circuit and the device cost inevitably increase in that at least four control loops are necessary: the drive, quadrature control, rate rebalance and mode matching loops. In some cases, passive post-trimming methods, such as laser trimming 21 , focused ion beam trimming 22 , and mass loading 23 are required for extremely small and stable frequency split. ...
MEMS: Fast Start-up gyroscopes A method to achieve reduced bias warm-up time in MEMS gyroscopes could lead to enhanced technologies. MEMS gyroscopes are widely used in tactical applications, including gun-launched projectiles and tactical missile guidance. However, such applications require that the bias warm-up time – the time period between turning on the gyroscope and it achieving a stable state – is as short as possible; for example, one can imagine that a projectile will only be in-flight for a matter of seconds in some instances, and achieving stability in the gyroscope as soon as possible is vital. Now, a team led by Guizhen Yan from Institute of Microelectronics, Peking University, demonstrates that suppressing the coupling stiffness provides a simple and cost-effective way to reduce the bias warm-up time, achieving a three order of magnitude reduction.
