Silicon Micro-gyroscope Research Articles

A Digitalized Silicon Microgyroscope Based on Embedded FPGA

This paper presents a novel digital miniaturization method for a prototype silicon micro-gyroscope (SMG) with the symmetrical and decoupled structure. The schematic blocks of the overall system consist of high precision analog front-end interface, high-speed 18-bit analog to digital convertor, a high-performance core Field Programmable Gate Array (FPGA) chip and other peripherals such as high-speed serial ports for transmitting data. In drive mode, the closed-loop drive circuit are implemented by automatic gain control (AGC) loop and software phase-locked loop (SPLL) based on the Coordinated Rotation Digital Computer (CORDIC) algorithm. Meanwhile, the sense demodulation module based on varying step least mean square demodulation (LMSD) are addressed in detail. All kinds of algorithms are simulated by Simulink and DSPbuilder tools, which is in good agreement with the theoretical design. The experimental results have fully demonstrated the stability and flexibility of the system.

Shock Analysis on Dual-Mass Silicon Micro-Gyroscope

Survivability in shock environment is an important reliability index of silicon micro-gyroscope. Shock response of dual-mass silicon micro-gyroscope is investigated in this paper. A lumped mass model was established for the micro-gyroscope based on the characteristics of the dual-mass structure. Analytic solution to the response of the structure under shock load in a half-sine acceleration form was then acquired. The analytic solution was applied to calculate the shock response of a well designed dual-mass silicon micro-gyroscope in our laboratory, while the correctness of it was verified with finite element method (FEM) in ANSYS. The analytic solution is serviceable in reliability prediction of dual-mass silicon micro-gyroscope in shock environment.

On-Chip Temperature-Control Technology for Silicon Micro-Gyroscope

A micro-heater is used inside silicon micro-gyroscope to keep the working temperature of gyroscope constant so as to minimize the effect of environment temperature on performances of gyroscope. The structure of gyroscope package is first given. With a heater inside, the characteristics of gyroscope, such as frequency, coupled vibrations, temperature distribution and thermal equilibrium time, are predicted with the aid of ANSYS, a finite element tool. Finally, surfaces of the package are optimized with anti-radiation shields covering. As a result, when gyroscope is subjected to an ambient temperature of 20°C, the temperature of itself could reach the equilibrium state of about 84°C within 2 minutes with a temperature difference of about 2°C between the anchor and the proof mass. Besides, if ambient temperature increases from -40°C to 80°C, heating power consumption is degraded from 1.27625W to 0.09712W. However, this design needs further improvement to decrease its heating power consumption and equilibrium time.

A Combination of Silicon Micro-gyroscope that Application Rotary Missile Attitude Control System

For the technical requirements of rotary missile attitude control, there developed a new type of combination of silicon micro-gyroscope, it mainly consists of two perpendicular installation of micro-mechanical pendulum and the circuit. This paper reports this kind of combination of silicon micro-gyroscope, which attitude control system in polar coordinate transformation, the combination can demodulate the horizontal angular velocity, yaw angular velocity, pitch angular velocity and the spin angular velocity of the rotary missile. This combination of silicon microgyroscope have been tested in rotary missile, the results show that it works very well in rotating missile attitude control system.

Development of a Prototype Miniature Silicon Microgyroscope

A miniature vacuum-packaged silicon microgyroscope (SMG) with symmetrical and decoupled structure was designed to prevent unintended coupling between drive and sense modes. To ensure high resonant stability and strong disturbance resisting capacity, a self-oscillating closed-loop circuit including an automatic gain control (AGC) loop based on electrostatic force feedback is adopted in drive mode, while, dual-channel decomposition and reconstruction closed loops are applied in sense mode. Moreover, the temperature effect on its zero bias was characterized experimentally and a practical compensation method is given. The testing results demonstrate that the useful signal and quadrature signal will not interact with each other because their phases are decoupled. Under a scale factor condition of 9.6 mV/°/s, in full measurement range of ± 300 deg/s, the zero bias stability reaches 15°/h with worse-case nonlinearity of 400 ppm, and the temperature variation trend of the SMG bias is thus largely eliminated, so that the maximum bias value is reduced to one tenth of the original after compensation from -40 °C to 80 °C.

Mechanical-Thermal Noise in Drive-Mode of a Silicon Micro-Gyroscope

A new closed-loop drive scheme which decouples the phase and the gain of the closed-loop driving system was designed in a Silicon Micro-Gyroscope (SMG). We deduce the system model of closed-loop driving and use stochastic averaging to obtain an approximate “slow” system that clarifies the effect of thermal noise. The effects of mechanical-thermal noise on the driving performance of the SMG, including the noise spectral density of the driving amplitude and frequency, are derived. By calculating and comparing the noise amplitude due to thermal noise both in the opened-loop driving and in the closed-loop driving, we find that the closed-loop driving does not reduce the RMS noise amplitude. We observe that the RMS noise frequency can be reduced by increasing the quality factor and the drive amplitude in the closed-loop driving system. The experiment and simulation validate the feasibility of closed-loop driving and confirm the validity of the averaged equation and its stablility criterion. The experiment and simulation results indicate the electrical noise of closed-loop driving circuitry is bigger than the mechanical-thermal noise and as the driving mass decreases, the mechanical-thermal noise may get bigger than the electrical noise of the closed-loop driving circuitry.

Device-level Vacuum Packaging of Silicon Microgyroscopes

The device-level vacuum packaging technologies of silicon microgyroscopes are studied in order to carry out vacuum packaging of silicon microgyroscopes to improve performance of microgyroscopes.First,the special ceramic packages for silicon microgyroscopes are designed and the soldering sealing technology is adopted.The alloy An/St is adopted to cater for the high temperature in the packaging process.The effects of degassing process on the quality factor of silicon microgyroscopes are studied,and the results of degassing experiments show that the quality factor of silicon microgyroscopes can be effectively improved when the silicon microgyroscopes chips and ceramic packages are baked in vacuum chamber.The device-level vacuum packaging process is established.The quality factor of packaged silicon microgyroscopes is about 10 363.7,which is about fifty times of quality factor of silicon microgyroscopes under ambient atmosphere pressure.The tracking test results of quality factor of silicon microgyroscope show that after the vacuum packaged silicon microgyrscopes are stored for five months,their quality factor is reduced to 55.1% of the original value,which shows that the vacuum retentivity of silicon microgyroscopes packaged with device-level vacuum packaging technology is poor and needs further study.

An x-axis single-crystalline silicon microgyroscope fabricated by the extended SBM process

A high-aspect ratio, single-crystal line silicon x-axis microgyroscope is fabricated using the extended sacrificial bulk micromachining (SBM) process. The x-axis microgyroscope in this paper uses vertically offset combs to resonate the proof mass in the vertical plane, and lateral combs to sense the Coriolis force in the horizontal plane. This requires fabricating vertically and horizontally moving structures for actuation and sensing, respectively, which is very difficult to achieve in single-crystalline silicon. However, single-crystalline silicon high-aspect ratio structures are preferred for high performance. The extended SRN/I process is a two-mask process, but all structural parts and combs are defined in one mask level. Thus, there is no misalignment in any structural parts or comb fingers. In this extended SBM process, all vertical dimensions of the structure, including the comb height, vertical comb offset and sacrificial gap, can be defined arbitrarily (up to a few tens of micrometers). For electrical isolation, silicon-on-insulator (SOI) wafers are used, but the inherent footing phenomenon in the SOI deep etching is eliminated and smooth structural shapes are obtained, because the SBM process is used. In the fabricated x-axis microgyroscope, the lower combs used to vibrate the proof mass are vertically offset 12 /spl mu/m from the upper combs. The fabricated x-axis microgyroscope can resolve 0.1 deg/s angular rate, and the measured bandwidth is 100 Hz. The reported work represents the first x-axis single-crystalline silicon microgyroscope fabricated using only one wafer without wafer bonding. We have previously reported several versions of z-axis microgyroscopes and x-, y-, and z-axis accelerometers, using the SBM process. The results or this paper allow integrating x-, y-, and z-axis microgyroscopes as well as x-, y-, and z-axis microaccelerometers in one wafer, using the same mask and the same process.

DRY AND WET ETCHING WITH (111) SILICON FOR HIGH-PERFORMANCE MICRO AND NANO SYSTEMS

Etching with (111) silicon is relatively new, but it represents very exciting opportunities in micro and nano system applications. By combining wet and dry anisotropic etching, high-precision, actuatable micro and nano structures can be fabricated in single-crystalline silicon. This paper reviews several relevant (111) microfabrication results reported in the literature. Among these, a single-mask process that we call sacrificial bulk micromachining (SBM) is reviewed in detail. Various electrical isolation methods as well as a number of applications to micro and nano systems are presented.