MEMS gyroscope is an important device for measuring carrier angular rate. It has the advantages of small size, low cost and low power consumption. However, singleaxis MEMS gyros can only measure the angular speed of one axis, while threeaxis MEMS gyroscopes can measure the angular speed of three axes, so threeaxis MEMS gyroscopes have become the main development direction of the industry.
There are three integration methods of threeaxis MEMS gyroscope: threeaxis gyro orthogonal integration method, singlechip singlestructure threeaxis gyro method and singlechip multistructure gyro array method. In the last article, we covered these three integration approaches in detail, and this article will explore how they compare.
Case study
1. University of California, Irvine (UCI) proposed two types of singlechip threeaxis MEMS gyroscopes with angular vibration. The structure is shown in Figure 1. The driving mode and Zaxis rate detection modes are inplane motion, and the Xaxis and Yaxis angular rate detection modes are outofplane motion. Structure I (FIG.1 (a)) is 1.49mm × 0.8mm in size, and the scale factors of X, Y and Z axes are 0.12µV /°/s, 0.09µV /°/s and 0.3µV /°/s. The driving mode resonance frequency of the structure is 67410 Hz. The detection mode resonant frequencies of X, Y and Z axes are 63260 Hz, 63430 Hz and 65000 Hz respectively.
Figure 1 Two structures of monolithic threeaxis gyroscope proposed by University of California, Irvine
2. University of California, Davis (UCD) proposed a singlechip threeaxis MEMS gyroscopein the form of fourmass block line vibration. Its structure is shown in Figure 2, with a thickness of 22.2μm and an area of 3.2mm × 3.2mm. The scale factors of the X, Y and Z axes are 28.5µV /°/s, 57.8µV /°/s and 19.4µV /°/s. The structural drive mode resonant frequency is 27964 Hz, and the detection mode resonant frequency of the X, Y and Z axes is 25901 Hz, respectively. 27115 Hz and 30559 Hz. Zerobias stability for the X, Y, and Z axes is 0.016 °/s, 0.004 °/s, and 0.043 °/s.
Figure 2 Structure of monolithic threeaxis gyroscope proposed by University of California, Davis
3. Georgia Institute of Technology (GIT) of the United States proposed a fourmass monolithic threeaxis MEMS gyroscope, as shown in Figure 3, with an area of 1.428 mm×1.428 mm and a scaling factor of 1.4 pA/°/s, 1.2 pA/°/s and 30.5 pA/°/s in the three axes of X, Y and Z. The resonant frequencies and quality factors of the structural drive modes, Xaxis, Yaxis and Zaxis detection modes are 138058Hz, 139140Hz, 139048Hz and 138043Hz, 3910, 1181, 1360 and 505, respectively. The bias stability and angular random walk for the X, Y and Z axes were 0.226 °/s, 0.166 °/s and 0.041 °/s, 0.292 °/√s, 0.357 °/√s and 0.028 °/√s, respectively.
Figure 3 Structure of monolithic threeaxis gyroscope proposed by Georgia Institute of Technology
4. Singapore Institute of Science and Technology (ASTR) proposed a combination sensor array of threeaxis gyroscope and threeaxis accelerometer, in which the Xaxis and Yaxis gyroscope adopted the form of angular vibration, and the Zaxis gyroscope adopted the form of line vibration, and its structure was shown in Figure 4. The three axis ranges of the gyroscope are 1000 °/s, and the Xaxis, Yaxis and Zaxis scale factors, nonlinearity, zerobias stability and angular random walk are respectively: LSB / 5.01 ° s, 5.09 LSB / ° LSB / ° / s/s and 12.91, 0.2%, 0.8% and 0.6%, 0.07 ° s, 0.04 ° and 0.03 ° s/s, 0.17 ° s /), 0.14 ° s and s, 0.04 ° /) /) The structure size is 2.0mm × 2.0mm × 0.5mm.
Figure 4 Threeaxis gyro array proposed by Agency for Science, Technology and Research, Singapore
5. University of California, Irvine (UCI) proposed a folding micromechanical array of threeaxis gyroscope and threeaxis accelerometer, which mainly adopts the way of microassembly, as shown in Figure 5. The gyro structure adopts a single axis mode, including ring and line vibration forms, and the overall folded shape is also proposed in hexahedron and pyramid shape. The integrated circuit can be configured in the center space of the folded shape without breaking the external shape and configuration. After testing, the scale factor, Angle random walk, bias stability and orthogonal error of ring gyroscope (structure diameter 2.8mm) and line vibration gyroscope (structure area 3.1mm × 3.1mm) used for assembly are respectively: 1.1 mV / ° / s and 1.94 mV / ° / s, 0.78 ° /) h/h and 0.11 °), 17 ° and 1.3 ° / h/h, 237 ° / s and the 404 ° / s.
Figure 5 Folding structure of threeaxis gyroscope array proposed by University of California, Irvine
Summary of parameters of threeaxis MEMS gyroscope
UCI  UCD  GIT  ASTR  UCI  
Structural form  Single structure  Single structure  Single structure  Twostructure array  Threestructure
folded array 

Mode of vibration  Linear vibration  Linear vibration  Linear vibration  Angular vibration+Linear vibration  Ring or line vibration  
Size (mm)  1.2mm2  3.2×3.2  1.4×1.4  2×2  diameter 2.8
or 3.1×3.1 

Resonant frequency
(Hz) 
drive  67410  27964  138058     
X axis  63260  25901  139140      
Y axis  63430  27115  139048      
Z axis  65000  30559  138043      
Scale factor  X axis  0.12µV/°/s  28.5µV/°/s  1.40pA/°/s  5.01LSB/°/s  1.1(1.94)mV/°/s 
Y axis  0.09µV/°/s  57.8µV/°/s  1.2pA/°/s  5.09LSB/°/s  
Z axis  0.3µV/°/s  19.4µV/°/s  30.5pA/°/s  12.9LSB/°/s  
Measuring range (°/s)  ±50  300  130  1000    
Quality factor  drive  34000  9840  3910     
X axis  53000  927  1181      
Y axis  45000  989  1360      
Z axis  36000  6744  505      
Angular random walk (°/s/√Hz )  X axis  0.06  0.023°/s  0.292°/√s  0.17°/√s  0.78(0.11)°/√h 
Y axis  0.12  0.01°/s  0.357°/√s  0.14°/√s  
Z axis  0.048  0.036°/s  0.028°/√s  0.04°/√s  
Bias stability  X axis  0.033°/s  0.043°/s  0.226°/s  0.07°/s  17(1.3)°/h 
Y axis  0.039°/s  0.016°/s  0.166°/s  0.04°/s  
Z axis  0.013°/s  0.004°/s  0.041°/s  0.03°/s 
Table 1 Summary of representative parameters of triaxial MEMS gyro research
It can be seen from Table 1 that the single structure has obvious advantages in terms of plane size, and the gyro resonance frequency ranges from 6 kHz to 140 kHz. In terms of accuracy, the Angle random walk index of the array triaxis gyro can achieve higher precision than that of the single triaxis gyro, and the zero bias stability index of the array triaxis gyro is obviously better than that of the single triaxis gyro structure. At the same time, although there is no crosscomparison data for the aspects of interaxis coupling and orthogonal error, the array structure should be superior to the single threeaxis structure from the aspects of structural complexity and processing difficulty.
In addition, in terms of gyro reliability, since the singlestructure threeaxis gyro structure is an integral design, if a certain structure (such as the support beam) breaks, all three axial gyros will fail; while in the array structure, if a beam breaks, one axis or two axes will fail, and the rest of the structure can work normally. This makes the reliability of the array type better than that of the single structure of the threeaxis gyro.
Comparison of three axis MEMS gyroscope integration methods
Through the analysis and summary of the above threeaxis MEMS gyroscope, it can be seen that although the three methods can realize the function of threeaxis gyroscope, each of the three methods has advantages and disadvantages, and the relevant comparison is summarized in Table 2 in this paper: The advantages and disadvantages of the two schemes of "three singleaxis gyro orthogonal integration method" and "singlechip singlestructure threeaxis gyro method" are basically complementary, while the "singlechip multistructure gyro array method" adopts the way of simple gyro structure plane overall arrangement and simultaneous processing, and uses mature structure and mature technology to solve the problem. It takes into account the advantages of simple structure, easy processing, high reliability, simple decoupling and high precision, and also meets the advantages of small volume, low cost and easy protection of the "single piece single structure threeaxis gyro method".
Mode  volume  structure  cost  precision  process  defense  reliable  error  decoupling 
Orthogonal integration of three single axis gyro  max  easy  max  The highest  easy  difficult  high  big  easy 
Singlechip singlestructure threeaxis gyro method  small  complexity  low  low  hardest  easy  worst  big  hard 
Monolithic multistructure gyro array method  small  easy  low  high  easy  easy  high  small  easy 
Table 2 Comparison of integration methods for threeaxis MEMS gyroscopes
Conclusion
"Three singleaxis gyroscope orthogonal integration method" is a method widely used at present, and the study of this scheme has become an engineering problem. This method mainly relies on the orthogonal placement of three singleaxis gyroscopes, and its performance is determined by a single gyroscope, which can achieve relatively high precision. However, in terms of volume, assembly error, packaging and processing cost, this method has obvious disadvantages. This is the case with the ER3MG03, a threeaxis MEMS gyroscope for navigation and stability control. The main function of the ER3MG07 is also stability control, but their platform body is different.
"Singlechip singlestructure threeaxis gyro method" is the research hotspot of various units at present, which mainly covers the research of new structure forms, new technology methods, new integrated circuits and so on. The method has the smallest volume, the highest integration, and the lowest packaging and processing costs. However, in view of the current processing technology level, the structure of this method is relatively complex, resulting in greater processing difficulty, low yield and poor consistency. Moreover, due to the complexity of vibration forms, there are more difficulties in signal decoupling and multistructure control in the later stage, and it is difficult to move to the application field of mass production in a short period of time.
"Singlechip multistructure gyro array method" is a practical compromise on the basis of the current processing technology. Its structure complexity is low, making the processing simpler and ensuring the yield. The planar integration scheme can greatly reduce the volume and improve the integration degree. Due to its small structure and high integration, its packaging cost is also low.
If you want to know more about threeaxis MEMS gyro, please contact us.
More Technical Questions
1.Integrated method of threeaxis MEMS gyroscope
2.Main features of MEMS gyroscope
3.Bandwidth test method of MEMS gyroscope
4.Impact resistance technology of MEMS gyroscope
5.Research on driving mode of MEMS gyroscope
6.Research on scale factor nonlinearity of MEMS gyroscope