Fund Project: International Cooperation Fund Project (011056): Li Jinming (1971-) Male, lecturer.
Quality Factor and Sensitivity; (2) When the coupling is completed, the gyro test point must be led to the glass cover so that the gyro output signal can be detected by the lead gyro simultaneously.
Through the above analysis, we can design the basic structure of the gyro glass cover. First of all, we define that the contact surface of the glass cover and silicon wafer is the front side of the cover, and the other side of the glass cover is the reverse side; to ensure that the glass cover and the silicon wafer are bonded together, a vacuum working environment can be provided for the moving parts of the gyroscope. The front of the cover should correspond to the moving part of the gyro to produce a groove with a high aspect ratio to ensure that all the moving parts of the gyro after bonding are contained in a vacuum 1 space formed by the grooves; then a number of through holes are made on the back of the glass cover. These through holes are used to guide the top of the gyro to the glass cover. Therefore, the position of the through hole must be very accurate. After the bonding, the through hole should correspond to the test point.
Given the design of a silicon microcomb electrostatic drive capacitance gyroscope that we have designed below, we can see from the figure that the gyroscope's detection mass (inner frame) is connected to the outer frame through four symmetrical beams, and the outer frame is Its surrounding comb-tooth capacitance is fixed to the anchor point by four beams so that the entire structure is suspended in a plane parallel to the substrate. After the driving voltage is applied to the driving comb teeth, the driving frame (outer frame) together with the detection frame (inner frame) will perform equal amplitude vibrations in the horizontal direction. If angular velocity n is input in the z axis direction at this time, the force is Under the action, the inner frame will vibrate in the vertical direction, causing the inner frame to detect the change of the capacitance value on the comb teeth (set to Ac). The detection circuit will modulate, amplify and demodulate the A c signal and output the voltage signal. This voltage signal Proportional to the input signal through the understanding of the gyro microstructure we know: the outer frame is the drive frame, it will move along the driving direction under the action of the excitation signal; the inner frame is the detection frame, it will detect the edge under the action of the Geishigong Directional movement. Therefore, the area of ​​the front groove of the glass cover must be slightly larger than the area of ​​the entire outer frame together with the comb teeth; at the same time, the position of the through hole on the glass cover must accurately correspond to the position of the gyro fixed comb teeth so as to ensure the bonding. After completion, the gyro test point can be led outside the glass cover.
2 Silicon micromachined gyro glass cover processing process According to the analysis of the role of the glass cover, we have been able to basically determine the structure of the glass cover, due to the front face of the glass cover to process a high aspect ratio groove, while playing in the opposite side of the glass cover A number of through holes, so we choose the surface etching method to process the groove, sandpaper polished Fig2Thef (wprocesschartofghssgap method to complete the processing of through holes. Is the process of glass cover (aa sectional view) first select the glass as the structural material of the processing cover, After the polishing and cleaning of the glass substrate, the front surface of the glass substrate is subjected to the first photolithography, and shallower trenches are etched. The size of the trench corresponds exactly to the movement portion of the silicon microgyroscope, and the profile thereof is shown in FIG. a) Select the position of the through hole on the back side of the glass substrate, and at the same time, sandpaper sanding at this position, in order not to affect the shape of the front groove, the through hole cannot be fully penetrated, and the result is shown in (b). A second photolithography is performed on the front surface of the glass substrate to etch the groove and perform a second etching. The depth of corrosion is deeper this time. The gyro moving parts have enough space, as shown in figure (c) After the groove is etched, the through hole is punched through the wet etching method, and the entire structure is cleaned and polished to lay the foundation for electrostatic bonding. Figure U).
After processing of the entire glass cover is completed, the silicon micromachined gyro can be vacuum-packaged by electrostatic bonding.
3 Electrostatic bonding process of glass cover and silicon wafer Electrostatic bonding technology is a common bonding technology in micro-machining. It can bond silicon, glass, silicon and metal and alloy materials through electrostatic field. There is no need to add any adhesive during the bonding process, and the bonding interface has good airtightness and long-term stability.
The process of electrostatically bonding the glass cover to the silicon wafer is as shown.
Electrostatic bonding process flow diagram First, the glass cover is connected to the negative pole of the power supply through the electrode plate, and the silicon chip is connected to the negative pole of the power supply. Before the power is turned on, they are put into the vacuum chamber for preheating. After preheating to a certain temperature, the voltage is slowly applied. In the energization process, the temperature of the bonding component is kept within a certain range through the heating plate. Only in this way can the bonding quality be ensured; during the bonding process, the change of the sealing current should be closely observed, and it is judged whether the bonding is completed according to the current change. When the voltage is fixed, the sealing current decays from the peak and finally goes to zero, which indicates that the bonding process is over.
The completion of the electrostatic bonding does not mean that the entire packaging process is over. We also need to perform the last processing step on the through hole in the glass cover, that is, apply a layer of aluminum film on the through hole (see below). This layer of metal film can The test point in the gyro is drawn out in advance, and each test point in the gyro is led to the gyro peripheral circuit through the lead wire. At this time, the gyro drive and the gyro output signal can be detected through the peripheral circuit.
4 Conclusions This article elaborated the use of electrostatic bonding technology to achieve all the silicon micro-machine gyroscope vacuum packaging process, including the glass cover for the processing of the processing, the processing of the glass cover is the premise of vacuum packaging, but also the difficulty of processing, The size of the groove area, the depth of corrosion, and the location of the vias all need to be studied. Therefore, we will devote more energy to conduct in-depth systematic research.
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