Thermal convection biaxial acceleration sensor wit

Thermal convection biaxial acceleration sensor of MEMS technology

consumer electronics and communication electronic products, such as, digital camera, digital video camera, PDA, MP3, PMP, p-dvd, DC, DV, Nb, netbook, etc., must have certain impact or fall resistance. The manufacturers of these products require that the whole machine must pass the free fall test of 1.2 meters or 1.3 meters. The free fall from 1.2 meters to the marble floor will produce an impact force of about 50000g on the whole machine. If the cushioning effect of the housing and the printed circuit board is removed, the impact acceleration applied to the accelerometer will also exceed 5000g. In order to resist this impact, the manufacturer requires the product designer to design a buffer system in the product, and use the acceleration sensor to obtain the drop information at the first time. At the same time, turn off the power of shock resistant electronic devices at the first time and protect them, such as high-speed rotating hard disks, optical discs, video tapes, etc., so that they can quickly enter the pause state. Therefore, the biaxial thermal convection acceleration sensor is one of the ideal available devices

thermal convection biaxial acceleration sensor

the thermal convection biaxial acceleration sensor uses a virtual "hot air mass" suspended in the air as a gravity block. There is no movable part in the micro mechanical structure, and its unique "bridge" structure is firmly fixed on the silicon chip (Fig. 1), so that it can withstand the impact of more than 50000g

Figure 1 structure diagram of thermal convection biaxial acceleration sensor

thermal convection acceleration sensor is a complete acceleration measurement system produced by MEMS technology and based on the manufacturing process of single CMOS integrated circuit. Like other acceleration sensors, it has heavy force blocks (mass blocks). The thermal convection acceleration sensor takes the movable thermal convection small air mass as the gravity block. The acceleration is measured by measuring the position change of the temperature air mass in the internal cavity caused by the acceleration. The thermal convection acceleration sensor takes gaseous gas as the mass block. Compared with the traditional solid mass block, this acceleration sensor has great advantages. It does not have the problems of adhesion and particles existing in the capacitive sensor, and it can also resist the impact of 50000g. This makes the qualified product rate of the thermal convection acceleration sensor greatly improved, and the production cost effectively reduced, so the failure rate is very low

working principle of thermal convection acceleration sensor

a heat source placed in the center of the chip generates a suspended "hot air mass" in this cavity, and at the same time, four thermoelectric coupling groups composed of aluminum and polysilicon are symmetrically placed in four directions of the heat source at equal distance. When it is not subjected to acceleration or placed horizontally, the temperature drop steepness is completely symmetrical with the heat source as the center. At this time, all four thermoelectric coupling groups generate the same voltage due to the same induction temperature (as shown in Figure 2). From Figure 2, we can see the sectional view of this sensor. Above is a hollow air chamber. Due to the external force without acceleration, the hot air mass is located on the central heat source in the center. Figure 3 shows that the international influence of the plastic extruder industry continues to rise. Under the effect of an acceleration, the hot air mass shifts to the right, the balance of the original four thermoelectric coupling groups is destroyed, and the temperature drop steepness is a deviation of △ to the right centered on the heat source. Due to the transmissibility of the free convection heat field, the acceleration in any direction will disturb the contour of the heat field, resulting in its asymmetry. At this time, the output voltage of the four thermoelectric coupling groups will be different, and the difference of the output voltage of the thermoelectric coupling group is directly proportional to the induced acceleration. Inside the acceleration sensor, there are two identical acceleration signal transmission paths, one for measuring the acceleration induced on the X axis and the other for measuring the acceleration induced on the Y axis (as shown in Figure 4)

Fig. 2 working principle profile of thermal convection acceleration sensor without external force

Fig. 3 working principle profile of thermal convection acceleration sensor with acceleration

Fig. 4 internal topology of dual axis acceleration sensor with analog output

Fig. 5 internal topology of dual axis acceleration sensor with I2C output

from Fig. 4 Figure 5 shows that the interior of the thermal convection acceleration sensor also contains the analog signal post-processing circuit of the sensor. After differential amplification, temperature comparison, analog-to-digital conversion, digital to analog conversion, low-pass filtering and buffering, the thermoelectric coupling group signals from the same axis and two directions output amplified analog signals, such as mxa6500 (Fig. 4); Or through differential amplification, temperature comparison and analog-to-digital conversion, the signal is directly processed into an I2C interface, such as mxc6202 (Figure 5). Therefore, the thermal convection acceleration sensor is a multi chip system on chip, that is, SOC or MCM

mxa6 can also provide basic support for the realization of manufacturing power in the middle of this century. The system accuracy of 500 and mxc6202 thermal convection dual axis acceleration sensors is g/fs, and the working power supply is 2 6V, analog output sensitivity is 500mv/g @ 3V

because the thermal convection acceleration sensor adopts MEMS technology and Standard Based CMOS manufacturing process, the yield of its wafer processing process is greatly improved, and the yield of the whole line reaches more than 90%. ADI and other famous integrated circuit companies have developed this type of acceleration sensor, such as two-axis ad with at least one and a half xl320/321 and three-axis adxl330; Others are mas-la/ld series biaxial acceleration sensors. MEMS IC is designed and produced in Chinese Mainland, which has the advantage of low cost and makes products more competitive

figure 65 × five × 1.55mm lcc-8f package

Figure 7 XY biaxial acceleration force direction

thermal convection acceleration sensor adopts 5 × five × The 1.55mm lcc-8 package (Figure 6) is small and thin, which is very suitable for the application of portable products. Figure 7 shows the force direction of XY biaxial thermal convection acceleration sensor. When they are applied and designed in products, attention should be paid to the direction of an important indicator force that requires testing acceleration, controlling product quality and studying friction and wear mechanism. (end)