MEMS inclinometer based on a novel piezoresistor structure
Introduction
Smart, highly integrated and low cost inclination sensor was a hot research topic recently due to the application on the robot, automotive field [1], [2], [3], telecommunication, electronic appliance and medical services [4].
The basic structures of inclinometers can be classified into three categories: solid-pendulum, liquid-pendulum and gas-pendulum [5], [6], [7], [8], [9], [10], [11]. In general, the movement of the pendulum mass corresponding to the rotation is most commonly detected by measuring the resistance or capacitance change. The detection principle of these solid-pendulum-based inclinometers is simple and straightforward. However, the structures of this kind of inclinometer are comparatively complex and big.
Some researchers reported inclination sensors using MEMS acceleration structure [12]. These inclinometers are also solid pendulum, but with relatively small sizes, their structures were also simple. These researches provide us many new ideas for solid-pendulum inclinometer design.
In this paper we mainly studied a novel inclinometer based on piezoresistance structure. The inclinometer has a pendulum structure. It used SOI technology for the fabrication, which proved to be a good way for a small sensor dimension and high sensitivity. The angle resolving method was studied for the sensor test and calibration.
Section snippets
Design
This paper presents a novel MEMS solid-pendulum inclinometer based on piezoresistive effect. The three-dimensional (3D) model of the inclinometer is shown in Fig. 1(a). It consists of four solid beams, the central mass and a rigid cylinder fixed on the center of the structure. The rigid cylinder is the solid pendulum, which is used to improve the sensitivity.
The sensation of the angle is mainly from piezoresistors, which are distributed on the beams. The gravity of the structure can make
Fabrication
The fabrication of the inclinometer consists of the processing of four-beam micro-structure and the manufacture of rigidity cylinder. The fabrication procedures [16] are illustrated in Fig. 4:
- (a)
Wafer preparation: A 4 in wafer was prepared. On the top of the wafer we deposited an SiO2 insulator layer of 2 μm with PECVD. Then another Si layer was bonded on it and the thickness was reduced to 10 μm which acted as the structure layer. On the surface we put a 2 μm thick SiO2 layer as a mask layer.
- (b)
Test
The test device is shown in Fig. 5, the plate can rotate in XOY plane. The plate rotate axis parallel to the z-axis, the sensitivity axis is always vertical to the gravity, the balance output voltage is observed in one channel only while the other channel shows the maximum output voltage, the ratio of the two channels also has a large change, use of this ratio can detect the rotate angle.
The inclinometer is fixed on the center of the index plate, the surface of the index plate is vertical to
Conclusion
A micro-machined solid-pendulum inclinometer is fabricated and presented in this paper. Using a rigid cylinder attached in the center mass to magnify the input angle signal, we can get a high sensitivity.
The inclinometer is fabricated with relatively low cost using the SOI technology. It has a measurement range of 360° (full turnover). Its high sensitivity, resolution added to its other properties made this new generation of inclinometer very attractive for the industrial applications. As
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