Novel Sensor Structure and Its Evaluation for Integrated Complementary Metal Oxide Semiconductor Microelectromechanical Systems Accelerometer

Abstract

This paper reports a novel sensor structure and its evaluation results for an integrated complementary metal oxide semiconductor (CMOS) microelectromechanical systems (MEMS) accelerometer with a wide detection range on a chip. The proposed sensor structure has the following features: i) a layer separation technique between the proof mass and the mechanical suspensions, ii) mechanical stoppers for the proof mass to avoid destruction, and iii) a SiO 2 film underneath the proof mass to prevent stiction and electrical short. Gold was used as the MEMS structure material to reduce the proof mass size and to lower the Brownian noise to below 100 g/ ffiffiffiffiffiffi Hz p . Furthermore, the micro fabrication was carried out below 310 C for the CMOS devices to remain intact. The evaluation results indicate that the Brownian noise was 90.6 g/ ffiffiffiffiffiffi Hz p. Thus, we have confirmed that the proposed MEMS structure has the potential for use in future integrated CMOS-MEMS accelerometers.

Design of sub-1g microelectromechanical systems accelerometers

“…Limited choices of materials and thickness for CMOS-MEMS accelerometer have been the major issue to reduce B N , which would become critical for low-acceleration sensing with high precision when the parasitic capacitance is minimized. 12 Thus, in our previous report, 13,14 we demonstrated a miniaturized MEMS capacitive accelerometer by using a post-CMOS process with high-density metal, which enabled further size reduction of the proof mass and the device footprint without compromising the sensitivity. In this Letter, we show a design approach of sub-1g detectable MEMS capacitive accelerometers for the miniaturization of CMOS-MEMS inertial sensors.…”

“…To accommodate sub-1g sensing, the reported accelerometer structures 13 have been modified as shown in Fig. 1; mechanical stoppers have been allocated on the top and the side surfaces of the proof mass to protect the movable parts from severe damages at excess acceleration.…”

Integrated CMOS-MEMS Technology and Its Applications

“…ii) It is applicable and scalable to various types of capacitive MEMS devices including an accelerometer in an arrayed format (13,14). iii) the calibration procedure is simple because the reference capacitor values are already known at the stage of circuit design.…”

Sub-1G MEMS accelerometer

“…For the further miniaturization and high functionality of MEMS accelerometers, CMOS-MEMS technology have recently been applied to MEMS accelerometer developments [5]- [7] by taking advantage of foundry service for mass production, smaller chip size followed by high functionality, and minimal parasitic capacitance; while the limited choices of proof mass materials and thickness have been the major issue for reducing B N , which would become critical on low-acceleration sensing with high precision when the parasitic capacitance is minimized [8]. Thus, in our previous report [9]- [10], we proposed an arrayed CMOS-MEMS accelerometer as illustrated in Fig. 1; with the use of high-density metal, the arrayed accelerometer with the downsized proof masses was capable of detecting a wide range of acceleration without compromising the mechanical noise.…”