This paper characterizes the sensitivity of a time domain MEMS accelerometer. The sensitivity is defined by the increment in the measured time interval per gravitational acceleration. Two sensitivities exist, and they can be enhanced by decreasing the amplitude and frequency. The sensitivity with minor nonlinearity is chosen to evaluate the time domain sensor. The experimental results of the developed accelerometer demonstrate that the sensitivities span from −68.91 μs/g to −124.96 μs/g and the 1σ noises span from 8.59 mg to 6.2 mg (amplitude of 626 nm: −68.91 μs/g and 10.21 mg; amplitude of 455 nm: −94.51 μs/g and 7.76 mg; amplitude of 342 nm: −124.96 μs/g and 6.23 mg), which indicates the bigger the amplitude, the smaller the sensitivity and the bigger the 1σ noise. The adjustable sensitivity provides a theoretical foundation for range self-adaption, and all the results can be extended to other time domain inertial sensors, e.g., a gyroscope or an inclinometer.

This paper presents a tilt sensor using two orthogonally arranged micro accelerometers. The arctangent function arctan(a₂/a₁) instead of the traditional arcsine function arcsin(a₂/g) or arcsin(a₁/g) is used to solve for the tilt angle. As a result, the tilt angle measurement is kept in the maximum value with a constant sensitivity (17.45 mg per degree) in the full measurement range.

A top-down design methodology and implementation of a time domain sensor is presented in this paper. The acceleration resolution of the time domain sensor is equal to the time-measurement accuracy divided by the sensor sensitivity. Combined with the sensitivity formula, the acceleration resolution is proportional to the vibration amplitude, the time-measurement accuracy, and the third power of the resonant frequency. According to the available time-measurement accuracy and the desired acceleration resolution, the parameters including the vibration amplitude and the resonant frequency were theoretically calculated. The geometrical configuration of the time domain sensor device was designed based on the calculated parameters. Then, the designed device was fabricated based on a standard silicon-on-insulator process and a matched interface circuit was developed for the fabricated device. Experimental results demonstrated that the design methodology is effective and feasible. Moreover, the implemented sensor works well. In addition, the acceleration resolution can be tuned by adjusting the time-measurement accuracy and the vibration amplitude. All the reported results of this work can be expanded to other time domain inertial sensors, e.g., a gyroscope or tilt sensor.

Thermal stress generally exists in wafer-level silicon-on-glass (SOG) bonding devices, which significantly affects the stability of the devices. The thermal stress mainly originates from the temperature-dependent Young’s modulus of silicon and the mismatched coefficient of thermal expansion (CTE) between silicon and glass. This paper presents a novel SD-2 borosilicate glass-based wafer-level SOG fabrication process for reducing thermal stress, in which the SD-2 glass exhibits closer CTE alignment with silicon substrate than conventional Borofloat 33 (BF33) glass. The SOG bonding parameters between the SD-2 and silicon substrates are then characterized by theoretical analysis and experimental validation. Through well-designed contrast experiments, the thermal stress from the mismatched CTE is isolated from the temperature-dependent Young’s modulus. The measured results demonstrate convincingly that the SD-2-based device exhibits 36.73% lower CTE-induced thermal stress compared to the conventional BF33-based counterpart. The presented fabrication process can be used to fabricate a temperature-susceptible microelectromechanical systems sensor, such as an accelerometer and an inertia switch.