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A semiconductor capacitance -type accelerometer utilizing a pulse width modulation (PWM) electrostatic servo technique has been developed. Highly accurate detection of very small and low frequency acceleration became possible with the PWM sensing method. The limited air gaps between the movable and fixed electrodes ensured compatibility between high sensitivity and durability, while transverse sensitivity and temperature coefficient were reduced due to the symmetric structure of the sensing device. This sensor has been designed for the measurement range of 0 to ±1g, ±2g and 0 to 50Hz. The accelerometer is composed of two chips: the sensing device made by silicon micromachining technology and the custom IC made by bipolar CMOS technology. In this paper, we present the fundamental sensing principle, the sensing device, the custom IC and the characteristics of the new accelerometer.

The detection range of an air-fuel ratio sensor is expanded in the rich A/F region. Using a simulation technique, the limiting cause of the detection range in the rich A/F region is identified as insufficient combustion rates of CO and H2 with O2 on the electrode, which prevent realization of a limited diffusion state which is necessary to detect the air-fuel ratio. Applying an improved diffusion layer to decrease the diffusion rates and an improved electrode to increase the combustion rates, it is demonstrated that the detection limit can be expanded to λ=0.6 while that of a conventional sensor is λ=0.8.