A micromachined integrated sensor for pressure, temperature and humidity

In this paper, the technology of a micromachined sensors chip, on which an absolute pressure sensor, a temperature sensor and a humidity sensor are integrated, is described. The absolute pressure sensor uses a bulk micromachined diaphragm structure with piezoresistors. For temperature sensing, a silicon temperature sensor is fabricated based on the spreading resistance principle. And the humidity sensor is a capacitive humidity one with polyimide film and interdigitated capacitance electrodes. The anisotropy of (100) n-type silicon is used to design and fabricate the integrated sensor chip. The different piezoresistive orientations are used for the absolute pressure sensor and the temperature sensor to reduce the interference between each other. The humidity sensor is made up of 49 pairs of aluminum electrodes and one kind of polyimide. This polyimide material consists of 65% polyvinyl alcohol and 35% carbon black. The fabrication and package processes are introduced. And the sensor chip size is 5mm ×5mm. Each sensor in the integrated chip shows good sensor characteristics except for humidity sensor. However, the linearity and hysteresis of humidity sensor can be improved by selecting the proper polymer materials and structure.