Silicon-based Humidity Sensor Characteristics, The Mechanism Of Its Design Of The Tester

The humidity sensor is fabricated with nanometer BaTiO3 film on silicon substrate. The nanometer BaTiO3 is synthesized by stearic acid method and is screen printed on silicon substrate to make the resistive type humidity sensor. The properties of the sensor were measured and analyzed. The results show that the sensor processes high sensitivity. The measurement voltage does not influence the properties of the sensor, while the impedance and the capacitance of the sensor change with the relative humidity (RH) and the measurement frequency. The best linearity of the impedance vs. RH curve is reached under the voltage 1V and the frequency 100Hz.Complex impendence techniques are used to analyze the humidity sensing mechanism of nanometer barium titanate humidity sensors on silicon substrate. The curves of resistance, capacitance and complex impedance of the sensors versus relative humidity (RH) are measured at different frequencies. An equivalent circuit model associated with resistors and capacitors is built. The complex impedance properties of the equivalent circuit changing with parameters of the resistance and the capacitance are coincident with complex impedance properties of BaTiO3 humidity sensor changing with RH in practice. The sensing mechanism of the sensor is discussed. In low RH range, the humidity sensing properties are determined mainly by the crystal grain resistance and the capacitance on the grain interfaces. In high humidity RH range, the polarization and ionization of the absorbed water makes a main contribution to humidity sensing properties.Nanometer barium titanate humidity sensor is a resistive sensor. The resistance changes from 103 to 106 in the RH range of 11%-98%, which shows the high sensitivity of sensor. A simple, intelligent, precision humidity measuring instrument is designed by using singlechip AT89C2051, programmable gain amplifier technology. The difficult design problems of wide resistance changing range are solved.