Exploration of Novel Silicon Devices Toward the Realization of a MEMS-Based Microsystem for Utilities (Water, Gas, Electrical) Monitoring

The work reported herein is the exploration of sensors to be used in a unified utilities (Natural gas, water and electricity) metering scheme. A unified utilities metering scheme with remote sensing capability will essentially be a viable alternative to the present stand alone systems which have not undergone sufficient changes to cater for present day demands. MEMS-based sensors that were explored in this effort support cost reduction due to batch production and sensitivity enhancement. Silicon bulk micromachined flow sensor developed locally was explored for both natural gas and water flow sensing. The silicon sensing element in the latter sensor gives rise to increased sensitivity and different unique operating modalities. More interestingly the novel thermal multivibrator modality of the sensor operation discovered, aids flow information to be translated to a frequency change at the sensor output. Unlike in the case of air flow measurements the biggest challenge in the water flow measurement is the sensor electrode passivation. The packaging scheme developed to achieve electrode passivation in this work, results in high water flow (testing up to 4 gpm) sensing via so called through-the-wall sensing scheme.

The sensors explored for magnetic sensing toward electrical energy monitoring were Hall effect devices and the deep impurity double injection devices. The silicon vertical Hall device configuration with the unique isolation scheme resulted in very high sensitivities such as 300 V/AT which will be highly desirable in a power measuring scheme.The silicon rectangular Hall effect device with the planar coil configuration shows drawbacks such as the need for high sensitivity Hall devices and the heating effect due to planar coil at high current levels which will directly affect their use in a power measuring scheme. The deep impurity double injection devices which were explored for magnetic sensing follows the theoretical prediction that the threshold variation is proportional to the magnetic field squared (Vth ∝ B²). The issue of having high electrically active gold concentration to improve the ratio of threshold voltage to holding voltage is an essential one. To our knowledge for the first time, magnetically induced bulk oscillations were observed in these devices.