"Burst" technology with feedback-loop control for capacitive detection andelectrostatic excitation of resonant silicon sensors

A method for excitation and detection of resonant silicon sensors based on discontinuous, "burst" excitation is presented. The solution eliminates the crosstalk between electrostatic excitation and capacitive detection by sep arating them in time. High excitation voltages can be combined with highly sensitive detection electronics. The method facilitates the use of large di stances between the resonator and electrodes used for elicitation and detec tion. The method was successfully tested with feedback-loop control on sili con resonant density and pressure sensors where the electrodes were positio ned outside a glass, Continuous measurements of gas pressures and liquid de nsities were realized, The simplified fabrication process utilized reduces the risk of leakage from the ambient pressure to the low-pressure cavities in which the resonators are encapsulated since electrical feedthroughs are not needed, Excitation voltages alternating between 0 and 150 V could be ap plied to the resonators with measured electronics sensitivities of 0.4 fF S ignal-to-noise ratios (SNRs) as high as 100 (density sensor) and 360 (press ure sensor) were obtained. The electronic evaluation revealed that the "bur st" duty cycle (i.e,, the excitation time relative to the free oscillation time) had a strong influence on the output detection voltage, As few as two excitation periods with a "burst" cycle frequency of 115 Hz and a "burst" duty cycle of 1% was sufficient to select and lock the resonance frequency (28 042 Hz) for the tested pressure sensor. The same electrodes could be us ed for both excitation and detection, A novel solution is also presented th at eliminates the charging effect of dielectric surfaces which otherwise ca n be a problem for capacitive detection.