Patent ID: 7317317
Filing Date: 2008-01-08
Classification: G01D,G01N

Abstract:
1. A micro sensor, comprising: a first dielectric layer; a conductive layer on said first dielectric layer; a second dielectric layer on said conductive layer; and a void micro feature that extends through said second dielectric layer and said conductive layer thereby defining first and second electrodes in said conductive layer on opposite sides of the micro feature, an impedance analyzer that applies ac measurement signal between the electrodes to measure the impedance of the micro feature as the ratio between an ac measurement signal voltage and current, said micro sensor having first and second parasitic capacitances between the first and second electrodes and a surrounding environment; a conductive guard layer in at least one of the first and second dielectric layers, said void micro feature extending through said guard layer to define first and second guards on opposite sides of the micro feature; and first and second buffers each having a first input connected to opposite sides of the impedance analyzer and a second input connected to a buffer output, said buffers having unity gain bandwidth larger than the ac measurement signal frequency to supply current to the first and second guards so that their voltages closely track the the ac measurement signals applies to the first and second electrodes, respectively, to separately shield each said first and second electrode from the surrounding environment and thereby reduce the loss of measurement signal through each of the first and second parasitic capacitances.