FABRICATION AND CHARACTERIZATION OOF A TWIN-MASS ACCELEROMETER

Three different monolithic piezoresistive accelerometer types, among them a novel twin-mass structure, were designed, fabricated and characterized. The new structure contains two masses and five beams, four outer and one central one. Its sensing resistors are all located on the central beam, where the stress distribution is very uniform and of single sign along the whole beam length. One of the main advantages of this new twin-mass design is the insensitivity to lateral accelerations, the 3D effect is quasi eliminated. The fabrication process of the accelerometers included a wet etch step with TMAH solution, used to recess the seismic mass backsides. A four-electrode electrochemical p-n etch-stop technique, together with implanted n-areas to define the p-n junctions, provided exact control of the beam thicknesses.