FABRICATION AND CHARACTERIZATION OOF A TWIN-MASS ACCELEROMETER

Three different monolithic piezoresistive accelerometer types, among t hem a novel twin-mass structure, were designed, fabricated and charact erized. The new structure contains two masses and five beams, four out er and one central one. Its sensing resistors are all located on the c entral beam, where the stress distribution is very uniform and of sing le sign along the whole beam length. One of the main advantages of thi s new twin-mass design is the insensitivity to lateral accelerations, the 3D effect is quasi eliminated. The fabrication process of the acce lerometers 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 jun ctions, provided exact control of the beam thicknesses.