A 2000-Atmosphere Bulk-Type Pressure Sensor Realized on (001) Substrate with Selective Stress-Filtering Trenches

Previously reported was a bulk-type pressure sensor without fragile movable microstructure and constructed on [110]-oriented silicon substrate. Hydrostatic pressure acting on the sensor was converted to biaxial compression inside an encapsulated vacuum cavity. Two pairs of piezoresistors were used to form a Wheatstone bridge, with one pair each aligned with the [001] and [110] orientations – thus optimally utilizing the anisotropy of silicon piezoresistance on the (110) substrate. However, such anisotropy is absent on the (001) substrate because of an inherent crystal-symmetry. Presently reported is the placement of stress-filtering trenches adjacent to a selected pair of the constituent piezoresistors forming the Wheatstone bridge, thus removing the stress-symmetry by converting the local stress field from biaxial to uniaxial and allowing the construction of the bulk-type sensor on the more commonly available (001) substrate. A junction-isolated version of the pressure sensor was realized and characterized to 200 MPa (∼2000 atmospheres) and 175 °C, with better potential for sensor-CMOS integration.