Patent ID: 7222536

Claim:
A semiconductor acceleration sensor comprising: a mass portion provided in a center of the acceleration sensor and having a top surface; a support frame surrounding the mass portion with a predetermined distance from the mass portion and having a top surface; and a plurality of flexible arms each extending from an edge of the top surface of the mass portion, bridging the top surface of the mass portion and an inside edge of the support frame and hanging the mass portion inside of the support frame; wherein each of the plurality of flexible arms comprises: two wider portions being both end portions of the flexible arm that contact boundaries between the flexible arm and the support frame or the mass portion and has an area of a cross section vertical to a longitudinal direction of the flexible arm; and a narrower portion that is part of the flexible arm interposed between the two wider portions at both ends of the flexible arm and has an area of a cross section vertical to a longitudinal direction of the flexible arm smaller than the cross section area of the wider portions; wherein a top surface of each of the plurality of flexible arms comprises: piezo resistors each having both terminals on the top surface of the support frame or the mass portion, extending in the longitudinal direction of the flexible arm from the both terminals and provided restrictedly within a top surface region of the wider portion of the flexible arm and a plurality of metal wires provided on the top surface of the flexible arm and symmetrically with respect to a center line of the top surface of the flexible arm and each extending in the longitudinal direction of the flexible arm from a top surface of one wider portion of the flexible arm to a top surface of the other wider portion of the flexible arm through a top surface of a narrower portion of the flexible arm; and wherein each of the piezo resistors comprises: at least two piezo sub-resistors provided symmetrically with respect to the center line of the top surface of the flexible arm and each extending in the longitudinal direction of the flexible arm; and a high concentration diffusion layer connecting every two ends of the piezo sub-resistors except for the both terminals of the piezo resistor to connect the piezo sub-resistors in series between the both terminals of the piezo resistor.