An acceleration sensor is formed on a top surface of a laminated silicon-on-insulator substrate. The acceleration sensor is composed of first and second capacitors each including a movable electrode that moves according to acceleration imposed thereon. The first and the second capacitors are so made that their capacitances change differently when the same acceleration is imposed and that the capacitance difference represents an amount of acceleration imposed thereon. A third capacitor having an output electrode solidly connected to the base substrate via the insulation layer is also formed on the same silicon-on-insulator substrate. An output representing amount of acceleration is taken out from the output electrode of the third capacitor.
Disclosed is a gyro sensor, which comprises a primary base plate (1) and a support base plate (2) which are superimposed on one another. The primary base plate (1) is provided with a driven mass body (11) to be driven in such a manner as to be vibrated in a direction intersecting with a surface of the support base plate (2), and a detection mass body (12) coupled with the driven mass body (11) through a drive spring (13) and adapted to be displaceable in a plane along the support base plate (2). Two detection springs (15) extending in the arranging direction of the driven mass body (11) and the detection mass body (12) are connected, respectively, to opposite side of the detection mass body (12), and the other ends of the detection springs (15) are connected together through a coupling segment (16). A fixing segment (17) provided at a longitudinally intermediate portion of the coupling segment (16) is fixed to the support base plate (2). A member formed by integrating the driven mass body (11) and the detection mass body (12) through the drive spring (13) is supported relative to the support base plate (2) by the detection springs (15) in a cantilever manner.
An accelerometer or accelerator switch and its method of manufacture are disclosed. The device is fabricated from two substrates: a top substrate having a moveable mass, and a bottom substrate having at least one conductive plate. The top substrate is preferably a SOI substrate, and the mass and its suspending beams are formed in the silicon layer under which the insulator layer has been removed. The bottom substrate is preferably oxide. In one embodiment, the capacitance is formed using the mass as the first capacitor plate the conductive plate as the second plate. As the mass moves, the capacitance is detected to indicate the magnitude of the acceleration, or whether acceleration is above or below a threshold indicting an open or closed switch. The beams which suspend the mass can be serpentines, which make the device compact and render the mass more flexible. Alternatively, the bottom conductive plate can be split into two plates each coupling to the mass. Depending on the capacitance between the two split plates, this configuration allows for the formation of either a normally-open or normally-close acceleration switch.
A symmetrical differential capacitive sensor (60) includes a movable element (66) pivotable about a geometrically centered rotational axis (70). The element (66) includes sections (86, 88). Each of the sections (86, 88) has a stop (94, 96) spaced equally away from the rotational axis (70). Each of the sections (86, 88) also has a different configuration (104, 108) of apertures (102, 106). The configurations (104, 108) of apertures (102, 106) create a mass imbalance between the sections (86, 88) so that the element (66) pivots about the rotational axis (70) in response to acceleration. The apertures (102, 106) also facilitate etch release during manufacturing and reduce air damping when the element (66) rotates. Apertures (126, 128) are formed in electrodes (78, 80) underlying the apertures (102, 106) to match the capacitance between the two sections (86, 88) of movable element (86) to provide the same bi-directional actuation capability.
