An accelerometer is fabricated by forming a proofmass and at least one associated hinge in a silicon substrate by ion implantation and the formation of an oxide support layer below the proofmass, subsequently integrally bonding two complementary proofmass and substrate structures together, and then removing the oxide support layer to leave the proofmass supported by the hinge within the body of silicon material. The proofmass may be electrically connected to a lead extending through an etched recess in one of the substrates; and the proofmass may be electrically isolated or separated from the substrates by an oxide layer and by a change in conductivity type of the semiconductor material where the hinge is structurally mounted to the substrates.
A force sensing component for use with a force sensing unit includes a planar flexure member having a moveable portion separated from a fixed portion by a strain sensitive connection and a removable tab partially defined by through cuts along a crystallographic axis of the flexure member. Upper and lower stops limit movement of the beam.
A structure and producing method of a three-electrode capacitive pressure sensor can integrate and produce sensor capacitor and reference capacitor in the same pressure sensor cavity. This dual capacitor integration structure can cancel off environment interference of the same mode by differentiated circuit. Avoiding connection between upper and lower electrode plates can be achieved through the existence of a third electrode plate. In working pressure interval from 25 psi to 40 psi, the sensitivity of said three-electrode capacitive sensor is a 0.21 pF/psi, while the sensitivity of an ordinary planar connection pressure sensor is 0.05 pF/psi. The merits of said three-electrode capacitive pressure sensor include trivial production procedure and connection with planar and high sensitivity.
A method of manufacturing a monolithic silicon acceleration sensor is disclosed. The monolithic silicon acceleration sensor includes one or more sensor cells, each sensor cell having an inertial mass positioned by beam members fixed to a silicon support structure. According to the method, a sandwiched etch-stop layer is formed. First sections of the inertia mass and beam members are also formed. In addition, a second section of the inertial mass is formed. Further, an inertial mass positioned by beam members fixed to a silicon support structure is formed. Also, a first cover plate structure is bonded to a first surface of the silicon support structure.
A system for measuring changes in an environmental parameter such as displacement, velocity, acceleration, or pressure, includes a laser for providing a pulsed, coherent light signal, and an interferometer having a first and second optical legs of unequal optical path lengths. The signal is split into first and second beams that are directed into the first and second optical legs. Either a fixed mirror disposed on a frame or a moving mirror on one side of the proof mass reflects the first beam received at the end of the first optical leg. The frame also suspends a proof mass at opposite ends. An optical pick-off embodied in a movable mirror formed on the proof mass reflects the second beam received from the end of the second optical leg. The proof mass with mirror moves in response to changes in the value of the parameter to be measured. An optical coupler combines the first and second beams after they have been reflected back into their respective optical legs, producing an interference signal, which is detected by an optical detector. The detector generates an electronic signal, which is analyzed in a microcomputer. To compensate for gravity, the proof mass has an asymmetrical profile. As a velocity sensor for seismic measurements, its construction is guided by the mass of the proof mass and spring stiffness of the hinges. Represented mathematically, those terms are selected to minimize the acceleration and displacement components, leaving only the velocity component as a function of the ratio of mass to damping coefficients.
An accelerometer formed from a semiconducting substrate and first and second active layers coupled to the opposite surfaces of the substrate. The substrate has a frame and a proof mass suspended from the frame by one or more flexures for rotation about an input axis in response to an applied force. The active layers each include a vibratory force transducer mechanically coupled to the proof mass for detecting a force applied to the proof mass. With this configuration, the transducers are located on either side of the substrate, which improves the differential design symmetry of the force detecting apparatus. This reduces the common mode non-linear response characteristics of the accelerometer, particularly in high dynamics applications, where high performance is required.
