Elastic Response
Structural suspension characteristics in micro-scale devices define the displacement of a mechanical element per unit of applied force. Silicon flexure compliance determines how easily a proof mass moves within an accelerometer or a gyroscope. Because monocrystalline silicon is a perfectly elastic material below its yield point, it does not exhibit the permanent deformation common in metals.
This property allows for the design of extremely precise sensors that return to zero once the force is removed. The compliance value is a direct result of the beam length and thickness.
Geometry Optimization
Small changes in the shape of the hinge can have a large effect on the stiffness. In a typical design, silicon flexure compliance is increased by making the support beams longer or thinner. This increases the sensitivity of the sensor but also makes it more fragile.
Spring Constant
Quantification of the stiffness is done by measuring the resonant frequency of the mass. A higher silicon flexure compliance results in a lower resonant frequency. This relationship is used during the design phase to set the dynamic range of the device.
Fracture Limit
Mechanical failure occurs if the flexure is pushed beyond its breaking point. While silicon flexure compliance allows for significant movement, the material is brittle and will shatter if overloaded. Stops are often built into the package to prevent over-travel during a shock.
