Directional Stiffness
Mechanical resistance to deformation that varies based on the axis of applied force defines the physical state. Anisotropic beam stiffness occurs when a structural component exhibits different elastic moduli or geometric moments of inertia along its primary axes. Bending behavior is determined by the specific crystal orientation of the silicon material.
Orientation Dependency
Calculating the response of a silicon beam requires an understanding of the crystal lattice orientation. Silicon typically exhibits lower resistance to bending along the primary crystal axes compared to the diagonal axes. Variations in the atomic spacing influence the resonant frequency of the sensor.
Design Influence
Design engineers use anisotropic beam stiffness to suppress unwanted vibration modes in high-precision sensors. By thickening a beam in the non-sensitive direction, the ratio of primary to secondary motion improves markedly. Prevention of cross-axis interference is achieved by aligning the flexures with the strongest crystal planes.
Manufacturing Variance
Variations in the etching process alter the final cross-section of a suspension member. Even a small undercut during deep reactive ion etching reduces the effective width, which changes the load response by the third power of the dimension change. Maintaining uniform dimensions across a six-inch wafer ensures that the directional resistance stays within the specified tolerance for the entire production lot.
Equipment drift and plasma density fluctuations represent the primary sources of this geometric deviation. Reliability depends on the precise control of these parameters during the micro-fabrication phase. Correcting for these factors involves adjusting the lithography exposure to compensate for the etch rate.
